Strip-Building on a Cylinder Mold

[ancient kayaker]

Finally got to try it out. It was a modest -not brilliant - success with some more development needed but it looks like it will work. However, I probably won’t pursue it further as I really should get back to work on a couple of boats that have been waiting for attention for several months and seem to be eyeing me reproachfully - unless I am becoming paranoid. Also, I desperately want to start building the Wee Lassie I have been mulling over for more than 4 years; the wood is gathering dust . . .

Pic 1: the strips are laid out flat and taped; note 1
Pic 2: the strips lengths (calculated from the plank developments) are marked off
Pic 3: the strips are bound to the straight mold and stapled to the center station form
Pic 4: the mold and strips are bent to the sheer curve
Pic 5: the strips at the turn of the bilge have a tendency to twist and lift off the station mold
Pic 6: a strip of adhesive applied to the back of the strips helps
Pic 7: view of stem from the side; note 2
Pic 8: view of stem along centerline; note 3

Note 1.
Packing tape worked best and pulls off easily without damaging the WRC.

Note 2.
The planks slide over each other during bending but not as much as expected so the stem cutting line still looks more or less straight.

Note 3.
The strips are supposed to be straight approaching the stem; it is not clear why they are bent and that may be why the stem marks do not form a perfectly plat plane, but the error is small - about the thickness of the strips.


I reported the problems first, as seemed appropriate.

On the plus side, the steps illustrated in the first 4 steps and step 6 went very quickly. The tape on the back of the strips did not interfere with the bending step as the strips don't slide against each other as much as I expected. I did not add staples except at the midships station, where they are essential to prevent the strips sliding and putting the stem markings out of alignment. Obviously, the small error in the alignment of the stem markings can be corrected by pulling the sheer curve back to where it was supposed to be - I did not notice the problem until after I took the photos and dismantled the whole thing.

Also, the twisting of the strips visible in image 5 could have been eliminated with an improved binding system. Alternatively a few staples could have been driven into the station molds on either side, but minimizing staples was one of the original objectives. The problem may have disappeared with the use of B&C or T&G planking but that would increase cost, and T&G planks would likely resist sliding past each other during the bending stem resulting in buckling.

[ancient kayaker]

I wanted to add a note to this thread in case I return to it later. The expected advantages of the method - reduced mold material and faster hull construction - have been established if the remaining problems can be overcome.

The only real problems with the concept are the tendency of the strips to slide up the station molds during the bending step, and the twisting of the strips partway around the curve of the bilge, due to the strips being bent in both directions -across their width and across their thickness.

I believe these are soluble.

the first problem can be solved by adding a stop at the top of the molds that the uppermost strip can rest against. The existing stop at the bottom of the molds is unnecessary. With the modified molds, the tendency of the strips to slide up the molds will be prevented by the step. Any tendency of the strips to lift off the molds must be prevented by adequate binding of course.

In the last test above I attempted to prevent the strips from twisting around the curve of the bilge with an improved binding system but this is not a practical way to go as the forces are too great. With the revised mold shape describe above, stapling after the bending step should solve this problem. Alternatively the strip width can be reduced, perhaps using a square cross section for the problem strips.