Alternatives to glass in sheathing the exterior of a Wharram Wooden Catamaran and resin/adhesive advice - aiming for sustainability - longevity, cost.

[angyd83]

Hello,
What are viable alternatives to glass in sheathing the exterior of a classic Narai Mk IV Wharram designs wooden catamaran?
Our project is here: The Floating Stories Lab — Voyage ∞ Virage
In the 80s, these boats were sheathed with 'Cas Cover' - nylon sheathing - and resourcinol glue, and seemed to require nil if minimal maintenance and lasted decades.
One builder has suggested we try cas cover with epoxy?
I do wonder if the quality of wood used in the 80s makes a difference to the longevity of cas cover, OR, if cas cover with epoxy on a WBP ply such as Rolpin Fir (which we can get locally here in France) would have good results.
As there is no 'green' boat, we are looking to both cut through greenwashing and ultimately for a trade off in which we build as sustainable as possible with local materials wherever possible, no GRP ideally, but with an objective of minimal maintenance and longevity.
I am aware that nylon is a plastic, but considering the above comments about its longevity (seemingly better than GRP) it may be a viable solution.
We are exploring flax, flax/basalt combo, and hemp, along with bio resins.
Open to receiving proven success stories, warnings, and links to relevant scientific papers
Thank you!

 

[DownWest]

Way back, we sheathed a couple of the plywood 20ft cruiser racers in Cascover for S Africa.
More recently, People are using nylon fabric with epoxy. It heaver (more resin) than glass, but very abrasion resistant. Not so structural as more flexible.
You might ask the question over on the Wooden Boat Forum, it comes up from time to time.

We have built several ply boats in France with an exterior quality ply sourced from a supplier in Saujon, not far from Saintes. Where are you? Also, look at Resoltech's site for resins, we have a local agent near Royan.
I did the usual test on the ply, several cycles in the dishwasher...

 

[Daydream believer]

I did the usual test on the ply, several cycles in the dishwasher...

Did it get all the dried gravy off?

 

[Keith 66]

I tried flax fibre cloth a few years ago as had some samples. Seemed to work well. To be honest cant see as if there will be much environmental difference between any of them, Glass or Basalt will take energy to make the fibre.
Epoxy resin is going to be the best for sheathing applications & you could use ordinary canvas impregnated with it to do the job. There are Bio epoxies but never used them.

 

[MisterBaxter]

If the sheathing isn't structural at all, ie the ply is fully stiff and strong enough without it, the fabric isn't that important. I would definitely use epoxy though.

 

[angyd83]

Way back, we sheathed a couple of the plywood 20ft cruiser racers in Cascover for S Africa.
More recently, People are using nylon fabric with epoxy. It heaver (more resin) than glass, but very abrasion resistant. Not so structural as more flexible.
You might ask the question over on the Wooden Boat Forum, it comes up from time to time.

We have built several ply boats in France with an exterior quality ply sourced from a supplier in Saujon, not far from Saintes. Where are you? Also, look at Resoltech's site for resins, we have a local agent near Royan.
I did the usual test on the ply, several cycles in the dishwasher...

Thank you, I will post on the Wooden Boat Forum, too.
Where are you building ply boats in France? We're now based near Douarnanez in Finistere, Bretagne. I would be very interested in your recommendations for ply suppliers, and the resin producer you mentioned.
We don't have a dishwasher haha, but I like that suggestion. We are planning on testing composites ongoing, too, even once we set off on our voyage. For the moment, we start building in March and will need to at least have confirmed ply and resin supplier to get started on the bulkheads, backbone, and stringers. We have a bit more time to keep researching the external sheathing that will go on the ply planks of the hulls and later the rest of the exterior.

 

[angyd83]

If the sheathing isn't structural at all, ie the ply is fully stiff and strong enough without it, the fabric isn't that important. I would definitely use epoxy though.

I have spoken with Hanneke Boon at Wharram about this. The sheathing is not structural, but it is required on the outside of the boat for longevity.
Hans Klaar didn't use any sheathing or resin at all on Ontong Java, though, but his boat is built of exceptional quality Mahogany as it was built in Africa. So it's just wood and paint.
I would like the peace of mind of some kind of long-lasting sheathing and resin combo on the exterior as I am also not confident the quality of ply available today is what it was in the 80s.

