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Old 13 December 2006, 14:33   #11
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Originally Posted by codprawn View Post
Would there be cause for concern regarding the baffles in the adjacent tube? It could be possible for there to be a gap between the new inner and the baffle which could put strain on it - a bit like fully inflating 1 chamber with the next one empty.
I believe the idea is that you inflate the sausage to a slightly flaccid state (ooer) then stuff it in till the end hits the baffle between the sections and then blow it up, so the baffle should be mostly supported by the end of the sausage I think. When I chop the end off my dud toob to stick the new end in that Paul made for me, I'm going to measure the distance back to the baffle so I already have the measurement without opening the tube, if it looks like I need to order the sausages!

I suppose you could say that if the baffle isn't man enough to hold the air pressure of a fully inflated tube then it isn't going to be much use if you get a puncture (same situation - full pressure fighting no pressure) which defeats the object of having sectioned tubes

There seem to be some concerns about the Gemini type inner tubes chafing on the inside of the tubes because of their thin construction, I think I would rather have a full-strength hypalon tube even if it were more expensive. Damn I'd even fit concrete tubes if it was the only way to stop the thing going flat
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Old 14 December 2006, 05:58   #12
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gemini inner tubes

Here's some recent correspondence I've had with Jack at Gemini. Interesting point about the old valve damaging the new inner - I'd cut out the old valve just to be safe:

1. The bow on my Delta is high and very pointy when compared to other RIBs - will the 2 inner tubes for the nose deform enough to completely fill the existing tubes when they squash together?
A. Yes they will fill perfectly.

2. How do the inner tubes work with the inter-chamber baffles in the existing tubes i.e. one tube may end up with a convex end as expected, but it's neighbour may as a result have a concave end with strain on a crease?
A. Each inner tube has to be installed overlapping the next one by about 20cm, They then blend into each other.
This is why you measure the chamber from the seam where the baffle is attached to the next. This works out to be the length plus 15%.

3. Measuring which lengths to order will be an estimate based on where the existing baffles are. Is it better to order the inner tubes slightly larger than estimate (and risk folds)or slightly smaller (and risk stretch)?
A. Longer is essential, creases have no bearing on the tube life, it is not a problem.
I would recommend the 0.68mm thick tubes which are the standard price on the web site, 1mm. have to be shaped to be a perfect fit.

4. How do you know where to cut the hole for the valve?
A. The valve is in the middle of the inner tube, same for the hole in the boat, the midpoint of the chamber the tube goes in.

5. Any issues with patching the insertion slit to minimise the risk of the slit extending?
A. You can put a strip of fabric over the cut and glue it at the top and bottom, leaving a "hand hole" for future use if . for example the tube is punctured.
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Old 15 December 2006, 09:53   #13
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would it not be better to make a 700mm long insert with valve in the cone ,put this in the end of the old tube glue up and inflate in place . as long as the old valve is far enough forwards in the rear chamber you have now added an extra chamber each side of the rib and fixed the cone end problem .
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Old 15 December 2006, 14:15   #14
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Originally Posted by paul tilley View Post
would it not be better to make a 700mm long insert with valve in the cone ,put this in the end of the old tube glue up and inflate in place . as long as the old valve is far enough forwards in the rear chamber you have now added an extra chamber each side of the rib and fixed the cone end problem .
Another good idea, will do some measuring and I might go for that though I do like the idea of the whole thing being removable in the event of any problems and also having a double layer of hypalon all the way down the aft chambers.

A seven chambered RIB would be verging on unsinkable, in fact I might even re-name it Titanic II. Then again maybe not...

I also thought of another idea which is that if you put relief valves (which I wish I had fitted) in the new sausages, and blow up the sausages first then the middle chambers and then the bow chamber, you would have some overpressure protection for the whole lot because the relief valves in the sausages would blow off at (say) 5psi and then the baffles would deform to reduce the pressure in the forward chambers.

Lots of options anyway, which is lots more options than I had a week ago
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Old 15 December 2006, 14:29   #15
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Originally Posted by BogMonster View Post

A seven chambered RIB would be verging on unsinkable, in fact I might even re-name it Titanic II. Then again maybe not...
Stephen, your tempting fate again
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Old 15 December 2006, 15:41   #16
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Stephen, your tempting fate again
Yep. Forecast says 50 knots of wind tomorrow, after the champers bottle bounces off the tubes in the renaming ceremony I might go out for a spin and see if I can make it fly straight
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