Dear Jim,
Thanks your response. Which indeed was very much interesting.
I was commanding large ocean going freighters for a number of years and the
basic knowledge I have in naval architecture deals with pure displacement
ships, stability, shearing forces and bending moments (most of which I have
forgotten after the electonic lodicators came on ships) and has nothing to
do with the pleasure boats. I didn't sail for the last 19 years. I am
located in Greece and there are many islands around, good places for summer.
The weather in the summer months in
the Aegean sea is nice warm but very often you face NNE-NNW strong winds
B5-6 and sometimes B7 or more and changing very frequently among the
islands.(something very exciting for sailing boat funs) .
I do not like sails. I am too old for this. So, three years ago I bought a
35 foot, cruiser, built 1992, 2 x 230 hp, which has not deep V and comes
to 15 degrees deadrise. I took her to the marina from the slip and I almost
smashed all the boats at the pier. The maneuvering software I had in my head
was for single screw and, believe me it is a bit difficult to erase the hard
disk and install the twin screw software. After I lived with the boat for a
while, and visited the nearby boats at the pier, I noticed that even
expensive boats were not built in a seamanlike manner. I asked some dealers
why the builders do not make the fuel tanks accessible and inspect, or why
they do not install a small booster pump before the separators or why they
do not put hand rails in the right places.
The dealers stared at me like I came from the Mars.
One told me : Look captain, we do not know what are you talking about but we
inform you that
the first question of the prospective buyer is what s the speed and the
final word comes from the wife, who looks at the bathroom, which make sure
is shining. The hand rail in the right place will
not make the boat look better.
I realized that in this industry of the small pleasure crafts the
Engineering Vs Design or vice versa
is very much respected.
When I encountered choppy seas, I realized that this thing is only a toy. I
joined my neihbor who has
a cruiser of about same length and I just saw another toy.
When I encountered (following) quarter seas I was surprised to see that this
is a dangerous toy.
Then I decided to build a custom boat 45-52foot, which will be a sea ship,
without christmas
trees of useless led lights, with the side lights at the proper height, with
inspectable fuel tanks, with the cables well secured and running above the
water pipes, with the batteries in a place where you
can remove them, with space between bulkhead and engine so you can change
the drive belts without scratching your hands etc etc etc - not to exhaust
your patience.
I understand you. I also understand that designing or choosing a boat is a
"sea of compromise"
All I want is not to pray when I encounter quarter seas and I am prepared to
pay for the extra fuel.
I beleive that the ballast tank, when necessary will make the boat stiffer,
I will make my hull lines
bit thinner in the quarters, I will lose surface to plane. I will be
overpwered and use more power to
plane/semiplane etc. Of course a planning hull cannot be a displacement
hull. If this doesnot pay, then I will go for a pure displacement boat,
slower but I will not be praying in heavy weather.
You sound like a man who knows the seas! I would much appreciate your
comments/advices.
My very warm regards
AP
"Jim Woodward" jameslwoodward at attbi dot com wrote in message
...
Of course, Fintry is different from your thoughts. That's why I said
"Broadly speaking ...."
I disagree with the thrust of this:
A deep V sails better through heavy seas, but you have to be prepared to
spent more
energy to make her push the water aside and make her way through it. A
planing
or semi-planing hull needs less power and is faster, provided the sea
is
calm. Once the sea gets rough, this advantage less power/speed is
lost,
you have to slow down to reduce the pounding and, if things get worse,
then you probably think that your choice of a semi or planing hull was
not
right.
Later you say
In every case I will be spending more fuel/mile.
With which I agree.
At a displacement speed (S/L ratio below around roughly 1.2 or so) the
displacement hull will use less power than the planing hull, assuming
speed
and weight are the same. As you go faster, eventually the planing hull
does
better, because it planes -- gets up and out of its wave train which
otherwise is making it go uphill. You feel this in the average outboard,
as
you go faster, the boat starts to push a lot of water, then suddenly it
gets
up on plane and you can actually throttle back, using less power, and
still
stay on plane. There is only a fairly narrow speed range where the planing
hull on plane actually uses less power than it does when it is not on
plane
and even in that range, it may use more fuel than the displacement hull at
the same weight and speed.
This is why the so called "trawlers" that will do twelve knots with a 36'
boat need a lot of power and at seven knots will use more fuel than their
full displacement sisters -- you can't have it both ways in "normal" hulls
(no Swath, cats, or other newfangled modern things here). This is one of
several reasons why we eventually turned down Tarapunga (see
http://www.mvfintry.com/boatsnotbought.htm) -- she was designed as a
patrol
boat and used too much fuel for a really long distance cruiser. For an up
and down the East Coast (of the USA) boat, she'd be great.
-------
Now, ballasting down could be a great idea if you wanted to be able to
work
in difficult, choppy water -- Lake Erie for example. It could make you a
lot more comfortable as the weather piped up. And yes, ballasted down
would
use more fuel, so it could be good to pump it out for flat-water work.
There are, indeed, multispeed marine transmissions. You raise an
interesting question. In ordinary boats, you choose the prop to use the
maximum horsepower available from the engine,usually at its top speed.
The
propeller law (hp required varies approximately with the cube of
revolutions) then protects you at every other speed, because the required
horsepower almost always is less than the available horsepower at any
shaft
speed.