 

[angyd83]

I tried flax fibre cloth a few years ago as had some samples. Seemed to work well. To be honest cant see as if there will be much environmental difference between any of them, Glass or Basalt will take energy to make the fibre.
Epoxy resin is going to be the best for sheathing applications & you could use ordinary canvas impregnated with it to do the job. There are Bio epoxies but never used them.

Thanks for sharing. What did you use the flax fibre cloth on and how did you apply it? I've heard it soaks up a lot of resin, and is typically applied with vacuum infusion, which we won't have access to.
Yes the environmental challenges are complex, there's the energy consideration (in both the process of production and end-of-life waste management), the petro-chemical base, VOCs, and more recently the discovery by researchers in Brighton that end-of-life GRP boats are causing a direct impact on bilvalves (ie oysters and mussels) due to the shedding. The research also found that there were contamination spikes during boat maintenance periods ie over winter in samples taken at Chichester Harbor.
Nylon is obviously also a micro-plastic, but my thinking from talking to a lot of people who have used cas cover is that it doesn't shed as easily as GRP and doesn't have the same weight aspect in respect to the 'glass' shards spearing marinelife (sea fleas, then they can't swim, sink and die).
It's all quite complex and there's no real 'green' solution in modern boat building at the moment despite a lot of greenwashing. Bio resins only have a small portion of bio content and once flax cloth is soaked in resin it most likely makes the end product very difficult to recycle, too. Products like Elium are being promoted as recyclable, however they are petro-sourced and the reclying processes are mechanical or chemical, both hugely energy intensive and not economically efficient. Very early days!

 

[Keith 66]

I was working in a school as a D&T technician & my D&T teacher asked me to get her some composite samples & do a talk on it, The Composites section in GCSE D&T was to be honest pretty useless & Carbon fibre was really bigged up as the be all & end all of composites, We had good year 10&11 Gcse groups & i opened their eyes a bit to the world of possibilities. I got some samples including Flax from Easy Composites but there wasnt enough to get a handle on how the stuff really performed. One sample was a flax fibre interwoven with PLA fibre, Heat & pressure & it melted the PLA & made a laminate. Not a lot of use for sheathing a boat but quite possibly a truly recyclable laminate
Another alternative to glass or nylon cloth would be diolen which is polypropylene cloth, very light but tends to float in the resin.
Im not surprised about microplastics, when i see grp boats abandoned & falling to bits its easy to see how the UV light degrades the gel & how the surface sloughs off with time, Regular polishing will do that too & i have seen many GRP boats that have had their gel coat half polished away over time. Where did it all go? down the slipway or drain into the creek thats where. As you say there is an awful lot of "Greenwashing" going on but in reality its just pissing into the wind. The only sustainable boat in reality is one made of tree wood preferably from locally grown timbers.

Easy composites do a range of flax fibre reinforcements in both matt & cloth forms, Also doing Hemp in matt.

 

[wrr]

I have a 62 year-old boat Cascover sheathed from new, Resorcinol glue is still available. I have been cautioned about the potential degradation of nylon by epoxies, perhaps as in: Interaction of nylon polymers with epoxy resins in adhesive blends. B. S. Gorton
First published: May/June 1964 https://doi.org/10.1002/app.1964.070080319 An alternative to nylon may be to use Kevlar cloth with either epoxy or resorcinol. The Cascover on my carvel hull below the waterline is still intact after 6 decades and seems not to have lost any thickness, suggesting that it has not shed significantly into the sea.

 

[DownWest]

Thank you, I will post on the Wooden Boat Forum, too.
Where are you building ply boats in France? We're now based near Douarnanez in Finistere, Bretagne. I would be very interested in your recommendations for ply suppliers, and the resin producer you mentioned.

Bit further south, between Saintes and Rochefort, Charente-Maritime.
Here is Resoltech:Résines de technologie avancée and I notice they have an agent at Arzal.
I will ask a fellow builder about the ply, as he looked into it's origens. Local stockist has it up to 20mm

 

[angyd83]

I have a 62 year-old boat Cascover sheathed from new, Resorcinol glue is still available. I have been cautioned about the potential degradation of nylon by epoxies, perhaps as in: Interaction of nylon polymers with epoxy resins in adhesive blends. B. S. Gorton
First published: May/June 1964 https://doi.org/10.1002/app.1964.070080319 An alternative to nylon may be to use Kevlar cloth with either epoxy or resorcinol. The Cascover on my carvel hull below the waterline is still intact after 6 decades and seems not to have lost any thickness, suggesting that it has not shed significantly into the sea.

