(SHEATHING Part 1 mainly covers pre‑sheathing of large panels. This Part 2, specifically covers a narrow hull, like the W17 ama.
Although for the W17, these tips may also apply to some other ply boats, so I figured it was worth sharing.)
Because only a few of us have the luxury of working with a mate while boatbuilding, one has to find ways of handling relatively large jobs like the sheathing of a hull while alone.
So let me take you through the sheathing of a W17 ama.
First, I'll assume that you have sealed the chine joint with a tape and then faired the edges and all is sanded ready for the sheathing.
[Some prefer to sheath before adding a corner (chine) tape, so that the main sheathing does not get abraded off. However, in this case I have gone with a tape over the joint, faired to the tape surface prior to sheathing, and will then protect the sheathing by adding a 25 mm wide 5oz Kevlar™ tape on the exterior as this material is more abrasion‑resistant than glass.]
If the boat were wider, one could just pull out cloth from an overhead roll as I do for pre-sheathing flat sheets like the decks (see Sheathing Part 1), but the amas are too narrow for this.
So first, lay out some plastic (polythene sheet) on a flat surface to spread out the glass cloth. Typically you will use a 5‑6oz so‑called 'boatcloth' for this—a standard bi‑directional weave with roughly equal strength in two directions. For a W17 ama, measure out 16 ft (4.9 m) and cut from the roll. A 38" wide roll is just perfect to reach gunwale to gunwale.
Now measure where the deepest keel edge is. I found mine was 17.5" (445 mm) from the gunwale on the inboard side. So I transfer that to the cloth with a marker, all along the full 16ft length.
I now fold the cloth all along its length, folding it just past the lines previously marked and flaking the rest back over. The sketch shows how, and is for the Starboard Ama looking forward.
Then roll this up from the far end, that is from the forward end, towards the stern. It will make a nice roll like this. (See pic. at left, which also shows the roll for the Starboard Ama. The Port side roll would have the guide marks towards the RH side of the roll.)
Now mix about 20 oz of resin—that's about as much as one can apply on your own without problems. (I'd mix even less on a hot day.)
Once thoroughly mixed, pour into an open tray, as the more the resin is spread out, the more time you'll have before it starts to cure.
I like to apply with a thin foam roller. Apply to the small bottom surface of the ama and also about 1⁄3 to ½ way down the sides. Then place the cloth roll at the stern and unroll it over the whole length, taking note where your marks come relative to the chine. At the stern, the marks can be 2‑3" (50‑70 mm) outside the chine but as you roll forward, the marks should come in towards the chine and for the forward 1⁄3 of the hull, fall right on the deepest chine (inboard edge). Only unfold down the sides once you've got it in position but do not roll the sides yet—let the cloth hang loose and free. Roll out and impregnate the bottom surface first, pulling the cloth gently but firmly from the bow to keep the fibers as straight as possible.
Now, pull the cloth down to make sure that the cross threads lie about vertical up the side, and then roll epoxy over the cloth down from the chines for an area about 600 mm wide at the center of the ama length. This is to 'anchor' the cloth with wet resin. Then start pulling the cloth at the bow, and also down by the gunwale, to get rid of any pleats or bubbles. Roll over the surface as you go. Then go to the stern and repeat the same action.
To roll and wet-out the cloth, you can either use a short bristle nylon roller, or one of the new textured rollers that I show here. They are not available in 3" (75 mm) rollers, but it's easy to cut 3 from a standard 9" roll with a hacksaw. I found that this textured roller does not create foam and air bubbles like the foam roller does and also, does not lift the cloth away from the surface either. Roll slowly though—fast rolling does create more froth and other problems.
Once the bow is nice and flat, go to the stern and pull the cloth there too—also pulling the threads downward to get rid of any apparent 'blisters' and down the sides.
For a narrow ama, it's not too complicated to get the cloth to lie well. A wide, round bilge monohull is certainly a tougher challenge.
But the bow does need some special attention. Don't even think of finishing the bow until the cloth on the hull sides is looking totally flat. Pull the cloth from the ends and then down if need be. That's why it's nice to have a few inches spare.
Once ready for the stem, cut the cloth back from the stem (on the outboard side) by about 15‑20 mm, on a line parallel to the stem. Roll that down in place.
Then, after totally completing the other side, curve the longitudinal cloth fibres down over the last 12" from the bow (300 mm), so that by the time they reach the stem, they are about at 45 degrees to the horizontal. This will allow the fibers to go around the stem more easily. Once around and overlapping the other side by about 1" (25 mm), the excess can be cut off, to be later sanded and filled.
Finally, starting at the bottom and working away from the center towards the ends and then from chine down to the gunwale, use a stiff, straight‑edge spreader as a squeegee—the WEST #809 is a good model to use. This will push any excess resin out of the cloth and keep it reasonably light. Scrape off any excess resin back into the tray.
If you made too much, pour this resin into a round container and add some filler so that you can use it to add fillets inside any other hull ready for them.
A useful tip to hold the cloth down at the stem, is to cut several pieces of wax paper in this shape.
Then wrap them firmly over the bow and the larger side areas will bond sufficiently to the wet epoxy to hold the smaller area at the nose in place.
A little added epoxy, at the wide side area between layers, will help.
When finished, remember to remove (and scrap) the used roller covers immediately—before the epoxy hardens—and clean the roller frame, spreader and other sticky tools or hands with a scrap piece of towel (or equal), soaked in white vinegar.
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