Narrow hull speed question
 

I am looking for data on the hull speed one can expect on high aspect ratio
(narrow) hull.

I want to build a motor canoe propelled by a 1.3 HP Honda 4 cycle with chain
reduction drive. The boat will be 4mm ply with about 17 or 21 feet of
waterline.

I know that narrow hulls exceed the standard hull speed formula. If this is
really significant, I would go with a 14" wide outrigger design versus a
monohull.

Thanks for any formulas or links.

Robert Haston

Narrow hull speed question
 

Robert Haston wrote:

I am looking for data on the hull speed one can expect on high aspect ratio
(narrow) hull.


LOL!! (see later)

snip question

Thanks for any formulas or links.

Try googling "hull speed" on google's Groups/Advanced search for this group.
Enjoy the reading, and the flame wars, and the trolls of numerous flavours.
;-)

Steve - but don't say I didn't warn you......

Narrow hull speed question
 

"Robert Haston" wrote in message
link.net...
I am looking for data on the hull speed one can expect on high aspect
ratio
(narrow) hull.

Just as a rough rule of thumb, at L/B ratios 8, the hull wave making
resistance is very low and you're limited to skin friction resistance.
However a 17-21' boat with a 2' or so beam is basically a kayak shape and
doesn't have a ton of stability. An outrigger (powered proa) design
suggests itself.

from
http://www.maths.adelaide.edu.au/App...on/taxdrag.htm

The viscous resistance Rv can be written as Rv=1/2 r V^2 S Cv where r is the
water density (herein 1025.9 kg/m3) and S the wetted surface area of the
hull. V is velocity in m/sec. Cv is the drag coeff.

When skin friction dominates, the drag coefficient Cv approximately equals
Cf, where Cf is a skin friction coefficient which can be estimated using the
ITTC 1957 ship correlation line (Proc. 8th ITTC).
Cf = 0.075/(log10(Rn)-2)2 where Rn = UL/n is the Reynolds number. Here L is
the overall length of the hull, and n is the kinematic viscosity (herein,
1.1883x10-6m2s-1).

Probably a lot more math than you'd like!

However if I was to guess (and it's a reall wild assed guess 'cause I don't
know how bit a prop you're planning), I'd say you'd get about 7 knots :)
with your 1.3 HP motor


--
Evan Gatehouse

you'll have to rewrite my email address to get to me
ceilydh AT 3web dot net
(fools the spammers)

Narrow hull speed question
 

Thanks. That makes sense. My 11/1 LB ratio kayak tops out in a sprint at
its conventional formula hull speed of 6 knots. Paddling "uphill" against
its small bow wave is part of the problem, but nothing compared to the
insurmountable speed bump my shorter and wider boats create.

I guess instead of designing the boat first, building the motor and putting
it on similar length but fatter hulls (I have three 17 foot kayaks, from 18
to 28 wide) would be a better way to see what I would get.

For what it is worth, the project is to make a "kids boat" without the cost
and dangers of a real powerboat, and easy enough to paddle a long way home
or to safety.



"Evan Gatehouse" wrote in message
...

"Robert Haston" wrote in message
link.net...
I am looking for data on the hull speed one can expect on high aspect
ratio
(narrow) hull.

Just as a rough rule of thumb, at L/B ratios 8, the hull wave making
resistance is very low and you're limited to skin friction resistance.
However a 17-21' boat with a 2' or so beam is basically a kayak shape and
doesn't have a ton of stability. An outrigger (powered proa) design
suggests itself.

from
http://www.maths.adelaide.edu.au/App...on/taxdrag.htm

The viscous resistance Rv can be written as Rv=1/2 r V^2 S Cv where r is
the
water density (herein 1025.9 kg/m3) and S the wetted surface area of the
hull. V is velocity in m/sec. Cv is the drag coeff.

When skin friction dominates, the drag coefficient Cv approximately equals
Cf, where Cf is a skin friction coefficient which can be estimated using
the
ITTC 1957 ship correlation line (Proc. 8th ITTC).
Cf = 0.075/(log10(Rn)-2)2 where Rn = UL/n is the Reynolds number. Here L
is
the overall length of the hull, and n is the kinematic viscosity (herein,
1.1883x10-6m2s-1).

Probably a lot more math than you'd like!

However if I was to guess (and it's a reall wild assed guess 'cause I
don't
know how bit a prop you're planning), I'd say you'd get about 7 knots :)
with your 1.3 HP motor


--
Evan Gatehouse

you'll have to rewrite my email address to get to me
ceilydh AT 3web dot net
(fools the spammers)

Narrow hull speed question
 

gren ) wrote:
: Because the engines are only 2-5 hp overtime they have developed a boat that
: is very slender and amazingly fast. The boats are designed to race a 42 mile
: ocean course around bermuda in some faily rough conditions with a crew of
: two and a cooler of beer. Some of them reach speeds of 7-10 knots.


If I read this one correctly:

: http://www.bermudasun.bm/archives/2002-06-28/06Sports09


someone rounded the 42 mile course in 2 hours, 36 minutes, which is much
better than 10 knots.

Narrow hull speed question
 

Thanks.
It looks like they use all kind of boats. I would love to know which ones
can sail around the island in two hours. There a few narrow things in there
that look like kayaks crossed with one of those James Bond thai boats . . .
weird but apparently efficient.
Is the Heineken umbrella used as a spi downwind?

If I took my Scilly Gig and redesigned her with an almost straight run aft
from midship plus a square stern, then lowered freeboard a bit, add a
sailboard skeg, we may have something. Would use foam sandwich with a thin
skin. I am tempted to try. With the current price of gas, going close to 20
knots with a 6 HP is very attractive.

--
Jacques
http://www.bateau.com


"Paul R. LaBrie" wrote in message
...
Hi Jacques,

Try http://www.geocities.com/seagullrace2001/Pictures.html

- paul

Jacques Mertens wrote:
Does anybody knows of a link to pictures of those boats?


--
Jacques
http://www.bateau.com


"Chris Crandall" wrote in message
...

gren ) wrote:
: Because the engines are only 2-5 hp overtime they have developed a
boat

that

: is very slender and amazingly fast. The boats are designed to race a
42

mile

: ocean course around bermuda in some faily rough conditions with a crew

of

: two and a cooler of beer. Some of them reach speeds of 7-10 knots.


If I read this one correctly:

: http://www.bermudasun.bm/archives/2002-06-28/06Sports09


someone rounded the 42 mile course in 2 hours, 36 minutes, which is much
better than 10 knots.