Transom for CS20 to hold 4 to 5 hp motor CS 20 #104

[Maria CS20 104]

I am looking at a putting on a 4 to 5 hp motor on the 104, is it necessary to change to 3/8th ply or double up on 1/4"?  How is the transom best braced for the additional loading and torque of the 75 lbs and operating motor?  Ideas?  I am ready to cut transom, any pictures of motor mounting and bracing that have proven successfull?

Jim

[wkisting]

Hi Jim,

I was just in your shoes (see the thread on Hull #102). If you're going to go with that big of a motor, I'd probably change the transom to 3/8" and also add quite a bit of reinforcement to stiffen the transom-to-hull joint (to prevent it from cracking).

Personally, having seen the CS20 up close, I decided that the kind of motor you're talking about was way too heavy and large (I had a 60 lbs. 8hp 2-stroke, but sold it and bought a Mercury 3.5hp 4-stroke that weighs 40 lbs.... not just to reduce weight, but also size). A heavy motor will likely impede sailing efficiency, and depending on its size, may also foul the aft lines if you don't mount it carefully.

Here's a picture of the reinforced transom (below). I used the cutout that was left over from the centerboard, so this reinforcement is 1-1/8" thick (the slab is 8-1/2" wide), and I later filleted and glassed it in place to make it even more solid. I still wouldn't hang a 70 lbs. motor off it, but I'm creating a custom bracket that will hold the motor off the transom about 13" which is quite a lot of leverage for anything that size.

Also, FYI, we had some discussion about this topic on this other thread: http://www.messing-about.com/forums/index.php?topic=6049.0