Duckworks Magazine

Return to the River

By Milton "Skip" Johnson - Houston, Texas - USA

Last years attempt at the Colorado 100 river race had been a grand adventure along with a lot of learning experience about down and dirty boat building. Chuck had opted out of paddling in the race again this year due to other commitments. At least the commitments were properly prioritized, Water tribe Challenge, float down the San Juan, various messabouts. I was going to paddle solo. A new boat was in order.

Construction is going to be a little more mainstream, but still a light sit-on-top 17-18’ loa a lot like the Bionic Log with a rudder and better ergonomics (higher seating). I’ve got a knee high stack of ½” 3# klegecell, bought 20 years ago, leftovers from a 65’ trimaran built down on Bolivar peninsula ($6.00/ 32”x48” sheet). And, there is that roll of 17 oz biaxial e-glass I’ve stored for my son for 10-12 years. That’s most of the makings of a new boat, along with leftover epoxy and other almost scrap. Just need to find the time to design, build and train.

Sue, Susie and I ready for the dawn start of the CR100

(click images to enlarge)

While all these pieces were running around in my head early in the month of May, Sue Van Natta, my long term aerobics instructor at the Y expressed an interest in paddling with me one of these days. I told her about the Colorado 100 and gave her the web links to official site and articles on Duckworks. A few days later she told me she really wanted to do it but needed to think and pray on it and get an OK from her family if it was a go. I told her to take her time but decide by June 1 for early registration. Actually June 10th was cutoff for early registration, but I was going to be out of the country then.

I’ve known Sue for a long time. Susie and I used to babysit and change the diapers on her twin girls who are going to graduate from high school next year. I’m not sure Sue has ever even been in a boat before but she has finished a lot of marathons for the Leukemia Society and just finished her first triathlon. Underneath that perky pleasant demeanor probably lurks the heart and soul of a competitor. I may be in trouble.

Sue said yes, so I’m going to paddle tandem adventure class again. That’s adventure class, Sue, please remember, adventure class.

A new boat design is in order and it needs to be done quickly so we’ll have some time to train before the (adventure) race. This time the boat will have a name. Sue and I have kidded each other for years about how in our respective venues bystanders will encourage the runners or paddlers by saying they are “almost there” when in fact there are several miles to go. Almost There will be paddled by the beauty and the beast, one of us is a cute, perky very fit redhead and the other is old, heavy and hairy (except for the bald part).

Based on the previous nameless boat, twenty-four feet long is about right. Any longer and the added surface area starts to be a drag, literally. Any less and wave making starts to be significant, even in deeper waters, such as they are. The shape is almost the same, just a touch narrower, slightly higher prismatic coefficient and a flatter fuller section toward the stern to take a little edge off of the shallow water drag.

click image to view PDF drawing

This time I spent a little more time actually calculating moments since I’d messed up previously and there is even more mismatch in paddlers weight this time. I weigh half again as much as Sue so she needs to have her center of gravity half again as far from the center of buoyancy as yours truly. When this was all doodled out, my foot well position was right at the midsection of the boat which meant that with a little connecting tunnel between footwells a single pump could do the job of keeping our feet dry most of the time. In theory a 500 GPH bilge pump could drain both footwells completely in just over a minute. Assuming they were completely flooded.

Basic rudder configuration had done a very good job previously and courtesy of Duckworks I had a set of new whizbang adjustable footrest/rudder pedals made by SeaDog that will let you move the pedals over a 9-1/2” range without fiddling with the cable connections. Still seems a little spooky, reminds me of quantum theory and action at a distance, but I’ve seen other similar adjustable pedals since. Rather than spectra rudder cables this one will use nylon coated stainless steel fishing leader run in bicycle shifter cable housing.

These adjustable footbraces are spooky like quantum theory.

A few comments and graphs (derived from Mitchlet) follow for those that are interested in the fiddly details of drag.

First, the drag curves for EasyB (12’), Preliminary Solo C100 (18’) and Almost There (24’- drag for one paddler). These curves are for a water depth of 0.5 meters and graphically show the influence of length and water depth. Drag is in kilonewtons and the speed range is from 1.0 meter/second to 4.0 meters/second in 0.1 meter/second intervals. Take some of this data with a grain of salt. I know from experience EasyB will be significantly easier to paddle in the lower speed ranges (1-5), the rest however is dead on. Two things are obvious. First, for speed, longer is better. Second, shallow water sucks, literally and figuratively. The hump in the graph at about 13 is strictly due to the added drag from being in shallow water. It’s also pretty obvious I lucked out when Sue wanted to paddle in the race. Whether it is going faster for the same effort or just being easier to paddle at any given speed, tandem is better than solo from a drag standpoint.

Drag curves A - click for PDF version

Then take a look at the second graph and some of the really obscure details of drag in shallow water. In this case for a water depth of 1.0 meters (the hump is shifted to the right).

Drag curves B - click for PDF version

These are both versions of Almost There with a slight change in the after sections. The rockered hull has virtually equal rocker fore and aft for minimum wetted surface area. The flat stern hull is identical except most of the rocker is taken out of the stern sections. For some reason the fullness in the stern takes a little of the edge off of the drag at the shallow water hump but adds a little extra surface area which adds drag in the slower speed ranges. Alas, still no such thing as a free lunch. In this case, with a sneaking suspicion that my new partner will be setting a pace that will put us in the higher ranges, Almost There will have the flatter, fuller stern sections.

Finally, I’ve included a couple of images of the wave patterns behind the boat in one meter deep water and two meter deep water.