Motor Shaft Length

[txnfish]

After looking back through the threads on this topic it looks like most people who run outboards on their catarafts are using long shaft motors (20"). I have a 13' cat with 20" diameter tubes, and I am on the fence about which shaft length to get. My transom to water level is 15" with a normal load, this puts the cavitation plate on a short shaft 2" under water, and a long shaft cavitation plate 7" under water on my boat.

Would those of you that have motors on your cats post how far under water your cavitation plates are? And how you consider the motor performance. Any cavitation or blow-out etc?

 

[AK Troutbum]

I run a 18' with 26 or 27" tubes (can't remember) and a 20" (long shaft) with my outboard. How much of the shaft that is in the water depends greatly on how loaded my boat is. I only have used the motor for getting across Skilak and I have never run this without a considerable amount of gear or people. Considerable being at least roughly a 1000 lbs. This includes the motor wt. I have on occasion cavitated in choppy conditions. I would recommend sticking with a long shaft, I don't think you can go wrong with a 20" shaft.

 

[Jim Strutz]

I used a short shaft motor on an Aire Cougar (four 18" tubes). It worked, but I often had cavitation issues unless I loaded the stern quite heavy.