bertram31.com

I currently have Yanmar 6BY260 engines with 2.43:1 gear ratio. I am wondering which would be the right prop ( diameter, pitch, 3 or 4 balde) for that combination.

Are we talking about a B31 installation?

Hi

Yes it is a b31 instalation

Hi, 4 blade 70 % DAR 21x25 will be fine and push you to 32knots.

Good luck, Gert

Hi

I used 4 blade 21x24 on this instalation. Im pushing 25 knots at 3600 rpm and around 28 at wot 4000. Would yo still recommend a pitch change on the props for 21 x25?

Are you hitting spec WOT with those props?

I'm actually going over about 150 rpm at full throttel.

Then you can add an inch of pitch (-100) and add some cup (-50). Both can be done with your original props at a good prop shop. Talk to them. You might get the same results with a super cupping that would work at your top end. To me, if you're going slow enough at idle and don't want to go any faster (re slow trolling), cupping may be the way to go.

Careful, those engines are rated at 4000 rpm. I've read that the new electronic governors won't rev much over rated like the mechanical ones do. On a mechanical engine, it is recommended to prop around 150 rpm over rated with a fully loaded boat. So at 4000, you may be underpropped. But if you do add pitch or cup to your props, be sure you don't get below 4000 rpm fully loaded. http://us.yanmar.com/products/marine-en ... /6by2-260/

Eddy G.

if you have the first series of BY 260 ( whit the plastic covers ) add an extra inch of pitch and you will be fine.

If you have the second generation of BY 260 ( with the steel covers) you can add a litlle more pitch.

The second generation gives a little more HP (10-15) and has a different power curve.

Ive build in over 30 of these engines , believe me !!

Regards Gert

Thanks for the response.

I had the first generation of the BY 260 but yanmar made an upgrade of that engine to the new BY 260 with the steel cover.

You still recommend adding more than an inch of pitch or an inch and cup?

Can props handle more than an inch of pitch without weakening?

Thanks

I have had it done, but to be truthful, I did it a half inch at a time. Not because I was afraid, but because I thought a half inch would do it and I was wrong.

try another inch, you can twist the blades 10-15 % of your original pitch.

Good luck