Confederation Marine Modellers
There are a number of ways you can construct a hull. The purpose of this article is to describe the ‘rib and plank’ method as it’s one of the most common among modellers. What will be described is not the only method of building a hull. At the end we’ll mention some other methods.
This article will describe how you go about building a hull that reproduces the shape and look of a full size vessel. The hull will be hollow so that it can contain the power and controls to make a sailing model. Building the hull will include fitting the deck, but not the superstructure.
The first thing you need is a plan, and specifically a “Lines Plan”. If you buy a copy of the shipbuilder’s plans then you will probably get the lines plan as a separate drawing sheet. If you obtain a plan that has been prepared specially for making a model, the information you need will probably be a part of the whole plan.
The first part you need from the Lines Plan is the Body Plan. To illustrate the method we’re going to use the plans for a Clyde Puffer. This is a free modeller’s plan available from www.freeshipplans.com. The method will be the same if you obtain copies of the original shipbuilder’s plan for your vessel.
The body plan for the hull of the Clyde puffer is shown in Figure 1. On this one diagram is shown the complete shape of the hull. The vertical line down the middle represents the bow-to-stern centreline of the hull. The shape of the hull from midships to the bow is shown on the right side of this diagram, and the shape from midships to the stern is shown on the left side. (You can tell the left is the stern because it has a hole for the propeller shaft.) This is sufficient to make a complete hull.
To understand what the body plan shows, imagine you have the finished hull. Then at different locations along the length you slice it into sections. Figure 2 shows such a section for a ship’s hull.
Now take the section of Figure 2 and cut it in half on the centreline, turn the open end towards you, and trace the outer edge of the face. You will get an outline as in Figure 3. This process is repeated for all the sections you cut; they are numbered from stern to bow and then all drawn onto one diagram with a common centreline, as shown in Figure 1. So building your model reverses this process. You make ribs to the same shape as the numbered outlines and assemble them. Once that is done you form a hull by glueing planks on the outside.
The second part of the Lines Plan you need is the “Sheer Plan”. This is a side view of the hull and the important information for us on this plan is the location of each of the ribs we will make. If you are working from a modeller’s plan, the Sheer Plan is probably incorporated into a profile view of the vessel. The profile view and Sheer Plan for the Clyde puffer is shown in Figure 14.
There is a plethora of excellent information on the internet about how to plank a hull, where you can learn all about ‘stealers’ and ‘spiling’. Almost all of it refers to old-time sailing ships, where all of the finished planking is visible. They provide a good introduction to the topic, but this article is about merchant ships which will have the planking covered in fibreglass and paint, and not be visible. It is not necessary on such models to continue the planking right up to the bow or to the stern. It is easier to use either solid blocks or layers in these areas and shape them as necessary. The blocks can be any suitable material, such as wood, or pink or blue foam insulation.
When shaping these blocks we need an external template for the shape, instead of an internal template for a rib.
Deciding how the deck will fit.
The third piece of plan information you need is the deck plan. For the Clyde puffer this is simply a drawing of the deck viewed from above. For a shipbuilder’s plan you will get the same information from a General Arrangement drawing showing the deck.
Neither of these sources will tell you how the deck and the hull fit together. There are two choices: the deck fits on top of the hull planking, or it fits inside the hull planking. If you fit the deck inside the planking, the deck forms a guide between ribs that you trim the top plank to. It’s the modeller’s choice about which way to do it.
Your choice will be influenced by how you make the bulwarks, which is discussed later.
Stacking the ribs.
Figure 4 shows the ribs that Ernie assembled for his model of the ferry Egremont. This shows you how the assembled ribs will look. There are 4 things in particular to note from this picture.
1 The ribs are set on a plank or board. This is a vital piece for the hull building process, and needs to be strong and flat.
2 The ribs are arranged with the bottom of the hull at the top. (This is called “keel up” - the keel is a longitudinal structure running along the bottom of the hull on the centreline.) The advantage in building the hull upside down is that the whole of the hull (except the deck) can be built in this position.
3 Most of the ribs have holes in the middle. This provides a reasonably clear space to fit the internal parts; the motors, radio, servos, etc.
4 Not all the ribs are the same height. This occurs near the bow and the stern where often the hull is not as deep.
Making the ribs and templates.
To make the ribs we first need to create templates of the right shape. This involves the following steps.
Step 1. Because the ribs have to be the full width of the hull we need to make a full-width template, and then cut a rib out of wood to that shape.
Step 2. One way to do this is to take a scan of the body plan, and digitally separate the bow and stern sides. Flip a copy of what’s left so that you make a mirror image, which you combine with the original to make the full-width template, as shown in Figure 5 for the bow portion of the plan. Suitable software is Photoshop Elements, or OpenOffice Draw (which is free).
For those without a computer, the alternative method is to print out a copy of the original body plan, fold it in half down the centreline, cut out the pattern of the template, and then unfold it.
Step 3. All of the ribs will need to be positioned on the building board so that their hull shapes are at the correct height relative to one another. We make sure that this happens by drawing a horizontal baseline at a fixed distance from the hull bottom. See figure 6. This is where we will cut the edge of the template, where the rib will rest on the building board. There is no hard-and-fast rule about where to position this baseline, but between 1 and 3 inches above the deck line is reasonable.
