Tahatsu 8 Hp 1993 2 Stroke Shaft Lenght Adjustment

[davio47]

I have a short shaft Tohatsu outboard on my small aluminum boat. I love the Tohatsu and I want to keep it. However, the shaft is a bit to long for the transom. At WOT water splashes back into the boat around the motor shaft. Is there a way to correct this distance or do I need to get a boat with a higher transom? What can I do to make it right? Thanks

 

[Lion hunter]

Re: Tahatsu 8 Hp 1993 2 Stroke Shaft Lenght Adjustment

They don't get any shorter than a short shaft. Where is the cavitation plate in relation to keel? Should be even give or take an inch or two. Have you tired to trim out?

My older 12' tinny is modified V with a very flat keel. The transom also drops down. I have tried alot of motors at every trim hole and water still comes over the transom if I don't have enough bow weight. Just the nature of the beast on some designs.

 

[davio47]

Re: Tahatsu 8 Hp 1993 2 Stroke Shaft Lenght Adjustment

The cavitation plate is below the keel by 2" and 2.5" below the hull. I have tried adjusting the trim at all settings. Some trim settings are just impossible anyway. Would putting larger cavitation plates make any difference? I have some plates that came with the motor. I want to try them, I took them off when I got the motor. It was used for a Dingy and they were needed for getting up on plane quickly. Interested in your thoughts on this. Thanks

 

[Lion hunter]

Re: Tahatsu 8 Hp 1993 2 Stroke Shaft Lenght Adjustment

The cavitation plate shouldn't be removable (made into the motor). The plate you may have are Doelfins or some other type. You can raise the transom a couple inches fairly easy. Find a way to put a 2" block and affix it to the top of the transom. I have seen wood block s used and also 2" square tube with flat iron welded to form a saddle that slips over the transom and gets bolted down. A pic of your transom would help.

 

[davio47]

Re: Tahatsu 8 Hp 1993 2 Stroke Shaft Lenght Adjustment

That is exactly what I would need to bring up the motor 2 or so inches. A transom elevator is what I really need, however they are quite expensive. $175 or so for the elevator, to much considering the boat is only worth $400. I do not think that a wooden bracket would a good solution from a structural standpoint. Here are some pictures of what I have. Let me know what you think. Thanks.

 

[Lion hunter]

Re: Tahatsu 8 Hp 1993 2 Stroke Shaft Lenght Adjustment

Measure from the upper inside of the transom bracket (where the motor goes over the transom) to the cavitation plate that is right above the prop.

In any event here is what I would do. Measure the width of your transom now. It looks like there is a 1/2" of wood on either side now.

1. Cut 2 pieces of plywood 1 at about 1.5'x3' and 1 at the depth of the inside of the transom + however many inches you need to raise it (looks to be about 6" now so a peice 1.5' x apx 8"). Remove the old wood that is there now. The edge of this plywood will sit however many inches you need to raise above the transom forming a "groove".

2. Measure the width and depth of that groove and rip a 2x4 to match.

3. Use a good oil based paint and seal everything the bolt it through the transom. seal all bolt holes and run a bead of 5200 about 1/2" on the outer piece. Bolt it all up and seal the edge on the out side with 5200.

I'm betting you can get this done for less that $50.

 

[davio47]

Re: Tahatsu 8 Hp 1993 2 Stroke Shaft Lenght Adjustment

OK. I think I understand you are saying, correct me if I am wrong. First, remove the old plywood on either side of the transom, while leaving the board embedded in the transom support. Second, cut the new plywood to place on either side of the transom. Third, rip a piece to fit down inside the groove. Fourth, bolt it and chalk. Then seal and paint.

I only need to go up 2.5 inches, it looks like more in the photo. The shaft length is like 16 inches or so as you described. Not a true 15" short shaft.

Should I go down with the plywood on the inside all the way to the floor?
Should I match it in the back? I am a bit confused on the execution. Thanks for your help so far.

Dave

 

[Lion hunter]

Re: Tahatsu 8 Hp 1993 2 Stroke Shaft Lenght Adjustment

OK. I think I understand you are saying, correct me if I am wrong. First, remove the old plywood on either side of the transom, while leaving the board embedded in the transom support. Second, cut the new plywood to place on either side of the transom. Third, rip a piece to fit down inside the groove. Fourth, bolt it and chalk. Then seal and paint.

Correct except seal prior to bolting up so you get all the edges.

[/QUOTE]
Should I go down with the plywood on the inside all the way to the floor?
Should I match it in the back? I am a bit confused on the execution. Thanks for your help so far.

Dave[/QUOTE]

Maybe these pics will help:

This is what the back should look like

This what the inside should look like. I just clamp this on my boat to give you an idea. Both front and back should at least be about 12" on either side of the motor. Best case is the back is 12" on either side and the front runs all the way across.

 

[davio47]

Re: Tahatsu 8 Hp 1993 2 Stroke Shaft Lenght Adjustment

Wow! Great pictures for illustration. It gives me a very good idea on how I may approach mine. My transom is quite different, but now I get the idea. Thanks for all your help and ideas. I will let you know how I do mine.
Thanks,

Dave

 

[davio47]

Re: Tahatsu 8 Hp 1993 2 Stroke Shaft Lenght Adjustment

Hi Lion Hunter,
I told you I would send you pictures after I raised the transom to accommodate my Tohatsu short shaft. Here they are. It works great with no splash-back. It brought the motor up just enough to be structurally strong as well as functional. Thanks for your help.
Sincerely,

Dave