Model - Plank Patterns & Stern Extension

Looking at a model from different directions gets you thinking whether your comfortable with the proportions of the boat. I already had a few thoughts yet to be settled re mast position and cabin size but the main thought on looking at the model is the stern looked chopped off too soon. Also the anticipated waterline being 3 inches higher gave part of the transom buried in the water. From my dinghy racing days I learned of the speed drop from dragging the back of the boat in the water. So I decided to extend the transom back 9 inches which should see its bottom just clear of the waterline and a bit of extra design length to fiddle with cabin shape and centreboard case positioning.  Here's the result of the change.

Now it's time to get the planking process underway.  The plan is to make cutting template patterns for the planks from thin light ply, then use these templates to cut one set of planking stock patterns (with generous trimming margin according to these templates), which will be then fitted and trimmed to perfect fit as the final version of patterns in stock thickness.  I am hoping these will be useful for the full size build (blown up 5 times) as templates for scarfing up stock for each plank pretty close to full size fit.

For the template patterns I am using 1mm Finish beech 'aircraft' plywood.  It's a bit expensive but I had some left over just enough to do do a full set of templates. It's light to handle and can be cut with a knife.

Here's some pics of the process of holding up the sheet to the model and progressively marking out and cutting the templates.  I hope to be able to remove most of the screws holding the ribands and glue these on and smooth the whole mould shape before I trim and dry fit final patterns from planking stock (this will be  2.7mm standard ply - 5 times this is a bit thicker than the 9mm ply I intend to use on the final boat but probably has more representative stiffness for the model than the thinner beech ply being used for templates).  Re the ribands I have been reminded  of the Tom Hill method which is to trim moulds by riband thickness and thus not have to rebate.  This gives more freedom to align them before fixing and no need to flatten moulds in between plank landings - I'll definitely be doing this on the final boat. 

 

Quite a stretch on available small clamps to be able to clamp the sheet and templates while they are fitted because of small gaps between ribands. Also had barely enough room to get my hand in under the jig to mark the sheet from underneath the ribands. By having most key points marked I was able to use a fairing batten to get the full template pretty close.

 It's good to mark each plank as you go for plank name, station positions and orientation.

 Leave trimming off both ends until the final planks are glued on the backbone - it's a bit of a disaster if you cut these off too short too early.  The forward overhang at the stem is referred to as "hoodends".  I got five plank templates out today - hopefully will finish the rest tomorrow.