If you chose the prop (or props) for top speed when your light/heavy boat
is
light and you have, say 1000hp, to get her going on plane while light,
then
the horsepower needed for eight knots or so when she's heavy is only
around
50hp. Since that's so much less than the max, you'll probably have
trouble
getting her to go slow enough, particularly while docking. A "trolling
valve", which essentially allows the transmission clutches to slip for
long
periods could solve this problem for, I think, less money, than a two
speed.
TwinDisc also has a new "QuickShift" as well as their "Omega Control"
which
address these issues. Tarapunga (see above) was built with Omega Control
so
she could run at very slow speeds for long periods for survey work.
As you say, free surface is an issue, but you'd probably always have the
tanks either full or empty.
As to
(1) my concept is wrong (2) my concept is right but
only few prospective buyers would make such choice- so no target group.
I think it is (2). Weight, complication, space taken away, are all
killers.
Remember, too, how few 45 foot power boats ever leave the marina for more
than a few hours.....
--
Jim Woodward
www.mvFintry.com
"AP" wrote in message
...
Jim, thank you for your posting.
What you have between Fr. 2-6 and Fr. 41-45 is sort of fore peak and
after
peak tank, which
as far as I understand the effect is to make a pure displacement vessel
even
heavier/deeper or
to change the trim. (this possibility was reduced since you converted
the
fore peak to a bow thruster
compartment.
Indeed, what I am talking about is a different thing.
I take for granted (if I am wrong please correct me) that
A deep V sails better through heavy seas, but you have to be prepared to
spent more
energy to make her push the water aside and make her way through it
A planing or semi-planning hull needs less power and is faster,
provided
the sea is
calm. Once the sea gets rough, this advantage less power/speed is
lost,
you have to slow down
to reduce the pounding and, if things get worse, then you probably
think
that your choice of a semi or planing hull was not right.
If we place the displacement hull on a scale on zero and the lightest
planing hull on ten, any hull
you find on the market will cover two points one the scale. No more.
Your
mv Fintry is 0-1, a
low powered Hatteras goes 3-4, a Sealine goes 6-7 and a Baja sport boat
goes
8-9 and competition boats go to 10. A prospectvie buyer will make his
choice according to his needs.
And the manufacturers of mass production try to make the best hull form
for
each (narrow) range.
What I want to do is to ample the range for a hull (lets say from 3 to 6
or
7) and I am prepared
to pay the price, which to my understanding is that I will have to be
overpowered and give the engines more fuel than that of the Sealine and
I
wil never peform like a Sealine in calm seas. Neither like a Hatteras in
rough seas. In evey case I will be spenting more fuel/mile.
Of course I will lose space for bigger engines and the ballast tank(s)
let
alone I will need good
tranfer pumps which are heavy and additional manhours and cost to make
transverse and longitudinal separations to reduce the free surface
inertia.
I will probably need Gear Box of two ratios (I have heard that ZF
started
producing something like that)
To cut a long story short, I want to be fast in calm seas and not to
start
praying in heavy seas. I will slow down, ballast and be closer to the
zero
on the "scale" I described you earlier. I would sail
not exactly like a Hatteras or a Bertram, but closer to them
I do not think that I have invented (or re-invented) the wheel. The fact
that manufactures of those
moving on the water machines have not made the slightset effort to ample
the
range using ballast/extra horsepower etc make me think (1) my concept is
wrong (2) my concept is right but
only few prospective buyers would make such choice- so no target group.
What makes me post this is my hope that somebody will reply and tell me
I
am
wrong because this
and that or will tell me : you maybe right but you are "minority"- most
people do not like it, or whatever..
I havent found any boat plans with ballast tank on the net.
Is my dream to build such a ballasted/deballasted boat an " utopia"?
Thanks for giving me your time to read this. Somebody has something to
say?
Regards
AP
"Jim Woodward" jameslwoodward at attbi dot com wrote in message
...
Broadly speaking, it's done all the time in larger vessels.
Fintry was built with tanks for 50,000 pounds of seawater ballast.
We'
re
putting a bow thruster in the forward one, so we'll replace the weight
there
with lead, but the aft pair (14,000 pounds each, p&s) allow us to get
her
up
to a draft of less than seven feet for sheltered waters or down to
over
eight feet at sea.
Actually doing it in a boat that will go between planing and
displacement,
is another thing. The hull forms are quite different and it might
prove
to
be a challenge. And, of course, you're talking about a lot of
water --
you
might not like what it does to the interior in a 46 foot boat. You
can
see
Fintry's tanks between frames 2-6 and 41-45 at
http://www.mvfintry.com/details.htm -- the scale on all the drawings
shows
frame spacing, which are 20" apart.
--
Jim Woodward
www.mvFintry.com
"AP" wrote in message
...
I want to build a cruiser with the following characteristics
46 foot with very deep V foreward. 25-28 degrees deadrise at
transom
Overpowered.
And I want to have a " ballast tank."
The idea is :
If the sea is calm I will have the ballast tank empty and I will
make
her
plan using my extra horsepower.
If the sea is rough (or I meet heavy weather on the way) I will
ballast
my
tank, increase the displacement, will slow down the engines and I
will
be
sailing like a deep V boat, good for
rough weather.
Does that make sense??
Comments/suggestions are kindly invited.
Regards
AP