Engine Height

[captmello]

my pontoon has them, if those are what he's talking about...
I agree the transom looks to high and too small for that motor. but from the description, a bad prop hub seems like the first thing to check.

 

[Faztbullet]

I suspect that the aluminum plate the red arrow and line next to it should be at the yellow line right arrow is pointing to. This will force the inner wake between toons to converge, and be directed downward adding to water flow to prop..

 

[ahicks]

That whole engine pod has a home made look about it, with more bolts than welds. Nothing wrong with that in my book. Thought being it might be possible to lower the transom without further modifying the rest of the engine pod or it's attachment points - other than to realign the bottom alum sheet so it lines up on the bottom of the transom (yellow line in faztbullet's diagram). -Al

 

[Brien S]

Lots of info. Thanks all. So what would be the best plan of action. I agree the pod looks very home made and rigged and small for that 115 engine. Prop is supposed to be new, and it looks like it is, other than the little stuff on the edges of the blades that happened the last time he and I were out. He got it a little to shallow in some mud, but anything is poss.
Am I correct in assuming that the top of the transom should really be no higher that the bottom of the floor framing? If I were to just change the pod, what do I need to be looking for, and what is the correct positioning it should be at on the boat ?

 

[Brien S]

First, sorry to hear of your loss.

Thanks

 

[HotTommy]

Do the easy thing first and that is check for prop slip. Your comment about shallow water makes that more likely. ... In case you don't know how it works, here's a picture:

Between the metal propeller and the engine shaft that drives it is a four-sided rubber sleeve (hub) with rounded corners. It is there protect the engine should the propeller hit something that tries to stop it. If that happens, the engine shaft and rubber sleeve will turn inside the propeller. Once that happens, the rounded corners will become more rounded and the prop will slip more easily under load. The diagnosis is to mark the prop and the hub/shaft and see if the marks lose alignment. The solution is to replace the rubber hub or possibly the whole prop. .... If your boat passes that test (i.e., it sounds like it is cavitating but the marks stay aligned) then you can address the much bigger job of the engine pod and transom.

One more thought: You can also test the prop by borrowing a good prop from someone else to see if the symptom goes away.

 

[ahicks]

I think you'll find, maybe after looking at a couple of pods, that the transom is generally about even with the top of the pod - which mounts under the floor. You don't see much variance from pod to pod. In any case, they'll be quite a bit lower than the one you have....

Are you the DIY sort of person, or would you hire this out? If you have the time, inclination, tools, and a place to work on it, this would not be a bad DIY project. A few more pics may draw some ideas on how what you have could be changed - or suggestions on why going with a used or commercially available pod might be a better plan. -Al

 

[skuhleman]

Check the prop for spun hub first. Guessing that's the problem.
Ours would cavitate pretty bad as well, took the prop in and had them add a bunch of cup to it and it helped a bunch. Then added a whale tale just cause we had one laying around. No cavitation problems now

 

[MillerIsland]

First, I can't imagine you have a slipping prop as all the interconnections are via clogged teeth gears or splined shafts. At first glance, it looks like the prop is much too low in the water. Look as the corrosion level - it is about 3" above the cavitation plate - but this could be proper at rest for your boat.

The difficulty with pontoons is that they plane differently (virtually not at all) than a standard V-hulled boat. With the V-hull, the boat planes on the water - if you look down the transom when at speed you will see a flat sheet of water coming out from under the bottom of your boat. That is why you match the shaft length of the outboard with the transom height: 15" transom height-short shaft motor, 20" transom-long shaft motor. The cavitation plate is just about even with the bottom of the boat - the top of the water coming out at speed.

Pontoons are different. the displaced water from the pontoon gives the pontoon it's flotation and little plane force is generated by speed. The only way to tell if you have the wrong shaft length (without the manufacturer's specs) is to get the boat up to speed and look at the cavitation plate. Where is it versus the surface of the water. Should be just about level with the top of the water.

 

[racerone]

MillerIsland.---Gears and clutch dog rarely cause this.---But.----The hub in the prop might be slipping.

 

[jlh3rd]

to the op...
are you still on here, and looking for opinions?