TWL: Re: High efficiency hulls
In a message dated 9/7/03 12:04:11 AM, Ben writes:
<< What's wrong about full displacement power boats? How come their design
seem
to be so poorly efficient comparing to the hull of a sailboat? Is there any
trawler on the market, except catamarans, which has some efficiency, >>
Ben,
Most sailboat hulls are designed to move efficiently at low speed with
moderate power. Without getting too technical, their prismatic coefficient, hull
surface area, etc. are optimized for S/L ratios of 1.1 to 1.4. Several full
displacement trawlers, notably the Willards, Gulfstars, and early Albins, are
designed along the same lines, and, in fact, could be ordered in a motorsailer
configuration. My 16,000 lb. Willard 30 Horizon slips along at 6 kts. using less
that a gallon of diesel an hour. But there are sacrifices for such easily
driven boats. The interior volume of a sailboat type hull is smaller than that of a
semi-displacement hull of the same LOA and weight. Full displacement boats
have a lower maximum practical speed. Most trawler owners are willing to trade
more fuel consumption for the additional creature comforts possible in a boxier
hull shape. However, if you are planning long passages under power where low
fuel consumption is essential, a full displacement easily driven hull is the
way to go.
A sailboat or canoe shaped transom is somewhat more efficient at low speed
but a faster boat needs a broader, flatter stern to provide adequate planing
surface. It also provides more interior volume at the rear of the boat.
Larry Z
At the risk of getting in way over my head about hull design, I wonder how
much of the difference between power boat and sailboat design is also a
function of sail boats having big heavy keels and big heavy masts. If you
have ever been aboard a sailboat without its mast you know it is not a happy
ride. Without the mast acting as a big balancing pole, the motion becomes
jerky and unpleasant. I would assume that the wider, flatter hulls of a
power boat are at least partly designed to make the motion in a seaway more
gentle. Or am I way off base?
Kent
----- Original Message -----
From: LRZeitlin@aol.com
To: trawler-world-list@lists.samurai.com
Sent: Sunday, September 07, 2003 6:49 AM
Subject: TWL: Re: High efficiency hulls
In a message dated 9/7/03 12:04:11 AM, Ben writes:
<< What's wrong about full displacement power boats? How come their design
seem
to be so poorly efficient comparing to the hull of a sailboat? Is there
any
trawler on the market, except catamarans, which has some efficiency, >>
Ben,
Most sailboat hulls are designed to move efficiently at low speed with
moderate power. Without getting too technical, their prismatic
coefficient, hull
surface area, etc. are optimized for S/L ratios of 1.1 to 1.4. Several
full
displacement trawlers, notably the Willards, Gulfstars, and early Albins,
are
designed along the same lines, and, in fact, could be ordered in a
motorsailer
configuration. My 16,000 lb. Willard 30 Horizon slips along at 6 kts.
using less
that a gallon of diesel an hour. But there are sacrifices for such easily
driven boats. The interior volume of a sailboat type hull is smaller than
that of a
semi-displacement hull of the same LOA and weight. Full displacement boats
have a lower maximum practical speed. Most trawler owners are willing to
trade
more fuel consumption for the additional creature comforts possible in a
boxier
hull shape. However, if you are planning long passages under power where
low
fuel consumption is essential, a full displacement easily driven hull is
the
way to go.
A sailboat or canoe shaped transom is somewhat more efficient at low speed
but a faster boat needs a broader, flatter stern to provide adequate
planing
surface. It also provides more interior volume at the rear of the boat.
Larry Z
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Kent & Gloria Lewis wrote:
At the risk of getting in way over my head about hull design, I wonder how
much of the difference between power boat and sailboat design is also a
function of sail boats having big heavy keels and big heavy masts.
snip<<
I would assume that the wider, flatter hulls of a power boat are at least partly
designed to make the motion in a seaway more
gentle. Or am I way off base?
Kent
REPLY
Kent you are quite right.
If you look at the very early steamships you will see that their hulls closely
resembled the sailing ship hulls.
I once owned a Sam Rabl designed sailboat which did not have any ballast.
Stability was derived entirely from hull shape with a hard chine.
