Leaky side tanks

[Nick in Bristol]

I've been lucky with previous boats being bone dry inside but my Cherub seems to have a couple of leaks.

Any one have any tips on how to check for where the source of the leak is, and then the best way to fix it.?

[JimC]

What boat is it? Which one- and what construction?

Side tank to cockpit floor joins were always notoriously troublesome in pre foam sandwich days: its because you stamp on a slighly flexy floor right next to the solid vertical side tank side. They can be sods to fix, depending on how the boat is built.

[Nick in Bristol]

It's 2654, a Flying Trifle design. Kevlar construction with no sign of any foam, at least in the side tanks.

I've had my borescope camera in both tanks but can't see anything obvious.

I'm thinking lots of flexible sealant and then a bucket-load of expanding foam to give some rigidity. Sensible or madness?

[tim_unerman]

Hi Nick
I think what Jim means is that some older cherubs were built with just a single skin of glass fibre or Kevlar I would think that the trifle would be a foam composite i.e. a few layer of composite either side of 8-10 mm thick PVC foam. This give a stiff light structure.
I would not fill the side tanks with expanding foam for the following reasons:
1)   The builders style foam absorb water thus would end up heavy
2)   It is a lot of extra weight in a light weight boat
3)   It still does not stop the leak.
From previous experience of leaky boats water normally get in through the fittings / hatches. The best way to check for how much of a problem you have is as follows:
1)   Put all the hatches / bungs in the tanks
2)   Leave the boat in the sun for a few hours to warm up
3)   Release hatches and if there is any pressure built up then the leak in quite small.
My personal method for finding leaks in boats is to find an spare bung / hatch cover then drill a hole in it, pass a small length of hose part way through this then seal the hose to the hatch.
Put the hatch / bung in the tank and blow / attach a compressor to it to create pressure, then chase round the tanks to check for leeks also using soapy water can help with this stage as, as the air escapes the soaps bubbles.

Hope this helps.

Tim
Part time cherub sailior

[Neil C.]

I would strongly advise against trying to fill the buoyancy tanks with expanding foam, as Tim says above. In my experience hardly any tanks are absolutely 100% watertight. Even those which are will develop some condensation on the inside in damp or cold weather. The expanding foam makes it impossible to get this water out again, and the boat will just get heavier and heavier. It's also virtually impossible to remove the foam once it's in without cutting the boat to pieces. The usual leakage points are where the tank side meets the floor, or through any screw holes for fittings etc. One of the biggest culprits is often the inspection hatches - usually the ring doesn't seal very well to the wall of the tank especially if there is any curvature in the panel. I have used silicone bathroom sealant (the clear stuff) with good results for leaky hatch rings in the past, but it may need re-doing every year or so as it's not really designed to cope with sea water, extremes of temperature and direct sunshine.

[JimC]

yep, agree with all above... Yours is a foam sandwich boat and they don't tend to suffer from intrinsic weakness round the tank/floor join like wood or single skin glass boats. You need to do all the usual stuff to search for leaks I'm afraid: very unlikely to be anything you can see with the scope. There's no point is just stuffing a flexible filler everywhere in the hope of sealing the leak: you'll spend any amount of cash on the damn stuff and the actual leak will turn out to be somewhere you never even considered when you were smearing it on... Having said that top of the list for leaks are hatch covers and bungs, (both through the bung/cover join *and* round the outside of the fitting, and sealing those up could be useful for testing. If you use Tim's method with pressure be *very* wary of putting very much pressure in there...  There's also the good old technique of putting the boat in the water on her side on a calm still day, sitting three people on the upside so the tank is immersed, and go looking for bubbles!


And yes, like the others say, expanding foam in the tanks will *at best* ruin the boat.

[Neil C.]

