[bolger] Re: Glen-L Sweet Caroline (non-Bolger)
In a message dated 3/20/00 5:40:04 PM Central Standard Time,
dhodges@...writes:
<< Bill, I will share ANYTHING I learn from this - >>
Don - glad to hear about the happy family occassions! Jeff and I have been
having great fun crunching numbers. I think it would be great fun if you
could provide all-up weights, installed hp, speed and prop diameter & pitch
when completed. I suspect most builders are too anxious to get on the water
to think about weighing their trailers before they get their boats on them
and determining weights thereafter becomes too logistically complicated for
the non-existent rewards of determining them. (The boat is done, knowing the
weight isn't going to make it perform any better, nows the time to just enjoy
it.)
Apart from having fun number crunching, I have given some thought, firmly
grounded in ignorance, on your powering decision and offer the following
suggestions, which probably have already occurred to you:
1) What hp motors are roughly similar boats in your intended operating area
running? a. this might be a clue as to what other folks consider suitable
power under conditions you are likely to face, and
b. in the abstract 18-20 Kts. may seem like plenty of speed, but if
everyone else
is running comparable boats with 40-50 hp at 25+ Kts., might you not feel
your boat is under-powered after a while?
2) I don't think that Glen-L has inspired the sort of cult following the
Bolger has, but if there was a way to solicit advice from other builders of
"Sweet Caroline", I think that if I was in your shoes, I would tend to
consider their opinions more reliable than the numbers that Jeff and I are
heedlessly bandying about.
3) Any possiblity of trying out someone else's motor just to verify your
decision empirically before committing to the big bucks?
3) DISCLAIMER, DISCLAIMER, DISCLAIMER - I'm skeptical about how much reliance
can be placed upon formulas for horsepower when applied to your specific
case, for a number of reasons, some of which I've bandied about with Jeff.
This is why I'd really like to see some hard data after you are on the water.
(You pay for My education! A once-in-a-lifetime deal!) If you were to be
foolish enough to rely on my calculations and ended up with a boat that
didn't get up and plane smartly, I'd say it was your own fault, but I still
would feel very badly about it.
dhodges@...writes:
<< Bill, I will share ANYTHING I learn from this - >>
Don - glad to hear about the happy family occassions! Jeff and I have been
having great fun crunching numbers. I think it would be great fun if you
could provide all-up weights, installed hp, speed and prop diameter & pitch
when completed. I suspect most builders are too anxious to get on the water
to think about weighing their trailers before they get their boats on them
and determining weights thereafter becomes too logistically complicated for
the non-existent rewards of determining them. (The boat is done, knowing the
weight isn't going to make it perform any better, nows the time to just enjoy
it.)
Apart from having fun number crunching, I have given some thought, firmly
grounded in ignorance, on your powering decision and offer the following
suggestions, which probably have already occurred to you:
1) What hp motors are roughly similar boats in your intended operating area
running? a. this might be a clue as to what other folks consider suitable
power under conditions you are likely to face, and
b. in the abstract 18-20 Kts. may seem like plenty of speed, but if
everyone else
is running comparable boats with 40-50 hp at 25+ Kts., might you not feel
your boat is under-powered after a while?
2) I don't think that Glen-L has inspired the sort of cult following the
Bolger has, but if there was a way to solicit advice from other builders of
"Sweet Caroline", I think that if I was in your shoes, I would tend to
consider their opinions more reliable than the numbers that Jeff and I are
heedlessly bandying about.
3) Any possiblity of trying out someone else's motor just to verify your
decision empirically before committing to the big bucks?
3) DISCLAIMER, DISCLAIMER, DISCLAIMER - I'm skeptical about how much reliance
can be placed upon formulas for horsepower when applied to your specific
case, for a number of reasons, some of which I've bandied about with Jeff.
This is why I'd really like to see some hard data after you are on the water.
(You pay for My education! A once-in-a-lifetime deal!) If you were to be
foolish enough to rely on my calculations and ended up with a boat that
didn't get up and plane smartly, I'd say it was your own fault, but I still
would feel very badly about it.
Bill, I will share ANYTHING I learn from this - the process has been ragged
due to several (joyous) family obligations; I'm obviously distracted but
should make some construction progress this week - weather is really great
here now, I just need to focus for a few days and make some chips!
Don Hodges
due to several (joyous) family obligations; I'm obviously distracted but
should make some construction progress this week - weather is really great
here now, I just need to focus for a few days and make some chips!
Don Hodges
----- Original Message -----
From: <Wmrpage@...>
To: <bolger@egroups.com>
Sent: Sunday, March 19, 2000 6:17 PM
Subject: [bolger] Re: Glen-L Sweet Caroline (non-Bolger)
> In a message dated 3/17/00 9:11:23 PM Central Standard Time,
>dhodges@...writes:
>
> << Lincoln,
>
> Of course you are right, I revised my estimate to circa 1000 lb, and I
may
> still be optimistic. >>
>
> Don:
>
> I've just posted a long message to "Jeff", an "OZ" fellow, regarding
> your query. He's bumped your weight estimate up to 1250# - and seems to
have
> done so on the basis of some serious thinking. We've arrived at different
BHP
> requirements, based upon formuale from different sources
Thanks Jeff! It'll take me a couple of days to digest - I returned from
D.C. to Florida today after another festive weekend, so my boatbuilding
brain is not engaged yet...
Don Hodges
dhodges@...
http://www.ecoastlife.com
Your Cyber-Vacation - Loafing on the Emerald Coast
Small Boats, Building, Fishing, Paddling, Rowing, Sailing
D.C. to Florida today after another festive weekend, so my boatbuilding
brain is not engaged yet...
Don Hodges
dhodges@...
http://www.ecoastlife.com
Your Cyber-Vacation - Loafing on the Emerald Coast
Small Boats, Building, Fishing, Paddling, Rowing, Sailing
----- Original Message -----
From: Jeff Gilbert <jgilbert@...>
To: bolger group <bolger@egroups.com>
Sent: Sunday, March 19, 2000 10:15 AM
Subject: [bolger] Re: Glen-L Sweet Caroline (non-Bolger)
> Re : Powering Glen-L "Sweet Caroline (SC)".
> For this 20ft Dory I came up with 15hp to achieve 19 knots at 100% power,
> using a formula from Ch 6 of Brewer's "Understanding Boat Design, and a
> weight
> which proved too low. The real power should be higher..here's the re-calc
> with the
> motor at 70% of full stress & a more realistic weight.
In a message dated 3/17/00 9:11:23 PM Central Standard Time,
dhodges@...writes:
<< Lincoln,
Of course you are right, I revised my estimate to circa 1000 lb, and I may
still be optimistic. >>
Don:
I've just posted a long message to "Jeff", an "OZ" fellow, regarding
your query. He's bumped your weight estimate up to 1250# - and seems to have
done so on the basis of some serious thinking. We've arrived at different BHP
requirements, based upon formuale from different sources. I'm certainly not
qualified to offer any advice, but I'm inclined to think that your 40 (rated)
BHP original estimate is not out of the realm of reason. I suspect that
Glen-L's prediction that 40 HP = 30 MPH = 28 Kts. = 40 HP is a top speed
prediction. Using the formula I'm using, this speed would require 40 SHP at
the propeller, optimistic, perhaps, but not out of the realm of reason.
I do hope that you will have your trailer weighed BEFORE you put the boat
on it, and weigh it afterwards, find out your performance, and give the
armchair sailors like me some reliable numbers to ruminate over. It won't
enhance your pleasure, but think of the home-bound.