The design was made for home construction with sawn frames as opposed to steam
bent frames.
When we modified the original gaff rig to a marconi rig and the mast was made 4
feet taller I added about 300 pounds of ballast by way of steel plates bolted
to the outside of the wooden keel. That helped give more righting moment to
compensate for the taller rig.
On the other hand my twin diesel double ended cruiser that I lived aboard
was almost a sailboat hull design.
At 24 tons displacement it could cruise at hull speed on about 2 gallons an
hour. The lead keel alone weighed 4 tons.
Robert Beebe was an early advocate of power boats with long narrow hulls. His
arguments are still valid.
Unfortunately, most people want more creature comforts than such a hull design
will accommodate and as a result we end up with ever beamier hulls that push
more water. That combined with the incessant demand for speed in our fast
paced society pretty well guarantees a preponderance of bulky, less efficient
hulls than what purely hydrodynamic theory would suggest as the ideal cruiser
hull shape.
Cheers
Arild
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Robert Beebe was an early advocate of power boats with long narrow hulls.
Also the late Bill Garden, who designed some extremely long/narrow boats
like "Captain Teach" (70' long, and 8' wide as I recall).
Unfortunately, most people want more creature comforts than such a hull
design will accommodate...
Accommodations are important, but I think a major driving factor in this
area is actually the cost of moorage. People are basically trying to
maximize the "value" that they can cram in a slip.
That combined with the incessant demand for speed in our fast paced
society pretty well guarantees a preponderance of bulky, less efficient
hulls than what purely hydrodynamic theory would suggest as the ideal
cruiser hull shape.
Actually, that relationship is backwards. Faster speed will come from
narrower boats.
Keith
Keith wrote:
Actually, that relationship is backwards. Faster speed will come from
narrower boats.
REPLY
I was thinking of the planing hull, not displacement hull.
The majority of boats, not just trawlers, are flat bottomed and beamy.
Even the big Carvers Bayliners and Searays often run at 10 knots or less
because the fuel cost at full planing speeds is too much for the owner.
Regrettably the average consumer eschew the traditional long and narrow hulls;
probably because they have been horn swoggled by the marketing hype in the
glitzy magazines.
Its time for a sea change and hopefully magazines like Georgs upcoming
publication will help educate the boating public.
cheers
Arild.
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Does anyone happen to have any data concerning the relative efficiency of
swath hulls compared to conventional catamarans.
regards
Arild
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Thanks Arild,
Reading Beebe's book, he also makes it clear that his designs need some form
of stabilization. But active fins are expensive and flopperstoppers are
difficult to set up, which may be OK on a long voyage but no fun on a three
hour tour. So how much of current hull design is an attempt to provide
"form stability" as a substutite for stabilization? And how successful
have they been?
Kent
SNIP<
Robert Beebe was an early advocate of power boats with long narrow
hulls. His
arguments are still valid.
Unfortunately, most people want more creature comforts than such a hull
design
will accommodate and as a result we end up with ever beamier hulls that
push
more water. That combined with the incessant demand for speed in our
fast
paced society pretty well guarantees a preponderance of bulky, less
efficient
hulls than what purely hydrodynamic theory would suggest as the ideal
cruiser
hull shape.
Reading Beebe's book, he also makes it clear that his designs need some
form
of stabilization. But active fins are expensive and flopperstoppers are
difficult to set up, which may be OK on a long voyage but no fun on a
three
hour tour.
Just a comment on the setup of flopperstoppers (a.k.a. paravanes). If
designed and rigged properly they are not difficult at all to set up. On
MOJO I simply use a shackle to connect the down wires and retrieval lines to
the birds (located on the aft rail), release the line that is used to
raise/lower the out rigger poles and give each pole a push. Once past about
15 degrees or so, gravity takes over and the poles self lower into position.
I then lift each bird out of it's holder and simply drop it overboard. The
entire process may take 5 minutes. Retrieval is equally simple. If it's
rough at all, I don't hesitate to deploy the "birds" for a three hour tour.
