new inline 200A prop help

[frontier man]

I have a friend that has 2014 frontier bay boat and he has thw new 200A on it. What prop should he put on that motor. He said when he is at 4000 rpm he is only gett 32 mph.WOT He is get 52mph. He has a 25 pitch prop on it. I think that proo is to big. I have the 175 on my frontier and I get same speed as my rpm 1 to 1 4000rpm 40mph. And WOT is 53-54 I have a 23 pitch prop. I told him that he should try drop the 23. What you guys think.

[Harper]

Boat speed is not the determining factor for prop selection. His RPM at WOT is the determinant. As long as his RPMs at WOT are within the specifications, he's propped well. There is room to play within the specified range, but it's not good to either over- or under-prop the motor outside those specifications. Under-propping will lead to hitting the rev limiter a lot, over-propping that will not allow the engine to reach the WOT specifications results in lugging the motor. Both of these conditions will shorten the life of the engine.

Trying to use boat speed as the determinant is unreliable, as there are too many other variables at play; hull condition and cleanliness, weight and weight distribution, trim, mounting height of motor, above water drag caused by topside people and apparatus, and so on. Although your two boats differ considerably in speed at 4000 RPM, they are essentially the same at WOT, so again, I find the speed an unreliable indicator of prop selection.

One more observation.....why do you think dropping from a 25" pitch to a 23" pitch would make his boat faster at 4000 RPM? That makes no sense at all. Doing that would achieve just the opposite.

[frontier man]

Boat speed is not the determining factor for prop selection. His RPM at WOT is the determinant. As long as his RPMs at WOT are within the specifications, he's propped well. There is room to play within the specified range, but it's not good to either over- or under-prop the motor outside those specifications. Under-propping will lead to hitting the rev limiter a lot, over-propping that will not allow the engine to reach the WOT specifications results in lugging the motor. Both of these conditions will shorten the life of the engine.

Trying to use boat speed as the determinant is unreliable, as there are too many other variables at play; hull condition and cleanliness, weight and weight distribution, trim, mounting height of motor, above water drag caused by topside people and apparatus, and so on. Although your two boats differ considerably in speed at 4000 RPM, they are essentially the same at WOT, so again, I find the speed an unreliable indicator of prop selection.

One more observation.....why do you think dropping from a 25" pitch to a 23" pitch would make his boat faster at 4000 RPM? That makes no sense at all. Doing that would achieve just the opposite.

Im not an expert in props. Im just explaining what he told me. I have the same boat as he does but the with a 175. So I figured his performance should be better than my boat. rpms at wot is 5200 and he said it blowing out, his has a jack plate as well. should it be 5900 r 6100 I dont remember exactly.

[Seaduck]

I know everytime you drop 1 pitch you pick up 200 rpms on top end. Like harper said you would need to know the overall rpm at WOT. As far as blowing out. How high is the motor mounted on the boat. Usually you see people in the top or second hole. Im not familar with that motor but I would think 5200 would be on the low end. Ive got a df115 and its max is 6000rpms which is what I have it at when WOT. Good luck with the prop.

[Harper]

Im not an expert in props. Im just explaining what he told me. I have the same boat as he does but the with a 175. So I figured his performance should be better than my boat. rpms at wot is 5200 and he said it blowing out, his has a jack plate as well. should it be 5900 r 6100 I dont remember exactly.

Okay, well, like I said, if the RPMs are too low at WOT, then yes, he's over-propped and should reduce the pitch. As Seaduck pointed out roughly 200 RPM can be expected for each 1" change in prop pitch. So if, for instance his WOT RPM should be 5800-6000, he would need to drop to around a 19" pitch to bring it up from 5200 RPM. In that he is experiencing prop ventilation, he needs to learn a bit about trim and engine height with that jack plate. It sounds like he needs a bit more experience to prevent the ventilation. My 20' boat has a DF150 on it, slinging a 16" diameter prop with a pitch of 18.5". It likely has a deeper V than your bay boats, and was not meant for shallow running. The 4000 RPM on your boats should be a reasonable cruise RPM, and might get your friend the same 42 MPH that you get if he can stop the prop ventilation. My 4000 RPM cruise is closer to 30 MPH. Sounds like you friend has a couple issues. He may well need a lower pitch, based on his WOT figure, but he also appears to need to work on what my former profession referred to as "pilot technique."

[Moonlighter]

This is a bit disturbing, that a brand new engine on what appears to be a new boat, hasn't been propped correctly by the selling dealer.

Unless there is a very good reason not to, your friend should take that boat back to the dealer and tell them what it is doing now, including the issues of max achievable rom and prop grip, and work with the dealer to get it set up and propped correctly. That is what dealers are paid to do. Most of them will work with owners to make everything work as it should.

As others have said, the aim with props is first to get one that will achieve close to max rpm at full throttle, in good conditions, with the engine trimmed to optimum position.

I am not sure what the max rpm for the new inline 200 is, probably it is 5500-6000, but I am certain that if the best rpm he can achieve now at WOT is 5200, then something is not right, big time. Needs to get sorted, because lugging a new engine by running it like that is bad.