Economic Fuel Consumption

[Kelly Hanson East]

2BonC

For just sailing only, you should consider just using a 9.9 HP motor which would get better fuel economy. The boat would be limited to hull speed of course, about 6 knots.

The economics of selling a 50 HP motor and buying a 9.8 HP motor (about 2000 USD here) might be hard, though.

Your fuel economy readings you post seem reasonable. You are not going to be able to do much better than this with this engine combination I think.

[James V]

At 4.8 mph (1800 rpm) I get .45 gals per hour. there is a lot of variables on this. Wind direction and seas and current. try backing off a little bit and see what happens. Not much differance in arrival time.

[DaveB]

With todays prices of fuel one would do good by increaseing pitch to cruise at 6 knots with a 4 blade cup prop.
If you want the best of fast and cruise, stay with the largest diamiter prop. and pitch (pitch 10-11 on 4 blade) (11-12 on three blade) assumeing less than 12 Diamiter.Aim for the low rpms for prop. specs for cruiseing.
This means in a Honda 50bf 11.4 Diamiter with a 12 pitch prop. for the X. and a 3 blade.
4 blade props. will have better grip on the water but usually requires 1 pitch less than a 3 blade. Cup 3 blades will grab the water more but slow the rpms down and best to go with the 4 blade at 6 knots.
My Alcup Solars 4 blade 11.8X9 does great at 15.8 knots with loaded boat but only 6 knots @ 2600 -2800 rpms at cruise (6-6.5 knots) no current.
Bottom line is if fuel cost and better milage is your concern go with a higher pitch 3 blade and max. diamiter. Stay with the bottom line of your engines rpms at top speed. This will give you best fuel milage, less noise but less top end.
Dave

Having read many inputs about performance there is less about fuel economy. Here in Germany the fuelprises have risen dramatically. E.G. at the present the price for one liter of unleaded normal fuel is about 1,60 € (Euro). As 1 € equals about 1.60$ this is about 2,56 $ per liter. One US gallon is 3.78 liter that means that we have to pay here 9,68 $ per gallon. By the way what is the everage price in the USA right now?
Looking at this prices You might emagine that I pay attention to my fuel consumption more than to speed.
The first thing I do, I try to sail where and whenever it is possible, even going with 2kts and less.
If I have to motor with my Suzuki DF50 from 2005 I usually go with about 2400 RPM at 6kts (not SM) with the ballast tank filled, rudders parcially down,fins fully down, mast raised, sailes attached but stowed in covers. At this configuration my fuelconsumtion is about 3liters (0,79US gallons) per hower. I have a 3blade prop as delivered with the engine, 11 6/8 x 14 is engraved on it.
Does this sounds reasonable to You, how about Your experience as far as the fuel economy is concerned?

My boat (MG26X) seems to be quite slow, in the configuration above but with ballast tank emty and everything up it goes about 12kts and gets only 4800RPM.
I now bought a 4blade 14inch prop from VolvoPenta. I think it is very similar to the piranha prop which was mentioned in the forum before. I´m going to try it out next week when I´m traveling to the Lake Geneva in Swizzerland. Some hints for the use of the 4blade prop as far as pitch is concerned?

The throttle of my engine is moving very strong, specially in the endrange. I had it to a Suzuki mechanic because I thought the lever was limited by something but everything seemed to be ok.

I really understand all the guys who like to go fast, from timt to time it´s fun for me too to overtake other sailors with their ordenary sailing boats and beeing first in the marina.
When I went out boating once with my grandson (5years) using my MG19 by that time which was really fast under engine (had a beautyfull white 50 PS Johnson 4Stroke engine) but was sailing like an injured duck he said: Boats with two engines I love, boats with a single engine are quite good but sailing is a sh~t!

Older folks sometimes have a different view on the things!

2BonC

[ronacarme]

1. You may reduce hull drag and so improve mpg by dropping from 6kn further down from hull speed, e.g. down to 5.5, 5, or even 4.5 kn.
2. Motoring with at least a little wind, not on the bow but rather on the beam or behind, sheeting in your sails (motorsailing) may add a bit of boat speed without adding more throttle, and thereby increase mpg. The sheeted in sails also reduce rocking of the boat by waves or motorboat wakes hitting the side of the boat.