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Stand Up Paddle Board

Motivation

I’m not sure why I even need this section. Who wouldn’t want a stand up paddle board? Oh, right, people who haven’t ever been on one. Basically it’s a large block of foam that you stand on while paddling slowly down a body of water. In other words, you stand roughly on the surface of the water enjoying the weather. “I’m not sure why I even need this section.”

Oh, there is one problem: nice paddle boards cost about $1000. You can get an inflatable paddle board for more like $500, but people say that those take a rather long time to inflate and don’t feel quite right. Plus you need to carry a compressor around with you and hope that you don’t hit anything sharp while you’re in the middle of a river.

In any case, I mentioned that “it’s basically a large block of foam,” so how hard could it be to build one for substantially less than $1000?

Research

As it turns out, I’m not the first person to have this thought. Plus (while I’m sure this is an over-simplification), surf boards are basically smaller, less stable paddle boards and making your own surf board is something of a celebrated art form in the surfer community. So there are lots of references on how to build your own board.

My primary reference for this project is Erin Egbert’s project write-up on building her own paddle board. Rereading that reference now I feel like I’m ripping it off a bit. In her more eloquent write-up, she gives a motivation that also boils down to “who wouldn’t want a stand up paddle board”? Then she discusses background research and introduce a coworker who worked on this project with her. Well, me too! I worked on this project with Terra Moran.

Sticking with the theme of ripping off someone else’s project, I’m going to quickly summarize her design/build process:

  1. Find a commercially available paddle board you like and copy its design (shape, deminsions) from a picture online.
  2. Purchase three 8’x4’x3.75" sheets of foam core. She doesn’t mention this detail, but other sources say it’s important to use a closed cell foam and that expanded polystyrene (EPS) is the most common option. Cut and arrange these sheets to form a 12’x4’x7.5" block.
  3. Embed four 1"x4’ dowlels into the foam for extra strength (see her write-up for details). Then glue it all together.
  4. Print out your board profile and cut it out roughly with a hand saw. Then switch to progressively finer cutting tools to finish shaping the board.
  5. Finish shaping/smoothing with a “SurForm” (non-food cheese grater). Take the time to make it really smooth and symmetrical; it is worth it.
  6. Buy 4 oz fiber glass cloth and epoxy resin; optionally also buy colored pigments. Lay the cloth on the board and cut it to shape, allowing overlap on the sides of the board. Smooth out the wrinkles.
  7. Mix the epoxy in small quantities and apply two thin layers to the board. Make sure the layers are even, sanding as necessary between layers. Repeat on the other side of the board.
  8. Add accessories (fins, handles, etc) by demeling a hole in the board, filling the hole with epoxy, and inserting the accessory.
  9. Make a stencil and spray paint a pretty design on the board.
  10. Buy a foam pad to use as a deck. Also zip ties and zip tie mounts to attach bungee cords.
  11. Profit by $1000 - material cost - an enormous amount of time * how much you value your time + $(how much happier you are to have built your board instead of buying it). Hopefully that’s positive.

…and that’s all it takes if you want to own a 12 foot long paddle board. I was ready to do just that, but Terra suggested that 12 is a lot of feet and it would be much more convenient to store and transport a modular paddle board instead. What would that involve?

It turns out people have thought of this too, and enough different designs have been produced that I can criticize a couple of them before describing a design that’s actually pretty good.

One intuitive way to break down a paddle board is to split it like puzzle pieces. The CubySUP does just that. Unfortunately this design is hard to get right without precise manufacturing – the pieces need to fit together snugly but easily. Also even with their precise manufacturing (judging from videos) it doesn’t fit as snugly as I’d hope – you can easily see a ridge where the pieces meet each other. I’d be worried about the interface wearing down over time and becoming loose and floppy.

