making rough shape of molds

[chergui]

I was wondering if anyone could tell me what the best way is to get the rough shape of the molds for a 7' pram. I don't know what Rossel was trying to say in his book. I also don't know how wide the stock should be. I'm planning on using 1/2" clear pine. I can get some that is 8" wide. The only other 1/2" thick pine I see around is knotty, but it doesn't look usable.

[Bob Cleek]

It's sort of hard to understand what you are asking. As for thickness of the molds, they only have to be heavy enough to support the boat when it is being built. Width isn't of much problem, since you will be builting them up anyway. The wider the planking stock, the less you have to connect the pieces, but there is not much point in wasting clear eight inch pine plank for molds unless you are planning on keeping them for other boats later. Otherwise, they'll be going in the fireplace when you are done. Knots are okay, as long as you can lay out the lofted edges to avoid them. As for "getting the shape," are you asking how to transfer the shape from your lofting to the molds? If so, there are many ways to do this. Give us some more detail and I'm sure somebody can answer your question.

[ 12-03-2005, 03:56 PM: Message edited by: Bob Cleek ]

[willmarsh3]

Only criteria I have for molds is cheap and stiff e.g. b/c grade plywood 3/8 or 1/2" thick (with voids). You want plywood instead of planks for dimensional stability. This is one time where you don't have to bother with picking.

Will.

[Harry Miller]

I had to read it a couple of times but Rössel did make sense eventually.

Here is a pic of mold # 1. It's just cheap pine I had around. The molds have been lying around for about a year and when I tacked this one back to the lofting board it still fit fine.

http://www.imagestation.com/picture/sraid195/pf0affc8cb44569775df4c2ab04835241/f1345793.jpg

Just yesterday I glued up the boards for the aft transom. A tiny bit of progress but better than nothing.

http://www.imagestation.com/picture/sraid195/p761b8f4804610e569e6e13594aa6880c/f1345700.jpg

[ 12-04-2005, 05:13 PM: Message edited by: Harry Miller ]

[chergui]

Okay. I see what Rossell is talking about now. He's got some really smart methods but it's sometimes hard to understand what the general idea is first, before understanding his neat way of doing it.

Harry, what was the width of the stock you were using?

[Bob Cleek]

With the caveat that if your molds must have beveled edges (e.g. lapstrake steamed frames) you are far better off with real wood. Planing a rolling bevel in plywood is a bugger.

[Harry Miller]

It's just ¾ in. pine from the Home Despot. And yes Bob we're both building Paul Gartsides 7 ft. clinker pram.

[almeyer]

I had a little difficulty on the last boat laying out the pattern onto the mold frame. My molds were built up like the picture that Harry posted. The trouble I had was getting the lofted mylar pattern to lie flat on the built up frame, then get it lined up exactly right when I flipped the mylar over to lay out the other half. The molds were drawn on only one side of centerline.
I'm thinking about a different approach on the next project, which will take a little longer, but should result in a more accurate mold. Instead of trying to lay out the pattern on the rough-cut mold, lay it out on a piece of 1/4" luan, then flip the pattern over and lay out the other side. It should be easier to lay out the pattern, mark the mold outline, flip it over, and mark out the other side on a piece of plywood. Because the plywood is only 1/4" thick, it should also be easier to cut/plane/sand to the mold outline. Now that I have a stiff template of the entire mold (shear to shear), this can be tacked to the rough-cut mold and a router with a flush trimming bit will cut the mold to match the template.
At least this sounds good in theory.
Al

[Mrleft8]

I drew the molds on "Herculon" (Drafting vellum), and sprayed adhesive on the roughed out mold stations. Then I just cut through the vellum and wood at the same time. The vellum can be removed and, after you let the spray adhesive dry 100%, saved for posterity.

[chergui]

I made 2 of the 3 molds but just noticed the clear pine I was using was 1/2" and not 3/4" that is recommended. Should I re-do them and get some thicker wood? For some reason I was thinking 1/2" was what I needed.

I also found it difficult to find suitable wood. I got more than I needed but most of it is now useless. One piece warped and cupped and looked like a dugout canoe a week after I bought it. I laid it down flat with some other wood on top of it and now it's cracked right down the middle. Any suggestions?

[Wiley Baggins]

Originally posted by Harry Miller:

...The molds have been lying around for about a year...

...Just yesterday I glued up the boards for the aft transom. A tiny bit of progress but better than nothing.Harry, you scoundrel! ;)

[Mrleft8]

Originally posted by chergui:
I made 2 of the 3 molds but just noticed the clear pine I was using was 1/2" and not 3/4" that is recommended. Should I re-do them and get some thicker wood? For some reason I was thinking 1/2" was what I needed.

I also found it difficult to find suitable wood. I got more than I needed but most of it is now useless. One piece warped and cupped and looked like a dugout canoe a week after I bought it. I laid it down flat with some other wood on top of it and now it's cracked right down the middle. Any suggestions?A 7' pram is a pretty small craft. I'd guess that 1/2" mould stock will do in a pinch...... BUT..... Why not double up the very edge so that you have a larger surface to fasten anything that needs fastening?
Next time you try to "uncup" a board, try laying it cupside down on the ground.In theory, the sun will dry one side, while moisture will wick into the other.

[chergui]

Thanks for the suggestion, sounds like a good idea. The molds do seem plenty strong enough even at 1/2". I'll make the last one 3/4".

[Harry Miller]

Merry Christmas Wiley. Have I got an insurmountable lead? I wonder how long before I can post this as real.

http://www.boatschool.com/pram.jpg

Silva Bay Shipyard School (http://www.boatschool.com/index.php)

My daughter who lives in Vancouver has a friend attending right now. According to her, waiting for the sun to uncup your board in Vancouver a bit optimistic.

[Wiley Baggins]

Originally posted by Harry Miller:
Merry Christmas Wiley. Have I got an insurmountable lead?Thanks, Harry. Merry Christmas to you and yours!

Insurmountable? Maybe(read as "probably") or...probably(read as "maybe"). ;)