Designing a new transom... whats the usual outboard mount bracket size?

Hey all, I am again designing a new little boat and I am having a hard time nailing down information on outboard bracket size. I know there is a standard for the bolt pattern, but I am wondering about the actual "clamp" / bracket length.

In short, how much transom do outboards need to fit the entire bracket? Especially smaller HP outboards in the 20-40hp range. I measured a few at a local retail store and got 13.25 inches in total bracket length.

As always thanks!

 

Depends on the leg length of the outboard that you intend to use. Legs come in several different lengths. Smaller engines usually, but not always, work well with a 13.5 to 14 inch clamping height. The cavitation plate is usually about an inch below the bottom of the boat at the transom. So measure the bottom of clamp assembly to the cavitation plate and build your transom height appropriately.

The above, is conventional wisdom but there are all manners of variations to be addressed. For starters describe the boat and its intended use. What size is it, will you be using it in very rough waters, how much cargo and how many people will be aboard..... and a bunch of other questions that concern the boat, not the motor. When you have detailed the most appropriate transom height for a particular type of boat use, then you can get an outboard that fits the transom, not the other way around.

 

Are you asking about height or width?

 

the height

 

That should match the leg of the outboard. 15", 20" and 25" are the common heights.