Building a Plank-on-Bulkhead Hull Framework
Before you begin
If you have bought your first wooden model ship kit, you will probably find several sheets of plywood containing laser-cut parts for the hull framework. Some kits use MDF or solid wood instead.
Throughout this tutorial, I will call the transverse hull-forming parts bulkheads. Although kit instructions sometimes refer to them as frames, they are usually solid profiles rather than the open structural frames used in plank-on-frame construction. We will look at plank-on-frame construction in a separate article.
The central longitudinal part into which the bulkheads fit will be referred to as the keel former. You may also see it called the false keel in kit instructions and other modelling guides.
The earlier an error occurs in a build, the more work it can take to correct later. Errors in the hull framework can be particularly difficult to put right once the planking is in place. In the following steps, we will look at both the assembly process and the potential problems worth checking along the way.
Treat this sequence as a general guide rather than a fixed assembly order. Always check the kit instructions: some internal fittings, deck components or finishing work may need to be completed earlier, while access is still available.
Step 1. Preparation
Do not remove any parts from the sheets or apply glue yet. Start by inspecting the contents.
Unpack the sheets containing the bulkheads, keel former sections and any additional transverse or longitudinal supports. Compare each sheet with the parts list, plans and instructions. Make sure that all the parts are present and that you understand the assembly sequence.
I recommend marking each part with its identification number in pencil before removing it from the sheet. Bulkheads can look very similar in both shape and size, and a mix-up may not become obvious until you start planking—when correcting it will be much more difficult.
Next, check that all the framework parts are flat and free from bowing or twist. Pay particular attention to long components such as the keel former.
If a part is distorted, decide whether it can be straightened safely or should be replaced. The appropriate method depends on the material. Do not assume that steaming or soaking is suitable for every part, particularly those made from MDF or plywood.
If necessary, make a replacement from flat material of the correct thickness, using the plans or a verified outline as a template.
A very slight distortion can sometimes be corrected during assembly by holding the part in alignment with a jig and the surrounding framework. However, check that this does not pull other parts out of position.
I usually keep a short list of issues to address during the build. It is also helpful to mark any affected part so that the problem is not forgotten.
Step 2. Dry-fitting the framework
Laser cutting is precise, but that does not mean every joint will fit perfectly without adjustment.
Carefully release the labelled parts from their sheets, cutting through the retaining tabs rather than forcing the parts out. Sand away any remaining tabs, then assemble the framework without glue.
The joints should be snug, but they should not require excessive force. If a joint is too tight, adjust it gradually and check the fit frequently.
Remove loose soot and friable laser char from surfaces that will be glued. Do not assume that the manufacturer has allowed extra material for this: sanding too much can turn a close-fitting joint into a loose one.
Another question is whether to bevel the bulkheads before or after assembly. My preference is to do the final fairing once the framework has been glued together. This makes it easier to check the relationship between neighbouring bulkheads. If the kit provides pre-bevelling marks or specific instructions, use them as a guide.
At this stage, check the straightness of the long components again, especially if the keel former is assembled from several sections. Make sure that its joints line up correctly and do not introduce a bend or twist.
Also check that the bulkheads sit at the intended heights and that their deck-supporting edges follow the lines shown on the plans.
Step 3. Gluing the framework
Once the framework fits correctly and the gluing surfaces are ready, you can begin the permanent assembly.
For this stage, I prefer an aliphatic resin wood glue, although a suitable PVA woodworking glue is also a good option.
During assembly, pay particular attention to three things:
• Squareness. Use a small engineer’s square or an accurately squared block to check that each bulkhead sits at the intended angle to the keel former—normally 90 degrees.
• Fully seated joints. Make sure that each part is inserted to its intended depth. An unnoticed gap of even a couple of millimetres can alter the hull shape or deck alignment.
• Overall alignment. Keep the keel former straight and check that the framework is not developing a twist as more parts are added.
Take particular care with any components that showed slight distortion during the initial inspection.
Use a building jig or a flat building board with suitable supports to hold the framework in alignment during assembly and while the glue dries. Do not rely on correcting a twisted framework after the glue has set.
Allow the glue to cure for the time recommended by its manufacturer before applying the loads involved in sanding and fairing.
Step 4. Sanding and fairing
Once the glue has cured and the framework is sufficiently rigid, it is time to prepare it for planking.
Bulkheads and longitudinal components have a finite thickness—often several millimetres, depending on the kit. Their unshaped edges do not automatically follow the changing angle of the hull surface. Without bevelling, a plank may touch only one corner of a bulkhead instead of bearing across the width of its edge.
The aim of fairing is to create a smooth, continuous set of supporting surfaces for the planking.
