shaft length

[chipben]

hi i have a 3,1m inflatable it specifys max 10hp engine.
could i get away with a say 15 or 20hp engine on this boat?
Also the depth of the transome is 16 inches, what length engine shaft should i be looking for, short shaft 18 inches or a long shaft?
thanks ben

 

[WillyBWright]

Re: shaft length

Depends on the laws where you live and the boat's ability to tolerate the added weight and speed. It's not so much can it be done as can it be done safely and legally. Being rated for 10 max already answers the safely question.

Sounds like you have a shortshaft transom.

 

[steelespike]

Re: shaft length

You need a short shaft motor.Under ideal conditions the
10 will give you about 20-21 mph a 15 22 -25 and the 20 about 25-29.In my opinion the 10 is the only way to go and be safe.You will only be a couple of mph lower than the 15.
Keep in mind that little boat won't carry much and a 20 hp will be like adding an adult to the load Then add the fact you are doubling the hp:: not a good combination.