prop size?????????

[finnlander]

i have a 1988 Cris Craft. scorpion 21 ft cuddy with a 5.7 mercruiser. what would be the proper propeller for this boat? would like to know what was on it when new. how do you find the right prop? it has a 19 pitch on it now.
thanks

 

[guyjg]

What is the WOT RPM? If it is between 4400-4800 the prop is correct.

 

[finnlander]

my wot rpm is only 3900 maybe 4000 with 2 peaple and half a tank of fuel. says it shoud be 4200 to 4500 thanks

 

[bondo]

my wot rpm is only 3900 maybe 4000 with 2 peaple and half a tank of fuel. says it shoud be 4200 to 4500 thanks

Ayuh,.... Either yer motor ain't puttin' out the Power it should be,...
Or,...
Yer prop is too big,...

 

[kghost]

Are you trimmed out? If not redo your wide open throttle test again and make sure to trim out to max rpms.

Typically a 21 ft with a 5.7 (350 ci) should be running a 19 - 21 pitch aluminium.

17 pitch is not as common but may be necessary.

 

[RicardoMarine]

I agree with the guys.

I'll add that in order to perform a WOT RPM test/check, the engine must be in full tune (including ignition TA), hull bottom must be clean, drive ratio correct for the engine, and the prop must be in very good condition.

Keep in mind that if you cannot achieve your OEM WOT RPM, and under conditions as you most commonly load the boat, your engine will/may be over-burdened at "ALL" rmp ranges.


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