Another Prop Question

[Genofish]

I have a 2003 17' Lund Angler SS with a 2003 Yamaha 2 stroke 90hp. With my current 3 blade 13 3/4 x 15 alum prop my WOT is 5200rpm @ 35mph. Am i in the "normal" performance range?? or can i increase the rpm's if change props?

[CatManLee]

RPM's sound a little low for a 15 pitch prop? I have a 1750 Crestliner Fish Hawk with a 90 Yamaha running a 17 pitch alum prop, and it turns about 5400 @ 37mph.

Speed wise, I think that sounds about right for a 15/prop, but your rpm's should be able to run higher? Are you trimming your motor up when under way? If not, this would explain the low RPM's, otherwise I don't know.

The upper RPM range on my Yamaha 90hp 2-stroke is 5500 I believe, and you want to be close to that. I have a 2002 model, and yours should be the same.

I hate prop stuff, so many things to add together when trying to determine the proper "prop". Boat weight, hull design, alum/SS, trim, engine height, etc.

Good luck...over-all it sounds O.K., but I think you can do better, unless your boat is just really heavy?

[Genofish]

I have it trimmed up, could maybe go a little higher.

[moviking]

CatMan, I have the same boat with a 90 Johnson. It runs about 40 on my GPS. My rpm's are low, about 4800. I chaged props & they came up to 5100. I have been told it should be running 5500, so I borrowed a couple props from my neighbor I think one is 13 3/4 X 17, hope this will bring up my rpm's

[LMITOUT]

Something doesn't add up. Seems like a small prop for a 90 and it should really be winding up with a 15P. Are you trimming the motor until you get to the point where it begins to porpoise? Try to get a tach reading right before it starts to porpoise. Maybe the engine is mounted too low? Maybe the tach is reading wrong?

I have a 90 4-stroke Yamaha with a 3-blade 16P prop and it'll spin close to 5800 RPM's/37 MPH, and my boat is heavier than yours unless you REALLY packed it full of gear.

[Genofish]

Last night i took it out and trimmed it as high as i could and

reached 5400rpms. The motor is mounted in the top slot. The boat isnt packed to full, maybe the tach gauge is off??

[marine_man]

When you had it trimmed out as high as you could, how was the boat behaving?

The tach could be off, but usually not by a lot. In general, they're more accurate than speedometers.

marine_man

[Genofish]

Not sure what you mean but the handling was good and all was normal.

[marine_man]

Then I'd say you're pretty close to where you need to be. If the handling was good and the boat wasn't porposing then you're propped pretty close to where you need to be. Running at this trim level will give you the best speed & performance as well as less boat is dragging in the water.

marine_man

[Genofish]

I am the second owner of this boat, i found on the original outboard predelivery checklist stating that the original prop

was a hustler 17???

[marine_man]

A 17 will make your rpm situation worse, you'll get a little more speed, but your holeshot will suffer.

marine_man