Step 4 On figures 1 and 5, the position of the deck edge is shown by the dotted line that runs across from side to side. This shows where the deck meets the hull side at each rib.
Step 5. At this point, let’s focus our attention on just one rib, say number 16, by erasing all the rest. This is shown in Figure 7. The position of the deck is shown by the “Deck line”, a horizontal line drawn through the intersection of rib 16 with the dotted deck-edge line.
Ensure that you draw the hull centreline all the way to the baseline. You will use this to position the ribs so that they all line up correctly.
The outline of the finished hull body at rib 16 is shown in green in Figure 7.
Step 6. It is at this time that you need to know the materials you will use to make the deck and the hull sides. The outline of the rib shown in Figure 7 must be lowered at the deck line by the thickness of material to be used for the deck. The outline must be reduced on the rest of the edges by the thickness of the planking. These new lines should be drawn inside the hull and deck lines, as shown by the red lines in Figure 8.
Step 7. The outline that we need to work with is thus shown in Figure 9.
Step 8. Rib 16 may be one of the ribs that should have a cutout in the middle. Some modellers like to have one or two ribs which do not have a cutout and, in effect, act as watertight bulkheads in case water gets into the hull. Let’s assume that rib 16 is to have a cutout. There is no fixed rule about what size it should be, but ½” (15mm) is reasonable for the rib width which remains. At the same time a notch should be marked at the bottom for the keel.
Step 9. If the rib is in a part of the hull where we want access to the internals, we will eventually need to remove the top piece. For example, if the rib is under the superstructure, or in way of a hatch, these areas can be used for internal access. In the Clyde puffer, rib 16 is not under the hatch or superstructure. (Another part of the plan - which is not shown here - indicates that the hatch opening extends only to rib 13.) For present purposes we will assume that we will want access at rib 16.
Mark 2 lines (shown dotted in Figure 11) where the top part of the rib will be cut out. (If there was a hatch or superstructure at this rib we would want these dotted lines to line up with the edge.)
Step 10. The last step in preparing this template for rib 16 is to extend the template to the baseline, so that we can position the rib at the correct height. The simplest way to do this is to extend the cutting lines we added in step 9. The final outline is shown in Figure 12, with the cutting outline shown in red.
After the hull has been planked, it can be turned right side up and a saw used to cut through the top cross-piece and so remove the extension that was necessary to position the rib on the building board.
To attach the rib to the building board you want to screw it down and have the screws accessible outside the edge of the hull. Glue wooden strips across the baseline edge of the rib as shown in Figures 19 – 21.
Step 11. Let’s go back to Step 9 and discuss how we should make the rib template when we don’t want access to the internals at the position of rib 16, or we don’t want a cutout. We go back to the outline as we had it in Figure 10, and add the extension that we applied in Figure 12. We have to separate the extension with a horizontal cut.
A suggested way of doing this is to drill two holes a short way in, say ½”, from the edge of the extension at deck level, and then make a cut between them, as shown in Figure 13. Ease of cutting off the extension is the reason for doing this. The cut between the holes can be done on a scroll saw, but the outside cuts must be done with a handsaw. Only two short cuts are needed to remove the extension. This is also a way of removing the extension if you do make a cutout in the middle of the rib.
Step 12. Steps 1 to 10 or 11 are repeated for the remaining ribs.
Step 13. After the rib templates have been prepared they are transferred to the material that will be used for the ribs. The templates can be printed on paper which is then glued to the material, or the outlines can be transferred by some other means. The ribs are then cut to shape.
Step 14. The cut ribs have to be mounted on a building board. The distance between each rib is found by referring to the side view on the lines plan or the profile. The side view of the Clyde puffer hull is shown in Figure 14. Along the bottom, this shows the location of each rib along the length of the hull. A line should be marked down the centre of the building board, and each rib centreline aligned with it. The ribs should be secured to the building board so that they do not move while the planks are glued.
Step 15. If this is indeed your first hull, it is probably a good idea to glue copies of the templates to cardboard (cereal boxes are good for this), cut them to shape, and then locate them on the building board. This will give you a clear idea of the shape and help you to decide where to end the planking near the ends and change to solid, shaped blocks.
Step 16. The position and size of opening for the anchors should be considered when deciding where to use solid blocks at the bow. The hawse pipe (which the anchor chain runs through between deck and hull side) is near the bow. You can decide whether you want to have the pipe fully represented by a through hole, or just a recess at each end. Some vessels, especially tugs, have a recess that the anchor fits into when housed. This would have to be cut out and modelled after planking the hull.
Step 17. Templates for checking the shape of the end blocks need to be external – you cut out the portion inside the line. If you took account of the planking thickness as described in Step 5, you can use the outline directly from the Body Plan. You can make a one-half external template and use it for both sides, as shown in Figure 15 for section 17.
Step 18. The edges of the ribs near the bow and the stern should be sanded to an angle so that the planks contact the full width of the rib. This can be checked just by placing a plank in position across the ribs.
Step 19. The final step prior to planking is to fit the keel. The outer edge of the keel follows the outline of the hull shown in red in the side view of Figure 14. Its depth is a matter of personal choice, but obviously has to match the depth of the notch cut into the ribs. The keel can be made in one piece, or several pieces glued together. If made from several pieces the joints should have overlaps to give it strength.