Outboard set-up question

[15hpevinrude]

Hi all, Just picked up my new 96 35HP Johnson for my 14 ft aluminum boat.

It is a long shaft, and my boat takes a short so I built this Jackplate

I know the anti-ventilation plate should be flush with the bottom of the boat. But which plate is it on this motor?

Is it the plate that bolts the bottom end on, or the plate immediately above the prop? Does the added Fin change how it should be set up hightwise?

Thanks

 

[steelespike]

Re: Outboard set-up question

The foil should not be in the water on plane,too much drag.It is on the antivent(cavitation) plate.
And the plate will need to be about an inch above the bottom of the boat.
It would be nice to try it without the foil and try to get the best setup to see if you can run without the foil.

 

[15hpevinrude]

Re: Outboard set-up question

Thanks, So the foil shouldn't be in the water on plane? If that should be about an inch out of the water, The water intake will be dangerously close to being uncovered

 

[Bob_VT]

Re: Outboard set-up question

Thanks, So the foil shouldn't be in the water on plane? If that should be about an inch out of the water, The water intake will be dangerously close to being uncovered

Nope The outboards all run with that plate skimming the water. Yes, your motor is still mounted a bit too low right now.

 

[15hpevinrude]

Re: Outboard set-up question

Thanks for the comments. These were my assumtions also, But I thought I would ask for other opinions, because the old owner worked at a marina and he gave me the measurements from the mounting surface to the anti cav. plate. I was making the Jackplate while his new motor was getting prepped to put on his boat. I didn't build enough adjustability into the plate for over 2 inches of travel.
The fin was on the motor, so I thought I would leave it to try it. My boat is a 14 foot aluminun with full floors, and front and rear casting decks, but it still should be lighter than the fibreglass boat this motor came off.
If I'm not mistaken, these foils are to help heavy boats get on a plane quicker, is this true?, are there any other reasons for using them

 

[steelespike]

Re: Outboard set-up question

The fin helps boats that are hard to get on plane.Not necessarily heavy.
My observation has been that as far as the correct prop goes many fiberglass hulls will be faster than similar sized aluminum boats though usually heavier.Sometimes hull shape determines hole shot as much as weight.If your foil is going to be underwater it will likely cause problems the least if which is loss of top speed. But give her a try;nothing ventured nothing gained.

 

[15hpevinrude]

Re: Outboard set-up question

Thanks for all the responses you guys gave me earlier. I raised the motor up some more as you guys suggested. I raised it approx 1 3/8", you can see the block of wood I added to the top of the Jackplate.

The motor sits a GOOD 1 1/2" to 2" above the bottom now. I added a piece of 1/4 rod along the bottom of the boat to illustrate where the motor is in relation to the bottom of the boat

I had the boat in the water all May 24 Weekend, and I find, If I am running on a plane 3/4 throttle or more, The motor will start to cavitate if I turn the wheel, even the slightest amount. If I am running in a straight line, it will hold its bite in the water, If the water is a little choppy It will cavitate running in a straight line. As far as the hydrofoil in the water, I think its probably just skimming the top of the water, I can't see for sure, because the white water spray coming off the bottom of the boat is so thick it completly covers where the foil is, But I can clearly see the upper plate where the bottom end bolts up, and I can see the waterline coming off the bottom of the boat is well below it. SO I am wondering if If I have gone too far, and should back it up a bit?. I tried many times to see conclusively where the foil sits in the water but there is just too much spray. Unfortunately I can't make height changes on the fly at the lake, I have to take it home and use my chain fall to raise and lower it. Any suggestions?
Thanks

 

[steelespike]

Re: Outboard set-up question

You got a little over excited.I suggested about an inch above.
But lower it about a 1/2" at a time to a point where venting is acceptable.

Depending on your stetup You might be able to do it without chain falls.
Block the trailer wheels and useing the trailler jack to raise and lower the tongue carefully rest the skeg on a block of wood and loosen the jack plate slightly, then raise or lower the tongue as needed to set the motor height.
There are props that help take advantage of the most height.

 

[15hpevinrude]

Re: Outboard set-up question

You got a little over excited.I suggested about an inch above.
But lower it about a 1/2" at a time to a point where venting is acceptable.

Thanks for the reply. I had also read somewhere that with a jackplate it might need to be upwards of 2 inches above the bottom, because of the motor being farther back into the water raising up from under the boat. And I had allready raised it up twice at that point, and didn't really want to do it again. BUT having said that, the hydrofoil could still be running under the water at the height it is now, I just can't see it through all the water spray. But I think I will lower it a bit because it is cavitating, unless there might be another cause?

 

[steelespike]

Re: Outboard set-up question

What you are experiencing is venting, cavitation is different and not usually felt.
The venting seemed a little touchy to me. Thats why I suggested a slight lowering.
A typical jackplate has 3 to 5" or more of setback I don't think yours is that much.
There are props that resist venting, Turning point hustler and rascal are two.
4blade props also do well as do many of the stainless props.
Before making a prop change you need to get setup so you can get a good max rpm and speed.

 

[PLP]

Re: Outboard set-up question

It is my understanding that the plate just above the prop should be level with the bottom of the boat if you are not running a stainless prop,and anywhere from 1/4" to 2" above the bottom if you are running a stainless prop.This has something to do with the fact that stainless props do not flex,and aluminum props do flex.It looks like you have an aluminum prop,and it also looked like your dowel that you measured with is at the bottom of the boat,but not on the same angle as the bottom of the boat..I'd say make sure your dowel is level with the entire boat,not just the edge..you will probably find you need to drop the motor some,especially if that is an aluminum prop....hope this helps..If I am mistaken I would love to hear different..

Also the hydrofoil can be an angel or a demon..There is a new design with wings that are angled upwards and are farther up out of the water on plane..The whole purpose of the hydrofoil is to help with planing off ,being able to maintain plane at lower speed,and stop hopping when the boat wants to jump b/c the front end is too light..Hydrofoils can kill you with drag,and cause a variety of issues..You dont always have to have them...Run the boat without it one time,and see if that makes a difference...Forgive me if I am explaining something you already know..Just trying to help..