Building Small-Scale Clinker Boats

[wefalck]

This has been buried deeply in my building-log for S.M.S. WESPE and not everyone is interested in 1870s warships. Thus, potentially interested people may have missed this description of building small-scale clinkered open boats. So, I decided to pull this part out, edit it for the purpose, and post it separately.

 

Clinkered open boats in small scale (the examples below are in 1/160 or N-railway scale) can be a challenge. The processes described below are based on paper parts cut with a small and cheap 3W laser-cutter. If one has a stronger laser-cutter, the same method can be used with thicker cardboard or even styrene and may give even crisper results. There are even various laser-cut kits for such small boats in 1/72 on the market.

 

Actually, the construction methods described below are adaptations of the well-known plank-on-bulkhead (POB) and plank-on-frame (POF) methods.

 

Starting point, of course, are a set of suitable plans, line- and body-plan, plus ideally information on the actual construction, dimension of scantlings etc.

 Example of a drawing for a gig from the early 1880s.

 

Two construction strategies are described one for boats covered with canvass, so that the interior structure is not visible and does not need to be modelled. The other example is for a plank-on-frame open boat model that shows all interior and construction details that one can possibly show at the chosen scale.

 

 

Plank-on-Bulkhead (POB) construction of open boats closed with a cover

 

Traditionally, one would carve a ‘plug’ for the boat from a piece of wood, that is based on the dimensions inside the planking(!). Such a plug can be re-used in case another copy of the boat would be needed. Otherwise, one can plank directly on the plug.

For the method proposed here, each individual framing stations from the body plan was redrawn as a bulkhead to be cut out with the laser-cutter. Additional material is left on the top, so that all bulkhead scan be glued to a building board arriving at the right height. As backbone, a longitudinal profile of the boat, inside the planking, is drawn. All pieces were slotted as it is common practice in POB construction. The slots were twice as wide as the paper, as all pieces were cut in double to be soaked and varnished together back-to-back with a view to increase their stiffness. In addition, two pieces that represent the outboard profile of the stem-post, keel, and stern-post were cut, plus two copies of the transom.

The bulkheads etc. were arranged on a drawing that controlled the laser-cutter. 

 

 Template for laser-cutting the keel-pieces and the stem-keel-combinations for a cutter

 

The material used is so-called Canson-paper, which is around 0.12 mm thick and an unglued, but heavily rolled paper. Its surface thus is quite smooth. This kind of paper turned out to be the most suitable for cutting with the low-powered (3W) laser-cutter.

 Laser-cut bulkheads and keel-pieces

 

The pieces then are assembled as is tradition for POB-construction and mounted onto a piece of Canson-paper for extra stiffness. The whole assembly is then mounted on a small piece of wood to ease handling.

The assembled parts for the POB-construction

 

To increase the stiffness of the assembly (which in fact is already surprisingly robust), the spaces between the bulkheads are filled with a hard foam. I am using an acrylic resin foam, that is being produced by the manufacturers of Plexiglas, but any hard foam will do. The foam is sanded back to the profile of the bulkheads and then soaked in varnish. Imperfection can be corrected with automotive putty. This will give ample surface for the planking to attach to. Note that due to their thinness, the bulkheads do not need to be bevelled.

 Foam-filled framework with three strakes on

 

The planks are laser-cut from the same paper. Tapering such planks by hand would be too much of a challenge and not quite feasible in paper, I think. However, my 2D-CAD program gives the length of the Bezier-curves used to draw the outline of the frames. So, one can simply take this length, divide it by the number of planks and add 50% for the clinker overlap in order to arrive at the plank width at each station. In reality that planks would overlap above and below only for about 25% of their width, but the extra width will not be seen on the completed model and gives extra leeway to accommodate small inaccuracies during construction. With this information somewhat too long planks were drawn with a few extras, as not all turn out well. A wider plank is provided for the garboard.

In theory, the planks should not only be tapered, but also curved in the plane, but I do not have a software to develop a full planking diagram. However, when wetted with varnish, the paper, unlike wood, can be relatively easily bent and shaped across the wide side of the plank.

Materials and tools for planking

 

When laser-cutting the tapered planks, the curves are so shallow, that the ‘stepping’ due to the 0.1 mm resolution of the cutter becomes quite pronounced. For this reason, the planks were drawn with a straight line on one side and the tapering curve only on the other. The straight edge will become the visible lower edge of the plank, while the stepped, curved side will disappear under the plank above.

When fitting the planks, the best way is to fix them in the middle first and then work towards the ends. As can be seen on some of the pictures, originally, I put the doubling of the stempost-keel piece in place before the planking in order form a rabbet against which the planks run. This turned out to be not very practical, as precise fitting is quite difficult with this material. Now I am drawing the backbone to the inside of the planking and add a false stempost-keel piece afterwards. This greatly facilitates the planking at the bow.

Planking progresses from the middle to the ends

 

All planks are cut flush to the interior backbone using a micro-scissors or cuticle scissors. When heavily soaked in varnish, the paper can be cautiously sanded. The soaking in fast-drying varnish has to be repeated after a few strokes with a diamond nail-file to prevent the paper from fraying.

