Re: [bolger] Second Installment - Emerald Coaster in the Keys
In a message dated 3/22/01 10:36:54 PM Central Standard Time,
don_dihodges@... writes:
Don:
Don't knock yourself out over this. But I think it would be very
interesting to the Bolger group, given Bolger's many light, long and narrow
power-craft designs, to have some hard (weight, length, horsepower and speed)
numbers to compare to the two very different formulae that Gerr uses.
As to "hobby-horsing" at full power and speed, you might try some
small wedges at the stern (beam?) of "Sweet Caroline". Some years ago, my
father did a rather complete rebuild of a ca. 1946 Garwood 16' runabout - a
perfectly miserable boat with an enormous 6 cylinder flat-head engine of
prodigious weight given the size of the boat. It was an absolutely miserable
vehicle when not on "plane". When run at full throttle on flat water, it was
still capable of approx. 40 mph, but it would begin to oscillate vertically
with ever increasing amplitude to the point that I was too frightened by it
to keep the throttle open. The addition of a pair of wooden wedges, of
rather small dimensions, under the stern killled the oscillation and
permitted me to run at full throttle to my heart's content without any
anxiety.
Ciao for Niao,
Bill in MN
don_dihodges@... writes:
Bill, thanks. I'll try to get her weighed this spring sometime.
Don:
Don't knock yourself out over this. But I think it would be very
interesting to the Bolger group, given Bolger's many light, long and narrow
power-craft designs, to have some hard (weight, length, horsepower and speed)
numbers to compare to the two very different formulae that Gerr uses.
As to "hobby-horsing" at full power and speed, you might try some
small wedges at the stern (beam?) of "Sweet Caroline". Some years ago, my
father did a rather complete rebuild of a ca. 1946 Garwood 16' runabout - a
perfectly miserable boat with an enormous 6 cylinder flat-head engine of
prodigious weight given the size of the boat. It was an absolutely miserable
vehicle when not on "plane". When run at full throttle on flat water, it was
still capable of approx. 40 mph, but it would begin to oscillate vertically
with ever increasing amplitude to the point that I was too frightened by it
to keep the throttle open. The addition of a pair of wooden wedges, of
rather small dimensions, under the stern killled the oscillation and
permitted me to run at full throttle to my heart's content without any
anxiety.
Ciao for Niao,
Bill in MN
Bill, thanks. I'll try to get her weighed this spring
sometime. I got into a "death march" to complete her and be in the Keys by
3/10, so I HAVE to do some work around the house right now. I'm very
pleased with the "width" of the performance envelope, from idling at 3 mph to
travelling at 20-24. After that, it gets pretty squirrelly and
hobby-horses pretty badly at 26-30. I would have been happy with 20
mph.
I should have bought the 4-stroke 25 hp for about the same
money, but the schedule didn't allow any experimenting and I was afraid she
would be sluggish to plane. Turns out these narrow, light boats
don't mush, just accelerate...
BTW, I got the rest of the pictures up tonight:
----- Original Message -----From:wmrpage@...Sent:Thursday, March 22, 2001 9:14 PMSubject:Re: [bolger] Second Installment - Emerald Coaster in the KeysIn a message dated 3/21/01 8:38:02 AM Central Standard Time,
don_dihodges@...writes:I got another page scanned in...
Don:
I believe that I got involved in an e-mail exchange about the powering
of your boat a while back and contrived a way to plug both the "Crouch" (i.e.
planing) and the "displacement" bhp/lbs./kts formulas from Gerr's "Propellor
Handbook" in a spreadsheet to produce hp/kts graphs with absolutely no
confidence in the results. I think it would be great if you could provide us
with lwl/lbs./hp/kts. data on your boat, as you seem to have all the
necessary stuff to do that and this kind of data is not readily available.
(Person, having built the boats. seem to be having too much fun with them to
bother with the hassle of weighing them. Without accurate weight data the
formulas are so much nonsense. One never knows how far one can trust reported
speeds, either.) I am pretty sure that neither of these standard formulae
provides a very good guide to performance of this kind of low-displacement,
flat-bottomed boat, but the points at which the hp/kts curves diverge (quite
dramatically) has not suggested any obvious relation to S/L ration or lb./hp
ratio or any other variable that I have divined. Even one max kts @ lbs.
disp. @ lwl data point could be the start of a useful database.
Lurking, as usual,
Bill in MN
P.S. I enjoyed your pictures. Water in my neck of the woods won't "soften"
for another month or so!
Bolger rules!!!
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In a message dated 3/21/01 8:38:02 AM Central Standard Time,
don_dihodges@... writes:
Don:
I believe that I got involved in an e-mail exchange about the powering
of your boat a while back and contrived a way to plug both the "Crouch" (i.e.
planing) and the "displacement" bhp/lbs./kts formulas from Gerr's "Propellor
Handbook" in a spreadsheet to produce hp/kts graphs with absolutely no
confidence in the results. I think it would be great if you could provide us
with lwl/lbs./hp/kts. data on your boat, as you seem to have all the
necessary stuff to do that and this kind of data is not readily available.
(Person, having built the boats. seem to be having too much fun with them to
bother with the hassle of weighing them. Without accurate weight data the
formulas are so much nonsense. One never knows how far one can trust reported
speeds, either.) I am pretty sure that neither of these standard formulae
provides a very good guide to performance of this kind of low-displacement,
flat-bottomed boat, but the points at which the hp/kts curves diverge (quite
dramatically) has not suggested any obvious relation to S/L ration or lb./hp
ratio or any other variable that I have divined. Even one max kts @ lbs.
disp. @ lwl data point could be the start of a useful database.
Lurking, as usual,
Bill in MN
P.S. I enjoyed your pictures. Water in my neck of the woods won't "soften"
for another month or so!
don_dihodges@... writes:
I got another page scanned in...
Don:
I believe that I got involved in an e-mail exchange about the powering
of your boat a while back and contrived a way to plug both the "Crouch" (i.e.
planing) and the "displacement" bhp/lbs./kts formulas from Gerr's "Propellor
Handbook" in a spreadsheet to produce hp/kts graphs with absolutely no
confidence in the results. I think it would be great if you could provide us
with lwl/lbs./hp/kts. data on your boat, as you seem to have all the
necessary stuff to do that and this kind of data is not readily available.
(Person, having built the boats. seem to be having too much fun with them to
bother with the hassle of weighing them. Without accurate weight data the
formulas are so much nonsense. One never knows how far one can trust reported
speeds, either.) I am pretty sure that neither of these standard formulae
provides a very good guide to performance of this kind of low-displacement,
flat-bottomed boat, but the points at which the hp/kts curves diverge (quite
dramatically) has not suggested any obvious relation to S/L ration or lb./hp
ratio or any other variable that I have divined. Even one max kts @ lbs.
disp. @ lwl data point could be the start of a useful database.
Lurking, as usual,
Bill in MN
P.S. I enjoyed your pictures. Water in my neck of the woods won't "soften"
for another month or so!
All,
I got another page scanned in...