serious delamination - how many layers should I put back

[corto-armitage]

Hi there everyone,
my Classis 35 - Lady Laura motorsailer ()moored in Rome, Italy, has a serious osmosis problem which we (my partners and I) are trying deal with, and was looking for some advice.

After grinding away (we're doing all the work ourselves to avoid paying 10,000 euros) the gelcoat, we verified with a "sinking" feeling the csm was delaminated (in places you could rip it off with your bare hands) and there was often liquid underneath. So we removed 1 layer, then a 2nd, and then a third arriving at a layer of woven roving. In some places the mat seemed good so we left it, but we are getting high humidity ratings in some of them (mostly on the bow and along the keel) so we are bringing all those areas to the level woven roving. Unfortunately in some areas (say five areas about 20-40 cm in diameter per side) there was liquid also underneath the first layer of woven roving so we removed that too in those areas. Once we did it the readings up to now say those areas were very dry. I am worried there might be other areas so we are removing all the remaining mat unless we have dry readings to better examine the woven roving.

When we are sure we've gotten all the liquid out and the readings are satisfactory (not in the red measured with a Tramex, hopefully in the green) we were thinking of replacing the layers of biaxial cloth with epoxy, before the epoxy barrier (Cecchi system)

Now some experts say that we need to replace as many layers as we have removed so fill-in the craters then 3. Others experts say none are necessary because old boats are thick and the mat had little structural purpose. The boat is 1 cm thick (after removing the mat) on the bottom, and about 2.5 where the two frames run, but I still have to figure out the sides. I think after the mat there are three layers of woven roving alternating with three layers of mat but my friends says 2 and 2 so we have to check that out.

Sorry for the lenghty introduction. My big question is: if I decide to play it safe and relaminate, how many layers of 300g (9 oz I think) biaxial would it take to equal the strength of the three layers of mat? (the original strenght, not the strength fo the soggy wall carpeting we removed).
Beyond that, any advice is more than welcome especially from those with _direct_ experience of similar cases (I've spent I year reading up on the subject so that part I think I got covered, but there are very few people who have had direct experience with cases as bad as mine seems to be).

 

[lpdsn]

If it were me I'd try to get it looked at properly. The osmosis shouldn't have been the cause of the de-lamination (if it is then you've got serious problems if it's progressed that far). Sounds like it may have been a poor lay-up in the first place.

Worth flying out a fibre-glass specialist. In the grand scheme of things, a couple of EasyJet flights and a night in the local hotel is not going to be that expensive.

Edit: any reasonable yacht designer should be able to specify the lay-up for the replacement cloth.

 

[macd]

+1 with lpdsn's comments.

In addition, it's unusual for osmosis to penetrate a layer of woven rovings, since little or no wicking of moisture can take place there. (Begs the question of whether the interior is, or has been, very wet.) Indeed there are recommendations that in cases of very severe osmosis, all the CSM layers should be removed to this woven layer before re-laminating is attempted. Any pox that's got that far and further sounds serious indeed.

I should add (with a sigh of relieve) that I've no experience of anything as bad as you describe. I doubt that many have.

 

[Poignard]

If he us still around, I would seek the advice and assistance of Hugo du Plessis, surveyor and author of "Fibreglass Boats".

https://www.iims.org.uk/iims-members/iims-membership-directory/5937/hugo-duplessis/

 

[corto-armitage]

Thanks,
Up to now, as I said, it is "only" in 10 places (say about 1 square meter out of 23) that I've found liquid under the woven. In those places, the liquid would ooze through woven once we uncovered it, so se grinded it out. I've done some sample grinding in other places where readings were higher but so far nothing.

It is possible the cause or concomitant cause in some cases may have been water from the inside. The boat was at least three years out of the water, prior to we buying it, but after we bought it we had to do all the seals of the hatches and of the skylight (sorry don't know all the English technical terms), as well as the chainplates, so I'm sure rainwater was seeping in and collecting in the bilge which could explain the high readings near the keel . I don't know about before that (the boat is 1982). The other points where we got high readings and liquid under the woven was the bow, where the anchor peak (?) was located and after that the water reservoir (which also was leaking when we bought it), and another really bad spot was at the bottom underneath a water pump placed on a wooden board under which water and muck gathered (we've completely redone it and placed the board on the side). There was also one point where there was a hole in a floor to let water flow in the bilge which was a bit off center and had not been resined so any water going through would also go into the floor (which was fiberglass but with a wooden core). The bottom of the floor was rotten as well as part of the bulkhead and we had to dig the rot out and redo it with wood epoxy and fiberglass.


