Re: 2/3 scale Anhinga adventures
--- Inbolger@yahoogroups.com, "Myles J. Swift" <mswift@...> wrote:
centerboard and rudder will help that. Ruell Parker said he had the
same problems with his Maryland crabbing skiff, fast but requires you
to plan ahead a bit. He says he hit the dock a couple of times until
he learned how to handle it.
trailer.
the water.
>that tacking will be slow. I'm looking at whether changes to the
> Actually, Sandy is reported to be "slippery as an eel". I do agree
centerboard and rudder will help that. Ruell Parker said he had the
same problems with his Maryland crabbing skiff, fast but requires you
to plan ahead a bit. He says he hit the dock a couple of times until
he learned how to handle it.
>something that is going to be in the 500 pound range for boat and
> The Black Skimmer is much bigger (nearly 8 feet longer) and not
trailer.
>Not a great picture, but it looked to me as though the bow is out of
>
> MylesJ
>
> [Non-text portions of this message have been removed]
>
the water.
Actually, Sandy is reported to be "slippery as an eel". I do agree that tacking will be slow. I'm looking at whether changes to the centerboard and rudder will help that. Ruell Parker said he had the same problems with his Maryland crabbing skiff, fast but requires you to plan ahead a bit. He says he hit the dock a couple of times until he learned how to handle it.
The Black Skimmer is much bigger (nearly 8 feet longer) and not something that is going to be in the 500 pound range for boat and trailer.
MylesJ
[Non-text portions of this message have been removed]
The Black Skimmer is much bigger (nearly 8 feet longer) and not something that is going to be in the 500 pound range for boat and trailer.
MylesJ
[Non-text portions of this message have been removed]
> Go herehttp://www.dngoodchild.com/divide_for_sail_boats.htmLookWouldn't build it myself, probably a dog, and difficult to tack. Compare
> under daysailers over 15 foot for Sandy. Stem and stern are in the
> water. I've like the hull but I'm not sure about the sail plan. I'd
> build it in ply and use a metal centerboard to get back to stock
> weight.
to Bolger's Black Skimmer, a very nicely handling boat in a breeze, esp.
in shallow water breezes with square waves.
Chris,
Go herehttp://www.dngoodchild.com/divide_for_sail_boats.htm
Look under daysailers over 15 foot for Sandy. Stem and stern are in the water. I've like the hull but I'm not sure about the sail plan. I'd build it in ply and use a metal centerboard to get back to stock weight.
MylesJ
Micro
Junebug
Tortoise
[Non-text portions of this message have been removed]
Go herehttp://www.dngoodchild.com/divide_for_sail_boats.htm
Look under daysailers over 15 foot for Sandy. Stem and stern are in the water. I've like the hull but I'm not sure about the sail plan. I'd build it in ply and use a metal centerboard to get back to stock weight.
MylesJ
Micro
Junebug
Tortoise
[Non-text portions of this message have been removed]
> Keep in mind that sailing boats heel, and often many degrees. ThisYes, exactly. "Plumb" bow refers to a different dimension than a
> will exaggerate differences in a pointy bow, with minimal flotation
> up there.
> I can imagine that digging into a wave with the bow, while heeled,
> can be a surprising and unwelcome experience. That's where clearing
> the water with an upturned bow might come in handy. Not so much with
> a powerboat or a rowboat.
> ________________________________________________________________________
> 1b. Re: 2/3 scale Anhinga adventures Posted by: "rick barnes"
>
> Yet most sharpies that are said to be very "seaworthy" and "are best
> sailed with a chine exposed", have a plumb, or nearly plumb bow stem.
> Rick
"pointy" bow. A plumb bow simply means that the stem is at 90 degrees to
the water's surface. But a pointy bow refers to the angle at which the
hull sides meet at the stem. (It can also refer to the prismatic
coefficient, but let's ignore that complexity for now.)
I am suggesting that the rocker forward is a good thing, and you will
find in most sharpies, whether indigenous to Long Island Sound, the
Chesapeake, or south Florida, will show significant rocker (upsweep)
forward. Bolger writes about this in several publications.
In short, in a sailboat, it's "A Good Thing" and is replaced with a
different design choice only rarely (multihulls is one example).
-Chris
Yet most sharpies that are said to be very "seaworthy" and "are best sailed with a chine exposed", have a plumb, or nearly plumb bow stem.
Rick
----- Original Message ----
From: Chris Crandall <crandall@...>
To:bolger@yahoogroups.com
Sent: Thursday, June 12, 2008 2:30:12 PM
Subject: [bolger] Re: 2/3 scale Anhinga adventures
exaggerate differences in a pointy bow, with minimal flotation up there.
I cam imagine that digging into a wave with the bow, while heeled, can
be a surprising and unwelcome experience. That's where clearing the
water with an upturned bow might come in handy. Not so much with a
powerboat or a rowboat.
-Chris
[Non-text portions of this message have been removed]
Rick
----- Original Message ----
From: Chris Crandall <crandall@...>
To:bolger@yahoogroups.com
Sent: Thursday, June 12, 2008 2:30:12 PM
Subject: [bolger] Re: 2/3 scale Anhinga adventures
> Posted by: "rick barnes" barnesrickw@ yahoo.com barnesrickw Date: ThuKeep in mind that sailing boats heel, and often many degrees. This will
> Jun 12, 2008 5:52 am ((PDT))
>
> I'm reading Chapelle's book, the American Small Sailing Craft, and he
> points out for sharpies the entry should be just clear of the
> waterline, and the exit more clear of the water line. Most Bolger
> boats I have see also do this. However, I have seen skiffs Forest &
> Stream Skiff (1890?) that have a plumb stem that is submerged in the
> water, but the exit is still clear. If the drag is little, as what
> would be there with a skeg keel or extended rudder that classic
> sharpies have, I can't see where there would be much difference in a
> sailing boat.
exaggerate differences in a pointy bow, with minimal flotation up there.
