shaft length question, will this work

Hello,

I have a 23 ft Robalo CC that I want to (need to) install a 150hp yamaha outboard. Eventually, I will buy a new engine that is also better suited power wise to the boat. For now, I have to work with what I have. So, my transom is 23 inches and the outboard is a 20 inch shaft. What kind of problems can I expect. Will it function decent under normal conditions? Any input would b appreciated.

Thanks,
Justin

 

Your transom is 23" and you are mounting a 20" motor.
For starters, a 20" longshaft motor usually has a shaft length of closer to 21-21.5 inches. The next size up is a 25" (actually about 26).
Your 23" transom is indeed designed for a nominally-20" shaft. Keep in mind that the prop is at least a foot or two aft of the transom. I'd mount the motor, learn to use its trim function appropriately, and not worry about it unless the prop is clearly ventilating.

 

You want to measure the distance from the top of the cut out straight down to where the bottom would intersect if their was no transom angle - maybe you did it this way, just checking.

If the 23' boat was built for a 25" shaft (makes sense) then a 20" engine will not work properly.


Joel

 

Adding to what Joel said: If your 23" measurement is along the transom, as I suspect it is, then your vertical distance will be a bit less- maybe 21-22", due to the angled transom. If your boat was built for a 25" shaft your transom would be closer to 27" measured along the transom, 26" or so vertical. On a boat this size the engine mount is usually designed so the ventilation plate is an inch or two above the keel, since the prop itself is set back a couple of feet from the keel.
Having said that, a 20" shaft on a 23' c-con is a bit of a rarity; boats this size do tend to be a bit higher in the transom.
Put the motor on its bracket and hold a 2x4 board against the hull bottom adjacent to the keel. The free end of the board should touch the ventilation plate.