Prop size

[jamesr1]

I have a 18.5' Searay Seville Merc 140, Alpha 1 and was hoping someone could tell me if I have the correct prop. The #'s on the prop are 48-815758/A45 19P Also says it is a Mercury High Five. The boat ran fine at the lake other than at 3/4 throttle I was at top speed ( 30mph ). Is this the correct prop? I may pull a tube this summer. <br />Not really concerned with speed. What are the dangers of over propping?

 

[Bondo]

Re: Prop size

What are the dangers of over propping?

Ping,.. Ping,... Ping....... Detonation...........<br /><br />There'll be pretty little Holes in the tops of the piston,....... In No Time..........<br /><br />If you can't pull 44/4600rpms,...... You'll Burn It Down.........

 

[jamesr1]

Re: Prop size

Sorry I should have stated, RPM was 38/4000. I just bought this boat and found that the valves on the #2 cylinder were busted up, and the piston was smashed down on the rings. I have repaired all of that and the boat runs good. Could the damage have been due to over propping?

 

[Don S]

Re: Prop size

What year engine do you have?<br />Overpropping may have caused your problem, if your WOT (Wide Open Trottle) rpm was only 38/4000, then you are WAY over propped. You need to be up like Bondo said, 44/4600, especially if you want to start pulling tubes.<br />The timing is critical on the 3.0L engines, along with carb adjustment. Too lean and they will diesel and suck in water through the exhaust, and on hot valves, that's not good.

 

[Northern Eclipse]

Re: Prop size

a 19p high five is in comparison like trying to turn a 23p 3 blade, to much for a 3.0. High fives are actually designed to work with large gearcase V6 outboards. If pulling a tube is what you want to do then go down to a 16p four blade or 17p 3 blade, I would think that your set up could turn 19p 3 blade for top speed, see if you can borrow a few prop's to try, then trade your high 5 for the one you like and lets your 3.0 spin up to max rpm.

 

[jamesr1]

Re: Prop size

Thanks to all for the info. I will get a new prop. I was thinking maybe a 16P three blade. <br /><br />I was thinking I read something about overpropping causing valves to suck. Is this true, and possibly what happened to cause my #2 cyl to smash the valves? Thanks again

 

[tommays]

Re: Prop size

james<br /><br />i run a 15 x 17 on my 3.0 on a 20 ft boat and its a littel small(but great for hole shot and fully loaded boat) a 14 x 19 is a littel big(very bad holeshot) this year i am trying a 14 x 18 to see if its a nice middle ground<br /><br />tommays