prop size for yamaha T60?

[glendam]

I bought a alumacraft navigator 165 with a yamaha T60 and the dealer installed a 10 7/8 x 11 prop. I checked out yamaha's spec. sheets on this motor and they tested it with a 11 1/4 x 14. My RPM's are around 5300 and a top speed of 27 mph/gps. Yamaha's specs show RPM's @ 6000 and top speed @ 33.5. I feel like the boat should go faster than what it currently does (I would think that it should go about 30 mph +). Do you think the dealer installed to small of a prop for this motor.

[Whoaru99]

Just based on RPM, it sounds about right to me. But, on the other hand, it does sound like a small prop for that combination.

The problem is if you put on a prop with higher pitch, then the engine RPM is going to drop and may be too low at max RPM. It will also make your boat slower to get up on plane.

Yamaha's top speed numbers really don't mean much unless they tested exactly the same configuration and weight of boat that you have.

[glendam]

The Yamaha test was done with the same boat and motor configuration as what I own.

[united jigsticker]

The 165 is a 16.5 ft boat, correct?

Is that the max HP for that boat?

And is the 27.5 the max speed with just you + gear in the boat, and the motor trimmed to optimum tilt at WOT?

If all above is true, then I agree, 33-35 mph is what you should expect for top speed, providing you don't have an above average amount of heavy gear.

[glendam]

Yes the boat measures 16.5 and is maxed out at 60hp. 27 mph is at WOT. I have 24 volt trolling motor with the battery storage about 1/3 way back from the bow, but its not like I'm overload because I'm only 150lbs soaking wet. Not to mention that the the boat was designed to hold two batteries up front.

I havent even had the boat for a month, should I contact the dealer about changing the prop out?

[united jigsticker]

WEll, you should have a spare anyways, so I'd reccomend buying the prop that was speced in Yamaha's test report.

Put that prop on, and see if your performance improves.

[glendam]

Thanks for the help UJ

[PerchJerker]

Quote:

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I havent even had the boat for a month, should I contact the dealer about changing the prop out?

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That is the best place to start, you want to try before you buy with props if at all possible. Also, look at the mounting height of your motor, can/should it be raised up higher on the transom?

[Whoaru99]

I looked at Yamaha's HSOforum and the performance bulletin for the 60hp engine and your boat. The quoted 33.5MPH is at 6000 RPM with a 14P prop.

I'd say there is something else to look at first instead of the prop. Yamaha's figures are with a 14P prop turning 6000 RPM and you are saying the engine can turn a 11P prop at only 5300 RPM. With a 11P prop, that engine should probably be turning 63-6400RPM.

Almost sounds like the tach is incorrect, or the engine is not opening to full throttle, or some other mechanical problem. Are you positive the tach is reading 5300 and not 6300?

I'd have those things checked before I purchased a different prop. If the tach is actually reading (or the engine is actually running at) about 6300, then a higher pitch prop is the right way to go.