Introduction: Stitch and Glue Rowing Boats
The Stamford American International School in Hong Kong got interested in boats as the Volvo Ocean race was sailing through town. 2 classes of students built 4 boats in total, all using the same technique of "stitch and glue". Using plywood and epoxy on fibreglass, the students got to enjoy the steps of building a real boat of their design.
The project was built both at Stamford American International School in Ho Man Tin with Linda, Tim, Mr Nichols, Alan, Elizabeth and at MakerBay in Yau Tong with Cesar, Eda, Maria, Paul, Jackie and Thomas. Before we go deeper into the stitch and glue technique, please watch the following videos. They demonstrate how easy that technique can be.
The goal of the class was to let the students learn about
- History of boats. How boats are the oldest transportation system, invented way before the invention of the wheel.
- Science: Archimedes buoyancy formula
- Technology: boat design, hydrodynamics, stitch and glue, composite materials, resin and fibreglass works
- Working in Team: leadership, being a team player
- Hands-on work: drawing, technical drawing at scale, 3D design, tracing, cutting, stitching, glueing, composite materials
- The scientific method, the engineering mindset: which design works best? Why? How do we make it better?
- Environment: the importance of water transportation in contemporary society. All life as we know it, comes from the ocean. And the ocean is our future. 90% of the world trade travels by water - and Hong Kong is a major port.
Step 1: Hand Drawing
A good place to start is to draw. We asked our students to let their imagination run wild. The goal was to achieve diversity in designs, so the students get to test how different designs behave. And that was a great success. The 4 teams came up with very different designs. They were given fancy names later on but for now, let's call them:
- Square tub
- Round tub
Step 2: Technical Drawing
From hand drawing to technical drawing. We then asked the students to design with dimensions in mind. Starting from the limited materials they would be allowed to use. Each team had the same amount of wood to work with:
- 1 hard sheet of plywood (15mm thick)
- 4 flexible sheets of plywood (3mm thick)
Step 3: 3D Model
This was an optional step, but for the students that were done way ahead of others, they could either help other students or refine their own designs on 3D software. Here, you can see mostly sketchup videos. in the 3D warehouse, there are plenty of boat designs.
Step 4: Paper Model
In this step, the students proceeded in some clear sub-steps:
Cut 5 pieces of paper, each representing and at the scale of plywood. 2440mm x 1200mm in reality, we cut 1 piece of paper 244mm x 120mm (24.4cm x 12cm). 1 piece is colored in a dark color to represent thick rigid wood (15mm). 4 pieces are left clear and represent the flexible wood (3mm).
Step 5: Plan Your Time! Prepare Your Space.
Because this was a school projects involving 10 students per boats (40 students total), we had to be well prepared. Because we are using epoxy resin, fibreglass to build full-size boats, we had to make sure we have:
- a smart use of materials. Enough, but not too much to avoid wasting.
- a smart use of space, keeping 1.5m between boats art least so students can work and walk around the boats
- a smart use of time. Only 3 sessions with the students, they had to make the most of their time.
- sufficient safety gear, in different sizes
Step 6: Role Model to Test the Scale
When you build a boat for the first time it is hard to imagine from a scale model how many people are going to fit on the boat. A good way to get a preview is to make a 1/10 scale model INCLUDING 1/10 scale characters, each representing a student. But the ultimate way to do that is to role play it with real world props. Here we used MakerBay tables and trestles to simulate the size of the boat.
Step 7: Trace and Cut Plywood
It is easy to unfold the scale 1/10 paper model, measure it and multiply by 10 on the real wood board. In a matter of minutes, the students designs can be transferred to the real world on real plywood. Black lines for construction. red line for cutting. Students traced in the morning. Teachers / technicians cut during the lunch break.
Step 8: Assemble, Stitch
This is the really magical part. When the pieces come together, the real boat appears! In was just a paper model, just minutes ago! We would have preferred to use copper wire, but in the interest of time, we used nylon cable ties. Just faster and tool free.
Step 9: Glue
The step we call "glue" is the time when we apply the epoxy resin with a lot of filler as a thick paste. In our case we use transparent epoxy resin + Fumed Silica Thixotropic Powder. There are many other additives you can add to your resin, including fine saw dust, it is really your call, when you are not looking for extremely high performance.
