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ksmith · 05-02-2009, 20:32

Sure wish there was a different title to this question.

There is probably a formula to detirmine the shaft length for a dingy/runabout. I know it draws 6" but not sure about the transom height? ie measured from where to where. Top of transom to bottom of boat would seem logical.

**Pblais** · 05-02-2009, 20:41

The idea is you don't want the prop getting out of the water. You are dealing with a short shaft (normal) vs. a long shaft. Most dinghy transoms won't need a long shaft. If your sailboat uses an outboard for it's auxiliary it usually does require a long shaft.

ksmith · 06-02-2009, 06:06

Thanks. Just thought there might be a common measurement. Short shaft 15" from where to where etc. Do all outboards have the same measurement? Is the Mercury short shaft the same as the short shaft on say a Nissan?

**GordMay** · 06-02-2009, 06:26

Outboard shaft length is measured from the top of the mounting clamp bracket to the bottom of the cavitation plate, and should equal the transom height of your boat (give or take an inch).

Generally”
Short Shaft = 15"
Long Shaft = 20"
Extra-Long Shaft = 25"

ksmith · 06-02-2009, 07:00

Gordy

Thanks, should have known you would have the answer.

**David M** · 06-02-2009, 08:58

Another idea is that you want the propeller to not be in the disturbed, non laminar flow water right behind the transom. You want the propeller to be lower than that for small planing dinghy's...in the undisturbed water.