Posts Tagged “Hull”

Rudder Movement Test

I have uploaded a video (to YouTube) of the rudder mechanism on Hull #1 working from end-stop to end-stop. (Excuse the video quality, I used my phone to record it.)

I connected an Arduino (Mega2560 if you want to know) and a SparkFun stepper controller to the stepper motor which drives the rudder. I wanted to exercise the tiller gears and the rudder shaft for a while. The video shows the rudder swinging from almost completely to Starboard, all the way back to Port.

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Impending Launch.

The view from the office.
Repurposing the #001 Hull for upcoming sea trials.

Hull #002 is coming along, slowly. The stations are mounted on the strongback and I’ve been double-checking the alignment. I have time to do this because 1/32nd inch balsa wood is hard to come by, and because I haven’t cut the keelson yet. Well, I have, but I need to re-cut it. The original was cut to the wrong profile.

While the work on hull 2 continues, I’ve been using Hull #001 to test out aspects of the boat design and control systems. In fact, I am very close to launching the hull…

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Hull 002.

The stations attached to the strongback.
The stations of Hull #2 attached to the strongback.

I have discussed the hull construction process in earlier posts, which you can find via the above search bar. To recap, you take the hull design and “loft” the shape of each section or bulkhead, from the drawing. You then cut this out of 6mm marine ply (or equivalent), mount each of the stations onto a strongback, and now you have something which forms the shape.

I also need to add a keelson to the picture. A keelson is a long, keel-like piece of wood which runs from stem to stern, connecting the bulkheads. I cut one already but it turned out to be too short due to a miscalculation on my part. Generally I cut a thin (about 2cm wide) outline of the keel of the boat, from a sheet of ply.

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The Reboot.

CAD drawing of the MegaMOOP hull, courtesy of Professor Paul Miller.
CAD drawing of the MegaMOOP hull, courtesy of Professor Paul Miller.

According to the calendar, it is now 963 days since my last blog posting on here. A lot has happened in that thirty month period, but not a lot in terms of the robotic boat.

I’ve worked on a variety of designs of winged sail and I think I have a design which will work really well. More about that, anon.

You may also notice I redesigned the blog, and switched from Wordpress to Jekyll. I had originally planned to code a Ruby on Rails site, and this is mostly why there haven’t been any blog updates for the last couple of years. I wanted to incorporate automatic blog updates from the boat when she’s at sea, but trying to decide on a layout for the new blog was like trying to choose the paint colour for the bike shed. Eventually I just went with Jekyll as it allows me to have boat updates, and doesn’t involve spending months tweaking HTML and CSS.

The big news though is a decision I made last year, to switch away from my own hull design, which you can find here. Chatting with Professor Paul Miller of the US Naval Academy, I came to the conclusion that the design he and his students had perfected, which they call the MaxiMOOP.

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The rubber hits the road. Sort of.

Now that the hull is (almost) complete, it's time to start soldering the electronics into place.
Now that the hull is (almost) complete, it's time to start soldering the electronics into place.

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.

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The First Sea Trial

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.

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The new rudder

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.

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The keel is attached.

The keel is being glued to the bulkheads along with the hatch frames.
The keel is being glued to the bulkheads along with the hatch frames.

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.

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Cutting out the Bulkheads.

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.

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The hull starts to take shape.

DelftSHIP hull design, version 0.4.
DelftSHIP hull design, version 0.4.

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.

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