Horizontal strongback

[jonathan]

Hi all,
I'm going to start building a boat in a dirt floor shed. Any ideas as to which is the best way to properly fix the strongback, so that it is horizontal and stable ? The floor is very irregular. I was thinking of using wedges nailed to the frame, but I'm not really sure...
Thanks for your advice.

[Dave Fleming]

J., you don't mention the size of the vessel but here is a URL for an album showing the setup for a 50+ foot vessel.
Dirt floor, well compacted, very slight movement after the Cast Iron ballast keel was added. Ballast Keel weight approx. 10,000 Lbs..

http://www.imagestation.com/album/?id=4292179377

[jonathan]

Whoooaa, no! ;-)
It's for a *much* smaller boat, about 6 metre day sailer. Take a look here.
I suppose that the way they did it is fairly unlikely to move, but looks like the stability is given by the weight of the keel, doesn't it?

[Dave Fleming]

Not really, the yard had built many a vessel in that shed from 20 footers to 75 footers and not all were fitted with a ballast keel.

The point is that it can be done and has been done for donkey's years.

My personal preference is for a nice wood floor with removable planking so if necessary a few can be removed and the inevitable hole dug for rudder shaft etc...
Second choice is well compacted dirt.

Concrete whilst the most usual floor is just hell on us old folk's backs and feet.
And for everybody young or old, it is not kind on dropped tools nor bodily accidents of the falling off scaffolding kind.

[Tohbi]

haven't done it but i always thought sinking fence posts and attaching the strongback to them is a solid way to go.

[Bob Smalser]

Or those Home Depot footing supports....pointed steel rods predrilled for deck screws....drive them in with a 10lb hammer and screw your strongback to them.

[betelgeuserdude]

I fail to see why some of you find it necessary to fasten the strongback to the ground. Make it level and stable. It's not going to blow away. If you build a ladder frame strongback with dimensionably stable materials, the strongback will be fine. If anything, just pour a rough concrete pier at regular intervals. The strongback will gain strength and stability as the boat is built.

Having just viewed the boat to be built, a proa, I would think that a plywood or OSB box beam would be quite sufficient.

Have fun. Looks like a great project.

DC

[jonathan]

Hello,
betelgeuserdude, I like your "box beam" suggestion, especially the fact that it's "quite sufficient"
Could you tell me a bit more about it, i.e. how it's done, how to attach the frames to it, etc...
Maybe just a URL would be good.
Thanks again to all.

[henrikb]

I used an 18mm HEB beam for my 33ft hull. The beam was levelled using laser, I then made a couple of concrete supports to avoid sagging. If the hull is only 6m, I doubt that you need any support other at the end of the beam.

[Bob Smalser]

It only has to pass the common sense test.

Evaluate your substrate. Soft lawn topsoil with a tent atop and I would certainly consider ground stakes to the hardpan or some sort of concrete footers to keep a heavy boat from sinking into the soil after heavy rains.

Compacted crushed rock or concrete or barn-floor soil that's had a generation of tractors parked on it and I wouldn't worry about it.

The most important issue may be the spead at which you build.

By the time you have much weight on the forms the boat/forms will be stiff enough to resist deformantion from shifting.


Make sure there is enough outboard support to prevent the whole mess from rolling over.

[betelgeuserdude]

Hi Jonathan.

A box beam strongback is just a long box, or two, side by side. Typically, the box beam is built 3 sided, with the bottom being open. Bulkheads are used at regular intervals, and the butts are backed with blocks. Fasten the building jig or bulkheads to the box beam, as you please.

The box beam is very stable and can utilize inexpensive materials such as OSB. The box beam may stand alone, with a twin, or atop level timbers for elevation and/or stability.

Have fun.

DC

[jonathan]

Thanks to everybody for your suggestions.
I think I will go for a box beam type of thing, supported by two strong timbers, and use these to level the strongback from the ends. If they bend or whatever, I'll add some support in the middle.
Sounds ok ?

[oddball]

jon ...dave flemming is right..nevermind that 18 foot rubbish the 54 footer looks tobe much more fun post some pics in a couple weeks when u have the hull laid and the sheeting on that 54 footer
good luck with your new project...the pics of the 6m boat look interesting

[jonathan]

hehe
I'm building a proper work bench at the moment. Big, heavy thing. I'll start working on the strongback when that is done, on monday probably. I'll keep you posted, even though it's only an 18 footer.