BUILDING MY SKI PULK
They told us we'd be pulling our gear in pulks during a Ski Patrol Mountain Travel and Rescue course at Sleeping Bear Dunes in western Michigan. While they're certainly no mountains, the immense sand dunes are perched atop the already towering glacial moraines, and offer ample opportunities to climb and descend steep terrain. We'll be on nordic skis, camping two nights, and it'll be considerably easier to pull our camping and rescue gear than to carry it on our backs.
While they said we could use any plastic toboggan and just use line tied to our waist, they did comment that many in the past have added tracers to keep the pulk from bowling them over on downhill runs ... And so the glove was thrown!
I found several web pages and many threads in discussion forums. But the most detailed discussion, and the design I liked best, was Ed Bouffard's at Ed's Wilderness Systems.
Ed now sells complete ski pulks, but offers a downloadable book, in .pdf format, documenting the various designs he tried in his quest to build a pulk that would stand up to the rigors of the backcountry.
His final version is quite cool. An inexpensive sled, pulled by six-foot fiberglass tracers. The tracers are connected to the sled by pinning ball joint rod-ends into aluminum channel receivers which are bolted to the front corners. Eye bolts on the other end of the poles are clipped to a padded waist belt. Stabilizer fins help prevent sideslipping whilst traversing a hill. This design has reportedly been used in expeditions from Mount Kahtahdan in Maine, to Denali in Alaska. I basically followed the guidance in the book, adding u-bolts on the front and back for hoist and belay points.
THE SLED: The Paris Expedition seems to be the sled of choice for do-it-yerselfers - It's 5'L x 20"W x 6"D, made of .125 mm linear polyethylene with 5 tracks for directional stability, and it costs just under $30.
Paris is now owned by EraPro and the Paris Expedition is carried by retailers in several regions of the US - Just not in mine ... I got mine from REI with a $15 oversized shipping charge on top of standard shipping charges ...
TRACERS: Conventional wisdom is that some PVC can split or shatter when stressed in very cold weather. Conduit is often used, but it can bends and kink when stressed. Fiberglass poles, built for electric fences, are strong and spring back to shape after being flexed. 6' x 1/2" poles are available through electric fence suppliers. I got mine for $2.50 each from Kencove Farm Fence.
HIP BELT: The concept is to use a backpack hip belt. To connect it to the tracers, short loops are sewn at the hips that can be drawn through the tracer eyebolts, and then clipped in with carabiners. I found one on eBay that came off a 1980's Coleman external frame backpack with loops sewn in in just the right places for $16. We'll see if they hold ...
HARDWARE: I got most of the specialized hardware from McMaster-Carr. Their web site is excellent in how it leads you to selecting the hardware which best meets your needs, and it is well illustrated.
Misc. nuts, bolts, washers, epoxy, etc. were bought at my local Home Depot.
METAL: Metals Depot had good prices and reasonably small minimum orders. I ordered two foot lengths of the following:
FABRICATION AND ASSEMBLY
I cut the aluminum channel into two 1 1/2" lengths with a hacksaw, then used a Dremel tool with metal cut-off discs to round off the tops. I drilled them to 5/16ths to accept the locking pins. A little time with file and sandpaper, and they looked like jewels.
I thought it would be cheaper to have IXL Machine Shop drill, tap and thread the tracers and coupling nuts than it would be to buy a tap and die set. I might have been wrong. But they did an excellent job. I had both ends of the rods threaded to 1/2-13 to accept the coupling nuts. I also had them drill and tap both ends so that the rod ends could screw through the coupling nuts and into the rod ends. While
I am concerned that this created thin walls in the rod ends, and therefore weak spots, I'm thinking the coupling nut will provide plenty of support, I filled any voids with epoxy, and I epoxied everything in place. Time will tell.Because I could not find any fine-threaded coupling nuts, nor any course-threaded ball-joint rod ends, I had two of the coupling nuts drilled and tapped from 1/4-20 to 5/16-24.
Whether to cross the tracers is a bit controversial. Ed's Wilderness Systems crosses theirs, claiming that it delays the turning of the pulk, allowing it to track better around obstacles like trees. I decided to cross them.
I clipped the tracers into the harness, pinned the other ends into the receivers, and clamped the receivers onto the front corners of the sled to set the proper toe angle. I mounted them with 1/4 x 1/2" bolts, nyloc nuts, with 1/8 x 1 1/2" aluminum backing plates. The plate is longer than the channel and is bolted to the sled with fender washers as backing.
I used some thin cable and associated hardware to create retaining cables for the retaining pins. Don't wanna loose those in the deep snow.
I mounted U-bolts to the bow and stern utilizing 1/8 x 2 1/2" aluminum as backing plates, and 5/16" bolts. The front U-bolt is mounted on top of the center track where it wraps up the bow. This left a gap under the backing plate which I filled with epoxy. Probably over engineered, but I'm no engineer.
I cut the 1.5" x 2" aluminum angle into 5" lengths, then cut the short side diagonally to create the fins. *I shoulda got the 1.5" x 1.5" but I didn't have the sled when I ordered the materials. The 2" woulda fit between the sled's inner tracks, but I wanted them further out so I cut a half inch off the 2" side. I bolted them to the bottom of the sled towards the rear by countersinking 1/4 x 1/2" flat head machine screws and fastening them with nyloc nuts backed up with washers.
To load it, I'll lay a tarp in the bottom, place my gear on top, and then do a burrito wrap to protect it from the elements. To strap in the load, I got 2" webbing and nylon web clips from Outpost, a local outdoors shop, and bolted them to the sides using 1/8 x 1 1/2 aluminum plate to hold in place.
up and took her to a local park. We had lots of fresh snow, and these
were not groomed trails. She handled very well both on and off trails,
up hill and down. I wound through some densely wooded off-trail stuff,
and she tracked around obstacles well. Haven't traversed a steep hill
Add up the cost of the sled, the hardware and the metal, add in shipping costs, and machining costs ... I coulda bought one from Ed's Wilderness systems for a bit less than what I spent. [sheepish grin] But the time thinking through it, hunting and gathering parts, spending time in my shop cutting metal, and putting it together was well worth the price of admission!
I am not an engineer, and this is not an engineered design - The backcountry is inherently risky. Pulling a sled behind you on skis adds complexity to an already complex environment. So, build and use such a contraption at your own risk. If you somehow kill or injure yourself, or someone else, while using any element of this design, don't blame me, I am not a responsible person!
I have no financial interest in any of the companies I mentioned except The Home Depot with whom I'm an employee and a very minor shareholder.