Laminating frames: learning points

joliette

joliette

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I've been using 1.25" X 0.25" oak to replace a couple of rotten frames in the lazarete where access is very restricted. Having attempted this job for the first time - having read a few (good?) boat building books from the library! - I'd like to share a few learning points with the forum.

1. Laminations only bend well in one direction. If you try to bend them in two directions then you get a twist. i.e. They're great at following the curvature of the hull, but will not necessarily follow the line of the frame that you've removed if the top of that frame curved forward / aft in relation to the heel. A steamed frame would probably be more flexible in this respect?

2. Five laminations of 0.25" oak takes a lot of force to get it to conform to the curvature of the hull - well, more than I had imagined, anyway! The options are to lay the laminations in situ, or to take off the curvature and build a laminating jig where strong clamps can be applied. If you laminate in a jig, then you can get some "springback" when the work is removed. So, do you allow a little extra curvature and if so, how much? I also did some laminating in situ and found that the best way to pull everything into line was to wind up an M6 bolt passed right through the laminations and the planking.

Although these laminated frames are going to be far stronger than the originals, I think that steaming would have been a more pleasant solution to work with ... next time. Although, I'm not sure how I'd manage to squeeze a steaming hot frame between a stringer and the planking!
 
Steaming the laminating timber was my first thought after reading your post but this would cause voids as the timber shrinks before the glue has set .
Maybe you need to epoxy the lot after to seal it if going down that road ?
 
Can I suggest wrapping two laminations in thick cloth, such as a towel, and pressing them into place in the hull, and holding them there with toms [props] backed against some other part of the boat. Once you have it securely in place, pour boiling water all over the towel for the full length of the frame. You may need to pour the water over it several times. While it is hot, try as best you can to get it to adopt the edge set that the original frame had. Obviously you need to wear some pretty substantial gloves while you do this. Repeat this for the other laminations. Allow them to cool completely in place. Hopefully they should have adopted most of the curvature that you want in both directions, and will be a lot easier to get into the final place when you have glued them up.
Peter.
 
You managed to avoid my Pitfall No. 1 - epoxy absolutely everywhere!

Like you I now think that steaming is quicker and easier.

The best way to get between stringer and planking is to take the covering board off. This is a classic case of something very common in boat repairing , viz: "do a job and make ten" and assumes, of course, that the boat...

(a) has got covering boards...

(b) that they are not associated with L. Giles' particularly cunning way of doing a canvas deck (those who have one will know what I mean!)

(c) that the covering board can be got off in one piece, bearing in mind the rail stanchions passing through it and bearing in mind that its probably teak, which is not very strong, much inclined to split and splinter, and costs sums of money beyond the dreams of avarice in the widths needed for a covering board...

which boils down to - by the time you've got the relevant length covering board off, you may as well re-frame that whole part of the boat!
 
In this case I'd already removed the covering board to access rot in the beam shelf, which is where the problems started in the first place, due to rain water penetrating a deck fitting. Having taken the teak covering boards off, without damaging them too much, I found Joliette's original 3/4" red pine deck (sheathed with grp). So, it has been quite a task to dismantle everything just far enough to enable a repair to take place.

I try to have a policy of minimum intervention when anything needs doing. This is based on my experience of restoring an old MG sports car, when I found that I took me two weeks to take it apart and two years to put it back together! In following this philosphy I hope to keep Joliette sailing....One sees too many cases - decaying in the corner of a boatyard - where somebody did too much dismantling and created a situation that they didn't have the time / money / energy / will power to recover from.

Anyway, enough of the philosophy! ... Other learning points were:

1. Just because a frame shows some evidence of softening it may have loads of life left in it. The need for removal is a judgement call.

2. My (good?) boat building books from the library suggested using unplaned laminations. My local yard frowned on this and produced planed laminations, suggesting I sand across the grain for improved adhesion of the epoxy. Having done the job I can see why planed laminations produce a superior result.

3. The strength of a laminated frame is extraordinary. I fastened them down with screws, which were much easier to install and probably stronger than rivets?
 
Steaming in a bag is a lot easier and more controlable than rags and hot water. Wedge it into final position complete with polythene wrapping, then rip the wrapper off, let it cool, and fasten up.
 
You can buy rolls of polythene in a tube, or as I have done just use strips cut from old fertiliser bags, fold the seam over and staple at intervals. Wrap this round the wood, as close as possible to the place where it will go. Feed the steam in from a pipe attached to a kettle on a handy primus, or better, use a DIY wallpapering steamer. Seal the ends of the bag with old rags. After say 10 minutes try bending the wood into place. If it resists, leave it longer. Wedge/clamp to the required shape, switch off the steam. I find it best to rip the polythene off as soon as possible to stop the wood tending to go black, and to drain out any condensed water.
For longer lengths, eg planks, fix into position at one end and slide the bag along as you bend the plank into place.
I've used the method for bending 20 foot lengths, just with scrap polythene and an old kettle. There is no need for steam boxes and grappling with scalding hot wood if you bend it in situ.
 
Have been franticly busy of late... so have not had time to respond.
Have considerable expirience with boil in the bag steaming
can prob make some time next week.
Could pop by and maybe advise
Where is the boat?
 
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