Outboard to high or to low?

[misfit171]

I bought an older pontoon with a 115 evinrude. 1978 . I sent it back to the fella I bought it from for repairs . It came back without the original prop. With the original prop the boat hauled butt. And ran great. I bought a 4 blade 13 3/4 with 13 pitch prop for it and put a whale tail on it and it won't get up and go. It runs fine and will go ok at low rpms but when you give her more throttle it just doing a cavitation thing???? The motor was taking off and put back on but I'm sure it was in the same place I don't have electric tilt and trim and can't find a spot where it doesn't do this. I'm wondering if the motor needs to be lowered ? In order to do that I'll have to lower the entire rear plate? Or is it to low ? Any info is helpful

 

[MinUph]

Re: Outboard to high or to low?

When you brought the boat back to the seller what exactly did he do to it and why didn't you get your prop back?

 

[alldodge]

Re: Outboard to high or to low?

I bought an older pontoon with a 115 evinrude. 1978 . I sent it back to the fella I bought it from for repairs . It came back without the original prop. With the original prop the boat hauled butt. And ran great. I bought a 4 blade 13 3/4 with 13 pitch prop for it and put a whale tail on it and it won't get up and go. It runs fine and will go ok at low rpms but when you give her more throttle it just doing a cavitation thing???? The motor was taking off and put back on but I'm sure it was in the same place I don't have electric tilt and trim and can't find a spot where it doesn't do this. I'm wondering if the motor needs to be lowered ? In order to do that I'll have to lower the entire rear plate? Or is it to low ? Any info is helpful

Correct me if I misunderstand but what I take from your posting is:
It use to run great with the old prop.
You had some repairs done and it came back with a different prop
Put a 4 bladed 13 3/4 x 13 prop, a whale tail and it runs bad
Only reason to change prop is it was not running good and the motor cavited

Why did you have work done to the motor?
What was the original prop size and pitch?
If the motor was cavitating, the prop is coming out of the water. So the motor is not down low enough. If the motor is not low enough, the mounting has been raised, the tile is changed and is higher or the lower tail shaft has been changed to a shorter one.

A pontoon sits fairly high on the water (shallow draft) and therefore I don't see a whale tail helping at all. I have a tail on my runabout and like them but they would provide little if any help for a pontoon.

A 4-blade prop has more drag then a 3-blade prop. A 4-blade prop produces more lift then a 3-blade so not having enough power to lift the pontoon out of the water as a bass boat would, your hurting yourself.

 

[misfit171]

Re: Outboard to high or to low?

It went back to the seller cause the pinion gear tore up in the lower unit. When I went to get it the prop was gone. We looked around but couldn't find it . He did find one for the motor a SS prop that was pitched pretty high. The original prop was aluminum and had a much lower pitch. I have no idea the size. Before the lower unit went out the boat was coming up on plane and would run in the 35 mph range it never cavitatef or anything like it. So basically I tried the SS prop and it would cavitate every time I got near 3/4 rpms. Read somewhere that the 4 blade lower pitch prop would help not hinder. The whale tail was a shot in the dark. Didn't think about lift . When running at the highest rpms I can before cavitation issues the water is going crazy back there. It rolls up under the deck on each side of the motor and just doesn't seem right?

 

[MaPaHa]

Re: Outboard to high or to low?

The water going crazy back there sounds typical to me. Unless you saw it before and know that it didn't do it then, I would say it's normal for a pontoon. There are many threads on under-skinning as the water normally hits the underside of the cross joists and the skinning deflects it and keeps it flowing back but its common to see a wall of water headed towards the motor. (The under-skinning is worth it if you don?t have it now).

It could be the old prop was a big ear style prop designed for pontoons and your new one is more of a standard design. Pontoons are famous for props loosing bite because of the rough water coming from the toons to the middle and that?s why they typically use a special prop. Getting the prop slippage down to a normal range can sometime be a bear. I ran a 140 Evinrude of the same vintage as yours for several years and fooled around with props to find the right one. Personally I like the 4 blade props and that's what I landed on as the final prop but I think mine was a 13 pitch modified up a degree because the 13 over revved just a bit. The prop shop I bought it from did that for a small fee.

Do some turns with it running below the blow-out speed and see if the prop comes out of the water. If so, I would lower the motor a notch if you can. If it?s all the way down and there's no way to go further, then I would see if you could borrow a prop from a shop to find the right one. Yours might can be be re-pitched once you find something that runs good. There are a ton of different prop designs for the 3 and 4 blade props and I'm really wondering if you have the right one for a pontoon. I don?t think the fin is hurting anything but you could always try it with and without. I have run them on about every boat I?ve owned in the last 30 years and they generally help.

The motor I have now is a 150 with a larger hub than my old one (and yours). The prop they recommended was a 4 blade, large ear ocean type prop and it works great.

By the way, I assume your pontoon is a twin toon and not a tripple toon?? Does your pontoon have strakes on it? 35 mph sounds very impressive for an older 115 hp motor (rated at the engine) on a standard twin toon.

 

[misfit171]

Re: Outboard to high or to low?

I'm going to look into the prop situation further. It is a twin toon. I was pleasantly surprised at how fast it was . I mean it would blow your hat off. It is a relatively light boat. No long seats just a couple In the back from the console to the front there's four pedastal seats and trolling motor. I think I'm going to try to lower the motor and see how that works before I try anything further. Very frustrating

 

[alldodge]

Re: Outboard to high or to low?

I'm going to look into the prop situation further. It is a twin toon. I was pleasantly surprised at how fast it was . I mean it would blow your hat off. It is a relatively light boat. No long seats just a couple In the back from the console to the front there's four pedastal seats and trolling motor. I think I'm going to try to lower the motor and see how that works before I try anything further. Very frustrating

Sounds like your motor is not low enough and lowering it is a very good plan. Hope the seller didn't install a shorter outdrive and you cannot get it low enough without a transom redo

 

[misfit171]

Re: Outboard to high or to low?

Thanks for all the responses Im going to lower it and see what happens I'll keep you posted.

 

[Mi duckdown]

Re: Outboard to high or to low?

get rid of the whaletail

 

[steelespike]

Re: Outboard to high or to low?

Yes, get rid of the whale tail before lowering.
You should always make one change at a time and test.

 

[suneshop]

Re: Outboard to high or to low?

This may sound crazy and could be dangerous but the factory reps that were troubleshooting my tritoon laid down on the front and watched the water flow under the deck at speed. I am having the same problem,the motor might be to high, mine also ventilates.We decided to lower the motor but it was in the lowest possible position. Bought a 5" extension then raised the motor to center set of holes essentially lowering the prop 3.5" Don't know if it did anything,have to wait till spring.
I also did try a Vensura SS 4 blade 17" .Did not do as well as the Enertia 17"SS more ventilation less speed.

 

[BrianMc]

Re: Outboard to high or to low?

I run a 3 blade Enertia,but picked up a 4 blade OFX4 as a backup prop for my tritoon/150 with a hydr. jackplate. I have to drop the motor 2 1/2"-3" to run the 4 blade. It's still not low enough as I can set off the temp alarm if I try to trim it all the way out. I'll have to drop the motor on the jackplate to go down any further. 4 blades are know as stern lifters. Hard to believe it's lifting my big butt that high,but it is.

Had to try one because a fella just gots to know. Overall I really didn't like it as much. 2-3 mph slower,and because it won't raise the bow as high it rides a lil rougher in chop.