Building the Eun Mara "Skerry"
Bilge boards, cases and bilge rails
I'm building the twin bilge-board version and have never been happy at the prospect of having the suggested metal winches in the cabin to raise the 40kg mild steel boards. I decided to replace the steel boards with glass-sheathed timber boards of the same dimensions with lead weights embedded to make them sink when lowered. I did a few scenarios on a spreadsheet and calculated that if I were to put 10kg of lead in each board I would need to widen the ballast keel by 3.5cm to preserve the overall ballast weight. The ballast keel would end up weighing 250kg, rather than the designed 190kg. I sent this idea past a professional boat builder who saw no problem with it.
The advantages I see are:
I made the boards out of 18mm walnut planks, leaving rectangular gaps for the lead weights. The plank joins were strengthened by embedding some of the 9mm stainless steel threaded rod that I had left over after attaching the skeg. I had never poured lead before, and was guided by Iain Oughtred's plywood boat building manual. This suggests using the protruding heads of screws to secure the lead in place. As my weights were to be larger than the manual describes, I further braced the inserts by extending a SS threaded rod across the gap.
These two shots show a bilge board after the lead had been poured and the whole thing faired. The SS ring bolt is epoxied deep into the top plank and will be used for the up-haul line.
This shot was intended to show the taper that was applied to the edge planks. The centre plank (and its lead inserts) retains the original 18mm thickness. The outer planks taper to 10mm at their edges.
Here are the completed boards, with woven glass mat and plenty of epoxy. The circular inserts are of thickened epoxy and will be drilled to take the pivot rod.
Here are the slots for the bilge board cases. I found it took a huge act of will-power to make that first incision! The floors are not yet epoxied in place (but see my note on the Fitting Out page). I deferred fixing the floors so that I could remove them when I cut the slots. However, I found that a plain old hand panel saw was the easiest tool to use, and so the floors would not have been an obstacle anyway.
Here are the completed BB cases in place, but not yet epoxied. (A main cabin bulkhead seems to have appeared from somewhere as well.)
You can also see part of the mast beams in the foreground. Click here for more details.
A close-up of the port BB case. The top surface has yet to be sanded smooth to take the capping piece.
At this stage I have just drilled a pilot hole through the epoxy bush that eventually will take the stainless steel pivot rod. I'll drill the final hole when I actually have the rod, to avoid any embarrassing mis-fitting.
I made the rails by joining two lengths of 3/4" (18mm) jarrah. This shot shows the completed rails, shaped to fit the hull, and each drilled to take three lengths of 1/4" SS threaded rod that will be bolted through the lower outboard BB case logs. (Thanks to Ian M for the threaded rod idea.)
As some (most?) builders have done, I made the bottom of the rails straight so that they will eventually rest securely on the trays that will be fitted either side of the trailer, as shown here in this detail from Ian's trailer.
The whole process of fitting the cases, then cleaning the resulting epoxy mess under the hull, then fitting the rails, was one of the least pleasurable jobs involved so far in building Skerry. I seemed to spend best part of a month on my back like this, so Janet felt compelled to record the period for posterity.
I think if I were ever to do this again I'd complete much of the work before turning the boat over. I assume there then would be a whole lot of different problems, but at least I'd be able to address them in an approximately upright posture.
As I have mentioned elsewhere in these pages, I neither like nor am very efficient at working with fibreglass. Rather than glassing the end of the inboard BB case side under the hull (where the edge of the plywood is exposed, and therefore vulnerable) I glued a thin strip of jarrah over it. This shows the starboard slot, looking forward, with the main bilge rail and the thin cover-piece. Having to sand back my nice paintwork to get to the bare timber prior to applying epoxy was a bit upsetting...
...however, it all cleaned up well eventually and I'm pleased with the end result. (This shot shows the starboard rail again, but looking aft this time.) As with the backbone, the rail is finished with Deks Olje. If it is scuffed when beaching, or when sliding on and off the trailer, it will be easy to retouch .
Eventually all was completed, and here's the finished starboard rail. Only another EM builder will appreciate the effort involved!