Finally, I hear you say, we're actually going to plank the boat! Yes indeed, in this episode the class completely planks up the snub dinghy in Huon Pine, and makes a start on planking the stem dinghy with Australian Red Cedar. The whole process is explained. When I first started teaching Clinker planking in the early 1990's, I found it hard to get people to understand the concept of jerralds (gains or rebates) where the planks are let into each other at the bow and stern. After students ruined a few planks, I came up with a sequence of processes which if followed correctly allows first-timers to get it right every time. It's not necessarily the way most boatbuilders did it, but it's the only foolproof way to learn. And seeing a fair proportion of the clinker boats being built today are done by first-timers, I think it's timely.
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With the mast step and engine beds in it was time to prime the bare ribs and the upper stringers as well as the area of hull planking in between. I am priming as I go because of the long period of building. I prime each plank before fitting as well as the outside of the ribs so the mating surfaces are all well coated. I have also sanded the inside hull surface as far up as the upper stringer in order to level any small discrepancies at plank seams, then primed any bare areas and then went over the lot twice more. So that the primer will not run through the seams I ran a thread of caulking cotton into each seam with a pizza-cutting wheel (from outside, naturally). More cotton will follow after the hull is complete and the planking is faired.
Now another pause while we get Christmas etc over with. I decided to fit the engine beds while I still had the central vertical post on the centreline as part of the midships mould which I will be removing soon. This enabled me to set up a string line that accurately represents the centreline of the shaft. My chosen engine, a Yanmar 2YM15 needs engine beds set up parallel to the shaft line but between 27 and 41mm below it. I split the difference and set mine up 34mm below the shaft line. I also had the timber for the mast step, and seeing there are similar techniques needed I decided to fit that as well. Both items require large timbers notched over several structural floors. The general principle to follow is to keep the notches fairly shallow, and take approximately half the depth out of each mating piece. It was easiest to lay the mast step stock exactly on the centreline 2" (51mm) above where it is going to live to mark the floors, and mark on the mast step where it crossed those floors. I notched the floor timber and the underside of the mast step 1" deep each on the only floor that it touched, and measured the gap to the other floors and deducted that figure from 2" and halved the result to get the depth of the notches on the four other floors and the matching notches under the mast step. The engine beds are more complicated on this boat. Only on the forward most of the three floors did I have enough meat to make the notches horizontal. On the other two floors the notches were cut with the bottom surface parallel to the top surface of the floor as in the second photo below. It was best to make templates out of thick cardboard (I could have used thin plywood), a total of four templates, two representing the inboard surfaces of the beds, and two representing the outboard surfaces. I cut conservatively and undertook multiple trial fits until all notches had no gaps. I chose to start with stock wider than I expected rather than try to guess the exact size of the beds. Once I was happy with the fit, I marked the line of the top of the engine beds with a laser level set to the correct angle and height. I trimmed to that height, drilled all necessary fastening holes, primed all mating surfaces and bedded the engine beds and mast step down on a flexible polyurethane compound and fitted the bolts. The whole sequence is illustrated in the video below. There's also a couple of brief shots of several boats of the Ranger class that this boat will eventually race against. |
AuthorIan Smith, Boatbuilder (ret'd) Archives
January 2024
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