Ciao for now;
Bill in MN
dhodges@...writes:
<< Lincoln,
Of course you are right, I revised my estimate to circa 1000 lb, and I may
still be optimistic. >>
Don:
I've just posted a long message to "Jeff", an "OZ" fellow, regarding
your query. He's bumped your weight estimate up to 1250# - and seems to have
done so on the basis of some serious thinking. We've arrived at different BHP
requirements, based upon formuale from different sources. I'm certainly not
qualified to offer any advice, but I'm inclined to think that your 40 (rated)
BHP original estimate is not out of the realm of reason. I suspect that
Glen-L's prediction that 40 HP = 30 MPH = 28 Kts. = 40 HP is a top speed
prediction. Using the formula I'm using, this speed would require 40 SHP at
the propeller, optimistic, perhaps, but not out of the realm of reason.
I do hope that you will have your trailer weighed BEFORE you put the boat
on it, and weigh it afterwards, find out your performance, and give the
armchair sailors like me some reliable numbers to ruminate over. It won't
enhance your pleasure, but think of the home-bound.
Ciao for now;
Bill in MN
Re : Powering Glen-L "Sweet Caroline (SC)".
For this 20ft Dory I came up with 15hp to achieve 19 knots at 100% power,
using a formula from Ch 6 of Brewer's "Understanding Boat Design, and a
weight
which proved too low. The real power should be higher..here's the re-calc
with the
motor at 70% of full stress & a more realistic weight.
The following
http://www.vacationlife.com/databoat/boatplans/GlenL/SweetCaroline.html
indicates a bare hull weight of 640lbs. Note the photo shows OB in a well
and of a good size,
25-40HP I'd guess.
Formula:
Brewer................"The following formula (Arthur Edmonds) seems
to work well for planing yachts (out of
context
-read 'Powered Planing Craft') of good hull
form:
BHP = (Disp in lbs) x (V**2) /
28750 ..........{1}
where V**2 means Velocity(kts) squared.
As the best planing hull form is a V bottom & SC is flat, i'm adding 5%
power to
cover this, so in this case:
BHP = (Disp in lbs) x (V**2) /
27381...........{2}
Manufacturer
Glen-L quotes a typical running displacement with 2-4 people aboard of
1600 lbs, and recommends a motor of 10-40 BHP. Note the mean - 25 BHP.
With the 40 BHP option they quote 30mph (or just over 26kts).
This fits formula {2} within 1% !!!
Displacement is calculateded for two people going fishing. I averaged
2-stroke
(160) & 4-stroke (200lb) 25 BHP motors with a full 6gal tank.
Displacement(lbs)
Bare Hull.....................................640
25hp OB & 6 gal fuel, tank..........180
2 people......................................320
Cooler, food,drink.........................30
Oars,anchor & warp,tools, spares..50
Tackle...........................................20
Wet gear, lifejackets......................10
TOTAL,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,1250
(with 2 more people youd reach at Glen-L's 1600lbs which is supposed to sink
the boat 6")
Calc:
BHP = (1250) x (19**2) /
27381...........{2} above
= 16.48 @ 100%
Running at 19kts & 70%power gives you a 23.5 HP requirement. To speed up to
20 you
need 26BHP or to lose 9% weight
So a 25BHP motor is the one you want, youll get your 19kts at 2/3 throttle.
Changing the formula about a bit, running your 25BHP flat out @ 1250lbs.
should give SC a top speed of
V = sqrt(27381 X 25 / 1250)
= 23.4 knots (or 27mph/ 43
kph)
SUMMARY (6 gal tank biggest 3, 3.3 gals smaller 2 motors):
###############################################
Top speed for a 40BHP (+75lb motor weight) is 28.7kts @ 1325lbs, at 70%
24.1 kts.
Top speed for a 30BHP (+10lb motor weight) is 25.5kts @ 1260lbs, at 70%
21.4 kts.
Top speed for a 25BHP (180lb motor weight) is 23.4kts @ 1250lbs, at 70%
19.6 kts.
Top speed for a 15BHP (-70lb motor weight) is 18.7kts @ 1180lbs, at 70%
15.6 kts.
Top speed for a 10BHP (-80lb motor weight) is 15.3kts @ 1170lbs, at 70%
12.8 kts.
Many manufacturers (eg Honda 499cc, Johnson 521cc) use the same
block for their 25 & 30HP motors. Thus the 25 is less stressed.
The same applies (only more so) to the 9.9/15 HP models.
Hope this helps
Jeff Gilbert
For this 20ft Dory I came up with 15hp to achieve 19 knots at 100% power,
using a formula from Ch 6 of Brewer's "Understanding Boat Design, and a
weight
which proved too low. The real power should be higher..here's the re-calc
with the
motor at 70% of full stress & a more realistic weight.
The following
http://www.vacationlife.com/databoat/boatplans/GlenL/SweetCaroline.html
indicates a bare hull weight of 640lbs. Note the photo shows OB in a well
and of a good size,
25-40HP I'd guess.
Formula:
Brewer................"The following formula (Arthur Edmonds) seems
to work well for planing yachts (out of
context
-read 'Powered Planing Craft') of good hull
form:
BHP = (Disp in lbs) x (V**2) /
28750 ..........{1}
where V**2 means Velocity(kts) squared.
As the best planing hull form is a V bottom & SC is flat, i'm adding 5%
power to
cover this, so in this case:
BHP = (Disp in lbs) x (V**2) /
27381...........{2}
Manufacturer
Glen-L quotes a typical running displacement with 2-4 people aboard of
1600 lbs, and recommends a motor of 10-40 BHP. Note the mean - 25 BHP.
With the 40 BHP option they quote 30mph (or just over 26kts).
This fits formula {2} within 1% !!!
Displacement is calculateded for two people going fishing. I averaged
2-stroke
(160) & 4-stroke (200lb) 25 BHP motors with a full 6gal tank.
Displacement(lbs)
Bare Hull.....................................640
25hp OB & 6 gal fuel, tank..........180
2 people......................................320
Cooler, food,drink.........................30
Oars,anchor & warp,tools, spares..50
Tackle...........................................20
Wet gear, lifejackets......................10
TOTAL,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,1250
(with 2 more people youd reach at Glen-L's 1600lbs which is supposed to sink
the boat 6")
Calc:
BHP = (1250) x (19**2) /
27381...........{2} above
= 16.48 @ 100%
Running at 19kts & 70%power gives you a 23.5 HP requirement. To speed up to
20 you
need 26BHP or to lose 9% weight
So a 25BHP motor is the one you want, youll get your 19kts at 2/3 throttle.
Changing the formula about a bit, running your 25BHP flat out @ 1250lbs.
should give SC a top speed of
V = sqrt(27381 X 25 / 1250)
= 23.4 knots (or 27mph/ 43
kph)
SUMMARY (6 gal tank biggest 3, 3.3 gals smaller 2 motors):
###############################################
Top speed for a 40BHP (+75lb motor weight) is 28.7kts @ 1325lbs, at 70%
24.1 kts.
Top speed for a 30BHP (+10lb motor weight) is 25.5kts @ 1260lbs, at 70%
21.4 kts.
Top speed for a 25BHP (180lb motor weight) is 23.4kts @ 1250lbs, at 70%
19.6 kts.
Top speed for a 15BHP (-70lb motor weight) is 18.7kts @ 1180lbs, at 70%
15.6 kts.
Top speed for a 10BHP (-80lb motor weight) is 15.3kts @ 1170lbs, at 70%
12.8 kts.
Many manufacturers (eg Honda 499cc, Johnson 521cc) use the same
block for their 25 & 30HP motors. Thus the 25 is less stressed.
The same applies (only more so) to the 9.9/15 HP models.
Hope this helps
Jeff Gilbert
----- Original Message -----
From: <Wmrpage@...>
To: <bolger@egroups.com>
Sent: Saturday, March 18, 2000 10:22 AM
Subject: [bolger] Re: Glen-L Sweet Caroline (non-Bolger)
In a message dated 3/17/00 8:55:41 AM Central Standard Time,
jgilbert@...writes:
<<
dhodges@...writes:
<< anybody want to venture a calculation
of the horsepower required to plane at 18 - 20 knots? The weight will be
about 600-650 lb all-up with provisions, etc. My guess is 40 hp. >>
I think you only need a about a third of that, say a 15hp outboard,
esp when you look at results with say Sneakeasy.
