Prop for new 16 foot fish and ski

[Buckle]

Sorry, I imagine this gets asked all the time

Just bought a new legend x16, and got a 90hp mercury fourstroke on the back, non CT.

I've only got 6 hours on the motor, but when I go wide open throttle, I hit about 5k before trimming up, and then I can maybe get to 5200rpm. Top speed is about 38mph. I was expecting to be in the 40s.

The motor is rated for 5000 to 6000, and has a black max 17p prop. The dealer has informed me that they would need to water test it, to see if it needs a different prop, and that if they decide it's propped fine, I have to pay them for two hours labour. Given the range from merc, I expect them to ask me to pay. I'd rather just put that money into the new prop.

From what I'm reading though, I should be aiming for close to 6k, correct? I was thinking of getting a spitfire x7 15p, but im truly lost here, and the dealer isn't being super helpful....which is annoying not even a week after purchase.

Any advise, tips or suggestions would be appreciated.

Thanks

[willy13]

Part of the final inspection of authorizing the warranty of a mercury is making sure a prop is on the boat that will allow it to reach an ideal RPM. Over propping, which you are at, is not good especially on break in. Your 90 Mercury needs to be in the middle to top of the spec'd 5000 to 6000 rpm range. I am willing to bet that Mercury customer service will help convince your dealer of this fact.

[Buckle]

Thanks @Willy13 , I've reached out to mercury now too, based on your recommendation.

I'm really thinking of just buying another prop and being done with it though. I bought the boat 5 hours away, and the more local dealer has been kind of a pain to deal with. They're talking about needing 2 to 3 weeks to be able to water test it, and then possibly charging me for that time. If I can find a more appropriate prop, and put it on myself it should save me a bunch of time, if not money.

Any thoughts on the spitfire x7 15p, compared to my black max 3 blade 17p?

[Buckle]

Thanks @Willy13 , I've reached out to mercury now too, based on your recommendation.

I'm really thinking of just buying another prop and being done with it though. I bought the boat 5 hours away, and the more local dealer has been kind of a pain to deal with. They're talking about needing 2 to 3 weeks to be able to water test it, and then possibly charging me for that time. If I can find a more appropriate prop, and put it on myself it should save me a bunch of time, if not money.

Any thoughts on the spitfire x7 15p, compared to my black max 3 blade 17p?

[willy13]

I don't know enough about bass boat props to recommend. I just knew that when my Mercury dealer repowered my boat he had to have a prop close enough to finish the final paper work. At least thats what he told me.

[Astroglass165v]

Have you checked the motor height on the transom? There's a good chance it's all the way down and may be too low. But I would expect a 16ft with a 90 to be in the 40s. But more rpm doesn't always mean more speed when you drop pitch to get the rpm. Also how loaded is the boat in your test runs?

[Buckle]

Not sure how to check the height, so no. I could take and post a picture of the transom if it might help. Boat was not heavily loaded, full tank of gas (11gallons), my wife and son, and then later on it was just me and a half tank of gas. Seemed the same.

[21XDC]

[Buckle]

Thanks! Look like my gap is around 5 inches...the diagram doesn't give an indication of where it should be at?

[Buckle]

I wasn't able to get things too level, but they seemed to be on similar angles. 20210716_110022.jpg

[Buckle]

I'm wondering if maybe the throttle isn't fully engaging? I popped the cowl off, and found the rod that controls throttle, im not sure how to adjust it though


Also, while out today, I was cruising at about 4400 rpm for 5 minutes, when all of a sudden the revs started dropping on their own, I thought maybe we were running out of gas, so pulled back and drove slowly to marina. Still had a couple of gallons left in it though. It hasn't done it again, but I dont like it. Any ideas? Could the two be related?