It seems that some relitvly slow boats(my 10’ Hornbeck)paddle with relitivly little effort,but some much faster and longer boats require more effort at the same speed.Is this a valid observation? And if so why? Wetted surface area?
Does hull shape enter into it? Turtle
Yes and yes
But as your speed rises the short boat will become harder to paddle whereas the long boat will not. (all other things being equal with a long list of possible exceptions)
I think your take is correct
and I think the reason being that the longer, faster boat might be too much boat for a smaller paddler.
My wife is a good example. She used to paddle and race a QCC-600, and when she switched to the baby QCC which is a couple of feet shorter and the same width she improved her times tremendously in the same races under the same conditions.
Our conclusion was the longer boat was just too much boat for her.
Cheers,
jackL
Normally;
a long thin boat with little rocker will be fast where a short fat or deep boat will be slow.
all other things being equal that is a statement of fact.
Now if you make a long thin boat so tippy or hard to turn that a paddler can’t keep it up that is another side the the equation that must be considered.
Fiona Stirling Bsc. did a little blurb on one of these news groups a couple of years ago. It was simplified but lengthily.
The responses were varied and apparently had no idea who they were responding to.
I enjoyed the responses more than the posting.
The Shape of the Canoe
By John Winters available from Green Valley Boatworks.
More than I’ll ever need to know.
If I understand it right, wetted surface is important at lower speeds, length and length to beam ratio are important at higher speeds.
At around 4 mph my 15’ x 30" Swift Osprey takes noticably less effort to paddle than my 18’ x 28" J200.
speed vs effort in short and long boats
I have three different 12’ Bart Hauthaway canoes. They are Rushton inspired designs, as are the shorter Hornbeck canoes. I find them very easy to paddle at slow hull speeds. Fine canoes for playing on a pond. However, they hit a hard wall if I try to go fast. I attribute this to the effect of short hull length being effectly even shorter due to the pinched in ends typical of Rushton pack canoes. Increased width to increase carrying capacity doesn’t help.
My 15’ Rapidfire is much faster due to 3’ of extra length and a modern (Yost) hull design without pinched in ends.
I have a Azul Sultan kayaks that is about 18’ and while it is quite fast (among the best of the rest of touring kayaks after the QCC 700 and 18’ Epic) it requires more effort to obtain and maintain that speed.
As noted above, Winter’s book “The Shape of the Canoe” is the source if you want numbers and dense reasoning to explain what many of us feel when paddling.
Dave
short vs long
two thing slow a boat down -
- Surface friction
- Energy dissipation due to the need to move water - wave making.
Both are always present.
1st is directly proportional to the surface area. You can certainly have a short boat with lower surface are than a long boat. This one does not depend on the speed.
2nd goes, typically as speed squared, and is dependent on the hull shape, length and some other factors. Characteristic most often associated with this is “hull speed” - 1.35*sqrt( water length in feet), in knots.
So, 1st dominates until you approach the hull speed, then 2nd kicks in. 2nd does not kick in as a switch, it is more of gradual influence.
For a short boat, 2nd kicks in sooner.
A few examples:(http://www.unold.dk/paddling/articles/kayakstatistics.html)
These are based on numerical sims, should be taken with a grain of salt.
- VCP Avocet is 16ft (4.8m) kayak. Its water length is around 4.2m, surface area for ~150lb load is 1.63m2
- Futura II, the surfski is 5.75m (~19ft) long. Its water length is around 5.57m, surface area for ~150lb is 1.96m2.
Now, just looking at the lengths of both kayaks, the ski would appear faster, but that number does not really describe the whole story.
Say, you are paddling leisurely with your friends at 2kt.
Avocet will be dragged down by 0.92 Newtons while Futura is slowed down by 1.01 Newtons.
That is whopping 10% difference in paddling effort !
However, at 4kt Futura is already easier to paddle than Avocet.
What does this all mean? Every boat is designed with certain purpose in mind. You can take Avocet and have your fun in the surf, rock gardens, slow leisurely paddles, or you can enjoy going fast in Futura.
Variables
– Last Updated: Oct-17-07 12:18 PM EST –
Weight also matters. A light boat will accelerate faster and feel more responsive to a paddle stroke. Weight doesn't have much effect on steady-state speed.
