prop size

[thereheis]

what are most of the faithfuls running prop size that have the 315 yannies with 1 1/2'' shafts on 31 flybridge ????i started out with 19x20 and only getting 3850 on wot,,,,is it true that for every inch of pitch taken off is about 75 rpm gain ?????if tru i would need to have 19x18 wheels .....seems small...
any help from the brains out there ?????

phil

[CaptPatrick]

Phil,

What's your gear ratio?

Br,

Patrick

[Bruce]

19x23 or 20x22 4 blade medium cup with a 2:1 gear box.
Every 1" pitch is about 200 rpm.

[thereheis]

runninng 1.5-1 gears

[CHolgerson]

We are running 18X21 3 blade DQX wheels on a light Bahia Mar with 315 yanmars. We spin 3950 WOT loaded at 34.6 knts. I would guess a flybridge version would need a little less wheel due to weight. Hope this helps.

Chris

[Bruce]

You got the wrong ratio gear box for the 31 for most of the guys here with those engines. (edit for clarity)
It should have been the 2:1.

With the 1.5:1 there was no need to go to 1.5" shafts as the prop size doesn't warrant it.

I would suspect you'll need to drop down to a 18x18 prop.

Edit:
The 1.5:1 gear box works okay. You just lose the low end bite.

However you do have better low speed control for trolling with the smaller wheel.

Some avid fishing guys do opt for this who like to troll regularly.