Team Rafta Obscura, Edinburgh Canal Festival and Raft Race, Saturday 17th June 2017

So a few years ago I moved to the Tollcross area of Edinburgh and discovered the annual Edinburgh Canal Festival and Raft Race, held in Fountainbridge nearby at the end of the Edinburgh-Glasgow canal. I really enjoyed the whole thing but especially the raft race whereby local teams (the greengrocers, a group of mates, the local hacklab…) built generally terrible rafts and tried (often unsuccessfully) to make it along a short stretch of the canal simply for the prize of winning.

I vowed that I would one day enter the race when I had the opportunity to both build the raft and the team to go with me (although I could enter solo but it’s about being silly and having fun so I feel a team makes that better).

This year, 2017, I was able to do so!

The Race

The race was held on Saturday 17th June 2017 and I have actually been checking up the date and entering it into my calendar every year since I discovered it and it was whilst doing that this year that I realised the opportunity. You see since October 2016 I have been working part time as one of the cleaners as Camera Obscura and World of Illusions, a crazy historic museum next to the castle up on the Royal Mile.

I work here sometimes! // Photo Credit: Erin Nolan 2017

The museum is not only awesome to visit as a customer but is also pretty awesome behind the scenes too, with staff going to lots of lengths and paying attention to the detail to try and make everything the best all around. This means as a cleaner that there is emphasis on recycling efforts and trying to minimise landfill waste which had at that moment in time brought up the question of what to do with our broken mop handles? These were largely aluminium but were firmly attached to the plastic handles and clip endings that made them composite and non-recyclable and so they had been accumulating in the corner of one the cupboards.

Why not put them to at least one last good use and build a raft out of them?

So I thought about it, and mentioned it to my colleagues, and then as with many of my plans it all sort of escalated and next thing I knew I was on the water that Saturday morning with a snow shovel paddle in hand…

The Rules

Before starting anything, I had to go through what the rules were that we had to comply with:

  • All rafts must be deemed Canal-Worthy by the assessment panel prior to launch (some advice).
  • Raft materials must not contaminate the canal in any way.
  • No more than 6 feet wide (that’s 1.8288m for the metrics).
  • Human power only.
  • No marine parts (canoes, paddles, speedboats etc…)
  • All participants must wear life jackets (if you can’t find one yourself let us know).
  • All participants are responsible for the removal or disposal of their raft following the event
    (all the bits… from land or water).
  • Any number of people can be on each raft but all must pass the finish line.
  • All teams must be able to carry their rafts overland from finish to start line if they
    are fortunate enough to win a heat.
  • The judges’ word is final

Forming the Team

Originally the team consisted of myself and two of my fellow Camera cleaners, with one of them John being the nominated Captain. Devastatingly our colleague Phillipa was going to be away on a different crazy adventure in America on the date of the race and so she would be unable to attend in human form so we decided to enter her in inflatable parrot form instead (although on the day she actually appeared as a plush manga doll onboard the raft).

The “Rafta Obscura” Plan

So although we did not yet have a team in order to answer the questions on the form about us, I did develop a name (Team Rafta Obscura) and a more general, cheesy description of the team to be submitted in the meanwhile making as many references to Camera Obscura as I could:

  It’s no illusion! That raft probably is sinking!

The overnight cleaners at Camera Obscura have got themselves lost in the Mirror Maze one too many times and decided to sail away into the sunrise but no sooner had they got good luck hugs from Cameron Bear when the other staff spied through the Camera coach loads of tourists approaching up the Mile and decided to jump ship and join them…

Their bosses think it really would be magic if they make it more than a few metres but Team Rafta Obscura think that with enough enthusiasm, some old mop handles, and a few tricks up their sleeve they might make it to the end of the race!

The Letter

Then to both inform my lovely colleagues about the event and try and get their help, the following letter was left in the staffroom alongside the sign up sheet:

…we are officially signing ourselves up for a team in the annual Edinburgh Raft Race along the Fountainbridge Canal on Saturday 16th June, and would like your help!

