Scratch Building a Model Warship

November 7, 2010

in Warship Construction Manual

Original Article by Phil Sensibaugh. Edited by Bill Pickl and Strike Models. Note: this is one section of a comprehensive model warship construction manual originally published on the BDE/RC website. This section is applicable to both Big Gun and Fast Gun combat.

Strike Models Note: We advise talking to someone who has already built a ship from scratch, as they can be a big help. Also, please check your club’s rules regarding rib spacing and allowed penetrable area and use those rules over what we included here. A very detailed instructional forum thread about scratch building a SMS Pommern (a predreadnought) is being chronicled on the RC Naval Combat website.

I have often been asked what I felt was the best way to construct a hull “from scratch.”  I’ve seen several methods used with some methods working better than others, yet still I’m not sure if there is one best method. I believe if the hull doesn’t warp, isn’t overly heavy, and floats somewhat level when empty (no major list) it’s a good hull. I suppose I should add in one other criterion as well, it shouldn’t leak. This article will cover: Making a Pattern Set, Selecting Construction Material, and Assembly.

The premise for developing patterns sets for a scratch built hull is that the ship will be built on a flat bottom plate with ribs, bow and stern keels being glued in vertically all topped by a caprail. Strike Models offers several such pattern sets ready for cutting and assembly, but this section will cover the basics of developing your own pattern sets should they not be commercially available. Using the baseplate method of building is recommended otherwise you will have to set the ribs on a keel, which requires jigs and fixtures to achieve good results and the keel will be in the way later anyway. Flat bottom boats are much easier to build, but don’t confuse a flat bottom with a shoebox shaped hull. The sides will still be rounded, as will most of the hull below the waterline. Real warships are generally flat on the bottom as can be verified by your ship plans.

First, obtain a set of plans for your ship. The greater the detail shown on the plans the better, but don’t be surprised if the detail is lacking. Often a set of plans consists of a top and side view of the hull and superstructure and a drawing of the ribs at a few stations along the hull, but this will suffice. [If you contact Strike Models, we can tell you the level of detail for each particular plan we sell.] The plans usually don’t provide enough ribs for the required spacing (1, 2, or 3 inches) so you will need to draw additional ribs. Look at the overhead view of the provided rib locations. Next decide the spacing you will use. Use of 1/4″ wide ribs on 2″ spacing is the most common selection, but for large ships 3/8″ wide ribs on 3″ spacing is also used (Big Gun only, and even that is dependent upon your club. Fast Gun has significantly different rules). With your spacing selected you will need to draw lines on your overhead view where you need to add ribs. You will often need to add one and sometimes up to three ribs in between those provided by the plan set. What I recommend is making a copy of the original ribs and hand sketching the correct number of ribs in-between the provided rib profiles.  Just eyeball even spacing for the number of ribs you are adding. Be sure to reduce the overall rib width by the thickness of the balsa sheeting on the hull, and the overall height by the thickness of the caprail and bottom plate. Do this by drawing a line below (3/8″ for plastic 1/4″ for wood) the top of the rib for your new rib top and a line 1/8″ above the bottom of the boat. Also draw reference lines for  the water line and a line one inch below the water line across the ribs. Note that often only half of the ribs are drawn, so you’ll have to draw the mirror image of each rib the best you can including the added ribs. When I do so I use a light tracing paper that you can see through easily, draw half the rib, fold the paper in half then copy the other half of the rib off the first half. Another method is to make a copy of the ribs then trace them on the back of the paper copy, thus making a mirror image. When you have a complete set of full width ribs COPY all of your work and save the original drawings. Make one copy for each of the ribs.