Good luck
Jeff Gilbert.
>>
I re-did my calculations to actually address Don's question. Using Crouch's
formula with C=150, weight of 650# and 70% of rated BHP as cruising SHP per
the "Flying Spray" example on page 17 of Gerr's "Propellor Handbook", I come
up with a power requirement of 14.9 BHP (rated power, not SHP) to cruise at
19 Kts. Did you do the math, Jeff? Or is this concurrence a serendipitous
coincidence of experience (yours) and blue-sky noodling (mine)?
This assumes propeller efficiency of 55%, but I don't think that would
be
a problem as this is a speed range that OB powered boats operate in as a
matter common practice. Assuming (big assumption) that these calculations
are
reliable, and that Don's weight estimate accurately took into account the
weight of the proposed 40hp motor and a fuel allocation, the lower weight of
the smaller motor and perhaps smaller gas tank would improve performance. I
calculate that a 65# reduction in weight would increase the cruising speed 1
Kt to 20 Kts. Of course, I'm informed only by ignorance and it would be a
rash fool who would select his power plant on the basis of my
back-of-the-envelope noodlings.
I'm a bit skeptical of some of the speed@bhp claims I've seen on the
"net", but absent actual operating weight data there is no way to compare
claimed results with theoretical ones derived from Gerr's formulas. I hope
Don will treat us to some good data, whatever his choice of power and how
big
his picnic lunch baskets are.
----- Original Message -----
From: <Wmrpage@...>
To: <bolger@egroups.com>
Sent: Saturday, March 18, 2000 10:22 AM
Subject: [bolger] Re: Glen-L Sweet Caroline (non-Bolger)
In a message dated 3/17/00 8:55:41 AM Central Standard Time,
jgilbert@...writes:
<<
dhodges@...writes:
<< anybody want to venture a calculation
of the horsepower required to plane at 18 - 20 knots? The weight will be
about 600-650 lb all-up with provisions, etc. My guess is 40 hp. >>
I think you only need a about a third of that, say a 15hp outboard,
esp when you look at results with say Sneakeasy.
Good luck
Jeff Gilbert.
>>
I re-did my calculations to actually address Don's question. Using Crouch's
formula with C=150, weight of 650# and 70% of rated BHP as cruising SHP per
the "Flying Spray" example on page 17 of Gerr's "Propellor Handbook", I come
up with a power requirement of 14.9 BHP (rated power, not SHP) to cruise at
19 Kts. Did you do the math, Jeff? Or is this concurrence a serendipitous
coincidence of experience (yours) and blue-sky noodling (mine)?
This assumes propeller efficiency of 55%, but I don't think that would
be
a problem as this is a speed range that OB powered boats operate in as a
matter common practice. Assuming (big assumption) that these calculations
are
reliable, and that Don's weight estimate accurately took into account the
weight of the proposed 40hp motor and a fuel allocation, the lower weight of
the smaller motor and perhaps smaller gas tank would improve performance. I
calculate that a 65# reduction in weight would increase the cruising speed 1
Kt to 20 Kts. Of course, I'm informed only by ignorance and it would be a
rash fool who would select his power plant on the basis of my
back-of-the-envelope noodlings.
I'm a bit skeptical of some of the speed@bhp claims I've seen on the
"net", but absent actual operating weight data there is no way to compare
claimed results with theoretical ones derived from Gerr's formulas. I hope
Don will treat us to some good data, whatever his choice of power and how
big
his picnic lunch baskets are.
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Re : Powering Glen-L "Sweet Caroline (SC)".
For this 20ft Dory I came up with 15hp to achieve 19 knots at 100% power,
using a formula from Ch 6 of Brewer's "Understanding Boat Design, and a
weight
which proved too low. The real power should be higher..here's the re-calc
with the
motor at 70% of full stress & a more realistic weight.
The following
http://www.vacationlife.com/databoat/boatplans/GlenL/SweetCaroline.html
indicates a bare hull weight of 640lbs. Note the photo shows OB in a well
and of a good size,
25-40HP I'd guess.
Formula:
Brewer................"The following formula (Arthur Edmonds) seems
to work well for planing yachts (out of
context
-read 'Powered Planing Craft') of good hull
form:
BHP = (Disp in lbs) x (V**2) /
28750 ..........{1}
where V**2 means Velocity(kts) squared.
As the best planing hull form is a V bottom & SC is flat, i'm adding 5%
power to
cover this, so in this case:
BHP = (Disp in lbs) x (V**2) /
27381...........{2}
Manufacturer
Glen-L quotes a typical running displacement with 2-4 people aboard of
1600 lbs, and recommends a motor of 10-40 BHP. Note the mean - 25 BHP.
With the 40 BHP option they quote 30mph (or just over 26kts).
This fits formula {2} within 1% !!!
Displacement is calculateded for two people going fishing. I averaged
2-stroke
(160) & 4-stroke (200lb) 25 BHP motors with a full 6gal tank.
Displacement(lbs)
Bare Hull.....................................640
25hp OB & 6 gal fuel, tank..........180
2 people......................................320
Cooler, food,drink.........................30
Oars,anchor & warp,tools, spares..50
Tackle...........................................20
Wet gear, lifejackets......................10
TOTAL,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,1250
(with 2 more people youd reach at Glen-L's 1600lbs which is supposed to sink
the boat 6")
Calc:
BHP = (1250) x (19**2) /
27381...........{2} above
= 16.48 @ 100%
Running at 19kts & 70%power gives you a 23.5 HP requirement. To speed up to
20 you
need 26BHP or to lose 9% weight
So a 25BHP motor is the one you want, youll get your 19kts at 2/3 throttle.
Changing the formula about a bit, running your 25BHP flat out @ 1250lbs.
should give SC a top speed of
V = sqrt(27381 X 25 / 1250)
= 23.4 knots (or 27mph/ 43
kph)
SUMMARY (6 gal tank biggest 3, 3.3 gals smaller 2 motors):
###############################################
Top speed for a 40BHP (+75lb motor weight) is 28.7kts @ 1325lbs, at 70%
24.1 kts.
Top speed for a 30BHP (+10lb motor weight) is 25.5kts @ 1260lbs, at 70%
21.4 kts.
Top speed for a 25BHP (180lb motor weight) is 23.4kts @ 1250lbs, at 70%
19.6 kts.
Top speed for a 15BHP (-70lb motor weight) is 18.7kts @ 1180lbs, at 70%
15.6 kts.
Top speed for a 10BHP (-80lb motor weight) is 15.3kts @ 1170lbs, at 70%
12.8 kts.
Many manufacturers (eg Honda 499cc, Johnson 521cc) use the same
block for their 25 & 30HP motors. Thus the 25 is less stressed.
The same applies (only more so) to the 9.9/15 HP models.
Hope this helps
Jeff Gilbert
For this 20ft Dory I came up with 15hp to achieve 19 knots at 100% power,
using a formula from Ch 6 of Brewer's "Understanding Boat Design, and a
weight
which proved too low. The real power should be higher..here's the re-calc
with the
motor at 70% of full stress & a more realistic weight.
The following
http://www.vacationlife.com/databoat/boatplans/GlenL/SweetCaroline.html
indicates a bare hull weight of 640lbs. Note the photo shows OB in a well
and of a good size,
25-40HP I'd guess.
Formula:
Brewer................"The following formula (Arthur Edmonds) seems
to work well for planing yachts (out of
context
-read 'Powered Planing Craft') of good hull
form:
BHP = (Disp in lbs) x (V**2) /
28750 ..........{1}
where V**2 means Velocity(kts) squared.
As the best planing hull form is a V bottom & SC is flat, i'm adding 5%
power to
cover this, so in this case:
BHP = (Disp in lbs) x (V**2) /
27381...........{2}
Manufacturer
Glen-L quotes a typical running displacement with 2-4 people aboard of
1600 lbs, and recommends a motor of 10-40 BHP. Note the mean - 25 BHP.
