Question For Those Experienced Rebuilders

[boatnamesue]

'76 170

Out of curosity, how does one know how much weight and torque a transom can safely endure?  The max hp plate affixed to every transom certainly cannot be a factor, since its manufacturers purpose is for boater safety, not weight. 

Aside from altering the hulls manufactured COG, dropping scuppers below waterline, etc.  I'd like to learn from those who have rebuilt/replaced transoms how to determine whats too much weight, what is ok, and more importantly, what factors play a part in this scenario (such as composition of materials, adhesives, stringers,????). 

[mshugg]

I won't claim to be an experienced builder, though i did rebuild a 14 skiff and I'm experiencing the full rebuild with my 200 CCP right now. 

I think your question will be difficult to answer in the abstract, but I will share some observations.

The original Core on my transom was 1 1/4" of marine ply with glass it was still less than 1 1/2" thick. This for a boat rated to carry up to 200HP.  My new transom is 1 1/2" Carbon Core 28  (similar to Coosa 26).  With glass it is over 1 3/4" thick.  This is in line with what Coosa recommends, useing the same core thickness and laminate thickness as original. Most of us can't resist adding thickness and transom knees or gussets to further beef up our transom.

I plan on installing a 200 Suzuki 4 stroke which will be  a bit more than 100 lbs over the weight of a 200 2 stroke in 1979.  Armstrong wants at least 1 1/2" for useing there bracket with up to 200 HP and I think 2" for larger outboards. I m moving the batteries to the console and the center of the fuel tank is 8" further forward too.  Plus the baitwell will be in the leaning post instead of at the transom.  When I'm finished and on the water iti believe that it will work out as planned.


If you want something to give predictions, there's a book called Boat Strength by Dave Gerr.  It's heavy on math, but you can use the formulas to calculate thicknesses and structure for any boat based on size, construction and use.  Honestly, the book drove me crazy, so I'm quite happy with going with what the Aqua engineers and designers did (plus a bit more for comfort).

[boatnamesue]

I know not to expect an exact answer to my question, rather just wanting to hear opinions of those who have intricate knowledge of the transom and weight.  Appreciate the response and book recommendation.