Prop Fiasco - Just can't seem to find the right one.

[WaterDR]

Have a pontoon with a Yam F115. 2012. Toon came with a Yam alum 15P. Runs to aboput 6,100 rpms lightly loaded and 5500 with 10 people plus 3 on a tube. Thats about the heaviest load I see. 28 mph with a light load. Boat is nearly 26ft actual length.

The alum prop does not grab that great, so I tried a nice 13P stainless. Grabbed great! Pulls hard and great for around the dock. Lost 2 mph and rpms run too high regardless of how many people I seem to have on it, though never got a chance to test a real heavy load.

So, I tried a 15P stainless....could not get it over 5,000 rpms with three people, so I put the 15P alum back on.

Prop shop wants to cup and re-pitch the 13P. At this point I told them to go for it. Not really any other options. Hoping they can slow it down a bit and grab a bit more water.

Any other ideas?

 

[Bamaman1]

Re: Prop Fiasco - Just can't seem to find the right one.

I'm not sure what you're wanting. When you put the 15 aluminum on the boat, you get optimum speed for your hull and engine. But you cannot be expected to get the same performance with 10 people pulling 3 on a tube. You're doing well to get 5500 rpm's under those conditions--especially with 115 hp.

With heavy loads, the front end drops (from weight) and the rear end rises--thus bringing out the propeller ventilation. You might overcome some of this by shifting weight, but it's hard to ask 10 people to move to the rear of the boat (to get more prop in the water.) I too have experienced this on my last pontoon boat.

Prop shops can sometimes make adjustments to keep the water on the prop longer. See if their expertise is right.

The only other alternative is to put a $1K hydraulic jack plate on the boat to get the prop lower when you load the neighborhood on your boat. And sometimes two props are needed--one for light loads and one for heavy loads and water sports.

 

[WaterDR]

Re: Prop Fiasco - Just can't seem to find the right one.

Fair question....I got sucked-in by a prop shop at a boat show

So, either way, I am now stuck with a stainless prop....either a 13P that would prob work great for tubing and heavy loads, or a 15P that won't work for ****. If they can cup it a bit, it might make it more useful across a wider range of use.

What is sucky about the alum prop, is it cavitates a lot....the 13P stainless, just seems to grab and go.

Prop swaps is simple enough for me. Takes 3 mins while pulled up on beach. Might be the best solution.

 

[MaPaHa]

Re: Prop Fiasco - Just can't seem to find the right one.

The 15 alum probably has some flex and slippage that the 15 SST does not have, therefore the rpm drop. I've been in between sizes more than once. Before I added my center toon I had the right 4 blade prop that I bought new and after the toon it was too small of a pitch and over revved. They (Power Tech) did exactly what your shop is saying do. They re-pitched up it as much as they could about an inch and added cupping. That worked out great and hit it just right.

I've got a 17 foot F/S with an older 140 Evinrude that I'm messing with now where a 15 SST over rev's (6,000+) and a 19 SST lugs a bit (5,000 rpm) with two full grown adults and 5,200 with just me. A 17 would probably be about right to a little low but the local shops don't have one and I'm not going high end on this boat because it's for sale or I would order a nice one from PT. I found a clean 18 SST today locally that has exhaust ports in it and he's going to put a new hub in that fits my motor. It should put me where I need to be for this boat, hopefully around 5,300 - 5,500. I don't know what the future owner would want so I'm setting it up "universal" if there is such a thing.

 

[WaterDR]

Re: Prop Fiasco - Just can't seem to find the right one.

BTW, I too am working with Power Tech.

I did suspect the alum is flexing....just surprized it did so much. I anticipated a 400 rpm drop....not 1100. Someone suggested to me that the Yams can be more finnicky with being impacted by rpm drop especially if the motor can;t get into the power band. Makes sense....but never heard anyone talking about that here.

 

[Sea Rider]

Re: Prop Fiasco - Just can't seem to find the right one.

You can't have just one prop that performs as a multi task, will need one for light to medium load and one extra for heavy loads. Is your engine correctly height seated ?

Happy Boating.

 

[QC]

Re: Prop Fiasco - Just can't seem to find the right one.

You can have a crappy Aluminum vs a good SS and get that kind of RPM drop. Different type, different material all bets are off. One of your notes mentions cupping the 13 (maybe good) and one mentions cupping the 15 (bad). And your grabbing comment . . . I think you mean that it accelerated better, that's what you would expect when dropping pitch. Unless there is something else you're trying to describe.

You could try props for a year, 50 of them, and each one will behave slightly differently.

 

[WaterDR]

Re: Prop Fiasco - Just can't seem to find the right one.

No...we are cupping the 13.

As to Aluminum vs stainless, the 1200 rpm drop was not even predicted by the prop company. No explaination, just shrugs. My alum is a standard Yamaha Alum. Nothing fancy and nothing cheap either.

As to the height, I have no idea if it is correct or not. It was delivered to me that way from the dealer who sells hundreds.