Hull weight estimate 2008-08-26

New Cuboid was created on 2008-08-18.  The styrofoam was sanded to 110.41mm x 93.66mm 
x 75.28mm and weighed 23 grams.  778470 mm3 = 778.5 cm3 = 0.0295 g/ cm3

Hull area = 0.053 m2. = 530 cm2. So if shell thickness is, say 0.4 cm, core volume = 530 * 0.4 
= 212 cm3 which weighs 6.24 g. 

Area coated with epoxide is 11,05 * 9.38 cm = 103.7 cm2. Weight increment is 8 g. Therefore 
weight of epoxide is 0.0772 g / cm2

Therefore weight of epoxide skin is 16 g. Two layers of epoxide is therefore 32 g or total 
weight 38 g – rather heavy. 


Try solid with one layer epoxide only. 

Kg/cm immersion = 0.213 = 213 g. Mean freeboard =4 cm => above water volume is approx 
852 cm3 Plus immersed volume = 366 g = total volume = 1218 cm 3. 

This gives blank weight of 1218 * 0.0295 g. = 35 g. + one skin = 51 g. Distinctly heavy. 

BUT this gives us a deck, much of the location for bits. Difference is marginal. Simplicity 
probably greater with solid block. 

We can also use a lightweight filler rather than solid epoxide for the surface finish. Say density 
is half that of epoxide and volume is equal. Gives blank 35 g + surfacing 8g = 43 g. This has to 
end up lighter than the hollowed out boat – not as light as a Gary Sanderson special but very 
reasonable given the relatively small amount of effort required. 

Go for solid. 


AJCR 
26 August 2008