Hull design, heavy weather and efficiency
Who drives the market? Is it the boat builders or is it what the
public thinks they want?--promoted by builders? Cost of boat is
pretty much by weight. There are disadvantages to long boats--they
cost more to moor, but are more comfortable at sea. One can put as
much accomidation in a long narrow boat, as in a short fat boat and
have it more effecient. Consumers are limited in their choices and
often don't consider the alternatives.
Builders are generally interested in selling boats. If the market
were clamoring for long and narrow boats--efficient as all get out,
but with accommodations stretched out in a long and narrow
space--they would be building them.
Is Steve Dashew a "promoter" or a person who gets out there and does
it? I have known Steve for over 40 years and he is a person who
definately is out trying out his ideas. He has made a lifetime of
voyaging, diseminating information and designing boats a passion. I
would hope that his expertise is welcomed into the powerboat circles.
I have nothing but the greatest of admiration for Dashew whom I have
known for about 25 years since we were both multihull sailors. The
fact is the guy has one of the best marketing minds in boating and I
called him a "powerful promoter" out of recognition and respect.
But as someone else pointed out in another thread, Dashew is still
very much a sailboat man and his unsailboat demonstrates it. His
concept, logic and explanations are dazzling, his site,
extraordinary, yet I don't expect there will be a stampede to skinny
boats as a result.
I don't mean to pour cold sea water on theorizing about hull design
et al. Just aiming to provide a dose of realism.
--Georgs
At 05:34 PM 2/21/05 -0500, you wrote:
very much a sailboat man and his unsailboat demonstrates it. His
concept, logic and explanations are dazzling, his site,
extraordinary, yet I don't expect there will be a stampede to skinny
boats as a result.
Georgs,
I agree with your assessment in that Steve's experiments are worth doing,
dazzling and that at least with the power boat there may not be any
stampede to long and narrow. On the other hand, imagine the unimaginable,
like $5 a gallon diesel. We are in uncharted soundings, where the price of
fuel is concerned. Steve, may yet hit the bulls eye. If so, we may come to
praise his prophesy instead of thinking of him as a little crazy and in a
crazy world a crazy man may be king.
Regards,
Mike
Capt. Mike Maurice
Tualatin(Portland), Oregon
Steve may indeed be a little crazy, but only a little. The change to long
narrow boats will cause a significant increase in cost. This might be
justified for people that are planning on many thousands of miles per year
of travel but for the vast majority of users a 5 or 10 thousand dollar a
year premium for fuel costs will not cover the added cost of dockage,
storage, and initial cost of a 50% longer and 33% narrower boat. (In my
opinion)
So, the long, narrow boat is only for the few.
John Harris
John Harris wrote, "The change to long narrow boats will cause a significant
increase in cost. This might be justified for people that are planning on
many thousands of miles per year of travel but for the vast majority of
users a 5 or 10 thousand dollar a year premium for fuel costs will not cover
the added cost of dockage, storage, and initial cost of a 50% longer and 33%
narrower boat. (In my opinion)"
I waited for someone else to dispute this point, but nobody has so I guess
I'll do it.
Most designers and Naval architects say that cost is roughly proportional to
weight and by definition weight is equal to length at waterline (LWL) times
beam at water line (BWL) times draft (D) times the block coefficient (Cb)
times the density of water (dw). Therefore, cost is proportional to
LWLBWLDCbdw. By the rules of proportionality, we know we can eliminate
any constants and maintain proportionality, therefore if we keep the block
coefficient (Cb) and draft (D) constant (and for practical purposes the
density of water is constant) therefore, cost is proportional to LWL*BWL.
Therefore, if beam and length are varied inversely (i.e. if length is
increased by 1.5, then beam is reduces by the inverse or 1/(1.5)= 0.667)
then cost is constant.
In engineering we would call this the first order comparison, but in the
real world, second order effects may be significant. The primary second
order effects include reduced initial stability and increased propulsion
efficiency.
If we reduce the beam at the water line and keep the center of mass height
constant, then the initial stability is reduced. Therefore, to maintain the
initial stability we must reduce the height of the center of mass. Generally
this is done by eliminating double decking, which reduces internal space.
Sometimes the center of mass height can be reduced by improving arrangement
efficiency (i.e. mounting denser items lower in the hull or reducing the
height or weight of elevated structures) or improving structural efficiency
(higher strength to weight ratio materials allow more ballast to be placed
lower), otherwise ballast must be added which increases draft and cost.
Increasing length improves propulsion efficiency, which allows higher speed
at constant power or reduced power and less fuel at constant speed and
range. Reducing engine size reduces weight and cost and reducing fuel
capacity reduces total weight and compensates for the weight increase due to
reduced initial stability.
Experience shows that over a moderate range of length to beam ratios (i.e.
from L/B of 2.4 to 6) the second order effects tend to cancel and cost is
roughly proportional to beam times length.
Therefore, if a long/narrow passagemakers cost the same as a shorter/wider
passagemakers, but the longer/narrower passagemakers rides better and
provide better fuel efficiency, why do all builders (that I know of) build
and most buyers buy shorter/wider designs?
I believe passagemaker builders, build shorter/wider "passagemakers" because
it is lower risk. It is what many are more familiar with and they can cross
over into the coastal cruiser market and have better odds of breaking even
on their investment.
I believe that passakemaker buyers buy shorter/wider passagemakers because;
(1) it is lower risk to buy a production design that a custom design, (2)
production boats have better resale value, (3) production designs are almost
all that is available in the used market and (4) they are ignorant to the
advantages of longer/narrower designs.
Just my humble opinion.
Regards;
Mike Schooley
Designing "Portager" a transportable Passagemaker
Could only guess on what drives manufactures to make wide/short (ratio)
boats (perhaps the better 'feel' of the space/room inside?). But when it
comes to cost, even if the initial purchase price is the same ongoing costs
for Moorage, Hallouts, (insurance?), washing, etc will be higher. Anything
that is priced by LOA++ (++ being whatever the dockmaster can 'figure in'
when they 'measure' your boat :-)
This despite the many operational advantages of a longer/narrow boat...
(Bulbous bows are another: Remember one Nav Arch commenting: for the cost
of a BB on a pleasure boat, just put in 2 more feet of boat instead!)
-al-
----- Original Message -----
From: "Mike Schooley" schooley@keyway.net
To: "'Passagemaking Under Power List'"
passagemaking-under-power@lists.samurai.com
Sent: Sunday, February 27, 2005 6:05 PM
Subject: Re: [PUP] Hull design, heavy weather and efficiency
John Harris wrote, "The change to long narrow boats will cause a significant
increase in cost. This might be justified for people that are planning on
many thousands of miles per year of travel but for the vast majority of
users a 5 or 10 thousand dollar a year premium for fuel costs will not cover
the added cost of dockage, storage, and initial cost of a 50% longer and 33%
narrower boat. (In my opinion)"
I waited for someone else to dispute this point, but nobody has so I guess
I'll do it.
I believe that passakemaker buyers buy shorter/wider passagemakers because;
(1) it is lower risk to buy a production design that a custom design, (2)
production boats have better resale value, (3) production designs are almost
all that is available in the used market and (4) they are ignorant to the
advantages of longer/narrower designs.
Just my humble opinion.
Regards;
Mike Schooley
Designing "Portager" a transportable Passagemaker
Passagemaking-Under-Power Mailing List