Need help with prop selection (Newbie)

[MindTheGap]

Afternoon all,
I'm new here and just recently bought a 2007 Sweetwater 2386 (23') with a Yamaha 115 4 stroke. Boat is in reasonably good shape and like all other things I take on, I'm already looking for ways to polish her up a bit. As far as the motor goes, when I increase throttle, she does well up to around 3700 RPM and then starts to blow out a bit. Cavitation plate appears to be just below waterline when underway with motor trimmed all the way down. If I trim it up more than a hair, the blow out gets worse and I have to throttle back. From reading on here, I've determined that this can be a multitude of things ranging from ventilation, cavitation, or prop slippage. When I go out tomorrow, I will mark the prop and hub to see if the line shifts during the day. Regardless of this, I believe the prop is in need of replacement soon as it is rather worn. It is a 3 blade aluminum prop and I'm not certain of the size and pitch but will check tomorrow. Max RPM I have gotten her to was 4200 with only 2 people on board and we achieved 23 MPH (GPS). She's quite a bit sluggish with more people on board and consistently blows out with more people. I run in saltwater (West Palm Beach, FL) so I plan on getting a SS prop. Additionally, I believe going with a 4 blade is also a good idea. Other than that, I've read the prop selection guide but am still at somewhat of a loss in what size and pitch I should get for my set up (23' pontoon and Yamaha 115). I'm not trying to build a "race" boat, just would like to get the best performance out of my motor. Obviously, there are far more nuances that come into play so I figured asking some of you with far more experience for a hand. Any help would be appreciated.
BTW, would adding a hydrofoil benefit performance or limit blowout at all? Would you recommend?

 

[MH Hawker]

Dropping the motor lower will stop it

 

[1983 ercoa 21']

Every boat seems to be a little different but I do know the more motor that's in the water the more drag you have. Find a local prop shop most will hold your cc and send you down to the lake with a few options to try out . Cupping is very important on pontoons. Good luck

 

[ahicks]

I agree that cupping helps delay the onset of cavitation/ventilating. I would suggest you get your prop "refurbished", and while at it, see if they'll add a little extra cupping? If the shop just gives you a blank look regarding that request, try another. The results should give you some useful data you can use to pick out the next prop.

 

[MH Hawker]

With pontoon boats due to the turbulence under the motor pod it is common for a prop to slip. Dropping the motor lower gets it in clean water and untill you can get it where it runs correctly with out slipping your wasting your time and money playing with props. One it is hooking up then you can find the prop that puts you in the right WOT range, then raise the motor till it suits you.

 

[1983 ercoa 21']

The prop is a vital part of any boat without it your going nowhere.a good prop shop will have test props to send you to the water with for testing as to what works best for your application therefore you are only spending money on the one that works for you. Just remember when testing the props and choosing the one for the best results to allow for normal load example testing will probably be done with one person on the boat and normal weekend will have 3 to 6 people which is more weight in return requires less pitch . Example 15 pitch works great on my boat with me and my son but get all my fishing gear and a buddy or two 13 pitch is not he best therefore I run the 13 all the time and watch my rpm when loaded lightly so not to over rev . I also noticed alot of fuel savings with the correct prop. And yes I had problems blowing out the prop till cupping was added now the only way to blow it out is to trim it out. My motor is also mounted high like in third hole .

 

[1983 ercoa 21']

The prop is a vital part of any boat without it your going nowhere.a good prop shop will have test props to send you to the water with for testing as to what works best for your application therefore you are only spending money on the one that works for you. Just remember when testing the props and choosing the one for the best results to allow for normal load example testing will probably be done with one person on the boat and normal weekend will have 3 to 6 people which is more weight in return requires less pitch . Example 15 pitch works great on my boat with me and my son but get all my fishing gear and a buddy or two 13 pitch is not he best therefore I run the 13 all the time and watch my rpm when loaded lightly so not to over rev . I also noticed alot of fuel savings with the correct prop. And yes I had problems blowing out the prop till cupping was added now the only way to blow it out is to trim it out. My motor is also mounted high like in third hole .

 

[MindTheGap]

Okay, I was unable to take the boat out today due to torrential rain damn near the whole day. I did go take a look at it and the motor is set as low as it can get on the transom so lowering any further is not a very reasonable option. I did speak with a boat mechanic and he said that if the cavitation plate was just below the surface when running, then it was at the right height. I'll try to run her again tomorrow and mark the prop and hub to determine if there is any slippage at all. I also plan on speaking with the local prop guy and let him know what my set up is and see if he has a better recommendation. I'll also check what the diameter and pitch is tomorrow when I take her out to clean the hulls. I appreciate all the responses.

Dave

 

[MaPaHa]

A 4-blade will help but the right 4-blade will really help. The 4-blade family of props are very diverse and your application is different from say a high powered bass boat or a heavy bow runner looking for hole shot. If you want to get an idea of what I'm saying look at the Power Tech website and there's 10 or so 4-blade props on the home page with different blade designs.

I'm running a 4-blade Power Tech Off-Shore series on a 22 foot tri-toon with a 150 Johnson and it holds it's bite well. It has what some will call "big ears" for blades. It has a great hole shot and good lift and mid range performance. They will help you select the right prop and you can buy it at any of their dealers.

I don't think buying a 4-blade just to have a 4-blade is the right approach. Choosing the right 4-blade for your boat and performance goals is I think the right way to go. I've bought several Power Tech props for different boat-motor configurations and the folks there are very helpful in spec'ing a prop.

 

[craigmack]

I run an Eneritia prop and it has never lost bite whereas my Black Max w/ extra cupping has in tight turns or rough water. Being a SS prop it's not cheap but I truly believe it one of the best props out there.

 

[WaterDR]

You will likely need a SS around 12 pitch with that set-up (for a 3 blade). Thats my guess. Adding cup will lower rpms. Many toon props I think are already cupped.

 

[MindTheGap]

Well after taking her out yesterday to scrub the logs, I noticed that the cavitation/ventilation plate sits about 2 inches above the bottom of the transom and the motor can be lowered down another hole. Additionally, the prop had the code L-19 stamped on it. Not sure what the L is for, but I'm assuming the 19 is the pitch. Looks like I have a couple things to test out; lower motor, and try a 4 blade prop with lower pitch…….17 maybe?

 

[MH Hawker]

That is way to high pitch. the common pitches for a pontoon is a 13,11,9 or a 7, I would suggest a 11 for that HP motor. That high of a pitch is more than likely why its blowing out, way to much thrust

 

[BrianMc]

Mr Hawker is right on dropping the motor,and the 11 pitch 3 blade would be close with your 2.15/1 gear ratio barely getting you in the operating range of 5300-6300 rpm. That's allowing 15% slip. In a 4 blade you'll need more like a 10 pitch,which Power Tech can do for you. The high pitch ratio would actually give you a lower thrust because your motor doesn't have the power to spin it. The reason it's blowing out so bad is probably the motor height,and the fact your trimming too high to bring your rpms up.

 

[steelespike]

If its a 19" pitch that alone could cause ventilation problems. Typical props for the 115 13" pontoon performance series and 15" al prop.