Help with identification of the hull construction

[Chapaef]

Hello,

I am trying to identify the type of deck-to-hull joint on this boat, as I need to carry out extensive renovations. The previous owners neglected to address multiple leaks, resulting in several areas of beam delamination and a rotted shelf beam. Unfortunately, I don’t have any drawings of the boat, nor have I been able to connect with anyone who worked closely with the designer—no one seems to have the drawings either. So, I am on my own with this project. I hope the knowledgeable members of this forum can help me figure it out.

 

[gonzo]

Is that plywood deck on a fiberglass hull? I see the shelf in the hull. If that is rotted the plywood is probably damaged too.

 

[Chapaef]

Is that plywood deck on a fiberglass hull? I see the shelf in the hull. If that is rotted the plywood is probably damaged too.

Yes, that’s correct. The hull is fiberglass with a sandwich construction using Airex foam, and the deck is built as follows: laminated deck beams, topped with plywood, and then fully fiberglassed.

I’ve also added close-up pictures from the outside for clarification.

 

[Rumars]

From what I see it's a pretty standard method. They installed a beam shelf wich is obviously bolted to the hull, possibly also glued. The deckbeams are notched into the shelf, probably with the usual half dovetail. The plywood is then nailed or screwed on top, probably also with some adhesive (5200, epoxy, etc.), possibly in multiple layers. The transport photo shows us the hull extending past the shelf, but that could have been trimmed later. So right now there are two possibilities, they trimmed it down and the plywood extends over the hull, in wich case the toerail is a separate piece screwed on top, or they didn't and the hull forms the toerail. In both cases they then would have fiberglassed over the ply, and possibly the toerail. The mystery will be resolved by a little grinding action in the toerail area. There are to many ways the job could have been done to list them all, just get under the paint and see what's there.

Repairing isn't rocket science, just tedious. You start grinding the toerail area exposing the joint, maybe 1m at a time. If you find rot you cut the plywood back until healthy. If the deckbeam ends, the shelf and possibly the toerail are rotten you cut them out and scarf in new pieces. Then you scarf in new plywood into the deck and fiberglass it.
You are not married to whatever hull-deck joint system they did, if you want you can change it.

 

[Chapaef]

From what I see it's a pretty standard method. They installed a beam shelf wich is obviously bolted to the hull, possibly also glued. The deckbeams are notched into the shelf, probably with the usual half dovetail. The plywood is then nailed or screwed on top, probably also with some adhesive (5200, epoxy, etc.), possibly in multiple layers. The transport photo shows us the hull extending past the shelf, but that could have been trimmed later. So right now there are two possibilities, they trimmed it down and the plywood extends over the hull, in wich case the toerail is a separate piece screwed on top, or they didn't and the hull forms the toerail. In both cases they then would have fiberglassed over the ply, and possibly the toerail. The mystery will be resolved by a little grinding action in the toerail area. There are to many ways the job could have been done to list them all, just get under the paint and see what's there.

Repairing isn't rocket science, just tedious. You start grinding the toerail area exposing the joint, maybe 1m at a time. If you find rot you cut the plywood back until healthy. If the deckbeam ends, the shelf and possibly the toerail are rotten you cut them out and scarf in new pieces. Then you scarf in new plywood into the deck and fiberglass it.
You are not married to whatever hull-deck joint system they did, if you want you can change it.

Thank you for your feedback.

I'll aim to provide more detailed observations. Regarding the toerail, it appears to be bare wood without any fiberglass covering. In the attached photo, you can see where the joint has come loose. I've also included the only document I have, which is a brief summary of the construction.

The most significant issues seem to be around the chainplates and the aft section (please refer to the attached photos).

One thing I'm trying to understand is whether the hull has a closed lamination. Specifically, is the foam fully encapsulated in fiberglass? If the foam is fully sealed on all sides, it would mean that any deck leaks wouldn’t impact the hull integrity as much, suggesting it’s in better condition overall.

 

[Rumars]

The photo of the topsides fully corroborates the description, you can see the fiberglass deck cover coming over the topside, under the toerail. If you remove the paint on top of the toerail you will find bungs covering the screws that go trough the deck and probably into the shelf. The toerail was probably initially varnished and might be salvaged (maybe not completely) if you desire. Removing it is the first thing on your list, and if you reinstall please don't fasten the stanchions to it, that was a major reason why the deck failed.

As to your other question, responsible yards would decore the last 1-2cm of the topside and backfill the void with thickened resin. Better yards would decore and backfill around any fastener. It is impossible to say what your yard did and previous owners clearly didn't care. If the foam is wet it's not the end of the world, it will dry out by the time you close her up again.

 

[Chapaef]

The photo of the topsides fully corroborates the description, you can see the fiberglass deck cover coming over the topside, under the toerail. If you remove the paint on top of the toerail you will find bungs covering the screws that go trough the deck and probably into the shelf. The toerail was probably initially varnished and might be salvaged (maybe not completely) if you desire. Removing it is the first thing on your list, and if you reinstall please don't fasten the stanchions to it, that was a major reason why the deck failed.

As to your other question, responsible yards would decore the last 1-2cm of the topside and backfill the void with thickened resin. Better yards would decore and backfill around any fastener. It is impossible to say what your yard did and previous owners clearly didn't care. If the foam is wet it's not the end of the world, it will dry out by the time you close her up again.

