Building a Hull

Building the hull is actually one of the easier parts of building an RC ship, and it can also be one of the cheaper portions of your project as well. My hulls are usually exterior plywood forms and keels with white pine planking, which in my case is often available as scrap from some other project.

The first step is to select which stations from the plan you'll use for the forms. Depending on how shapely the hull is, you may not need a lot of the stations through the middle portion of the hull, but you may at the bow and stern, especially on ships with fuller shaped bows and sterns, like the British frigate in the example here. This vessel is very shapely and I felt merited more forms to help maintain that shape.

The next step is to produce full-sized paper patterns for each of the forms you will use. Enlarging plans is another topic in it's own right, so we'll assume you've gotten that out of the way already. I usually use 3/8" or 1cm exterior ply for the forms. It's cheap and easy to find though it can sometimes have so many voids it in to render it useless - so look over what you're using.

It's simplest to glue these patterns onto the plywood using a gluestick, spray-glue, or rubber cement. Liquid glues will deform the paper and therefore deform your hull. Roughly cut out the forms so you can deal with them individually; then cut them finer, and bring them to the line with sanding.

With the forms cut out you need to determine how you'll attach them to the build-board. The build-board is the flat, stable surface your hull will be built on. It need not be it's own bench with legs, like mine, it can be a sepate board that you can move around, like the kitchen table, or on saw-horses in the driveway, what-ever works for you. It also doesn't need to be wider than the hull will be, it can actually be narrower. I user a narrower base for ship's boats so I can get clamps and such in place as the planking nears the sheer. A build-board wider then the hull makes this difficult.

My build-board's been used for two other models prior to this one as well as being used for a work-table, so it was pretty dinged up. I sanded, filled holes, and gave it a coat of flat white paint. A centerline was marked with a very fine-point marker, and, using a square, the lines where each form will be placed was marked.

The forms need to be vertically square to the build-board and the best way to attach them that way is by using wood blocks you know are square to the forms. I use strips about 3/4 inch or more square and at least as long as the form is wide. You can see in the image that some are plywood and some are solid. I attach them to the build-board using screws set at an angle so they can be removed as required, which will be soon.

Once the forms are mounted in their places on the build-board, they need to be faired, that is their edges need to be angled so the planking will lay flat on their edges as it follows the curves of the hull. I use a plank and lay it on a form. Using a drawing compass set it to the space on the side where the plank isn't touching the form. With it set, use it to mark the other side of the form using current edge as a guide. You need to cut and or sand off the wood between the mark you just made and the edge of the other side of the form. (I'll add a better illustration soon.) This process will be the most work towards the ends of the hull. The forms nearer the middle won't need as much removed, and the few center forms may not need any at all. It pretty much depends on the shape of your hull. You can probably get away with not doing any fairing at all, especially if the forms won't be staying in the finished hull. If you opt not to fair your forms be aware of what side of the line on the build-board they are set up on. Generally all forms should be stood up on the side of the line towards the middle of the hull. (again, I'll get an illustration for this up soon)

Before attaching the forms to the build-board, I cut notches in each one for the keel-son, or inner keel; which in this case was made of 1/4 inch plywood. This keel-son doesn't extend outside of the hull and for some hulls may not be necessary. It really wasn't necessary for this hull, but I planned it in, so in it went. It's only job at this point is to tie the forms together fore-and-aft. A simple strip of wood, a stringer, would have done the job as well.

This keel-son is not glued to the forms at all, as the forms are meant to be removed and the keel-son is a structural part of the hull. Note also the blue masking tape on the edge of the forms. This is so the planking doesn't stick to the forms. The planks are glued to each other and tacked to the forms as they're installed. This facilitates removing the forms when planking in complete.

With the forms faired and firmly attached to the build-board, you need to address how the bow and stern will be handled. How the planking ends at the stern post, stem, transom, etc; there has to be something there to catch the plank ends, and support everything where no traditional framing exists. In the case of this hull, the stern consisted of a transom, a counter below that with the planking ending on the counter planking. There would need to be a ledge to thicken the counter planking to give the side planking something to land on. Below that I installed an inner stern-post that the planking would lay against. The planking finishes flush with the aft edge of this stern post as you'll see below.

