An alternative strategy that would burn less fuel but would go

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

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

Actually, the original owner repowered the boat from a Perkins 4-108 to>a 4-236. The boat lived in Newfoundland. Fighting currents was>definitely his goal.

My 3GM30F in my previous 36' boat only burned 3/4 to 1 GPH.

That's what my 4-108 burns in my 37' boat. The OP definitely has a> problem.>

Steve

A prop calculation will cost you an extra 50 cents, but your goal >there should be to have a large enough prop to handle the power, and >the engine reving at a sweet part of its power curve. My rough guess >(and admit this is one area I never really understood) is that the >blade area your prop is small for the horse power you may be putting >through it - this would cause cavitation.

I truly do not know how much fuel it uses but am saying 1-1.5 gal/hr as>a maximum. I have major problems filling it as the fuel backs up and>tries to backflow even though I have unclogged the breather line.>

As far as finding time to sail, I am blessed with loving my work and>really cannot decide if I would ever really want to go sailing for long>periods.

I don;t actually know. The calibration of the tach is off because the > alternator is> not stock. When we first bought the boat I measured the actual RPM and> made a graph to convert from indicated to actual. Converting the> proper cruising RPM> to the indicated gives 2500 so that is where we run unless we need> some extra. I've forgotten what the actuals are. 1800 sems to stick in> my mind but> I'd have to go look it up.>

Doug>

Propping a sailboat is always a big tradeoff between sailing> efficiency and motoring. For motoring a big 3 or 4 bladed pop is> ideal for a displacement hull but that is deadly to sailing> performance unless you got a feathering prop, and that is another> level of compromise and expense.>

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.

Something must be wrong with your figures or your engine/prop>situati­on. I run a 1985 Perkins 85 HP 4 cylinder pushing a 43'>boat. I consistantly burn 1 GPH.>

Doug>s/v Callista>

<dbohara@mindsprin­g.com> wrote in message >news:1109181860.22­7648.46240@o13g2000c­wo.googlegroups.com.­..>> 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.>>

"Wayne.B" <waynebatrecdotboat­s@hotmail.com> wrote in message >news:i6kq11hh2qp1s­qhejgfdfqlk60nh0apig­v@4ax.com...>> On Wed, 23 Feb 2005 20:41:51 -0500, "Doug Dotson">> <dougdotson@NOSPAMc­ablespeedNOSPAMcom> wrote:>>

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

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

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>

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.>