Robotic Yacht The construction of Birdy II Paul
Table of Contents Introduction... 3 Construction... 4 Superstructure... 4 Birdy II... 5 Building Frame... 6 Bulkheads... 7 Drawing the Waterline... 7 Keel Reinforced... 8 Chine and Inwale... 9 Lead Keel... 10 Balsa Wood Sides... 11 Fibreglass... 12 First Sea Trials... 14 Low Density Filler... 15 Spray Putty... 16 Second Sea Trail... 17 Appendix... 21 Aluminium Mast and Lead Flashing for the keel... 21 Balsa Wood... 22 Fibreglass... 23 2
Introduction This report is to document the steps taken to construct Birdy II and autonomous robotic model yacht. While I m building the boat, this document will be a working document. I hope to document the key points, both in construction of the hull and the electronics. I ve been sailing model boats since the age of 10, if not before. My first boat I named Pluto, a 575 yacht. Alas decades have passed and I have lost the boat. Not in a lake but in the house. My second sailing boat was built (mainly by my parents) from the 1970 s plan of PANACHE, a 30inch scale Ocean Racer by Vic Smeed. Alas the boat has been called little more than Blue Boat. Being a slightly larger model it could handle stronger wind conditions. 3
Construction Superstructure The only model yacht plans I have was the PANACHE so it became base camp. From my experience of sailing Blue Boat I wanted a more stable model, especially if it was going to carry electronics and sail on larger lakes. I am aware of Universities building autonomous yachts to sail on the open sea but that s beyond my budget. The easiest way to make the boat more stable was to make it bigger. So my objective was to scale up the plans to be twice the size. Compared to Sun Sail yachts, Blue Boat was fairly narrow and thus heals over. All yachts clearly do heal, but to make the proposed boat more stable I decided to scale up the plans to be 2.5 times the width. Pressing a few buttons on the Works scanner and folding the plans in several directions, produced the A3 plan I required. 9mm External Plywood for the backbone of the yacht 6mm External Plywood for the bulkheads of the yacht Once the Plywood arrived from Wickes I proceeded to cut out the bulkheads and backbone from the A3 plans and having drawn around the plans then used a jigsaw to cut out the pieces. The bulkheads were slightly altered from the PANACHE plan to have cabin superstructure. The initial assembly is shown below. 4
Birdy II The name for the robotic boat is planned to be Birdy II. The name comes from having a Cockatiel called Birdy. Birdy is first very affectionate and second has shown great interest in the building of the model and has a unique skill of cable stripping with his beak pretty annoying when the electronics are being developed and tested. Below, Birdy is inspecting the superstructure. 5
Building Frame To proceed with the construction of the boat I was advised by my father to have a frame to ensure the superstructure remains straight as the boat is built. Otherwise I ran the risk of making a sailing banana. His other advice was to have a flat deck on the boat while under construction. Alas I had already proceeded and stubborn in my determination. 6
Bulkheads I then proceeded to hollow out the bulkheads. This would enable the electronics, batteries, servos, etc to be connected to each other. Knowing I would be adding weight to the boat I was getting concerned about its potential waterline. Would I be launching a submarine? The boat has a sloping stern, so it is essential the stern is above the waterline. Drawing the Waterline *** CALCULATION OF FINAL & KEEL WEIGHT 7
Keel Reinforced The keel would be holding lead flashing. Concerned about the keel snapping off when the yacht is healed over, I decided to reinforce the junction between the keel and the hull. This was done by adding more 9mm Plywood to both sides. This reinforcement continued along the underside to the stern with an effective width of 3*9 = 27mm. Drilling holes for the rudder and propeller shaft would be hopefully easier. 8
Chine and Inwale The next task was adding the side stripes of wood. This step of the construction uncovered the curves of the yacht. Starting from the bows the strips where nailed into the bulkheads. The stripes bow naturally and uncovered some bulkheads that needed to be re cut. 9