For each rib highlight the correct exterior hull line the top and bottom (remember to follow the lines that allow for the bottom plate and the caprail). Also on the exterior line mark an 1/8″ deep notch on each side of the rib at a point starting one inch below the waterline and extending to the bottom of the rib. Hardwood stringers will be installed here later on to help form the impenetrable area of you hull. On some of the wider ribs you will not need a rib that goes completely across the bottom of the hull. If the flat spot in the rib is more than 4.5″ wide then you will draw a left and right piece. You may wish to read the section on water channels at this point so you can design your rib patterns to accommodate water channeling. The water channel will be 2.75″ wide so measure 1-5/8″ inches left and right of the center point on the flat bottom of the rib profile to allow for the water channel stringer. Make these marks 1/4″ high. At the outer edge of the flat spot measure 1/2″ up and draw a diagonal from that point to the top of the 1/4″ tall line that marked the top of the innermost edge of the rib’s bottom.  Next sketch in a line about 1/2″ in from the exterior hull line to complete the inside edge of your rib. You will want to mark the location of the prop shafts on the appropriate rib patterns, usually the rib just forward of the propeller and the two ribs forward of where the shaft enters the hull. For the rib just forward of the prop you will need to draw in braces to support a circle big enough to drill the hole through for the prop packing tube.

The next items to make patterns for are the bow and stern keel plates, the caprail, and the baseplate. Start with the base plate. Take your rib patterns and measure the “flat” width at the bottom of the ribs. For all ribs with a flat spot at least 3/8″ wide and that touch the bottom plate transfer those measurements over to a sheet of paper. Remember to also measure the distance from the bow to each rib from your overhead view and transfer these to your base plate pattern. You should end up with a center line with rib locations marked and each rib location will have a perpendicular line centered on the center line that represents the width of the flat bottom of the rib. To complete the base plate pattern just connect the outer edge of the rib lines. Next to make the bow and stern keels trace the side view of the bow and stern profile. Measure in about 1/2″ in from the profile and make another line. You will want to make the keels long enough to overlap the base plate at least 3 inches. Remember to make a 1/8″ allowance for the base plate. Also note that a few of the forward and stern ribs will not attach to the base plate but to either the bow or stern keel. These rib drawings should be modified with a notch to slide onto the keel and remember to keep the depth of the ribs all the way to the bottom of the keel, since they do not rest on the bottom plate. Some ribs that are on the base plate may need to have a notch added to their pattern to allow for the overlapping bow and stern keels. To make a pattern for the caprail trace the outer edge of the ships deck from the overhead view (please note that some odd ships are wider at the waterline then at the deck or caprail level). Draw a second line a half inch in to complete the pattern. You may also wish to design in some cross braces into the caprail pattern. These help the ship maintain its desired width and to reinforce the hull should it ever need to be pulled from the water with 100 pounds of water in it!  Make copies of all these patterns as well.

You are now ready to select the material for your scratch built hull. Some people prefer 5-layer plywood, while the MBG (Midwest Battle Group) now has three plastic hulled ships. The plastic is foamed PVC and can be obtained in various thickness’ from an industrial plastics supplier. Foamed PVC enjoys the advantage of being lightweight and strong, easily cut and glued with CA glue, is inherently waterproof and will not warp or rot. If you do chose to use plywood the following precautions must be followed. Cut your caprail and base plate patterns into pieces between 12 to 18 inches to prevent the wood from warping. Cuts should be made at a rib location.

Glue the copies of the tracings to plywood using Elmer’s glue, or some other water-soluble glue, then saw them out slightly oversize. Use material of the appropriate thickness corresponding to the rib spacing of your pattern. For the base plate use 1/8″ and for the caprail use 3/8″ for plastic and 1/4″ for wood. Next sand the pieces to the correct size. Finally remove the paper from the wood or plastic with warm soapy water, then dry the parts well. Don’t be concerned if the wood parts warp somewhat. If the wood is going to warp, now is the time to find out. If warping of the longest sections of the cap rail or bottom plate occurs just cut them into shorter sections, preferably at rib location. A little warp won’t hurt anything at this stage of construction. We’ll fix it later.