Another option it to split the board with clean cuts across the width and use straps on the top to attach adjacent pieces. The Rum Runner takes this option and also carves out holes in the deck in which you can store the paddle. I don’t like either of these decisions. The straps on the top seem kind of like a hinge in the bad direction – if you step on the middle then the sides want to flip up on top of you. It looks like this is addressed with alignment features at the interface (i.e. not quite a clean split), but that has the same problems as with the CubySUP. Also while it’s nice to store the paddle in the board, not having a flat board to stand on seems like a high price to pay for that convenience. Here on Youtube.

The best design I found was a clean cut across the width of the board with the pieces aligned by thick foam rods perpendicular to the cuts, bridging the gaps between the pieces. The pieces are secured to each other by straps that loop through adjacent pieces – the alignment rods don’t need to fit snugly enough to hold the pieces together. This design seems fairly simple to build and tolerant to imprecise construction techniques. Plus it’s pretty much indistinguishable from a normal paddle board once its assembled. Unless you want to take a trip on a mini paddle board, in which case you can just leave out the middle section and connect the ends together directly. Now that’s modularity! This board is Corran Addison’s Kickstarter project (Youtube), and it’s much cheaper than most paddle boards. Unfortunately I seem to have missed the boat on this one – the Kickstarter ended in 2014. But fortunately I also seem to have jumped ship on a product with a substantially delayed production schedule, followed by an indefinite delay in production after Kayak Distribution bought the company and decided to ignore its Kickstarter obligations (the last update on Kickstarter about the legal battle was in October 2015 – I don’t think anyone is getting their boards). I’ll be making my own version of this board.

Build plan/BOM

My initial BOM plan was to buy everything (except perhaps epoxy and fiber glass cloth?) from Home Depot because hell if that isn’t convenient. First step: foam.

Foam

Home Depot sells foam for “rigid insulation”. Some product descriptions specify “closed cell” or “extruded polystyrene” (XPS). Wikipedia explains that both EPS and XPS are closed cell foams and good for insulation. As far as I can tell XPS should be a fine replacement for EPS in my board. The cheapest price I could find was $34 for a 4’x8’x2" sheet – $170 for a 4’x12’x6" block (and some extra) or $204 for a 4’x12’x8" block.

Alternatively, US Blanks produces foam in single chunks that are large enough to make into boards without first gluing several together. Their reseller Greenlight Surf Supply sells a 12’ EPS board $150. Less money and less work for a more nicely shaped foam board than I would be able to produce myself? No one ever said I’m not a cheater. It’s probably still worth buying some foam from Home Depot to experiment on though.

Fiberglass cloth

Like Erin, I found the best fiberglass prices at US Composites. Interestingly fiberglass cloth cost doesn’t seem to be linear in weight – you pay less than twice as much for 8oz cloth as 4oz cloth. Heavier cloth is generally more expensive, but there is more cost variation between companies than between 4oz and 8oz cloth.

This should go without saying, but the width of the cloth is important. You want something slightly wider than the width of your board so it will drape over the sides, but not much wider or you’re wasting cloth. I found it easy to select for this dimension at US Composites and harder at other sources.

Green Light recommends 2 layers of 6oz cloth on the top and one on the bottom. The board is 12’ = 4 yards. This will be split into four 1 yard chunks, each of which requires a few extra inches to wrap around the sides. Let’s say that’s 4/3 yards per piece per layer * 4 pieces * 3 layers = 16 yards. Round that up to 20 yards so I have plenty of extra for testing and messing up.

US Composites sells 38" wide 6oz E Glass (“very common in small craft boat building”) for $4.45/yard, or $89 in total.

Epoxy resin + color

US Composites sells epoxy resin and colored pigments for use with their fiber glass. Based on their description I want a 3:1 resin to hardener ratio. Greenlight sells glassing kits with 1.5 gallons of epoxy for 10’ boards, so 2 gallons should be more than enough for a 12’ board. US Composites sells 2 gallons of 3:1 epoxy for $128.

