Earlier this month, once the hull and keel were mostly finished, we took the boat down to Aughinish bay to see how she performed. I have some video footage of the hull in the water, which I will upload a little later on. To ruin the suspense, Beoga Beag didn’t sink! In fact, she moved through the water quite nicely, but more about that later on.
Thanks go to Colman Corrigan for designing and building the keel and rudder. The keel follows the traditional NACA shape, with a rounded leading-edge, tapering off to a narrow trailing edge. It is approximately a 6318 shape, with the maximum width being about 36% of the length of the cross-section. Overall, the keel is coming in at about 750mm from hull to the end of the bulb, and about 240mm from front to back. That’s a 3:1 aspect ratio.
The above photograph is of the new rudder box with a NEMA17 stepper (underneath) and the two gears. The smaller gear is on the stepper and the larger, quarter gear will be clamped to the rudder shaft. It’s a 4:1 ratio and the rudder gear is 90 degrees so one complete turn of the stepper will bring the rudder from end to end. That’s plus or minus 100 steps.
This box will be mounted above the deck, with the rudder shaft disappearing down through the hull.
Rudder angles greater than around 40 degrees either side are counter-productive, as the rudder stock starts to act more as a brake than a steering surface. So a 90 degree swing is plenty.
The above image is a quick photograph of the rudder stock once it was filled with a mixture of West System 405 microfibres and West System epoxy. I formed a basic mould out of wood, added “shrink wrap” to prevent the filler from sticking to the mould, dropped in the rudder stock frame (see below) and then poured in the filler. It took around a week to fully harden, and I will sand and paint the finished product.
As of about an hour ago, Igor and Mother exchanged communication. It was awkward, stilted communication, like a first date, but they talked! One of the issues with the RS232 stream is that the kernel is chatty. I’ve suppressed a lot of the boot-up messages, but there are still all those /etc/rc startup messages. As the ALIX board only has one serial port, those messages are sent to Igor. To avoid sending Igor into a tail-spin, or more importantly, sending the boat into a tail-spin, Igor ignores all RS232 output when Mother boots, until the magic word is sent over the wire. The magic word is XYZZY. Anyone want to try and figure out where that comes from?
There are four power supplies on board the boat. The main voltage rail is 12 volts, give or take. The solar panels feed into that via two separate DC to DC converters. Ideally, they would provide a 13.7v “float” voltage to the main rail. That voltage is the ideal float voltage for a sealed lead-acid battery at 20 degrees C.
There are two problems with this. Firstly, it is unlikely the battery will be pegged at 20C. In the Northern latitudes, we can expect the night-time temperature to drop well below that level. Likewise, once the boat catches the trade winds, the battery temperature will increase dramatically. I have concerns that the temperature could get well up into the 40’s, due to the fact that the battery is enclosed inside the hull.
It’s been pretty quiet here on the blog front for a couple of months due to work and life pressures, but efforts on the hull and keel have continued unabated.
Much to report since the last post, including two transatlantic attempts (neither of which have succeeded, yet).
In order to test the spiffy, new Wind Direction Indicator mentioned in a previous post, I assembled the mechanical components (without the potentiometers) and mounted it outside. As we live in a wind-swept area, with a high concentration of sea salt in the air, it was a useful test of how the system would perform. What I couldn’t test was the effect of high temperature/humidity in a salt-water environment. To do that, I’d have to move to the Caribbean (which seems like a good idea, given the Irish summer we’ve had so far!).
Anyway, I digress. After a few weeks of spinning freely in the breeze, I disassembled the unit to examine the condition of the internal parts, and the news is not good.
As the hull is now watertight, and we’re mere weeks away from having a sealed hull with keel and rig, it’s OK to start looking at actually getting this thing to sail.
Up until now, I’ve been somewhat obsessed with getting the physical aspects of the boat to a certain juncture. The reasoning is simple; until there’s a boat, all of this other stuff is just a waste of time. Well, now there’s a boat…
After a polishing sand on the outside of the hull, the three compartments were filled with polyurethane foam. This is “closed cell” foam, which means it doesn’t take on water. Use the wrong foam here, and the boat will fill with water like a sponge. The different hatches can now be seen more clearly. In the above image, at the base of the middle compartment, you can just see the epoxy and microfiller which will take the keel plate and the battery.