TOPIC: Prop Pitch and the Tower of Power

Is 15P (printed on my prop) refer to the pitch?
Is that a normal pitch for a 1976 Merc 1500?

How much horsepower do you need to pull a 280 pound skier out of the water?

1. Yes. 2 and 3. Depends on the boat style, weight, passengers, etc. etc. etc. Do you have a tachometer? Prop that turns 5500 RPM's at full throttle with a couple adults in the boat should be capable of pulling a skier with the same prop.

Amigoid wrote:

Is 15P (printed on my prop) refer to the pitch?
Is that a normal pitch for a 1976 Merc 1500?

How much horsepower do you need to pull a 280 pound skier out of the water?

What are you getting at wide open throttle for an rpm reading? How many blades? Are the blades in good shape? Are they cupped at all?

I'm no expert, but I know there is a lot to props. I've learned a lot testing props on my Power Cat, and they're all different. Right now with my old Merc 1000 (probably 75-80 hp at the prop) and a 300# boat, I'm running a 17P right up to 6000 rpm, too much. I hope to soon test an 18P cupped 3 blade SS. Cupped blades get you bow lift, something I need. I tired a 20P cupped 3 blade SS prop and the boat hanldes better then ever, but only turned 4400 rpm. Like Kerry says, you want something at WOT that will get you to 5500 or so.\

Good luck!

Frank

If the hull and motor in question is the one in your Avatar, then you almost certainly need more pitch and you are probably over revving the snot out of your motor. Do you have a tach and what is it reading at wide open throttle?

That hull is similar in size to my Challenger(thats 17 foot or so, correct?)...i run a 135HP Merc with a 21P cupped bronze prop. With the hull you show and 150HP, you should be in the 19-21ish pitch range.

15 pitch is fine for skiing, it'll give plenty of grunt out of the hole and allow the motor to rev on it's power curve at ski speeds. This would NOT be suitable for everyday boating as motor would in general be reving too high. Looking at the picture of you boat, I would imagine a 19 to 21 would be appropriate for non ski times. A tach is the right tool to use, fully trimmed, Wide open throttle, one person I'd prop to have the motor rev to 5800 to 6000. The 1500 will do fine there, these motors will self destruct if allowed to lug on too big of a prop but, don't mind reving a bit. The 1500 is particularly sensitive to detonation. I would also check to make sure your total timing is at 21 degrees NOT the original spec of 23 degrees, this helps a lot with detonation prevention. Merc sent a bulliten out on this years ago (70's) I would also run ONLY premium 92 plus octane as insurance against detonation. Nothing is more expensive than a rebuild because of a burned piston from detonation.
I have a 74 Hydrdrostream with a 74 1500, where I run a stainless 24 chopper for speed and before I got my inboard ski boat, I would swap on a 15 pitch cupped aluminum for skiing. It's really the best thing to do rather than make a compromise on a prop that does neither speed or pull well.
Randy

Looks like the next thing on my list is to replace the Tachometer. The Mechanic at Valentines said it was broken. And yes, its the boat in my Avatar pic.

Thanks for the detailed responses. Here is a pic of the prop, I don't know what cupped means... taken in context I presume it means that the prop is curved in such a way as to scoop more water.
Its been repaired, and it looks like a few notches in it were patched.

Yes it is cupped as far as I can tell. Cupping is when the trailing edges of the blades around the tip are cupped upwards as you look at it here. It improve bite & can reduce cavitation on cornering. As Frank says there is a whole science out there on its own concerning props, but all the advice above is sound.

Geoff UK

Get a 19p for good over all performance. Find a used craigslist $100 aluminum. Look around this winter... That would be imo a good place to start. Way better then the 15p. Save that for a back up. The 19p compared to the 15p will be FAST, Mike