Use abrasive paper attached to a sanding block of a suitable shape and size. Coarse paper, such as 60–80 grit, can be useful for initial shaping on a robust framework, but use it cautiously. For delicate parts or small adjustments, start with a finer grade.
Where the hull shape allows, use a block long enough to span at least two adjacent bulkheads. This helps you fair them in relation to one another rather than shaping each edge in isolation. Tighter curves may require a smaller or differently shaped block.
You can work from amidships towards the bow and stern, or follow another sequence that suits the hull. The important points are to work gradually, compare both sides frequently and avoid removing too much material.
Use a flexible test batten or a strip of planking to check your progress. It should follow the hull in a smooth curve without abrupt bends, bumps or hollows, and it should bear properly against the bevelled bulkhead edges.
Repeat this check at several heights along the hull. A fair line in one position does not guarantee that the rest of the framework is ready for planking.
This work can take several sessions. As I have often found in model building, patience matters more than speed.
Step 5. Fitting filler blocks between the bulkheads — optional
Where the planking has to follow tight curves, support from the bulkhead edges alone may be limited. Filler blocks can provide a larger gluing surface and make it easier to shape and secure the planks.
They are particularly useful around the bow and, depending on the hull form, at the stern.
This operation is not included in every kit’s instructions, and many models can be built successfully without it. Nevertheless, I strongly recommend considering filler blocks in these areas.
Some modellers fill all the spaces between the bulkheads. If you choose this approach, check the plans carefully first. Do not obstruct visible interior spaces, hatch openings or areas needed for fittings and later assembly.
I use balsa blocks because they are easy to cut and sand. Smaller pieces can be glued together to form a larger block where necessary.
Fit the blocks without forcing the bulkheads apart. Once the glue has cured, trim away the excess carefully with a modelling knife, then sand the blocks to blend into the surrounding framework.
Step 4 can be treated as an initial fairing pass, followed by final fairing after the filler blocks have been installed. Alternatively, fit the blocks before beginning the main fairing work if that suits the kit’s construction sequence.
Step 6. Installing additional internal components
Check the plans for any components that must be installed before the framework is covered. These may include:
• mast steps and mast supports;
• bowsprit supports;
• gunport reinforcement;
• supports for the cap rails;
• lower-deck structures and decking;
• any other fittings that will become inaccessible after planking or deck installation.
Install these parts at the stage specified in the kit instructions, checking their positions carefully against the plans.
Where possible, dry-fit the components they will support.
This is particularly important for the masts and bowsprit. Check their positions, rake and alignment while you can still adjust the internal supports. Discovering that a mast sits at the wrong angle after the hull and deck have been covered is an unpleasant surprise.
If access to any of these parts will be lost earlier in the build, install and check them before reaching this step.
Step 7. Painting or finishing visible interior spaces — where required
The plywood, MDF or timber used for the framework is usually not intended to remain visible on the finished model. However, unfinished surfaces may still be seen through hatches, gunports, doorways or other openings.
Study the plans and identify these sightlines before closing up the hull. You can then decide how much finishing each area needs.
Option 1. A dark interior finish
For a small opening with a limited view inside, a matt black or other dark finish is often sufficient.
I use this approach for spaces behind doors and hatches on smaller models, and for areas visible through hawseholes or similar openings.
The aim is to make the unfinished structure recede into shadow without spending time on details that will not be visible. Check the result from the expected viewing angles before covering the area.
Option 2. A detailed interior finish
If an interior will be clearly visible through a large opening, an open deck or internal lighting, a more complete finish may be worthwhile.
Depending on the vessel, the available references and the level of detail you want, this could include internal planking, painted surfaces, stained timber, deck finishes and furnishings.
Keep the treatment appropriate to the vessel being modelled rather than adding decorative details simply because there is space for them.
I have great respect for modellers who fully finish interior spaces even when those spaces will never be seen from outside. My own preference is a more selective approach: I concentrate the effort where it will contribute to the finished model.
Carry out this work while access is still convenient, and keep paint or other finishes off surfaces that will need to be glued later.
Final checks
Before moving on, compare the completed framework with the plans once more.
Check that:
• the keel former is straight and the framework is free from unintended twist;
• the bulkheads are correctly aligned;
• the deck-supporting edges and hull outlines form smooth, continuous lines;
• the port and starboard sides are symmetrical where intended;
• all internal supports and other concealed components are installed;
• any interior finishing that requires access has been completed.
If you have plans printed at the model’s actual size, compare the relevant outlines and dimensions directly with the framework. Check the print scale first, especially if the plans have been copied or resized.
I also recommend photographing the internal structure before it is covered, particularly any fittings that will later be hidden. A clear photograph can save a great deal of guesswork when, perhaps a year later, you need to remember exactly where a mast step is located and how it was built.
Once these checks are complete, the hull framework is ready for the next stage of the build.
