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Old 27-03-2014, 11:37   #16
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Re: Question About Spray Hoods/Dodgers?

I am at the very early planning stage of a dodger (here in the US) project and am considering a somewhat novel approach adapting a system used for architectural awnings.

I have done some design work with these awnings and some exterior sun control systems as well and know if properly designed they can be very robust. If you notice down at the bottom of the extrusion manufacturer's cut-away drawing they claim the twist and lock staples are good up to 110 MPH.

The system is based off an aluminum extrusion which features a recessed channel into which the fabric is stretched then stapled and a vinyl or PVC spline is inserted to provide a finished appearance.

The advantages from a fabrication standpoint is that, as the fabric is stretched and fastened in place, it eliminates the need for pattern making and is a major time saver because it eliminates sewing except for windowed panels.

It is possible to recover at least once, maybe twice, before the frame gets tired, but each time the work involved is significantly less than would be for a sewn cover.

A potential problem lies in that the aluminum extrusion is typically a 6061 T6 or 6063 T52 alloy whereas I am limited to stainless or monel for the staples. This is a source of concern, but like I said I am at the very early planning stages.

On the up side the system is quite user friendly and allows for in-progress mock-up and modification during fabrication, and can be adapted to be as strong as desired while remaining very lightweight.

If I go that route I will have to figure out a nice way to have an opening panel but there are a couple different ways to make that work. As far as styling goes I think you could make it as classy or trashy as you like. Personally I am about function and as they say form follows function. Just kicking the idea around....
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Old 27-03-2014, 17:36   #17
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Re: Question About Spray Hoods/Dodgers?

Interesting idea, Delancy! Do you know what the dimensions are for the alloy "tubes"? And how hard is the stuff to bend on the fairly short radius required in many dodgers? And finally, are there suitable hinged terminations for the tubes for making the connections to the deck or would you have to fab up your own?

It would be good to have an alternative to the conventional construction methods, and I will watch for your further comments.

Cheers,

Jim
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Old 27-03-2014, 21:48   #18
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Re: Question About Spray Hoods/Dodgers?

I link below to one manufacturer here in the US called Milliken who has a variety of shapes available including 1" x 1" and 1" x 2" in wall thicknesses from .125 down to .063, as well as a couple other shapes.

In general I would have to say it bends pretty similarly to other rectangular tubing which means better to use a roller than not and the tighter the bend, the more the distortion but I think for the purposes of a dodger it should do just fine.

My experience has been with MIG welding but having you enquire about end-fittings makes me realize that thanks to the rectangle shape, this extrusion would lend itself fairly well to mechanically fastened gussets for connections. While a little erector-set-ish, this approach would make it a lot more accessible.

One of the issues I have in the project, that others may share, is that my boat was not built to include a coaming for the dodger which usually means either making one, which is a real PIA, or fastening to the deck with snaps or whatever, a method a view as really unsatisfactory.

Thinking back about another project has got me going on trying to use a bolt-rope type extrusion, as pictured below, to secure the deck edge of the fabric. On the down side, it means a lot of screw holes to be drilled and filled with epoxy to secure the bolt rope extrusion.

On the up side, that is a lot less work than making a coaming. The bolt rope extrusion is fairly small in section and should be relatively easy to make it conform to the curvature where the deck camber and the dodger meet.

Also, since the deck is strong enough to support itself, anything more in terms of structure is not needed to simply attach the canvas and so would be a waste. I figured some butyl tape would do nicely to seal the extrusion against the nonskid.

The whole bolt-rope method of attachment is interesting as well, I have a boom tent for my cockpit that is literally made out of a length of boom for a strong back that has a folded-in-half-with-a-piece-of-rope-in-the-middle canvas tarp threaded into the groove on the boom that works quite nicely.

I have to get a chunk of the staple track and play around with it as I have a couple thoughts for a way to do make the whole thing with very little to no sewing. Also, any type of friction fit as opposed to the staples would be favorable from the standpoint of eliminating the dissimilar metals issue, so will have to see.

http://www.millikendistribution.com/...extrusions.pdf
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