As mentioned in my previous post, the aft section of the keel and the integrated deadwood has some checks (splits), resulting from the seasoning (drying out) process.
Having pondered for some weeks, whether to simply use epoxy/other filler, or to do a formal repair, I finally resolved to do the latter. Firstly, because it will probably be more effective and longer lasting; secondly, because is a lot easier to do it now, rather than after I have attached the hog to the keel – let alone after I have planked the boat!
A Dutchman’s repair – or “Dutchman” for short – is also known as a Graving or Graving Piece, which again may be corrupted to “gravy bit.” Why have just one term, when a few synonyms will do?!
This technique is used to repair a defect due to rot, split, or a knot in the timber. A piece of matching wood is cut in a diamond or coffin shape, with a very fine bevel, then placed over the defect.
Here’s one I did earlier, during my IBTC course, repairing a defect in a keel, involving a knot. The knot extended right through the keel, so I did the repair on one side, and another student did t’other.
A keel in need of repairs!This knot should probably have been repaired when she was built.A graving piece is cut and placed on the keel, …… and the corresponding recess is marked and chiselled out.Some deeper holes were plugged.A two-layer repair was needed.Here is the outer graving piece, …… glued in place, …… screwed, and plugged, …… and planed flush to give the finished repair.
The current repair is smaller in extent and less complicated. However, there’s rather more at stake!
Generally, I eschew electric routers, because they are noisy and produce a lot of dust; and because they are not without risk – especially to the workpiece. However, for this job – cutting a shallow straight-sided flat-based groove – an electric router is otherwise the ideal tool. So, with careful planning and measuring; checking and re-checking the clamping and guide fence, I set about my dutchman repair(s).
There are two significant surface checks (splits) on one side of the one-piece keel/deadwood.This view shows their depths.With a length of softwood, clamped firmly to serve as a fence, I used a 9mm router bit to cut the recess. The recess was deepened progressively, to aid control of the router.To make the second recess a little wider, I used a ruler as a shim, once I had cut the initial groove.After roughening the surfaces with 60 grit paper, it was on to the glue up, using Collano Semparoc 60 Polyurethane adhesive. It is waterproof, very strong, and better than epoxy for oak. Unclamped and ready to trim level.With the repair completed, it’s time to clamp the hog back onto the keel/deadwood, while I get back to work on the transom.
It may be helpful, for those not familiar with the anatomy of wooden boats, if I describe some of the parts of what is called the centreline structure(s) – the backbone, if you like.
On a bigger boat, the deadwood – a wedge-shaped piece of wood that sits on top of the straight keel – is separate (viz dotted line), and attached to the keel. I have made the keel and deadwood in one piece – one less joint to fit and have exposed to the elements … and risk it opening up in future years!
I tried clamping the hog to the keel for well over a week, hoping to ‘dry bend’ it to the shape of the deadwood. However, when I took off the clamps, there was hardly any bend to the hog. So, I decided to apply some steam!
The structure of wood can be compared to a bunch of drinking straws, held together with glue. That ‘glue’ is lignin, and its property of softening with heat, making the timber pliable, allows woodworkers to bend wood to shapes it would otherwise not form without breaking. Direct heat from a fire has very largely been superseded by steam.
While I will need a steam box for the ribs, the foremost ends of planks and this rear section of the hog can be steamed using a plastic sleeve.
After 30 minutes (1 hour per inch thickness of timber, is the rule), Sylvia and I quickly clamped the hog in place, with a backing piece of plywood to protect the hog, and help prevent cupping (transverse curvature), which may occur with the wood in its relaxed state.
There is still a slight gap between keel and hog, an inch or so in from the end, but this should work out OK when I cut the hog back, to make room for the bottom edge of the transom.
Just visible on this view are some shallow checks (splits) in the deadwood, which I aim to formally repair, rather than just fill with epoxy/filler. I know, I’m not making a piano, but …
While I was waiting for the hog to ‘dry bend’ I took the stem to my bench, and cut the rabbet.
The rabbet is the recess in the stem into which the ends of the planks are seated. The lines that form the rabbet are shown below, and are derived during the lofting process, where the boat is drawn full-size on the floor.
The first job was to reduce the thickness of the stem forward of the rabbet, for which I used a router – with not a little trepidation!Here, you should be able to see the two ‘stop-waters’ – pine dowels fitted through the stem, where the joints that make up the stem cross the rabbet. These are for insurance purposes: if the joints open up a little in years to come due to the boat being in and out of the water, repeatedly drying out, the pine dowels will swell when wet, blocking the water’s path into the boat.
The router work went better than I dared to hope. I re-drew the rabbet line and proceeded to chisel out the recess.
The angle at which the planks meet the stem alters progressively down the stem. Using a piece of wood, the same thickness as the planks, a series of recesses is produced. These are then joined up.One side done, time to repeat the process on the other side!
There is a risk that the bearding line might not be quite right, and one should make allowance by not cutting all the way back to the bearding line. This allows some ‘fat’ that can be trimmed off when fitting the planks. I think I have gone a bit closer to the bearding line than I should, but hopefully it will be ok – the students at IBTC have found that they have needed to extend the bearding line so … fingers crossed!
The final shape of the stem narrows to the front edge (a feature called the ‘cutwater’). I have left the stem square for now, as this will make clamping here easier when I come to doing the planking.
What’s next? Well, the timber for the transom and planking arrived safely, and those pieces that are too long for the garage are on the conservatory floor! I have started work on the transom, and am facing and edging some boards prior to ‘thicknessing’ them before jointing.
