I’m looking to swap from a long shaft Tohatsu 6 (Sail Drive) to a short shaft Tohatsu 6. I have measured the distance between the bottom of the outboard well to the ant- ventilation / cavitation plate and this is approximately 6 ½ inches on the long shaft. The measurement was taken at the aft end of the outboard leg.

The difference between the Tohatsu long shaft and short shat is 5 inches. With the Parker 235 the short shaft motor appears to be mounted 3 inches lower than the long shaft which would mean the theoretical distance between the bottom of the outboard well and the anti ventilation / cavitation plate on the short shaft is 4.5 inches (I’m sorry for this sounding like a school exam question).

I would like to know if these measurements are similar to those of other owners for both short shaft and long shaft.

I would also be interest in comments from any owners, who have converted from a long shaft to a short shaft, in relation to performance and boat handling caused by the loss of 2 inches.

I am planning to fit a sail drive prop on the short shaft.

Many thanks for your replies

Andrew

Sorry, I can't really help at the moment as the boat is in the water for the summer. I have what I believe is the original long shaft Tohatsu, if that is any help.

Don't know if this helps, but my 21 came with a short shaft Mariner, which I think has the same origins. It also has a sail power prop. It is in many ways a good engine, at least in forward gear, in reverse it is incredibly slow to respond. Whether the short shaft makes it worse than a long I don't know.

A man at EP Barrus tells me that this is a recognised problem, due to the through prop exhaust. I suggest you go for a make which doesn't have this feature or you may end up with the same problem. Yamaha apparently don't vent their props this way, there may be others. There are some on line threads about this.

Jon Stockton P21 Shivra

Thank you for the feedback so far.

I measurement I am very interested in is the distance between the bottom of the outboard well (not the hull) and the anti ventilation / cavitation plate when a short shaft engin is fitted. This can be measured with the boat in the water using a ruler.

With this measurement I will be able to tell if I'm looking at the right design for the outboard mounting.

Many thanks in advance

Andrew

I'm afraid it's probably too late to reply to your question now but, in case it helps, my anti-cavitation plate is only 3 inches below the aft edge of the hull aperture. Owing to the shape of the hull there, it's only 1.5 inches below the forward edge of the aperture.

You are correct in that the short-shaft engine needs to sit about 3 inches lower in the well than the long-shaft engine. On my boat, the limitation in dropping it any lower is the depth of the cut-out in the forward side of the well to accommodate the engine's clamp screws.

I've been very pleased with the performance of the engine since changing to a short-shaft Tohatsu (with 'sail-drive' prop).

Thank you for your reply. Sounds like we have approximately the same distance betweeen hull and anti-cavitation plate. I have had a couple of trial runs and there doesn't appear to be any impact upon performance. I haven't used it in anger as I have been waiting to fit the charging circuit which is now complete (thanks to ebay).

Best regards

Andy

Now that's a job I haven't got around to! I'd be interested in the details and performance of your charging circuit. I've doubted it would contribute much, especially at 'cruising revs', but perhaps it is worthwhile.