Hello Doug J. Since you went into trouble to illustrate your work with superb pictures I am sure that your post is seen by everybody on the forum. Perhaps you or Crazy Dave or anybody with Hunter 26/260 experience can address/ alleviate my concern regarding the outboard mount on the 2000 260 that I just bought. Very nice, high quality boat but even before I bought it the outboard mount made me cringe. The original stainless steel brackets were significantly deformed. First I assumed that the boat was backed into a dock or something and the bracket were bent as the result. Since High Thrust Yamaha 9.9 did not show any sign of damage I started scratching my head and realized that (all numbers are rounded and the Yamaha is a long shaft, not the extra long shaft):
Yamaha is 110 lb with center of gravity 12 inches from the bracket. This is 110 ft lb of moment just from the weight.
The distance from the bracket to the prop shaft is 2.5 feet. After some digging I was able to find the thrust from this particular engine/prop combination at 220 pounds. With 2.5 ft arm this is 550 ft lb of moment on the bracket. It adds to the 110 ft lb component from the motor weight to a total of 660 ft lb.
The bracket has to counteract this with two pairs of 3/8 bolts exactly 2.5” apart. This is about 3200 lb per two pairs or 1600 lb per bolt in tension and compression. That’s about 2x of what I would design the load for 3/8 thread in low grade SS fastener.
But actually this is not really my primary concern. It would be easy to go to a larger bolt, by retapping the reinforcing plates behind the fiberglass. My concern is the fiberglass part of the hull itself. Can it really take those forces without eventually cracking? Clearly those boats are in use for many years without loosing their outboards so looks like I am wrong somewhere here.
Than again, if Doug would feel 100% confident in the original bracket, he would not go to such great lengths to improve on it, no matter how breathtakingly beautiful the result.
So, am I needlessly paranoid or is the problem real?