Leaking deck on a 48
Dear all (especially Lars),
I am looking for information regarding the deck construction of a later 48. Our hull number is 39, built in 1974.
A new teak deck was installed by the former owner in the early nineties. The wood was (probably) glued to the deck but also screwed down. Years ago, when the caulking was redone, the Greek workers took out many of the wood screws (unfortunately, not all of them). They also closed many of the resulting holes in the GRP deck (unfortunately, not all of them). Finally, the re-glued the teak to the deck (unfortunately, not everywhere). The result became obvious when we crossed the Bay of Biscay in late September, submarining a lot: the deck is leaking water into the cabin. And not all of it is the result of old sealant around vents or hatches but comes through the deck itself, at a place where it should be solid.
To plan the works with the yard, we would welcome information about the deck construction. The yard says that with this model and year, the deck will be a solid laminate instead of sandwich. I am not sure about that -- is that so? If it is a sandwich construction, there must be reinforced areas under the winches and cleats -- is there a reliable way to find out where exactly they are? I have heard rumours that this may vary from boat to boat as the layout was more optional in later years. Is that true, anyway?

I will post more once we know more ... but in the meantime, we would be very grateful for advice, from anyone who tackled a similar problem. What can be done in terms of repair vs replacement?
Thanks, Martin (Age of Swan, 48/039)

Dear Martin
The deck is a sandwich construction with reinforced solid areas and alloy back-up plates under fittings. You can see this inside if a few overhead panels are taken down.
Re the leaking screw holes afraid there is no other way than to locate every one - probably the leaking ones can be spotted after taking take down the panels - take out the dowel from the teak, and seal the hole from above. Not difficult but time consuming.
If teak battens are loose from the GRP deck this can be seen when walking on the wet deck - if water comes up through the seams the battens are not attached.
Would appreciate your comments
Kind regards
Lars

Dear Lars,
many thanks for your reply, even though I was a bit afraid to hear that it is indeed a sandwich construction ...
I think it is feasible to take down the liner, to locate the holes, to open the respective teak dowel and to close the hole from above. That should take care of the water coming through to the inside.
However, what really worries me: There are definitely holes where the screw has been removed and the hole not filled. For the holes going through both GRP layers, that can be tackled as you suggested. My concern is that there still may be any number of holes where the screw was removed, the hole not filled but not going all the way through the sandwich. In that case, the hole is invisible from underneath. Water would not come into the cabin but would run into the sandwich construction. And I would never know.
It probably depends on the filler material in the sandwich to decide what needs to be done then. What happens to the sandwich deck if water can come in but has no easy way out? How does it affect the deck if the filler is soaked? Or am I on a completely wrong track?
Comments very much appreciated ...
Best, Martin

Martin
The sandwich core material is Divinycell PVC foam, which is highly resistant to water.
For 80 kg/m3 foam the manufacturer reports a water absorption of 0.046 kg/sq.m. if kept under 5.1 cm head of water for 96 hours (ASTM D2842-69). If we assume that a leaking hole has an exposed area of 1 sq.cm, and the head is half of the above, this would correspond to 0.0000023 kg/sq.cm, and it would take approximately 4.8 years to absorb 1 gram of water in such a hole.
Nevertheless it would be good to seal all holes.
The Divinycell core sheets were probably scored, and this creates channels in the core. You could drill a small hole through the bottom skin at the lowest point of sandwich areas for checking if there is water in the channels.
Regards
Lars

Dear Martin,

I am intrigued by the issue that you raise. Even though Lars has the upper hand in terms of expertise, I might cautiously venture with few thoughts.
-Farouche has now a new teak deck altogether, but before that, I did a number of things to extend the life of the old deck. It was done quite successfully.
1- I re-caulked the whole deck and it worked just fine without any leak ever.
2- I remove all the dowels and all the screws and filled all the holes with an epoxy mixture. This work was time consuming but the deck looked the part for years and still no leaks.
3- I wonder about one thing: the screws that I have removed are relatively short and should not reach the second layer of the sandwich. They go through a part of the teak and a little into the first layer of the sandwich only. If this is true - it was true in my case - then I suggest that your leak might have different sources. Perhaps the source can be found under some fittings.

Good luck!//Philippe
(Farouche 47/050)

Dear Lars and Philippe,
thank you very much for the information. Lars, may I ask what "scored" means in this context? I am not familiar with the term, unfortunately.
The deck was laid in the Caribbean - it is nowhere near the standard I'd expect Nautor would have adhered to, and some of the screws unfortunately go right through both GRP layers. The fittings are another problem, but one that does not raise the question of salvaging a deck.
I agree that it would be preferable to close all the holes from the top side. But Lars' information suggests that this can be done step by step, while it is immediately important to close the holes that go through -- which can be identified from below.
Thanks again,
Martin

Martin
Scored means there are slots in the foam for making it conform to bent surfaces easily. There are different ways of scoring, one direction or two, one side or both, narrow or wide. Not sure which one was used at the time. Appended below is wide scoring.
Kind regards
Lars

Dear Lars,
thank you for the very helpful illustration - I live and learn ... We will have an appointment with the yard in the next week to take a closer look and discuss strategies. I'll keep posting.
Fair winds, Martin