It's more complicated. And the answer depends on what you mean.

If you simply take the drawings and blow them up 50% in all
dimensions, you get a boat 50% longer, but that will require
theoretically 1.5*1.5*1.5 = 3.375 as much weight to bring down it to
its lines. However, the boat itself will weigh only about 1.5*1.5 =
2.25 times as much, unless you increase its scantlings (the thickness
of all the materials). So you have something that will be perched on
the water, probably very tippy.

If, what you mean, is to just increase the length 50%, with no change
in beam or height (draft plus freeboard), then you stand a chance, but
even this will be less than ideal. You might get away with adding two,
maybe three feet, but I wouldn't do seven. It probably won't be
strong enough and it will be too narrow.

Better look for similar designs that are 21'. You'll be much happier.

Jim Woodward
www.mvfintry.com





"Hcarson" wrote in message ...
I have built a small stitch and glue skiff, (14ft.), I would like to make a
bigger version of the same boat, say 21ft, do I just add 50% to the
patterns? or is it more complicated than that, the boat I built is a Glen L
"power skiff",,, give me some help guys,
Thanks,