If you’re like me then you probably assumed that a company called “US Composites” would have a very official-looking, formal website. You wouldn’t be entirely wrong, but purely in the interest of being well informed about the world around us let’s examine thier epoxy FAQ. There are many entirely ordinary, useful questions along the lines of “what is blush?” and “should I use a respirator?”. But they also provide the (frequently?) asked question “I need an epoxy to build a thermonuclear support valve …” and a quality response. I don’t know about you, but I find it quite refreshing to discover humor leaking out through the cracks in what is otherwise a very formal business website.

Besides a few tidbits on using epoxy in thermonuclear devices, I picked up several other useful tips from the FAQ:

Everything is better when it is blue, paddle boards included. US Composites recommends 4oz of their pigment per gallon of resin to make a completely opaque color. Keel Blue pigment costs $6.95 for 4 oz of pigment, or $14 to go with two gallons of resin.

PVC pipes for connecting sections

My tentative plan is to align board sections and fasten them together with separate mechanisms. Board sections will have thick PVC tubes (1) embedded in them (centered vertically). Matching PVC tubes will be aligned by smaller tubes (not shown) that fit snugly inside of them, bridging the gap between the two sections. 3.5" PVC pipe has an average inner diameter of 3.521" and 3" PVC pipe has an outer diameter of 3.5" – perhaps those can be used for the outer and inner tubes. The two sections of the board can be tightened together with webbing (4), attached with a buckle. The webbing goes through holes reenforced with 2" diameter PVC tubes (3). There is a small, slightly recessed area (2) around these holes so the webbing buckles don’t stick out/it’s hard to step on them.

I’m a little concerned that 3" PVC pipe might not fit nicely inside 3.5" PVC pipe (either too tight a fit or not a tight enoug fit). One alterantive I can think of is to use foam (i.e. a pool noodle) for the inner tube because a pool noodle could be compressed to fit snugly in a tube too small for it. A pool noodle on its own wouldn’t be rigid enough, but it could be reenforced by putting another PVC tube inside of it. This construction makes me think of “boffers” – foam swords with a stiff rod in the middle to make them feel more like swords and less like pool noodles. Perhaps I need to make myself some boffers? For science?

I’ll also need something to bore the hole in the foam. In theory I could try to find a large enough bit to put in a drill, but that sounds like an expensive misuse of tools. Some guy on YouTube used a hot, sharp tube to melt large holes in foam for hydroponics – perhaps that would work for me too? Or I could do the bulk of the cutting with a knife and finish/smooth the holes with a hot soldering iron.

I found a four-pack of pool noodles on Amazon for $12. It was surprisingly easy to find pool noodles with specs for their inner and outer diameters (1“, 2.5”), although some products had reviews complaining that the advertised diameters were incorrect. Hopefully this company didn’t noodle around with their numbers.

TODO measurement picture

TODO boffer picture

Creating boffers was a success – I can now sword fight with friends whenever I want to! But I don’t think it’s a good idea for the paddle board. The PVC on the inside of the boffer makes it reasonably stiff, but there’s still a reasonable amount of flex between the inside and the outside of the pool noodle. This is a good thing for making it not hurt when you’re hit by the foam sword, but I don’t think it’s rigid enough for attaching pieces of paddle boards.

Instead of using (reinforced) pool noodles for alignment, I’m going to use PVC couplers to … couple the PVC tubes. On the plus side it will be a tight fit and should stay together pretty well. On the minus side it will be a tight fit and maybe not the most convenient for assembly. I probably want the PVC to go no more than 6" into the foam, which is 2’ of PVC (and 2 couplers) for each pair of foam pieces I need to connect.

I found buckles and webbing on Amazon.

Accessories

It seems to be fairly standard for paddle boards to have a single large fin centered at the back of the board. This makes my life easy – if I were building a surf board I’d have to learn about cant and the tradeoffs of different fin positions. It might not be that bad, but it’s definitely more involved than “just put a big straight fin in the back”.