With the 40 BHP option they quote 30mph (or just over 26kts).
This fits formula {2} within 1% !!!
Displacement is calculateded for two people going fishing. I averaged
2-stroke
(160) & 4-stroke (200lb) 25 BHP motors with a full 6gal tank.
Displacement(lbs)
Bare Hull.....................................640
25hp OB & 6 gal fuel, tank..........180
2 people......................................320
Cooler, food,drink.........................30
Oars,anchor & warp,tools, spares..50
Tackle...........................................20
Wet gear, lifejackets......................10
TOTAL,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,1250
(with 2 more people youd reach at Glen-L's 1600lbs which is supposed to sink
the boat 6")
Calc:
BHP = (1250) x (19**2) /
27381...........{2} above
= 16.48 @ 100%
Running at 19kts & 70%power gives you a 23.5 HP requirement. To speed up to
20 you
need 26BHP or to lose 9% weight
So a 25BHP motor is the one you want, youll get your 19kts at 2/3 throttle.
Changing the formula about a bit, running your 25BHP flat out @ 1250lbs.
should give SC a top speed of
V = sqrt(27381 X 25 / 1250)
= 23.4 knots (or 27mph/ 43
kph)
SUMMARY (6 gal tank biggest 3, 3.3 gals smaller 2 motors):
###############################################
Top speed for a 40BHP (+75lb motor weight) is 28.7kts @ 1325lbs, at 70%
24.1 kts.
Top speed for a 30BHP (+10lb motor weight) is 25.5kts @ 1260lbs, at 70%
21.4 kts.
Top speed for a 25BHP (180lb motor weight) is 23.4kts @ 1250lbs, at 70%
19.6 kts.
Top speed for a 15BHP (-70lb motor weight) is 18.7kts @ 1180lbs, at 70%
15.6 kts.
Top speed for a 10BHP (-80lb motor weight) is 15.3kts @ 1170lbs, at 70%
12.8 kts.
Many manufacturers (eg Honda 499cc, Johnson 521cc) use the same
block for their 25 & 30HP motors. Thus the 25 is less stressed.
The same applies (only more so) to the 9.9/15 HP models.
Hope this helps
Jeff Gilbert
----- Original Message -----
From: <Wmrpage@...>
To: <bolger@egroups.com>
Sent: Saturday, March 18, 2000 10:22 AM
Subject: [bolger] Re: Glen-L Sweet Caroline (non-Bolger)
In a message dated 3/17/00 8:55:41 AM Central Standard Time,
jgilbert@...writes:
<<
dhodges@...writes:
<< anybody want to venture a calculation
of the horsepower required to plane at 18 - 20 knots? The weight will be
about 600-650 lb all-up with provisions, etc. My guess is 40 hp. >>
I think you only need a about a third of that, say a 15hp outboard,
esp when you look at results with say Sneakeasy.
Good luck
Jeff Gilbert.
>>
I re-did my calculations to actually address Don's question. Using Crouch's
formula with C=150, weight of 650# and 70% of rated BHP as cruising SHP per
the "Flying Spray" example on page 17 of Gerr's "Propellor Handbook", I come
up with a power requirement of 14.9 BHP (rated power, not SHP) to cruise at
19 Kts. Did you do the math, Jeff? Or is this concurrence a serendipitous
coincidence of experience (yours) and blue-sky noodling (mine)?
This assumes propeller efficiency of 55%, but I don't think that would
be
a problem as this is a speed range that OB powered boats operate in as a
matter common practice. Assuming (big assumption) that these calculations
are
reliable, and that Don's weight estimate accurately took into account the
weight of the proposed 40hp motor and a fuel allocation, the lower weight of
the smaller motor and perhaps smaller gas tank would improve performance. I
calculate that a 65# reduction in weight would increase the cruising speed 1
Kt to 20 Kts. Of course, I'm informed only by ignorance and it would be a
rash fool who would select his power plant on the basis of my
back-of-the-envelope noodlings.
I'm a bit skeptical of some of the speed@bhp claims I've seen on the
"net", but absent actual operating weight data there is no way to compare
claimed results with theoretical ones derived from Gerr's formulas. I hope
Don will treat us to some good data, whatever his choice of power and how
big
his picnic lunch baskets are.
Re : Powering Glen-L "Sweet Caroline (SC)".
For this 20ft Dory I came up with 15hp to achieve 19 knots at 100% power,
using a formula from Ch 6 of Brewer's "Understanding Boat Design, and a
weight
which proved too low. The real power should be higher..here's the re-calc
with the
motor at 70% of full stress & a more realistic weight.
The following
http://www.vacationlife.com/databoat/boatplans/GlenL/SweetCaroline.html
indicates a bare hull weight of 640lbs. Note the photo shows OB in a well
and of a good size,
25-40HP I'd guess.
Formula:
Brewer................"The following formula (Arthur Edmonds) seems
to work well for planing yachts (out of
context
-read 'Powered Planing Craft') of good hull
form:
BHP = (Disp in lbs) x (V**2) /
28750 ..........{1}
where V**2 means Velocity(kts) squared.
As the best planing hull form is a V bottom & SC is flat, i'm adding 5%
power to
cover this, so in this case:
BHP = (Disp in lbs) x (V**2) /
27381...........{2}
Manufacturer
Glen-L quotes a typical running displacement with 2-4 people aboard of
1600 lbs, and recommends a motor of 10-40 BHP. Note the mean - 25 BHP.
With the 40 BHP option they quote 30mph (or just over 26kts).
This fits formula {2} within 1% !!!
Displacement is calculateded for two people going fishing. I averaged
2-stroke
(160) & 4-stroke (200lb) 25 BHP motors with a full 6gal tank.
Displacement(lbs)
Bare Hull.....................................640
25hp OB & 6 gal fuel, tank..........180
2 people......................................320
Cooler, food,drink.........................30
Oars,anchor & warp,tools, spares..50
Tackle...........................................20
Wet gear, lifejackets......................10
TOTAL,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,1250
(with 2 more people youd reach at Glen-L's 1600lbs which is supposed to sink
the boat 6")
Calc:
BHP = (1250) x (19**2) /
27381...........{2} above
= 16.48 @ 100%
Running at 19kts & 70%power gives you a 23.5 HP requirement. To speed up to
20 you
need 26BHP or to lose 9% weight
So a 25BHP motor is the one you want, youll get your 19kts at 2/3 throttle.
Changing the formula about a bit, running your 25BHP flat out @ 1250lbs.
should give SC a top speed of
V = sqrt(27381 X 25 / 1250)
= 23.4 knots (or 27mph/ 43
kph)
SUMMARY (6 gal tank biggest 3, 3.3 gals smaller 2 motors):
###############################################
Top speed for a 40BHP (+75lb motor weight) is 28.7kts @ 1325lbs, at 70%
24.1 kts.
Top speed for a 30BHP (+10lb motor weight) is 25.5kts @ 1260lbs, at 70%
21.4 kts.
Top speed for a 25BHP (180lb motor weight) is 23.4kts @ 1250lbs, at 70%
19.6 kts.
Top speed for a 15BHP (-70lb motor weight) is 18.7kts @ 1180lbs, at 70%
15.6 kts.
Top speed for a 10BHP (-80lb motor weight) is 15.3kts @ 1170lbs, at 70%
12.8 kts.
Many manufacturers (eg Honda 499cc, Johnson 521cc) use the same
block for their 25 & 30HP motors. Thus the 25 is less stressed.
The same applies (only more so) to the 9.9/15 HP models.
Hope this helps
Jeff Gilbert
For this 20ft Dory I came up with 15hp to achieve 19 knots at 100% power,
using a formula from Ch 6 of Brewer's "Understanding Boat Design, and a
weight
which proved too low. The real power should be higher..here's the re-calc
with the
motor at 70% of full stress & a more realistic weight.