I cam imagine that digging into a wave with the bow, while heeled, can
be a surprising and unwelcome experience. That's where clearing the
water with an upturned bow might come in handy. Not so much with a
powerboat or a rowboat.
-Chris
[Non-text portions of this message have been removed]
> Posted by: "rick barnes"barnesrickw@...barnesrickw Date: ThuKeep in mind that sailing boats heel, and often many degrees. This will
> Jun 12, 2008 5:52 am ((PDT))
>
> I'm reading Chapelle's book, the American Small Sailing Craft, and he
> points out for sharpies the entry should be just clear of the
> waterline, and the exit more clear of the water line. Most Bolger
> boats I have see also do this. However, I have seen skiffs Forest &
> Stream Skiff (1890?) that have a plumb stem that is submerged in the
> water, but the exit is still clear. If the drag is little, as what
> would be there with a skeg keel or extended rudder that classic
> sharpies have, I can't see where there would be much difference in a
> sailing boat.
exaggerate differences in a pointy bow, with minimal flotation up there.
I cam imagine that digging into a wave with the bow, while heeled, can
be a surprising and unwelcome experience. That's where clearing the
water with an upturned bow might come in handy. Not so much with a
powerboat or a rowboat.
-Chris
I'm reading Chapelle's book, the American Small Sailing Craft, and he points out for sharpies the entry should be just clear of the waterline, and the exit more clear of the water line. Most Bolger boats I have see also do this. However, I have seen skiffs Forest & Stream Skiff (1890?) that have a plumb stem that is submerged in the water, but the exit is still clear. If the drag is little, as what would be there with a skeg keel or extended rudder that classic sharpies have, I can't see where there would be much difference in a sailing boat. But i just like to look at them, and am not qualified to design them. On that and your other calculations, John Teal has a book "How to Design a Boat", ISBN 0-7136-3529-0. It shows ways to calculate a lot of what you are looking for.
Rick
----- Original Message ----
From: graeme19121984 <graeme19121984@...>
To:bolger@yahoogroups.com
Sent: Thursday, June 12, 2008 7:58:49 AM
Subject: [bolger] Re:2/3 scale Anhinga adventures
Hi Rick,
I assumed propelling the model at less than its hull speed might be
something technical to do with Froud and wave physics, resistance
curves, etc. I guess that could apply to the slowmo videoing, which
when played back at normal speed should look something like the
performance of the full sized boat at hull speed, which is all a bit
beyond my ken...
I think all that may be more data than I'm after. I think a full
sized Anhinga would sail just about as you could expect it to for
what it is, and a bit more or less here or there is not a big deal.
And the Economy Seagoing Cruiser, no race boat or commercial vessel
either, is primarily about economy and perhaps a stylistic statement
too - given some fundamentals like safety and so on. The safety and
functional issues of concern, as far as I know, haven't a lot to do
with time, speed or fuel cost, but with knockdown, capsize, self
rescue and righting, and flooding. I think mostly those issues can be
studied in static pull down tests of a close to type model. If the
model is as big as a useable dinghy, and is at all tolerable for that
use after testing, then that's a plus. I have an idea that a large
model and the testing procedures can have a bit more leeway in the
allowable tolerances than a much smaller model, and still be
acceptable proof one way or the other. A much smaller model is
cheaper in materials, but this will be a rough and dirty dinghy
anyway - and I'm inclined to back Bolger who has backed Anhinga as
workable more than once. Eeek! worked and I expect by playing around
with ballast, and rig this 2/3 Anhinga (give or take) dinghy can be
made to work. What's important first though are realistic capsize
tests to prove something bigger fit for the sea.
Assuming (and I do) that the concept of the deep pointy stern proves
not to be fatally flawed, then after taking performance into account,
will it really hold up as economical in comparison to Bolger's other
types of larger ballasted sharpies?
Graeme
Rick
----- Original Message ----
From: graeme19121984 <graeme19121984@...>
To:bolger@yahoogroups.com
Sent: Thursday, June 12, 2008 7:58:49 AM
Subject: [bolger] Re:2/3 scale Anhinga adventures
Hi Rick,
I assumed propelling the model at less than its hull speed might be
something technical to do with Froud and wave physics, resistance
curves, etc. I guess that could apply to the slowmo videoing, which
when played back at normal speed should look something like the
performance of the full sized boat at hull speed, which is all a bit
beyond my ken...
I think all that may be more data than I'm after. I think a full
sized Anhinga would sail just about as you could expect it to for
what it is, and a bit more or less here or there is not a big deal.