For some reason I can’t fathom, Greenlight Surf Supply only sells surf board fins and not paddle board fins, so I turned to Amazon for this part. I picked a simple SBS fin box and 10" SBS fin.

I found a video of someone installing a fin box. It looks like all accessories are simple to install in concept – you grind out a hole that fits them snugly, add epoxy, and insert the accessory. Fin boxes in particular are sold taller than necessary with the expectation that you will grind them down to be flush with the board after installing them.

The video is part of a long series of videos where this guy builds a complete surf board with a camera strapped to his head. It’s quite informative, but 5 or 6 videos in I realized that the footage was making me nautious.

TOOD grinding + routing mechanism

Erin’s other accessories were handles and a vent, but I am going to skip both of them. It doesn’t make much sense to me to put handles on a disassembleable paddle board – do I need a handle on every piece? Do I need a hand for every handle? If so then I’m in trouble.

As for the vent, if you’re thinking “what is a vent in this context anyway?” then we’re on the same page. As usual, the internet has the answer. Soulr Surfboards explains that paddle boards have vents to avoid pressure buildup when the paddle board is exposed to heat or altitude changes. Without a vent, these events can cause the board to delaminate.

Greenlight sells vents for a little less than $20 each. Not bad for a single part, but I need one of these for each of the four paddle board sections. Maybe there’s another option? Yes there is, according to Soulr. Their paddle boards all have vents, but apparently their surfboards have sufficiently little foam volume that the pressure buildup doesn’t overcome the strength of the epoxy coating. One quarter of a paddle board presumably has even less volume than a surfboard, so I should be fine without any vents.

Erin also mentions a deck pad, bungee cords, and spray painting a pattern on the board. These seem like good ideas but I can figure out the details later.

Misc

Brushes for applying resin

Measuring and mixing containers:

Foam again/how does Amazon do it?

That’s everything – time to start acquiring materials! …or that’s what I thought, anyway, until I tried to buy the EPS board from Greenlight. Apparently large items are subject to extra freight shipping charges. Greenlight often ships their smaller boards cut in half to avoid these charges, but even splitting my board into quarters (which I wanted to do anyway!) wasn’t enough to avoid expensive shipping. They gave me a quote for $168 for shipping, which is notably more than the cost of the board. How does Amazon do it?

So now I’m back to getting foam from Home Depot. Thinking a bit more about the design, I can make a few changes to cut down on cost and difficulty. First of all, Greenlight’s board fit within a 32" x 6" x 12’ box, so I probably don’t actually need the 8" x 4’ x 12’ that I estimated earlier. Also the exact dimensions 32" x 6" x 12’ tile really nicely into 4’ x 8’ x 2" sheets – each sheet gets cut in thirds to 4’ x 32" x 2". If I make the paddle board split into 3 sections instead of 4 then each section can be made from a single sheet (split in thirds, which are then stacked on top of each other). How convenient! 3 sheets to build the board plus one for mistakes experiments at $34 each is $136 – not bad.

I’ll also need some supplies for shaping and gluing. I’m going to use whatever sharp things I have lying around for coarse shaping. Erin recommended the Surform (small, large) for the final shaping/smoothing. I’m going to use contact cement I already have lying around for gluing. And it will probably be nice to have a tarp to help keep the mess contained (plus it might be possible to make a bag for the finished board out of an 8’ x 10’ tarp).

Gluing foam

TODO write some stuff here. Also post pictures.

Post-gluing dimensions: all three blocks look like they include a rectangle with dimensions at least 30.5" x 47"

Copied the shape from the image on Greenlight’s website and rescaled it to 30" x 138" x 6" (gimp/xcf)

BOM

Product links and costs:

This adds up to $501. Much less than $1000 and roughly in line with the price Erin quotes (“we spent less than $500 and made our own boards…”). Or roughly double Erin’s price; it’s hard to tell from that sentence. But I know her source for fiber glass and resin and that costs $200 on its own, so I don’t think she meant less than $500 for both boards.