Novice DIY deck replacement coosa+epoxy

[AKfisher]

Hello, I'm installing new fuel tanks on my salmon troller which will require removing and replacing the aft third of my deck this spring (About 10'x10') in cool weather. Due to limited local options I will probably have to do the work myself. I have done some glasswork on the boat in the past that has held up well (on keel and holds) but I got lots of advice.... I'm still definitely a novice.

Hull was built in 1980 solid glass. Deck to be replaced was reportedly redone in 2009. It is glass over plywood with 2x6 ground contact treated lumber beams surrounding the alum tanks. Deck leaks in several areas and that moisture saturation combined with the treated lumber up against tanks caused premature aluminum corrosion.

I have ordered "The Fiberglass Boat Repair Manual and Fiberglass Boat Repairs Illustrated" to help guide me.

I plan to rebuild deck using 1" coosa, glassed with 2:1 epoxy and 1708. One layer of 1708 on underside and two layers on top then probably Petit EZpoxy paint. I would fabricate solid, 10', 2x6 replacement beams by sistering strips of coosa and covering with 2 layers of 1708. Any thoughts on that general combination of materials would be welcome. Would foam be a better choice for the beam cores?

-Are there any current reference books you'd recommend that could help me determine the best combination of coosa/core thickness, laminate layers, and beam size/number/span? Currently I plan to copy the same layout as current deck which, despite the moisture, is quite solid.

-I chose epoxy rather than PE for several reasons. In particular, I've read the fumes are not nearly as bad as PE, I don't know whether they used epoxy or PE in tying existing deck to hull, and it sounds like epoxy would be little better suited for working the cooler spring temps (40 to 50 degrees) in my area.

I would welcome any feedback/advice on any of this....especially suggestions on up to date books/guides that cover any of this.

Thanks!

 

[gonzo]

In a commercial fishing boat, puncture and impact resistance is very important. It is difficult to beat fiberglass over plywood for that. I think finding data to compare would be a good idea.

 

[tpenfield]

Post some pictures if you can as that will help with further guidance.

As for the epoxy, keep in mind that once you start a project with epoxy, it is difficult to switch back to PE or VE since epoxy does not play nicely with the other 2. I use VE on most of my projects, but the fumes are pretty bad. I assume that you will be using a laminating epoxy (?)

You mentioned cool weather. Sometimes that can be helpful in extending the working time of the resin, but you will have to balance that with the ability to cure. Be ready to tent the working area and apply heat as needed in order to promote curing.

1708 cloth is going to give you about 0.05" of thickness per layer . . . so figure 3 layers to get to 1/8" thickness (+/-).

Keep in mind that with stitched cloth (the 1708), wetting out the cloth requires a different technique than with chopped strand (CSM). You will want to apply a healthy amount of resin to the '08' side of the cloth so the liquid resin can force air out of the cloth as you lay it up on the pre-wetted Coosa and adjoining areas.

If you try to work resin into the outer surface of the 1708, the 'tightness' of the fibers will tend to trap air and be difficult to get the cloth fully wetted. It can be done, but it is not as easy and takes extra time, which you may not have.

I am about to start a project with fiberglass over Coosa, so I will be watching this thread with interest.

 

[comfisherman]

I'm a smidgen north of you, and have done several boat deck and deck repairs with coosa for fishing boats. Your gonna have to tent and run a tube style heater for humidy and temp regardless of what resin you use. If it were me, Id go ve as it makes more sense than using a combination mat with an epoxy. On a project this size a 3m face mask and cartridge is not that much in the total cost of the project.


Gonzo is right, your probably going to have a thicker deck due to abrasion than is needed for structure. Granted trolling is probably tied for gilnetting in terms of low impact. Bouncing some lead weights on deck is way different than skipping 6x pots across the deck.

The puncture resistance of coosa and ply appear similar, seems like the stuff that would tear up my ply deck tears up coosa as well. Its certainly tougher than similar laminate on divinycell.

My guidance from the technical guys had been to treat it like ply and you'll likely end up a little heavy and over engineered, but thats fine on a 45 year old displacement speed commercial hull.

Fisheries can get the 5x10 sheets of coosa, but its been much cheaper to get 4x8 sheets as they ship to the distributor for less and to alaska for a lot less. It is nice on decks to use the biggest pieces possible, but it was probably 30-35% more to get big sheets here per square foot because of the non traditional sizing.

On coosa beams, we cut them in trapezoid shapes so they are easier to laminate under the deck. Have one 5 year old deck with coosa beams, seems to be doing pretty good.

The hot coat is a solid reccomendedation especially with tighter combination mat. That first coat always feels like it sucks up more than the divinycell foam.

 

[Rumars]

If I understand it correctly the current deck is plywood on wooden beams (2x6 common lumber) glassed on the outside, no fiberglass on the underside? You wish to replace a piece of it with a cored deck, using coosa, and make composite beams.

Normally I would advise consulting a local engineer or NA, because this is going to pose some challenges. If you can't find one, this is what you need to solve, and no, we can't give you any guidance without knowing specific details.
1. Cored deck to topside connection, I assume some form of wooden beam shelf exists for the current ply deck. Several versions of how to do it, depending primarily on access.
2. Cored deck to ply deck connection. Again access is important, they need to be connected on the underside.
3. Install deckbeams or not, a cored deck doesn't necessarily need them. If you do use deck beams what type.