And the Economy Seagoing Cruiser, no race boat or commercial vessel
either, is primarily about economy and perhaps a stylistic statement
too - given some fundamentals like safety and so on. The safety and
functional issues of concern, as far as I know, haven't a lot to do
with time, speed or fuel cost, but with knockdown, capsize, self
rescue and righting, and flooding. I think mostly those issues can be
studied in static pull down tests of a close to type model. If the
model is as big as a useable dinghy, and is at all tolerable for that
use after testing, then that's a plus. I have an idea that a large
model and the testing procedures can have a bit more leeway in the
allowable tolerances than a much smaller model, and still be
acceptable proof one way or the other. A much smaller model is
cheaper in materials, but this will be a rough and dirty dinghy
anyway - and I'm inclined to back Bolger who has backed Anhinga as
workable more than once. Eeek! worked and I expect by playing around
with ballast, and rig this 2/3 Anhinga (give or take) dinghy can be
made to work. What's important first though are realistic capsize
tests to prove something bigger fit for the sea.
Assuming (and I do) that the concept of the deep pointy stern proves
not to be fatally flawed, then after taking performance into account,
will it really hold up as economical in comparison to Bolger's other
types of larger ballasted sharpies?
Graeme
--- In bolger@yahoogroups. com, rick barnes <barnesrickw@ ...> wrote:
>
> I don't know much about models, but why would the velocity not be
the square root of the water line length times 1.34 like that of
other boats. (Unless it's a non displacement hull). I saw a video
once where a guy increased the motor for a model tug. He succeeded
in making a bigger wave, but not a longer wave, and therefore,
basically made his tug into a sub.
>
> Rick
__________________________________________________
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[Non-text portions of this message have been removed]
Hi Rick,
I assumed propelling the model at less than its hull speed might be
something technical to do with Froud and wave physics, resistance
curves, etc. I guess that could apply to the slowmo videoing, which
when played back at normal speed should look something like the
performance of the full sized boat at hull speed, which is all a bit
beyond my ken...
I think all that may be more data than I'm after. I think a full
sized Anhinga would sail just about as you could expect it to for
what it is, and a bit more or less here or there is not a big deal.
And the Economy Seagoing Cruiser, no race boat or commercial vessel
either, is primarily about economy and perhaps a stylistic statement
too - given some fundamentals like safety and so on. The safety and
functional issues of concern, as far as I know, haven't a lot to do
with time, speed or fuel cost, but with knockdown, capsize, self
rescue and righting, and flooding. I think mostly those issues can be
studied in static pull down tests of a close to type model. If the
model is as big as a useable dinghy, and is at all tolerable for that
use after testing, then that's a plus. I have an idea that a large
model and the testing procedures can have a bit more leeway in the
allowable tolerances than a much smaller model, and still be
acceptable proof one way or the other. A much smaller model is
cheaper in materials, but this will be a rough and dirty dinghy
anyway - and I'm inclined to back Bolger who has backed Anhinga as
workable more than once. Eeek! worked and I expect by playing around
with ballast, and rig this 2/3 Anhinga (give or take) dinghy can be
made to work. What's important first though are realistic capsize
tests to prove something bigger fit for the sea.
Assuming (and I do) that the concept of the deep pointy stern proves
not to be fatally flawed, then after taking performance into account,
will it really hold up as economical in comparison to Bolger's other
types of larger ballasted sharpies?
Graeme
I assumed propelling the model at less than its hull speed might be
something technical to do with Froud and wave physics, resistance
curves, etc. I guess that could apply to the slowmo videoing, which
when played back at normal speed should look something like the
performance of the full sized boat at hull speed, which is all a bit
beyond my ken...
I think all that may be more data than I'm after. I think a full
sized Anhinga would sail just about as you could expect it to for
what it is, and a bit more or less here or there is not a big deal.
And the Economy Seagoing Cruiser, no race boat or commercial vessel
either, is primarily about economy and perhaps a stylistic statement
too - given some fundamentals like safety and so on. The safety and
functional issues of concern, as far as I know, haven't a lot to do
with time, speed or fuel cost, but with knockdown, capsize, self
rescue and righting, and flooding. I think mostly those issues can be
studied in static pull down tests of a close to type model. If the
model is as big as a useable dinghy, and is at all tolerable for that
use after testing, then that's a plus. I have an idea that a large
model and the testing procedures can have a bit more leeway in the
allowable tolerances than a much smaller model, and still be
acceptable proof one way or the other. A much smaller model is
cheaper in materials, but this will be a rough and dirty dinghy
anyway - and I'm inclined to back Bolger who has backed Anhinga as
workable more than once. Eeek! worked and I expect by playing around
with ballast, and rig this 2/3 Anhinga (give or take) dinghy can be
made to work. What's important first though are realistic capsize
tests to prove something bigger fit for the sea.
Assuming (and I do) that the concept of the deep pointy stern proves
not to be fatally flawed, then after taking performance into account,
will it really hold up as economical in comparison to Bolger's other
types of larger ballasted sharpies?
Graeme
--- Inbolger@yahoogroups.com, rick barnes <barnesrickw@...> wrote:
>
> I don't know much about models, but why would the velocity not be
the square root of the water line length times 1.34 like that of
other boats. (Unless it's a non displacement hull). I saw a video
once where a guy increased the motor for a model tug. He succeeded
in making a bigger wave, but not a longer wave, and therefore,
basically made his tug into a sub.
>
> Rick
I don't know much about models, but why would the velocity not be the square root of the water line length times 1.34 like that of other boats. (Unless it's a non displacement hull). I saw a video once where a guy increased the motor for a model tug. He succeeded in making a bigger wave, but not a longer wave, and therefore, basically made his tug into a sub.