The following
http://www.vacationlife.com/databoat/boatplans/GlenL/SweetCaroline.html
indicates a bare hull weight of 640lbs. Note the photo shows OB in a well
and of a good size,
25-40HP I'd guess.
Formula:
Brewer................"The following formula (Arthur Edmonds) seems
to work well for planing yachts (out of
context
-read 'Powered Planing Craft') of good hull
form:
BHP = (Disp in lbs) x (V**2) /
28750 ..........{1}
where V**2 means Velocity(kts) squared.
As the best planing hull form is a V bottom & SC is flat, i'm adding 5%
power to
cover this, so in this case:
BHP = (Disp in lbs) x (V**2) /
27381...........{2}
Manufacturer
Glen-L quotes a typical running displacement with 2-4 people aboard of
1600 lbs, and recommends a motor of 10-40 BHP. Note the mean - 25 BHP.
With the 40 BHP option they quote 30mph (or just over 26kts).
This fits formula {2} within 1% !!!
Displacement is calculateded for two people going fishing. I averaged
2-stroke
(160) & 4-stroke (200lb) 25 BHP motors with a full 6gal tank.
Displacement(lbs)
Bare Hull.....................................640
25hp OB & 6 gal fuel, tank..........180
2 people......................................320
Cooler, food,drink.........................30
Oars,anchor & warp,tools, spares..50
Tackle...........................................20
Wet gear, lifejackets......................10
TOTAL,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,1250
(with 2 more people youd reach at Glen-L's 1600lbs which is supposed to sink
the boat 6")
Calc:
BHP = (1250) x (19**2) /
27381...........{2} above
= 16.48 @ 100%
Running at 19kts & 70%power gives you a 23.5 HP requirement. To speed up to
20 you
need 26BHP or to lose 9% weight
So a 25BHP motor is the one you want, youll get your 19kts at 2/3 throttle.
Changing the formula about a bit, running your 25BHP flat out @ 1250lbs.
should give SC a top speed of
V = sqrt(27381 X 25 / 1250)
= 23.4 knots (or 27mph/ 43
kph)
SUMMARY (6 gal tank biggest 3, 3.3 gals smaller 2 motors):
###############################################
Top speed for a 40BHP (+75lb motor weight) is 28.7kts @ 1325lbs, at 70%
24.1 kts.
Top speed for a 30BHP (+10lb motor weight) is 25.5kts @ 1260lbs, at 70%
21.4 kts.
Top speed for a 25BHP (180lb motor weight) is 23.4kts @ 1250lbs, at 70%
19.6 kts.
Top speed for a 15BHP (-70lb motor weight) is 18.7kts @ 1180lbs, at 70%
15.6 kts.
Top speed for a 10BHP (-80lb motor weight) is 15.3kts @ 1170lbs, at 70%
12.8 kts.
Many manufacturers (eg Honda 499cc, Johnson 521cc) use the same
block for their 25 & 30HP motors. Thus the 25 is less stressed.
The same applies (only more so) to the 9.9/15 HP models.
Hope this helps
Jeff Gilbert
----- Original Message -----
From: <Wmrpage@...>
To: <bolger@egroups.com>
Sent: Saturday, March 18, 2000 10:22 AM
Subject: [bolger] Re: Glen-L Sweet Caroline (non-Bolger)
In a message dated 3/17/00 8:55:41 AM Central Standard Time,
jgilbert@...writes:
<<
dhodges@...writes:
<< anybody want to venture a calculation
of the horsepower required to plane at 18 - 20 knots? The weight will be
about 600-650 lb all-up with provisions, etc. My guess is 40 hp. >>
I think you only need a about a third of that, say a 15hp outboard,
esp when you look at results with say Sneakeasy.
Good luck
Jeff Gilbert.
>>
I re-did my calculations to actually address Don's question. Using Crouch's
formula with C=150, weight of 650# and 70% of rated BHP as cruising SHP per
the "Flying Spray" example on page 17 of Gerr's "Propellor Handbook", I come
up with a power requirement of 14.9 BHP (rated power, not SHP) to cruise at
19 Kts. Did you do the math, Jeff? Or is this concurrence a serendipitous
coincidence of experience (yours) and blue-sky noodling (mine)?
This assumes propeller efficiency of 55%, but I don't think that would
be
a problem as this is a speed range that OB powered boats operate in as a
matter common practice. Assuming (big assumption) that these calculations
are
reliable, and that Don's weight estimate accurately took into account the
weight of the proposed 40hp motor and a fuel allocation, the lower weight of
the smaller motor and perhaps smaller gas tank would improve performance. I
calculate that a 65# reduction in weight would increase the cruising speed 1
Kt to 20 Kts. Of course, I'm informed only by ignorance and it would be a
rash fool who would select his power plant on the basis of my
back-of-the-envelope noodlings.
I'm a bit skeptical of some of the speed@bhp claims I've seen on the
"net", but absent actual operating weight data there is no way to compare
claimed results with theoretical ones derived from Gerr's formulas. I hope
Don will treat us to some good data, whatever his choice of power and how
big
his picnic lunch baskets are.
Lincoln,
Of course you are right, I revised my estimate to circa 1000 lb, and I may
still be optimistic. As they say at Glen-L, it's just 8 sheets of 1/2 ply
(343 lb - and probably only 75% or so of the 8 sheets survives the trimming)
and it's hard for me to find 300 more lb of framing and furniture. I have
almost finished the frame, but it's still attached to the strongback so I
can't heft it for an estimate. A guess: 100 lb. including 30 lb transom.
My cabin version will probably reach 650 lb dry weight, and that's the
figure I flipped out without logging the engine and crew. (stupid but true -
I have been hanging out with too many sailors, rowers, and paddlers - maybe
even golf handicappers). Glen-L also says 30 mph with 40 hp, but I'll have
to measure that to believe it.
At any rate, we are a long way from having enough finished to weigh it!
(Time out til Tuesday - another wedding party weekend is here, and Monday is
a travel day.)
Don Hodges
From: Lincoln Ross <lincolnr@...>
To: <bolger@...>
Sent: Friday, March 17, 2000 8:03 PM
Subject: [bolger] Re: Glen-L Sweet Caroline (non-Bolger)
Of course you are right, I revised my estimate to circa 1000 lb, and I may
still be optimistic. As they say at Glen-L, it's just 8 sheets of 1/2 ply
(343 lb - and probably only 75% or so of the 8 sheets survives the trimming)
and it's hard for me to find 300 more lb of framing and furniture. I have
almost finished the frame, but it's still attached to the strongback so I
can't heft it for an estimate. A guess: 100 lb. including 30 lb transom.
My cabin version will probably reach 650 lb dry weight, and that's the
figure I flipped out without logging the engine and crew. (stupid but true -
I have been hanging out with too many sailors, rowers, and paddlers - maybe
even golf handicappers). Glen-L also says 30 mph with 40 hp, but I'll have
to measure that to believe it.
At any rate, we are a long way from having enough finished to weigh it!
(Time out til Tuesday - another wedding party weekend is here, and Monday is
a travel day.)
Don Hodges
From: Lincoln Ross <lincolnr@...>
To: <bolger@...>
Sent: Friday, March 17, 2000 8:03 PM
Subject: [bolger] Re: Glen-L Sweet Caroline (non-Bolger)
> According to GlenL, the hull alone would be 640 lbs! Maybe this is why
> common sense disagrees with the numbers approach.
Actually, my experience is that the narrow bottom tends to "bog down" in the
rear, and a wider, flatter aft section goes on plane quicker. That's one
reason I'm going for a transom-mounted engine - the motor well reduces the
bottom area exactly where it's needed most. If it is too slow to plane or
runs excessively "bow-high", I'll add some fixed plates with a negative
"hook" alongside the engine. Stay tuned, it will all be done empirically in
time.
As for "Fingers Crossed", I think that is (was?) an F-40ish catamaran in the
UK - in any event, not me. I gave up my multihull quest - this dory will be
faster and easier to manage in lots of ways, more suited to the senior
loafer.