This is all very complicated and difficult to describe. Your hull may be much simpler. Like this schooner hull pictured, it may simply require an angled post with the transom attached to it and you'll plank right on and past the transom, trimming the planks back flush with it later. This is how the counter portion of my hull is actually done.

The bow is a little different. Simpler maybe. Like the stern-post, I made an inner stem-post. This was faired so the planks would lay flat against it. The planking at the bow extended right past the stem-post and was trimmed back to it. The shape of the bow, in paticular how round and full it is, or isn't, may require more than I show here to plank it. The planks will tend to flatten out in their run from the forward-most form to the stem when they should curve out maintaining the fullness of the bow. A ship has frames and cant-frames right up to the stem to accomplish this. You can add forms or simpler, use blocking of balsa or foam cut in lifts to the waterlines of your plan. This blocking ought to be removed when planking is completed - I'll get to why I think this below.

Planking starts from the sheer-line as shown on the plans. You may also set planks coming from the bottom of the hull which will give rigidity to the forms. On this hull I used two 1 inch wide by 1/8 inch thick planks at the bottom of the hull, and all the rest or the planking was 3/8 inch wide. None of the planking ran the full length of the hull, most were 1/3 to 1/2 the length of the hull. Real planking tends to be about 20 feet long. If a plank runs the full length or the hull, you would have to deal with complex shaping and bending at both ends. With partial length planks, you don't. Where planks butt together, end-to-end, the butt is typically reinforced with a butt-block inside the hull. I used a block and a clamp to keep the plank's ends flush with the neighboring plank, but didn't use any permanent butt-blocks. It's important that butts are not in-line with butts in other strakes of planking which will create a weak area in the planking. Stagger the butts about 1/4 to 1/3 a plank length from each other.

At the bow the planking had to be tapered to fit into a narrowing area, and even then all the planks wouldn't fit without tapering them to less than half their thickness. This required a drop-plank where a plank ends short of reaching the end of the hull. At the stern where the space widens, and the planks don't fill the gaps, filler planks are inserted.

Back aft the planks curved up and faired into the counter planking until they got to the sides where they ran past the counter and were trimmed back as shown on the schooner hull above. When the counter was planked, some wood was glued inside to form a ledge for the plank ends to attach to along where the red clamps are in the picture.

The outer keel, stem, and stern-post were made from 3/8 inch playwood in sections that could be applied as the planking was completed in each location. These parts were pinned in place with finish nails in predrilled holes to hold them down and keep them aligned as the glued dried as there's no easy way to clamp these items.

Planking at the bow overlapped it's twin from the other side. This overlap was alternated left and right with each strake of planking. It all would get shaved back to make a flat surface for the outer stem to be attached.

Once the hull was planked, it could be removed from the build-board and the planking above the sheer-line planked with the hull right-side up.

The head-knee, stem, keel, and sternpost are all applied outside the hull. This allows planking without having to cut a rabbet in the keel, etc. The surface is planed flat, and the sections glued and fastened to the hull. These are made of 1/2 inch plywood.

The hull is planed, sanded, puttied, and sanded some more, until it's fair and smooth. I use "water putty" or "wood flour" powder that's mixed with water to make filler, and I mix it a little loose so it'll get into any voids, cracks, and openings. Sanding sponges are great for this step too, and even a soft disk-sander in a drill with 100 grit paper works nicely. That's for a hardwood planked hull, if you used balsa, remember that the putty is often harder than the balsa, and you could wind up gouging out wood and leaving putty. Scraping is better as it knocks off what's standing proud without digging in, then a A 220 sponge is probably all you'll need after a good scrape.

With the hull sanded and faired, the forms can come out and the inside scraped and sanded a bit. The forms should come loose with a little tapping with a screw-driver handle or very light hammer if you taped the edges to prevent them from sticking.

