DIY dodger

[chp]

https://48north.com/instructional/do...urable-dodger/


Has anyone tried to make this Dodger. Looks a lot better than most DIY dodgers. Just wondering about expansion and contraction of the Lexan.

[JBP]

I would think you need to get UV coated lexan so that it doesn't yellow in the sun.

[s/v Jedi]

Unless in arctic regions, you will quickly overheat when sheltering in it.

[Jim Cate]

^^^^^

I don't see why it would be any different in heating than a cloth dodger with the same window area. The painted panels should be just as effective as Sunbrella panels at blocking IR radiation.

What I don't see is how the edges of the panels are joined where they meet.

Looks easier than making a good fitting cloth model to my eye.

Jim

[s/v Jedi]

Originally Posted by Jim Cate

^^^^^

I don't see why it would be any different in heating than a cloth dodger with the same window area. The painted panels should be just as effective as Sunbrella panels at blocking IR radiation.

What I don't see is how the edges of the panels are joined where they meet.

Looks easier than making a good fitting cloth model to my eye.

Jim

You wish… you will need two coats of primer and at least three top coats before you get anywhere near the same level as proper dodger material.

[Katapult Mike]

Looks pretty interesting to me!

Originally Posted by Jim Cate

^^^^^

What I don't see is how the edges of the panels are joined where they meet.

Looks easier than making a good fitting cloth model to my eye.

Jim

For joining the panels, it's really just a question of sealing them. They get strength from being riveted to the frame. I wonder if you could just use a couple strips of butyl tape?

I have seen write ups on similar projects using FRP panels: http://www.cruisingworld.com/homemade-hardtop/

But they are uuually only FRP on top and use standard strataglass and sunnbrella (or whatever) for consturction of the windows and the forward facing part.

I wonder if you could do this using lexan for the windows / forward facing part, and FRP panels for the top. FRP presumeably better at not retaining heat. FRP paenls also available at HomeDepot.

[Don C L]

The big question I have is where are they getting their tubes bent? Around here when I have asked in metal shops they look at me and sigh and say, "we don't do that." So that $46 at Home Depot is pretty suspect right off the bat.

[Katapult Mike]

Originally Posted by Don C L

The big question I have is where are they getting their tubes bent? Around here when I have asked in metal shops they look at me and sigh and say, "we don't do that." So that $46 at Home Depot is pretty suspect right off the bat.

In the article, the guy says he took it to a friend's shop and gave him a case of beer. So you have to add the cost of the beer ($21) to the cost of the tubes. This presumes that you have a friend with the right equipment. Also, don't forget, he is using aluminum framing.

I am putting together a frame now for my Islander 36. I took a different tack. I bought a used bimini from off of Craigslist. I think it was origianlly on a power boat and was much wider than I need (aabout 88 inches and I only need 76 inches. But it had a shape that worked pretty well for me, was made from 1 inch stainless tubing, and came with most of the end eyes and jaws I need. Best part is it only cost me $25!

I then cut the bows into three pieces, with a J-shaped piece on each side and a gently curving center section. Then I cut the outer edges of the center section to fit so I would preserve the curve of the crown in the middle. Next step is to rejoin the center section to the J shped pieces. I am doing that by insering a short piece of 7/8" tubing inside the two adjoining frames, and attaching with stainless self tapping screws.

This is still a work in process for me and I don't have pictures. But this is basically how you fit the frame to your boat if you buy a kit from Sailrite, and they have great video explaining the process here:

http://www.youtube.com/watch?v=tXeqyqPP_t8

The difference is, the Sailrite kit is $800, and you still have to do all the fitting work. Mine is going to cost me $25, plus $7 for the 7/8" tubing from a marine consignment store and some additional end fittings from E-Bay!

[Katapult Mike]

Originally Posted by JBP

I would think you need to get UV coated lexan so that it doesn't yellow in the sun.