Don Hodges
dhodges@...
http://www.ecoastlife.com
Your Cyber-Vacation - Loafing on the Emerald Coast
Small Boats, Building, Fishing, Paddling, Rowing, Sailing
rear, and a wider, flatter aft section goes on plane quicker. That's one
reason I'm going for a transom-mounted engine - the motor well reduces the
bottom area exactly where it's needed most. If it is too slow to plane or
runs excessively "bow-high", I'll add some fixed plates with a negative
"hook" alongside the engine. Stay tuned, it will all be done empirically in
time.
As for "Fingers Crossed", I think that is (was?) an F-40ish catamaran in the
UK - in any event, not me. I gave up my multihull quest - this dory will be
faster and easier to manage in lots of ways, more suited to the senior
loafer.
Don Hodges
dhodges@...
http://www.ecoastlife.com
Your Cyber-Vacation - Loafing on the Emerald Coast
Small Boats, Building, Fishing, Paddling, Rowing, Sailing
----- Original Message -----
From: Jeff Gilbert <jgilbert@...>
To: <bolger@egroups.com>
Sent: Thursday, March 16, 2000 9:12 AM
Subject: [bolger] Re: Glen-L Sweet Caroline (non-Bolger)
> Don,
> the fact that it is narrow (but not ludicrously so) will,
> IMHO, actually help you to plane off smartly (well put!)
> as you have a reduced wetted area = reduced drag. Unless
> your displacement & hull shape drop you into
> a semi-displacement category.
> Which I dont think is the case.
> Didnt you own "Fingers Crossed"?
> Good luck
> Jeff Gilbert
>
> ----- Original Message -----
> : Donald Hodges <dhodges@...>
> To: <bolger@egroups.com>
> Sent: Saturday, March 18, 2000 4:35 AM
> Subject: [bolger] Re: Glen-L Sweet Caroline (non-Bolger)
>
>
> >thanks for all the calcs, guys - I think I missed the weight a bit - more
> >like 1000 lb all up. 25 hp will probably sustain my target speed, but
I'm
> >not sure it will plane the boat off smartly because it's so narrow.
>
>
> ------------------------------------------------------------------------
> GET A NEXTCARD VISA, in 30 seconds! Get rates
> as low as 0.0% Intro APR and no hidden fees.
> Apply NOW!
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>
>
>
According to GlenL, the hull alone would be 640 lbs! Maybe this is why
common sense disagrees with the numbers approach.
"jeff gilbert" <jgilber-@...> wrote:
original article:http://www.egroups.com/group/bolger/?start=3737
common sense disagrees with the numbers approach.
"jeff gilbert" <jgilber-@...> wrote:
original article:http://www.egroups.com/group/bolger/?start=3737
>will be
>dhodges@...writes:
>
> << anybody want to venture a calculation
> of the horsepower required to plane at 18 - 20 knots? The weight
> about 600-650 lb all-up with provisions, etc. My guess is 40 hp. >>
>
> I think you only need a about a third of that, say a 15hp outboard,
> esp when you look at results with say Sneakeasy.
> Good luck
> Jeff Gilbert.
>
In a message dated 3/17/00 11:36:12 AM Central Standard Time,
dhodges@...writes:
<< hanks for all the calcs, guys - I think I missed the weight a bit - more
like 1000 lb all up. 25 hp will probably sustain my target speed, but I'm
not sure it will plane the boat off smartly because it's so narrow. >>
Don - I've re-run Crouch's formula using C=150 and 1000# weight - I come up
with a rated BHP requirement of 22.9 BHP to achieve 19 Kts at 70% output,
25.4 BHP to achieve 20 Kts. I do not offer these figures as guidance - I am
utterly without any qualifications to judge. I'm just genuinely curious as
to how boats perform in the real world compared to these mathematical
estimates. I hope you will treat us with some good, honest weight, power and
speed data after you hit the water. Good luck.
dhodges@...writes:
<< hanks for all the calcs, guys - I think I missed the weight a bit - more
like 1000 lb all up. 25 hp will probably sustain my target speed, but I'm
not sure it will plane the boat off smartly because it's so narrow. >>
Don - I've re-run Crouch's formula using C=150 and 1000# weight - I come up
with a rated BHP requirement of 22.9 BHP to achieve 19 Kts at 70% output,
25.4 BHP to achieve 20 Kts. I do not offer these figures as guidance - I am
utterly without any qualifications to judge. I'm just genuinely curious as
to how boats perform in the real world compared to these mathematical
estimates. I hope you will treat us with some good, honest weight, power and
speed data after you hit the water. Good luck.
In a message dated 3/17/00 8:55:41 AM Central Standard Time,
jgilbert@...writes:
<<
dhodges@...writes:
<< anybody want to venture a calculation
of the horsepower required to plane at 18 - 20 knots? The weight will be
about 600-650 lb all-up with provisions, etc. My guess is 40 hp. >>
I think you only need a about a third of that, say a 15hp outboard,
esp when you look at results with say Sneakeasy.
Good luck
Jeff Gilbert.
formula with C=150, weight of 650# and 70% of rated BHP as cruising SHP per
the "Flying Spray" example on page 17 of Gerr's "Propellor Handbook", I come
up with a power requirement of 14.9 BHP (rated power, not SHP) to cruise at
19 Kts. Did you do the math, Jeff? Or is this concurrence a serendipitous
coincidence of experience (yours) and blue-sky noodling (mine)?
This assumes propeller efficiency of 55%, but I don't think that would be
a problem as this is a speed range that OB powered boats operate in as a
matter common practice. Assuming (big assumption) that these calculations are
reliable, and that Don's weight estimate accurately took into account the
weight of the proposed 40hp motor and a fuel allocation, the lower weight of
the smaller motor and perhaps smaller gas tank would improve performance. I
calculate that a 65# reduction in weight would increase the cruising speed 1
Kt to 20 Kts. Of course, I'm informed only by ignorance and it would be a
rash fool who would select his power plant on the basis of my
back-of-the-envelope noodlings.
I'm a bit skeptical of some of the speed@bhp claims I've seen on the
"net", but absent actual operating weight data there is no way to compare
claimed results with theoretical ones derived from Gerr's formulas. I hope
Don will treat us to some good data, whatever his choice of power and how big
his picnic lunch baskets are.
jgilbert@...writes:
<<
dhodges@...writes:
<< anybody want to venture a calculation
of the horsepower required to plane at 18 - 20 knots? The weight will be
about 600-650 lb all-up with provisions, etc. My guess is 40 hp. >>
I think you only need a about a third of that, say a 15hp outboard,
esp when you look at results with say Sneakeasy.
Good luck
Jeff Gilbert.
>>I re-did my calculations to actually address Don's question. Using Crouch's
formula with C=150, weight of 650# and 70% of rated BHP as cruising SHP per
the "Flying Spray" example on page 17 of Gerr's "Propellor Handbook", I come
up with a power requirement of 14.9 BHP (rated power, not SHP) to cruise at
19 Kts. Did you do the math, Jeff? Or is this concurrence a serendipitous
coincidence of experience (yours) and blue-sky noodling (mine)?
This assumes propeller efficiency of 55%, but I don't think that would be
a problem as this is a speed range that OB powered boats operate in as a
matter common practice. Assuming (big assumption) that these calculations are
reliable, and that Don's weight estimate accurately took into account the
weight of the proposed 40hp motor and a fuel allocation, the lower weight of
the smaller motor and perhaps smaller gas tank would improve performance. I
calculate that a 65# reduction in weight would increase the cruising speed 1
Kt to 20 Kts. Of course, I'm informed only by ignorance and it would be a
rash fool who would select his power plant on the basis of my
back-of-the-envelope noodlings.
