Propeller Recommendation

[DonM1166]

BOAT & MOTOR DATA TO CHOOSE BEST PROPELLER


1983 Crest II Pontoon Boat Model 25, Load: 2400 lbs., Max HP: 85
Pontoons 24? long X 8? wide, Circumference: 61?, Diameter:20?
Aluminum Deck installed August 2011, Aluminum Ski/Tubing platform installed
Total boat weight: 2060 lbs.


1995 Mercury Bigfoot 60HP Purchased and installed September 2011 (Compression
is 127, 125 and 119 lbs.)
Purchased and installed HS CMC Hydraulic Jackplate PL-65
Purchased and installed Mercury Spitfire 4-Blade Aluminum Pontoon
Propeller 13.8 x 13P (488M8026570)

Initial adjustment of carbs was performed with boat secured to trailer in water
using tach on each plug wire as I adjusted the corresponding carb.


Test Run with 1/2 tank of gasoline and usual load. The outboard ran best with
Jackplate approximately 1-2? above the lowest setting. The speed and RPMs were
the same going downstream against the wind as they were going upstream with the
Wind. The readings I got was 7 MPH top speed (Phone App) and 2350-2400 RPMs.


I want to find a propeller (Maybe an adjustable pitch) to get my best tubing speed
(with 2-3 tubes) and RPMs between 5000-5500.

Thank you for any assistance you can provide.

 

[ThomW]

As a general rule, each inch you drop the pitch of your propeller, you will gain about 200 rpm's, give or take. In your case, it seems as if something is off. You would not be able to drop your pitch enough to get it anywhere near the 5000 RPM range you are looking for. Is the timing set correctly on the motor? Good spark on all cylinders?

Either way, a 25 foot pontoon with a 60HP motor is going to have a hard time pulling a tube, not to mention 2-3 tubes.

 

[NYBo]

Yep, something very wrong here. A prop change isn't going to get you where you need to be.

 

[jimmbo]

Spark to all cylinders?, Fuel system good? Control linkages adjusted so full throttle can be requested? Tachometer accurate? That is a lot of boat for a 60hp, it would be a lot of boat for an 85hp.

 

[DonM1166]

OK

Thanks. Thinking about it, that does make sense, but I wasn't sure that was the answer.

Don

 

[ahicks]

A BigFoot uses large diameter props, the same as a 90+ hp engine would use, so prop pitch needs to be pretty low on the 60. A 9" would likely be close, but using your performance data that doesn't seem right.

Have you verified that your tach has been set correctly?

If so, I'm suspicious of your state of tune. Does it seem to be running smooth at idle rpm? Is idle rpm as low as what Merc. says it should be?

Are you sure you're getting full throttle?

Not sure of the need for a jack plate on a pontoon boat either. With some care and maybe a little experimentation to get the engine at the right height, what might the advantage of a jack plate be?