Nutshell Pram construction questions

[Raven 271]

I am an experienced woodworker,building my first
boat,a Nutshell Pram for my new grandson.I have
made the station molds,laminated the frames,cut
the transoms and built the ladder or constuction
frame.
My question is,since I have to move the boat with-
in my shop in between construction,I was wondering
why both the book and the video stress that the
ladder or building frame must be perfectly level
especially since the station molds and laminated
frame can be set using a carpenters square.What's
wrong with just placing the ladder frame with the
uncompleted pram on a couple of stable sawhorses
each time Iwant to work on it?
My next question concerns ceder,the seats call
for white ceder.I use western red ceder at work
(I carve signs),why is white ceder associated with
boat construction?What is the difference between
red and white ceder?

[On Vacation]

The jig should be level to work on the boat. Moving the jig eveytime before completion will create a twist in the boat before total planking is done if positioned differently on the floor. I am sure that the writer takes for granted that your jig stays in place while construction is done.

You can accomplish almost this same thing everytime by marking you position of your sawhorses on your floor.

White cedar, while being soft, is harder than red cedar. Red cedar seems to be more common in the northwest area, and white cedar is on the east coast. Other than that I can't tell you the reason for specing out white cedar. Maybe someone here will chime in.

[ 10-28-2002, 08:21 AM: Message edited by: oyster ]

[bud]

Whenever I stack plywood I put a level on each support & make 'em level. Not because they need to be level but because it's the easiest way to know that the 2 supports are in the same plane. You could run a string from each corner diagonaly across & see if they just touch in the center - I've done that in a large window frame.
You don't want twist.
White cedar is more springy, less splintery than western red, & I think more rot resistant as well.

[landlocked sailor]

I would not hesitate for a moment to substitute the red for the white cedar. Paul Gartside uses it exclusively in his boats. I used it for my "Heidi" skiff several years ago with very nice results. Rick

[Bruce Hooke]

Pine would also work just fine for thwarts (seats) too...it is not rot resistant but thwarts rarely rot because they are out in the open. Red cedar and white cedar are quite different woods in terms of how they work but as others have said I think either would work for this application.

As to the building frame -- there are lots of times during the building process when it is very useful to be able to check alignments by dropping a plumb line or using a level. Also, as others have noted you need to be careful about throwing things out of alignment by moving the frame around. That said, you can probably get away with the approach you are taking if you check for twist each time you set it up, and plan on just leveling it when you need to, or get it level once and then carefully mark where the sawhorses go. Before you take the major steps like adding the plywood 'planks' I would check things very carefully to make sure everything is still where it is supposed to be. Also, unless you've got some helpers I think you may find that the whole thing will get pretty heavy to move around as you get more parts in place...

[Raven 271]

In referenceto my question about keeping the ladder or construction frame level,I guess it
makes sense to mark the floor so that the saw
horses sit on the same spot each time Ihave to move it.
As for the white ceder,does anyone know where
to purchase it in the boston area? I'd still like
to know more about the difference between white
and red ceder reletive to boat construction.

[Bruce Taylor]

For seats on a dinghy red cedar will work well, if that's what you have at hand. Both cedars are light and rot resistant. Red is softer, as Oyster says, and it has a greater tendency to split when twisted (especially when quartersawn). For your seats this shouldn't matter a bit.

Joel White probably specified white cedar because western red doesn't grow in Maine.