Boat Builder Central - Builder Forums

Shine what shaft length did your tohatsu have. I've always assumed 20. I started taking measurements, a 20" shaft will put the top bolt throughs even with my stern casting deck... I don't have a motor well opening, the rear deck is flat/flush with the transom camber. Like shine's fs17. So I'm thinking I need a 15" shaft with the low sheer fs17?

It depends on how you cut your transom and that does not change with a low sheer.
Look at the plans: the clamping board is at 19.5", that dimension is on the plans.
That means a 20" shaft.
You can use a longer or shorter shaft and cut the transom accordingly but I do not recommend a 15": too close to the water and you have to lower the splash well bottom.

Right, I see it in the building plans. The low sheer doesn't have a motor well though, so the ~20" or 19.5" from the keel ends up being right at my rear casting deck. Also I don't have a clamping board, but its no problem to glue some scrap inside the transom.

I guess I'm just confused as to where my top motor bracket holes will be. I'll be using a bobs hydraulic jack, and I know those match the BIA standard pattern... So do I just get "close" to the correct height mark? And let the jack correct it?

I'm obviously confused, and not trying to say there's anything wrong with the plans. I probably measured incorrectly early on or something similar, but that's where I sit now. Scratching my head!

Suggestions?

Make sure that you measure the specific motor you will run A 20" motor should measure 20" from the top of the bracket (where it sits on the transom) to the top of the cavitation plate, when the motor is tilted all the way down. I measured a F20 Yammie at 22 inches This will affect where you want to mount the jackplate.

I don't have a motor well opening, the rear deck is flat/flush with the transom camber. Like shine's fs17.

The plans show a curved transom but I don't think it matters.
See Joel's thread "FS17 low sheer", page 37 and after.
He shows where he drilled for that jackplate. Even if you did cut the transom top edge flush, it should work.
He had a 20" shaft.

Joel will jump in if necessary. I was present and designed the hull but Joel made the decisions about transom etc. He drilled for the jackplate and may remember something that we overlook.

For the other builders reading this:
- transom height: it's the same whatever the sheer option is. The way it is cut at the top is different but the height of the clamping board is exactly the same. I designed the low sheer version and when I superpose the two drawings, the transom height is exactly the same: 19.5" = for a 20" shaft but all that becomes irrelevant if you use a jackplate.
- no motor well in the low sheer version because we expect builders to use a small bracket. For the height, either refer to the instructions of the jackplate or see the complete thread that Joel wrote about his FS17 low sheer. He shows that jackplate.

One last point: as LSUred says, check your engine. In most cases the shaft length will follow the industry standard but I have seen and heard of a few rare exceptions.

my FS17 transom was cambered and I had no motorwell, and I used a jackplate The motor was a 20"

I positioned the jack plate so that whne it was in it middle setting (3" travel available up and down), the cavitation plate was 2" above the bottom of the hull. In other words, I could have a range of adjustment from -1" to +5" relative to the bottom of the boat. launched in that position and it was perfect, never once adjusted the jackplate.