Replacing transom plywood, what to do with the aluminum cut out

alex2293

Cadet
Joined
Jun 6, 2013
Messages
15
Hi everyone,

I bought a 16'2" MirroCraft that is probably 20-30 years at least and I am in the process of replacing the rotted transom plywood. The space between the knee brace and the transom sheet metal is 1.25" so I'll use two pieces of 5/8" glued together with epoxy.

I think this utility boat was made for a long shaft as you can see in the picture below. (I'll add the picture tomorrow)

The highest part of the transom near the handles is 24" high. The factory made notch was 21" and the homemade notch is 14.5".

The outboard I have is a short shaft 1971 Johnson 25HP (25R71). The distance between the cavitation plate and the bracket that rests on the transom is 17.5".

Is it ok to cut the plywood higher than the aluminum? I would prefer to have the highest transom possible (24") except a 17.5" cut out for the outboard. I would use something like 3M 4200 between the plywood and the aluminum skin.

Thanks
Alex
 

Watermann

Starmada Splash of the Year 2014
Joined
Jan 12, 2013
Messages
13,747
Yeah unfortunately people who shouldn't, do own a saws all.

fetch


I'm facing a similar repair on a 25" transom cut down to 20". My plan is to put an outer motor plate of AL over lapping the cut out with another piece of AL cut to fit inside the cut out using 5200 to adhere / seal the 2 pieces. When finished it will look like this AL pad on my SS.

Click image for larger version  Name:	IMAG2317.jpg Views:	3 Size:	281.6 KB ID:	10749307
 

rirory

Seaman
Joined
Feb 20, 2009
Messages
69
I would use a piece of 3/16'' aluminum all the way across and extend 3-6'' below the plywood.
Thru bolt and 5200 it together after plywood is epoxied. have a machine shop make you a cap to go over the top of it all--probably run you $100 or less--that cap is key to keep water out-- make the sides come down 3/4-1'' and attach by thru bolt or pop rivet each side

good luck

ri rory
 

alex2293

Cadet
Joined
Jun 6, 2013
Messages
15
I've finished the transom but had some outboard issues this summer. I'm looking to replace it and I'm wondering if I could go to 30HP with a 1 1/4" transom?

On the mirrocraft website their model 3672/3673 is about the same dimensions as mine and it has a 30hp capacity.

I replaced the floor and added a front deck so I'm wondering if 25hp will still make it plane nicely. I doubt that when the floor and deck is done the total weight would be over 400#, the weight of their 3673.

When I removed the old floor and deck, my guess would be that the bare hull was between 225 and 250 pounds. I could easily lift the stern alone.

Any advice?

Thanks
Alex
 

Watermann

Starmada Splash of the Year 2014
Joined
Jan 12, 2013
Messages
13,747
Utility boats are always rated lower but not knowing the HP max for yours it's tough to guess what a particular motor will do. Rule of thumb with most boats if your within 75%+ of the boats max HP will yield the best results.
 
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