The Home Depot Lexan has #GE-100 UV coating, but it is not the highest level. #GE100S is their better level of UV coating. It might be hard to buy that locally.

http://www.homedepot.com/p/LEXAN-48-...100S/205351342

[Don C L]

Originally Posted by s/v Jedi

You wish… you will need two coats of primer and at least three top coats before you get anywhere near the same level as proper dodger material.

Do you mean sunbrella offers greater IR protection than 2 coats of primer and 3 coats of paint?

[s/v Jedi]

Originally Posted by Don C L

Do you mean sunbrella offers greater IR protection than 2 coats of primer and 3 coats of paint?

Okay, I’ll retract “near the same level” and make it “the same level”

It’s easy to test, just get a thin piece of lexan from Amazon and paint half of it and tape a piece of Sunbrella over the other half.

[BenBowSirocco]

If it were me, I would find cardboard to use for patterning, or do it right with "pattern ply*" and hot glue. Using the sheet plastic (visqueen) can be such a PITA if there is a breeze and it also doesnt have any form/shape stability like the lexan your patterning for does.



Found this figure in a PDF about the product:

Coeff.of Thermal Expansion ASTM D696 in/in/ºF 3.75 x 10-5


Which I believe is science speak for: .0000375 per degrees F.

So a 60 degree swing is worth: .00225"

Based on that: if you cut your pattern out at 70 degrees: dont worry about expansion as it will only move half the above amount (.001125)" from 30 up to 100 degrees.
You will still want to slightly over-drill your holes by 1/32.



Regarding the tubes, if using stainless: this part is really the tricky bit.
I have had great luck in the past using 1/4" copper pipe for bend patterns: but its hard to transport.
I think you might be best to cut pattern ply strips 2" wide and chop them to 4-6" long pieces you can hot glue up to make up your arch patterns. Then cut fresh "normalized" or smoothed out curves from the pattern ply and re-test in position to make sure you have their outermost edge exactly where you want the BOTTOM of the tubes.

This allows you can bring these plywood patterns to a shop and the guys can match the tubes directly to your patterns.



If using aluminum tubes: grab some cheap OSB 3/4 plywood and cut some large "French Curves" out of it. You can then just hand bend the tubes over these curves into the shapes you want by making small repeated adjustments.

You need a good propane torch for annealing the aluminum: write upon the aluminum with permanent marker on both sides of the area to be annealed and heat it until the marker flashes off. It is then annealed.

The annealing allows you to un-bend or re-bend areas over and over. If you feel it getting hard to bend: anneal it again!





https://ff.sabic.eu/uploads/resource...2021-%20US.pdf


*Pattern Ply refers to 1/8" door skin sheets: also available at home cheapo. These are a plywood product that can be cut with a good pair of shears or tin snips and hot glued together to make very reliable patterns.

[Katapult Mike]

BenBow, thanks for providing some actual data for this thread! Sounds like the thermal expansion may not be a big deal in practice.

Question on the electric shears. You mentioned that a "good pair" could cut 1/8 plywood. I have read elsewhere that they could cut 1/8 FRP panels. Do you think they could cut 1/8 Lexan? What about 1/4 Lexan? I am thinking about doing somehting like this, but only using Lexan for the front curtain, the windows, and using two layers of FRP panels laminated together for the top.

For things I rarely use, I tend to favor tools from Harbor Freight. What do you think of these:



http://www.harborfreight.com/35-amp-...lectric+shears

Or these from HomeDepot:

http://www.homedepot.com/p/WEN-4-Amp...676586#overlay

Or do you have a recommendation?

[Don C L]

Originally Posted by s/v Jedi

Okay, I’ll retract “near the same level” and make it “the same level”

It’s easy to test, just get a thin piece of lexan from Amazon and paint half of it and tape a piece of Sunbrella over the other half.

Are we talking InfraRed here or UltraViolet?

[Don C L]

If you can get smooth curves out of stainless, or aluminum for that matter, in your garage, more power to you and do you have any videos of it? In my case I am going to be experimenting with an arch of thick wall 1.25" aluminum tubing with sections cut with 11.25 degree angles welded. I want it to be strong.