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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

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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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Old 01 December 2010, 11:10   #11
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tubes

if you want a cheap way out spray expansion foam the stuff for roadside puntures into the tubes it locates the leak and seals it if you want you can use cavity expansion foam and need never pump it again i have used both with success the latter where the hole is large and have had 2 seasons no prob at all, tubes are expensive and require experieance to correctly install cheers
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Old 01 December 2010, 14:27   #12
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Quote:
Originally Posted by walla View Post
if you want a cheap way out spray expansion foam the stuff for roadside puntures into the tubes it locates the leak and seals it if you want you can use cavity expansion foam and need never pump it again i have used both with success the latter where the hole is large and have had 2 seasons no prob at all, tubes are expensive and require experieance to correctly install cheers
Erm....yeah......

Do not do that (ever)
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Old 02 December 2010, 11:23   #13
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misunderstanding

with regard to the foam that i used ill just explain i carried out the repairs on a jet rib[restricted] that i let my 3 kids mess around with strictly under my supervision and with every safety aspect taken into account except their driveing of course and ill tell you there is not one rock or lobster pot off the west of ireland that they did not strike at some stage, my attitude is to let them make all the mistakes now when i can be there and tell them i told you so, also if i were to buy a new tube every time it would not be possable to have this form of hands on training and fun for my young lads my eldest 14yrs has improved so much with this carry on in the last 2 seasons that soon he will get his own little craft but im not recomending this to everybody far from it, we never go too far from shore and im always always there in my own rib a tomcat [which does not have any repairs] when it comes to teaching them to drive a car its a field and a 100eu car ill use first, this is much the same thing, as any parent will know its expensive to support a family and any little shortcuts can be the differance between looking and doing for the kids im sorry if anybody misunderstood i did not mean that as we all know there is no compromise with water safety
cheers
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Old 02 December 2010, 11:36   #14
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cheak out

have you heard of, tuff coat rib repair if not google it it might be of interest
cheers
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Old 02 December 2010, 13:20   #15
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I'm very sorry, I was not criticising in any way at all, I had in fact meant to reply again to the thread and explain why in my opinion (and from what I have read on here) that is not a good idea, it wasn't anything personal or anything at all in relation to you.

I think that there are two main reasons why people always advise against expanding foam in tubes:
1. It soaks up water extremely quickly
2. It will struggle to regain its shape after an indentation is made.

Some background:
BogMonster's thread

Select quotes:
Quote:
Originally Posted by Tim M View Post
If your talking about filling the whole tube with foam you might want to consider getting a "bladder" made for it instead.
Quote:
Originally Posted by ADS View Post
What ever you do DON'T fill it with expanding foam!!
Quote:
Originally Posted by ian parkes View Post
Expanding foam soaks up salt water like a sponge at least the stuff I have come across does .
I knew a guy who filled the ends of the club kayaks with it and they all wieghed a ton after a little use and sank if they were capsized .
The stuff was near impossible to get out again .
Other related reading:
Foam tubes thread
Another guy who thought about it
Polwart's link to a guy planning on filling a dinghy
Couple of interesting points

I'm very sorry if I caused any offence, but AFAIK very few people have had successful results using the technique. However, if it works for you, I'm not going to stop you

Quote:
Originally Posted by walla View Post
eldest 14yrs
Only 2 years younger than me
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Old 02 December 2010, 15:18   #16
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my faULT

GOTCHIT GUY
absolutely no offence taken or any need for you to say sorry im the one at fault here for not explaining correctly it will not happen again im new to this forum thing but think its brill im also pretty new to ribs sold my beloved draco cruiser 2yrs ago and got the baby ribs but im converted big time,as for the expanding foam, my own sterling moss hit a reef that can be seen from space and ripped a 10in hole in the front of it on the first day of a weeks hols so i put a blow up toy raft in the hole put a section of car inner tube covered with glue at inner contact points over that with a tiny hole for the nozzell and let fly with the foam i then ratchet strapped around the area to regular size[as the foam solidafied] but left the nozzel of the foam can protrudeing and poked this clear reguarly with a coat hanger to allow for expansion, after it cured i patched it like normal with a bike repair kit it worked a treat there are many reasons pointed out in the thread and all are correct in their own way but it all depends what the circumstances are that nesesatate the repair, in a emergency its handy and maybe can help get you home safe and sound its only a small can to carry
cheers bryan
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Old 02 December 2010, 17:07   #17
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Quote:
Originally Posted by walla View Post
my own sterling moss hit a reef that can be seen from space and ripped a 10in hole in the front of it on the first day of a weeks hols
Haha! Sound like me last year

I was ferrying people back and forth from boats-shore which necessitated going round the slipway which extended quite far out, and was 1 or 2 inches below the surface. I haven't really any idea what happened, but I suddenly found the boat on top of said slipway

Conveniently I had chosen the perfect spot for my manoeuvre - right on top of a steel ladder Suffice to say when I relaunched, it quickly began taking on water


Quote:
Originally Posted by walla View Post
i put a blow up toy raft in the hole put a section of car inner tube covered with glue at inner contact points over that with a tiny hole for the nozzell and let fly with the foam i then ratchet strapped around the area to regular size[as the foam solidafied] but left the nozzel of the foam can protrudeing and poked this clear reguarly with a coat hanger to allow for expansion, after it cured i patched it like normal with a bike repair kit it worked a treat there are many reasons pointed out in the thread and all are correct in their own way but it all depends what the circumstances are that nesesatate the repair, in a emergency its handy and maybe can help get you home safe and sound its only a small can to carry
cheers bryan
Unconvential, but I'm glad it worked There's nothing worse than being stranded on holiday with a busted boat
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Old 02 December 2010, 17:37   #18
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Originally Posted by gotchiguy View Post
I'm very sorry, I was not criticising in any way at all, I had in fact meant to reply again to the thread and explain why in my opinion (and from what I have read on here) that is not a good idea, it wasn't anything personal or anything at all in relation to you.

I think that there are two main reasons why people always advise against expanding foam in tubes:
1. It soaks up water extremely quickly
2. It will struggle to regain its shape after an indentation is made.
On this occasion it may not be crazy though. The OP has accepted it needs new tubes, he just wants a short term way of testing the engine and hull to decide if it worth parting with big bucks for new tubes - or if he should scrap the whole boat....
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Old 02 December 2010, 18:05   #19
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Let's go back to the beginning chaps!!

He is trying to find the leak!
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Old 03 December 2010, 01:06   #20
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Dear All,

Thanks for all the input, in real terms, we are talking about a 4m Narwhal NK400 with an 81 Mercury Blueband thunderbolt, the engine has been seen running both in and out of gear, pumps water well, and has a good smooth tick over. The tubes will stay in shape for maybe 30 minutes before starting to go soft and and then loose shape in a few hours.

The boat was brought off ebay for 600 in a moment of madness as an upgrade to a 1yr old 2.7 m Plastimo with a 3 yr old Mariner 9.9 mostly used in the Thames Estuary by my 13year old son, in the full awareness that the tubes needed some work. The proper Rib will allow more use when the wind/sea state picks up a little & can generally be stretched a little further.

In the 1st place, If I had done the research on older Narwhals, probably wouldn't had made the purchase but having had a look, can probably justify the re-tube as equivalent Hyperlon boat will certainly cost more than a couple of grand.

As I mentioned at the top, the target is to make sure everything else works before lashing out on the tubes, but suppose that the other question could be whether I am better scrapping the hull and selling the motor, trailer etc and looking to start again while adding the money for new tubes but doubt this will stretch to an SR4 which seems to be the choice for a smallish Rib.

All opinions welcome
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