Outboard, how long a shaft does it need to be?

alexdz · #1 (**permalink**) 09-19-2011

I have a Cal 24 (Hunt) that I just traded another boat for, and it came equipped with a 6hp Mercury outboard that runs very well. It is, however, a short shaft model which I at first thought adequate, but now wonder if I really need a long shaft model. The day I got the boat I brought it across the Bay from St. Michaels to Deale and it functioned perfectly, but that was a windless day and the water was flat.

Last weekend I finally took her out for a sail, and in about a foot of chop it seemed to me the prop was surfacing more than it should. I looked at guidelines for determining prop shaft length, but I guess those are primarily for powerboats. On my boat the outboard is mounted on one of those fancy mounts that go up and down (Garelick I believe) and it places the cavitation plate several inches below the surface, but now that doesn't seem deep enough. Of course I think that mount also moves the motor back another foot from the transom, so that doesn't help.

I suppose I'm answering my own question--if I'm worried about it I need a longer shaft--but wanted to get more knowledgeable opinions. I've had outboards before, but they were mounted in wells that kept them down more reliably, AND they were long shafts (even on a Kittiwake, which is spec'ed for a short). I suppose I was looking for a more sailboat oriented guideline for how deep it should be?

Thanks.

(BTW I did do a search for this, but there's a LOT of discussion on outboards and I honestly didn't wade through the entire list of results.)

DRFerron · #2 (**permalink**) 09-19-2011

Our first boat, a 22-footer that we kept on the Bay, came with a short-shaft outboard. It was horrible. We bought a new long-shaft outboard the next year and wondered why we had not bought it immediately after buying the boat. We bought a Nissan long shaft. Some brands have an extra long shaft but the regular long shaft was sufficient.

Our boat had a transom cut out that lowered the prop about six inches or so and still didn't give us a decent ride with the short shaft.

dabnis · #3 (**permalink**) 09-19-2011

Alex, suggest you get the longest shaft available as long as it doesn't interfere with your rudder (not familiar with your boat). When it gets really rough and you are trying to get back home you will be glad you made the change.

Dabnis

MarkSF · #4 (**permalink**) 09-19-2011

Tohatsu make a special Sailpro sailboat version of their 6hp, with an extra long shaft, alternator, and high-thrust prop.

Tohatsu make the smaller Mercurys, so your engine is essentially a Tohatsu anyway.

alexdz · #5 (**permalink**) 09-20-2011

Yeah, I knew talking about it wasn't going to make me feel any better about it! It does make it easier to justify going through the hassle of replacing it though, so thanks everyone.

Does anyone have any experience with the shaft extension kits on the market? There's one that appears to be available for my motor and I'm considering it just because it seems easier than dealing with selling and buying and hoping the new motor is in as good a condition. But then I'd like charging capability too, so that's another kit. I could just buy a new outboard, I suppose I could get enough money for this one to make the price more palatable. This boat has been raced hard and needs a lot of work so I hate to spend money on a big ticket item like that yet.

emoney · #6 (**permalink**) 09-20-2011

I've had a 6hp Johnson that had the extension and it worked flawlessly. If you're handy, it's not a tough job at all, four bolts (usually) and little tinkering. If you go this route, go ahead and buy a new impeller and change it out while you have the lower unit dropped. You'll thank me in the morning (metaphorically speaking, of course)

dabnis · #7 (**permalink**) 09-20-2011

Quote:

Originally Posted by emoney

I've had a 6hp Johnson that had the extension and it worked flawlessly. If you're handy, it's not a tough job at all, four bolts (usually) and little tinkering. If you go this route, go ahead and buy a new impeller and change it out while you have the lower unit dropped. You'll thank me in the morning (metaphorically speaking, of course)

I also did the long shaft conversion a long time ago. The only tricky thing was an O ring where the water tube goes into the block. I had to coat it with gasket sealer to get it to stay in place while re-installing the lower unit. Getting the water tube back in was tricky, but do-able. Don't know how long the extension kit is but I think the Sailpro motor mentioned above has a 25" shaft and with the charging feature and high thrust prop that sounds like the way to go.

Tohatsu 6hp Four-Stroke Outboard Model # MFS6CUL

Dabnis