Thursday, July 11, 2013

the long and the short of it

UPDATE: I am leaving this post below intact, but need to point that I was incorrect about the shaft length on the outboard.  I have a standard (short) shaft model.  A correction can be found here.


Please excuse the technically poor photograph.  I use direct flash about once every two or three years, and then only if it can't be avoided.

This is some visual information for Seth, who is building a Pathfinder.  We were discussing in a recent post the shaft length for the outboard.  Seth tells me the plans call for a short - 15" - shaft, and I seem to remember reading that in the Pathfinder plans.  I have always used a long shaft - 20" - because that is what I had from my last sailboat and it seemed to work fine on Spartina.

Tonight I measured and marked the position of the prop.  You can see the top of the blade at the five inch mark on the measuring tape.  Going up five inches from there, to the very top of the tape, it seems that on Spartina the upper portion of the short shaft prop would be to some extent blocked by the hull.  I'm sure the short shaft would work, but I have to wonder if it would lose some efficiency in the "dead" water of the outboard well.

I'm not saying that the long shaft is the way to go, though it does work for me on Spartina.  What I am saying is that it is worth getting some specs from the outboard manufacturer and doing some measurements before placing an order.  Small four-stroke outboards run $900 to $1200, might as well get the right one for the boat.


1 comment:

S R Wood said...

Steve, this is very helpful, thank you. At first I was bewildered because your outboard seemed to be pointing forwards! Then I realized you have your well on the opposite side as I have mine.

I haven't cut out the hole for the shaft yet, so measuring has been tricky. Maybe I'll cut out just enough to let a tape measure through.

In any case, you may be spot on about the short-shaft prop not having enough "clean" water to work effectively.

Thanks for this! More to come...