right size propeller

[hoavannguyen]

Good morning,<br />I need some help and suggestion in choosing the right propeller for my boat. I have been reading a lot on this subject but would like some opinions from the experts.<br />I have a 20 foot power catamaran that I just bought as used boat. I cannot find any specification on this boat called Defiance Cat made by Alliance Marine. The boat weight is 2500 lbs, fully loaded with fuel will be 3000 lbs. At this time, I just installed twin 4-stroke 60-HP Big Foot Mariner. What size propeller with pitch and diameter do I need for maximum speed and fuel efficiency? I do a lot of offshore fishing in Guam. Thanks a lot for the help.

 

[DJ]

Re: right size propeller

hoa,<br /><br />I assume the boat has props. now?<br /><br />It should be propped for the engines to obtain an rpm within the engines max. rpm range with a moderate load.<br /><br />That's a pretty heavy load for 120 total hp. If I had to have a starting point, I would select props in the 11-13" pitch range.

 

[ob]

Re: right size propeller

hoa , Here's the stats on your motors.As djohns touches on ,pay paricular attention to the WOT operating range of the engines in selecting props for your application.Prop your motors to turn up at the upper end of the range and you will get the best throttle response and engine longevity.<br /><br />Propshaft Horsepower: 60-hp (44.8 kW) <br />Max RPM (W.O.T.): 5000-5500 <br />Cylinders/Configuration: 3 <br />Displacement: 59 cu.in. (967cc) <br />Bore & Stroke: 2.99 in. x 2.80 in. (76mm x 71mm) <br />Fuel Induction System: Loop Charged <br />Exhaust System: Through Prop <br />Lubrication System: Single point variable ratio oil injection <br />Cooling System: Water cooled with thermostat and pressure controlled <br />Ignition System: Modular CDI <br />Starting System: Electric <br />Alternator: 16 amp (201 watt) with voltage regulator <br />Gear Ratio: 2.3:1 <br />Gear Shift: F-N-R <br />Steering: Remote <br />Trim System: Power Trim <br />Shaft Length: 20 in. (508mm) <br />Weight-Dry: 2242 lbs. (110 kg) <br />Operator Warning Systems: Overheat, low oil level <br />Propeller Options: Black Max, Vengeance, High Five, Laser II, Trophy Plus, QA3, QSS, QS2000

 

[hoavannguyen]

Re: right size propeller

Thank you Djohns and OB for the suggestion. I will try to use a 13 pitch to see if I can get close to the max rpm. The reason that I have to use twin 60-HP because of the weight of the 4-stroke engine. I ran twin 90-HP 2-stroke in the past. The dealer also said that catamaran required less power. I will see if it is true or not. Does the diameter of the prop play any role in the performance? Should I go with the large or small diameter prop? Thanks again.