There is another leak-finding technique which I tried a few years ago. I would definitely NOT recommend doing it as it's probably very bad for the structure of the boat, but...
Basically it's the inverse of Jim's technique above. You put the boat on it's side on the lawn, fill the side-tank with water from a hosepipe and see where it pours out from. The danger is that's a huge weight of water in an unsupported hull and carries a high risk of breaking the boat. 

[Nick in Bristol]

Interesting, I thought 2-part Urethane foam was a fairly common filling for buoyancy tanks although maybe more on big boats than dinky lightweight dinghy's. The marine stuff certainly doesn't absorb water and apparently seals leaks. However you guys are the subject matter experts which is why I was asking

Inspection hatches were sealed not long after I got the boat as this is an obvious entry point but there was still a good 5 litres of water in all the tanks when I tipped it up mid-week. Unsealing the inspection hatches and taking a peek in showed lots of dampness around where it disappears under the foredeck.

Is there ever an issue with the kevlar / foam sandwich (thanks for the info on this too) becoming porous over time as the hull ages? Some of the joins here and there do look a little amateur too.

[tim_unerman]

Hi Nick,
Kevlar / epoxy / foam systems can absorb water but this is very small, what you describe sounds like a larger leek they may have been an issue around old joints but you will see a lot of flex in  the system.
From previous experience I find pressuring the tanks give a good idea of where the problem is coming from and using a bit of lung power will not over stress the hull.
I live in Bristol as well and still have an RWO style hatch cover set up ready.
Tim

[phil_kirk]

Nick,

I feel your pain!  We used to have a leak in Slippery when wet.  We noticed a couple of cracks in the cockpit floor so cut away the glass skin and found some areas of damp in wooden pads. Once these redundant pads had been removed and I had re laminated  the glass we still had the leak.  Approx 2 litres every time we sailed.  I then did the soapy water test and applying air presure to the tanks and found a tiny screw hole that had been filled and painted was still leaking.

The moral as others have said is that you will struggle to find the leak by just looking and you are more likely to fix other things that are not contributing to the leak.  I used a foot pump from an air bed with the noxxel pushed into the bung hole with a bit of progrip to create a seal. Itr didn't apply to much pressure but was sufficient to make bubbles.

I believe that Roland has contacted you to see if we can help in person.

[Will_Lee]

We had the same issue with Norwegian Blue. We found lung power plus either careful listening or soapy water found the leak. I think it was the shroud points. The back of the case is a big leak spot.

The other thing to add is that as you improve you'll spend less time capsized which usually means less leakage.
 

[Nick in Bristol]

Many thanks to Roland and Phil for dropping by for a quick look that turned into over an hour of getting the mast up and playing with the rigging  I really appreciated you checking the tanks and spotting the likely ingress points, which fortunately look like they won't be a problem after all. Lots of advice to take in but it's gradually all coming back.

I did realise as soon as you'd gone that I'd not offered you a cuppa - my shout for the first of something stronger at the sticky weekend.

Debs has point-blank refused to sail in 'that thing' until it's painted so will probably crack on with the hull at least. But a day at Chew still sounds like a great plan and very willing to take you up on the offer.

[roland_trim]

She'd be welcome at Chew in any state. We'll happily sail her as crash test dummies regardless of paint state :-)

[phil_kirk]

Less of the crashing please! We'll be happy to be dummies though.

For the rest of you on the forum. Nick's boat has a port and starboard tank under the false floor. These extend all the way to bow. The side tanks sit on top of the bottom tanks and extend from the cockpit floor out to the gunnels and forward to the shroud bulkhead.

It is worth sailing the boat a few times just to find out if there are any areas that need attention and fittings that could be moved before she is painted.  I wish we had sailed Slippery before the refit because we may have avoided reworking things  later that year. However we bought her with many fittings already removed and all the paint sanded back.

It is possible to fill in the inspection hatches with a composite panel and get rid of potential leaks there and it would be worth reinforcing a few areas to save them requiring work in the future. 

Just to make the boat look prettier I would fair the line of the gunnels.