How do you calculate the wet surface of a boat?

I am looking at getting my boat hull powdercoated with anti-fouling. The company says that it will do this for x$ per square foot.

The question is: Are there any formulas that will tell me how to calculate the square footage of my inwater hull area? I understand that this area would be different for a flatbottom john boat vs. a deep draft trawler or sailboat. Any suggestions?

Thanks
Bob

 

Multiply the length (in feet) by the beam (width), then multiply the result by .8, which will get you close enough for bids. If your boat is particularly fine in the bow, then use .7 as the last multiplier.

 

PAR has given a good approximation but if you want a more accurate measure it will need a lines plan or you can measure the boat when she is next out of the water. From the lines plan measure each station from the waterline to the center of the boat around the skin of the hull. Then for the area between each pair of stations add the lengths measured for the two stations and multiply by the station spacing. Add all of these areas together and then add the area of the rudder(s) and keel or skeg (dont forget both sides), also add any submerged transom area. This should give you a pretty accurate measure of the ares. If measuring the hull follow the same procedure but set up your own stations and measure in the same way.