Transom replacement or design flaw?

[bikerider]

I have a 12 ft Starcraft, model sl-12 aluminum boat. It has a 5hp four stroke outboard on it. I notice that the transom on it flexes when I get past about 1/2 throttle. Enough that I don't go much more than that. I thought the transom wood was shot. But, as I've started removing screws, and what not, the transom wood seems surprisingly solid still. I'm wondering if the transom flexing under power is a design flaw. The transom wood in the center is only about 4 1/2" top to bottom, and about 5 1/2" top to bottom on the outside ends. There is no place (that I can find) where a brace would have been on the inside of the boat, and the very back of the boat has no brace either. It is just the aluminum skin. This thin transom wood seems like a poor design that would flex with any outboard except an electric trolling motor. What do you all think?

 

[Scott Danforth]

The wood looks like it dried out and delaminated.

I would get some 3/4" exterior grade plywood, laminate two pieces together to make a new transom and be back on the water by the weekend

 

[cyclops222]

Cut 2 FULL width Ply wood pieces to go SIDE TO SIDE. Should be thick enough to just easily slide under the inside Aluminum skin. It should go from side to side. Trim as needed. If you can slide in a 12" HIGH piece ? Do it. You might need to remove some bolts. Use S S hardware.

 

[racerone]

They forgot ( saved money ) by not putting a brace ( knee ) between transom and bottom of the hull.-----Easy fix for me here.

 

[airshot]

Owned many small 12' and under aluminum boats over my 60 plus years of boating, not unusual to see some flexing at the transom. How much is ok is the question !! These small boats are made to be light in weight so they can be cartopped. The makers use minimum strength materials to save weight. Just the way it is...when you get into larger, higher hp rated boats you will see far less transom flexing. If it bothers you, do as mentioned and replace that old wood with plywood, not that difficult and much stronger, even add an extra knee or other support....won't hurt a thing and might help you feel safer.

 

[cyclops222]

On my Lowe 16' With the 30 hp. I bought a piece of Aluminum heavy gauge, 2" X 2 " angle. Cut it to fit completely from side to side at the top of the transom. Some notching for motor mounting bolts. SOLID
Did add a few bolts, nuts and washers close to the hull sides. The engine clamps are on the angle.

 

[Grub54891]

That bottom piece looks compromised to me. At this point I would replace that, make the plywood go further down and it’ll be much stronger. Adding a knee brace would be appropriate also.

 

[Chris1956]

The transom cap is cracked thru. Likely from the plywood flexing. That does not help with lateral strength. See if you can find a way to repair/replace it.

 

[cyclops222]

If you have a LONG shaft motor on a SHORT shaft transom ? It will have a lot of extra pushing TORQUE on the transom. Oh well.