The previous owners of my Cosine Wherry had moved the thwarts around to install (horrors!) folding plastic seats and a trolling motor.
I'm trying to reposition the center thwart, and will have to build the other two as they were trimmed to be narrower by the previous owner (who was not the builder).
Question is this -- how do you determine where the center thwart should be in a pulling boat?
Should the rower's center of gravity be over the middle of the boat's waterline, i.e. thwart just forward of the middle of the boat on the water? I assume the middle is not determined by measuring the actual length, as parts of the bow and raked transom are out of the water.
I know that in most boats you want a little more weight aft than forward when rowing, giving the skeg more directional ability and leaving the bow a bit higher for boat wakes and swell.
I don't plan on setting the wherry up for doubles rowing, and may pass on the third thwart entirely. But I do want to have the forward and center thwarts correctly located, so that I can row alone from the center thwart, and row from the forward thwart with a passenger in the sternsheets.
Looking at the marks on the rail/riser on each side, it looks as if the builder had placed them all differently from what is called for in the plans.
Not that the plans make it easy, but from what I can tell the plans call for this (all thwarts = 10" wide):
A bow seat (sheets?) forward edge maybe 12-13" from the bow.
First thwart starting maybe 43" from the bow.
Second thwart (middle rowing seat) starting maybe 77" from the bow.
Third thwart starting aprox 111" from the bow.
(all thwarts 9" wide)
No bow seat/sheets.
First thwart 38" from bow.
Second thwart 72" from bow.
Third thwart 90" from bow.
The overall length of the boat is 168", half being 84". The waterline length is probably 162", half being 81".
So I'll guess that the center of the boat's waterline is roughly 85" aft of the bow (leaving off/adding 4" for overhang of the bow). If correct, that puts the AFT EDGE of the designed center thwart at 87", with the center of the rower's weight probably a bit aft of that.
That means that if I put the center thwart back in my boat as the builder placed it, it will be roughly 6" forward of the designed location, and possibly throw the balance of the boat off.
That means that the forward thwart will be 5" forward from what the plans call for, but that may work well since I weigh more than most passengers.
Any thoughts or experience on this issue?