Classic AquaSport
Aquasport Mechanicals - things that need a wrench, screwdriver or multimeter => Props => Topic started by: sebas54 on May 26, 2009, 11:28:18 PM
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I have a 22' ff 1980 aquasport with a 4.3l merc. alpha. I am running a 15x15 prop and max rpms are 4300. I put on a 15x18 and was running at 3900 rpms. So, if my math is right I need a 15x13 prop.
Do 22' boats usally take a prop pitch that small?
Does this seems right?
How fast is my boat supposed to go?
Thanks
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Anyone with a similar set up??
How fast do you go???
What size prop do you have???
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A 15X13 would get you up to 4600 or 4700 RPM, and Merc says the 4.3 is good to 4800. But IMHO, I don't like running the 4.3 V-6 that high. It is a 90 degree V-6 that basically is a 350 (5.7L) small-block with 2 cylinders cut off. It is an inherently unbalanced engine that does not like to run high RPMs. The early 4.3 blocks were real buzz machines, but GM went to split bearing journals to smooth it out and that worked OK... Still did not fix the basic problem of a 90 degree V-6. :roll:
So my recommendation is to stay with the 15x15 - it will keep the engine in a good RPM range and be fairly efficient. You would get a better hole shot with a 15x13, but it's not clear if your problem is with top speed or hole shot. You did not state what kind of prop it is - aluminum, stainless, or composite - or 3, 4, or 5 blade. You would benefit from switching to a stainless 15x15 if you are running aluminum. Also what speeds are you running at top end? I would guess upper 30s trimmed out - pretty close? :?:
Hope this helps - see ya on the water!
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Thanks for the reply. I get 26-27 mph with the 15x15 at wot
15x15 wot 4300 rpms going 26mph
I tried 15x18 wot 3900 rpms going 28mph
the props are aluminum with 3 blades. Does this sound right?