Inside doesn't usually need to be smoothed to the extent the outside did, just knock off any putty blobs that oozed through the planking and any major bumps and ridges. I sometimes thin some PVA with water and paint inside with a light wash to get some nore glue into the plank seams. When it's dried for a day or two - really, it needs to be truely dry - brush and vacuum out the hull, and paint in a couple of coats of resin. I use polyester resin as it's cheaper, easier to sand, and perfectly fine in this situation. Excess resin I pour into the tight spaces in the bow and stern. Filling these spaces keep any water that gets in the hull from causing mold and rot in the future.

In the case of this hull, it's shape and tumble-home needed some support to keep it from trying to flatten out. Once the interior structure for decks and gear was installed it would have been fine, but that was a ways off and the easiest way to support the shape till then was some minimal framing. The frames were cut from the forms to a scale depth with deck beams left in. They were glued into the hull with an epoxy paste made with fine sawdust from my bandsaw, after the interior was resined. When the hull was glassed later, some resin was painted on the frames so they weren't exposed bare wood.

Fiberglass time! Some folks dread the thought of working with fiberglass. It's really not that difficult. YouTube has several good videos on applying glass cloth that can help you get used to the idea before you actually do it. Don't be afraid to lay a bit of cloth on some disposable test sublect, like a cardboard tube, or a laundry detergent bottle, just to get the feel for dealing with the cloth on an object with some shape. The best thing to do is have your work area, materials, and implements ready and at hand before you start. Once the resin is mixed, you're on the clock and can't go wandering off looking for something you forgot.

Because this hull has a broad flat transom, I started by glassing it. When the resin had nearly set, I trimed the cloth back to the hull with a utility knife.

Even before the transom had fully set, I went forward with glassing one side of the hull. Cut the cloth to rough fit, have a place to sit things down when you need too. Make sure the hull is stable and not going to fall on the ground. It's best to get it on it's side, or more, so gravity is working in your favor. Make sure to wear rubber gloves and eye protection. It's also best to have an apron or smock. Things are going to get sticky.

I use 4 ounce cloth because the weave is fine and when you get resin on it, it practically dissapears. Cut the cloth to cover one side of the hull. Set it aside and mix up your resin. Again, I use polester resin for this. I paint this side of the hull quickly with a brush or roller, and lay the cloth on the wet hull. Then I apply resin onto the cloth, pushing and moving the cloth around as need be to get into hollows and around bends and get rid of wrinkles. It's important the cloth lays right against the hull everywhere. I don't worry about getting cloth on the sides of the head-knee, keel, and stern post.

Glass cloth doesn't like to lay inside angles like that between the keel and bottom planking. If the resin gets tacky and thick, stop using it or you'll just wind up pulling the cloth off the boat when it sticks to your brush or roller.

When the resin has begun to harden, you can trim the cloth back with a utility knife. Be careful not to pullit off the hull. In this case I trimmed the cloth back to the where the planking meets the keel. The keel, stem, sternpost, etc, all get painted with resin and being plywood, don't really need cloth on them; they do need a good coating of resin though.

In an hour or so, poly resin will be set up enough to turn the hull over and glass the other side. Trim the cloth before the resin gets too hard, and after a couple of hours you can sand the hull a little and paint a coat of resin on the whole thing, especially the edge of the cloth where it was trimmed back along the keel and what-not. Depending on how things turned out, this second coat of resin may be fine. If you find places where the cloth lifted, basically forming blisters, cut or sand them out, get rid of the unstuck cloth, and resin in a patch. You can over lap edges with 4oz cloth and the overlap of so fine a cloth will almost disappear. Whatever you do, don't leave any blisters, cut them out, patch the bar spot, and resin over it again. once that's done, and the hull's sanded, give it a final coat all over.

It's very tempting to not glass your hull, just paint it and it'll be fine, right? If you've planked your hull in wood, it will expand and contract with temprature and humidity. If water gets into the wood without being able to dry, it will cause it to rot, mold will grow, and your hull will be made of spongy muck in a couple of weeks. This hull, just sitting on a shelf in a garage opened a seam in the bow that would have let water into the wood. Even if you didn't see water inside the hull, the planking would have swelled and opened more seams, even coming loose. The glass cloth acts like shrink-wrap, not only sealing the hull from water, but holding things together. It's also what allows you to plank such a hull in balsa and it be strong enough for a working model.