I'm a bit skeptical of some of the speed@bhp claims I've seen on the
"net", but absent actual operating weight data there is no way to compare
claimed results with theoretical ones derived from Gerr's formulas. I hope
Don will treat us to some good data, whatever his choice of power and how big
his picnic lunch baskets are.
thanks for all the calcs, guys - I think I missed the weight a bit - more
like 1000 lb all up. 25 hp will probably sustain my target speed, but I'm
not sure it will plane the boat off smartly because it's so narrow. It'll
be fun guessing until we are interrupted by someone running this
combination... and, there's something to be said for running less than
wide-open-throttle for longevity (this boat has to outlive me!).
Got both chine logs glued on before the monsoon; hope to get the inwales on
today - another wedding trip over the weekend, so no planking till next
week. I have scarphed up two 22 ft Doug fir 1x3's from 2-1/2 10 footers for
the inwales, and they look pretty good - about $.50 per foot. Found a very
nice sheet of 3/4 ACX fir for the transom, no voids, placed the A-side in,
will patch the knots outside where I can power-sand, $36 a sheet.
Don Hodges
dhodges@...
http://www.ecoastlife.com
Your Cyber-Vacation - Loafing on the Emerald Coast
Small Boats, Building, Fishing, Paddling, Rowing, Sailing
like 1000 lb all up. 25 hp will probably sustain my target speed, but I'm
not sure it will plane the boat off smartly because it's so narrow. It'll
be fun guessing until we are interrupted by someone running this
combination... and, there's something to be said for running less than
wide-open-throttle for longevity (this boat has to outlive me!).
Got both chine logs glued on before the monsoon; hope to get the inwales on
today - another wedding trip over the weekend, so no planking till next
week. I have scarphed up two 22 ft Doug fir 1x3's from 2-1/2 10 footers for
the inwales, and they look pretty good - about $.50 per foot. Found a very
nice sheet of 3/4 ACX fir for the transom, no voids, placed the A-side in,
will patch the knots outside where I can power-sand, $36 a sheet.
Don Hodges
dhodges@...
http://www.ecoastlife.com
Your Cyber-Vacation - Loafing on the Emerald Coast
Small Boats, Building, Fishing, Paddling, Rowing, Sailing
----- Original Message -----
From: <Wmrpage@...>
To: <bolger@egroups.com>
Sent: Thursday, March 16, 2000 11:33 PM
Subject: [bolger] Re: Glen-L Sweet Caroline (non-Bolger)
> In a message dated 3/15/00 3:27:10 AM Central Standard Time,
>dhodges@...writes:
>
> << anybody want to venture a calculation
> of the horsepower required to plane at 18 - 20 knots? The weight will be
> about 600-650 lb all-up with provisions, etc. My guess is 40 hp. >>
>
> Don - I'm virtually innumerate and a total computer klutz - but here goes:
>
> Dave Gerr, "Propeller Handbook", International Marine Publishing, 1980, p.
15
> gives the following formula ("Crouch's Planing Speed Formula"): Kts =
> C/(LB/SHP)^.05. (i.e. a constant "C" divided by the square root of
LB/SHP).
> The constants he gives are 150 = average runabouts, 190 = high speed
> runabouts, 210 = race boat types. Translated into Lotus 1-2-3 spreadsheet
> symbols, I believe this is rendered as Kts = (C/((LB/SHP)^0.5)). Using
> constant C = 190 and SHP = 40, I get a Kts = 47! Using C = 210 and SHP =
40,
> I get Kts = 52 Kts! These numbers seem rather on the high side, but not
> unreasonably so - as a child I believed that a lightly loaded 14'
Glastron
> runabout with a (nominal) 55 hp OB would go about 40 mph. This was surely
a
> much heavier package than your projected boat.
>
> My algebra is very shaky, but if the formula is rearranged as: SHP =
> (LB/(C/Kts)^2) ( SHP = the weight divided by the square of the constant
> divided by speed) (translated into Lotus as (LB/((C/Kts)^2), then at C=190
I
> get a mere 6 SHP to go 20 Kts., or 5 SHP to go 18 Kts. At C=210 I get a
mere
> 5 SHP to go 20 Kts., or 4 SHP to go 18 Kts. These results seem
unreasonably
> low to me. I don''t know if the fault lies in my faulty mathematics or
> pushing the formula (which is surely a rough, empirical guide) beyond its
> useful limits.
>
> With a little low cunning, it is possible to get Lotus 1-2-3 to draw speed
v.
> horsepower graphs using the formulas in Gerr's book. I don't have a great
> deal of confidence in my results, however. This is a pretty harmless and
> entertaining computer game however and corrections and comments would be
> welcomed.
>
> Bill in MN
>
>
> ------------------------------------------------------------------------
> GET A NEXTCARD VISA, in 30 seconds! Get rates as low as 0.0%
> Intro or 9.9% Fixed APR and no hidden fees. Apply NOW!
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>
From experiance 20 hp should do it on a reasonably flat
bottom. My dad has a 14 foot boat with a 15 hp motor that
will do 15 or 16 at that weight. My 16 foot aluminim boat
with a tired 40 hp will make 20 on a good day and I guess
it to weigh close to 1,000 or so.
Gordon W5RED
G. C. Cougergcouger@...Stillwater, OK
www.couger.com/gcouger
"You miss 100 percent of the shots you never take." - Wayne Gretzky
bottom. My dad has a 14 foot boat with a 15 hp motor that
will do 15 or 16 at that weight. My 16 foot aluminim boat
with a tired 40 hp will make 20 on a good day and I guess
it to weigh close to 1,000 or so.
Gordon W5RED
G. C. Cougergcouger@...Stillwater, OK
www.couger.com/gcouger
"You miss 100 percent of the shots you never take." - Wayne Gretzky
----- Original Message -----
From: <Wmrpage@...>
To: <bolger@egroups.com>
Sent: Thursday, March 16, 2000 11:33 PM
Subject: [bolger] Re: Glen-L Sweet Caroline (non-Bolger)
> In a message dated 3/15/00 3:27:10 AM Central Standard Time,
>dhodges@...writes:
>
> << anybody want to venture a calculation
> of the horsepower required to plane at 18 - 20 knots? The weight will be
> about 600-650 lb all-up with provisions, etc. My guess is 40 hp. >>
>
> Don - I'm virtually innumerate and a total computer klutz - but here goes:
>
> Dave Gerr, "Propeller Handbook", International Marine Publishing, 1980, p.
15
> gives the following formula ("Crouch's Planing Speed Formula"): Kts =
> C/(LB/SHP)^.05. (i.e. a constant "C" divided by the square root of
LB/SHP).
> The constants he gives are 150 = average runabouts, 190 = high speed
> runabouts, 210 = race boat types. Translated into Lotus 1-2-3 spreadsheet
> symbols, I believe this is rendered as Kts = (C/((LB/SHP)^0.5)). Using
> constant C = 190 and SHP = 40, I get a Kts = 47! Using C = 210 and SHP =
40,
> I get Kts = 52 Kts! These numbers seem rather on the high side, but not
> unreasonably so - as a child I believed that a lightly loaded 14'
Glastron
> runabout with a (nominal) 55 hp OB would go about 40 mph. This was surely
a
> much heavier package than your projected boat.
>
> My algebra is very shaky, but if the formula is rearranged as: SHP =
> (LB/(C/Kts)^2) ( SHP = the weight divided by the square of the constant
> divided by speed) (translated into Lotus as (LB/((C/Kts)^2), then at C=190
I
> get a mere 6 SHP to go 20 Kts., or 5 SHP to go 18 Kts. At C=210 I get a
mere
> 5 SHP to go 20 Kts., or 4 SHP to go 18 Kts. These results seem
unreasonably
> low to me. I don''t know if the fault lies in my faulty mathematics or
> pushing the formula (which is surely a rough, empirical guide) beyond its
> useful limits.
>
> With a little low cunning, it is possible to get Lotus 1-2-3 to draw speed
v.
> horsepower graphs using the formulas in Gerr's book. I don't have a great
> deal of confidence in my results, however. This is a pretty harmless and
> entertaining computer game however and corrections and comments would be
> welcomed.
