Estimated vessel weight and designed draft

I made some guesses beforehand about weight and resulting draft of my vessel. Before going ahead with the build, I thought I’d make an effort to get a slightly more accurate estimate.

The plan is to use 15 mm marine plywood throughout the design. The transom will get a double layer, as do the bottom runners. I will use the stitch-and-glue method to put everything together. The bottom and sides will be covered in glass/epoxy. Above the waterline I plan to use only epoxy and paint.

3D design of my tiny scow

So I took my design and measured all the parts, put that into a spreadsheet, added some columns to calculate the weight of paint, glass and epoxy and came up with a total weight just shy of 230 kg (507 lbs). With a bottom area of close to 5.8 square meters the vessel is able to lift 58 kg for every cm of draft. This results in a designed draft of 230 / 58 = 4 cm for an empty vessel.

Designed waterline

If we add some payload of let’s say 250 kg (2 adults and the proverbial case of beer) then we get a draft of roughly (230+250) / 58 = 8 cm. Not bad in my eyes. It leaves a healthy safety margin before the sideboards get dangerously close to the water.

Behind the link at the end is my calculation sheet.

Vessel weight calculation (PDF)