Full disclosure, I'm looking into the issue of engine/propeller for a diesel. But I have a hunch I'm going to get a more informed opinion here as I'm interested in favoring range over power. I'm also interested in seeing if I can eventually add an electric motor above the prop shaft to turn it into a parallel hybrid.
So, my engine choice is down to a Beta 35 or 38. They are identical except that the 35 injector pump has higher cams, pumps more fuel and gets it's peak torque at lower RPM, and is limited to 2800 RPM. The 38 injects less fuel and is governed to 3600. (and has an oil cooler added)
My understanding from following discussions about electric boats is that the #1 factor in range is speed. After that, I know that hull speed, displacement, drivetrain and propeller efficiency are important. I'm prepared to slow down a bit if I can increase range--and not be hard on the engine. And I understand that a diesel motor's peak torque can be matched to the propeller's much more narrowly than an electric motor, and only at the upper end (if you ever want to make use of full power). Which is why I'm trending towards the 35.
I'm a little more hazy on propeller issues and would appreciate some education there. Bigger diameter, bigger blade area, more blades, more cupping are more efficient, right? What about trading off gearbox reduction ratios with different propeller diameters and pitches? The boat has an aperture, and I think the current prop is an 18 x 10 with about 15% clearance. Most people are using 16 x 14 props with whatever reduction is appropriate for the 38HP. Finally, on the propeller, I was hoping I could go with a very efficient fixed prop and then "disappear" it with a few amps from the electric motor, but since that may never happen, I'm thinking of going for a feathering prop. However, those flat blades look very inefficient to me. Am I going to take a big hit in motoring performance with the flat profile? On the other hand, feathering will allow me to play with the pitch to my heart's content, just not on the fly. Going with feathering is supposed to require a shorter shaft, i.e. might lock me in with that.
The boat's a Westsail 32. 10 tons. Both the 35 and 38 sound like they'll get me to near hull speed in calm water but supposedly the 38 will give just a little more punch in adverse conditions. More HP than that is said to just make the boat squat and not go any faster.
Ideas? Thanks in advance!
Mike
Posted by: likeabikemike@gmail.com
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