There are other things like the presence of hatches, deck curvature and the actual process of making it. If I understand correctly and the current deck beams contact the fuel tank it means the deck underside can't be laminated in situ, you need to do it off the boat and install it like a lid.

 

[AKfisher]

Wow, thanks for all the excellent replies.

Since posting, I have touched base with a local glass guy who came and took a look and measured. I am awaiting on an estimate but either way I will likely be doing a good part of the work/assisting to keep costs down. So your advice is much appreciated.

After talking to him and reading your posts I am now leaning to PE....and I think topside will need at least 4 layers of 1708 (Glass guy recommends additional CSM between each layer). I realize heat is a must for cure. I'm planning to build a tent/wrap over the stern with enough room to set up a table for lay-up.

I was planning on getting the 4x8 sheets of coosa from Fisheries Supply (Seattle), as comfisherman suggested. I have to ship it up by barge to my island. If I end up hiring the glass guy I will probably have him handle the resin/glass order.

Speaking with coosa, they actually have an even stronger version called bluewater 32 but I have not seen it fir sale so I will probably end up with the bluewater 26.

He had some different ideas about supporting the deck. Rather than beams going across as it is now, he suggested stringers running fore/aft. They would be made with laminated coosa and encapsulated in glass. He thought stringers would make it simpler to produce a curve/camber in the deck as well. It may also make it a bit easier to glass in the sections of the deck that tie to the hull before installing the tanks.

Once tanks are installed, there will be no room to access/glass the underside deck/hull connection.

So One idea, I think, would be to glass in the new stringers or beams and the deck to hull but leave enough of an opening in the middle to drop the tanks in, which would then be shifted into place under the sections of deck that have already been glassed to the hull. Once tanks are in place port and starboard, then there will be rom to glass the final, central deck panel in place top and bottom.

You've raised good points about coosa as core. While impact is not as much of a concern, the deck needs to support the fish I land as well as my hayrack - an aluminum shelter that covers the deck and serves as the mount for heavy bronze trolling winches called gurdies. The hayrack rests on for legs bolted to four glassed blocks in middle of deck.

So I think I will need to do beams or stringers, potentiality with some uprights running to the hull stringers below the hayrack legs.

I'll snap some pictures to give you a better idea of what the whole think looks like.

Anyway, I am on standby waiting for the glass and tank estimates.....so I will continue to research and plan.

Thanks again for the awesome comeback and advice.

 

[fallguy]

I wouldn’t discount wood for the structural portion. It will be greatly protected by new work.

I don’t think 1” coosa is going to behave well for camber.

Does the deck have camber in multie directions? Like for and aft and abeam both?

You ought to consider compression ratings of the coosa alongside wood.

Wood may be a better choice for all of it. If so, I would use epoxy. Sounds expensive, but it might be easier to sand in the deck camber and overall better.

go slow and side by side compare

 

[gonzo]

Coosa is a very stiff material. If you are looking for camber it will be difficult. If you laminate the bottom first, it will most likely crack because of the tension before bending enough. Maybe you could use thinner material and laminate it.

 

[AKfisher]

Good to know. Thx. I see that some coosa users recommend kerf on underside for bending.

 

[AKfisher]

I'm thinking deck would have a very slight camber abeam to facilitate drainage through scuppers.. Not fore aft. Current deck is flat.

 

[comfisherman]

Most the decks we did on gilnetters and small seiner are 3x layers of 2415. So 4 of 1708 would be right around the same.

Call rev chem and get a quote on pe and coosa, they have a very reasonable delivery cost to the freight forwarders in Tacoma.

Its stiff but for minimal camber its fine. We did our first by doing a complete deck out of divinycell with molded in camber and then skinned it with coosa. Was a ton of extra work and now we just rig up slightly heavier jigs and it works fine.

 

[AKfisher]

Its stiff but for minimal camber its fine. We did our first by doing a complete deck out of divinycell with molded in camber and then skinned it with coosa. Was a ton of extra work and now we just rig up slightly heavier jigs and it works fine.

So you just use the coosa and glass now...no divinycell? What thickness coosa do you prefer for a commercial deck core?

 

[comfisherman]

Ive only used coosa, but thats mainly due to what Ive had on hand and the use case. No knock on divinycell, but the sections weve done were going to have cleats ans other things bolted down and the coosa does better for that. Thickness has varied. Most of my work as been sections of deck, usually just duplicating thickness of existing deck.

Usually its like every fishing boat project, probably overkill and could have used to hire an engineer... but we did monkey see monkey do and its done just fine.

The 1 inch divinycell deck with a 1/2 inch coosa 26 skin has been bomber. Its probably significantly overkill but has been nice not worrying about the point loading placing cleats and other hardwear. It just took a lot of time to do.

Commercial hull is vague. Under the deck winch of my seiner its 2 inches of blue water 26 and some substantial glass. The aft deck is skinned with 1/2 under the glass over the divinycell. My gilnetter only has coosa under the cleats and net reel.

My guess is the ply mimic laminate schedule is overkill, or at least it appears on the boats weve done. But were old displacement hulls, a few hundred extra pounds of glass, core and resin on a segment of deck on a 7 knot 45 year old boat doesn't hurt much.

 

[fallguy]

I’d only use bw26 and no lighter core or wood. The nice thing about the coosa is it’ll take some compression/bolt loading. Still pay attention to psi compression ratings for it vs say doug fir or preferred wood options.

 

[AKfisher]

26 is the plan.