Long shaft / Short shaft

Brian-Bear · 13-01-2006, 04:23 PM

Presently I run a 225 johnson longshaft on the fletcher. I fancy changing to a short shaft Mercury Promax 150hp is there a handy rule of thumb measurment from the top of the transom to see if I could run a short shaft motor.

Burty · 13-01-2006, 04:54 PM

merc lengths go up in 5's ie. 15" short shaft, 20" normal shaft and 25" long shaft. dont know about johnsons but if the same standard lengths then you would need to drop the saddle by 5"

roofer · 13-01-2006, 04:56 PM

You'll probably have to cut your transom down.

Brian-Bear · 13-01-2006, 07:13 PM

I think the johnny is 25" longshaft, if the promax was 20" is there a formula for where the centreline of the prop should be in relation to the bottom of hull or waterline etc.

Burty · 14-01-2006, 01:28 AM

yeah, 5" less than the johnny

roofer · 14-01-2006, 09:13 AM

I thought you said the promax was a 15" mid?

Brian-Bear · 14-01-2006, 09:17 AM

Quote:

Originally posted by Burty
yeah, 5" less than the johnny

This may not be true. If you consider the overal rotating mass, at the end of the swing ding in conjuction with the high lift pump cam on the end of the blue widget................ohh my aching head