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Old 24-07-2018, 08:37   #1
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Inflatable inner diaphragm repair

I have a WM/Zodiac. It is about five years old. A couple of years ago my wife and I accidentally dropped it on its side on the beach. The pressure of falling on one side damaged the inner diaphragm that prevents a single puncture from completely deflating the dinghy. It seems like a difficult repair at best, requiring opening up one or more seams then closing the seams up again successfully.

I was wondering if anyone has encountered a dinghy diaphragm rupture and managed to successfully repair it with typical DIY tools and experience.

Given that this is a PVC dinghy with five years on it, I might assume a replacement in in our near future and use this as a learning experience.

Suggestions on the repair process?

Harry
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Old 24-07-2018, 11:11   #2
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Re: Inflatable inner diaphragm repair

The adhesive will not work unless you have an air conditioned workshop. The carrier solvent is hygroscopic and absorbs moisture from the air. When it starts absorbing moisture from the air, it reacts negatively with the isocyanate reactant, which breaks down in to gaseous CO2 and non-helpful liquids (such as urea). This whole reaction trashes the bond strength of the gluing, and your patchwork falls off in two weeks.

It can be done though.
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Old 24-07-2018, 11:27   #3
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Re: Inflatable inner diaphragm repair

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Originally Posted by KD8NPB View Post
The adhesive will not work unless you have an air conditioned workshop. The carrier solvent is hygroscopic and absorbs moisture from the air. When it starts absorbing moisture from the air, it reacts negatively with the isocyanate reactant, which breaks down in to gaseous CO2 and non-helpful liquids (such as urea). This whole reaction trashes the bond strength of the gluing, and your patchwork falls off in two weeks.

It can be done though.
I have a dehumidifier set for 45% in my basement. Hopefully that will be dry enough. Is a 2-part adhesive any more forgiving to humidity?

What about repairing the diaphragm? I'll need to open up the seams. Do you have a suggestion of how to do that in a way that I can join them back up when done?
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Old 24-07-2018, 11:31   #4
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Re: Inflatable inner diaphragm repair

Quote:
Originally Posted by hlev00 View Post
I have a dehumidifier set for 45% in my basement. Hopefully that will be dry enough. Is a 2-part adhesive any more forgiving to humidity?

What about repairing the diaphragm? I'll need to open up the seams. Do you have a suggestion of how to do that in a way that I can join them back up when done?

That'd work. Temp is important too.

And that is two part adhesive I'm talking about, one part adhesive is premixed and junk...

The term is "baffle".

To repair the baffle, it is better to cut open the tubeset with a fresh razor in an easy-to-access area. You'll need to make the cut big enough to access the baffle. West Marine by Zodiac inflatables have welded seams, so you can't separate them anyways.

Repair the baffle, then make an inside patch and outside patch on your way out. If you're a pro, you'll remove an accessory such as a d-ring, handle, logo, or floor seam, do all of the work, then re-install the accessory to hide your inside-outside patch.
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Old 25-07-2018, 15:27   #5
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Re: Inflatable inner diaphragm repair

Your repair will probably be weaker than the rest of the skin so if you are going to cut the tube open for access you should make your cut around the tube rather than along it as the greatest stress is the hoop stress around the circumference of the tube .
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Old 25-07-2018, 16:07   #6
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Re: Inflatable inner diaphragm repair

The glue I use on PVC is Bostik 1669. It requires some care if the repair is to be a good one.

Personally I would not bother fixing your Zodiac. Dump it and buy a Swift, an Achilles, or some other Hypalon craft and leave the PVC in the garbage. Better still--get a Polycraft or its American equivalent if there is one.

However--to get back to patching the boat. Once you have to patch it, it can never be inflated to the level it was with welded seams. Personally, I never inflate them hard anyway, because the sun heats them and they develop excess pressure which ruptures the hull. There is no NEED to inflate them hard. If you want it to last--do not do so. I got five years out of mine--and it was a BASTARD on fuel with its stick-to-the-surface inflatable floor and keel--and a pig to row. I fitted mine with a honeycomb-glass floor I made and solved the problems--temporarily.

Back to patching your PVC Zodiac.

Clean off the area you wish to patch both inside the hull edges of the hole as well as outside using MEK or acetone. This leaves the surface a little tacky. Using a cheap disposable brush, paint it with the glue on the INSIDE of the hull edges of the tear or seam. Allow it to dry thoroughly.

Now prepare your patch, a piece of the same sort of PVC, by cleaning it on the one side, and then painting it with glue and allow it also to dry completely. Do not touch either surface, and keep them free of dust.

Return to the hull and re-glue over the already dried glue. Let it dry once more. It is messy so wear disposable polyurethane surgical examination gloves, I buy 'em by the box.

Return to the patch and apply another layer of glue. Let it also dry, not quite as thoroughly as before though Just dry to a light touch (wearing gloves).

