Cataraft performance attributes - waterline vs. "rocker" - Mountain Buzz

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Old 01-16-2015   #1
SpeyCatr's Avatar
Coquitlam, BC, Canada
Paddling Since: 2013
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Cataraft performance attributes - waterline vs. "rocker"

I was just thinking the other day about the details of cataraft design/tube shape and how it contributes to specific performance attributes (or lack thereof). I guess in my mind I was trying to rationalize things if it's fair to say. Not to say one boat is better than another, but obviously each design has specific advantages over others.

So lets look at boats like the Wave Destroyer, & Legend. Radically upkicked ends, BUT, for the portion of the boat in the water, a relatively flatter waterline, on average. I've heard some suggest the WD may have a little flatter of a waterline but this is really just semantics at this point.
Some have speculated that due to this flatter waterline, these types of boats tend to "track" better. Now correct me if I'm wrong, but the common understanding of "track" in this application (as a connotation) would mean the boat stays pointed the way you wanted it go, to stay on course, requires less input to stay from the oarsman to stay on course, as varying currents are encountered. Now if we think about that portion of a boat with a flat waterline that is in the water, the depth from the bow to stern, of the boat that's in the water, is relatively the same - say a couple inches as an example (changes depending on load). If the boat is coming down the river at some kind of an angle or encounters varying currents, if the current towards the back of the boat is stronger than the near the front of the boat, the current is not only pushing against the back of the boats waterline, but it is also pushing in a sort of pendulum effect on the front end of the boat which also may have downward current acting upon it. Since the stronger current at the back of the boat still has to pendulum the front of the boat against the current that is acting upon it, it makes it tough for varying currents to change the angle of the boat or in this case, to change how it tracks, as easily. Does this rationalization make sense? For the same reason, assuming what I am saying conveys my thoughts, and makes sense, and IS true for that matter, it is also the reason that a boat that tracks well may also be a bit more difficult to "steer."

Compare this to say a bit like an AIRE Ocelot or similar designs that has more of a bottom curvature like Banana. The common comparison to boats like the WD of Legend is boats like the Ocelot don't track as well and require more input from the oarsman to stay on track. But when you look at the boats waterline, you see the middle of the boat in the water is deeper than the rest of the waterline essentially acting like a "pivot point." As the waterline tapers up towards the ends of the boat less boat sinks into the water making it easier to steer, but tougher to track. If a boat is on an angle, it is easier for stronger currents to push it off course or mis track it due to the pivot point in the middle and the fact it doesn't have to push as hard against the current acting on the other end of the boat to mistake it.

Any thoughts on this topic?

15' AIRE Wave Destroyer - MadCatr Frame - Sawyer MXS oars w/Duramax blades
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Old 01-17-2015   #2
Bayfield, Colorado
Paddling Since: 1980
Join Date: Sep 2010
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Boat design is all about trade offs. A tube with a long straight section like a nrs will carry much more weight than my hyside tubes. The hyside 16 foot tubes are only 24 inches in diameter for 7'6" then they begin to taper. They pivot (steer) really well and punch holes really nice but you cant load them like the nrs tubes. I was lucky last spring and got to run numbers with a bunch of guys that run legends. After following them down and pondering for a while I have come to the conclusion that tracking is more about trim. These guys all run idaho style ie weight/ trim slightly forward. This trim makes the current pull the front of the boat down stream. I was trimmed slightly ass heavy and I remember following one of those guys down a churning maelstrom and his oars rarely touched the water where as I was constantly having to make minor corrections as the current grabbed the heavy end of my cat and tried to pivot it down stream. This winters project is to set up the cat to run idaho style and see how it works for me. I have never run a banana shaped tube so I cant offer any input as to how they perform but to me a couple of rules of thumb apply. A long straight tube like a jacks plastic or a nrs will carry an amazing amount of stuff without sinking too far into the water. They will not pivot as well as a rockered tube. Rockered/tapered tubes will not carry as much weight but are sportier/pivot easier then a straight tube. They also punch holes better. A long straight section tube should track better than a banana tube but like I said I have never run one so I dont know.
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Old 01-17-2015   #3
over the horizon
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Carbondale, Colorado
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We need to meet and drive each others' boats sometime, James.

I drive a couple JPW cats, one a Cutthroat, one a Royal Flush. Both are about 14' long with that straighter waterline profile. They track well, punch holes alright, and pivot pretty quickly when rigged for a day run. On overnighters they can take on an impressive amount of gear, but you still have to quit loading them before the floor is close to the water.

