Divinycell sandwich deck?

[Max S]

Hey guys. Currently my girlfriend and I have been looking for a liveaboard boat we plan to coastal cruise with in the near future. We've looked at about 9 boats so far over the last month. One of these is a 33ft Hallberg Rassy from the 80s that needs a bit of work, but overall seems relatively sound (we haven't had it surveyed yet).

So HR have the original specifications on their website and the thing is, it's a divinycell sandwich deck laid with teak that's screwed in... Now, as far as the teak is concerned we don't mind doing a full restore on the teak decking (or tearing it up) plus the maintenance since we plan to do some long term coastal cruising. I've restored a Catalina 30 over 2 years with a friend so I understand the work that goes in to a degree.

But my question is how likely is it that there's any soft spots under that teak? from what I could find divinycell seems to stop water from moving through its closed cells but in this area the winters do get to freezing levels so I'm worried any water intrusion through the million screw holes could have caused some cavitation. Is this likely? And how would a surveyor determine and of this without pulling the teak up. I have a moisture meter and can pull some of the trim from the inside to see from underneath the deck if there's water intrusion. But I won't be able to do the whole deck.

Thanks

[SailingHarmonie]

Divinycell is a premium product for this application. It is very good at keeping mosture from moving around. But it is not perfect. Surveying a teak deck reliably requires a bit of a specialized knowledge base that not all surveyors will have.

[clockwork orange]

Why would they do that? They had a perfect deck and then screwed it up. There is a possibility that they removed the screws and injected the holes once whatever they bonded the teak down with cured. Probably not but that would be nice. So, i used to own a 1977 Lindenberg 26 that was actually well engineered which was uncommon for back then. The boat was cored where needed but not where it was not. The core used was not balsa but polyurethane foam. All the interior furniture was also foam cored composite but the screwed up by screwing 1/4" x 2" teak slats on the cockpit sole with spaces in between. Presumably for grip? They also did this in one small area of the sole inside ahead of the saloon where your feet would be when sitting on the toilet. When i bought the boat it had been sitting in a yard abandoned and full of water up to the settee tops for long enough to develop osmosis in the tops and green slime. Anyhow after pressure washing it cleaned up fine but when i removed those slats obviously water had penetrated the core through the screws. I cut out a section and created a lift out to install a transducer and the jigsaw was throwing water in my face. To my amazement everything dried out and the piece i removed showed absolutely no sign of ever having been wet. This was PU foam, not PVC like klegecell. I have built boats with klegecell and would expect it to be just as good. It is difficult to use a moisture meter through the teak.

[Fore and Aft]

Max you should be able to put the moisture meter on the underside parts of the deck. I would expect some issues but because it's foam that would not stop me from buying the boat. You also might cause some more damage when removing the teak, depending how well adhered to the deck it is.
Cheers

[coopec43]

My deck is Divinycell and it is regarded as a top core material but there is no way I would screw into it. Why not use a flexible adhesive to secure the teak?

[clockwork orange]

Originally Posted by coopec43

My deck is Divinycell and it is regarded as a top core material but there is no way I would screw into it. Why not use a flexible adhesive to secure the teak?

When you lay a teak deck unless you lay it parallel to the centerline which is not commonly done, you need to spring it to follow the deck edge This takes quite a bit of force to spring it as well as to hold the planks down while the adhesive, whatever it is, cures, hence the use of screws. Once the adhesive has cured you can, depending on the adhesive used, remove the screws and inject epoxy into the hole. Most people don't do this but should as the screws serve no purpose at this point.

[coopec43]

Originally Posted by clockwork orange

When you lay a teak deck unless you lay it parallel to the centerline which is not commonly done, you need to spring it to follow the deck edge This takes quite a bit of force to spring it as well as to hold the planks down while the adhesive, whatever it is, cures, hence the use of screws. Once the adhesive has cured you can, depending on the adhesive used, remove the screws and inject epoxy into the hole. Most people don't do this but should as the screws serve no purpose at this point.

Thanks for that.