I once fired up Excel and plotted a bunch of the archive data from the drag prediciton spreadsheets at the Mariner Kayaks website(the same one that Sea Kayaker uses).
Overlaying the curves showed that smaller boats had slightly less drag at lower speeds, but the longer boats had much less drag at higher speeds -- just what you'd expect.
My wife, who's 5'0" and not strong, felt much faster and more comfortable when she moved from a 16' x 22" boat to something smaller in all dimensions. Top speed is not important to her -- she just wants to be able to maintain a relaxed group touring pace with minimal effort.
Friction = f(Velocity)
Friction does depend on speed - a motionless boat has no frictional forces slowing it down.
yes it does
Have to apologize, something else was on my mind.
Low speed ~V
High speed ~V*V.
OK, yes, all better, NM
OK so
OK so the shorter the boat-the less effort but slowest top speed.Kind of an inverse ratio?For me in touring, effort is more important than ultimate dash speed-so the shortest boat that will float me(pun intended) would be my best choice.It seems paddleing ease is not mentioned much-maybe it’s less glamorous,but a lot of tired paddlers would benifit from that info.
P.S.I just paddled a 14’ Hornbeck,which is just like my 10’,but 4’ longer and it followed this idea exactly.It required noticably more effort at lower speeds,but I could push it much faster.
Thanks for your feedback,Turtle
Double Bladed Paddle?
Are you paddling your 10’ Hornbeck with a double bladed paddle? Are you comparing your “ease of paddle” relative to a “faster and longer” solo lake tripping boat? The “effortlessness” of paddling has so much to do with the paddler’s style. I’ve seen guys out in tough conditions who look like they aren’t even generating a sweat. By the same token, I’ve seen guys out in dead flat conditions, who look like they are fighting whales.
I think the best test of your thesis is for you to get into one of those “longer and faster” canoes, and see how it goes for you.
Yes
For the sake of comparison dubble paddle on all.I also paddle a Swift Osprey which is a pretty fast boat and the comparison holds there.I was hoping Charlie would weigh in on this one-he speaks from a lot of knowledge.I have seen lots of scientific speed measurments,but never effort measurments.
Turtle
here’s my layman’s hunch
At slower speeds, the less hull friction of the shorter hull requires less effort to paddle. But, as speed increases and you begin to create a bow wave, the shorter hull becomes more affected by the bow wave than the longer hull and effort increases per unit of speed for the shorter hull.
Yes, we need to be careful
not to assume short more efficient. Certainly a short stubby kayak will hit it’s “hull speed” before a longer boat, and require lots of effort to paddle beyond that. So, provided one does not want to paddle faster than 3 knots or so, it doesn’t matter. I believe this is why Rec. boats are so popular. People are experiencing what hydrodynamics is all about. They find they poke along just fine at the speeds their friends in longer boats may paddle, and they have stability and maneuverability to boot.
Truth is these little boats do a great job of addressing the needs of many. However, there’s a balance, and just as too long is disingenuous for many, so is too short! The issue is balancing Frictional Resistance and Residual Resistance around the power supply and intended speed range. Start with the engine and match the boat to it.
Hemlock Example
Intuitively, I believe that a longer canoe, once at speed, should paddle with less effort than a short canoe with somewhat the same width.
However … I know not to trust my intuition very far …
Dave Curtis says that a smaller paddler in a Hemlock Kestral can keep up with a stronger paddler in the foot longer Peregrin. When he says it, it must be valid. And that certainly supports “Turtles” supposition.
Intuitively
I feel that the shortest boat that would be efficient for extended paddling would have a waterline length of not less than 12 feet. A while back I paddled a couple of kayaks in the "rec’ class that I thought were both quick and fun, the Necky Manitou 13 and the Epic GP. The Epic seemed faster but the Manitou was better in choppy conditions. Makes me wonder what the boats would be like if the width were to be reduced to about 24 inches. I think a change like that would enhance their performance and make them feel and fit better as well. OTOH, they might feel less stable, at first, to the novice paddler and that could be a negative for mass marketing.
John