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mapleleaf
06-25-2009, 06:14 PM
Tune up on the boat has solved all running issues.....so great!
The boat is idling great, sounds right (low), but the tach reads 1100, which if the tach is right would be too high.
It also tach's out at 34 mph (6000 rpm, motor screaming) I've only been there for a few seconds...
So I went under the boat, hoist not working properly, to get the spec's on my prop, thinking it was the reason for tach and speed, and can only get OJ 803 off the prop. is there a specific spot on the prop where the dia. and cup is stamped and i missed it? Is my tach off by 3 or 400 rpm?
The idle was set by a marine mechanic who has 35 yrs. on the water....
Anyway to test tach????
rickr
06-25-2009, 06:29 PM
Maplelesf
Borrow a tach or dwell meter from one of your hot rod (boating or street) buddies to check yours. But, first check the tach housing for cracks. Many tachs get broken from tightening the hold down screws too much.

If you can get a good tach and GPS speed reading you can calculate the prop pitch with this web sight. I am not sure about ski boat props but performance sterndrives have a prop slip between 8 and 15%.
http://www.rbbi.com/folders/prop/propcalc.htm
csuggs
06-25-2009, 10:22 PM
The prop diameter and pitch should be stamped into it, but you may not see it with the prop on the shaft. Mine was stamped on the flat surface next to the bore of the prop - that doesn't make sense but . . . . either the retaining nut or the strut bearing would be blocking the information you want.
mapleleaf
06-25-2009, 10:31 PM
The prop diameter and pitch should be stamped into it, but you may not see it with the prop on the shaft. Mine was stamped on the flat surface next to the bore of the prop - that doesn't make sense but . . . . either the retaining nut or the strut bearing would be blocking the information you want.

Yeah I think that's where it is...I was using a kids mask diving under there, couldn't see much!
mapleleaf
06-25-2009, 10:33 PM
Maplelesf
Borrow a tach or dwell meter from one of your hot rod (boating or street) buddies to check yours. But, first check the tach housing for cracks. Many tachs get broken from tightening the hold down screws too much.

If you can get a good tach and GPS speed reading you can calculate the prop pitch with this web sight. I am not sure about ski boat props but performance sterndrives have a prop slip between 8 and 15%.
http://www.rbbi.com/folders/prop/propcalc.htm

Hey thanks, may just take it easy til the end of my vacation, those buddies are back home with the gear!!!!