I had no idea how they managed to curve the planks since a teak deck has never been a consideration. But I've just looked at some photos of (expensive) teak decked yachts and they look awesome.

I like Errol Flynn type yachts but his deck doesn't have sprung teak planks

[clockwork orange]

That deck you show is parallel to the centerline and that style is a lot easier to lay as the planks just lay there. Not many are done that way these days. Most are sprung decks which are a lot harder to do. I have laid about 20 teak decks over the last half century from 20ft to 90ft. All have been sprung.

[Max S]

Originally Posted by clockwork orange

Why would they do that? They had a perfect deck and then screwed it up. There is a possibility that they removed the screws and injected the holes once whatever they bonded the teak down with cured. Probably not but that would be nice. So, i used to own a 1977 Lindenberg 26 that was actually well engineered which was uncommon for back then. The boat was cored where needed but not where it was not. The core used was not balsa but polyurethane foam. All the interior furniture was also foam cored composite but the screwed up by screwing 1/4" x 2" teak slats on the cockpit sole with spaces in between. Presumably for grip? They also did this in one small area of the sole inside ahead of the saloon where your feet would be when sitting on the toilet. When i bought the boat it had been sitting in a yard abandoned and full of water up to the settee tops for long enough to develop osmosis in the tops and green slime. Anyhow after pressure washing it cleaned up fine but when i removed those slats obviously water had penetrated the core through the screws. I cut out a section and created a lift out to install a transducer and the jigsaw was throwing water in my face. To my amazement everything dried out and the piece i removed showed absolutely no sign of ever having been wet. This was PU foam, not PVC like klegecell. I have built boats with klegecell and would expect it to be just as good. It is difficult to use a moisture meter through the teak.

Yeah well that would've been a nice idea (in fact we saw a Van De stadt design that had just screwed into the top layer of FG to hold the teak down as the adhesive cured and not all the way into the core) but on this one they went all the way through.

I'll give it a shot running the moisture meter along the bottom of the deck in some spots but what can I say... this boat might be going to the bottom of the possible candidates list. There's another few Halberg Rassy's here that don't have any teak (and are more expensive) to look at first.

[FPNC]

Divinycell is a wonderful product and will not absorb water when the density is high enough. 6 lbs density being optimum. However, the sheets are block scored and water can enter that scoring and that water can travel all over the cored laminate via those scores. I have cut into the bottom of cored vessels and watched water poor out. As stated, this is more of an issue in freeze thaw conditions.

[clockwork orange]

I live in an area that gets lots of freezing. I have not seen issues with freezing in cores that just have water in the kerfs. You can visually see when water has frozen in the core by the cracking, but i have only seen this with balsa boats where enough of an area has already turned to compost, separated from the top skin and created a space for enough water to freeze to cause damage. It is amazing what damage can be done when water freezes and expands but it does need enough volume for this to happen.

[coopec43]

Originally Posted by FPNC

Divinycell is a wonderful product and will not absorb water when the density is high enough. 6 lbs density being optimum. However, the sheets are block scored and water can enter that scoring and that water can travel all over the cored laminate via those scores. I have cut into the bottom of cored vessels and watched water poor out. As stated, this is more of an issue in freeze thaw conditions.

When I laid my Divinycell deck the supplier told me to get a 44 gal drum (200L) and put the Divinycell sheet across the drum to open up the scoring and force the Divillette in as far as the scrim. I then had to turn the sheet 90 degree and repeat the process. It was quite hard to do but I'm sure it did improve the lay-up

[clockwork orange]

Originally Posted by coopec43

When I laid my Divinycell deck the supplier told me to get a 44 gal drum (200L) and put the Divinycell sheet across the drum to open up the scoring and force the Divillette in as far as the scrim. I then had to turn the sheet 90 degree and repeat the process. It was quite hard to do but I'm sure it did improve the lay-up

Absolutely that is what you should be doing with any contour core. Knowing how time consuming it is to do you think production builders do this? The answer is no. Which is why balsa is such a problem but it's not the balsa fault.I expect much better long term outcomes now that most builders use infusion.