I'm sure a good expert would be useful. It would have to be the right expert though. A couple of experts told us the boat had a little osmosis before we bought it but it was no big deal. Another one (who was incidentally very nice and lended us for free his moisture reader) said our readings were ok. When we compared them with those of a Tramex instead they corresponded to readings that were well in the red and in some places it turned out there were liquid underneath. He also suggested reparing it with CSM and epoxy, so at that point I stopped asking questions and just nodded at whatever he said.

 

[lpdsn]

I'm sure a good expert would be useful. It would have to be the right expert though. A couple of experts told us the boat had a little osmosis before we bought it but it was no big deal. Another one (who was incidentally very nice and lended us for free his moisture reader) said our readings were ok. When we compared them with those of a Tramex instead they corresponded to readings that were well in the red and in some places it turned out there were liquid underneath. He also suggested reparing it with CSM and epoxy, so at that point I stopped asking questions and just nodded at whatever he said.

Hugh de Plessis is a well-known author on fibre-glass, but he must be getting on if still alive. Shouldn't be too difficult to find a good fibre-glass surveyor. You want someone who has studied (been taught) the engineering properties of fibre-glass and the effect of water in the laminate. Not some big ship guy whose only experience of fibre-glass is his bath (to borrow a phrase from a recent Sailing Anarchy post).

I'm very surprised your surveyor missed the de-lamination. Having been shown how to check for it a couple of times it's as plain as day when you find it. I find a big socket from a socket set is a handy thing to tap on the hull. I think it is harder to detect water in the laminate especially with thick hulls.

When it comes to laying up woven cloth you need a plan of how to lay the cloth - mate who has built a couple of racers gets very precise instructions from the designer on cloth type, weight, direction of lay-up etc. You'll also have to think about the construction method used. I'm under the impression that vacuum bagging is really necessary for woven cloth, or at least heavily preferred.

May not be practical for a cruising boat, but I've heard of cases with de-laminated racers where it is easier to just build a new hull and transfer all the gear, keel, mast and rigging, engine etc. across.

 

[MagicalArmchair]

Sorry for the lenghty introduction. My big question is: if I decide to play it safe and relaminate, how many layers of 300g (9 oz I think) biaxial would it take to equal the strength of the three layers of mat? (the original strenght, not the strength fo the soggy wall carpeting we removed)..

To answer the original question, the chaps at EC Fibreglass gave me a cracking rule of thumb. For every 1mm of finished thickness, you will need two layers of 300gm cloth. So check the original depth of layup, and calculate based on this. I hasten to add, that rule of thumb is not strictly speaking accurate, and the chief of EC called me directly when I was writing the below article for PBO to distance themselves from that rule of thumb, as in a lab environment, it will be LESS that 1mm per two layers as you should be able to draw out more resin (less resin = more strength to your repair). In reality, that rule of thumb, in the real world, is just about perfect (I've now used it a whole lot!)

http://www.albinballad.co.uk/how-tos/fix-a-crack-in-your-keel/

Use bi-axial cloth, use epoxy, get the bevel right, and read, in full, this from WEST: http://www.westsystem.com/ss/assets/HowTo-Publications/Fiberglass-Boat-Repair-and-Maintenance.pdf. And of course, read my tripe above :encouragement:

 

[blan321]

Hi
Sorry to hear of your problems. I treated a Ranmeer 20 foot dayboat myself that had very similar serious osmosis about 20 yrs ago. I accept its not as big as your yacht and was never going to venture far from land. It had large deep blisters up to 20 cms diameter. Some could be seem with an oblique light as faint bulges. However, in other areas hard prodding with a spike demonstrated soft laminate and deep blisters with the characteristic fluid spraying out under pressure so I would also suggest looking for soft laminate..... I had gelcoat peeled, ground out all craters, pressure washed and dried over winter, filled craters with epoxy and glassfibre mat (cannot remember type) and then two layers of woven laminate with epoxy over entire underwater hull, followed by fairing and epoxy coating. Lots of work even on 20 footer, but doable, but as others have said, you really do want expert opinion (and that's not me!). Hope helpful, Good luck,

 

[Poignard]

(...) And of course, read my tripe above :encouragement:

You do yourself a disservice. That's not tripe, that's a well-written and well-illustrated article.

