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15" or 20" shaft?

S

Sirtree

New member
I have a 9.9HP Mercury outboard with a 15" shaft on an 18' pontoon boat (limit on this pond is 10HP, many pontoons with small motors). The transom measures 15", which is why I bought the 15" shaft. But when I accelerate I get gurgling and what someone called cavitation, with little power being transferred to pushing the boat. I know 9.9HP is low, but the other boats don't seem to have this problem. Should I switch to a 20" shaft to help with this? I plan to buy a new motor with power tilt rather than manual as I have now. Thanks.
 
Either purchase a standard shaft motor since you are wanting tilt, which the Honda is best in my opinion or use a dropdown jackplate.
 
If my transom is 15", isn't a 15" shaft "standard"? Regardless, the jackplate sounds very intriguing. I was reading about them this morning. I suspect, in my case, buying a manual jackplate and finding the best performance spot and locking it in would be the best option. This is only a 10HP on an 18' pontoon, so performance boating is not an issue here. Thanks for the idea. Any further thoughts would be much appreciated.
 
15" is a short shaft, 20" is a standard or some OEM call them long shafts. The dropdown plate is cheapest fix
 
I absolutely plan to buy a new motor, since the current one lacks power tilt and it's too awkward and difficult to raise the motor manually when on the water. So you think the 20" shaft is the way to go, in which case I won't need the dropdown plate? Thanks so much for your input.
 
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