RPMs - when to get nervous

[seedlings]

1978 Evinrude 70hp
1979 15' Crestliner tri-hull
2 adults, 1 teenager riding plus another in tow

The Evinrude manual says 5500rpms, but the 13p tubing prop hits 5500rpm with throttle to spare. I start to get nervous around 5500rpm. The 17p cruising prop WOT is 5500rpm, but I've never given WOT to the 13p prop.

I've read that 5800rpm may be better on the motor. At what RPM should I get nervous?

CHAD

 

[basspirate]

Re: RPMs - when to get nervous

especially since that is an older motor i would say anything over 5500 is risking damage. if you have throttle to spare i would look for a larger pitch prop. read the forum about prop selection. essentially what you are doing is burning a lot more fuel to go at a slower speed than what your boat/engine combo can handle.

 

[F_R]

Re: RPMs - when to get nervous

The literature I'm looking at says that the approved full throttle operating range is 5200-5800 RPM. I'd say you are right on the money.

Hm.m.m, I wonder if you really need that 13" for the tube (?) If you pull him at WOT and can't get 5200, then I suppose you do. But it doesn't sound like you are towing at WOT.

 

[seedlings]

Re: RPMs - when to get nervous

The 17p is slow to hit plane with the tube, and often dunks the front end of the tube down. A 15p would probably be perfect in-between, and I'll be on the lookout for one of those.

I'll just keep it near 5500 and call it good.

Thanks,
CHAD