Lift the Sunfish, read the scales, average the readings, subtract your weight, and you'll have successfully weighed your Sunfish accurately AND by yourself.
Lift the Sunfish, read the scales, average the readings, subtract your weight, and you'll have successfully weighed your Sunfish accurately AND by yourself.
If you have two scales, then why bother to lift the boat yourself? Instead, put one end of the boat on one scale, and the other on the other, then add the two readings. This works because gravitational force is a vector, and parallel vectors add linearly, i.e. the springs of the two scales are together exerting just enough force to hold the boat, and that total force is its weight.
Then, once you accept that method as valid, you realize that really you only need one scale, since the same force at each end would be exerted on an inert block, as long as the boat is in the same horizontal position. So put one end on a block and the other end on the scale (keeping the boat level since that keeps the force vectors the same at the ends), then reverse the process, and add the two weights.
"Can I accurately weigh it using just one bathroom scale and just one person?"
Yes. Just choose Alan as your one person.
We use Alan's method and take along towels to place under the hull to prevent scratches, as this method needs to be done on a flat surface, usually concrete. Some folks take a board to put under the scale if they have to weigh on grass.