Rick
----- Original Message ----
From: graeme19121984 <graeme19121984@...>
To:bolger@yahoogroups.com
Sent: Wednesday, June 11, 2008 3:26:19 AM
Subject: [bolger] Re:2/3 scale Anhinga adventures
Here's some scaling factors I've garnered from yahoo boating groups'
discussions here and there (thanks to all those boaters):
Length x 1.
Volume ( including design displacement ) changes at the cube of the
increase/decrease in length.
Stability changes by the square.
Wetted area by the square.
Change scale dimensions to 1/2 , the wetted area will be 1/4,
stability 1/4, and displacement goes to 1/8.
Change scale to 1/3, the wetted area is 1/9, and the displacement
1/27, etc.
Change scale to 2/3, the wetted area scale is squared to 4/9 (0.44,
or say 1/3 for ease of approximating to 1/16th inch fractional
imperial measure), and the displacement scale is cubed to 8/27
(0.296 -- say 0.3, or again say 1/3) etc.
As for sailboats: radiocontrolled modelsailyachts have to set
stormsails at windforce 2 or 3 beaufort, also due to their light
weight.
When you study modelboat behavior on video you have to watch at
slowmotion, the degree of slomo depending on the scalefactor.
A modelboat should have a speed of the root of the scale to present a
realistic wavepattern, for instance a 1/100 scale boat should sail at
a speed 1/10 of the real thing.
------------ --------- --------- ------
Scaling up or down is a very tricky thing for judging boat behavior.
------------ --------- --------- ------
As you know, displacement is total weight. Thus if you row in person
a model of half the size, your CG will be extremely higher than
rowing the full size. Thus for a 2/3 scale Anhinga capsise test the
body weight of two average crew, say, 360lbs total, should be scaled
down by 8/27 (say 1/3) to 120lbs, and that COG of the scaled crew
weight should be at a scaled height above the bottom of, not the
linear scale of 2/3, but of the square of the scale being 4/9 (say
1/3)... (Or should the crew mass be scaled down by the square, and
not by the cube, as the crew mass and position are to do with
stability factors??? -- hmmm, no matter, either way here in
approximation that would still be a value of 1/3 - Whew!!)
Thus, should the 120lbs scaled crew COG be vertically repositioned by
9" (according to the square of the linear scale of 2/3, ie 1/3 the
distance for seated crew of approximately 27" in the full size
Anhinga) down from the position in the full sized model or up from
the bottom?? In other words by this reckoning should 120lbs crew COG
be 9" or 18" above the bottom. A smaller person half reclining, or
fully so, should cover either option, but does the COG of the water
ballast under them affect this? Should the 2/3 scaled length model
waterballast mass (weight), and COG position, be found and
repositioned by this same figuring as for the crew rather than the?
If the ballast COG height has to be scaled 1/3 off the bottom rather
than 2/3 then that might require solid ballast (sand, concrete?)
rather than water - as in Eeek!
Scaled speed testing for slow motion study for 2/3 Anhinga should be
by (2/3)^1/2.
Thus: approximate testing speed = 0.8 x WLL^1/2 x 1.34 = 0.8 x
21ft^1/2 x 1.34 = 4.9, say 5kts
------------ --------- --------- ----
To sum up the queries I got to today:
Should all included mass COG heights for crew, ballast, and gear, be
to the 2/3rd model scale, or to the square of that, approx 1/3? If to
the square, is that distance also measured from the bottom?
Are there any other issues/problems arising here I've missed?
Graeme
[Non-text portions of this message have been removed]
Rick
----- Original Message ----
From: graeme19121984 <graeme19121984@...>
To:bolger@yahoogroups.com
Sent: Wednesday, June 11, 2008 3:26:19 AM
Subject: [bolger] Re:2/3 scale Anhinga adventures
Here's some scaling factors I've garnered from yahoo boating groups'
discussions here and there (thanks to all those boaters):
Length x 1.
Volume ( including design displacement ) changes at the cube of the
increase/decrease in length.
Stability changes by the square.
Wetted area by the square.
Change scale dimensions to 1/2 , the wetted area will be 1/4,
stability 1/4, and displacement goes to 1/8.
Change scale to 1/3, the wetted area is 1/9, and the displacement
1/27, etc.
Change scale to 2/3, the wetted area scale is squared to 4/9 (0.44,
or say 1/3 for ease of approximating to 1/16th inch fractional
imperial measure), and the displacement scale is cubed to 8/27
(0.296 -- say 0.3, or again say 1/3) etc.
As for sailboats: radiocontrolled modelsailyachts have to set
stormsails at windforce 2 or 3 beaufort, also due to their light
weight.
When you study modelboat behavior on video you have to watch at
slowmotion, the degree of slomo depending on the scalefactor.
A modelboat should have a speed of the root of the scale to present a
realistic wavepattern, for instance a 1/100 scale boat should sail at
a speed 1/10 of the real thing.
------------ --------- --------- ------
Scaling up or down is a very tricky thing for judging boat behavior.
------------ --------- --------- ------
As you know, displacement is total weight. Thus if you row in person
a model of half the size, your CG will be extremely higher than
rowing the full size. Thus for a 2/3 scale Anhinga capsise test the
body weight of two average crew, say, 360lbs total, should be scaled
down by 8/27 (say 1/3) to 120lbs, and that COG of the scaled crew
weight should be at a scaled height above the bottom of, not the
linear scale of 2/3, but of the square of the scale being 4/9 (say
1/3)... (Or should the crew mass be scaled down by the square, and
not by the cube, as the crew mass and position are to do with
stability factors??? -- hmmm, no matter, either way here in
approximation that would still be a value of 1/3 - Whew!!)
