Transom Motor Height

[carbineone]

I have a question and have searched alot on here and still have a question.My Older 1974 Johnson 50HP says in the original owners manual the Cavitation plate should be even with the bottom keel.How much will the power and such suffer if its a inch below the keel?I would not think alot as I will have ample power with the 50HP on the little ten foot boat..Anyway if you have any opinions let me know.

 

[bob johnson]

Re: Transom Motor Height

you are right on track...

you will not reach top potential speed with the motor 1" below the hull

but it might only be 2 mph....!!!!!!!!!!!

if you are not worried about hitting bottom, going shallow or getting super top speed.

dont let it concern you...

enjoy

bob

 

[Vic.S]

Re: Transom Motor Height

Apologies if you have already seen this web page http://www.smalloutboards.com/shaft.htm but note toward the end it says, "Keep in mind that the cavitation plate should be flush with the bottom of the boat. You can get away with an inch or two either way but it is wise to keep it close."

It probably wont be difficult to raise your engine by an inch ( a spacer block on the transom top??) to compare the effects of it being "correct" or 1" deeper.

 

[F_R]

Re: Transom Motor Height

If you are happy with what you have, just leave it alone. However if you want to get the best possible speed out of it, you can raise it up. If we are talking about the little boat in your avatar, you probably can run the plate somewhat above the bottom. The usual procedure is to raise it up until you get excessive cavitation/ventilation, then drop it down till you can live with it.

The catch to all this is you have clampscrew type transom brackets on that motor. Not exactly freindly to experimentation. If you raise it without installing the safety bolts, you run the risk of losing the motor. As I said, if you are happy with it, leave it alone.

 

[carbineone]

Re: Transom Motor Height

Thanks very much to all of you..Problem is that its as high as I can possibly go with it and keep it bolted on correctly.Just wanted to verify if the 1 inch below would make much differance.Was doubtful it would and yes it is going on my little 10 Foot Invader in the avitar.I should have plenty of ooomph with fifty I would think and can put up with a little loss I am sure...It will surely outperform the 28HP I have on there in the avitar..Thanks Again

 

[Pokertrampp]

Re: Transom Motor Height

Problem is that its as high as I can possibly go with it and keep it bolted on correctly.

Have you thought about adding an outboard bracket similar to a jack plate only it is fixed. I think it is mostly used for adding a kicker motor to larger vessels but it served my purpose, I had the same problem and that was what I did, it worked perfectly.

This is a photo of the one I have installed on mine, as you can see there are many holes down the sides, so it is very adjustable, which makes setting the height easier. good luck, hope this helps.

 

[carbineone]

Re: Transom Motor Height

Actually I thought I may make a homemade Jacking mechanism that I have seen done on here by someone..Maybe see how it runs an inch below before doing anything else...Thanks for the idea though..What do they cost made like yours? Thanks

 

[TRBenj]

Re: Transom Motor Height

Have you thought about adding an outboard bracket similar to a jack plate only it is fixed. I think it is mostly used for adding a kicker motor to larger vessels but it served my purpose, I had the same problem and that was what I did, it worked perfectly.

This is a photo of the one I have installed on mine, as you can see there are many holes down the sides, so it is very adjustable, which makes setting the height easier. good luck, hope this helps.

Judging by the pic, Im guessing you bought the T-H Mini Jacker available here in the iboats store?

T-H Mini Jacker

 

[carbineone]

Re: Transom Motor Height

This is as far as I dared to go for now and made a homemade plate.Going to give it a test run later this week and see how it acts and go from there.Heres a few pics of what I did...Thanks

 

[bob johnson]

Re: Transom Motor Height

the hieght looks good..

i am wondering what the transom mount looked like bfore your plate assembly went on!!

what do you have inside the hull under the splashwell that holds the bolts for the aluminum transom plate you added??? straps? big washers? another plate?

if you hit something with the LU, will it snap that extension off??

you need a lot of continuity down into the boats transom..

i am guessing you ditched the adjustable jack plate idea, right?

bob

 

[carbineone]

Re: Transom Motor Height

Yes ditched the plate idea as we just cannot afford one right now.Maybe in the future but for now this only cost me a few dollars to do as I had most of the stuff here and it really looks OK as far as asthetics too...As far as under the splashwell it just has big stainless washers on the inside.The original transon thats there is rock solid and very well made and designed.It was after all designed to take a 55HP motor rating and have seen some with 60s on them.The part I added is as solid as hitting a rock with your fist,I will update this and let you know how it went..New rotary steering system came today so it will get installed today and we will try it out this weekend..Wish us luck,LOL Thanks

 

[71Windsor]

Re: Transom Motor Height

Im an inch below. No problems. Stick with what you have if it works and your ok with it.