I've wanted to try some tubes with massive rocker. I would think they would have less of a "glued to the water" feel. Perhaps a bit more of a rodeo?
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Old 01-17-2015   #4
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Sandy, Utah
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I've had two Maravia catarafts. 14X22 older style and 14X24 newer style. I've attached a picture to show the difference in the tubes. Of course the 24 inch tubes held gear weight better, but not a huge difference. The pivoting and hole/wave punching ability of the newer tubes with more rocker was noticeable, but again not a huge, OMG type thing. The 14X24 cat, with more rocker was to me, the best of both worlds.
"We are all visitors to this time, this place. We are just passing through. Our purpose here is to observe, to learn, to grow, to love....and then we return home."
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Old 01-17-2015   #5
Cottonwood, Arizona
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This is an interesting subject one which I've been learning more and more about in a trial and error experience, but in the smaller ducky and paddle cat arena. The designs of boats I have paddled over the last 12 years have all varied drastically, and for the kind of paddling I do and kind of rivers I run demand a lot out of a design for load handling, steerability, and stability. It's difficult to find a boat that can handle all of these equally.
Last year I was intrigued to try a paddle cat setup like a Cuttroat/Fat Cat hybrid to replace my Tomcat Solo which just couldn't keep up with the rigs of the guys I paddle with. An opportunity came up to pick up a Pack Cat Tandem for relatively cheap just to try out the paddle cat concept. The tubes are 12" in diameter and 13' long with zero rocker. I reasoned that what it lacked in diameter it would make up for in length. The original width was 35", I wanted 40", so I built frames to accomplish this. The very first run I did with this setup was the Salt at 170 cfs and a 450+lb gross load. It's greatest attribute was stability, being followed by tracking. But I found the bad far outweighed the good as the steerability was horrible, the speed was snail-like despite my 20 strokes to every one that my buddies took as they rounded the corners out of sight ahead of me. And if being instant self bailing is an attribute, the opposite can be said of it's instant self pinning. To be fair, I understand that the boat was originally designed for two people to paddle the flat flow of the Sand Yawn, and not the hairpin cobble bars of a low flow desert river, but I was quite frustrated with the performance.
Floatation is the first difference as well as handling characteristics that can be seen between a cat and a ducky or raft of a similar tube diameter and length. So, for what I do, decided to go back to a ducky.
The bomber IK that I wanted and finally had the opportunity to paddle was a Sotar Fabreezi, flat bottom, foam floor rig with 13" tubes, 42" width and 11.5' length. They are super stable, load carrying horse that handles fantastic despite what many people think. What I did end up getting was a Sotar SL IK with similar dimensions but 12' long. My first time on the water, with a relatively full load, find that it spins on a dime, and moves quickly thru the water. The design difference is noticeable compared to the Fabreezi because the SL has a shorter water line with a continuous rockered design, whereas the Fabreezi has about a 7' - 8' waterline.
I bring this book-post back to what you were saying about the difference between a flat waterlined tube and one that has continuous rocker and what you describe as a "pivot point". There are many aspects and dimensions that come into play with tube and boat designs that are either understated or not thought about at all that can either make or break what you're looking to get out of a rig. Boat manufactueres are a huge source of info on this since they get to design and test, and have more than likely worked out what they "think" or "believe" to be an optimum design. Problem is rivers vary, paddling styles vary, and boaters vary making a one design fits all mentalty archaic.
I also still want to play with the paddle cat concept, but with completely different tube designs.
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Old 01-18-2015   #6
Wondervu, CO, Colorado
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In my AIRE Panther (15' twin tube, dead flat tubes) the trim is everything. I want her dead center. Then the boat is agile, fast and spins well, stern heavy means I am always on the oars and it won't track at all in slack water. If the load is in front she rows slow.
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Old 01-19-2015   #7
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New Castle, Colorado
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Custom Inflatables is building me a paddle cat with 10' long 15" diameter tubes and a total width of 44". I don't know yet what my favorite types of runs will be. It will all depend on how it handles. I want it for sections I can't get the 16' cat down whether it is poor access or low bridges or tight boulders. I might find it can be used for lightly packed multidays on remote tributaries like the Dirty Devil or low water Dolores or Gunny Gorge.

I'm kinda taking a gamble but love Western Colorado for the wide variety of choices.
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Old 01-19-2015   #8
Cottonwood, Arizona
Paddling Since: 2000
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Gremlin, I will be interested to see that setup and hear about it's performance. The dimensions sound like a good combination for doing some class III to IV day runs or possibly a super light overnighter.(?)
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Old 01-19-2015   #9
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Denver, Colorado
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Second for pics of the paddle cat from C.I. when you get her!
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Old 01-19-2015   #10
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New Castle, Colorado
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My wife got the C.I. Thrillseeker last year and it exceeded expectations for construction and attention to detail. They were also great with recommendations for rocker and length to attain the desired performance attributes. As others have stated, there are definitely trade-offs.

I am very excited to be getting a new ride soon. That it is being built to my specs is even better. I hope I got it right. I had six choices for the built in beer holder location and I'm pretty sure I got that one right!
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