What's the cabin roof made of?

[Ranzo]

Hey gang!

The blue non-skid sections on the cabin roof of my 1974 have some give in the skin. The white strip between them with the mast step is very hard and the area around the mast step is solid, but there is some "bowing" of the skin on the blue non-skid sections if I push or step on them. I can push the skin down a bit and then feel it resist against the core underneath. The core underneath feels solid when I push on it, and it seems to hold my weight OK.

A Catalina Direct forum post here says that the roof on a first-gen 1985 is marine ply with a skin that is not bonded directly to it, with space between. Surely some of you guys have drilled or cut into the cabin roof: what is there? Is the "bowing" skin in this spot an OK thing or a harbinger of certain doom?

Thanks!

 

[LakeShark]

Not good for sure. Generally give in the deck is an indication of the core material rotting inside and delaminating due to water intrusion. Repairs vary widely from replacing the entire core and deck skin to drilling small holes in the problem areas to inject penetrating epoxy.

it will all come down to how bad the “flex“ is and how wide spread. Check the archives here and you’ll find many pictures of what others have done.

 

[LakeShark]

On a side note if the soft deck is wide spread it may be time to find a better hull and scrap the boat while keeping the best parts for both. I know it sounds harsh but unless you’re really dedicated to DIY on a boat where you’ll have more into it then you’ll ever get back out, it may be the wiser and more effective method. My opinion is that time spent sailing is far more fun and worthwhile than time spent in the yard.

just one man’s opinion though.

 

[ShawnL]

I did the injection method on my 1972. It worked ok. Not great, but ok / good. I was sure that the core was dry and drilled a bunch of 1/4" holes. Waited until we had a good cold week (less than 40 degrees) and poured warm epoxy into all of the holes (so it would flow well).

Once all the holes were filled until they wouldn't take any more I covered them with tape and put a space heater in the cabin to keep the interior temps in the 70s overnight. That let the epoxy that was too cold to do anything cure. It's not perfect, but good enough for me. Once spring hit, I used total boat fairing compound to cover the holes and then re-painted. My paint was a mess from a PO so whatever I do paint-wise is an improvement.

In hindsight, it would have been better to cut the fiberglass, re-do the core and re-glass. But it's a '72 and older than I am and is fine now. So I guess I saved myself some work and got some more sailing in. If you don't have an enclosed space to tear it all apart, it's a big job and weather dependent. I'm familiar with epoxy (built a couple of stitch and glue kayaks) but it was more than I felt I could tackle in the 'it's warm enough to epoxy, but cold enough not to want to sail' season.

 

[pclarksurf]

Dare I say not a whole lot?

Included some deck pictures in case you haven't had the joy of tearing through yours just yet. Your '74 should be more like my '73 than not -- I wouldn't call it a harbinger of doom-- the Catalina layup was quick and easy in the day-- heck it lasted for 45+ years, but all the deck material is a layup of two thin ply layers with epoxy. 90% of what I see is one of two things: 1) the bond between the layers is either sketchy (may not have been perfect to start with) which causes the gel coat to crack. Seems ominous but easily fixed with grind, glass/ epoxy in place. 2) Dry Rot or water intrusion over time-- clearly worse, and needs to be remediated, but again if you can stop the leak (you can), then you can make a permanent repair. Folks on this forum (me included) have replaced entire decks, cockpit floors-- you name it.

 

[dlochner]

I doubt Catalina used epoxy, it is too expensive and takes too long to cure. Most boats built in the 70s were built with polyester resin. A significant difference between epoxy and polyester resins is epoxy's much better adhesive strength.

Getting resin to adhere to plywood is a challenge because of the large areas of hard grain. The resin will soak into the softer parts and bond there, but not bond to the hard areas. As a result the the deck skin will flex and gradually separate from the skin. Balsa core is end grain which allows the resin to soak into the core and form a stronger bond. Balsa is also much more expensive than soft wood plywood which is why it was used in smaller boats in a competitive market.

 

[Ranzo]

Thanks to everyone for their input and help! I appreciate everyone!

Looks like a recore job is in order on the cabin top to get it fixed properly, then. I'm not opposed to it and do actually appreciate the chance to try and develop new skills, though it will be my first rodeo with such work. It doesn't look all that much different from replacing the plywood subfloor in the bathroom, though!

@pclarksurf: what's your preferred method for sealing the cut back up? Do you scarf and glass it over?

Also I am disinclined to mess with the mast step. The deck seems solid there and I don't currently anticipate needing to remove it, but: is it difficult to remove and restore correctly if I need to?

 

[pclarksurf]

@pclarksurf: what's your preferred method for sealing the cut back up? Do you scarf and glass it over?

Exactly-- my go to is grind/Glass/epoxy/fill/fair -- will obviously depend on how big an area as to whether you need to come back with fiberglass or just spot epoxy fill. When I tear up a big section (cockpit floor in my case) I take an extra step to completely encapsulate the marine plywood in penetrating epoxy, then build up structurally as needed with fiberglass and epoxy resin for strength. I am a big fan of West Systems - and have worked up my preferences for filling / fairing and structural bonding --but there are excellent alternatives on the market as well.

Unless you know the mast step under the deck is rotten -- I would pot any and all holes for prevention and rebed hardware. My example below: you can see where I "investigated" a gelcoat crack that turned out to be no rot and dry plywood-- fill/fair/paint and I was off to bigger challenges

 

[Ranzo]

Beautiful, thank you so much!

I have already ordered some of the parts. Also did some reading up on the mast step removal, and being basically just one hefty screw it doesn't look so bad. I may go ahead and pull it off so I can take the whole cabin roof skin off following jmczzz on page 2 of this post. I think I like the idea of a full overhaul and knowing for sure that it's done right more than I fear taking the mast step off, now!