Thus, should the 120lbs scaled crew COG be vertically repositioned by
9" (according to the square of the linear scale of 2/3, ie 1/3 the
distance for seated crew of approximately 27" in the full size
Anhinga) down from the position in the full sized model or up from
the bottom?? In other words by this reckoning should 120lbs crew COG
be 9" or 18" above the bottom. A smaller person half reclining, or
fully so, should cover either option, but does the COG of the water
ballast under them affect this? Should the 2/3 scaled length model
waterballast mass (weight), and COG position, be found and
repositioned by this same figuring as for the crew rather than the?
If the ballast COG height has to be scaled 1/3 off the bottom rather
than 2/3 then that might require solid ballast (sand, concrete?)
rather than water - as in Eeek!
Scaled speed testing for slow motion study for 2/3 Anhinga should be
by (2/3)^1/2.
Thus: approximate testing speed = 0.8 x WLL^1/2 x 1.34 = 0.8 x
21ft^1/2 x 1.34 = 4.9, say 5kts
------------ --------- --------- ----
To sum up the queries I got to today:
Should all included mass COG heights for crew, ballast, and gear, be
to the 2/3rd model scale, or to the square of that, approx 1/3? If to
the square, is that distance also measured from the bottom?
Are there any other issues/problems arising here I've missed?
Graeme
[Non-text portions of this message have been removed]
Here's some scaling factors I've garnered from yahoo boating groups'
discussions here and there (thanks to all those boaters):
Length x 1.
Volume ( including design displacement ) changes at the cube of the
increase/decrease in length.
Stability changes by the square.
Wetted area by the square.
Change scale dimensions to 1/2 , the wetted area will be 1/4,
stability 1/4, and displacement goes to 1/8.
Change scale to 1/3, the wetted area is 1/9, and the displacement
1/27, etc.
Change scale to 2/3, the wetted area scale is squared to 4/9 (0.44,
or say 1/3 for ease of approximating to 1/16th inch fractional
imperial measure), and the displacement scale is cubed to 8/27
(0.296 -- say 0.3, or again say 1/3) etc.
As for sailboats: radiocontrolled modelsailyachts have to set
stormsails at windforce 2 or 3 beaufort, also due to their light
weight.
When you study modelboat behavior on video you have to watch at
slowmotion, the degree of slomo depending on the scalefactor.
A modelboat should have a speed of the root of the scale to present a
realistic wavepattern, for instance a 1/100 scale boat should sail at
a speed 1/10 of the real thing.
------------------------------------
Scaling up or down is a very tricky thing for judging boat behavior.
------------------------------------
As you know, displacement is total weight. Thus if you row in person
a model of half the size, your CG will be extremely higher than
rowing the full size. Thus for a 2/3 scale Anhinga capsise test the
body weight of two average crew, say, 360lbs total, should be scaled
down by 8/27 (say 1/3) to 120lbs, and that COG of the scaled crew
weight should be at a scaled height above the bottom of, not the
linear scale of 2/3, but of the square of the scale being 4/9 (say
1/3)... (Or should the crew mass be scaled down by the square, and
not by the cube, as the crew mass and position are to do with
stability factors??? -- hmmm, no matter, either way here in
approximation that would still be a value of 1/3 - Whew!!)
Thus, should the 120lbs scaled crew COG be vertically repositioned by
9" (according to the square of the linear scale of 2/3, ie 1/3 the
distance for seated crew of approximately 27" in the full size
Anhinga) down from the position in the full sized model or up from
the bottom?? In other words by this reckoning should 120lbs crew COG
be 9" or 18" above the bottom. A smaller person half reclining, or
fully so, should cover either option, but does the COG of the water
ballast under them affect this? Should the 2/3 scaled length model
waterballast mass (weight), and COG position, be found and
repositioned by this same figuring as for the crew rather than the?
If the ballast COG height has to be scaled 1/3 off the bottom rather
than 2/3 then that might require solid ballast (sand, concrete?)
rather than water - as in Eeek!
Scaled speed testing for slow motion study for 2/3 Anhinga should be
by (2/3)^1/2.
Thus: approximate testing speed = 0.8 x WLL^1/2 x 1.34 = 0.8 x
21ft^1/2 x 1.34 = 4.9, say 5kts
----------------------------------
To sum up the queries I got to today:
Should all included mass COG heights for crew, ballast, and gear, be
to the 2/3rd model scale, or to the square of that, approx 1/3? If to
the square, is that distance also measured from the bottom?
Are there any other issues/problems arising here I've missed?
Graeme
discussions here and there (thanks to all those boaters):
Length x 1.
Volume ( including design displacement ) changes at the cube of the
increase/decrease in length.
Stability changes by the square.
Wetted area by the square.
Change scale dimensions to 1/2 , the wetted area will be 1/4,
stability 1/4, and displacement goes to 1/8.
Change scale to 1/3, the wetted area is 1/9, and the displacement
1/27, etc.
Change scale to 2/3, the wetted area scale is squared to 4/9 (0.44,
or say 1/3 for ease of approximating to 1/16th inch fractional
imperial measure), and the displacement scale is cubed to 8/27
(0.296 -- say 0.3, or again say 1/3) etc.
As for sailboats: radiocontrolled modelsailyachts have to set
stormsails at windforce 2 or 3 beaufort, also due to their light
weight.
