TWL: Re: Hull Speed
Sorry to burst your bubble, but a full displacement hull will never, ever
plane! Put enough power on it and the stern will submerge!
I remember a surface run in a Skipjack class submarine. The boat, with the
hull form of a sewer pipe, took a 17 degree up angle. I can't tell you the
speed or power - whenever I do, my driveway fills up with black Chevy
Suburbans.
Al Schober
On the subject of hull speed and hull form there are two timely articles in
the latest wooden boat magazine and a very interesting article about
light weight passage maker yachts in the current issue of Professional Boat
builder magazine.
Tad Roberts, a Naval architect associated with Bruce King Yacht design for
about 14 years now has his own design office on Gabriola Island in BC.
The Tad Roberts article titled Passagemaker Lite explains how the designer
was inspired by such designs as Robert Bebee's original passagemaker and
also the Avard Fuller designed "Jim Hawkins" a 61 foot motor sailer,
built in 1969.
Both magazines have articles that would contribute to the present thread.
regards
Arild
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http://www.tadroberts.com/pssgmkrlite.html
----- Original Message -----
From: "Arild Jensen" elnav@uniserve.com
To: trawler-world-list@lists.samurai.com
Sent: Thursday, February 13, 2003 10:47 AM
Subject: TWL: RE: Re: Hull Speed
Tad Roberts, a Naval architect associated with Bruce King Yacht design
for
about 14 years now has his own design office on Gabriola Island in BC.
The Tad Roberts article titled Passagemaker Lite explains how the
designer
was inspired by such designs as Robert Bebee's original passagemaker and
also the Avard Fuller designed "Jim Hawkins" a 61 foot motor sailer,
built in 1969.
From National Geographic: "hydrodynamic teardrop hull design that was first
tested on a conventionally powered sub. All U.S. nuclear subs since have
used this basic combination." It is a highly sophisticated sewer pipe.
Although listed as going 25+ knots, I do remember a newspaper story about a
Skipjack tailing a nuclear carrier west in the Pacific. After a great many
miles, the carrier pulled ahead.
----- Original Message -----
From: "Al Schober" aeschober@snet.net
I remember a surface run in a Skipjack class submarine. The boat, with
the
hull form of a sewer pipe, took a 17 degree up angle. I can't tell you
the
speed or power - whenever I do, my driveway fills up with black Chevy
Suburbans.
At 12:05 PM 2/13/03 -0500, you wrote:
A few observations about the 2 boats at the URL above.
The draft is pretty shallow, 3' 6" and 2' 10".
Horsepower total , 150, 120.
For hulls 55', 45'.
Narrow beam, 13 for the 55.
The claimed top speed seems a little high for that little power, BUT the
narrow beam, light weight, shallow draft might make it realistic.
If so, then both hulls are exceeding the 1.34 rule, I estimate about 1.55
or thereabouts.
I don't see that the hull profile would lead to a boat that would be
particularly rolly, but it would be more susceptible to chop, than a hull
with more draft.
The higher speed, if even only used in a pinch is very valuable in my opinion.
I would be very leery of such a design with it's limitations, if it did not
have a good turn of speed.
Overall, I like the boats and think they would both be fine cruisers, but
the design has it's limitations.
I doubt this is intended for blue water work.
Capt. Mike Maurice
Wilsonville, Near Portland Oregon
-----Original Message-----
From: Mike Maurice
A few observations about the 2 boats at the URL above.
The draft is pretty shallow, 3' 6" and 2' 10".
Horsepower total , 150, 120.
For hulls 55', 45'.
Narrow beam, 13 for the 55.
The claimed top speed seems a little high for that little power, BUT the
narrow beam, light weight, shallow draft might make it realistic.
If so, then both hulls are exceeding the 1.34 rule, I estimate about 1.55
or thereabouts.
Overall, I like the boats and think they would both be fine cruisers, but
the design has it's limitations.
I doubt this is intended for blue water work.
REPLY
My first boat with an overall length of 49' 6" beam of 10' and draft of
4'6" did achieve such speeds using two Perkins of 65 HP each.
At 10 knots and no wind or heavy seas the engines were not WOT. probably
only about 85%
Admittedly such a design is not what we are accustomed to and might not
be agreeable for living aboard.
Although I did live aboard for slightly more than a year, beginning in
November in Toronto harbour ( Brrrr! -20F )
I think the claims are not outrageous nor unduly exaggerated. but as
mentioned in other articles these are essentially flat water conditions.
Cheers
Arild
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