'75 Evinrude 115 Prop Recommendations...Porpoising

[ksubigbuck]

Hey all, I have a '89 Stratos 266FS with a '75 'Rude 115 that is porpoising badly. I'm sure I'm running the wrong prop or something, its the prop the previous owner was using. Cav plate is even with the pad and the only way to get the porpoising to stop is to trim the motor all the way in, which greatly reduces top speed. Would a 4 blade prop help this? I should also mentioned I have moved as much weight foward as I can, including 2 trolling motor batteries to the bow.

Thanks for the help.

 

[Bondo]

Re: '75 Evinrude 115 Prop Recommendations...Porpoising

Hey all, I have a '89 Stratos 266FS with a '75 'Rude 115 that is porpoising badly. I'm sure I'm running the wrong prop or something, its the prop the previous owner was using. Cav plate is even with the pad and the only way to get the porpoising to stop is to trim the motor all the way in, which greatly reduces top speed. Would a 4 blade prop help this? I should also mentioned I have moved as much weight foward as I can, including 2 trolling motor batteries to the bow.

Thanks for the help.

Ayuh,.... Check the bottom of the hull for straightness,...

The last 4' to 6' should be Straight,...

Sounds like you've got a Rocker situation goin' on,...

 

[ksubigbuck]

Re: '75 Evinrude 115 Prop Recommendations...Porpoising

Ayuh,.... Check the bottom of the hull for straightness,...

The last 4' to 6' should be Straight,...

Sounds like you've got a Rocker situation goin' on,...

Thanks for the reply. Bottom is straight, that was the first thing I thought of, too. I have been told that this boat carries most of it's weight in the stern because it is much wider at the stern than it is at the bow. Not sure if I need a prop with more bow lift or stern lift??? It is a padded hull.

 

[ksubigbuck]

Re: '75 Evinrude 115 Prop Recommendations...Porpoising

Anyone have any other ideas?

 

[jestor68]

Re: '75 Evinrude 115 Prop Recommendations...Porpoising

Describe your set up in terms of the prop shaft to pad measurement. It doesn't have anything to do with where the AV plate sits.

With the boat/trailer on a level surface, measure the distance from pad to ground. Then measure distance from prop shaft center line to the ground. You want the prop shaft to be about 3-3.5" below the pad to start.

If the motor is mounted on a jack plate, it makes it easier to adjust the height. If the motor is not mounted at the correct height, it can cause abnormal handling.

What brand/type of prop are you running?

 

[ksubigbuck]

Re: '75 Evinrude 115 Prop Recommendations...Porpoising

Describe your set up in terms of the prop shaft to pad measurement. It doesn't have anything to do with where the AV plate sits.

With the boat/trailer on a level surface, measure the distance from pad to ground. Then measure distance from prop shaft center line to the ground. You want the prop shaft to be about 3-3.5" below the pad to start.

If the motor is mounted on a jack plate, it makes it easier to adjust the height. If the motor is not mounted at the correct height, it can cause abnormal handling.

What brand/type of prop are you running?

I will measure when I get home in 3 hours.

 

[ksubigbuck]

Re: '75 Evinrude 115 Prop Recommendations...Porpoising

Well it appears to be about 7" below the pad, but I can only go up one more hole on the motor mount...which looks to be about 1". Maybe I need a jack plate? The prop is an aluminum 13 1/4 X 17.

 

[WillSDQ]

Re: '75 Evinrude 115 Prop Recommendations...Porpoising

I too was having performance problems with a 3 blade prop. I was having problems with kick out on turns and also porpoising when the motor was trim all the way up. I changed my prop to a Solas Amita 4 blade. No more problem with kick out and no more problem with porpoising. Now my set up is different from yours. I have a 16 foot bass boat with a 75 hp. So I recommend the Amita 4 as you can buy a new one for about $110. It is an aluminum prop. If you don't like it, it won't be the end of the world. Top end speed will suffer a little, but if you're not racing for pink slips, who cares? I like my 4 blade so much that I am now thinking about buying a 4 blade stainless.

 

[jestor68]

Re: '75 Evinrude 115 Prop Recommendations...Porpoising

Well it appears to be about 7" below the pad, but I can only go up one more hole on the motor mount...which looks to be about 1". Maybe I need a jack plate? The prop is an aluminum 13 1/4 X 17.

Wow. I've never seen a Stratos come out with 7" before; even with the engine mounted directly on the transom.

Do you have a 25" motor or something?

Are you certain that you measured from the lowest point of the hull? (Not the bottom of the transom.)

 

[ksubigbuck]

Re: '75 Evinrude 115 Prop Recommendations...Porpoising

Wow. I've never seen a Stratos come out with 7" before; even with the engine mounted directly on the transom.

Do you have a 25" motor or something?

Are you certain that you measured from the lowest point of the hull? (Not the bottom of the transom.)

Yes. Measured from the bottom of the pad. Motor is a short shaft, so I'm not sure what the deal is. I found a CMC jack plate locally, so I will install it and see what happens.

 

[Mi duckdown]

Re: '75 Evinrude 115 Prop Recommendations...Porpoising

How about Pics of you set up? One picture is worth a thousand words.