prop quandary

[packman]

Good Morning all,
I have a Lancer 27 powersailor to which I've mounted a Honda BF 150 outboard. Prop sizing is giving me fits particularly as it's a counter rotation motor. I've tried various prop calculators available online and gotten answers from 16x11px3 to 14.6x9.9px3. The hull is modified by "surface piercing foils" alleged to allow the boat to attain speeds around 18 kts with this motor. The waterline length is 22". The displacement weight is 4600 lbs but adding another 1000 lbs, for fat folks, fuel, gear, water, and stuff seems close to me. The draft (with keel) is 4' 3", the beam is 8' 7", ballast is 1700lbs. Can anyone help me out with this?, the available calculators can't seem to cope with the hybrid design of the boat.

Thanks in advance

Rich

[Perm Stress]

Resistance calculations and prop selection process is far from the state when you can just take lines drawing, displacement, motor data (power/RPM/turning moment) and have a perfectly fitted propeller. (for what? max speed in calm water, max range at whatever speed happen to most economical, for punching against gale force wind and steep shallow water waves? all these propellers will be quite different.)

Basicaly there are several ways to solve the problem:

1) Ask for info at engine manufacturers; they well could have useful statistics on what kind of propeller work with particular make of engine on particular KIND of boat. But if your boat is not the kind they normally supply engines to....

2) Take calculation you trust most, order a propeller according to it, try it, adjust calculation, order next one. 3d ...5th prop will be Ok.

3) Order a calculation to company specialized on semi planing boat propulsion, and order a prop to their recommendations; 2d prop should be Ok.

[packman]

There lies the rub, a company who specializes in semi planing (semi displacement?) boats. Seems kinda like sizing a prop, the 1st ....3d company might be the right one, just got to keep trying. Thanks for the advice.

[Perm Stress]

Same company will be better at second try as new company at first one.

[Jeff]

Duplicate thread: Continue discussion here prop quandary