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Old 04-09-2008, 06:45   #16
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Originally Posted by Jack Long View Post
Zach- run with me for a bit and lets see if we get somewhere.

Witz- I hear your concern but I am not sure its correct. PVC isn't all that brittle. A long piece has a LOT of flex. If I can't imagine a scenario where it would snap into an impaling device that didn't also involve me going overboard. At that point we may be dealing with a gunshot or stabbing sort of scenario. Maybe you mean with the fiberglass wrap? In which case...

I don't think I would do any stiffening work. I think for the application I have in mind the structural properties of PVC would be okay- my main concern is degradation from the UV. I would love a bimini frame that I could hang and monkey around on. Failing that, my goal is shade. Heavy winds pulling on the cover could certainly represent a problem but I don't think light and medium winds would be too much trouble- just like sail I would reef early and often. And it would be cut-away-able.

What I am thinking is a three piece design. Blue is the PVC pipe itself.

The first piece is a cage where each of the verticle posts has two "T" fittings and a 3-way fitting. I would use the 3-way fittings to create a square shape with 4 legs. The two "T" fittings would brace the legs together to add lateral strength. This contraption would be held to the boat with some lines tied around the 3-ways and going down to the deck. Green are 3-way fittings, yellow is "T" fittings, purple is line.

The second and third would be two simple rectangle pieces that are the same length as the cage but each slightly more than 50% of the width. I would tie these together and then to the frame to create a peak. Red is a standard corner fitting.

The black lines show canvas draped over the whole thing then tied to something on the deck. If the wind did come up it could take the canvas and leave the PVC. If there is enough wind to snap PVC based on its own resistance I've got WAY bigger problems.

Why not just buy an EZ-UP?? I am constantly amazed at the lengths some will go to, to chew on a penny and poop out a diamond..

Try haunting the local canvas shops for some throw-away stainless bows. In time you'll find two that meet your criteria. Oh and yes PVC becomes very brittle with a little UV and some colder temps.

Trust me I've tried PVC for winter cover frames and had it snap and impale a $400.00 cotton duck tarp with very sharp edges..
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Old 04-09-2008, 06:54   #17
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Yves Gelinas of Cape Horn Windvanes made a dodger out of PVC pipe and canvas for his Alberg 30 and circumnavigated. I suppose the same principle could apply to a bimini.
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Old 04-09-2008, 06:56   #18
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I am constantly amazed at the lengths some will go to, to chew on a penny and poop out a diamond..
That was my good belly laugh of the day. Thanks man.
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Old 04-09-2008, 07:04   #19
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PVC isn't something I would want to grab onto if I was being thrown overboard....sheet happens. You could apply a zipper to the back of the dodger. Cleat off an expandable pole to the backstay. One zipper, a hole for the pole to slip through, and a couple of rear tie downs.. You can roll it up in a minute for night sailing, or extreme weather, and will look a whole lot more professional than PVC.
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Old 04-09-2008, 08:52   #20
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That was my good belly laugh of the day. Thanks man.
I gotta agree! I'm guilty of that... but 1 in 10 work out, the rest just teach you something, and show what not to do...

Jack:

I think in that design the legs would be most apt to break. It's going to flex enough side to side and forward and backward to want to snap something. Or at the least, not inspire much confidence.
Most of your stiffness comes from diameter (geometry) while breaking strength results from wall thickness. (mass) I don't know the dimensions you you are working with... but 4 three foot pieces of pipe are going to want to flex quite a bit with any wind, or if someone wants to grab hold of it. You could do it but unless you are using heavy wall, and 1 inch or larger I'd figure out a different way. I built a set of guide pipes to line up a powerboat on its trailer. Heavy, but not going anywhere, I grabbed the end and gave it all I could and it didn't complain. Sheesh, they are unsupported for all but the bottom foot and you can lay a powerboat against them...

You could get around some of the weight and flex possibilites by triangulating with some 45 degree T's... But they can be a pain in the rear to get lined up and measured properly. Choice is either to go leg to leg, or from you horizontal cross bars to the legs as corner gussets.

I would ditch the two free floating rectangles that lash on to form the peak. A T fitting and a 90 degree elbow on each side would give you a peak. If its free floating, you get all the weight without any strength.

(Or just don't put a peak... and make it into a water collector when it rains. )

Any of your cross bars (like the double runs of pipe running horizontally under the fabric) I'd do with t's and 90 degree elbows, so that the load is carried through a different plane, rather than just adding mass... Might even keep some drips from running into the cockpit too.

If you choose to run them parallel and in the same plane, the further apart they are the stiffer it'll be. So if you can, a foot or so shortens the unsupported span of the legs, and stiffens each of the panels. Probably make life difficult to climb into the cockpit though...

You can shorten the unsupported spans of both horizontal pipes, by using two T's, and a short stubby piece of pipe to connect them.

