...what are the measurements for a springboard ?and how much taper ?
That's the hard part...I've never actually made a springboard myself. Not from scratch. Not a nice fancy one anyway like I'm planning here.
I know, I know, us old farts are 'sposed to have
done everything and know how to
do everything. I wish that was so. Frequently. Whenever I needed a springboard I just grabbed one off the pile in back of the shop or cut a limb or free handed a little slab of some kind. I want
these springboards to be something special.
The ready made boards that we had were made mostly from 2" df if I remember right. Rough cut. I never measured the length but I'd say between five and six feet. The width varied but I only saw a couple of 2x6. Most were 2x8 or 2x10. We had some 2x12s too but those bastards were heavy and I never packed one.
Some were under-tapered directly back from the shoe in a straight line ending at about an inch thick on the end. Others had the full 2" for maybe half the board and then a taper. Some had no taper at all...these tended to gravitate toward the bottom of the pile and I never saw them used.
The ones I liked had a gradual subtle taper starting at the back of the shoe and sweeping back to the end of the board...again ending in about an inch thick. The taper was obviously hand drawn, maybe with a draw knife, because it had a curve to it like the bow sheer on an salmon troller. I don't know that they were any better but they looked nice. And it's what the old timers used. I copied them.