Bought used boat, does it have the wrong size prop for 97 Vmax TRP?

[aphextwin]

Hey guys, so now not engine related. Further to my other thread on if I need to replace a prop. Started doing some research and because my prop is a Quicksilver I thought to get another prop the same size since I have the hub kit for it already. The one I have is a 15 x 17.

Here comes the odd part. The Vmax is actually a TRP? so didn't realize it was supposed to be two props but for whatever reason the owner ended up just using one prop. Now when I went to Quicksilver's documentation for Yamaha 150 HP recommendations, it shows that for 15 x 17 prop size that's for boats 21 - 25 feet in length. My boat is only 18 feet in length and propeller size recommendation is 14 1/4 x 21 for 18-22 feet boats.

Do I just assume here the original owner used the wrong prop and I should be getting the correct size as recommended by the QuickSilver documentation?

Prop.jpg

[boscoe99]

If a single propeller (particularly a Quicksilver) is being used I would suspect the contra rotating propeller lower unit has been replaced by a conventional lower unit.

[aphextwin]

Nice...ugh. So going back to the prop...is the assumption here that I should go back to getting a 21 pitch prop? The 17 would have have caused it to over rev on WOT since the pitch is for a much bigger boat?

If a single propeller (particularly a Quicksilver) is being used I would suspect the contra rotating propeller lower unit has been replaced by a conventional lower unit.

[boscoe99]

With the propeller that you have, what is the wide open throttle RPM with the boat loaded and the engine only trimmed up to the neutral position?

[99yam40]

you also need to find out what lower unit and gearing is installed.
but like Boscoe mentioned, knowing how well the boat and motor runs at WOT will give you an idea if it is too much or too little prop on it right now

[aphextwin]

Thanks guys I will take it to the lake tomorrow and see what rpm I have at WOT. Hopefully my tach works this time.

[DennisG01]

A slightly different tactic I take when propping a boat is to load the boat with your NORMAL load - how you expect to run the boat most of the time. Then, going WOT, continue to trim up till the speed no longer increases or the prop starts to ventilate. The point just before that will be your MAX RPM. Once you know that info, the proper propeller can be figured out. Along with knowing the spec RPM MAX range for your engine, of course.

Like mentioned above, it should be quite obvious if the dual prop gearcase is still on there since if it only had one prop you would see a bare propshaft.

FYI, I have heard LOT'S of good things about Ken at Prop Gods in regards to getting a proper prop for you.