cross section from hull - techniques?

Must be all sorts of clever ways to make a plywood sheet to the exact dimensions, but it may not be desirable structurally, to install it flush to the skin.

 

The advantage of Plywood scraps is that they are able to be 'sharper' and stiffer, therefore more accurate. With Foam, the 'pointy' bits are a bugger to get a reliable mark established when you lay the hot glued 'mask' on the new plywood and have to trace the outline. Also, depending on the thickness of the foam, strips can bend and distort the pattern.

 

Right, I've seen smaller with wire pins for taking curves off smaller objects.

 

Thanks. The second I've seen, the first looks very useful! In North America, Busybee in Canada seems to have the best price.

 

Just pulled a couple of spillettos outa my tool box.... Did my apprenticeship with Maltese and Greek tradesmen, for all I know it may translate into pointy spiling block, same idea as joggle stick but no numbers so less confusion, with one strait edge a line or point can be defined by L or P or L+P... easy.
just trace and replace accurately.
My spiling block looks nothing like your link, same tracing concept as joggle/spilletto & join the dots/lines, just a rectangular peice of ply often with a small 45 degree snipe at one end and a larger at the other... so can reach into more acute corners.
A steel rule can do the same with using the perimeter and the hole at the end makes centering and reaching correct distance easy, also good for spiling then scribing steel plates, sometime we use the full 8 x 4 sheets joined together to take off the shape of large plates.
One bloke I know used 3/4 pvc conduit for taking off bulkhead shapes, he would heat till floppy, lay into the shape, screw a light timber brace to the ends & once cooled down remove and mark out the melded perimeter to the bulkhead stock.
Plenty of ways just pick one

Jeff.

 

The joggle stick method uses virtually no measurements, just drawing around the stick a bunch of times and transferring to the bulkhead material and connecting the marks with a fairing batten, very fast and elegant. Its a very easy method that works great, its the method I used for many years before the advent of hot melt glue guns and is still the method I would use if I were installing bulkheads in a bare hull that I didn't build so didn't have the loftings (otherwise I would pick the shape off the loft floor)

Steve.

 

The joggle stick was developed because most boatbuilders until relitivly recently couldn't read. The joggle stick doesn't require anything other then a pencil and the stick. Attached is a joggle stick drawing I provide with all my plans and it's self explanatory.

 

Personally a 'joggle stick' is what I've used for many years, for this type of tracing but for foils I tend to use a profile guage. A bit easier to get a properly accurate profile/section.

I thought most kitchen fitters etc use a 'joggle stick' to fit work tops etc to a tricky wall?

 

What is the beam of the boat where you want the bulkhead to go and what is the height from the bottom of the boat to the gunnel?

 

also, is the top of the hull open?

 

I found this picture of the joggle stick method, you mark the pattern board with each location of the stick. simple, could be faster with several sticks and clamps.

 

Google is amazing isn't it. If you look closely, you'll note that's a slightly different version the drawing I've attached above. It's been cut an pasted for years on various sights, so I'm not sure which one you got it from, but it's mine and it's good to see it used.

 

It'll be about 7' beam and about 3'6" deep. Eventually it will have a deck, but not when the mesurements/drawing are taken.

 

Thanks all for excellent info on joggle sticks and related techniques. Much appreciated.

I just ordered one of these - the device Gonzo identified - it should be interesting to test out.

 

I have scanned a drawing and but do not know how to import it into the Reply to Thread box.
How is it done?

edited message
I guess it came across though as a pdf which will have to be opened, rather than a picture

So here is a simple way to get the image of the cross section transferred to a pattern
Place a 2 x 4 across the gunnels, screw on a piece of 3/8 inch ply, mark the center line for a reference. Take a 1 x 3 inch strap, drill about a 1/8 inch hole as near to the edge as you can and push through a ballpoint pen refill.
The distance from the ball point pen to the lower left corner of the 1 x 3 should be about 1 inch longer than the height that you want to scribe.
Then you place a level on the 1 x 3 put the point X at point B and the ballpoint pen at A
Keeping the 1 x 3 vertical with the level run point X along the inside curve. It will trace out the curve. If you are very careful, it should be within 3/16 inch or so. We need to get this profile into the
hull for the second scribe.

Unscrew the ply and drop it into the hull, re-screw the ply to the 2 x 4 when the centerline is vertical

Then take an ordinary compass, the type you used to draw a circle with, open the point to the pencil to say 1 /2 inch, keeping it perfectly horizontal, run the pointed edge on the hull and the pen on the plywood and it will almost perfectly create a line that when cut will fit tight to the hull. Do the same for the other side, screw the ply together and you have the form


Lee Valley Tools has a tool that we used to copy curves from a hull to internal structures, and stringers to the hull. It is called a log scribe and makes it extremely easy to transfer curves for fitting