An update, according to the tech lead at Wessex, Cas Cover is no longer available.
See below from their correspondence:

Cascover Sheathing

This was a system owned, marketed and sold by Wessex Resins for many years and was an excellent product. The system was a nylon fabric applied with a specific grade of resorcinol resin and overcoated with a vinyl paint. Cascover sheathing was gradually replaced with glass sheathing and WEST SYSTEM Epoxy. Also, the various materials that made up Cascover Sheathing were harder and harder to source and eventually became unavailable. It is now impossible to source the specific grades of material that made up Cascover sheathing. So, completing new Cascover sheathing is no longer possible.

 

[westernman]

Thank you, I will post on the Wooden Boat Forum, too.
Where are you building ply boats in France? We're now based near Douarnanez in Finistere, Bretagne. I would be very interested in your recommendations for ply suppliers, and the resin producer you mentioned.
We don't have a dishwasher haha, but I like that suggestion. We are planning on testing composites ongoing, too, even once we set off on our voyage. For the moment, we start building in March and will need to at least have confirmed ply and resin supplier to get started on the bulkheads, backbone, and stringers. We have a bit more time to keep researching the external sheathing that will go on the ply planks of the hulls and later the rest of the exterior.

These guys build plywood sheathed in epoxy yachts.

RM Yachts: French sailboat manufacturer - 30 ft to 45 ft

 

[DownWest]

Found a bit of ply with the info on..
SAS Allin/Allin Plex Combi 13 EN 13986 2004+A1 2015 EN 636

For a low tech boat like a Wharram, I would have thought this stuff is good, if well sheathed. I can give you the name of our local supplier, if that helps.
It is way cheaper than Marine Ply.
Incidently, I had a look at Spirit of Gaia and a brief chat with Wharram when he was moored in Ferragudo, quite a few years back. Free copy of his book too..

 

[B27]

Kevlar or Diolen are good choices for tough sheathing.

It depends what material properties you are looking for.

A hull should really be designed with the sheathing as part of the structure, more so if the sheathing is a stiff material like glass.

 

[angyd83]

Kevlar or Diolen are good choices for tough sheathing.

It depends what material properties you are looking for.

A hull should really be designed with the sheathing as part of the structure, more so if the sheathing is a stiff material like glass.

Wharram classic designs don't require sheathing as structural, the way they are designed with the ply and epoxy makes them strong enough as is. The sheathing is recommended on the exterior for longevity and durability, particularly below the waterline.
I've heard Kevlar is a devil to repair?

 

[Keith 66]

If you are building a new plywood catamaran you are not going to save the planet by worrying about what to sheath it with. Sheathing is only used to protect the plywood. A thin layer of glass is not going to make that much difference after all glass is just silica, Sand in another guise. Its the resins that are the issue to me.
Kevlar is a pig to work with as it is hard to cut & furs up when you sand or grind it.
Its overkill in this application.
I would be more worried about the shockingly poor quality of most plywood on the market today.

 

[angyd83]

If you are building a new plywood catamaran you are not going to save the planet by worrying about what to sheath it with. Sheathing is only used to protect the plywood. A thin layer of glass is not going to make that much difference after all glass is just silica, Sand in another guise. Its the resins that are the issue to me.
Kevlar is a pig to work with as it is hard to cut & furs up when you sand or grind it.
Its overkill in this application.
I would be more worried about the shockingly poor quality of most plywood on the market today.

A few things here.
1. We're not trying to save the planet, but would like to be thoughtful in our process of building our boat and source better materials wherever possible, viable and affordable.
2. Fiberglass shed from boats is causing extensive damage to marine ecosystems. We are partnered with the scientist who uncovered - by accident - these findings: https://www.sciencedirect.com/scien...?ref=pdf_download&fr=RR-2&rr=8cde1cafe93676f0
3. Resins are certainly an issue. We're looking into the current state of bio resins, but most still contain a huge portion (as high as 80%) of petro chemicals and the bio content is also not environmentally benign - soy and cashew based bio content has issues with deforestation and land grabbing. Furthermore, once the bio content is mixed in with non bio content, the resin is no longer biodegradable, and the existing recycling processes for resins are extremely energy intensive, expensive, and this includes thermoplastic resins (ie Elium) which is being tainted as 'sustainable' - we all need to look beyond the greenwashing. From my research, 100% bio resins have not been tested enough in marine environments and much more R&D and funding is required.
4. The poor quality of plywood today and the high cost is a pain in the ass.