The original sled was built from ethafoam in 1980 and was my first squirt design- named the “Slake”. I used it to do the first eddyline mystery move at Lost Paddle rapid on the Upper Gauley of Sept. of 1981. I called it an “Under” because I was actually going for an ender but bit off more than I could chew- over and over again. It’s the lower green boat- compared to the Hunch made in 2014. The Slake seemed small at the time.
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Figure 1: a work in progress…
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A “sled” is a small genre of make it yourself sit on top craft which is used for mystery moves (intentional submersion) in safe arenas. Please don’t do anything scary in them. I’ve created this blog to show the steps I took in creating my latest. This one took 21 hrs. and about US$400 in materials to make. I used abandoned (contributed/re-purposed) styrofoam and epoxy.
The steps are pretty simple. Think of it as similar to building a surfboard- a foam core- then surrounded by glass layers. The beauty of it is that you can evolve the design if you please as you go along – with no real detriiment. Keep in mind to build it strong. I give standard recommendations as I go along.
So.. you start with a design. I like to start by carving foam- but you can also design on the computer or a sketch . But- ultimately- you need a full size paper copy of the side view and top view profiles of the sled.
For the top view- I like ellipses- but anything goes. I’ve found 20” wide and about 8’ long is a good starting point. But this is a good format for trying new designs- so follow your instinct and imagination.
For the side view- you need to cue in on certain crux dimensions- like the thickness at the feet, knees, hips, and just behind the seat. You can guess, or take measurements from a squirt boat- or another sled. But think of it as 7” is usually plenty for the knees- often less. Behind the seat should be less than 4”- don’t worry too much about it- everything can be adjusted as you go. Hips- maybe 6” and toes- 4”.
So- for the side view profile- buy a 4X8’ sheet of ¼” luan paneling- or if you can’t find that- try some strong paneling. Use it as a table and put a long sheet of paper on it to make your pattern out of. Then draw a long line and set up the arc of the hull in relation to that line by using a curved stick to set the curve. This is the ‘rocker’ of the hull- except in my case this boat has negative rocker- or what I call a ‘drop bow’.
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Figure 2 Here I am setting up 3″ of negative rocker for the drop bow.
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Figure 3 Start by mapping out key points like the knees. Where is your center of gravity? (Just inside the front of your belly as you sit) Where is the center of buoyancy? ha ha- there is a lot to learn!
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Figure 4 HIPS! 6″? They need to be high enough to support your hips and translate a feel for the sled.
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Figure 5 I strike critical dimensions then blend them together on the paper.
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Figure 6 I’m using a pattern for a paddle blade- but any bent stick will do.
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Figure 7 Yeah- that’s really what it’s going to look like.
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Figure 8 OK- so now the point is to make three identical copies of this pattern out of the luan paneling. So- cut out 3 pieces of the paneling that are maybe 1 cm wider than the pattern in every way.
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Figure 9 Start like this
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Figure 10 Yea! room for 3- if you want a longer boat- find a way to make the luan longer…
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Figure 11 Trace exactly but cut about 1 cm. wide of excess beyond the pattern.
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Figure 12 Not perfect- they don’t need to be. Relax!
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Figure 13 Glue the pattern to one of them with spray adhesive- not too much!
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Figure 14 Now- the exciting part?
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Figure 15 Put the screws to her! The paper pattern was glued to one sheet with Scotch 77 spray adhesive.
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Figure 16 A little scary looking- but note how the screws allow for one side to still be flat.
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Figure 17 A little sander action like this can take it to final spec- but any kind of sander will work. A 2″ drum sander on a drill is an excellent choice.
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Figure 18 Now is the time to bring it in exactly. Give it a final go over with a 6″ long wood block with 50 grit
OK~ that step is over and you can set it aside. You’ve made one ‘stringer’ that will remain in the sled and two side templates which will help with the shaping later on. Now you need to source foam- 2 lb. Styrofoam is a good choice. Try to get as big of pieces as possible because glue lines will give you trouble later on. If you can find someone who has boat docks- they have to replace their dock flotation sometimes and may have scrap pieces laying around that they would be glad to re-purpose. My friend Peggy Pings was my ‘angel investor’ on this project.
So… now.. you are ready to start assembling the sled. You need to bond it together with epoxy. I like WEST system with the fast hardener and I make a slurry of it with micro spheres and glass strands. So- this sled is to be 20” wide and I want the plug to be oversized to start with so I’ll make a 21” wide plug. That means I need two 11” wide halves assembled to each side of the central stringer. First I prepare the foam for bonding by cutting the foam into 11” wide by 8” thick foam blocks- added up to make the 8’ length.
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Figure 19 You can do this with a handsaw two- but it might be a good idea to jig up a couple of wood guides for the saw blade. After the cut is made- flatten each surface with a 15″ long 36 grit sandblock.
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Figure 20 Then rough out the sideview profile. See all the flaws in the foam? Don’t worry about it.
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Figure 21 Starting to make sense? See what we are building?
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Figure 22 I use weights, ropes, sticks- anything to get the bond pretty good. I pre-checked the fit of the foam to the stringer so I know it’s pretty good.
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Figure 23 Beauty eh? See the lack of glue joints- very helpful soon.
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Figure 24 I supported the stringer with a base board when I did the gluing so it would remain pretty straight. Now- I assemble the other half to the remaining side of the stringer.
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Figure 25 Voila!
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Figure 26 The little camp on the left is making SURE the foam is right at the delicate tips.
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Figure 27 Ready for the next stage!
So- now- set up a jig across both ends to help position the side templates.
