Prop for 4.3L Merc I/O

[stephanofd]

Re: Prop for 4.3L Merc I/O

Stephanof, you need a 21" pith Solas Amita 4 blade prop, it will derease your prop slip a lot and improve your hole shot and aeleration very muh. You should be as fast or maybe faster with this prop and you will like the way the boat moves up higher in the water olumn and how smooth it runs.

H

Thanks hwsiii, I will check with the local Prop Shop to see if they have one for me to try. If not, I may go ahead and bite the bullet and buy one from iboats. I was kind of thinking that I might need to go to a 4 blade to bring up the hole shot and drop the WOT to the right range. I'm just surprised that I was actually fairly close with my original guess considering how little practical experience I have with picking props. I am good at research, and read quite a bit on this forum. That is part of the reason that I have gained so much respect for Hwsiii's opinion on props. Kind of like Don's on motors, or Ondarvr or Ooops on fiberglass.

Thanks for all the help, I will let you know my results whenever I get to try it out.

 

[hwsiii]

Re: Prop for 4.3L Merc I/O

I will be waiting for the results.



H

 

[stephanofd]

Re: Prop for 4.3L Merc I/O

how about gear ratio? Is there any chance the boat wound up with a 4 cyl upper ratio at some point? That would put you at 10% slip and make a lot more sense... a 21" prop should be about right or maybe even a little tall for your setup based on what I'm reading...

No, the ratio is correct, I checked the serial numbers. Of course I guess that it's remotely possible that some PO changed the gears at some point, but that seems pretty unlikely.

 

[wca_tim]

Re: Prop for 4.3L Merc I/O

the 4 blade 21 I mentioned above was a solas titan (not the "HR"... not sure they make that prop any more, might be the amita now). It's among the best values out there in terms of new props.

 

[stephanofd]

Re: Prop for 4.3L Merc I/O

the 4 blade 21 I mentioned above was a solas titan (not the "HR"... not sure they make that prop any more, might be the amita now). It's among the best values out there in terms of new props.

From looking at IBoats prop store, the Amita is Solas's 4 blade aluminum, and the HR Titan is the 4 blade SS. The Titan without the HR is a 3 blade SS prop. I guess they've changed the names around.

 

[stephanofd]

Re: Prop for 4.3L Merc I/O

it sure sounds like something isn't right...

running a 21" prop on a ca. 18 foot boat with a 4.3 in it 5000 rpms was 50+ some change and it planed in nothing flat, a 23" prop was upper 50's touching 60 or 61 some days at 4700 or so. that was with almost a thousand pounds less than you carry and 50 horsepower more. surely something is wrong.

If you were running a similar set up with a thousand pounds less and 50 more horsepower and were getting speeds in the 50+ range why do you think that means that something is surely wrong. That's a lot of difference. I mean you might be right, but I ain't following your logic.

is something bent (ie skeg)? is your bottom dirty (the BOAT!!)? how about waterlogged foam or something - any chance that you're carrying hundreds of extra pounds of weight? what about trim? is your trim working right and is it trimming out as far as you think it is or trying to plow it's way through the water... or the other way is it trimmed way out or something? that's a LOT of slip for such a small boat and maybe more prop than you should be able to turn...

That is something that I hadn't considered, waterlogged foam that is. My deck has some soft spots in it. I bought the boat back in May. I checked the engine mounts and they seem very solid, not even discolored. When my mech. had the engine out replacing the gimbal ring, he said the transom looked very solid with no signs of rot. I haven't drilled any core samples, but that will happen this fall. My plan is to enjoy the boating season this summer and early fall, then rip out the deck, replace stringers if needed, glass in a new deck and gel coat it and never even say the word carpet in that boats presence again. Anyway my point is that there may be a few hundred pounds of foam in the hull. My bilge is dry except when the kids are getting in and out and dripping all over the place, (another reason to get rid of the carpet) so I didn't really think about there being water in the foam. Can the foam hold water and not even drain with the boat tilted to the stern? That might be why Hwsiii's calculations weren't coming out right.