Now you need to have a large strong paper clip or a couple of clips--the sort that you have to squeeze to open. If the repair is to be a long one--you may need two of them. Place a piece of polythene over the middle of the patch, fold it in half, and put your clamp on it so that the surfaces without glue on the back of the patch are pressed together and the glued surface is protected by plastic where the clamp holds.

Open the seam, and work your patch INSIDE the hull, holding it by the clamp so it does not drop inside the hull. Some people use string threaded through the patch and back out again to get a better grip. It does provide a couple of holes though--but these may not be a problem as they are comparatively more easily fixed. Make sure these holes are on the join in the seam.

This paper clamp does not hold strongly , so the sooner one gets this interior patch in place the better. Ease the seam apart and gently insert the patch making sure only the plastic shield makes contact with either glued surface. As soon as one end is in place reach in with a pair of curved long nose pliers and, still holding your patch with the clip, and the other third hand behind the hull pushing from the other side, begin to peel off the plastic. The instant the glued surfaces come in contact they will try to stick together, so the seam has to be folded over the patch as the plastic is withdrawn. As soon as the end is glued, one can reach the patch from the other side of the hull to push it into place over the seam, and the clip can be removed and the seam and patch pressed together over the whole length of the opening.

Now get a hot air blower, and heat the entire patch area quite strongly while firmly pressing the patch into place from the outer side of the thoroughly deflated hull. Tap it firmly but not too firmly with a flat-faced hammer against a block of wood. Allow to cool.

Now, move to the outside patch. If you had used strings to hold your patch instead of a clip--strings being more reliable but leaving holes, you will have to patch these holes.
For this I inject a little polyurethane glue while keeping the repair as horizontal as possible. This stuff foams and spreads--making a satisfactory sort of seal, since the air pressure of the completed hull will hold it on instead of trying to lift it off,, The same logic as for the interior patch. The patch should still be clean so it should stick OK.

Now to the exterior patch. This one will be much easier to do--but it is the interior one that will be the strongest in resisting impacts on the hull--the exterior one is to reinforce it, and greatly increase the bond strength as it will be in double-shear.

Pretty much the same process--but you might try THREE layers of glue instead of two--just to be certain. Heat it when you have rolled and tapped the patch into place, working from one end to the other and ensuring a good contact. Now heat it with an air gun to quite warm, put a flat block of wood over the entire sandwich and one behind it, and use three G clamps to press the whole job tightly together and leave overnight. In the morning take off the clamps and half-inflate the hull--just enough that the patch is lifted from the other side of the hull, and no internal adhesion is possible however unlikely.

Leave it for at least another day---then inflate it to about 2.5 to 3 psi no more--and test it for leaks with detergent and a brush. If it is OK--you are good to go.
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Old 25-07-2018, 17:52   #7
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Re: Inflatable inner diaphragm repair

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However--to get back to patching the boat.
Mike, excellent job of describing a complicated process! Well done.

Jim
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Old 25-07-2018, 18:09   #8
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Re: Inflatable inner diaphragm repair

A lot of years ago, when Zodiacs were higher quality, we had a diaphragm blow out. took it to a Zodiac repair facility in Red Hook, and he really didn't want to do it. Felt that the repairs would sacrifice the integrity of the rest of the boat. We kept it for a few more years, then it was complete junk.
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Old 26-07-2018, 05:14   #9
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Re: Inflatable inner diaphragm repair

Quote:
Originally Posted by Mike Banks View Post
The glue I use on PVC is Bostik 1669. It requires some care if the repair is to be a good one.

Personally I would not bother fixing your Zodiac. Dump it and buy a Swift, an Achilles, or some other Hypalon craft and leave the PVC in the garbage. Better still--get a Polycraft or its American equivalent if there is one.

However--to get back to patching the boat. Once you have to patch it, it can never be inflated to the level it was with welded seams. Personally, I never inflate them hard anyway, because the sun heats them and they develop excess pressure which ruptures the hull. There is no NEED to inflate them hard. If you want it to last--do not do so. I got five years out of mine--and it was a BASTARD on fuel with its stick-to-the-surface inflatable floor and keel--and a pig to row. I fitted mine with a honeycomb-glass floor I made and solved the problems--temporarily.
"Once you have to patch it, it can never be inflated to the level it was with welded seams." - This is not correct. The OEM Bostik S.A. adhesive used by Zodiac is rated to a 13 psi overpressure.

Personally, I never inflate them hard anyway, because the sun heats them and they develop excess pressure which ruptures the hull. There is no NEED to inflate them hard. - In my time working, selling, and manufacturing inflatables, I have condemned hundreds of boats and denied warranty claims due to damage from underinflation. It causes the material to delaminate, just like flogging/luffing does to your sails. I have never had a properly inflated boat rupture. I have also never had a boat rupture due to overinflation. I have had boats rupture due to old/aging glue on 20 year old Hypalon boats though, or zipper-open because the material is severely degraded and people think Hypalon lasts forever (it doesn't).

You can deflate them a little for storage, but they should be maintain at manufacturer's specification during operation or towing. Use a pressure gauge. Adjust the pressure through the day / evening.
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