Flexofold advice

[aur]

Hello,

Im wondering if any of you have experience with flexofold propellers?
I bought a 30mm taper 20R from a fellow cruiser but cant work out the pitch, there is only merely a 2 stamped near the hinging gears? Im guessing it must be 12 pitch ?, but is it model 2?

Im trying to work out which gear ratio gearbox to try to find and install.
the vessel is a steel joshua type around 17 tonne 36 foot waterline about 12' beam at water line, and has full keel

Engine is yanmar 4jh3-te 50 KW 75 Hp @3700 Rpm
presently has a crazy 1:1 ratio ZF with 18" fixed 3 blade and engine can never make revs , so Im thinking maybe around 2:1 would be more realistic?

[DougR]

Can't help you with info on the flexofold, but here is some info based on the vessel data which you provided:

All sizes refer to fixed three blade props and assume you have the ability to fit these prop diameters with adequate/recommended clearances. The diameters are adjusted to commonly available sizes. Speed approx. 7.9 Kts

Ratio 2:1. Prop- 18 X 9.5 X 3 Available thrust- 1210 lbs. efficiency-34%

Ratio 2.5:1. Prop - 20 X 11.5 X 3. Available thrust- 1320 lbs. efficiency-37%

Ratio 3:1 Prop - 22 X 13.5 X 3. Available thrust- 1400 lbs. efficiency - 40%

Hope this is helpful.

DougR