Following on from my first posting under the Chit-Chat banner, for those that are interested some more thoughts and details on the Fairmile C project. Obtained the plans on three sheets by John Lambert – great detail of the real thing and construction methods, but translating into a scale model gives much food for thought. I chose the Fairmile because I like the hull form, curves and flare of the bow; in order to keep those lines it has to be a plank on frame/bulkhead build, decided to double-diagonal as per the original.
Once that was sorted, how do I power it. First thought was a diesel/electric arrangement, but after some investigation decided the scale was too small and the generation/power supply/voltage regulation was far beyond my meager electrical knowledge and abilities. IC by itself is noisy and problematical with going astern unless gearbox is introduced, but can do without that type of complication. So electric it is.
Model boat electrics have moved on considerably since my early efforts in the late 60s/early 70s so after considerable research, a lot of which was on this fine forum, I decided on brushless outrunners with lipo batteries. Four of them. Props will be outward turning (ie right-hand props on starboard shafts, left-hand props on port shafts, as per traditionally viewed from astern). Outboard props will have ahead and astern, inboard props ahead only; the intention with the electronics is to have the inboard props cut in at half-throttle or so. She will take 40 mm props no problem, may even take 45 depending on clearances, but that will be looked into once the hull is planked. Twin rudders, independently controlled. No helm mixing on the throttles. I used to drive multi-engine vessels for a living so tank steering and split rudders is the way to go (I have stopped short of fitting a bow thruster). Thrust bearings? Why not.
Not exactly how the original craft was configured, but I can live with that.
So, how to squeeze it all in? Looking at the available motor mounts and considering other options I decided to utilise cage-style motor mounts designed for model aircraft – very light but robust; bolt the motor on one end, the shaft coupling within the cage, the thrust bearing on the other end of the cage. The tubulars of the cage clamped to the hull structures. It will be easily removable as a unit and should make replacement or up-sizing of the motors fairly straightforward if necessary. There are a couple of photos attached of the experimental drive train. The motor is a 1050 rev per volt outrunner rated at about 220 watts with a 40 mm prop. Four cages will fit neatly across the beam of the boat at just about the LCF (slightly forward of it to be precise) so trimming issues should not be too great. Some drawing extracts of the motor arrangement are also attached.
Now the drive train is sorted, at least in theory, the current job is designing and drawing the keel structure and the lower part of the transverse frames/bulkheads. I want to try and get as big an opening in the deck as possible to give good access to the innards. Ideally I would like the deck structure completely removable from about frame 3
½ aft to about fr.12 but I am still looking into the feasibility of this and the best method of waterproofing the joints, and how to secure the removable section in place – I have a few ideas but not fully developed any of them yet. Hence only the bottom half of the frames being designed at the moment.
It's going to take while to complete the overall design and form of the individual components so I am nowhere near introducing bits of wood to a saw blade, but that will come. Still got to make space in the garage to build it, my nearest and dearest wouldn't appreciate me taking over the kitchen worktops indefinitely! I'll post an update on design aspects for anybody interested when things have advanced suitably.