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Old 29 November 2010, 17:34   #1
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Its a mystery!!!

Posted a little while ago re my 4 metre Narwhal , usual story of tubes failing to hold air longer than a couple of hours, but bizarrely after several bottle of finest fairy liquid , repairing several holes, there are no more obvious leaks (on the seams, the valves or anywhere else obvious) but the boat is still starting to go soft after 20minutes and quite saggy in 2/3 hours.

Appreciate to fix this properly will be a nightmare, and have spoken to Paul @ Tidel re new tubes, but am quite keen to make sure everything else works prior to lashing out on the re tube.

Does anyone have any clever thoughts about where I should look for what must be a reasonable leak, that I can hopefully sikaflex to keep the boat a float long enough (and close enough inshore) to test the engine etc
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Old 30 November 2010, 04:47   #2
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Pump it up a bit harder, ie more pressure and have a good look in those tricky places. My tornado (before retube) had dodgy seams but obviously they were hidden under the rubbing strake and only allowing air out in places that was no where near the actual leak in the tubes.
Also where abouts are you?
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Old 30 November 2010, 06:01   #3
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Hi Jizm,

As you say, I think the only option will be to leave the pump running, to keep the pressure up.

Have tried to seal the end of the rubbing stake, as there was a small amount of bubbles eminating from one end.I have also gone around the underside, where the tubes meet the boat (after having done everything else) and even though the tubes are far from well stuck there does not appear to be a leak.

I was kind of hoping someone would have a flash of genius, but as the title says, its all a bit of a mystery.

Location wise I am down in Southend (Thames Estuary) so if you have any recommendations locally that would be really useful.
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Old 30 November 2010, 07:36   #4
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If it's losing pressure that fast it shouldn't be too hard to locate the leak. How many compartments does it have? Are they all going flat? What is common?
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Old 30 November 2010, 11:57   #5
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As above, if the boat is going down that quickly you should be able to see/hear the leak.

As it is a Narwhal I would go round the seams and rubbing strake with extra attention with your soapy water.

Also, you do have the valves tight and with caps on?

Cheers

Steve
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Old 30 November 2010, 20:49   #6
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I've never done this but I've heard that talcum powder inside the tubes does an ok job at sealing leaks.
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Old 30 November 2010, 21:00   #7
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when you find the leaks, a dab of superglue, then dry it with a hairdryer. this will seal small leaks well
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Old 01 December 2010, 01:25   #8
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Hi Guys,

Thanks for the comments, I think i just need to keep going, the idea with the talc sounds an interesting one, if it works for long enough to test the engine, controls etc, I'll be happy.

All the tubes go flat simultaneously so the internal baffles are shot, (but at least that's talc in one valve and not five) even with the valve firmly shut/caps on the boat still goes soft very quickly.

I did notice that some Narwhals seem to be fitted with emergency pressure release valves and some time in the past these have been removed, so I guess this might explain the internal baffles issue.

I will go round the seams again with more soapy water but really suspect the leak might be somewhere else, the only thing I could think of is somewhere where the tubes met the hull , but this seems a really odd place to pick up a hole or for their to be a seam that has let go.
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Old 01 December 2010, 07:18   #9
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Don't rule out a simple pinhole(s) in the fabric.. Slosh that soapy water carefully and methodically all over.
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Old 01 December 2010, 09:58   #10
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Quote:
Originally Posted by scratch-boy View Post
Have tried to seal the end of the rubbing stake, as there was a small amount of bubbles eminating from one end.
The most telling thing is the bubbles from the end of the rubbing strake, I have seen and repaired a few Narwhals with this problem.

The Narwhal has a seam that runs right around the tube under the strake, if it separates the air tries to find it's way out and sometimes comes out of the end. Put soapy water around the rubbing strake and you will more than likely see bubbles appear where the strake runs across vertical tapes, the problem is you have to take the rubbing strake off to locate the split seam and that could be anywhere if all chambers are going down and if you repair the weakest part of the seam you will normally find it will separate elsewhere afterwards because you have made the weakest part stronger and now the next weakest part will separate, you will be chasing it around the boat.

I agree with Paul Tilley, replace the tubes if you can.
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