When you study modelboat behavior on video you have to watch at
slowmotion, the degree of slomo depending on the scalefactor.
A modelboat should have a speed of the root of the scale to present a
realistic wavepattern, for instance a 1/100 scale boat should sail at
a speed 1/10 of the real thing.
------------------------------------
Scaling up or down is a very tricky thing for judging boat behavior.
------------------------------------
As you know, displacement is total weight. Thus if you row in person
a model of half the size, your CG will be extremely higher than
rowing the full size. Thus for a 2/3 scale Anhinga capsise test the
body weight of two average crew, say, 360lbs total, should be scaled
down by 8/27 (say 1/3) to 120lbs, and that COG of the scaled crew
weight should be at a scaled height above the bottom of, not the
linear scale of 2/3, but of the square of the scale being 4/9 (say
1/3)... (Or should the crew mass be scaled down by the square, and
not by the cube, as the crew mass and position are to do with
stability factors??? -- hmmm, no matter, either way here in
approximation that would still be a value of 1/3 - Whew!!)
Thus, should the 120lbs scaled crew COG be vertically repositioned by
9" (according to the square of the linear scale of 2/3, ie 1/3 the
distance for seated crew of approximately 27" in the full size
Anhinga) down from the position in the full sized model or up from
the bottom?? In other words by this reckoning should 120lbs crew COG
be 9" or 18" above the bottom. A smaller person half reclining, or
fully so, should cover either option, but does the COG of the water
ballast under them affect this? Should the 2/3 scaled length model
waterballast mass (weight), and COG position, be found and
repositioned by this same figuring as for the crew rather than the?
If the ballast COG height has to be scaled 1/3 off the bottom rather
than 2/3 then that might require solid ballast (sand, concrete?)
rather than water - as in Eeek!
Scaled speed testing for slow motion study for 2/3 Anhinga should be
by (2/3)^1/2.
Thus: approximate testing speed = 0.8 x WLL^1/2 x 1.34 = 0.8 x
21ft^1/2 x 1.34 = 4.9, say 5kts
----------------------------------
To sum up the queries I got to today:
Should all included mass COG heights for crew, ballast, and gear, be
to the 2/3rd model scale, or to the square of that, approx 1/3? If to
the square, is that distance also measured from the bottom?
Are there any other issues/problems arising here I've missed?
Graeme
Hi Myles,
thanks for your experienced input and the numbers. The ballast would
be like having two crew aboard!
I don't expect this boat to perform as well as June Bug - if at all
it has a second life as a tolerable boat to be kept going for just a
year or so after the scaled Anhinga capsize testing. I'm not real
sure of what it means exactly: this scale model pointy sterned boat
loses out in the quarters to June Bug in the ability to carry sail,
but then it has some ballast in that pointy stern to withstand sail.
However, the ballast probably means a deeper draft on the same beam
which should make it more tender initially, and the aft bottom likely
has more slowing wetted surface. I think it may be likely that it
will sail steadily enough after first settling into a heeled
attitude, but never as flat and fast as a June Bug.
It might row about as good as a Surf or June Bug, once up to speed
that is, never as fast on flat water; but the weight will count for
something as the chop rises (again, I think but don't know). Under
sail it won't be as nimble or lively as a June Bug or Surf: wetted
area and dragging the deep stern through turns will see to that I
think; but again the ballast weight may see it carry some way on...
If it has a post test life, and I'm hoping that can be arranged, I
think it would be more of a plodding estuary cruiser than good day
sailer. If it's able to get back after bobbing around sedately on the
bay in reasonable safety, then that'll do. I believe the actual
scaled down sail should be 62sqft, but you're right - a reefable
Jinni mainsail would give more options.
Graeme
thanks for your experienced input and the numbers. The ballast would
be like having two crew aboard!
I don't expect this boat to perform as well as June Bug - if at all
it has a second life as a tolerable boat to be kept going for just a
year or so after the scaled Anhinga capsize testing. I'm not real
sure of what it means exactly: this scale model pointy sterned boat
loses out in the quarters to June Bug in the ability to carry sail,
but then it has some ballast in that pointy stern to withstand sail.
However, the ballast probably means a deeper draft on the same beam
which should make it more tender initially, and the aft bottom likely
has more slowing wetted surface. I think it may be likely that it
will sail steadily enough after first settling into a heeled
attitude, but never as flat and fast as a June Bug.
It might row about as good as a Surf or June Bug, once up to speed
that is, never as fast on flat water; but the weight will count for
something as the chop rises (again, I think but don't know). Under
sail it won't be as nimble or lively as a June Bug or Surf: wetted
area and dragging the deep stern through turns will see to that I
think; but again the ballast weight may see it carry some way on...
If it has a post test life, and I'm hoping that can be arranged, I
think it would be more of a plodding estuary cruiser than good day
sailer. If it's able to get back after bobbing around sedately on the
bay in reasonable safety, then that'll do. I believe the actual
scaled down sail should be 62sqft, but you're right - a reefable
Jinni mainsail would give more options.
Graeme
--- Inbolger@yahoogroups.com, "Myles J. Swift" <mswift@...> wrote:
>
> Graeme,
>
> I think that you are off considering the 59 foot sail. That may be
what is on June Bug but June Bug and I weigh about 300 pounds under
sail. Add another person and things get slow. Maybe you should look
at the Jinni sail plan.