I'll also deploy them in a rolly anchorage - they do a remarkable job for
that as well. Based on my experience and the knowledge I've gained from
others who own and use flopperstoppers, I've come to the conclusion that
there is a great deal of mis-information among those who have never used
them as to the so-called difficulty of deploying and retrieving
flopperstoppers! It simply ain't so if you've rigged your boat properly!
As the great prophet Jimmy Buffet said, "Don't try to describe the ocean if
you've never seen it. Don't ever forget, you might just wind up being
wrong"!
Ray B.
m/v MOJO
Bebe Design #112 Passagemaker 49-10 in steel
www.mvmojo.com
I think Ray has said it all, I have talked to a lot people that have told me
how hard they are to use(paravanes) when in fact they have never even been
on a boat with paravanes.Also all the talk about the fish coming out of the
water and doind damage to the boat,too much movies I think. It takes me
about 10 min to depoly the rig and the wife a few min longer(only because
see dose not do it as much as I do.but she can!!) Also the use of them at
anchor is a great reason to have them.At anchor we use 600 sq in valves as
they seem to work better than the 300sq in fish(birds). A side note we also
have both active fin(Naiad's) and the paravanes.
I know a lot of people on this list like to bad mouth Nordhavn, But the
people at PAE have really got a great system for deploying and retrieving
the paravanes anyone can use it.
Andrew & Linda Fraser
M/V KAISOOBA N46
N6ZPK N6ZPL
----- Original Message -----Ray said< I've come to the conclusion that>
<there is a great deal of mis-information among those who have never used>
<them as to the so-called difficulty of deploying and retrieving>
<flopperstoppers! It simply ain't so if you've rigged your boat properly!>
-----Original Message-----
From:Ray B. m/v MOJO
Based on my experience and the knowledge I've gained from
others who own and use flopperstoppers, I've come to the conclusion that
there is a great deal of mis-information among those who have never used
them as to the so-called difficulty of deploying and retrieving
flopperstoppers!
REPLY
Something which I have seen very little mention of is the use of bilge keels to
reduce rolling while under way.
I agree that they are not as effective as flopper stoppers or active fins, but
when I look around the yards where a lot of fishing boats are hauled, I see an
number of these fitted to round bilged hulls.
Evidently there was some credence to use of these at one time.
Regards
Arild
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But active fins are expensive and flopperstoppers are difficult to set
up, which may be OK on a long voyage but no fun on a three hour tour.
Does anybody have any source of good information on designing and building
these things?
I've been contemplating adding paravanes to my 44' trawler (ferrocement,
round bilge, fairly heavy at 30 tons). One of the sites - I think it was
Krogen's - had a fairly long piece about how active fins were better and
that the cost was almost the same, so fins were the clear choice. Well,
Wesmar estimates about $23K for my boat and I simply can't believe that it
would cost anywhere near that much for paravanes.
Unfortunately, Kolstrand (fabricators of the fish) here in Seattle have
absolutely no design guidance to offer. I've been taking pictures of F/S
rigs that I run across and there is darned little commonality. There was an
article in PassageMaker a couple of years ago about a guy who built his own,
but everything else about that boat was so wacky looking that I hate to base
anything on that.
Keith
Keith,
Find a copy of the Robert Beebe's original Voyaging
Under Power - not the Leishman edition.
In the original, Bebee writes at some length about
para-vanes, their placement and deployment.
There's several used book stores on-line - I found my
copy at www.powells.com I think that there were two
copies available when I found mine about 2 months ago.
YMMV as always.
I'm sure that there are other resources available.
Have you googled 'em?
Regards,
Leo
--- Keith Pleas keithp@guideddesign.com wrote:
Does anybody have any source of good information on
designing and building
these things?
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Find a copy of the Robert Beebe's original Voyaging
Under Power - not the Leishman edition.
Ah, that explains it. I have the newer edition and it didn't have the
background info I expected from trolling references in the list archives.
Keith
Also the late Bill Garden...
I found it, and it was Good Old Boat. The piece was titled:
Bill Garden: A memoir
But I missed the subtitle:
One of Bill's pupils reminisces as the one-time mentor turns 85.
Keith
Subject: TWL: Bill Garden turns 85!
Also the late Bill Garden... ------- I was not aware he had passed away in
the past few days since I last saw him ???????