Factor in beam…
… and you get a bit closer to reality.
To make any real sense you have to add “at same beam” - but even that isn’t enough because a shorter boat with same beam will sink deeper with a given displacement!
You have to think 3D & 4D, not 2D.
Short boats are nearly always fat boats. Fat boats plow, skinny boats glide. Paddle what you want.
I do
I do, and my P&H Vela isn’t fat.
Short and long boats with same beam
Comparison of short and long boats with same beam
(from http://keelhauler.org/khcc/seakayak.htm ).
Speed/knots - 2/3/4/4.5/5/6
(16’x20.625") - 0.96/2.10/3.88/5.22/7.11/12.6
(20’x20.625") - 1.00/2.14/3.77/4.86/6.22/10.3
As you can see, they are within 0.04 lbs (just over 1/2 ounce) of force at 2-3 knots. At 4 knots the difference is still only 0.11 lbs (1 3/4 oz)- but the advantage is to the long boat already, and it increases quickly beyond that.
I can understand someone not really caring about going over 3 knots if they never do while paddling (if you can call that paddling!), but below that there is no real advantage. Certainly not a reason to pick a shorter boat. There are other good reasons, but efficiency of forward motion is just not a factor.
If you really still think there is some serious efficiency advantage, I suggest you download Matt Broze’s drag prediction spreadsheet and plug in some numbers.
http://www.marinerkayaks.com/mkhtml/downloads.htm
Lots of kayaks already on it to compare. The Vela isn’t (and no Sea Kayaker review), but the Neck Elaho isn’t too far off for LWL/BWL (Vela should be just slightly slicker) and here are it’s numbers at the same 2/3/4/4.5/5/6 knots marks as in the example above):
0.90/1.92/3.71/5.62/8.76/14.07
Compare that to the examples above - and again the "advantage below the crossover with longer boats (which again is at close to 3 knots) is extremely small - even when using a 20’ boat for comparison. Barely over an ounce at best point on the curve (around 2 knots or less), and that is at an already VERY low effort range where no one would notice.
Claim your “advantage” if you like, but if you think the longer boats are at any real disadvantage at 3 knots or below I again suggest you check the numbers and think about what the values (particularly under 3-4 lbs) actually mean.
For cruising efficiency/energy saving you’d be far better off using a lighter paddle than a shorter boat. Doesn’t change the pull much (though most lighter paddles are also better designs and do pull better too) but the effort saved on the return is far more than any minuscule drag break you’re gaining with a shorter LWL.
i wish you could paddle
my phoenix pelican, 14’x22" with a lot of flare, maybe 18"wl beam. no not a typical boat but there are a lot of generalizations being thrown out in this discussion.
From the article
"The shorter boat has less drag at low speeds, the longer at higher speeds, as expected."
“Shorter boats have less friction at low speeds, longer boats have less residual drag at higher speeds”
The difference at higher speeds is bigger, sure. But there are much more things affecting speed, as you said already. If you want to paddle fast, you need a long, narrow boat. If you stay within the 3-4 knot range, you also can use a shorter boat. OK?
Less yes - but ridiculously less L
– Last Updated: Sep-09-05 11:44 AM EST –
I'm not saying it's not true - technically it is. I'm saying it's insignificant and of no real use to anyone. The numbers are quite clear on this.
Absolutely you can use a shorter boat - at lower speeds it makes no real difference in effort.
I'm not saying everyone should be in longer boats. All I dispute is the so called advantage of shorter hulls at lower speeds. It's a meaningless technicality that people hear about and think it is a reason to get a short boat. As I said already - there are lots of good reasons to get a shorter boat. This just shouldn't be one of them.
agreed
I’ve got boats from 16’8" to 21’8" sitting on my deck. Up to 6mph I can’t really tell a difference in drag on any of them. Back when I had a 14ft boat it felt the same as the others up to 4mph. It is only at and above “hullspeed” that drag matters. Like Greyak said, there are plenty of good reasons for a shorter boat but hydrodynamic efficiency gains at lower speeds are nominal.