Load on Halyards

[Triton318]

I have the formula for calculating the load at the clew of a headsail (or the end of the boom) given the sail area and wind speed. However, I'm trying to figure out the approximate load on the main and jib halyards for my Bristol 19. Other than placing some kind of measuring device inline in the halyard, I have no idea as to how to figure it out or what a good estimate would be. The reason I'd like to know is 1) to make sure the jib halyard block is strong enough and 2) to see if one of those Forespar marelon winches would work for the main halyard.

Thanks in advance for any guesses on the load or for advice on how to measure it without purchasing a special piece of equipment.

Jay