Firstly, of course, we are looking for a few other people to join our crew and help us paddle down on the day under the good Captain ‘Vampire’ John! We are limited by the rules and physics as to how many people we can actually fit on board, and will need to collect a few details from those willing to join, as outlined in the form, although for privacy you can just write your name and pass on the other details to us separately if you want.

Secondly, we need help with building the raft itself! We are planning on assembling and building the thing on the day before, Friday 16th June, with more details to be confirmed soon. However, we are vaguely planning on going for the classic, simple raft design of a H shape craft, so we need flotation volume and we are thinking of using the old mop handles to build a frame and then other things to make a platform on top to sit on. Probably shovels as paddles.

Rafts work on the Archimedes Principle – that means that for every one kilogram of raft weight (crew, kit and platform/seating) needs to be balanced byone litre of volume of material that is ‘lighter’ than water (e.g. polystyrene, empty bottles) submerged in the water to make us float. So if you can both keep back any such materials from around work (shop staff, looking at you and your polystyrene packaging in the stock room) but also bring any such things from home too, or clean bottles and put them aside instead of in the recycling bin in the staffroom. We believe that the “k cupboard” is going to be allocated for accumulating this material?

If for example the crew is 7 people weighing 80kg each, with about 5kg of kit and raft platform, then we need 565 litres of empty bottles to stay afloat!

Thirdly of course, you can help us build the raft on the 16th (we both study engineering but lol, this is probably going to descend into a good old fashioned Duct tape job…) and ideas are always welcome! You can leave ideas in the staffroom table, the K cupboard, get in touch with us directly, or just turn up on the day.

Finally we would love your support on the day of the race! If you can make it along to cheer us on then that would be cool, and the festival is always a fun little local affair worth going along for anyway!

In the end? I learned that there was too short notice given to the day staff to change their plans and join us on the team and actually Hamish also dropped out at the last minute, leaving just John and I for the actual race. Although a member of management did indeed turn up to cheer us on from the side. Oh well, lesson learned for next time.

Building The Raft

As mentioned earlier, the basic plan was to build a frame out of the broken mop handles we had accumulated over the years, and then use this structure to create the volume necessary below the water to keep the team floating.

My original idea was to put them to use as a sort of platform by tying them together. However given their length we could not use them to create depth or height without cutting them as they were too long.

Initial Rafta Obscura idea // Image Credit: Erin Nolan 2017

As mentioned in the letter the basic physics requires that approximately one litre of water is displaced for every kilogram of weight that is to float (that is to say that it is in equilibrium with the water and not accelerating towards the bottom i.e. sinking). Therefore we needed to figure out where that total displacement volume was to be contained and what it was to be made of.

Raft design using the 1st main method of floating // Image Credit: Erin Nolan 2017

The first main method typically used here is to find the total volume needed using materials with density lighter than water, such as polystyrene and empty bottles, and then ensure it is submerged in the water and so displacing it and reducing the total density (of the raft and the team and the kit like paddles) relative to the water. This means that you float above the water level.

This requires you to find lightweight materials in large enough volumes, requires the density of the team to be distributed so that it submerges the volume in order to work, and most importantly raises the centre of gravity above the water and so makes the design less stable.

Raft design using the 2nd main method of floating // Image Credit: Erin Nolan 2017

The second main method is including the volume of the team in the submerged volume to create equilibrium (the total density still needs to be lighter than water) which means that the you are floating below the water level.

This is more the approach of boats than rafts, as it makes you more stable because of lowered centre of gravity but typically requires more complex manufacturing as the volume containing the team generally maintains a lower density by containing air not in a sealed volume but an open top to let the team in and out, and generally consists of only the one open shell. This means that the design is more vulnerable because one leak, or too much splashing of water over the top, and the density becomes too much, whereas the submerged volume design can have greater redundancy by being free to shape the volume in segments.

The greater the barrier between the volume and the water, the safer from gaining weight, but the more restricted the motion of propelling forward using the team – if you built really high thick sides to the boat then how do the team reach the water to push against it?

It is for this reason that crafts relying on alternative methods of locomotion such as sails or propellers prefer the second method because they can gain the benefits of the more stable design without worrying about the team needing to be in contact with the surrounding water.