The photo below shows the reinforced keel section. Lead Keel The next step was to add the Lead Flashing. Lead is poisons and so wearing washing up gloves I cut out sheets of 3mm lead in the shape of the keel. The outer sheets were cut slightly shorter to create a curved affect on the keel. With all the lead sheets cut out I then proceeded to weigh the total. It came to around 8Kg on the bathroom scales. Knowing it would be easier to add ballast than to take some away I proceed to hammer nails through the lead sheets and nail them to the 9mm Plywood keel. 10
Balsa Wood Sides The next step was to add 3mm width Balsa Wood to the sides. Balsa wood thinner than 3mm would inward bow between the bulkheads and Balsa thicker than 3mm was harder to bend to the shape of the hull. A skilled craftman would have spent time cutting the Balsa Wood into strips and beautifully layered the strips to form an attractive hull. My approach was rather faster and less eligant but adding Balsa sheets. My reasoning was that my interest and challenge will be in the electronics. 11
Fibreglass The boat required being more solid than having balsa wood sides and thus I decided to cover with fibreglass. Fibreglass fabric comes in several weights per meter squared and I decided upon 125 grams per metered squared. The glue Epoxy Resin comes in two containers. One container is 5 times the size of the smaller one. Using the supplied pumps they correctly get the ratio 5:1 correct as the combined mixture is added to a Budget Calibrated Cup, or more simply a plastic cup. I then used the supplied brushes to soak the Balsa wood, lay the fibreglass fabric, and then coated with more mixed resin and left 24 hours to dry. 12
Once dry the boat was turned over and using a knife the fibreglass ends were cut to make a smooth top. A small piece of Fibreglass was added to cover the stern. 13
First Sea Trials The boat was starting to become heavier with fibreglass, resin and an 8 kg. The burning question was, is it too heavy? So before the boat was 100% water tight a quick visit to a local lake would give results. The home bath was too small for the boat. Even adding 9 kg of bottles of water, she still floated above her final waterline. A good result. 14
Low Density Filler Happy the keel was not too heavy, I proceed to mix some powder low density filler to more mixed resin. The mixture was spread thickly over the fibreglass, forming an additional shell and watertight layer. Then using wet and dry sandpaper I started on the lengthy task of smoothing the hull surface. 15
Spray Putty Sanding down with wet and dry was taking a long time with no noticeable improvement in the smoothness of the hull. My attempted solution was to use Spray Putty. Spray the boat in yellow paint and then sand smooth. 16
Second Sea Trail Back at the lake of my childhood the second sea trial appeared 100% success. No leaks. 17
Electronics Unknown at the moment, but the brain of the Robot is going to be a device running Microsoft Windows. Probably Linux, Google would be a better choice, but my skill set is in writing C# programs using Microsoft Visual Studio. GPS The boat was going to know its location using the GlobalSat BU 353 WaterProof USB GPS Receiver (SiRF Star III). The key points were its accuracy of 10 meters. It had a USB connection and software code showing how to read the GPS signal via a COM port. Continuously reading the GPS signal every second one could deduce the heading of the boat. However experience of walking around the local Green with the laptop and GPS, I discovered at slow speeds the deduced direction can be easily confused. The solution would be to find an electronic compass. 18
Electronic Compass This boat was going to know its heading by using the OceanServer OS5000 US Solid State Tilt Compensated 3 Axis Digital Compass Kit (USB or RS 232 Serial). Again the key point was that the compass had a USB connector. To my surprise the compass can in addition to point to North, it also is aware of its pitch and roll. The ability to measure the roll (the amount of heal) of a boat would be useful later on when sailing. The compass was not cheap and ordered from the USA. I have subsequently found EU suppliers and a 10x cheaper digital compasses perhaps without the software, accuracy and pitch/roll readings. 19
Servo Controller Board The Microsoft computer would need to control the servos on the boat. For example if the program wanted to turn the boat to the right, then instructions must be sent from the computer through something to the servo. There are a lot of controller boards out on the market, probably 99% of their descriptions unintelligible to myself. I did discover one, the Serializer 3.0 from RoboticConnection.com 20
Appendix Aluminium Mast and Lead Flashing for the keel. 21
Balsa Wood 22
Fibreglass 23
24
25
26
27
28