>
> Bill in MN
>
>
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>
In a message dated 3/15/00 3:27:10 AM Central Standard Time,
dhodges@...writes:
<< anybody want to venture a calculation
of the horsepower required to plane at 18 - 20 knots? The weight will be
about 600-650 lb all-up with provisions, etc. My guess is 40 hp. >>
Don - I'm virtually innumerate and a total computer klutz - but here goes:
Dave Gerr, "Propeller Handbook", International Marine Publishing, 1980, p. 15
gives the following formula ("Crouch's Planing Speed Formula"): Kts =
C/(LB/SHP)^.05. (i.e. a constant "C" divided by the square root of LB/SHP).
The constants he gives are 150 = average runabouts, 190 = high speed
runabouts, 210 = race boat types. Translated into Lotus 1-2-3 spreadsheet
symbols, I believe this is rendered as Kts = (C/((LB/SHP)^0.5)). Using
constant C = 190 and SHP = 40, I get a Kts = 47! Using C = 210 and SHP = 40,
I get Kts = 52 Kts! These numbers seem rather on the high side, but not
unreasonably so - as a child I believed that a lightly loaded 14' Glastron
runabout with a (nominal) 55 hp OB would go about 40 mph. This was surely a
much heavier package than your projected boat.
My algebra is very shaky, but if the formula is rearranged as: SHP =
(LB/(C/Kts)^2) ( SHP = the weight divided by the square of the constant
divided by speed) (translated into Lotus as (LB/((C/Kts)^2), then at C=190 I
get a mere 6 SHP to go 20 Kts., or 5 SHP to go 18 Kts. At C=210 I get a mere
5 SHP to go 20 Kts., or 4 SHP to go 18 Kts. These results seem unreasonably
low to me. I don''t know if the fault lies in my faulty mathematics or
pushing the formula (which is surely a rough, empirical guide) beyond its
useful limits.
With a little low cunning, it is possible to get Lotus 1-2-3 to draw speed v.
horsepower graphs using the formulas in Gerr's book. I don't have a great
deal of confidence in my results, however. This is a pretty harmless and
entertaining computer game however and corrections and comments would be
welcomed.
Bill in MN
dhodges@...writes:
<< anybody want to venture a calculation
of the horsepower required to plane at 18 - 20 knots? The weight will be
about 600-650 lb all-up with provisions, etc. My guess is 40 hp. >>
Don - I'm virtually innumerate and a total computer klutz - but here goes:
Dave Gerr, "Propeller Handbook", International Marine Publishing, 1980, p. 15
gives the following formula ("Crouch's Planing Speed Formula"): Kts =
C/(LB/SHP)^.05. (i.e. a constant "C" divided by the square root of LB/SHP).
The constants he gives are 150 = average runabouts, 190 = high speed
runabouts, 210 = race boat types. Translated into Lotus 1-2-3 spreadsheet
symbols, I believe this is rendered as Kts = (C/((LB/SHP)^0.5)). Using
constant C = 190 and SHP = 40, I get a Kts = 47! Using C = 210 and SHP = 40,
I get Kts = 52 Kts! These numbers seem rather on the high side, but not
unreasonably so - as a child I believed that a lightly loaded 14' Glastron
runabout with a (nominal) 55 hp OB would go about 40 mph. This was surely a
much heavier package than your projected boat.
My algebra is very shaky, but if the formula is rearranged as: SHP =
(LB/(C/Kts)^2) ( SHP = the weight divided by the square of the constant
divided by speed) (translated into Lotus as (LB/((C/Kts)^2), then at C=190 I
get a mere 6 SHP to go 20 Kts., or 5 SHP to go 18 Kts. At C=210 I get a mere
5 SHP to go 20 Kts., or 4 SHP to go 18 Kts. These results seem unreasonably
low to me. I don''t know if the fault lies in my faulty mathematics or
pushing the formula (which is surely a rough, empirical guide) beyond its
useful limits.
With a little low cunning, it is possible to get Lotus 1-2-3 to draw speed v.
horsepower graphs using the formulas in Gerr's book. I don't have a great
deal of confidence in my results, however. This is a pretty harmless and
entertaining computer game however and corrections and comments would be
welcomed.
Bill in MN
Don,
the fact that it is narrow (but not ludicrously so) will,
IMHO, actually help you to plane off smartly (well put!)
as you have a reduced wetted area = reduced drag. Unless
your displacement & hull shape drop you into
a semi-displacement category.
Which I dont think is the case.
Didnt you own "Fingers Crossed"?
Good luck
Jeff Gilbert
the fact that it is narrow (but not ludicrously so) will,
IMHO, actually help you to plane off smartly (well put!)
as you have a reduced wetted area = reduced drag. Unless
your displacement & hull shape drop you into
a semi-displacement category.
Which I dont think is the case.
Didnt you own "Fingers Crossed"?
Good luck
Jeff Gilbert
----- Original Message -----
: Donald Hodges <dhodges@...>
To: <bolger@egroups.com>
Sent: Saturday, March 18, 2000 4:35 AM
Subject: [bolger] Re: Glen-L Sweet Caroline (non-Bolger)
>thanks for all the calcs, guys - I think I missed the weight a bit - more
>like 1000 lb all up. 25 hp will probably sustain my target speed, but I'm
>not sure it will plane the boat off smartly because it's so narrow.
dhodges@...writes:
<< anybody want to venture a calculation
of the horsepower required to plane at 18 - 20 knots? The weight will be
about 600-650 lb all-up with provisions, etc. My guess is 40 hp. >>
I think you only need a about a third of that, say a 15hp outboard,
esp when you look at results with say Sneakeasy.
Good luck
Jeff Gilbert.
<< anybody want to venture a calculation
of the horsepower required to plane at 18 - 20 knots? The weight will be
about 600-650 lb all-up with provisions, etc. My guess is 40 hp. >>
I think you only need a about a third of that, say a 15hp outboard,
esp when you look at results with say Sneakeasy.
Good luck
Jeff Gilbert.
Well, I got back to the project this week after a gala wedding in London on
March 4 (one down, one to go!).
God, am I a wood-butcher! I have the stem/keel/frames/transom on the
strongback, and got one chine log on today. Beveling is a real drag, but I
like the flared dory shape which is emerging. I have elected to build for a
transom-mounted outboard instead of the well, and the result is a 19 1/2
footer instead of 20 feet. However, I won't have the engine in the boat
with me! The flat bottom is 16 feet long with a max beam of 46 inches -
straight run of 5 feet to the stern - anybody want to venture a calculation
of the horsepower required to plane at 18 - 20 knots? The weight will be
about 600-650 lb all-up with provisions, etc. My guess is 40 hp.
I'll have a small cabin with v-berths, stove, and porta-loo.
Cedar Key on May 6 is still possible, but not probable...
Don Hodges
dhodges@...
http://www.ecoastlife.com
Your Cyber-Vacation - Loafing on the Emerald Coast
Small Boats, Building, Fishing, Paddling, Rowing, Sailing
March 4 (one down, one to go!).
God, am I a wood-butcher! I have the stem/keel/frames/transom on the
strongback, and got one chine log on today. Beveling is a real drag, but I
like the flared dory shape which is emerging. I have elected to build for a
transom-mounted outboard instead of the well, and the result is a 19 1/2
footer instead of 20 feet. However, I won't have the engine in the boat
with me! The flat bottom is 16 feet long with a max beam of 46 inches -
straight run of 5 feet to the stern - anybody want to venture a calculation
of the horsepower required to plane at 18 - 20 knots? The weight will be
about 600-650 lb all-up with provisions, etc. My guess is 40 hp.
I'll have a small cabin with v-berths, stove, and porta-loo.
Cedar Key on May 6 is still possible, but not probable...
Don Hodges
dhodges@...
http://www.ecoastlife.com
Your Cyber-Vacation - Loafing on the Emerald Coast
Small Boats, Building, Fishing, Paddling, Rowing, Sailing