How to sheath a hull

[Cyrus Jordan]

The hull I've acquired has been unsealed and exposed to weather for at least a decade.  It seems structurally intact on inspection.  It was built from a kit made by Rainbow Boatworks in New York State, US. The firm no longer exists. The garboards are Okoume plywood; the other strakes are Meranti. The initial builder sealed up to the waterline with epoxy resin; the remaining surface which was unsealed has begun to absorb moisture superficially. (The hull is outside and the unsealed strakes absorb a bit of rain.) I intend to sheath the entire hull in epoxy saturated fabric. The principal goal is to create a moisture barrier. A secondary goal is to increase resistance to abrasion.  I'd appreciate advice on appropriate materials, e.g. fabric type, fabric weight, single layer, multiple layers. I'd also appreciate any input on technique. I'll be doing this myself.

My tentative approach after cleaning and sanding the hull is to: 1) initially saturate the hull with resin; 2) using a "wet technique" apply a single layer of small-enough-to-manage pieces of overlapping 10 ounce biaxial fabric thinned on overlapping edges; 3) apply enough resin to fill all fabric weave; 4) fair with Awlgrip Awlfair; and 5) overcoating with Awlgrip 545 Epoxy Primer. 

I'm also considering laying on some aramid for Dynel fabric along the keel for additional protection against abrasion, but have no experience with these fabrics and am concerned whether they'll drape enough over the edges of the keel to leave a fair surface.

Thanks in advance for your input,   Cy Jordan, Vermont, USA.

[Ron Jesche CH21' Sealion']

Hi Cyrus, Whilst not always necessary, I am a big believer in fibreglassing a hull. Sealion is completely sheathed outside and part of the reason for this is I keep her on the water year round, and the other is that it stops surface checking of the plywood.This is especially important if going to the trouble and expense of painting with 2 pack paint. On lapstrake hulls like ours this is not a simple job but I think very worthwhile. Firstly I would recommend to break the job down into smaller sections. I have used a very light [160 gram/sq.metre] double bias cloth. Use the lightest cloth you can get as you do not want to add any unnecessary weight.I sheathed each side of the hull in one hit, but wouldn't recommend that if no expericnce with fibreglassing. These are the steps I would suggest. Firstly I would give the complete hull a coat of epoxy resin particularly concentrating on sealing the endgrain on the bottom edges of the planks. The plank edges need to be radiused so that the glass can go over the laps.A 5mm radius should be fine, and needs to be done before coating with resin. The hull then needs a really good sanding so that there is no shiny resin left. Don't go any finer than 100 grit sandpaper though. Next I would glass the plank lands. Cut the double bias glass into 50mm strips so that the orientation of the strands are at 45 degrees to the plank lands so that it drapes over them easier.Then coat the plank lands with some resin and lay the fibreglass over the wet epoxy pushing it into place with a brush and coating it with resin as you go. Don't use too much resin at this stage. I would then use pre cut strips of peel ply and brush and squegee it over the glass until you can no longer see any see any air bubbles. You will now have a nicely sealed plank edge. If you are not familiar with peel ply I'm sure there are videos on YouTube to look at. Max also has some good photos on the wooden boat builders forum of his CH21. Once the resin has cured you can remove the peel ply and will have a nice smooth finish. some builders are reluctant to use peel ply as you throw it away after use, but you get a much better finish and use less resin, off-setting the cost.I would then do the rest of the plank laps, the stem and over the plank-transom join.By this time you will be proficient with the technique, and learnt with smaller sections at a time. Next all of the edges of the fibreglass need to be feathered down leaving a smooth transition to the rest of the plank.You can then cut the glass to fit the planks, and glass them one at a time, using the same process.It does not matter if the glass over laps the bottom of the plank a little as you can trim it off later.Once you have completed the whole hull and keel you can sand ready for some fairing and high build primer. Don't worry if you get an occasional bubble as you can always grind it out and fill with thickened resin. It is not a simlpe or quick process, and I hope this information helps. Keep in touch if you need any further help.Cheers Ron

[pablobesser]

hello to all.

i agree you need to protect the hull and glass it. in my boat i am doing from both sides because is just pine plywood and i now will check badly. in other boat i builded a few years ago no was  too difficult. first i suggest to put the hull upside dow. in a lapstrake hull is a lot easier that way, second round all edges, fibeglass dont like to be forced arround. then i will reinforce all the seams and corners  with some 5 cm long strips of glass and aply them. this will easier the radius then sand the edges. some will like then to precoat the hull is just epoxy to saturate the superficial layer of wood so the surface  will absorve lest in the next stage when you aply the glass fabric. you must sand this surface always to get good grip. but not complete just take away the shinny look.. others like to aplly the glass fabric in dry wood.  to me is almost the same. but now using more nd more peel ply and heat gunn to remove bubles i think is better to do by the dry metod. just get some help another hand is good in that part and cover the hull from top to bottom. in one row usin the 1 meter wide fabric. protect the hullo below that to keep clean it with some plastic and tape. use the squeges or plastic spreader more the a foam roller but both are usefull. use twill fabric. not biaxial. is stronger, less prone to open voids and flex better. a more expensive too but not big difference. and aply your coat ideally in the shade or when the air is cooling not getting warmer or the wood will release some air. if yoy precoat, this is less a issue. just use epoxy to fix the fabric and wet it until get transparent. no more. use the squegge to roll down excess of epoxy otherwise ther fabril will float in a too saturated epoxy away from the hull. then cover with pell ply. this fabric is expensive. i got my one from aliexpress china much cheaper really. is not flexible dont strech so cut shot sections in  the curved surface. and laterl using a foam roller press the fabric this will wet too and at the same time use a heat gun and the peel ply will wet even more removing all the air inside. is a big difference.

once the epoxy set. check some corners and get solid enougth to remove the peel ply safely do it and aply the second and trird layer of just bare epoxy to fill in the wave and give a nice surface i use in this some silica powder or microballons to get a soft epoxy easy to aply with foam roller and always after use the heat gun again to remove bubbles.

hope this help you some way. probably by the end of the year my own hull will be done and will do this too.

here is twill fabric in a rudder i am repairing.