Builing an IOM Model Yacht
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Making foam plug
  Glassing Hull  
  Finishing hull  
Making a Wooden Boat
  Making wooden plug / hull  
  Making a wooden deck  
  Finishing hull  
 

To build a wooden IOM shell you will need planks, typically of either Balsa (lighter, weaker, easier to work, but will need glass sheathing, probably inside and out) or Wester Red Cedar (still best to glass sheath, but not essential and thinner glass possible). For most people best to pay a specialist for the planks, cutting your own is very tricky. Mine were actually "Brazilian Cedar", very pretty, but a little heavier than Western Red Cedar.

 

Planks should be at least 1100 mm long, ideally 10 mm wide and 3 mm deep. Slightly thinner (2.7mm) is better, but hard to obtain.

Make a method of holding the planks so you can plane them. I used bits of old venetian blinds 3 mm apart, and deeper in the middle secured to a flat 1.3 metre piece of wood, held in my vice .

 

I also hold the plank with one hand while planing with the other hand. The small block plane works well for me. Modellers planes also good. Planks tend to be narrow at the front and back depending on boat shape, and angled on one edge.

 

My building frame is a piece of 1" MDF, about 1.3 metres * 400 mm. I have a very straight line drawn down the centre of this to align the (shadows / sections (just a name, same thing), and because I choose to have frames every 50 mm I marked off lines at rt angles to the centre line every 50 mm, starting at the transom. Some just have shadows every 100 mm. For me I made the shadws from 6 mm plywood, cut on a bandsaw and finished with spokeshave. All shadows were traced from a set of full sized plans (in my case from Ian Vickers V8 design). All have a centre line and in this case the chines are pen marked on them. All are glued to a piece of 11/2" *1" and screwed to the board so they are exactly in the right place (from the widest point of the boat aft the back of the shadows are exactly on the lines across the board, and from the widest point forwards the front of the shadow is on the line across) are and the centre line is vertical, so the boat is straight. It is possible to get laser cut shadows, more accurate than I can do.

  All shadows are covered in parcel tape where the planks will touch en to stop they glueing to the shadows. I started planking with 2 planks either side of the centre line, so I have a perfect centre line for putting in keel case and mast, frames etc. Planks are glued to each other, in my case with "Titebond 111", a water resistant PVA. The bow and transom shadows are a special case, where I have the actual bow and transom in place, so no parcel tape, so the planks can be glued to them. I also attached a false bow in front of the real bow (see picture above) and a false transom behind the true transom to help make the planking easier. In the case of the V8, the bow is very fine, so it needs extra support as shown with the foam between shadow 0.5 and the bow. The bow, transom and false bow and transom need a bit of shaping to let the plank fit flat on the frames.
The next planks are on the gunwale line, helping steady the boat sideways
 

I secured each plank with fine staples or pins. This shell was actually a plug for a glass fibre boat, so pin holes did not matter. With care, sticky tape and small clamps and pins into the shadows but not throught the plank you can glue each pair of planks without damaging them. You will though only be able to work with 4 planks at a time (2 on centre, 2 either side. Always work in pairs of planks either side.

  Note that with the exception of the gunwale plank, the planks are thinner at the transom and bow. No angles shaping is needed on these planks as this boat has a slab sided topside, whereas the centre line planks do need angled shaping.
 
With the bow being so fine, the planks can easily pull the bow off centre, hence the string while glue is setting.  

Note always working in pairs of planks. The chine was a particular case where lots of angled shaping was needed. I run all planks the full length, but this is not necessary, and you can for example have a long scarf like join at the chine. This will allow for less narrowing of the planks.

 
Last 3 planks to go in each side.  

All planked up. Note the planks run beyonde the bow and transom at this stage

   

Time to pull out the staples.

   
 
Planks sanded with long board with Aluminium oxide abrasive paper. Bow and transom trimmed off (but still over sized because of the false bow and transom). Note the pin holes are almost impossible to see and fill with wood dust if you are lucky.  

I epoxied and sheathed the shell with 40 gram glass fibre for extra strength and protection. The stripes you see above is in fact peel ply which is put on top of the glass when wet. This helps soak up any excess resin. You later pull that off, and it leaves a surface that you can sand easily without damging the glass much, again sanding at least initially with a long board.

 
I made this cradle (external set of 4 frames cutout to to the outside shape of hte hull at specific locations). This allows the boat to be placed in the cradle and keep a comparatively accurate shape  

Undo the shadows from the board, remove each shadow leaving just the bow and transom to help it keep an accurate shape. Put at least one temporary bulkhead in place roughly mid-length to stop the boat growing thinner and longer (not show here). I then glued 2 planks (one either side) to the inside of the gunwale, with the top a few millimetres above the existing gunwale to help re-enforce the gunwale allowing for hull to deck joint. I used clothes pegs as clamps.

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