If you chose wood as your material you will need to glue sections of the caprail and base plate together, end to end on a flat surface and while laying over a tracing of the plans. This will ensure the sections have the proper curve to match the hull. Likewise, with the bottom sections of the hull. Epoxy glue works well for this purpose, but CA is too brittle and will not work well. Don’t be concerned if they look weak lying there. We’ll strengthen them plenty later on. When the glue dries, lay these sections over the plans and mark the positions where the ribs will attach. Now attach the ribs to the base plate with one or two drops of CA glue. Don’t glue them too well right now since you may need to remove the later if something doesn’t line up right. Next, look at the hull from the end and visually verify that the ribs are symmetrical on both sides of the hull. There’s a photo of this step later in this article. Now attach the cap rail to the top of the ribs. Some of the ribs may not line up with the cap rail well, but don’t force the caprail down, or up to the ribs. Trim or file the ribs as needed to line up with the level caprail. Note the word level!  There are photos accompanying this article that will help you visualize how the hull will go together.

Once the hull is glued (tacked) together in this state it will still be very frail so handle with care, but don’t panic yet. Next will come the strengthening. Place the hull on a flat surface and inspect carefully to see if the hull has developed a warp. If so just break a few glue joints to relieve the pressure, then glue them again. You may also need to make a few cuts through the caprail or base plate to relieve pressure to eliminate the warp. Make as many cuts as needed to get the warp out. Once again, don’t worry, you’re not weakening your hull permanently.

Now the strengthening of the hull begins. For wood hulls install hardwood (spruce) strips the thickness of the balsa sheeting allowed (1/16 to 1/8 inch). These stringers will be 3/8″ wide. This width will allow the strip to overlap the ribs by 1/8″, since the wood caprail is only 1/4″ thick. These strips are installed around the caprail on the inside and outside of the hull. You can cut the stringers into shorter sections, but make sure the joints are staggered and the inside stringer joint does not occur on the same rib as the outside stringer.  Again installing them on the bow and the stern is the trickiest part to accomplish. To allow the hardwood to bend around the curved areas cut notches about 2/3 though the wood stringer about every 1/4″ in the inside the side that will be next to the hull, then bend the stringer until it cracks at the notches. I use the Dremel tool and cut off wheel to make the notches.

Next, install 1/8″ by 1/8″ stringers (preferably spruce) in the notched portion of the ribs that starts 1″ below the waterline and extends down to the base plate. The stringers do not need to butt up closely together, as you will cover this portion of the hull with fiberglass. Assuming your hull is still true and not warped go back and brush epoxy glue on all wood joints that were tacked with CA glue. For plastic joints a bead of CA glue along both sides of the joint will permanently bond the plastic parts together. Invert the hull and brush the epoxy inside the sandwich formed by the two hardwood stringers and the caprail. Wait for the epoxy to cure and you’ll see that this step will have strengthened your hull dramatically.

Now the hull should look nearly complete save for the side skin. Sand all outer surfaces of the hull so that they are smooth in preparation for fiberglassing the bottom. Next, place the hull top down on a flat surface and add spacer beneath it to allow it to lay flat and be supported. If the hull has taken on any warp you must get the warp out at this time. Check the hull closely for warping. Don’t be afraid to cut the hull in two and glue it back together if needed to correct a warp. Now is the best time to fix them.

Fiberglass resin has quite an aroma (it stinks) so find an area to work with good ventilation. Cover the work area with a sheet of plastic. Now make a stand to hold the hull off the work so it can lay inverted (upside down) and be stable. The stand must hold the entire hull (for wood only) off the work area to include the bow and cap rail since we’ll be glassing them also.

