Outside the box or am I barking mad
Gary,
I own a planing cat slightly smaller, and find that it is not perticularly
effecient in displacement mode. In fact I found when running with trawlers,
it w. as more effecient and more comfortable to run ahead a few miles at
planing speed and anchor until the trawlers caught up with me. The fuel burn
(I have flow meters) showed less miles per gallon at 8 to 10 knots than at 25
knots. In a chop there was some slam under the wing deck, and the ride left
something to be desired. Under the same conditions at cruising speed, the
ride was comfortable. To be effecient you have to be down to about 6 knots.
It depends on the design as to if the monohull is more or less effecient. If
the cats hulls are narrow, and displacement form, and the wing deck is well
clear of the water, then the cat will be a bit more effecient. For the
planing boat with a low tunnel, I think that there is not much difference at
the low speed.
You may get by with even less power than you are planing, with speed of only 8
knots as the end point. For comparison. I have a friend who has a very light
weight, wave piercing cat, wide beam, and high wing deck, which does 10 to12
knots with a single15 hp outboard.
Bob Austin
You cant generalize but a high efficiency light displacement catamaran with
hull fineness ratio above 11:1 is almost impossible for any mono hull to beat
when it comes to fuel efficiency, unless it is extremely narrow in design and
even then probably not. It's all about wave making drag, and displacement to
length. Just make sure you have enough bridge deck clearance.
----- Original Message -----
From: bob Austinmailto:thataway4@cox.net
To:
power-catamaran@lists.samurai.commailto:power-catamaran@lists.samurai.com
Sent: Sunday, September 20, 2009 10:07 PM
Subject: [PCW] Outside the box or am I barking mad
Gary,
I own a planing cat slightly smaller, and find that it is not perticularly
effecient in displacement mode. In fact I found when running with
trawlers,
it w. as more effecient and more comfortable to run ahead a few miles at
planing speed and anchor until the trawlers caught up with me. The fuel
burn
(I have flow meters) showed less miles per gallon at 8 to 10 knots than at
25
knots. In a chop there was some slam under the wing deck, and the ride
left
something to be desired. Under the same conditions at cruising speed, the
ride was comfortable. To be effecient you have to be down to about 6
knots.
It depends on the design as to if the monohull is more or less effecient.
If
the cats hulls are narrow, and displacement form, and the wing deck is well
clear of the water, then the cat will be a bit more effecient. For the
planing boat with a low tunnel, I think that there is not much difference
at
the low speed.
You may get by with even less power than you are planing, with speed of only
8
knots as the end point. For comparison. I have a friend who has a very
light
weight, wave piercing cat, wide beam, and high wing deck, which does 10
to12
knots with a single15 hp outboard.
Bob Austin
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