MWCI How-To

Building A Quick Fiberglass Hull

by Bart Purvis

So you want a fiberglass hull for your next combat masterpiece? The first place to look is in Swampworks Mfg's latest catalog because this company sells quality products at reasonable prices. I don't think anyone can build a one-off fiberglass hull at a really significant price savings and I know you spend a lot more in labor. So, in my opinion, Skunkworks is the way to go. But if your heart is set on the HMS INEDIBLE (INDIGESTIBLE class) and this particular hull isn't yet manufactured by Skunkworks, why not consider building a fiberglass one-off hull that will meet the criteria of fast and easy construction along with light weight, roominess and high strength.

Basically, the procedure consists of building a 1/64" plywood hull form over throw-away formers and fiberglassing both sides of the plywood, thereby making a light and strong sandwich type of construction. Let's build an INEDIBLE hull and see how it goes.

Step one is to make a building board with the proper offset between maindeck and foredeck upon which an upside down hull form will be constructed. Next, make a sub-deck using 1/8" ply, cutting a 5/8" rim and leaving two or three transverse braces about 3/4" wide. Using 1/8" ply to make the deck proper, cut a 3/8" rim and glue the deck rim to the sub-deck rim. Now, lay a piece of waxed paper on the building board and using small brads or finishing nails, nail the deck assembly to the building board. Don't use many and don't nail the nailheads flush with the deck because the nails will need to be pulled with pliers later.

Cut the hull formers from a suitable material. I have used 3/16" balsa, James Foster has used thick cardboard. Both materials work fine. Remember when cutting the formers to make allowance for a thickness of 1/64" ply, a thin layer of fiberglass and 1/32" balsa on each side. Glue the formers to the deck assembly at their proper stations. At the bow, the first former should be 1-1/2" back from the beginning and at the stern the last former should be 1" forward of the end. Between each former, glue a piece of balsa (1/4" square or whatever you have in the scrap wood box) to act as a temporary keel on which you will glue the 1/64" plywood.

Using scissors, cut and shape 1/64" plywood segments or sections to fit between formers and the keel. Try to go from the centerline of one former to the other and to the centerline of the keel. Gaps between plywood segments are not important and may be ignored since the fiberglass covering will conceal them handily. When ready, glue the segment in place. Place the segments in no particular order, except that areas where nails are holding the deck assembly in place should be covered last. Allies are reminded to pull the nails before installing the 1/64" plywood segments. Of course, our Axis friends may leave them in place. Don't try to use 1/64" ply at the extreme bow and stern segments. Instead balsa blocks are glued to these areas and then shaped and sanded to the proper contours to complete the hull form.

What weights of glass cloth are suitable for use? It's not critical by any means. On my cruiser hulls, 2 layers of 6 oz. cloth on the outside of the hull and one layer on the inside was used. With a large GENERAL class convoy ship, one layer of 10 oz. cloth on the outside and one layer on the inside was used. Just make your best guess as to weights and layers and get started. You can always add another layer if you feel the need. However, many layers of light 1 or 2 oz. cloth are not recommended. Five 2 0z. layers will weigh more, have less strength and require more time to apply than one 10 oz. layer. Select a cloth weight that will allow you to do the job with 2 or 3 layers. We're going to use 10 oz. cloth, one layer outside and one layer inside, on this article's cruiser hull.

Next, decide on the type of resin you're going to use. Of course, the old reliables of polyester or epoxy resins are available and the following procedures can be accomplished using them, but, I prefer using thin cyanoacrylate "superglue" or CyA. The big advantage of CyA is that there is no waiting for slower resins to cure. This means that your fiberglassing job is finished as fast as you can do the procedure. The major disadvantage of using CyA as the resin is the odor and the fumes associated with it's use. You are encouraged to work in a well ventilated area and use fans to divert fumes. And, of course, there is the school that says if you can't handle streaming eyes and toasted nasal hairs then you aren't a REAL warship combat modeler anyway.

CyA glues are expensive but a surprisingly small amount is used in this method. Between 3-4 oz. is all that has been used on each of several cruiser hulls and one large troop transport hull. Satellite City, the makers of "HOT STUFF", will give you a complimentary two for one voucher on their products. Contact them as P.O. Box 836, Simi, CA 93062. They have the best prices I have been able to find.

O.K. you have a form and have selected the proper cloth and resin. Let's fiberglass a hull. Prepare the hull's surface for glassing by spraying a very light coat of 3M 77 spray adhesive (available at hobby shops and hardware stores) over the area to be glassed. The spray adhesive should cover the surface with little pinhole-sized dots rather than a heavy coating. Spray from 18 to 24 inches away and don't linger on any one spot. Since the 3M 88 adhesive stays tacky for hours, there is no reason to rush to the next step.

