Just another prop question

[beerbudget]

1983 Sleekcraft Ambassador. Volvo penta 350/280. Prop on there is a 15X17 aluminum. Tach pinned at wot. No good. Any recommendations on correct prop size? Any idea on ideal rpm's at wot? Thanks.

 

[steelespike]

Re: Just another prop question

Thats a pretty good chunk of boat.3500 dry. "Tach Pegged" doesn't tell us much,and what is the speed?Just a guess 46-4800 on the rpm.

 

[beerbudget]

Re: Just another prop question

Don't know the speed. Seemed slow though. I'm thinking 30? The tach was pinned at 5000.

 

[Silvertip]

Re: Just another prop question

Let's get some terminology clarified. Are you saying the tach scale reads 0 - 5000 rpm? Most read 6000, 7000, or 8000 rpm. If the engine is turning 5000 rpm but the tach can actually read higher, that's one thing. If the tach only reads to 5000 rpm and the needle is indeed up against the pin at the top of the scale, that's quite another and in fact may be reving way higher than 5000. So which way is it? As for recommended wide open throttle RPM with an average load - 4600 - 4800 is the target.

 

[beerbudget]

Re: Just another prop question

My mistake. Yes the tach reads 0-6000 rmp, not 5000. At wot, it is pinned at 6000. Yes, at the "pin" therefore "pinned". So if 4600-4800 is ideal, What pitch prop would be a good starting point? It has a 17p on it now.

 

[steelespike]

Re: Just another prop question

My mistake. Yes the tach reads 0-6000 rmp, not 5000. At wot, it is pinned at 6000. Yes, at the "pin" therefore "pinned". So if 4600-4800 is ideal, What pitch prop would be a good starting point? It has a 17p on it now.

Something is screwy either the tach is wrong or the prop has a spun hub.
Mark a line across the hub with indelable marker and run the boat and check the mark.Does the tach indicate the proper idle rpm?

 

[beerbudget]

Re: Just another prop question

I will have to check both. Don't remember the idle tach but i think it seemed high.