construction method change

[jorgoz]

Hello,

I'm going to build a wooden runabout, don't know what design yet, so many to choose from. But my question is about changing from batten-seam construction to cold moulding.

What needs to be done for changing the construction method, or is it just ok to put your plywood or the layers 3mm mahogany 'veneer' on the battens intended for batten-seam construction, but using the 90° technique intended for cold-moulding. I think there are quite a few more battens in batten seam construction than there are in the cold-moulding technique. But i was also thinking of just leaving all the battens for the batten-seam construction to preserve the weight originaly intended by the designer, so the boats rides like originaly designed.

Does this make any sense ?

George

[Dan McCosh]

It doesn't seem as if the battens would serve any structural purpose if the sides are cold-molded. On the other hand, they would likely make the laminating process easier by supporting the shape of the hull while under construction. The weight distribution wouldn't be all that relevant, as it isn't concentrated in any particular part of the hull.

[Andrew Craig-Bennett]

Can you be confident of avoiding voids in the cold moulded construction, if cold moulding over the original frames and battens? I would be inclined to doubt it, and would suggest a much more radical change, using a close battened male mould.

[Gerald]

>>>>>But i was also thinking of just leaving all the battens for the batten-seam construction to preserve the weight originally intended by the designer, so the boats rides like originally designed.<<<<<
My building theory is to always build as light as possible. You can always add weight, if necessary. You can add back into the area where the weight helps the performance.
Gerald

[mmd]

I think that ACB's comment is the salient point here - will diagonal veneers fit properly on a hull form designed for longitudinal planking? Most likely they will, but assumptions can become costly.

As for number & placement of battens, reducing their number will entail re-engineering to determine the new structural arrangement and scantlings, as well as alter the weight distribution characteristics; leaving the original arrangement in place will not require these efforts.

[jorgoz]

Dan, this was what i was thinking as well. Whith more battens the layers will follow the shape of the hull easier, but serving no
strucutral purpose.

And what would be the big problems avoiding gaps between veneers ? I trust my woodworking skills enough to know i work 'quite' accuratly. :cool: :D

Are there any good books on this subject ? (especially for the nulber crunching)

George

[Bob Perkins]

George,

Having some experience here (however, I'm not a pro..)

I'd say you could use the batten seam layout and go for it. It batten seam has more battens - there would be 1 (or at most 2) per flat surface. (i.e. left side, left bottom, right bottom, right side). Maybe 50 pounds in battens? however, 4 layers of 3mm ply on the bottom and 3 layers on the sides would make for an overall lighter boat.

You could go to Glen-L.com and see plans for cold molded runabouts if you haven't already.

Take a look at my site:
Bob Perkins' Imagestation - Biscayne 23 (http://www.imagestation.com/album/?id=4291051329)

Hopefully you will see what I mean about batten counts.

Take Care,
Bob

[jorgoz]

Bob, real nice work. I really like the vacuum bagging part, i'd like to do that as well, but i'll have to learn in with the project ;) (haven't done it before, but i like a challenge ).

Yes, there are i think twice the number of battens, so i was maybe thinking of ommiting one batten every other batten (ie. batten 2,4,6,...).
But as i'm a novice in boats maybe i'm being a bit naïve ?

George

[jorgoz]

A new thought occurred to me. Just leave all the batten for the batten seam construction. Divide the thickness is say 3 layers and stagger the joint, widhtwise. First layer could practically be clapmped, second stapled or screwed and third vacuum bagged. I don't know if this is done ?

The reason for all this tinkering is i would like to use fibreglass to sheat hull. Don't think it would be wise to sheat a conventional batten-seam hull, as the movement of the wood might be to strong ? Or will the epoxy completely immobilize the movement of the wood, i haven't got complete faith in epoxy yet ;)

George

[ 09-10-2005, 04:38 AM: Message edited by: jorgoz ]

[Bob Perkins]

George,

The way I contructed mine was to fair the skeleton of the hull first (of course..)

The first layer was mostly 6" wide stips of 3mm Okume. I carefully epoxied them to the battens/frames and stapled them down. They were all started at 45 deg to the centerline for the most part.

Each piece was beveled at the edge to that it was not a butt joint, but more of a slight scarf joint. Also - as I got to the more concave areas - I had to custom fit each plank to get a close fit to the plank next to it.

Now - I'll tell you that the only reason I did it that way was because I knew I was going to experiment with vacuum bagging at the time and it won't work if there are leaks from below.

Once the entire first layer was complete, staples pulled and it was smoothed out - I skimmed on a layer of epoxy with filler to close up any gaps, staple holes, etc.. An easier way to do this is apply a layer of 4oz cloth to seal in the hull.

The second layer was put on with very few staples, just enough to keep everything from moving while sealing in the vacuum bag.

The final layer was 1/8" mahogany veneer that was spiled to look like real planks and applied the same way.

The 3mm material will hold well with staples - with out vacuum as a clamp, you just have to use thousands of them (and remove them if metal).

You want to do the double diagonal if you use this method - not a staggerd lap joint.

Glassing over traditional batten seam would not work because of wood movement. The reason this works is because the 3mm wood is so thin that it can't move enough to break the glue joint if it gets wet.

Good luck,
Bob

ps. Take a look at:

Runabout Construction (http://www.bronkalla.com/)