>
> MylesJ
>
> Micro
> June Bug
> Tortoise
Graeme,
I think that you are off considering the 59 foot sail. That may be what is on June Bug but June Bug and I weigh about 300 pounds under sail. Add another person and things get slow. Maybe you should look at the Jinni sail plan.
MylesJ
Micro
June Bug
Tortoise
[Non-text portions of this message have been removed]
I think that you are off considering the 59 foot sail. That may be what is on June Bug but June Bug and I weigh about 300 pounds under sail. Add another person and things get slow. Maybe you should look at the Jinni sail plan.
MylesJ
Micro
June Bug
Tortoise
[Non-text portions of this message have been removed]
Having looked at a slightly scaled up quick and dirty model of Eeek!
from time to time to more economically test the merits of a better
built Anhinga, which in turn would be to better test the merits of
the truly seductive Economy Seagoing Cruiser, I once more found
myself considering the problem via circuitous and web-like pathways
through Bolgerdom.
Eeek! has been proven to perform her role as a cruising sailing canoe
well. She seems a little tight to accomodate it, and of slightly
disimilar scale for the water-ballast test though. (She may be
somewhat more useful as conceived (cruising) if simply lengthened a
meter or so.) Dimensionally, she doesn't seem to fall into any ready
multiple for a larger overall scale-up. Her proporions are a bit
fiddly, and that means fairly detailed drawings, and probably a bit
of materials wastage.
Looking at June Bug as a more or less suitably proportioned and
dimensiond boat for a scaled up water ballast Eeek! test as a
comparitive design I found that Anhinga when scaled down by 2/3 hits
a lot of easy marks.
A 2/3rd Anhinga has the beam Bolger says often shouldn't be exceeded
for easy rowing. It's just a fraction more than the June Bug beam, so
I propose making it the same as the plumb-sided June Bug beam.
A 2/3rd Anhinga is exactly 15'6" LOA -- same as Surf, so sides can be
got out of two butted ply sheets.
A 2/3rd Anhinga has plumb sides about 30" high. I propose at this
stage they be 28", with the oar ports, though those will have to be
repositioned away from the stern.
A 2/3rd Anhinga of 4mm ply would be to scale, but I think
expensive. So about 7 sheets of 1/4" / 6mm ply to be used as in the
full sized. Not sure to double up the bottom per the plan - maybe one
layer of 3/8 / 9mm? Unlike JB or Anhingha, but like Surf which I
expect it to most closely come near to in performance, external chine
logs for quick and dirty construction, and foam in the very ends.
Most scantlings per Surf, or June Bug. Probably of the cheapest
possible marine ply and house paint, but may be Bunnings best, bog,
bondo and bitumen paint all slapped together. And some string.
A 2/3rd Anhinga would have a sail, reduced by the square of the scale
reduction to quite near to that of the Surf, June Bug, etc, so
probably will be the Bolger 59'er.
A 2/3rd Anhinga will have a diplacement, reduced by the cube of the
scale reduction, of near 1/3, so ~700lbs+
A 2/3rd Anhinga will likewise have reduced water ballast of about
145lbs.
A 2/3rd Anhinga will have a draft of ~5".
A 2/3rd Anhinga rudder is about 16" wide, I think. Are there
dimensions shown anywhere for the rudder frame? Anyone ever seen the
noted "inboard profile"? Does that have a pattern for the frame?
The idea would be to end up with a boat that may be more useful than
not after some Anhinga (Sandy Bottoms) flooding and ESC type tests. A
true scale model would be largely unuseable for regular sized people,
so the midships bulkhead and cockpit seats would be removable and
water proofed by duct tape, if not actually held in by it. I think
the water ballast tank may also be an easily removable box, though
these cockpit components and aft bulkhead may all be per the reduced
plan and just held for capsise testing etc by more duct tape and the
odd screw.
I am giving some thought to using solid ballast, both for the tests
and later use. ~~Perhaps if the water works out ok then that part can
be made permanent.
"Permanent" here means only a season or two if that- the boat once
modified for some actual use after the ESC test may well be a dog. So
it's chine logs, 'cause thery're quick and give some purchase when
attemping wet re-entries etc. 28" high as this is about the under-
deck heights of the Enigma and Otter, and I've had some ideas for a
while of adapting June Bug to the Enigma solo decked dinghy cruiser
role via sides raising and 3/4 decking. For the testing of water
ingress, righting, etc, the sides have to be proportionally about
this high but later, depending, they could be cut down to 15" or so.
If this works and proves the Anhinga I may go right past A and
prevail upon PB&F for the ESC. In the meantime a bit more thought, a
bit of building, documented testing, a bit less of rebuilding, and
then perhaps a tolerable water ballasted canoe yawl type cruiser for
a few seasons approaching Surf in size and performance.
I've really noticed now that the same point (well, it has to be the
same as I can't see what's different) on the ESC and Anhinga is
labelled differently by Bolger. On the Anhinga framing plan of the
bottom he shows the COB, and this corresponds to a point in the
profile plan of ESC that would be below a point he's labelled as COG.
I still think this may be so for level trim, but can't see how it
remains about midships as heeling progresses. I note he hasn't shown
COG on Anhinga, perhaps because of the water ballast which will shift
it, as I believe. The ballast in ESC may be metal and centrally
located and so the heeling effect on COG/COB won't be so noticeable.
The extra length and fineness may help too. We'll see.
Can anyone see how PCB gets a displacement for ESC of 8300lbs??
