[flyingfrizzle]

Most people just use Douglas Fir marine grade plywood for transoms and bulk heads. A lot of people use the Fir in transoms due to lower cost and it is stiffer. Douglas fir is stiffer than meranti and meranti is stiffer than okoume. (modulus of elasticity: fir = 1,560,000 to 1,950,000, meranti = 1,500,000 to 1,630,000, okoume = 1,140,000) Okoume and Meranti can be a better choice for marine applications but at a higher cost. Each has its place. On the down side Okoume is less resistant to rot than fir or meranti. Meranti is less resistant to rot than fir so the Fir would be the best far as rot resistance. Okoume and Meranti have a much better finish that wont check with less flaws. Doing a transom the ply wont be seen so it's not a big deal but places that are seen Okoume or Meranti is much easier to do a finish quality surface on. My Master Angler hull has a Okoume transom in it (3 layers of aquateck) and it was not sealed up well at the top. Two years in the weather it was rotted away near completely. Seems like the Fir transom weather the water much better but if it correctly sealed up with epoxy it dosent matter and you should be fine no matter what you use. I have done transoms with ac grade exterior pine and had them last but they were sealed 100%.