On Aug 24, 12:47*pm, "Wilbur Hubbard"
wrote:
...
Not much of a sailing trip. Sounds like more motoring than sailing. But,
that seems to be the norm for cruising catamarans that tend to be so below
their designed LWL by the time a family loads them up with all kinds of
extraneous crap. ...

I don't see why it matters what power was used. By oar, paddle, mule,
gas, diesel, sail or whatever, if it's cruising it's on topic. I also
don't see where you're getting your ideas about catamarans. Rodger
says he used 35 gallons of fuel to travel less than 500 miles on his
monohull. On my catamaran I used about the same amount of fuel
traveling from Honolulu to San Francisco and I thought that was
excessive. I used much less than that sailing from New Zealand to
Honolulu. Two of us live on my Catamaran and have done so for years
and yet we still make pretty quick passages. Anyway, if Rodger uses
35 gallons of fuel on a Maine cruise and Jeff uses some similar amount
of fuel in similar cruising grounds I think that probably says more
about Maine in the summer than it does about differences between cats
and monos.

-- Tom.

wrote

(Sensible stuff)

The dramatic speed differences between sailing cats and monohulls are due to
the ability to generate the required sail carrying power on very slender
hulls. The speed differences, for equal horsepower and displacement,
between power cats and monos are significant but much less dramatic. At low
speeds, a cat may even require more.

The large fuel consumption on my recent trip does mostly reflect the
weather, lots of wind for brief periods but more long calms than I've seen
on most cruises of similar length. Boat and personal characteristics do
play a part though. This trip was on an ambitious schedule, one leg to get
to a birthday party, and the rest to see some of far downeast Maine. I'm as
happy motoring as sailing as long as there is shore to look at. Although my
engine is louder at max continuous RPM, it is smoother and the overall
effect is more soothing. Throw in a pinch of impatience and you have a
perfect recipe for large fuel bills, by sailboat standards anyway.

Now that I've revisited all the cruising grounds of my youth and seen all
the coast from Buzzards Bay to Cutler, I feeling an urge to make next year's
cruising a lot slower and more relaxed as well as reducing my carbon foot
print. This recent trip would have been a much better 2 - 3 week cruise but
my schedule made it a choice between seeing places I've spent a lot of time
or getting past Schoodic delivery style. Next summer, I should have much
larger blocks of time, hopefully the whole summer, and will take it much
easier.

--
Roger Long

On Aug 24, 5:17*pm, "Roger Long" wrote:
...
*The speed differences, for equal horsepower and displacement,
between power cats and monos are significant but much less dramatic. *At low
speeds, a cat may even require more.
...

I think you're being generous. At low speeds a cat will very likely
require more power to attain the same speed as a mono of the same
displacement. As Ted Hood was fond of pointing out, at very low
speeds fat and heavy may have less resistance than slim and light. Of
course, once a boat gets above a very modest speed to length ratio (Fn
if you must) a long skinny hull offers less drag than than a short fat
one. At some point a really skinny hull will have a tendency to roll
over and one solution to that is to split it in two. Another might be
to add outriggers. If we're talking fuel consumption at speeds that
we're willing to put up with the graph in this paper of fuel/speed for
three hull types is interesting:
http://www.hiswasymposium.com/pdf/20...el%20Irens.pdf .

-- Tom.

On Sun, 24 Aug 2008 16:28:24 -0700 (PDT), "
wrote:

Rodger
says he used 35 gallons of fuel to travel less than 500 miles on his
monohull. On my catamaran I used about the same amount of fuel
traveling from Honolulu to San Francisco and I thought that was
excessive.

500/35 is 14 MPG, which is not bad at all by powerboat standards.
Both my tow vehicles, a F-150 and a Navigator, get just over 14,
unloaded.
A logical comparison is a motor home or travel trailer with the same
accomodations. Mileage is not good with either of those.

Casady

On Aug 25, 12:50*pm, (Richard Casady)
wrote:
...
500/35 is 14 MPG, which is not bad at all by powerboat standards.
Both my tow vehicles, a F-150 and a Navigator, get just over 14,
unloaded.
A logical comparison is a motor home or travel trailer with the same
accomodations. Mileage is not good with either of those. ...

FWIW (and I don't think IW much), HNL-SF is greater than 2.2k naut
miles as sailed/motored. That puts the mpg of our house on its least
efficient passage into typical Prius numbers, but, of course, we go
very slowly by Prius standards... I don't think it signifies much
when you get right down to it as the services involved aren't
comparable.

-- Tom.

"Richard Casady" wrote

500/35 is 14 MPG, which is not bad at all by powerboat standards.

I wish it was that good. Strider has nice lines but she is fairly heavy. I
get 8 mpg at max continuous RPM and 5.71 at cruising speed. I tend to run
near the top end.

One thing I forgot to mention: I checked fuel usage a few hours after the
first fill up and a long power leg and it was significantly more than I
expected. When boarding after a walk on Roque Island beach, I noticed a
flash of blue color on the prop. Got out the hook knife and discovered a
ball of poly rope around the hub and blade roots. It doesn't take much to
really cut into prop effeciency. I heard it wrap on the first day but the
engine was so smooth that I didn't think it had stayed.

Zigging and zagging through the lobster pots also doesn't show up on the GPS
track and must have added 5% - 15% to the distance in some areas. I've
never seen them so thick and close together. I think fuel prices are making
the lobstermen concentrate the traps on the best ground.

Fuel consumption graphs for the boat, taken from engine data and careful sea
trials can be found he

http://home.maine.rr.com/rlma/StriderSpeedRange.gif

--
Roger Long

On Aug 25, 6:09*pm, "Roger Long" wrote:
...
I wish it was that good. *Strider has nice lines but she is fairly heavy. *I
get 8 mpg at max continuous RPM and 5.71 at cruising speed. *I tend to run
near the top end. ...

Nice graph. It shows 5.4 at max and 8 at cruising, no? I thought you
had a fast running 18hp Yanmar like mine. Shouldn't it show 16 @ 34
or so for continuous (DIN 6270A)?

-- Tom.

No, mine (2QM20) is the older engine. Maximum RPM is 2800 (up to 1 hour
according to the rating) and Maximum Contiuous is 2600.

My prop is also matched to the boat which isn't always the case with
sailboats. That raises the fuel consumption because the engine is actually
producing its rated horsepower at maximum RPM. I'm getting more speed and
bucking ability but I'm paying for it.

--
Roger Long

On Aug 26, 3:03*am, "Roger Long" wrote:
No, mine (2QM20) is the older engine. *Maximum RPM is 2800 (up to 1 hour
according to the rating) and Maximum Contiuous is 2600. ...

Ah yes. I've got 2GM20s and they never get 20hp -- 18 max, 16
continuous -- and they rev a lot higher as well... According to the
manual they consume, more or less, 0.065 gallons per horse power per
hour from 22 to 32 rpm. I suppose they cost less, otherwise the QM
seems like the better beast...

-- Tom.

wrote in message
...

I suppose they cost less, otherwise the QM seems like the better beast...

It's a wonderful beast. My installation is very smooth and, with just two
cylinders firing at 2300 2400 RPM, it has much the cadence of a big, slow
turning, diesel. I love listening to it.

--
Roger Long