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# Kayak speed in Shallow Water

-- Last Updated: Apr-25-10 7:01 PM EST --

Paddling in a 16-mile river race that this year included long sections of shallow flatwater (a dry spring in Maine) has got me to thinking.

What is the effort-to-speed curve look like in water of 1 - 2 feet deep? Obviously it takes more effort to maintain speed in shallow water, but how much more effort? Is there any data on this? Even some anecdotal numbers from someone who has paddled in shallow water with a GPS would help.

And the related questions:
(1) If I am racing on a river with alternating sections of shallow and deep water, is it more economical (in terms of energy output) to ease up in shallow sections? (In other words, if maximum hull speed drops to 4 knots, no sense in trying to push the boat to 4.1 knots, or even 3.9, right?)

(2) How does shallow water affect speed of a longer kayak vs. a shorter one? Rockered vs. straight-keeled? V-hull vs. flattened or shallow arch hull? Tandem (two "motors" but more weight) vs. single kayak.

Any insights or speculation will be appreciated.

Tagged:

• 2 feet of water=50%speed
-- Last Updated: Apr-25-10 7:31 PM EST --

David Birch's Fundamentals of Kayak Navigation had some interesting tidbits on paddling in shallow water as well as just about everything else related to moving a small boat through water. Good book. I learned a lot from it. However it is kind of like reading the tax code.
The longer the boat the more speed reduction in the shallows but it may be proportional to the theoretical hull speed. Something to do with the bow wave bouncing off the bottom increasing drag.
I am sure more knowledgeable paddlers will chime in but the 50% speed in 2 feet of water thing stuck with me because I thought it was interesting. Read the book 20 years ago. Cant remember what I ate for breakfast but I remember that.

• depth Froude number.
I have experienced the same thing and will wade through this along with you. Dont ask me to splain!

http://www.hydrocompinc.com/knowledge/whitepapers/HC124-ShallowWater.pdf

Sounds like you did the Kendukeag bump and grind this year. Early snow melt, not much pack and not much rain..while the other end of the state drowned.
• A Lot
I seem to recall someone here posting a reputable source that stated that when an average sea kayak is paddled in water only 12" deep, the drag and resistance increase by 90%, or nearly DOUBLE!

Speaking from personal experience, I can certainly believe it ...

Delphinus
• GPS
In the Epic 18 on my local reservoir, the GPS says I slow down from 6.5 mph to 5.5 or so when I hit shallow water. And no matter how hard I push, I cannot regain the speed I lost until I reach deep water again, so I don't try to fight it. Never noticed this in a whitewater boat, probably because they are slow anyway. If I am racing a long boat through shallow rapids, I notice a slowdown. If I'm paddling a whitewater boat through shallow rapids, my speed usually picks up with the current.
• Hull shape..
From my experience the very hard chine boats suffer the most. Boats like the Arctic Tern and Caribou are slugs in 12" of water. A Romany can out run a Bou in shallow water but when it gets deeper the Bou will prevail.
• Interesting
Any idea why this is so?

• My guess would be...
-- Last Updated: Apr-25-10 11:25 PM EST --

That the very flat panels force the water down rather that letting much of it slide up and around the more rounded hulls. My Nord LV was much quicker in the shallows but slower than the Bou in deep water. When I was training in the Bou I (and my GPS) could tell when I left 3' water and entered a deeper channel. One day with a mixed bag of boats my Arctic Tern and Tern14 were left in the dust over a very shallow sandbar by boats that were normally slower or the same speed. We just looked at each other wondering what was going on.

• Options
Energy management.
You are correct as to the point of not trying to regain the lost speed by adding more muscle. Seek instead the deeper water. Best to train with a heart monitor and GPS. Keep that heart pumping in your maintenance zone. If you can add a bit of power and gain a bit of speed without blowing out of your heartbeat zone, then you will gain some time. If you burn out trying to burn through the shallows, you will lose the time farther down the course. So, maybe if the shallows are near the finish, I would use what energy I had left to squeeze out the last few seconds. You don't need to save anything at that point. As long as you don't blow up before the finish line.