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Old 30 October 2006, 08:29   #1
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Inner tubes?

Gemini Industries inner tubes

Found this on here but that is the only comment on these I can find.

Anybody else use them, that might have missed that last thread?

Might be an economical solution to my disintegrating boat .... though I don't like the sound of having chafing problems? It would have to be deflated when tied to the marina (to guard against getting too hot and going bang!) and then the tube might chafe on the inner tube? It's quite choppy compared to what most people would expect to see in a marina, the boat bounces around a bit sometimes.
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Old 30 October 2006, 12:22   #2
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Given your current situation, I can't see how chafing problems would even concern you.

Personally, I'd go for a complete re-tube, assuming sufficient funds are available (or attainable.)

Best of luck, Stephen;


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Old 30 October 2006, 12:26   #3
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Given your current situation, I can't see how chafing problems would even concern you.

Personally, I'd go for a complete re-tube, assuming sufficient funds are available (or attainable.)

Best of luck, Stephen;


jky

I think the problem is finding someone to do it on a small island in the North Atlantic

Best of luck too Stephen.
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Old 30 October 2006, 14:26   #4
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I think the problem is finding someone to do it on a small island in the North Atlantic

Best of luck too Stephen.
Aye.

It's even worse on a small island in the South Atlantic

Thanks for the good wishes!

For peace of mind I probably would do a complete re-tube and I might even tackle it myself over next winter, but I can't get anywhere to do it in a remotely dry or temperature controlled environment, trying to do it outside is a bit of a non starter - today there is about 35kt of wind so the new set of tubes would be last seen at about 200 feet heading towards the minefields on the south coast!!
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Old 30 October 2006, 14:52   #5
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Matt,

Was upside down trying to get his Gimp suit off when he wrote that one. LOL.
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Old 30 October 2006, 14:53   #6
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I think the problem is finding someone to do it on a small island in the North Atlantic

Best of luck too Stephen.
Matt,

Was upside down trying to get his Gimp suit off when he wrote that one. LOL.
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Old 30 October 2006, 15:04   #7
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Matt,

Was upside down trying to get his Gimp suit off when he wrote that one. LOL.
You can say that again!
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Old 30 October 2006, 15:19   #8
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stephen,

When I heard of your latest woes - this was certainly the solution that jumped to mind.

I would speak to Gemini - I don't think you would need to deflate the tubes all the time. Even if you inflate them to 5 psi at 0 deg C and it heats up to 60 deg C without finding anywhere to expand to (probably less of an issue for an inner tube than an actual tube - which is fixed rigidly to the hull) the pressure will only be 6.2 psi.

If nobody here can act as a reference - then Gemini should be able to point you to someone that can. Tell them you will post the results here - and they might even give you a discount for the advertising

If the plan is to replace the tubes eventually anyway this could be the way to go -- and doesn't look too expensive - compared to a retube. If it works well you might even keep them (they have a 6 year garuntee - longer than your original humber tubes!).

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Old 30 October 2006, 15:33   #9
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Matt,

Was upside down trying to get his Gimp suit off when he wrote that one. LOL.

Well I'M not the one who was taking pictures...
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Old 30 October 2006, 15:36   #10
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Even if you inflate them to 5 psi at 0 deg C and it heats up to 60 deg C without finding anywhere to expand to (probably less of an issue for an inner tube than an actual tube - which is fixed rigidly to the hull) the pressure will only be 6.2 psi.
Really? I'd have thought it was a lot more than that, purely going on "feel" (I have no pressure gauge). The tops of the tubes have black wear patches on them and a couple of weeks ago I saw them go from slightly sagging one day (to the extent of there being wrinkles in the tubes) and then zinging tight the next day in about 18 deg C and direct sunshine. I let some air out of them because I was worried they were too hard! But maybe it was only a few psi then, how do you work out the pressure change with temperature?

I'm waiting for advice from Paul T at the moment on supply/pricing for new tube ends, after that I'll decide what to do. It'll probably be whatever is the lightest and quickest option to get here by air, and see where it goes from there.