 

[William_H]

I would be inclined to say that the laminate even with many layers removed is still pretty strong. GRP has to not only provide a thick hull skin but also to provide stiffness to the whole hull. ie to resist rigging loads. Hence especially on older boatsd laminate was very thick.
I think that if you replace what you have removed with epoxy and woven cloth to a depth that will bring the whole back to similar original thickness you will be OK. After all you have to fair the hull lines so must fill in the holes you have cut.
Osmosis is generally not thought to be a problem in the overall strength of the hull. While yours is obviously bad I think that you could repair and go sailing confidently. Even if it is not a perfect repair it will be adequate.
Regarding previous comments about racing boats. These are built to max strength minimum weight so do need vacuum bagging to get best cloth to resin ratio. But your motor sailer is hardly in that class. Just fix it and get out sailing olewill

 

[lpdsn]

Regarding previous comments about racing boats. These are built to max strength minimum weight so do need vacuum bagging to get best cloth to resin ratio. But your motor sailer is hardly in that class. Just fix it and get out sailing olewill

My comment was meant more along the lines that if you don't ensure the resin penetrates the cloth then you'll end up with more air gaps which could encourage more osmosis.

 

[corto-armitage]

I am on a budget here, as you all may have guessed, so flying in surveyors, vacuum or having experts do it is unfortunately not an option. On the plus side, based on a limited experience, I think that in some cases if you are careful, plan ahead, and resist the temptation of cutting corners, doing it yourself may be less risky than entrusting it to an expert. At least that's what I tell myself...
:ambivalence:

 

[macd]

if you are careful, plan ahead, and resist the temptation of cutting corners, doing it yourself may be less risky than entrusting it to an expert. At least that's what I tell myself...
:ambivalence:

Often the case, especially with low-tech jobs which require care as much as trade skills. I'd follow William's advice (which is invariably sound). Since you have to make the hull fair, you may as well do the bulk of it with good stuff rather than filler. You may very well find yourself doing more remedial work in the future, but I daresay you're resigned to that.

 

[PuffTheMagicDragon]

When I had some small blisters on a boat that I had just bought I started to grind them away with an angle grinder. The trouble was that the boat had had a preventive treatment many years before and what looked like solid pristine epoxy began to show water seepage after it came into contact with the abrasive disk of the grinder. I calculated that it would take me (working alone) more than three weeks to do the whole bottom. I figured that it was better to use those three weeks for drying out.
I got a quotation from the yard and decided to have their contractor do sand blasting. This was around €750 plus VAT. He had to do it twice (at the original agreed quotation) because the old epoxy was so hard to remove and I did not want to risk leaving trapped water. The original treatment was done with Veneziani products.
Then followed many weeks of wetting with fresh water daily so that any uncured chemicals would dilute and be washed away. When the readings had stabilised I started re-building the missing layers using alternate layers of CSM and woven rovings, largely following the original lay-up specifications as per the drawing of which I had a copy.
The new treatment was a repetition of the original Veneziani, which has the advantage of getting a darker shade of blue with each coat of epoxy that is applied.
Waiting for the hull readings to stabilise is a long process but I used that time to do other work, including replacing all the wood that was exposed, including the toe-rail and capping, cockpit coamings, hand grab-rails, cockpit seat slats, etc.
The whole process from lift-out to splash took me 24 weeks, working only three or four days a week. I am retired and tend not to hurry too much. Very satisfied with the result and with the fact that I now know every square centimetre of the hull.

Buon lavoro!

 

[corto-armitage]

Do you remember how many and what types of layers you removed and how many you put back? You didn't use the Veneziani epoxy with the CSM right?

