Due to other, exciting distractions (which I will mention in a later post), I haven’t had a chance to keep the blog up to date. Still, work progresses on the boat, and that’s the important part. Last month, with the keel now in its new position about 30mm further back along the hull, and sealed into place, it was time to add the electronics board.
Posts Tagged “Keel”
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.
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.
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.
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.