does a tra some have to be an exact height when planning on mounting a 20-30hp tiller motor?
im wanting to know how this effects your skeg and where it rides in the water. Im going with a manual jackplate
Depends on the prop you select. Some perform best really close to the surface and some need to be submerged several inches. So pick your prop then speak with the prop manufacturer about how deep it needs to be for best performance.
What is your goal? Most standard transoms are 15-16ish" and most high transoms are 20-21ish". If you just want to throw a stock short shaft motor on a 15" transom or a stock long shaft motor on a 20" transom and go fishing, you'll be close enough. If you want optimum performance, you need to be able to tweak the height, which is influenced by the prop and the set back which are influenced by load and HP. If that is your thing, cool, but don't bother with this mess if you just want to go fishing. If you are making a boat, make it have a a standard 15" or 20" high transom to prevent headaches.
I have a 25 Yamaha tiller 2 stroke, run it with 2 different props: PT on manual jack plate and on 16" transom. It performs at 19" high
The Turbo Prop performs at 17.5" on the Jack Plate. They both run well, but the PT does not blow out at any height or turn.
The Turbo blows out easier but runs better on a stock transom, it has very little cup. Only 1 mph difference gps speeds, Turbo ran light 35, PT ran 34 light......PT does better with loads and overall beter prop......