Help - performance ?

[muskiemike12]

I have some questions. I asked in the prop forum, but didn't get a good answer. I have a 20' Lowe sf214. 90 hp 1979 merc I-6. I can run by my self and I get 18 mph @ 5000 rpm, very high prop slip. I figured around 48%. I can pull 2 tubers with 4 other people in the barge and I get 18 mph @ 4600 RPMs.
The motor feels better when it's pulling the tube and does not slip as bad.
I have a 4 blade 13 1/2 x 13 pitch. Is there anything that would help my performance with a light load other than adding under skinning or a 3rd tube?

 

[crb478]

Re: Help - performance ?

Where is your motor mounted? can you lower it? Sounds like you get a better bite when the pontoons are pulled down into the water more. Your prop is in the ballpark and I am a fan of four bladed props on pontoons.

 

[muskiemike12]

Re: Help - performance ?

It's mounted as low as it can go. When I look at the motor when it is running full speed the ventilation plate is about even with the surface of the water. It sits about 1" below the bottom of the motor pod.

 

[Old Screwball]

Re: Help - performance ?

I've got an 18' party barge with a 75hp Merc 4 stroke. I can get 22 mph (GPS) using an 13.75 X 13 3 blade. I've ordered a 13.75 X 17 aluminum and already have a 13.5 X 15 stainless (old Boat). Having it re-hubbed, it is from a Force. Hopefully they will arrive today or tomorrow and I'll take them to the river and give them a try. I'll let the forum know.

 

[muskiemike12]

Re: Help - performance ?

I should also mention that with a light load I can get 16 mph @ 3600 RPMs. Once I push it up to 4000 RPMs it just slips crazy. Has anyone else experienced this?

 

[Rancherlee]

Re: Help - performance ?

Sound like you need MORE blade area and LESS pitch. 16mph is probibly the point where the wake between the tubes grows big enough to start pushing up on your transom pod and forcing the bow down, at which point the prop is forced closer to the surface and the water is getting aerated from all the "Violence" happening under the pontoon.

Fixes:
Prop with "big ears"
Hydrofoil, one of the few applications I'd recommend trying one.
Smooth the water flow with under skinning and re route dangling cables and wires.

 

[MH Hawker]

Re: Help - performance ?

I may be way off on this ,but it is my understanding that while a 4 blade prop will give you a lot better hole shot with a load on the boat it dose lose a lot of performance on top end on a pontoon boat.

 

[muskiemike12]

Re: Help - performance ?

I can try the hydrofoil, I already have one. If I go to a 3 blade with big ears should I stay with a 13 pitch or go to a 11? I'm afraid a 11 would put me over the recommended RPMs.

 

[Rancherlee]

Re: Help - performance ?

I can try the hydrofoil, I already have one. If I go to a 3 blade with big ears should I stay with a 13 pitch or go to a 11? I'm afraid a 11 would put me over the recommended RPMs.

I'd try the hyrdofoil first and post back your results. If you can feel it start to slip at 4000rpm I'm willing to bet though that big ear 13 pitch will probably end up being too big. With 75-80hp (prop rated) and a 2.0 gear ratio a 13 pitch prop is more suited to a toon that could run ~22-25mph which your might if you can get it to bite.

 

[muskiemike12]

Re: Help - performance ?

Well I found out that the hydrofoil that is still in the un-opened packaging in the boat house is at least 12 years old. I think I'll buy a new one. Looking at the Sting Ray XRIII. It has a very wide body and looks like it would do the best in keeping my prop in "calmer" water.

 

[muskiemike12]

Re: Help - performance ?

I was at Cabela's yesterday and they had a new out of the box 14 x 13 pontoon prop hanging on a peg. $82 out the door, so i have some serious testing to do next time I make it to the cabin.

 

[Old Screwball]

Re: Help - performance ?

I've got an 18' party barge with a 75hp Merc 4 stroke. I can get 22 mph (GPS) using an 13.75 X 13 3 blade. I've ordered a 13.75 X 17 aluminum and already have a 13.5 X 15 stainless (old Boat). Having it re-hubbed, it is from a Force. Hopefully they will arrive today or tomorrow and I'll take them to the river and give them a try. I'll let the forum know.

UPDATE UPDATE UPDATE

Put the 13.5 X 15 stainless on thinking it would run great.... WRONG. Terrible slippage at anything over 4500 rpm. Best speed was 19 mph (GPS) Really guesses wrong on this one. Put the 13.5 X 17 Aluminum on, worked great, no slippage at all. Runs 22mph. DRAWBACK, can only get 4300 rpm at WOT. Guess that is good, will get better gas mileage, but I don't really care about that. Thinking I'll take the original 13.5 X 13 to the Prop Dr. and get it re-pitched to a 13.5 X 15. That should give me about 400 rpm and another mile an hour or two. In the mean time, using the hell out of the 'toon. Great platform for river running!

Granddaughter 'Pirate' Charlotte plundering the Colorado River at Blackies Cove.

 

[MH Hawker]

Re: Help - performance ?

Sadly pontoons are in a class all of their own when it comes to props, Hands you a cold one.

 

[muskiemike12]

Re: Help - performance ?

Well I finally got to test out the new prop over the holiday weekend. I was suprised to say the least. My top speed was 23 mph @4700 rpm's. Not sure why the rpm's dropped going to a 3 blade from a 4, but it could be because the prop is grabbing the water better. The prop is a Mercury Black Max 14 x 13, Im sure it is the prop they put on the 60hp Bigfoot motor. The Solus Rubex hub works perfect in it. Over all I am satisfied with the new prop. Looks like I'll save the 4 blade for pulling tubes.

 

[Bamaman1]

Re: Help - performance ?

We seldom see pontoons performing to their potential with 4 bladed props. They're really designed for bass boat owners that want maximum acceleration. They'll always cut back on maximum mph, however.

Your Black Max is a good prop for your usage. It should do just about anything you want to do.

 

[Bamaman1]

Re: Help - performance ?

We seldom see pontoons performing to their potential with 4 bladed props. They're really designed for bass boat owners that want maximum acceleration. They'll always cut back on maximum mph, however.

Your Black Max is a good prop for your usage. It should do just about anything you want to do.