In clinker construction, at the bow, where it meets the stem-rabbet, the lower planks are thinned out by the width of the overlap and over a length of 1.5 to 2 plank widths or so. In this way the planks are flush at the rabbet. This is a feature, that at this scale is neigh impossible to reproduce, so one needs to cheat a bit again. Luckily, as long as the varnish is still wet, the paper can be squeezed and moulded. The thinning can also be simulated by squeezing the edge with flat pliers or splinter tweezers that have been ground flat at the end. While the varnish sets, the edges are squeezed tight using locking tweezers. The same thinning procedures is applied to where the planks touch the stern-post or the transom.

Clamping the planks tight at the bows

 

The planking is done mostly by eye, as it is difficult to mark out the planking run with sufficient precision on such a small workpiece. It is advisable to use an organic solvent-based varnish for the purpose. A drop of acetone softens the varnish and allows to make small corrections in the run of the planking.

 

To be continued …

 

Edited 21 hours ago by wefalck
Missing pictures

[tkay11]

Looking forward to the illustrations and the rest of the guide. Great idea.

 

Thanks

 

Tony

[shipman]

It would be convenient to me if the illustrations were jpeg files not png's.

[wefalck]

@tkay11 Sorry for the missing pictures initially. Don't know what happened to them, as they appeared while I was composing the post. Now corrected!

 

@shipman My original pictures are JPGs and uploaded as such. However, it seems that the MSW forum software converts these into PNGs so that their size can be automatically adjusted to the width of the screen. I have no control over that.

Edited 18 hours ago by wefalck

[wefalck]

Continuation ...

 

Planking of a gig completed

Once the planking is completed, the excess material at the stem and stern/transom can be trimmed off flush. For this so-called cutting-tweezers as used by watchmakers to shorten watch springs are a very handy tool. The planked hull can now be given a coat of varnish to consolidate and further stabilise it. It then is rubbed down cautiously with fine (0000) steel-wool to smooth it. If needed, imperfections can be touched up with putty and sanded.

The next step is to glue the combination of keel and stem-post into place using the same varnish. This was laminated from several copies of the same laser-cut shape to achieve the necessary thickness. Any gaps can be filled with putty.

Many boats are fitted with rubbing strakes. Depending on how they look, they can be made from either very narrow laser-cut strips of paper or from thin wire that glued down with varnish.

 

Rubbing strake from 0.2 mm copper-wire installed on a gig

 

This basically completes the boat construction and it is ready to be cut from the building base. The next steps depend on how the prototype is arranged, i.e. whether it is suspended from davits, stands in chocks, or may be is placed upside down on a boat-skid. The bulkheads have to be cut down and the backbone be trimmed to a line that e,g, would be followed by the tarpaulin cover or that of the gunwale.

 

The completed planking on a cutter

 

If there are hoisting chains fore and aft to which the falls of the boat-davits will be hooked, only the top ring would be protruding from the boat-cover. This chain can simulated using a twisted-together piece of coper-wire of suitable thickness. The wire will be hooked into a bulkhead and glued down with varnish.  

Gig cut free from the building base (note: here the hull was not filled with foam)

 

Completed cutter cut free from the building board

 

Boats slung from davits or sitting upright in chocks are exposed to the elements and, therefore, often covered with a tarpaulin. The designs for such covers vary, but typically triangular pieces of canvass are sewn to the edges to which lanyards are spliced to tie the cover down. Other designs may use a draw-string in a hollow seam that goes all around the boat below the rubbing strake – much like purse-strings.

 

Very light-weight Japanese silk-paper for tarpaulins, sails etc.

Gig with simulated cover

 

The boat-cover is cut to the rough shape from a piece of thin silk-paper, draped over the boat and soaked in sanding filler. It is then smoothed down over the edges and down to the rubbing strake. Once dry the paper is cautiously cut back to the rubbing-strake with a new scalpel-blade. Now, if necessary, the canvass triangles can be added. The draw strings are only added after painting.

 

Rudder-pintles are made from short pieces of copper-wire or appropriate diameter and the respective bands are simulated by flattened copper-wire. All parts are cemented in place with varnish.

 

The boat is now ready for painting. The procedure depends on the colour scheme, of course. As the boat-covers are typically off-white (i.e. oiled canvas), it may make sense to give the whole boat a coat of white paint with the airbrush. This kind of basecoat (though technically not needed) allows to better see imperfections, that may need to be fixed before final painting. To be honest the results can be quite sobering: all the imperfections that were not visible in the ‘raw’ state now begin to stick out. Any jagged edges from the laser cutting that seem to disappear under the varnish become now rather visible. So some more filing and putty-work may be required. It is important to remember that we are talking about small boats, perhaps two to four centimetres long with a beam of barely one centimetre  …

 

Painted cutter in 1/160 scale

 

One should add, that laser-cut parts can also be used as templates (when drawn to the outside of the planking) for the frame-stations when carving solid hulls from wood to make carvel-built boats. They could be completed then with the same kind of laser-cut stem-keel-piece. Trying to build carvel-hulls with laser-cut paper planking may not be so successful, as paper does not sand very well. However, a good amount of putty could help here and at the bottom line may be quicker than carving with frequent checking of the shape against templates.

 

To be continued …

[BANYAN]

Thanks for this wonderful mini-tute Eberhard.  It is a great reminder of what can be done at such scales. The strakes turned out very symmetrical and look the real deal.  Those boats were very low in the water with a low freeboard by the looks of it.  When fully loaded the troops must have gotten a tad wet I think.

 

cheers

 

Pat