For sandblasting in Rome they asked us twice what you were saying (2000 euros but that would have been only the gelcoat, not the other three layers of mat). We agreed because, strange to say, we were not keen on sanding, but then a month went buy (sandblaster was missing a part (sic), didn't have the right sand yet...) so we got fed up and grinded it. It took about approx. 16 man / days (four of us, so four days, but the whole thing lasted two months because some us are a bit lazy) for 23 square meters.

 

[JumbleDuck]

Hi there everyone,
my Classis 35 - Lady Laura motorsailer ()moored in Rome, Italy, has a serious osmosis problem which we (my partners and I) are trying deal with, and was looking for some advice.

From what you write, it has an even more serious "not actually being properly made in the first place" problem. How confident are you that there is resin in the bits of the hull you haven't yet checked?

 

[PuffTheMagicDragon]

The drawing is on the boat and I don't remember the weights. What I did was to examine the exposed fibreglass and work inwards counting layers of CSM and woven rovings. You cannot tell the individual CSM layers but I would know from the drawings that, for example, there would be 600 grams/sq.m. before the rovings and worked from that. It is not mathematics and old hulls were usually over-engineered and not built down to a price; having my hull plus or minus ten kilos or so different from specs does not bother me.

These three photos show the hollow aft edge of the fin that was re-built from scratch, before and after.

In this photo you can see an exposed part of the hull that was sand-blasted, surrounded by the hull that has already been re-built, filled, faired and anti-fouled. The exposed square is where one of the props was placed when the rest of the hull was being treated.

 

[corto-armitage]

From what you write, it has an even more serious "not actually being properly made in the first place" problem. How confident are you that there is resin in the bits of the hull you haven't yet checked?

In the case of a couple of large holes we had to patch out for other reasons there was resin and woven roving - mat all the way. In the case of the one's I haven't checked I don't know. I suspect that given that the mat was delaminated, if there hadn't been any resin in the rest of the boat it would have folded over when they pulled it out of the water. What would you recommend?

 

[JumbleDuck]

In the case of a couple of large holes we had to patch out for other reasons there was resin and woven roving - mat all the way. In the case of the one's I haven't checked I don't know. I suspect that given that the mat was delaminated, if there hadn't been any resin in the rest of the boat it would have folded over when they pulled it out of the water. What would you recommend?

I'd recommend a good GRP surveyor. From what you say, the layup - whatever it was - wasn't wetted properly in a lot of areas to start with. Perhaps that makes them most vulnerable later, but I;d want someone who knows about ot to check. Good luck. As you say, it hasn't folded up yet.

 

[keesvugts]

Corgo-armitage,
I have taken the underwater part of the hull of a Sadler 34 completely back to the first layer of roving and build the hull back up with biaxial and woven glass in epoxy in order to deal with my osmosis. Whist not especially complicated, this is a massive undertaking of which the various sanding operations are the worst part. It is therefore worth doing a thorough job as this does not increase the work load / cost disproportionately but does significanty increase your chances of success. Although the matting outside the last roving and gell coat don't contribute massively to the overall hull strength, it is difficult to establish to what extent the hull stiffness has been compromised, especially if the first layer of roving has been compromised. This very likely means that their is further deterioration deeper inside the laminate. In my case as fas as I could judge the roving was not significantly affected although some small fibre bundles needed to be ground out to remove any signs of affected resin. The roving contains very long fibre bundles and will thus allow any moisture to travel easier over large distances. This may mean that deeper layers of matting can be affected at locations that are significantly away from the observed damage. For what it is worth, I decided that I did want to reduce my reliance on possibly compromised deeper layers and therefore decided that the new layup needed to provide significant strength in its own right. I ended up putting on 2 layers of 200 gr, 2 layers of 450 gr and 1 layer of 600 gr, with additional pieces of 600 gr at high stress locations and orientaded such that the loads are as much as possible inline with the fibres. As an earlier poster already said 600 gr per mm is a good guideline as it will be very difficult to get less than 50% resin content in a non vacuum layup. This is not an issue but it means that you will use a bit more material than a commercial operation for the same strength. I don't want to write an article on the whole process that I used but I'm more than happy to discuss my experience as well as the rationale for some of the steps that I took with you, please get in touch if you think that would be helpful. What you are planning is quite possible but it is an enormous amount of rather unpleasant work that you want to do only once!
Best wishes,
Kees.