Hi Utnik,

It's definitely not about the hydrodynamics:  I'm looking to figure out things like how deep I can make a sink before it won't drain on one of the tacks, or how I might route the forward cockpit drains' plumbing.

I think that the method I'm using may underestimate the freeboard too much to be of use, though.  If I use it, I may end up making the countertops unnecessarily high.  I may have to think of something else.  I'd like to avoid having to make a detailed model of the hull - I'd have to lift the lines myself for a Pearson 10M.  I haven't been able to find a good drawing or table of offsets anywhere.

I know that this is a subject, that done correctly, needs all sorts of models and design programs and smarts, but none of those are available to me.  I'm looking for a general rule of thumb.

There are many plumbing in instruction that say things like, "above the waterline when heeled".  Not so easy to determine, that heeled waterline, especially when the boat's on the hard for the next several years.  So would the following work?  

tan(angle of heel) * distance from boat's centerline to hull at waterline.  This is would be the estimated distance the waterline moves up one side of the boat and down the other. This assumes that the boat simply rolls on the axis created by the horizontal plane of the waterline and the vertical plane of the centerline.

For instance, at 30 degrees of heel near the main bulkhead, it's 4 feet from the CL to the hull at the designed waterline.  tan (30) * 4 ft = 2.3 ft.  So I'd mark up from the waterline 2.3 ft, which leaves about 6 inches of freeboard.  This kinda coincides with my vague memory of how it looked the one time I had her on her ear.

I think that this quite conservative:  the actual waterline will be lower on most boats as they heel, because the underwater profile becomes flatter and more barge-like.  Is perhaps this too conservative an approach?