Next, cut the lightweight fiberglass cloth in to small sections about 12″ square, or whatever size or shape is needed to cover the hull. Small sections of cloth are easier to work with and to keep air pockets out of. At this point I would recommend purchasing an ultra violet cured resin sold by SolarEZ. This stuff is just like epoxy resin with the added bonus of only hardening when exposed to about 30 minutes of strong sunlight. If you keep the windows covered in your shop you will be able to work at your own pace rather than at the pace of the setting time of normal resin. Apply a thin coat of resin to the hull bottom and sides down to the penetrable area, then lay on a section of fiberglass cloth and apply another thin coat of resin over the cloth. Repeat this procedure to apply the next section of cloth, overlapping the previous section by 1/4″ to 1/2″. Continue laying cloth until all the wood stringers on the bottom of the hull are covered with fiberglass cloth and resin. Remember a thin coat of resin is all that is desired. Applying more resin just makes a mess and increases the amount of sanding needed. Sanding fiberglass is no fun. The cloth will try to “slip” across the wood as you brush resin on, so reverse directions of your brush strokes regularly and use a gloved hand to push or pull the cloth. As you are progressing smooth out the cloth, working out all air pockets and wrinkles. Cut the cloth with an Exacto knife to let the air escape if necessary and overlap the cloth at the cut then smooth it down. This will be especially necessary in the bow and stern where there are a lot of curves. Continue this effort until the hull is covered, bow to stern, to include the solid bow and stern blocks.

Allow the fiberglass resin to partially set, then using an Exacto knife cut away any excess fiberglass cloth that has extended into the penetrable areas of the ship. After cutting, smooth the cloth down again along the cut edge using a gloved hand. Wetting the resin with water first to provide some lubrication helps to keep the resin smooth. As soon as the resin on the bottom of the hull is set enough (but not fully cured) invert the hull and apply cloth and glass to the top of the bow stern and cap rail, overlapping the sides of the caprail down to the penetrable area. When you are through the entire outside of the hull will be covered with fiberglass cloth and resin except for the penetrable areas. Once the resin begins to set up trim away any cloth that extended into the penetrable areas and smooth down the cloth. Remember no wrinkles or air bubbles should be allowed in the cloth. Now invert the hull and sit it back on the wooden block upside down.

Apply another layer of glass cloth and resin down the center of the hull bottom from bow to stern. This sheet does not need to extend up the side of the hull to the penetrable area, but just cover the flat part of the hull bottom to provide more reinforcing in the base plate to strengthen the butt joints that were glued together.

At this point you may want to install optional frames to butt your balsa sheeting up against. Some people like these since they create a “window frame” that you cut the balsa to fit into. The advantage is that all the work in tapering the balsa sheet to the hull profile is done once with the frame the disadvantage is that when you install the balsa it has to be cut to fit this frame. If you decide to add this frame you’ll need to get some wood stringers that are 14″ wide and the thickness of your balsa sheeting. Glue these 1.25″ below the waterline (this gives a 1/4″ of hull for you balsa to glue on to) and 1/4″ fore and aft of the penetrable areas. Use automotive putty to taper the edge of the framing to the ship’s hull. Let dry and sand. You may need to apply a few layers to get it smooth.

Brush another thin coat of resin over the entire hull and caprail. As this coat of resin sets make sure the job “looks right.”  Look for thin spots in the resin. If it looks good and you are happy with it then let the hull dry completely. Otherwise, apply another thin coat of resin. If there are a few “rough” areas it won’t make all that much difference and they will be corrected later. On a warm day this could take only a few hours for the resin to cure, other times it can take several days for all “tackiness” to vanish. Again the two part resins are tricky things to mix and the solar cured resin is preferred although use of an old mirror might be required to get the sun to all parts of the hull for complete curing.

Once the fiberglass resin has set completely sand lightly with fine grit (150) sandpaper on a sanding block or orbital sander. Sand lightly is a key word. You do not want to sand through the resin and into the cloth anywhere! After the sanding is complete wipe off the hull with a damp cloth then skim on a coat of automotive putty over the entire hull surface that was fiber glassed. A plastic putty knife works well to skim on the filler, allowing the filler to fill in only low spots and to smooth out rough areas. I recommend the automotive filler putty because it is easy to work with, is waterproof, and is easy to sand. Once it dries sand the hull again. You may have to repeat this procedure to get a really smooth finish, especially in the areas where the glass cloth was overlapped.

Now all you need to do is to skin the ship by gluing the appropriate thickness of balsa wood sheeting.

Click each image to enlarge. We apologize, but this is the best resolution we have for these images.

Previous post:

Next post: