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Old 15-06-2009, 01:09   #1
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Wet Foam Sandwich Blues

Hi,

When you google for advice on buying a foam sandwich boat, you come across the suggestion that if the boat's skin fittings are not correctly installed, water will have leaked into the core and the boat is a disaster - run away!

I have a 30' catamaran, and every screw and bolt and some skin fittings have leaked. The survey didn't pick it up. My experienced advisors didn't either (various friends with decades of boating experience). With hindsight, I now know I can spot a soaked core from across the other side of the boat yard - brown stains where water is leaking out of the core is a giveaway ( this is a Airex core in the bottom of the hull, Divinycel in the topsides and some of the deck. Polyester/glass skins. Some deck is solid grp.)

I have already done a lot of other work that I was aware needed doing when I bought the boat - rebuilding the daggerboards and rudders, rewiring, replacing some bulkheads that had delaminated. The aft beam had been laminated with polyester/glass. The mainsheet track was screwed to the aft beam, and the screws leaked water in. I stripped the beam. There was just a little rotten ply, which I replaced. I dried the beam ( covering in bubble wrap, and applying low level heat below it for several weeks ), and glass/epoxied it. More work than I care to list....

Anyway, I saw someone in the yard playing with a moisture meter, and I borrowed that. I was aware that in one or two places there was water in the core. The meter showed where the water had reached.

Almost every deck fitting on the coachroof shows water nearby and downhill from it. Each window in the bridge deck roof has many screws in it, and below each window the core is saturated. In a couple of places, the water has travelled into the hulls - there are areas from the deck to the bottom, perhaps a couple of feet wide that show elevated moisture levels. In other parts of the hull, wheer I have needed to drill a hole or I have removed an area of the skin, no water has come out.

The net between the hulls is tied to the hull with a sailtrack, and the sailtrack is held on with screws through the hull and into a timber beam that is glassed onto the inside of the hull. The screws leaked, the timber is soaked - a hole in the bottom part of the glass encasing leaks water slowly - I have replaced the screws with through bolts, with big washers on the inside, trying to seal the track by using Sikkaflex between the track and the hull, and applying polyurethane wood glue to each of the bolts before putting them in ( the polyurethane reacts with water, and expands into the wood - I figured I'd never get the wood dry, so I can't use epoxy, but if I could prevent more water getting in, and use the fibreglass which encases the wood as a support for the track, well, it's a bodge, but it might work...). I mention this because there is an aluminium rub rail attached to each hull in the same way, the whole length of each hull - a lot of screws, and without looking, I am pretty certain the builder has just put a bit of sealant on each screw, and many of the screws will have leaked.... I think the wood laminated on the inside of the hull will be wet, but I think the core is OK.

I am thinking I shouldn't have bought this boat, but I already have, and I wonder how viable it is to rescue it.

That's a long list of woes, and I could go on. On the upside, I'm thinking that 90% of the core of the hulls is dry.

Yep, I should have run away, but I didn't. No-one would want to start from here, but here is where I find myself. Here's my plan - tell me if you think it is feasible or...

Put the boat under cover next winter, and remove every fitting and screw through the hull.

In the couple of places where there is water in the core of the hull, drill many small downward-sloping holes through the inner skin with the hope that the water will eventually escape, driven by the repeated diurnal heating/cooling cycle. Install some ventilation in all outside lockers.

Either remove the rub rail, or replace the screws with through bolts in the way that I have dealt with the sail track that suports the net.

In the spring, make all the deck fitting holes the right way, with an epoxy filler between the skins around the holes for the bolts. I appreciate this might be difficult due to any remaining water in the core, but perhaps applying some heat to the area first, I can get it dry enough for the epoxy.

Replace the windows with new perspex or acrylic winows, using 3M tape to bond them in, and no screws.

Advice, other than I shouldn't have bought it...?

Thanks,

Eric
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Old 15-06-2009, 01:51   #2
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Awwwww poor you. Sounds like a night mare.

Just think, when you finish her, you know what you got and that should give you peace of mind
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Old 15-06-2009, 01:59   #3
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If you can do it, I'd say using vacuum would be a better way to remove the water than trying to do it with heat.

After you've gotten as much water as you can out, your idea of drilling and epoxy filling all the holes is the right way to go.

What I've been doing is to de-core under the laminate for around 10mm, which can be done with a cut off allen key, then make a sausage out of wetted out unidirectional glass tape, and stuff that into the hole, then top it up with glue mix.

I've found using the glass takes no more time than just using glue, but it gives me the extra security that it's very unlikely to crack under a load.

Interestingly there's a well known designer who swears that foam cored boats don't need to be de-cored and epoxy filled at hull penetrations.

I'd always do it, regardless of what core is used.

Who knows, maybe you got one he built.
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Old 15-06-2009, 03:58   #4
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I like the idea of the glass sausage - much easier than trying to squeeze in the some thickened epoxy, and stronger.

I'm intrigued by the designer you mentioned - if he recommends this publicly, then why not name him?

I've never heard of a recommendation to seal holes through a cored boat with just a bit of sealant.
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Old 15-06-2009, 05:43   #5
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You may want to tap all the areas to identify where it has de-bonded. Then, you really should open up a section and see what the foam looks like, I've seen too many foam boats that have turned to powder and need to be recored. Sorry, this is a big big job. Ouch.
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Old 15-06-2009, 05:56   #6
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I've tapped all over, and only hear a difference where there is a bulkhead. I don't think the glass has de- bonded from the core anywhere (is this feasible?). There is one area that water dripped from - where the bridgedeck meets the hull and forward beam, in the angle there. I chiselled the glass away from that area to try to see where the water was coming from, and whether the foam was still intact with the glass bonded to it. The foam is darker in colour than I'd expect but solid, and the glass seems to be bonded to the foam just fine.

I guess I'll have to chisel another patch away to get a good look at it.
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Old 15-06-2009, 06:00   #7
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Sorry to hear of your problems,the good news is its foam,not balsa.It seems you have a good handle on what you need to do but before you get too carried away you need to establish what the particular meter you are using is telling you starting with a known dry area as a baseline.Drilling a lot of little holes will work to a degree with foam .Buy yourself a good size dehumidifier to aid with the drying process but most importantly use a plastic hammer in conjunction with the meter when mapping out the wet areas,the meter alone wont show you delam areas and ultimatly you will just do your best to dry it out but you must repair any delams.I would map out the areas and write the readings on the skin and then remove small sections of inner skin in a few accesible areas that show the highest reading to get a look at the core,if its barely damp i wouldnt worry too much.
Steve.
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Old 15-06-2009, 07:19   #8
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As suggested, vacuum is your friend both for drying and putting in resin. Drill a few holes in the center of an area, tape down square of plastic taped to a vacuum hose and then drill holes in the perimeter. Let it run for a day. You can use a home vacuum cleaner with the vent partly open - it will burn out pretty quick but they're cheap.

When you're ready to put in the epoxy set up the vacuum again and use a syringe or a caulking gun to force in the epoxy. You can even attach a short piece of plastic tubing.

Always put some thickening in the resin - something like "milled fibers". Even a little makes it much stronger in voids. Start with it very runny mix and then add more thickener to fill the final hole.

The wood is the scariest problem. Your repair has left that moisture trapped and the rot will keep going. I'd open up the beam and try to dry it. Then treat with an epoxy like CPES that has some spore killing additives to kill the rot. There are a lot of ideas on the CPES site

Wood preservation, rot repair, and restoration using epoxy resin on boats and homes.

You've really got to worry about some of the techniques used to build your boat. What else might be lurking? I'd have a yard that does boat restorations and major repairs go over the boat and give you an estimate. While the whole job is likely to be too expensive, some of the things might really need a pro. Price is pretty negotiable right now.

Best,

Carl
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Old 15-06-2009, 22:08   #9
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Quote:
Originally Posted by pir8ped View Post
I like the idea of the glass sausage - much easier than trying to squeeze in the some thickened epoxy, and stronger.

I'm intrigued by the designer you mentioned - if he recommends this publicly, then why not name him?

I've never heard of a recommendation to seal holes through a cored boat with just a bit of sealant.
Here: To balsa core or not to balsa core?
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Old 15-06-2009, 22:29   #10
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A world of difference between urethane foam and PVC foam
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Old 15-06-2009, 22:46   #11
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Isn't Divinycel a PVC foam?
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Old 15-06-2009, 23:46   #12
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Thanks for all the feedback folks - it is all very reassuring. I knew I had my work cut out, but the situation no longer seems as bad!

Doesn't Derek Kelsall use vacuum bagging? If so, this might explain why he feels no need to seal the ends of a foam core board with glass. I don't think the fellow who built my boat used vacuum bagging, and so inevitably there's be small air bubbles and gaps - perhaps enough for a little water to penetrate.

Divinycell is a kind of PVC foam, google tells me.
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Old 16-06-2009, 21:24   #13
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Sorry to here about your woes.
I wonder if you could drill multiple small holes in the areas that are saturated and then cover the area with a delta drain DELTA® Systems, Drainage products made by Cosella-Dörken type product, then thick plastic over that. Attach on real vacuum pump to the plastic cover. This way you could vacuum much larger areas at one time. It may alleviate trying to draw moisture through and between the layer of lamination (through a singular location) so as not to cause further de-lamination?
Just a thought.

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A world of difference between urethane foam and PVC foam
Which world is best?

Best of luck,
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Old 16-06-2009, 23:02   #14
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Ex,

Thanks for that. I don't think I need that product, but you got me thinking any sort of corrugated material with holes in it, like some sort of plastic mesh, placed between the hull and the sheet of plastic when I try vacuuming the moisture out should be helpful, drawing the water from a bigger area.
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Old 18-06-2009, 17:13   #15
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Originally Posted by alleycat View Post
Ex,
Thanks for that. I don't think I need that product, but you got me thinking any sort of corrugated material with holes in it, like some sort of plastic mesh, placed between the hull and the sheet of plastic when I try vacuuming the moisture out should be helpful, drawing the water from a bigger area.
Let me know how it works out. You should know, it was just an idea and I real don't have a clue what I'm talking about!

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Then treat with an epoxy like CPES that has some spore killing additives to kill the rot. There are a lot of ideas on the CPES site
Wood preservation, rot repair, and restoration using epoxy resin on boats and homes.
Does anyone know a supplier of CPES in Canada??

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