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Figure 28 You screw the templates into the foam with 4″ screws. Now I work the foam down to the center stringer and side templates. This step actually goes pretty fast I’m using 36 grit Green Core self-adhesive sandpaper.
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Figure 29 I wanted this one to have a concave hull (mistake in retrospect) so I set up a sandblock with the curve just right.
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Figure 30 1 cm of cancave- beautiful- but- kind of a drag.
OK- the side view profile is established quite accurately now. It’s time to put on the paper top view profile template and cut the shape out with a hack saw blade or handsaw- be gentle- it’s fragile now.
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Figure 31 I left the side view templates on to help secure the fragile ends of the foam.
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Figure 32 And now- you do this to your heart’s desire- 36 grit Green Corps. This step is fun and goes fast. Thankfully you have the perfect symmetry of the original pattern working for you here. This is the last chance to easily change the top view profile.
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Figure 33 This is where you would suffer with a lot of glue lines- they sand at a different rate and you get hard to reconcile bumps all over the place.
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Figure 34 So now- side view and top view profile all cleaned up.
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Figure 35 This is my guess at seat and knee placement- turned out to be 1″ too far astern- I can fix it!
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Figure 36 Roughing out the foot area.
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Figure 37 Can you see the knee hooks hiding in there? They are integral with the hull of course- and need to be VERY strong.
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Figure 38 The stern is FRAGILE! Don’t let the kids play around here- yet….
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Figure 39 This design required tight little chines- which I worked in at this point.
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Figure 40 Be super careful on this work- it’s easy to screw things up and sand too far.
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Figure 41 Then EPOXY a single layer of 10 oz. glass to the hull. Don’t use polyester resin~ It will melt the foam- just like contact cement will. This step creates a base for the laminate and covers any big flaws in the foam.
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Figure 42 I wrapped it around the corner of the chine a little bit where I could. Note how I covered big potholes in the original foam with black Gorilla tape to support the glass for this first step.
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Figure 43 Isn’t that a pretty shape? Don’t worry about all the drips. After the resin cures you will gently sand the entire edge of the glass you just epoxied on.
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Figure 44 And then pick up any tiny indents/shape problems with a thin coat of putty- that you sand flat.
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Figure 45 See? This is STILL easy. And now you’ve secured the stern from warping or getting bumped and broken.
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Figure 46 It’s still fragile.
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Figure 47 I’m getting ready for the real glassing now. It will get about 7 layers- including polyester fabric which keeps everything from breaking up- quite key.
I don’t want to go into a long spiel about layups- you can do your own. But suffice it to say I’m not a big fan of Kevlar- I prefer polyester fabric- available from Sweet Composites. A good lay up- in order of assemblage- is: polyester, 4 layers of 10 oz. glass, polyester and finally a couple ‘scratch’ layers of 10 oz. glass. Later- you can paint it with white epoxy to make it smooth.
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Figure 48 With the hull secure- I start caving out the insides -leaving the bumps where the knee hooks will be.
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Figure 49 Start into the fine shaping now! Excavate the body well. You are approaching a stage where you will glass over the knee hooks.
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Figure 50 This is an epoxy slurry glue line. No problem- a little black Gorilla tape over it and I can land the glass.
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Figure 51 Can you visualize where I’m going now? Doesn’t have to be perfect- but check your symmetry with the central stringer. Note the pointy heel chocks for your foot brace- they really work well- if they are in the right spot. I set the hip well width based on previous kayak seat measurements.
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Figure 52 I’m ready to land glass on the deck now because I was sure of the geometry. You can also just glass the knee hooks and go test it on the water- and come back and adjust the remaining foa deck to your satisfaction before you glass it over.
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Figure 53 Triple tape the hull- you don’t want any changes on it now!
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Figure 54 Black tape over the gaps- equipment ready, glass cut. A good layup is based on a good prep.
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Figure 55 I’ll wrap the layup over the hull a bit- but let it overhang in the sharp corners- there’s another stage later where you add a dynel ‘bumper’ to protect the ends.
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Figure 56 Elevating the sled from the table lets me have the freedom to wrap the deck glass over the hull layup.
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Figure 57 The glass has landed and I’ve ground it smooth after it cured. The key thing here is the knee hooks are strong- about 9 layers including a couple of polyester.
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Figure 58 And now I cut off the excess. This is a good tool. That cutter will also work in a drill.
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Figure 59 Cuts are done- now I can really dig into it and see how the knee hooks fit. They might not- but can always be changed for the better.
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Figure 60 Big chunks first- take it all the way down to the floor.
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Figure 61 Prying out chunks- this is really pretty fun.
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Figure 62 The initial shape ready for testing. I’m counting on having to modify things later on. When I’m finally really happy with it- I’ll lightly glass the foam on the inside to make it strong- maybe 2 layers of 6 oz. glass- no polyester.
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Figure 63 Concave hull hiding down there- turned out to be a bad idea. I can make it better. The river likes a bland wing- it’s most adaptable to a thousand different situations.
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Figure 64 This was the original concept. I got close enough to it to prove it wrong. I can modify the ‘wrong’ sled to get it right.
So- basically- that’s how you get to a testable sled. If it isn’t perfect- go after it with a grinder, putty, more glass, wood- whatever. Jungle rules apply- do whatever works. Once the shape is established- I add dynel bumpers (about 15 layers) around the last 15” of the tips to take rock hits better. Then grind them smooth. Once all the shape is fine and dandy- you can paint it over- hull first and deck later- with epoxy mixed with white pigment. Email me if you have any questions or suggestions. jim@rivrstyx.co
Keep the knowledge going- free fun for everyone!