I personally like to cut a plastic card in a gentle arc shape, and apply the thick sticky paste in all corners.
This is how you mix and prepare the resin to be thick like peanut butter.
to make clean seams some people like to use a simple wooden spatula, that works too.
Step 10: Dry Inside (one Night)
Every resin is different. The one we used can polymerise (the more accurate way to say "dry") in
- 24h at 25ºC
- 48h at 10ºC
Our workshop was at about 15ºC so it took about 36h to be hard enough to sand.
Be careful if you operate
- in a very hot weather, your resin might start to harden before you are done working with it.
- in a cold country, it might take many days until your resin is actually hardened.
Step 11: Remove the Stitches
Your resin is dry, it is time to remove the "stitches"!
Prepare your space by covering the floor with a large tarp. Some of the next steps will produce a lot of dust and many of the students will drip resin on the floor - that is for sure!
Cut as close as you can to the hull. To make sure your surface is smooth and ready to apply the fibreglass "skin" next.
Step 12: Trim
If your boat has inaccurate alignments, it is possible to trim it. We used a combination of pull saw and push saw to work easily at every angle. Be careful to not trip the boat when you saw as it is very light.
Step 13: Decorate and Spray
This step is optional. The students used markers, spray cans and stencils to decorate the boats.
Step 14: Outside Skin
First, turn the boat hull upside down. The students measured the boat and cut a thin fabric of fibreglass to lay over the boat. They added about 50cm extra at each end, to make sure that even if the boat design is curve, there would be sufficient fiber to cover the boat.
They started by applying the liquid resin from the middle of the hull, towards the sides. Gravity always helps.
If they were missing pieces of fiber, they would simply overlap about 20cm of fiber on top of the existing fiber.
Step 15: Inside Skin
We actually did not do this step. We only partially patched the hull. Wherever we saw that the boats might be weak, we added small strips of fibre and coated the boat overall. The reason why we did not do it was a lack of time. We recommend you cover the inside of your boat.
Step 16: Dry Outside (one Night)
After coating the inside, leave to "dry" one night or more, depending on the temperature (hot dries fast, cold dries slow).
Step 17: Trim and Sand
Than it was time to trim again. Followed by a lot of sanding. This is a boat for kids, so made sure that there was no sharp edge anywhere.
Step 18: Patch and Waterproof Inside
As we were sanding, we found some small leaks. If you find more leaks down the line we recommend you using 5 minutes epoxy putty.
Step 19: Paddles!
We have actually ordered 4 pairs of paddles - but that was without counting that some of the boats may allow much more than 2 people paddling! So, some of the groups made extra paddles, with bamboo handles, nylon twine, coated with resin and fibreglass.
Step 20: Admire Your Work
Before you put your work to the water, look at it! How far you've come!
From a simple napkin drawing, to a paper model, to a real boat you can sail! Magic! Or hard work? Both!
Step 21: Farewell Boaty McBoatface
It is that moment everyone has been waiting for - and has been so scared of! Will it even float? Time to race!
Step 22: Evaluate Performance of Designs and of the Teams!
Racing should not only be about the body strength, but also about the mind. And frankly, this boat exercise is less about the athleticism and more about design. So how will we find out which is the best design? And which is the best team?
Let’s consider teams TA, TB, TC and TD. Let’s consider boats BA, BB, BC and BD.
About Best Boat and best team, in 4 runs
- TA vs TB
- TC vs TD
Winning team fight for 1st and 2nd. Losing team fight for 3rd and 4th place.
The speed is total time of every single person crossing / number of people in the team. Result is “Average crossing speed per person” on each team!
About Best Team overall, and best boat performances
To find the best team on different boats:
- TA tries BB, BC, BD against time = Add all the runs / number of runs = best team
- TB tries BA, BC, BD against time = Add all the runs / number of runs = best team
- TC tries BA, BB, BD against time = Add all the runs / number of runs = best team
- TD tries BA, BB, BC against time = Add all the runs / number of runs = best team
To find the best boat, regardless of teams:
BA, BB, BC, BD average of all runs above will tell us which is the best boat.
This is the testing protocol!