In my last post I was envisioning a set of hoops attached to the deck by a hinge, like a conventional bimini. So the whole mess could lay down on deck. Be heavier than aluminum for the same strength... but no reason why you can't reach the same breaking strength as aluminum with thicker material and a little bit of thinking. (Or a little fiberglass... )

I'd use the purple primer, so you can see that everything is covered... and paint the whole structure when you are done.

Cheap, strong, or pretty. Pick any two...

Zach - Humming Weird Al's song... Dare to be stupid.
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Old 04-09-2008, 10:58   #21
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That sounds wonderful! I actually started this process hoping to create a "sport cage" out of tubing. Sort of a bimini frame, dodger, davit, hoist, solar mount, wind gen mast, and roll cage all in one. Oh, and with lots of places to put stuff too- fishing rods, hammock...

The trouble is I can make this out of PVC for about 37 dollars. 37 dollars would buy me about 4 feet of tube. I could still make the frame- it would just be really small- and I wouldn't fit under it.

The arguments about replacement cost of PVC over time are fairly compelling. It is similar to the inexpensive battery logic. Or buying a home instead of renting. I always lose some steam after reading them because "I get it" but ultimately I need a solution so I have to find a solution.

Just wait until I start my "outboard mount" thread. I am thinking plastic wrap. Elmer's Glue, and toothpicks.
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Old 04-09-2008, 12:30   #22
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Jack,

Not many are tighter fisted with a buck than I. Sometimes cheap is not the way to go. One last mention of....... this is not something I would want to grab onto while falling. Something strong can save your life. Some weak just might impale you, or let you go over the side.......BEST WISHES in your choice......i2f
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Old 04-09-2008, 13:12   #23
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I hear you. And I hope it isn't your last comment!

Let me ask you this though... My choice (at this time- these things change) isn't tubing vs. PVC. My choice is no frame vs. PVC. The boat came with this goofy thing you could hang from the backstay and attach to the dodger but it barely stays up when there is NO wind...

So, the question is:

Is a PVC frame worse than nothing?
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Old 04-09-2008, 13:31   #24
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Jack,

No I wouldn't stop commenting. We all need help in figuring this thing, sailing, out. It's just that I have been thrown from my boat, so I may have a strong opinion on staying aboard.

I will look for some better pics that show how my shade was attatched. I sailed with it in storms. The good thing is you are always looking for a way to accomplish something. That is the personality that will survive some tough times....
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Old 04-09-2008, 14:33   #25
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I was going to use the big stuff- 2 inch or whatever- for the frame and maybe 1 inch for the top piece. I don't want a 90' peak, it will be too tall. I thought about using a 45' but more than the peak I need the pipe that would run lengthwise down the center and they don't make 3-way 45' pieces. They also don't make any inside angles as far as I can tell.

I need very little peak. I could actually just lash another piece- lengthwise down the centerline... cut it a little longer than the whole thing.

Remember- the cover won't attach to the frame at all. It will lay across it and be strapped to the deck- pushing down on the frame. I made a profile view that includes the current systems so you can see... It would be under the mast but over the dodger.
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Old 04-09-2008, 14:38   #26
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Think about the configuration making it hard to get in, and out of the cockpit. Especially it if continues forward past the dodger. Will the straps catch your ankles & feet?
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Old 04-09-2008, 14:59   #27
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Just a thought about a canvas shop in S.F. North Beach Canvas at Pier 40 in S.F. is a great place. Elizabeth is smart, resourceful, and helpful. She made the arch for me for my solar panel. I bought all the pieces, and put it together. If you decide if you need some help from a canvas shop. Give Elizabeth a call.
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Old 04-09-2008, 17:55   #28
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It's just that I have been thrown from my boat, so I may have a strong opinion on staying aboard.
Imagine makes a good point here. Think about it. When and if you lose your balance, your natural tendency is to grab the closest thing. Make sure it can hold your weight. Make it strong. Because we can not afford to loose you and your stories.

Good luck man
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Old 06-12-2009, 20:49   #29
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Originally Posted by Jack Long View Post
I was going to use the big stuff- 2 inch or whatever- for the frame and maybe 1 inch for the top piece. I don't want a 90' peak, it will be too tall. I thought about using a 45' but more than the peak I need the pipe that would run lengthwise down the center and they don't make 3-way 45' pieces. They also don't make any inside angles as far as I can tell.

I need very little peak. I could actually just lash another piece- lengthwise down the centerline... cut it a little longer than the whole thing.

Remember- the cover won't attach to the frame at all. It will lay across it and be strapped to the deck- pushing down on the frame. I made a profile view that includes the current systems so you can see... It would be under the mast but over the dodger.
What did you end up doing?
Do you have any pic's?

Regards,

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Old 07-12-2009, 16:15   #30
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Instead of PVC, how about making it from galvanized conduit? My winter frame is made from 7/8" conduit, with the larger pieces breaking down into 2-3 parts for easy storage.

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