However people-powered typically rafts go with the first method because the materials used tend to be cheaper anyway and not so many reach sufficient acceleration to be too bothered about instability as long as it is sufficient for the process of the team getting on and off the craft.

The display frames! // Photo credit: Erin Nolan 2017

Whilst discussing the raft race plans with our Maintenance team at Obscura, I was redirected to their current collection of scraps and assorted odd waste which very fortunately contained two former display frames. This therefore guided the design to becoming a classic raft shape with the two frames connected by the mop handles and thus making it easier to simply fill the volume below.

Slightly more developed Rafta Obscura design //Image Credit: Erin Nolan 2017

To create the material of the volumes we collected lots and lots of plastic bottles, some which could be attached directly to the mop handles themselves, some gathered into bin bags to be attached. I was lucky to gain a weird twirly thing otherwise being thrown away by the local Tollcross Central Hall whilst renovating their children’s play area that not only added volume but aesthetically looked rather Camera-Obscura-y or so I thought!

Having gained no extra teammates the pressure was off building a big raft and so it was somewhat procrastinated until the early hours of the morning of the race, after finishing my night shift.

Our awesome colleagues very kindly entrusted us with the building’s snow shovels to be used as paddles and so once finished and checked over off we went with it!

Racing The Race

Me looking fabulous next to the raft before the race // Photo Credit: John Sturrock

When we arrived and compared ourselves to the other rafts I think we felt fairly average. Some teams had built incredibly elaborate, well-crafted pieces (didn’t necessarily stop them sinking though) whilst others were actually building their rafts there and then out of wheelie bins and barrels.

I think we were the most environmentally friendly raft given that we were made almost entirely out of rubbish and think that we should be proud of that! However, we had not thought through all of the logistical issues before racing such as any paddling technique, nor testing how well we actually balanced on the water and after witnessing one raft require repeat attempts to support its paddlers in the heat racing before us, we were a little nervous.

When it came to our turn though we floated! …We also fell apart though!

So although we had started the race with sufficient volume to keep above water, the twirly thing at the back quickly detached from the frame and the two bags it was holding in place came free and floated up behind us, instead of underneath us. Oh and the seat wasn’t attached so it slipped out from underneath and basically we spent the race sitting with butts submerged.

Because of the asymmetry of the detached flotation though we had to try and rearrange ourselves front and back instead of side by side in order to balance and John nearly fell in the water in the process and ended up maintaining a really weird position (which I couldn’t see without rocking the raft too much) which made it difficult to paddle. So we came very clearly last in our heat finishing several minutes later than the rest as I had to paddle mostly for both of us while John balanced the thing.

We finished afloat though, albeit slowly!

If you want to watch, here is a video summary of the whole race (in which we only star briefly as example losers throwing our raft away afterwards):


More importantly though here is a video that someone has uploaded just of us somewhere towards the end of the race:



….Okay, so we didn’t win any prizes!

However we learned a lot of things for next time:

  • Making a raft out of rubbish was good because we didn’t invest money into it because it is not guaranteed to survive!
  • Need to make sure that everything is secured to the raft and unlikely to detach or float away, not just that there is enough of it there…
  • Ideally want a team of three or more so there is some more contingency to change paddling strategies if necessary.
  • Talking to other teams whose craft survived the race intact, having a sturdy build proves useful for providing floating sitting space to enjoy drinks on afterwards on the water when the paths get really crowded. Thank you friendly zombie team for that advice!
  • Ideally need to take the raft down to the water at some earlier date than the race itself and practice getting on and off of it, and paddling on it then rather than leaving it until the day.
  • Build the raft earlier than the morning of the race is probably a good idea but don’t worry too much because no one will judge you if you build it on site.
  • Start recruiting team members and collecting materials more than a month in advance!
  • Need to make the raft and team outfits even more fun as others were dressed as foxes, and riding inflatable bananas…

Most importantly though it was a lot of fun, definitely worth it, and I am already looking forward to hopefully doing it all again next year!


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