What's shakin' Tom

I have no scribed waterline myself. Perhaps Bishop has an etched line where she settled in the fresh water.

Big questions you pose. Too big for my britches, but I have a couple things to throw out anyhow.

Here is a formula I dug up from my apprenticeship notes:

The PPI formula. How many pounds required to sink or raise a boat 1 inch.

PPI = 5.33 X WPA (saltwater)

PPI = 5.25 X WPA (freshwater)

The result is expressed in lbs.

WPA for the formula is in cubic feet and is the water plane area as she currently sits. The designed WPA could be different, but it should be a known number and can be used as an approximate for your estimations.

I mention this because you mentioned your bobstay fitting is at the WL now. Use the formula and you can predict relatively accurately where that fitting will sit with added ballast.

The second formula I have for you is the Moment required to Change Trim 1" -- M.C.T.1"

..which is, the moment of weight in ft. lbs. that will cause a change in trim totalling 1" at the bow and stern, added together.

Added together implies that if the bow raises a half inch and the stern sinks a half inch, then added together they are 1"

The exact value of MCT 1" for any boat is not easily calculated, however a useful approximation is one twelfth of the displacement in pounds.

That is:

                 M.C.T. 1" (ft lb) = Displacement (lbs) divided by 12

The point at which Tantramar pivots in the horizontal plane is the CF.... Center of Floatation.

For the small angles of trim that will be effected by your new ballast, the CF is, essentially, the exact center of the WPA. That point (CF) should be a known mark on the CG36.... so you could then work out the moments and see how the weight added in ballast will effect your trim.

Phew.... what a mouthful. Hopeful it makes some sense to ya

Just to add.... Tallowah an' Petrel currently have about 4" difference in freeboard. Crazy.... I better put some iron wood into the interior

Adam