It would just be nice if I only had to throw money at it for fuel (which is bad enough), rather than every bloody thing else as well
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Old 30 October 2006, 15:51   #11
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Really? I'd have thought it was a lot more than that, purely going on "feel" (I have no pressure gauge). The tops of the tubes have black wear patches on them and a couple of weeks ago I saw them go from slightly sagging one day (to the extent of there being wrinkles in the tubes) and then zinging tight the next day in about 18 deg C and direct sunshine. I let some air out of them because I was worried they were too hard! But maybe it was only a few psi then, how do you work out the pressure change with temperature?
its either Boyle's law or Charles' law I can never remember which is which. But anyway :


Assuming the total amount of gas stays the same, and the volume is fixed (its not - but near enough - and the volume is getting bigger - so will relieve the pressure).
pressure at high temp = pressure at low temp x (high temp / low temp).
TEMPERATURES MUST BE ABSOLUTE - i.e. deg C + 273.
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Old 30 October 2006, 16:20   #12
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OK, so a 20 degree increase in temp is not going to make a very big difference in pressure. Interesting, thanks

On the theme of inner tubes, are there any other manufacturers apart from Gemini? I am told somebody here got a set of really heavy duty ones that needed to be inserted by cutting the end off the cone and have lasted for years, but I haven't caught up with him yet. Sounds like a different product to this but Google was mostly silent on the subject. Must be UK based, not worth the hassle of trying to get stuff shipped here from the States etc.
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Old 31 October 2006, 05:19   #13
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OK, so a 20 degree increase in temp is not going to make a very big difference in pressure. Interesting, thanks
I beg to differ. On a hot summers day with dark coloured tubes they could be pumped up hard, but by dusk they will be soggy just down to changes air temperature during the day.

An idea - If its just the cones that are gone and the rest of the tubes are fine you could try solid end cones out of GRP, been done before. I think some of Dave Pictons early ribs had these.

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Old 31 October 2006, 06:17   #14
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An idea - If its just the cones that are gone and the rest of the tubes are fine you could try solid end cones out of GRP, been done before. I think some of Dave Pictons early ribs had these
Where would those be available from? Just thinking about it I guess they might be a lot easier to fit than floppy ones!

Forgot to take photos of it yesterday, will do it at lunchtime if I remember, and post tonight...
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Old 31 October 2006, 06:32   #15
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Where would those be available from?
your going to have to make a plug and mould two (if the wifes pans set isn't close or you can't find a paint / chemical drum the right diameter, or try e mailing Dave Picton to see what diameter theres were.

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Just thinking about it I guess they might be a lot easier to fit than floppy ones!
Agreed the thought of trying to glue a floppy end cone into a deflated tube thats covered in contact glue, hmm
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Old 31 October 2006, 07:30   #16
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I don't think you would need to deflate the tubes all the time. Even if you inflate them to 5 psi at 0 deg C and it heats up to 60 deg C without finding anywhere to expand to (probably less of an issue for an inner tube than an actual tube - which is fixed rigidly to the hull) the pressure will only be 6.2 psi.
Neil . Assuming an 18" dia tube compartment 48" long, I make that about 1.44 tons of increased load for that tube compartment to contain.
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Old 31 October 2006, 11:30   #17
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Agreed the thought of trying to glue a floppy end cone into a deflated tube thats covered in contact glue, hmm
The thought of ending my days starving to death while irrevocably bonded to the punctured wreckage of an inflatable boat had crossed my mind
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Old 02 November 2006, 09:07   #18
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stephen you could try covering a circle of ply and sticking that in the end of the tube .it does work i have seen it on some of the p&o ferries rescue boats
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Old 02 November 2006, 10:53   #19
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Neil . Assuming an 18" dia tube compartment 48" long, I make that about 1.44 tons of increased load for that tube compartment to contain.
Jeff, I haven't checked your calculation - but that is certainly one way of looking at it. I don't think you would inflate to 5psi normally anyway - more like 2-3 so the increase is also proportionately smaller. My point was that if "nominal" pressure was x, then ~20% over doesn't seem that high. (and that is in the extreeme case of filling at freezing and it reaching 60 deg C).

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I beg to differ. On a hot summers day with dark coloured tubes they could be pumped up hard, but by dusk they will be soggy just down to changes air temperature during the day.
I think this is a slightly different phenomena. When the tube is inflated to normal working pressure it has essentially reached its maximum volume (in this case the inner tube has reached the volume determined by the hypalon outer) and therefore any heating either has to "stretch" the fabric - or increase the pressure. However, if a tube is firm when hot and then cooled down, the volume of the tube can contract as well as reduce in pressure.
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Old 02 November 2006, 12:10   #20
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I think this is a slightly different phenomena. When the tube is inflated to normal working pressure it has essentially reached its maximum volume (in this case the inner tube has reached the volume determined by the hypalon outer) and therefore any heating either has to "stretch" the fabric - or increase the pressure. However, if a tube is firm when hot and then cooled down, the volume of the tube can contract as well as reduce in pressure.
Hmm, I think its the same thing and agree with what you saying. So at 30.c on a hot summers day the tubes are hard and at 10.c that night they are soggy - so a huge difference in tube pressure with a change of 20.c in temperature. Pump them up at night time and leave the boat cover on during a hot summers day and you could end up with a burst seem, probably along the weakest link.

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