prop help

[Coors]

I have a 1988 four winns 205 sundowner, about 3200 lb loaded. New to me and had to install new engine 5.7, omc cobra, has a ss 15x17 prop. I got far enough into break-in today and put it to 4600 rpms. Got 42 mph, but had alot of throttle left, which I didn't want to use , in order to see how much rpm was left. Any suggestions?

 

[Chris1956]

Re: prop help

You need to know your max RPM. It sounds to me like you are underpropped, since 4600 on a Sterndrive motor is got to be near or over the max RPM.

 

[Coors]

Re: prop help

That is what I mean; I still have more throttle left @4600 rpm (max).

 

[QC]

Re: prop help

Well Coors, it is a little hard to tell how far you can go without knowing how far it would've gone. Yes, I know you were being carefull, which was the right thing to do. At a minimum she'll pull a 19 inch pitch. How were you loaded? Typical? Extra light? Extra heavy? This info may help us zero in some, but the fact is you need data from a 19 and maybe even a 21 . . . 21" on a 20 footer would not be out of the realm of possibility for sure. Might want to start there if you were running heavy or typical. If you were lightly loaded, then maybe try the 19. Only way to know for sure will be after you have tested . . .

 

[Coors]

Re: prop help

Thanks, it was 4 adults, 3/4 tank of gas(34 gallons in it), heavy chop-whitecaps; kinda trimmed down to plow through the chop. But I had alot of throttle left to use; just went to 4600 @42mph once.

 

[QC]

Re: prop help

Thanks, it was 4 adults, 3/4 tank of gas(34 gallons in it), heavy chop-whitecaps; kinda trimmed down to plow through the chop. But I had alot of throttle left to use; just went to 4600 @42mph once.

If all of that is correct (i.e. tach, throttle) then I think she'll pull a 21 no problem. She must really jump on plane as is.

 

[Coors]

Re: prop help

Thanks QC, yes, it planes quick. will see if I can borrow one and check it.