Transom Q with picture & drawing

[rburlington]

I will try my transom question again with a picture and a drawing.  The boat is a 1981 24'6" EXFish O/B.

The picture below shows the transom with exterior skin cut away below the cap down to the drain and with the wood mostly dug out.




Note that I did not cut the skin away from the risers (or some call them wings) of the transom.  The portion of the transom that is currently expossed is 1 1/2" deep.  Behind it at the bottom of the boat are two huge stringers and behind it from the cap down about 11" is a 1/2" thick back that froms the inside skin of the transom and splash well.  

My questions are:  Is this the main support for the engine?  If so, is there any reason to cut away the skin over the risers (or wings)?  It does not appear to me that they have anything to do with supporting the engine, but mainly give some structure to the the risers.

The drawing below shows two wood cores that form the entire transom.  The top one labeled # 2 is 1" thick and was behind the 1/2" thick portion labeled # 1.  The current cut portion of my exterior skin is equal to section # 2.  My question here is:  Is it safe to assume that inserting new transom material into the cavity I have dug out is sufficient even though it will not be tied into risers (wings)?

My motor is a 220 HP Yamaha, 1986.



Thank you,
RGB

[damnitbadger]

I would replace the entire transom with 1.5 inch thick material from the inside to maintain the integrity and strength of the transom as a whole. I'm sure the 1" piece was laminated to the .5" piece you show. You are going to hang 400+ pounds there. Now is a good time to beef it up. Mine was 1-1/4" thick and now it's 1-1/2". I'll sleep better knowing it's better than before.

To answer your question, yes the lower portion of your transom was dependent on the upper for strength, and was installed as a single unit despite the varying thicknesses. Since you have already started from the outside you should replace the upper and lower pieces laminated together with epoxy for added strength as a unit. I would cut back the sides to 3" (yours appears to be about 4") and grind back to the sides. Use generous amounts of cabosil to eliminate any voids.

Not being a structural engineer I tend to err on the side of caution and overbuild for safety.

[rburlington]

Thanks for the input.  I ma, on your advice, go ahead and dig out the old wood in the risers, but I doubt I could increase the depth of the whole thing without some major surgery.  One thing about the wings or risers (I am not sure what is the right term) is that they have a lot of heavy structure around them; about 11 1/2 inches on the three sides that are not part of the hull exterior.   This makes the boat very strong in the corners and I hesitate to cut into that to get at the back of the transom.  I doubt it would ever be as strong again.  

Also, in spite of the fact that many are not in favor of it, I am going to put Seacast into this transom, in part b/c going in from the outside and leaving a lip around the cuts large enough to bevel back and get a good strong bond would require me to jig-saw-puzzel the pieces back in and that will make it a weaker transom I think.

The cosmetic work does not worry me b/c I have some excellent help on getting that back in shape.