So as I understand it, cupping makes a prop act bigger? If so then the best way would be to have the 15" cupped or the pitch adjusted up to 16". That would be easiest since the 15" is stainless steel and more malleable? It does not look to be cupped, it is an OEM SS. The 17 is aluminum and a little crusty, and I know aluminum doesn't like to bend. I have no idea of the top speed, but it is pretty fast, and the 15" makes you feel like you need to upshift, but can't. I had this motor on an 18 foot Lund aluminum boat and the difference was not so acute. This little Whaler has such an efficient bottom the difference is glaring.
Doesn't make it bigger, makes the blades grip the water better and doing so acts like calculated 1" more pitch besides eliminating some ventilation issues as I mentioned at wot.
If you are talking about the OMC SST (Stainless Steel, Teflon coated) prop of the day then it is already cupped. I bought one when they first came out. I'd tear up my alum on every outing. After the SST, never had my prop off again.
On Steelspike's recommendation on a Turning Point brand, Hustler, it is aluminum but other than material type, is designed and marketed as having the features of a SS high performance prop. I have one and it is aggressive as he said and it cost me $100. It is cupped, high rake for good bow lift (reduces drag and allows the boat to go faster at most trim settings, and is made from a special alloy alum. that is said to be tougher than the norm. Only thing I found different was that the blades were thicker than my Ballistic SS props and that makes a slight improvement in mph vs rpm.
I just did your homework for you. Go to the top of this page and click on "Boat Parts & Accessories". Select props and input your vitals. Once it answers the "Select a Prop" Question scroll down the page and it has a listing of from 9 to 17" pitch for that engine. Select 15" and the first item is the Hustler, prop number 21311510 with hub.....don't forget the hub, for $90. You can't beat that with any rework at a prop shop. Over on the right under the price, click on the more info box and scroll through that. It tells you about the special alum process, the high rake and the fact that it is cupped. As Spike said, that is where I'd put my money. As I said, high rake design lifts the hull out of the water and what you can get from that, at the right trim setting, is less drag which will allow the engine rpms to increase and as a result more mph...which the cupping is already helping you to obtain.
One thing you need expect: The prop is ported.....specifications said so and mine was. Ported props have holes drilled under the leading edge of each blade whose purpose is to reduce the density of the water across the blade in the "hole shot" (getting on plane) which allows the engine to rev slightly (500-1000 rpm) allowing your horsepower to develop early and spin the prop shaft harder and faster, result of which gets you out of the hole faster.
In running this Hustler prop, on your hole shot, firewall the throttle from idle. The engine will rev more than you are used to but that's what it is designed to do. You will get on plane faster and once on plane, as you get up to speed, the engine rpms will drop (back to more normal somewhat) and when they do the boat will speed up that much more. If you have your trim set for a slight bow high attitude, you will be amazed at what your rig can do.
Personally, I'd trim it out till it starts porpoising at your current speed for max mph. If you slow down, expect it to porpoise and curing that is nothing more than tucking your trim in till it stops. If you don't have trim, you will just have to experiment with your tilt pin till you get the sweet spot of performance where you want it since porpoising has to be dealt with if you are looking at maxing your mph. No doubt you won't get the kind of performance your rig is capable of producing, but I'm going to bet you that there will be a significant difference in performance.
If you get confused, ask!
Good luck,
Mark
