My original plan was to use a traditional mast and mainsail, with Yannick Lemonnier of West Sails volunteering to produce the sail. Yannick is no stranger to mad schemes himself, having competed in far too many Figaro races. These days, he spends his time sailing his Moth winged-beast, or racing his International 14. That is, when he’s not making sails for everyone from Beoga Beag to the Volvo Open 70s.
Posts From Category: Boat Design
On September 1st, we launched the hull in Aughinish bay, without sails, rudder or electronics. The purpose was to see how the hull performed in open water, with the keel attached. As the keel wasn’t properly attached or sealed in place, the main compartment flooded with water, but as the compartments are individually water-tight, this wasn’t an issue. It did lower the boat in the water somewhat, but not to any significant degree.
As the compartment wiring wasn’t completed, and the deck panels weren’t glassed in place, they were attached to the hull using duct tape. Not pretty, but it works.
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.
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).
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.
Now that the hull is looking solid, it’s time to start thinking again about the wind direction indicator. It is possible to detect wind speed by using an ultrasonic sensor and receiver, and measuring the delay between the two. You need to account for temperature changes and gusts can cause issues, but it is fairly reliable and has no moving parts. Generally, you use two transducers offset by a distance of perhaps 20cm for the North/South computation, and another pair in the East/West direction. I think if we were using a larger hull, such as a 4m boat, this would be a good plan. But, for the 2.4m (or the 1.2m) boat, it’s just too big and awkward. Also, this jury is undecided about how well they would work, over the long haul.
After applying 3/32” balsa wood to the bulkheads and transom, the hull is starting to look like a real boat!
You can clearly see the deck support frames now. They are 6mm below the sheer line, to allow for 6mm exterior (or marine) ply deck pieces. But first, the balsa needs to be sanded and patched a bit. Also, the 3 or 4 layers of chopped strand matt need to be applied. When it is finished, the balsa wood will be completely enclosed in fibreglass. This is a standard “sandwich” construction. The balsa adds a layer of strength (believe it or not!) to the two layers of glass either side. It is similar to the central section of an I-beam or girder in that it separates the two outer layers and means that the bend radius is increased. Or at least, that’s my understanding of it…
After much sanding and polishing of the keelson, and the frames for the hatches and top deck, the hull is starting to take shape.
The bulkheads are cut from 6mm exterior grade plywood. The wood which resembles a picture frame is pine, and it is used to hold the bulkheads and transom into a square position, and to provide additional strength to the hull. Eventually those frames will be covered over by 6mm ply on the deck.
The original plan was to stretch 6mm ply across the bulkheads, to form the hull. However, the ply doesn’t bend too easily, and it seemed easier to use a sandwich construction instead.
A slight change from the version of the hull from the previous post; the hull height from the base of the hull to the deck (not including the keel) was 180mm. As I started to look at cutting bulkheads and the transom, it struck me that the hull is quite shallow. It looks fine from DelftSHIP but that’s a low freeboard.
The beam of the boat is around 360mm, which is twice that depth. The original intent was to create a hull which wasn’t too “beam-y” but that’s a 2:1 aspect ratio. I decided to increase the hull height by 50%. Luckily, DelftSHIP will scale your drawing in any or all of the three vertices. So, five minutes later, and we have a new hull with a 270mm depth.
On Henry’s advice, the round hull of earlier designs has been discarded in favour of a hard-chined hull. We were originally planning a fibreglass hull from a round mould. The complexities of first producing a “plug” and preparing a mould from the plug, not to mention having to then fibreglass the hull itself, are quite involved. Henry suggested hard chines an 6mm marine ply for the construction, and a light bulb lit up.