Thanks for the tip on the stanchions; I will definitely follow your advice! Should I remove the toerail all at once, or is it better to work in sections? I’ll use the decore procedure for all fittings, as it is plywood (which they say is the worst type of covering).

One thing I’m unsure about: if a section of plywood is wet or delaminated, should I cut out only the damaged part, or should I replace the whole piece at once? The plywood is visible from below and isn’t covered with fiberglass, so I wonder if cutting out multiple areas where it’s bad will impact the deck's structural integrity. Can I replace a square section between the beams? I’ve added a couple of pictures to clarify what I mean.

And then, two additional questions, if you don’t mind:

1. Shelf Beam: As you can see in my first post, some parts are completely rotten. Can I repair it partly with a scarf joint (using glue) to join it with a healthy part of the beam?
   
   
2. Laminated Beams: Is it possible to fix these without replacing them? Please see the pictures of the beams, as there are several places where they’re delaminated.
   

 

[Rumars]

The toerail itself is built from sections, so it will come out in pieces. You will have to remove all of them by the end, so it's your decision how you do it. Typically people remove all the deck fittings (everything that's bolted down) in one go if it's a big repair, and in sections only if it's a small repair.

You cut the plywood back about 10cm beyond the first solid wood to remove possible rot spores. It doesn't matter where you scarf or how many pieces you use, just that you do a proper scarf. It won't be the same everywhere, for example that stern area it's probably best to just remove the entire deck to the first bulkhead and work comfortably on the shelf and knee. Side decks are also a case where it's probably simpler to cut right to the cabin edge.

Yes shelf and beam ends can be scarfed, epoxy is your friend. A completely delaminated beam is something else, if the glue has failed you must take it out, clean the old glue of the surface (sanding) and reglue the whole thing back together. The beam shelf can also be laminated in place, stapled and glued directly to the hull.

The underside of the deck isn't a good indicator of what's going on. It's likely that the deck consists of at least two layers of plywood and the top one could be worst. There's also the sheathing to consider, if it was done with polyester the fiberglass could come off the ply in big sheats. The truth is you won't know until you start cutting, but you should be prepared to have to replace a significant part of the deck.

 

[fallguy]

It is hard to compete with Rumars. As usual, his advice is worthy of a fee. I can only augment his expertise.

I think going 10cm or 4” is probably a bit more than I might, but the rot must be gone or it’ll return. And also on the decks. In some of my repairs, I opted to use CPES to soak the edges of the remaining plywood. I did this as a rule whenever I had trouble viewing the plywood real well or access challenges where I faced unknowns, etc. I hate the smell of the stuff, but it performs well afaik, and you can epoxy onto wood that has been treated with it.

For deck delamination; you ought to be able to tap test it and get a decent idea where to dig, My surveyor uses a small plastic mallet, I use a plastic screwdriver and hold the metal end. Delam rattles compared to solid laminates. Basically, the space between closes and hits inside the laminate. Start by tapping obvious possible trouble areas where fittings may not have been overbored.

The challenge is being disciplined enough to remove all the rot. I repaired an old 1960 ply hull years ago and left two spots with a bit of poorer wood. One of them needs a full repair now. I remember at the time looking at the one spot rationalizing that’ll be okay, but it was a bit soft. It actually broke underway in a mild chop one day and I heard it!

ps - If you find scarfing in some area to be impossible; you would be best served going to the beam center. This is not the case for the hull, mind you, but that is not the subject.

 

[fallguy]

 

[Chapaef]

It is hard to compete with Rumars. As usual, his advice is worthy of a fee. I can only augment his expertise.

I think going 10cm or 4” is probably a bit more than I might, but the rot must be gone or it’ll return. And also on the decks. In some of my repairs, I opted to use CPES to soak the edges of the remaining plywood. I did this as a rule whenever I had trouble viewing the plywood real well or access challenges where I faced unknowns, etc. I hate the smell of the stuff, but it performs well afaik, and you can epoxy onto wood that has been treated with it.

For deck delamination; you ought to be able to tap test it and get a decent idea where to dig, My surveyor uses a small plastic mallet, I use a plastic screwdriver and hold the metal end. Delam rattles compared to solid laminates. Basically, the space between closes and hits inside the laminate. Start by tapping obvious possible trouble areas where fittings may not have been overbored.

The challenge is being disciplined enough to remove all the rot. I repaired an old 1960 ply hull years ago and left two spots with a bit of poorer wood. One of them needs a full repair now. I remember at the time looking at the one spot rationalizing that’ll be okay, but it was a bit soft. It actually broke underway in a mild chop one day and I heard it!

ps - If you find scarfing in some area to be impossible; you would be best served going to the beam center. This is not the case for the hull, mind you, but that is not the subject.

Yes, you're right; I get the feeling that Rumars knows exactly what he's talking about.

I've been tapping around some critical spots, like the chainplates, and unfortunately, it wasn’t good. In some places, I didn’t even need to tap because I could feel with my feet how soft and saggy it was.

So far, from what I can see, the issues seem centered around the chainplates on both sides of the deck. The bow will need a complete rebuild due to extensive rot, and the aft and cockpit areas don’t look good either. I’ll also have to rebuild everything around the backstay chainplate.

The cockpit is built from plywood, but I don’t see any fiberglass there. Is that possible? And if so, how would you keep water out of the hull in that case?