Can someone explain props

[mouse action]

can anyone try to recommend the proper prop for my craft
its a 21 ft trophy walk around with a Yamaha 150 four stroke.
the current prop is a solas 3511-150-15
now hidden in the cabin I found a stainless Yamaha Y14 1/4 x18 prop
will this prop work with out giving up any of the performance I’m experiencing with the alum one ????
or should I just replace the one that was on with a new one?.

[boscoe99]

Propping a motor is not as simple as it might appear. What you might want from your boat and motor might not be what the next guy wants. First thing that we need to know is what is your wide open throttle RPM when the boat is loaded with the motor trimmed up only to the point of best efficiency, and no further?

How do you feel that the boat performs with the propeller that is on it? Are you satisfied or not? It is a simple enough matter to swap propellers to see how you feel about each one.

[99yam40]

same thing I was thinking,
if you have another prop that you want to see how it performs,
why not slap it on and see

[boscoe99]

There is such a difference between the two that one or the other is not going to be satisfactory IMO.

[99yam40]

yea looks like a 15/15 alum and a 14 1/4/18 SS
SS tends to be cupped different too

but he already has it, so only costs him a little time to see what the difference is

[FabricGATOR]

Yeah mouse action, what I learned here years ago, is that the propeller is selected so that ideally, at WOT, the RPM are turning a specified speed determined by the manufacturer. That is, how the boat is loaded for that particular mission mind you. One day you may have a 1/4 tank of fuel, just you and the kids and a light cooler with beverages. The next week you may have 200 lbs of ice, full fuel tank, 40 gallons of fresh water and enough food and camping gear for a month on the Amazon River expedition....

My boat came with the original aluminum propellers that are 'over propped' (the engines can not attain 5500 RPM under my standard conditions/weight) , and then a set of stainless steel wheels that are great for my usual fishing expeditions. Three to four portly aged men, several cases of beer and ice, five gallons of rum, one lime, 100 lbs of chum, bait, and three hundred gallons of rec 90 fuel... I may be a little long in the tooth, but that is what fishing stories are meant to be...

Point being is to find a propeller that is good for your usual conditions and expectations / needs. Number of blades, diameter, pitch, material, cupping.... there are lots of things to consider. So not an easy question to answer in a single sentence.

Is there a Trophy 21 'walk around' forum or a club? Certainly someone there is piloting ahead of a Yamaha F150. Perhaps asking the guys that have already done the leg work might be a better source.

[Jason2tpa]

What's the issue you're experiencing with the prop currently installed? Refer to your motor spec rpm range at WOT to compare what your prop is turning at WOT. Reply back w/that info and you'll definitely receive helpful advice.

[mouse action]

Thanks for the help
the aluminum prop is a little worn and I was going to replace it in kind ,but then I found the s/s one and got to wondering.
the aluminum prop is perfect for the boat as is,I get about 38 mph at 5000 rpm normally,I was hoping the s/s one was going to be about the same.

[zenoahphobic]

Sounds to me that aluminium prop only gets to 5000 rpm, that the stainless prop would be way over propped. I wonder why it is in the wheelhouse and not on the motor, perhaps the previous owner already determined it doesn't work. Swap it and see.

[walleye1]

You need to get your rpm's closer to 6k at wtfo and full trim, means dropping in pitch.

[boscoe99]

Thanks for the help
the aluminum prop is a little worn and I was going to replace it in kind ,but then I found the s/s one and got to wondering.
the aluminum prop is perfect for the boat as is,I get about 38 mph at 5000 rpm normally,I was hoping the s/s one was going to be about the same.

Far from it. We don't know what we don't know.

You are way over propped. As noted, that motor needs to be able to turn at or near 6000 RPM when the throttle is wide open, the motor is trimmed up just to the point of best efficiency (and no further) when the boat is loaded. Motor will be happier, you will be happier, and the boat will probably be considerably faster.

I would try a Reliance SDS propeller in a 15" pitch. Or maybe a 14" or 13" pitch.

[FabricGATOR]

Remember mouse action, that propping is like gear selection.
Imagine tooling around Rome in your Ferarri, you wouldn't lug around in too high a gear, your engine and drive train will eventually pay the price.

Perhaps go visit a propeller shop and talk with them. They can repair aluminum and stainless steel propellers, and advise what other boaters with the same or similar vessels are happy with. I've even had them give me credit for my 'wrong' prop (trade in) towards purchase of a better fit. Perhaps you can make a deal for the perfect ss manatee slayer.