On Thu, 24 Feb 2005 21:22:37 -0800, Skipper
wrote:


It seems you are well passed the speed you want for fuel economy.
My boat is about 36,000 lbs (46') and my big 85 hp burns between 1 and
1 1/2 gph at 6 knts.
You might try a self-pitching prop like the Auto-Prop. You can
still use sail power and the prop will self-pitch to still give speed
at slower rpm. Take a look at their web site. Over time, the fuel
economy will pay for the prop. You'll also get a real prop in reverse.

A friend has a 35 hp Volvo from the late '70s pushing an 18 ton ketch
with an AutoProp. He loves it and says the efficiency is huge as is
his control. His heavy displacement full keeler now docks like a
minivan parks, and he's getting more knots from the same revs.

He says that investing in the Autoprop (around $4K Cdn.) saved him
from repowering to 55 or 85 HP ($20K-$35K). Yes, he's a liveaboard and
knows he's got too heavy a load, but he was sailing here in Toronto
yesterday and today...in February...so overbuilt steel has an upside.

His one caveat is that he feels he should install both an AquaDrive
and a shaft lock to better protect his transmission.

As I may buy his boat one day, I keep track of all his mods.

R.

On Wed, 23 Feb 2005 23:51:31 -0500, "Doug Dotson"
dougdotson@NOSPAMcablespeedNOSPAMcom wrote:

"Wayne.B" wrote in message
.. .
On Wed, 23 Feb 2005 20:41:51 -0500, "Doug Dotson"
dougdotson@NOSPAMcablespeedNOSPAMcom wrote:

I run a 1985 Perkins 85 HP 4 cylinder pushing a 43'
boat. I consistantly burn 1 GPH.

==================================

If so, you are only using about 20 hp out of your 85 available. At
85% of full RPMs it should be burning about 3 gph unless you are way
under propped.

Scoots me along at just under hullspeed. Last surveyor said it was
propped just fine.

I do 5.8 knots at 1/2 throttle on a direct drive Atomic 4 with a 12" x
6" "standard" two-blade prop pushing a 10,000 lb boat with a 27' LWL.
Hull speed is just under seven knots. RPM is around 1,500-1,600.

I can get to 6.6 knots SOG at 3/4 throttle, but the noise is
unpleasant and I start burning a lot more gas...it's not worth it.

I can sail in heavy air favourably angled slightly above hull speed
(7.3 knots SOG) for sustained periods, or about 1.5 knots

I have logged a pretty consistent gas usage of 0.73 Imp. gal/hr. which
is about .825 U.S. gal, I think. That's at a typical cruise speed of
1/3 throttle or 5 to 5.2 knots. A 12 gallon tank gives me a range of
about 84-90 NM or just under two round trip Toronto-Niagara River
crossings. Motorsailing increases this significantly, of course.

If I drop it to 4 knots, I burn one half gallon an hour. This means 24
hours of constant use and nearly 100 NM of range. (It's a
racer-cruiser, not a passagemaker).

I only use full throttle in reverse, actually...if ever.

The point? You pay hugely in fuel consumption and engine wear getting
that last knot.

R.

On Fri, 25 Feb 2005 20:23:14 -0500, Larry W4CSC
wrote:

The mechanic said it
wouldn't be good to freewheel that shaft all the time, but I've forgotten
the "why" he told us.

============================================

The reason is that the tranny depends on being powered by the engine
to receive proper lubrication. You will definitely shorten the life
of the transmission if you allow the prop to free wheel for long
periods of time.

"Doug Dotson" dougdotson@NOSPAMcablespeedNOSPAMcom wrote in
:

We have 2 95 gallon tanks. Great cruising range but having that much
fuel when
one only consumes 1 GPH has it drawbacks.

Doug



Fuel polishing is probably an issue, mostly ignored by sailors until it's
clogged the injectors or at least the filters. It always disturbs me how
so many sailors will just leave the tanks half empty all the time, instead
of topping them off before docking. Being down a gallon or two is probably
ok, but the condensation in a half-empty fuel tank of any size is just
awful here in Charleston.

It's just laziness. All those that have half empty fuel tanks all have
plenty of money to fill them.

http://www.gulfcoastfilters.com/fuel_polishing.htm

Brian Whatcott wrote in
:

A diesel could be 50% more fuel efficient, let's say.
So 0.3 lb diesel fuel per HP.hr would need 26 lb fuel per hour
to produce 85HP
That's 4 gallons or more....for 84HP



That should be about right, even for the biggest diesel engine in the world
over 108,000 HP
http://www.bath.ac.uk/~ccsshb/12cyl/

" Fuel consumption at maximum power is 0.278 lbs per hp per hour (Brake
Specific Fuel Consumption). Fuel consumption at maximum economy is 0.260
lbs/hp/hour. At maximum economy the engine exceeds 50% thermal efficiency.
That is, more than 50% of the energy in the fuel in converted to motion.
For comparison, most automotive and small aircraft engines have BSFC
figures in the 0.40-0.60 lbs/hp/hr range and 25-30% thermal efficiency
range.

Even at it's most efficient power setting, the big 14 consumes 1,660
gallons of heavy fuel oil per hour."

Do bunker oil barges take VISA?....(c;

I just want to be in the engine room for the sea trials....

In article . com,
wrote:

Another thread discusses sailboats motoring "too much" but I think most
sailboats will use their engines to supplement sail but we still worry
about fuel economy. Even motoring alone, my yanmar 2GM seems to burn
only about 1-1.5 gals/hr at 6 kts in my 28' S2 but still I wonder about
the best way to conserve fuel in very light air.
Normally, in light air, I start with sails and no engine and eventually
get impatient with going only 3 kts and start the engine and put us up
to 5 and then eventually 6 kts or more. It is this last little bit
that I think burns the most fuel because she is most efficient at
slower speeds but as we get closer to hull speed fuel use rises
sharply.
An alternative strategy that would burn less fuel but would go a little
slower might to be ALWAYS run the engine at sufficient rpm to get to
3.5 kts and then use the sails to supplement that.


You've got it, I think, but I suspect the 1.5 GPH. We don't burn 1 GPH
until we're at max throttle, which gives us a solid 7 knots.

Xan's numbers are similar to yours; I've been tracking our usage over
1200 hours and a dozen or so years. Ours is a 2GM20F; best prop we used
was a 15x11" 2 blade. They recommend 16x10, which I'd prefer.

At 6+, we burn about 0.6; 5.6 = ~.33; 5.3= ~.25; 5=~.20. Below 5, no
noticable improvement as we're only turning about 1500.

--
Jere Lull
Xan-a-Deux ('73 Tanzer 28 #4 out of Tolchester, MD)
Xan's Pages: http://members.dca.net/jerelull/X-Main.html
Our BVI FAQs (290+ pics) http://homepage.mac.com/jerelull/BVI/