Best prop for fuel econ.

[maverickconner]

Ok, this has prob. been ask a thousand times, but I am new to trying to figure out props. I have a 1983 Bayliner 28' Contessa (10' beam) with twin 260s and outdrives. We live here in Alaska and use it out of Whittier, Homer and Seward. I am looking to get more range out of it, with the fuel tank only being 125 gallon. I can currently hit 43mph (yes, varified with GPS and speedometer) at WOT, roughly 4200 RPM and the gas gauge going down at about the same speed. The water here is too rough to ever get there though. I would like to trade top end for lower planing speed and better fuel economy. Right now I can get planed off at 3300 RPM and roughly 30mph (conditions pending). I have a set of 19 three bladed aluminum props on now.

Seems like right now I am burning close to 23-26 gallons per hour, and have to carry extra fuel all the time.

Please help if possible. I expected to be burning 14-18 gallons per hour.

 

[capngregorus]

Re: Best prop for fuel econ.

Dont really know a lot about inboards, but i'd say if thats where the boat builder set the wot, i'd say leave it be.

Going any lower in pitch will make the engines rev out harder by 200rpm every pitch size down, so a pair of 17p will give you 4400, 15p 4600. Could cause engine damage giving them too many rpm, and will only increase hole shot, and lose a bit in top end.

Going any higher in pitch will force the engines to labour, so a pair of 21p may give it 4000 wot, hole shot will be lost and you may not even notice any top end improvements.

If you want better range, get bigger tanks.
If you want better economy, and don't mind putting around, get smaller engines.

If it were me i'd keep the setup as it is and run at lower speed.

Hope this made sense and it helps.
Greg

 

[Bondo]

Re: Best prop for fuel econ.

Ayuh,... You're at the rock bottom acceptable rpms at wot now,...
You might possibly do better with a set of 17" 4 bladed props,...
The drop in pitch will free up some hp,+ the 4 blades might lend abit of lift to help with the economy...
Getting it to 10gal.s less per hour, I think is nothing but a Dream though...

 

[steelespike]

Re: Best prop for fuel econ.

Typically gph at wot is about 10% of the hp rating.That would put you at
about 52 gph at wot. Cruising at about 23to 26 gph is certainly in the ball
park. As suggested 4 blade props with a little less pitch might give you some lift so you can cruise at lower throttle setting.Play with the trim tabs for the best throttle and tab position.To me it would seem you need another 125gal tank.
to get any serious range. I realize conditions pretty much control your speed but:: Your ideal cruising speed could be anywhere from just on plane to 1,000 rpm higher.
A flow meter is probably the best way to be sure of your best speed/rpm.

 

[smokeonthewater]

Re: Best prop for fuel econ.

am I the only one who thinks it is odd that he can't plane below 30 mph......

 

[maverickconner]

Re: Best prop for fuel econ.

Smoke, I agree with you. The boat seems like it takes too much speed to keep it on plane. For a big fat boat she moves pretty good, but has too much top end for what we can use. I think I will try the 17 4blades a chance. It would be nice to have some low end and a lower plane speed,,,, if at all possible.

 

[hwsiii]

Re: Best prop for fuel econ.

Maverick, I am like Smoke I can't believe that it requires 30 MPH to get that boat to plane, that is ridiculous.

For your particular boat I would recommend a pair of Solas Amita Aluminum 4 blade 15" props in aluminum at about $ 250 a pair, instead of the 17" pitch as you will need the 15" pitch to raise that stern up and for cruising at slow speeds. You will probably lose about 3 MPH, but you may not because the decreased prop slip at WOT, and your RPM ought to be about maximum, but you will find your acceleration and your low end cruise speed should change to at least 8 MPH slower than you can plane at now.


H

 

[maverickconner]

Re: Best prop for fuel econ.

hwii,

That sounds about perfect, if I could plan out and cruise at 22mph I would love it. The biggest problem I have is getting it there. I cruise right now at about 3200rpm and am close to 30mph. I think I am going to get a fuel flow meter also. Where is the best place to get those props?

 

[trendsetter240]

Re: Best prop for fuel econ.

Where is the best place to get those props?

http://boatpropellers.iboats.com/