Displacement, and ballast scaled up from Anhinga, and adding
reasonable scantlings, people, stores, and gear seems to come well
short by, depending, up to a few 1000lbs!! It seems a smaller boat
than AS29 but... Hey, is it steel?
Are my Anhinga 2/3rd scaling factors, etc, anywhere near right? All
corrections gratefully received.
to other adventures
Graeme
from time to time to more economically test the merits of a better
built Anhinga, which in turn would be to better test the merits of
the truly seductive Economy Seagoing Cruiser, I once more found
myself considering the problem via circuitous and web-like pathways
through Bolgerdom.
Eeek! has been proven to perform her role as a cruising sailing canoe
well. She seems a little tight to accomodate it, and of slightly
disimilar scale for the water-ballast test though. (She may be
somewhat more useful as conceived (cruising) if simply lengthened a
meter or so.) Dimensionally, she doesn't seem to fall into any ready
multiple for a larger overall scale-up. Her proporions are a bit
fiddly, and that means fairly detailed drawings, and probably a bit
of materials wastage.
Looking at June Bug as a more or less suitably proportioned and
dimensiond boat for a scaled up water ballast Eeek! test as a
comparitive design I found that Anhinga when scaled down by 2/3 hits
a lot of easy marks.
A 2/3rd Anhinga has the beam Bolger says often shouldn't be exceeded
for easy rowing. It's just a fraction more than the June Bug beam, so
I propose making it the same as the plumb-sided June Bug beam.
A 2/3rd Anhinga is exactly 15'6" LOA -- same as Surf, so sides can be
got out of two butted ply sheets.
A 2/3rd Anhinga has plumb sides about 30" high. I propose at this
stage they be 28", with the oar ports, though those will have to be
repositioned away from the stern.
A 2/3rd Anhinga of 4mm ply would be to scale, but I think
expensive. So about 7 sheets of 1/4" / 6mm ply to be used as in the
full sized. Not sure to double up the bottom per the plan - maybe one
layer of 3/8 / 9mm? Unlike JB or Anhingha, but like Surf which I
expect it to most closely come near to in performance, external chine
logs for quick and dirty construction, and foam in the very ends.
Most scantlings per Surf, or June Bug. Probably of the cheapest
possible marine ply and house paint, but may be Bunnings best, bog,
bondo and bitumen paint all slapped together. And some string.
A 2/3rd Anhinga would have a sail, reduced by the square of the scale
reduction to quite near to that of the Surf, June Bug, etc, so
probably will be the Bolger 59'er.
A 2/3rd Anhinga will have a diplacement, reduced by the cube of the
scale reduction, of near 1/3, so ~700lbs+
A 2/3rd Anhinga will likewise have reduced water ballast of about
145lbs.
A 2/3rd Anhinga will have a draft of ~5".
A 2/3rd Anhinga rudder is about 16" wide, I think. Are there
dimensions shown anywhere for the rudder frame? Anyone ever seen the
noted "inboard profile"? Does that have a pattern for the frame?
The idea would be to end up with a boat that may be more useful than
not after some Anhinga (Sandy Bottoms) flooding and ESC type tests. A
true scale model would be largely unuseable for regular sized people,
so the midships bulkhead and cockpit seats would be removable and
water proofed by duct tape, if not actually held in by it. I think
the water ballast tank may also be an easily removable box, though
these cockpit components and aft bulkhead may all be per the reduced
plan and just held for capsise testing etc by more duct tape and the
odd screw.
I am giving some thought to using solid ballast, both for the tests
and later use. ~~Perhaps if the water works out ok then that part can
be made permanent.
"Permanent" here means only a season or two if that- the boat once
modified for some actual use after the ESC test may well be a dog. So
it's chine logs, 'cause thery're quick and give some purchase when
attemping wet re-entries etc. 28" high as this is about the under-
deck heights of the Enigma and Otter, and I've had some ideas for a
while of adapting June Bug to the Enigma solo decked dinghy cruiser
role via sides raising and 3/4 decking. For the testing of water
ingress, righting, etc, the sides have to be proportionally about
this high but later, depending, they could be cut down to 15" or so.
If this works and proves the Anhinga I may go right past A and
prevail upon PB&F for the ESC. In the meantime a bit more thought, a
bit of building, documented testing, a bit less of rebuilding, and
then perhaps a tolerable water ballasted canoe yawl type cruiser for
a few seasons approaching Surf in size and performance.
I've really noticed now that the same point (well, it has to be the
same as I can't see what's different) on the ESC and Anhinga is
labelled differently by Bolger. On the Anhinga framing plan of the
bottom he shows the COB, and this corresponds to a point in the
profile plan of ESC that would be below a point he's labelled as COG.
I still think this may be so for level trim, but can't see how it
remains about midships as heeling progresses. I note he hasn't shown
COG on Anhinga, perhaps because of the water ballast which will shift
it, as I believe. The ballast in ESC may be metal and centrally
located and so the heeling effect on COG/COB won't be so noticeable.
The extra length and fineness may help too. We'll see.
Can anyone see how PCB gets a displacement for ESC of 8300lbs??
Displacement, and ballast scaled up from Anhinga, and adding
reasonable scantlings, people, stores, and gear seems to come well
short by, depending, up to a few 1000lbs!! It seems a smaller boat
than AS29 but... Hey, is it steel?
Are my Anhinga 2/3rd scaling factors, etc, anywhere near right? All
corrections gratefully received.
to other adventures
Graeme