Prop question on a 4.3 Mercruiser Pontoon

[RedneckRich]

Hi Everyone,

New to pontoons and the forum, lots of info to take in! :redface: Not sure if I needed to post this in pontoons or props but I just couldn't find the info I was looking for. I have a 2005 22' Lowe Suncruiser Jamaica series pontoon with a 4.3 Mercruiser i/o and a alpha 1 drive. (WOT 4400-4800 RPM Rating). The current prop is a Vortex 15.25x15 Aluminum. Its pretty beat up, it had a nick in it I ground out and its pitted pretty bad. It takes the boat up to about 27mph and WOT is only at 4200 with the current prop. With 190hp I expect it to go much faster?! We cruise alot and sometimes take a tube. I've had very different suggestions made to me.. the local prop shop suggested a 15.25x13 and the 'prop wizard' I filled out on .turningpointpropellers . com suggested a 14.25x21 so you can see my confusion! Anyone have any suggestions one where to start, I know it might take one or two to try but would like to have an educated guess on which one to start with. I've been told about the cupped props, my friend has a 150 outboard with a cupped prop same size as mine and has pretty good luck with it.

 

[lncoop]

Re: Prop question on a 4.3 Mercruiser Pontoon

Nice looking barge, Rich. If your WOT RPM max is 4800 you've definitely got some wiggle room. Each 1" decrease in pitch will net you approximately 200 RPMs, so that's probably why the shop recommended a 13 pitch. There are many variables that factor into boat performance, so whether the increase in RPMs will result in more speed is anyone's guess, but it certainly wouldn't be a bad idea to get them up into the max range. To keep things simple start by trying to find the identical prop with the 13 pitch, then go from there. If it's feasible, look for a place that will take the prop back (assuming it hasn't been damaged) if it doesn't work out, that way you can experiment without burning through a pile of cash. Good luck and welcome to iboats.

 

[bruuuuce]

Re: Prop question on a 4.3 Mercruiser Pontoon

I think I would take the word of the prop shop, assuming he has been in it a while and has a good reputation.

On Table Rock Lake in SW Missouri their is a shop called, Dyna Props (google they have a website) and he will take your boat out with different props and make sure what he sells you is what your wanting, he knows his stuff. I am sure you can find someone in your area that does business like he does, that would be the best route.

Make sure they know the style of boating you do so they can get you the right prop, tell them you do 90% cruising and 10% tubing (evaluate yourself and plug in your numbers) that should be important to the prop selection.

 

[Silvertip]

Re: Prop question on a 4.3 Mercruiser Pontoon

Me thinks the prop calcualtor is not taking into account that you have a pontoon -- not a planing hull. If your current wide open throttle rpm is only 4200 RPM with a 15P prop, it would drop like a rock with a 21P. You want to go the other way to bring the RPM up. Now understand this. Just because you bring the rpm up to 4800 does not mean speed increases. It might, but the fact is the reason rpm comes up is because thje prop takes less bite on the water so it must therefore turn faster to accomplish what you had before the swap. If you went from a 15 to a 13 it may just put the engine into is power band and once "over the hump" so to speak, speed will increase. This is why prop selection is such a crap shoot. When fine tuning it is a trial and error situation at best. You can get into the ball park with calculators but there is no substitute for experience.

 

[buzzman]

Re: Prop question on a 4.3 Mercruiser Pontoon

i have 3.0 mercruiser 23ft fisher pontoon ran a 15 x 15 4200 rpms went to a 15 x17 4 blade and got 4600 rpm and 4 miles faster now all i run is 17 would like to try a19