Prop Size

[weknight]

Need assistance in selecting the proper size 3 blade prop for 1990 Hunter 35.5 with 3GN30F Yanmar engine. I currently have a 15x12 3 blade but can not get poper speed with this prop.

[Sailmonkey]

Find your gear ratio and call a prop shop. They'll be a huge help.

Also when you say you can't get proper speed are you referring to the boat speed or engine speed?

And what is the speed you're ataining?


Sent from my iPhone using Cruisers Sailing Forum

[TurninTurtle]

If the engine is lugging and can't develop proper engine rpm due to the load... you need a smaller prop. (pitch and/or diameter)
(make sure its not a problem with the engine)

If the prop is whipping froth and you can't go anywhere near the speed the prop is TRYING to push the boat, you need a bigger diameter prop. Maybe more pitch, maybe less. (I'd start with less)

We ASSUME the prop you have is reasonably close (or it wouldn't be the one that got installed)... Maybe one step of pitch and/or diameter will fix it.

If its not even close... you need someone with as close to the same hull and engine (+ transmission) as possible to say what works for them.

[wrwakefield]

Originally Posted by weknight

Need assistance in selecting the proper size 3 blade prop for 1990 Hunter 35.5 with 3GN30F Yanmar engine. I currently have a 15x12 3 blade but can not get poper speed with this prop.

Weknight, welcome to the forum.

This is your opportunity to optimize engine performance [and longevity by putting the proper load on your diesel...] and hull speed. You didn't mention which speed you were not satisfied with... I will assume hull speed...

As Sailmonkey mentioned, a good prop shop and/or manufacturer can get you close. What they don't always include is the engine optimization side of the equation...

If you want to better understand this yourself and not be as dependent upon others, I can recommend two sources among many:

-The Propeller Handbook by Dave Gerr

-There is an entire section in Attainable Adventure Cruising on precisely this topic. [Modest membership fee required, and well worth it to me...]

Best wishes getting things dialed-in the way you desire.

Cheers!

Bill