HELP!!! I built a transom riser....Is it SAFE???

[Whoopbass]

First off excuse my nasty looking transom. I'm going to clean it up and paint it one of these days.

What do you guys think?

I used a transom off an old inflatable boat as the riser. It's 1" thick and it has the metal bracket in the front and a 1/4" piece of wood in the back to spread out the stress of the outboard.

1978 Evinrude 25 hp but I have a carb from a 35 i'm going to put on it so it will be a 35hp motor (in theory).

It rises 7 1/2" above the transom. There is only 7" below the top of the transom. Is that enough??

I have four 3/8" X 4" long bolts holding it in. I don't care for how I have em spaced but I had to put them near the edge since the riser will be removed and a prop outboard put in its place (didn't want the bolt heads in the way of the clamp screws). Do I need a bolt or two in the middle?

Is the wood thick enough?
Does the jet look like its high enough or to low or about right? It hangs about 1/4" under the boat.

I want to make a run on the river tomorrow but i'm kinda nervous about this (tower of power).

 

[ondarvr]

Re: HELP!!! I built a transom riser....Is it SAFE???

You'll need to about triple the thickness of the wood and then use larger bolts.

The other thing is the shoe on the pump is mounted backwards.

In other words, don't take in near the water in the condition its in right now.

 

[Whoopbass]

Re: HELP!!! I built a transom riser....Is it SAFE???

When I got the outboard mounted the the 1" wood was looking pretty thin and I was having serious concerns about it.
You really think I need a 3" thick transom? I was going to redo it and go with 2" of plywood. After I installed everything I found a link here to make a jack plate that looks pretty easy to make and would work sweet for both of my outboards.

I was wondering what was going on with the foot since it wasn't looking right.
I guess the previous owner turned it around enabling the outboard to stand on the ground.

I guess I will be building a jack plate tomorrow. Sucks I drilled those holes.....

Thanks for the advice.

 

[5150abf]

Re: HELP!!! I built a transom riser....Is it SAFE???

I would say it would have snapped between the 1/4 and the top of the transom, ya ,that is a little thin.

You can try to put some weight on it, since you are replacing it anyhow it won't matter if you crack it so put a good bit of weight on the lower with your foot and see what it will take, the metal bracket is the wild card here.

Boats are kinda like airplanes, it is best to be a little redundant so overbuild everything to avoid failures and getting stranded.

Anyhow, I am sure you would rather rebuild it than watch your motor go swimming.

 

[marine4003]

Re: HELP!!! I built a transom riser....Is it SAFE???

Go to a welder shop and have them cut a piece of 1/4 aluminum same configuration as the plywood..bolt that to the plywood..cheap..40-60 bucks,cheap insurance.

 

[Ram58]

Re: HELP!!! I built a transom riser....Is it SAFE???

I would definitley add a piece of metal to the riser. I had an old boat one time that I question the condition of the transom and found a wrecked semi, the guy gave me the front bumper, I cut it out and added to the transom and ran it for a few years. All it cost was my labor.

 

[tashasdaddy]

Re: HELP!!! I built a transom riser....Is it SAFE???

2 pieces of 3/4 ply is all you need. but you need to continue further down the transom. and put some backing on the inside of the lower transom.

this is a 50 hp on my pontoon.

 

[tashasdaddy]

Re: HELP!!! I built a transom riser....Is it SAFE???

jack plate i designed.

 

[ondarvr]

Re: HELP!!! I built a transom riser....Is it SAFE???

What you're trying to do is common, the normal method here (NW, lots of jet boats) it to use plywood as a core with a piece of aluminum on each side. The aluminum drops down on the outside and inside of the existing transom and is bolted in place. This way you can spread the load over a larger area on the transom. Raising the transom up (at least the part the motor bolt too) that far will increase the leverage on it a great deal, so its also common to put some kind of additional support across the top of the old one.

TD your toon has the motor mounted lower, plus the lower bolts go through the old transom, so the stress would be far less. On this one the bottom of the transom bracket is several inches above the top of the old transom. It will need to be mounted lower when the shoe is mounted pointing forward though.

 

[ondarvr]

Re: HELP!!! I built a transom riser....Is it SAFE???

The other thing is how big is the boat (pics would be nice)? A pump will loose 30% + of the power it had as a prop, so performance drops a great deal.

 

[clarkbre]

Re: HELP!!! I built a transom riser....Is it SAFE???

I don't think I'd trust that transom riser. Being that it's just wood and it will go through some major stress I would overbuild it completly. I do have some experience with a riser. I have a 16' Lund with a 15" transom and a long shaft Suzuki 15hp motor. When I got the set up, the previous owner didn't have a riser at all. I designed a transom riser that raised the engine 6" so the cavitation plate is even with the bottom of the boat. Here's what I did:

For the 6" rise, I used (4) 1 1/2" square tubing that were 12" long each. The tubing was stacked and welded together and the 1 1/2" was the right width for my transom. To support the riser tubes to the transom, I used (2) 1/8" thick aluminum 12"x12" plates. One went on the insed of the boat and the other on the back. I had the plates weleded on to the tubing to help stiffen everything up. I then, slipped it onto the transom and drilled my holes. I used (4) 3/8" x 2" galvanized bolts and washers to mount the riser to the transom.

In the end, the riser has proved to be very strong and has helped the performance of the boat. More than anything though, you want to over-engineer it. PM me if you'd like my drawing of it.

 

[Whoopbass]

Re: HELP!!! I built a transom riser....Is it SAFE???

The boat is 15' aluminum Gregor. 35hp should be able to push it ok.

I pretty much knew when I installed the outboard the riser was not going to cut it. My cost was just some nuts and bolts so no biggie.

This is what i'm thinking about making since its adjustable.
http://www.dillon-racing.com/jackplate/index.htm

If I can't make it or you guys don't think it will work for my application then I am just going to go with the suggestions here and make up some type of heavy duty plywood and metal riser.

Thanks

 

[ddrieck]

Re: HELP!!! I built a transom riser....Is it SAFE???

I would suggest a CMC Jack Plate like the this one.

http://www.dhcampingandfishingsupply.com/55012.html

Darren

 

[ondarvr]

Re: HELP!!! I built a transom riser....Is it SAFE???

The bracket you linked will work fine, its done either way, a riser or jack plate, with a riser a little more common.

A 35/25 ( 35 prop, 25 jet) will be at the very low end of what may work, for example, a good friend has a 13' aluminum jet boat with a 60/40. another friend has a light 15' jon boat with 60/40 and I have a 15' aluminum jet boat with a 90/60 and none of these are over powered.

 

[Whoopbass]

Re: HELP!!! I built a transom riser....Is it SAFE???

That cmc jackplate is nice and priced fair. If I can't make one I will look into getting one of those.

ONDARVR- You seem pretty knowledgeable about jet propulsion. Is the ideal position for the foot dead even with the bottom of the transom? Is a 1/2" to low or high going to screw things up?
I like the idea of the jack plate since I can adjust it for optimal performance and then I can lower it back down when I switch to a prop. I think i'm going to have to custom make one since it appears i'm going to need around 8" of lift in order to get the foot even with the bottom of the boat.

I know the jet drive is going to be a slug compared to a prop but I mounted a 9.9 Johnson on it the other day and it pushed it a little over 17mph so i'm hoping to get atleast that speed. My 30hp Suzuki only pushes it 28 mph but it gets there in a hurry.

Thanks for help....

 

[ondarvr]

Re: HELP!!! I built a transom riser....Is it SAFE???

This link should answer most of your questions.

http://www.outboardjets.com/index.php