new boat prop question???

[ratking20]

so i bought a 1992 sea ray 220 bowrider last week. it has a 350 mercruiser 5.7 v8 (260 hp i believe). at WOT it was running at 3500 rpms. i looked it up and it should be running at 4600 WOT. so i had a tuneup and it raised it to 3900. my mechanic said we should look at the prop now. it had a 15x17 on it. he looked it up and so did i, it should be using a 14x19. will changing props get me to the 4600 rpms i want at WOT? what else can i do to get my boat running at where it should be???

 

[sethjon]

Re: new boat prop question???

A different prop will raise the RPM, but are you sure you want that? Do you pull skiers or inflatables? If so, you want a better hole shot and then you give up a little on the top side. You can't have it both ways. Also, is the prop you have now steel or al?

 

[ratking20]

Re: new boat prop question???

the prop is aluminum. im in a bay area where sand bars aften destroy props. so i rather use aluminum over ss because theres less of a chance of damage to the drive if i do hit bottom. i dont pull skiers but i do pull tubes(inflatables). i think im not getting the top speed i should have. im not sure how fast im goin(broken speedometer) just have a feeling. but either way my boat should be running at 4600 rpms at WOT.

 

[jtmedical]

Re: new boat prop question???

I'm no expert on this by any stretch of the imagination, but I have two props that I use depending on what I will be doing that day. If I'm going to be pulling skiers/tubes, I will put on my 17 pitch prop so I can get a better "hole shot". That makes the RPM's higher, but my top end speed is decreased. If I'm just going to be cruising with the boss (my wife), I will put on my 21 pitch so I can get better speed. I guess what I'm trying to say is that the RPM's at WOT depend on what size prop you are running. 4600rpm is your max or redline for your engine. You should not run over 4600rpm no matter what size prop you have. I hope that makes since and it is on the right track. If I'm wrong, somebody please correct me!

 

[Bondo]

Re: new boat prop question???

. it had a 15x17 on it. he looked it up and so did i, it should be using a 14x19. will changing props get me to the 4600 rpms i want at WOT?

Ayuh,.... Going from a 17" prop to a 19" prop will Lower the rpms at wot...

 

[ratking20]

Re: new boat prop question???

i know the higher pitch should lower the rpms
and the smaller diameter should raise them
leaving me probably right where i started.
but since the 14x19 is what the boat came with, what the sea ray website says i should be running as well as what the mercruiser book my mechanic has says. should that be the prop i use? im just asking because im not too knowledgeable in this subject.

 

[Bondo]

Re: new boat prop question???

and the smaller diameter should raise them

Huuuuh, Not Really... Diameter is the function of Blade Design....

When talkin'/ shoppin' props, you're workin' with Pitch,...
Diameter is just along for the ride...

If you can't pull/ over-rev a 17",... You probably have a sick/ tried motor....

 

[ratking20]

Re: new boat prop question???

well that doesnt sound good. its a 1992 with 450 hours on it. the boat runs great. it was out of the water for about 3 years. only in the water about twice a year and ran for a bit then taken out. what else should i have my mechanic be looking into with this. i will try the new prop and see what happens but is there anything else i should try????

i mean is it soo bad that my engine is only at 3900 at WOT?????

 

[Bondo]

Re: new boat prop question???

what else should i have my mechanic be looking into with this.

Ayuh,...
In the Adults Only section is a posting by Don with a title of something like, Boat won't go WOT,...
Read it...

 

[ratking20]

Re: new boat prop question???

thanks bond-o .... i think i have a few ideas of where to look now. first i know my current prop isnt in the best condition. that could be a factor. and second ive been running the boat with the trim all the way down(or in) im goin to try and play around with that and see if i notice any changes. anything else would be out of my league and better left for a mechanic... do u think those 2 could affect my wot rpm by about 700????? well thanks again

 

[Bondo]

Re: new boat prop question???

and second ive been running the boat with the trim all the way down(or in)do u think those 2 could affect my wot rpm by about 700?????

Ayuh,.... Absolutely,....