Pre-cut the glass cloth to the appropriate shape needed, allowing a little to hang over the edges. There is no particular advantage to covering the hull in one or two pieces, so plan on using several smaller, more manageable pieces. Don't be concerned about how much or how little adjacent pieces overlap. It doesn't matter if the overlap is 1/4 or 1-1/4 inches. Lift the cloth into position and lay it on the surface. Perfect alignment isn't necessary. Starting from a side that has some excess, lift the cloth and replace it in the desired position. Lift the other end and pull just enough to remove folds and wrinkles. Replace while maintaining a slight tension. The cloth can be relifted and realigned if desirable. When your placement of the cloth is satisfactory, pass a flat hand over the cloth surface to adhere it to the 3M 77 adhesive and smooth out all wrinkles. Large wrinkles or "bubbles" should be slit with an Xacto blade and rubbed smooth. The cloth will now stay put over unusual contours and even while inverted. Add more pieces until the hull is completely covered with a layer of cloth.

You may need to lightly spray more 3M 77 adhesive on the edges of adhered cloth so that adjacent pieces will stick. The spray adhesive neither weakens or interferes in any way with the fiberglassing procedure. Also, when cutting glass cloth, you should try to make all cuts on the bias (45 degrees) rather than with or across the weave of the cloth. This markedly reduces the tendency of the cloth to unravel.

Now, it's time to apply the thin super glue resin (CyA) to the hull. Tip the hull and start applying CyA at the higher end. As one area of the cloth is saturated, the glue moves on to another area. Because of this, a small amount of CyA goes a long way and weight is held to a minimum with no sacrifice in strength. Tip and rotate the hull so that the CyA runs downhill without puddling while being applied. Apply CyA in horizontal passes following the CyA from previous passes down towards the lower portions of the hull. As you apply the CyA, you'll see the saturated areas instantly become more transparent. When you have a length of 10-12 inches of one side of the hull saturated with CyA, spray a light fog or mist of kicker over the surface. Spray from 2-3 feet above and with the bottle held to the side of the hull. The objective is to mist on a small amount of kicker to initiate a slow cure of the CyA. Too much kicker will cause a bumpy surface as the CyA cures too quickly. Although these bumps are easily sanded off, it is even easier to avoid them. When the sprayed area has cured in 30 to 60 seconds. turn the hull over and apply CyA to 10-12 inches of the other side, hit it with a light mist of kicker and repeat until the entire hull is completed. Remove the gross excess of fiberglass from the deck edges of the hull with scissors and then complete the removal of excess with a disc sander, Dremel tool or hand instruments. If necessary, add another layer of cloth to the hull exterior. Remember that you will be adding cloth to the interior later and this will give considerable strength and rigidity to the hull. Don't worry about the flexibility of the hull at this point.

Now comes the fun part. Rip the formers and keel pieces from inside the hull with a hammer, pliers or a chainsaw............whatever suits your fancy. Don't worry if some of the plywood comes out with the balsa because the strength of the hull comes from the fiberglass, not plywood.

Your next step is to draw the penetrable windows on the hull exterior. Make the deck rim 3/8" deep and make the ribs between windows 3/8" wide. Cut out the windows with a reinforced fiberglass cutting wheel on a Dremel tool. Caution! Don't use a carborendrum disc because it will shatter.

Use some care with the ribs because, at this point, they are quite weak. Don't worry because the next step will give them adequate strength. Cut strips of glass cloth to cover the ribs. I cut these strips from 1" fiberglass tape because it is convenient and the sewn edges of the tape do not unravel. However, strips cut on the bias from a regular piece of cloth will do just fine.

Working on the inside of the hull, spray 3M 77 adhesive on the ribs, place a strip of cloth, saturate with CyA and cure with a light mist of kicker. The ribs will still be quite flexible and fragile. Repeat the process until, almost magically, the ribs will become absolutely rigid and quite strong. This required two and sometimes three internal strips on my hulls. Trim the excess fiberglass from the ribs with a reinforced fiberglass cutting wheel.

The last step in glassing the hull is to cover the bottom inside the hull. Spray with 3M 77 adhesive, place pre-cut pieces of glass cloth, saturate with CyA, cure with kicker and trim the excess. That's it! The HMS INEDIBLE is now ready for fitting-out and covering.

The weave of the glass cloth will still be visible but all areas of the hull will be covered with 1/32" balsa, silkspan or water so to me, this rough texture is not important. The extra resin (of any type) that it takes to fill the weave adds nothing to overall strength but, adds lots of unnecessary weight and also typical resins are miserable to sand. However, if you are building bulletproof superstructure, using 1/16" plywood, 10 oz. glass cloth and CyA, and desire a smooth finish, then weave may be filled by spraying and sanding several coats of automotive spray primer or else by applying and sanding Hobby Poxy "SMOOTH 'N' EASY" finishing resin. In no case should you use polyester resins over CyA resins because the chemistry of the two is not compatible and the polyester resins may never cure.