Are longer kayaks slower?

There, I knew that that title might get some attention… :- )

Brian Shultz of Cape Falcon kayaks writes:

At 14’3" many people are worried the F1 won’t be fast enough to meet their needs, but in my experience most people vastly overestimate the speeds they actually travel and will never reach the “hull speed” of their kayaks. What this means is that we have a whole generation of paddlers paying a skin friction/drag penalty for boat lengths they don’t really need. For normal kayak touring speeds of 3-4 mph the F1 isn’t just as as fast as these other boats, it’s faster. Reducing the waterline by a couple feet dramatically reduces the skin friction and this results in a noticable reduction in paddling effort. Easier paddling is just the beginning though. By reducing the length we create a kayak that is better behaved in the wind, easier to manuver, fits better into sea caves, tight channels, and your garage. The F1 is a design created not by fashion or dogma, but rather years and years of testing how we actually use our kayaks. … Longer boats are less maneuverable, less stable, worse in the wind, and more work to paddle at normal speeds (due to the increased wetted surface). My point is, if you aren’t pushing hard enough to make use of that waterline, all you’ve bought yourself is a worse version of my shorter boat. The LPB is for the the dedicated fitness paddler who is out there pushing hard. Want to know if that’s you? Grab a cheap GPS and a kayak and push that baby up to 4.5mph. If at the end of an hour you’re hungry and ready for more, you need an LPB. If you feel like you’re going to blow an artery, you want an F1. (https://www.capefalconkayaks.com/choosing-a-kayak.html)

This makes sense to me. Unless you are paddling at hull speed you are paying a penalty for that long sexy boat. So why are all the great kayaks long boats? Sure, the athletes can use them, but I’m am most certainly not an athlete. The best I’ve done is 3.9mph sustain over 1km and that really tired me out. (That works out to about 15 minutes). There is no way that I could ever sustain 4.5mph for an hour. Ok, maybe if you factor in the ambulance ride, but on the water, no.

Most of my paddling is long afternoon trips. Speeding along from here to there on flat water, then stopping for extended periods of time to look at birds, turtles, aquatic plants etc. We stop a lot and look around, that’s why we paddle. (On our last trip to Lake Umbagog we travelled 7.4 miles in 4:55, averaging only 1.5mph!)

So, by Brian’s reasoning above, if I had had a longer boat I would have either paddle with more effort or slower, since the longer boat would have had a greater wetted surface and therefore greater resistance.

I can see the need for a long boat for gear storage for camping, that’s not at issue here. But it just seems that all the fast boats are long and all the medium length (14-15 feet) boats are barges.

Brian’s reasoning makes sense to me but I’m open to other views. And where are all the fast, sleek, sexy 14 and 15 footers?

PS: I have no relationship with Cape Falcon Kayaks aside from a strong admiration for Brian and the high probability of being a future customer.

Huh !!!

The above article does not mention the width of any of the boats involved. Nor is this info findable on their web site - I just looked. Or anything more detailed about the F1 except what is said above, it exists and is shorter than 16 ft.

Note also that the are SOF boats, extremely light. Annnd maybe not something that people would want to expedition and risk landing on rocks with.

Unless I have entirely the wrong kayak maker.

Those who really want to delve into this would have an easier time with complete dimensions. I have the landing on rocks issue when in Maine and am not all that interested in speed, so the full extent of this debate is best left to others.

Depends on your weight. A shorter boat has to be wider to accommodate a fixed weight than a longer boat therefore adding wetted surface area which works against efficiently.
Paddle fast if you can and stay thin if you can…

Sure…I’m taking my 14 ft boat , with the wide seat, this weekend to play in the surf and slug around with the dippers I will be paddling with. Same width as my sea kayak but a lower aspect ratio. But if I was doing miles I’d be in the 17 ft boat. I can’t imagine doing 7 miles in 5 hours in any boat unless you were fishing.

Frankly it doesn’t matter. Just do what you’re comfortable doing.

I built a Cape Falcon SC-1 (precursor to the F-1). It is 13’9" by 23" wide, and paddles incredibly easily, has excellent glide and tracking, as well as being the quietest boat I’ve ever used. It is a version of the Mariner Coaster, a legendarily good short kayak from the early days. Brian thinks about his hulls more thoroughly than most designers, in my opinion. The boats are developed over multiple full-size prototypes and end up being quite sophisticated. I believe the width of the F-1 is tailored to the paddler, but is in the 21" to 23" range.

I fully agree with his discussion above from a hydrodynamics viewpoint, and the claims he makes about his boats are justified. I have to disagree strongly that 14’ and 15’ boats are all barges. I have a QCC Q400 (aka Caspian Sea) which is 15’3" by 24" and is certainly no barge. Not surprising since it’s by John Winters, a well-known small-craft naval architect. There are plenty of other factory boats in this range that are not barges.

It’s a fact that at ‘normal’ paddling speeds, skin friction dominates so wetted surface area is a controlling factor. Generally speaking, a shorter, wider boat will have less surface area than a long skinny boat with equal displacement (i.e. same overall boat and paddler weight), although maximum draft will influence that. It’s also true that excessive width can slow down a hull, but a fair hull shape can limit this effect significantly. Transverse hull section shape is more important than overall width or draft in determining resistance - there are a number of coefficients used by hull designers that incorporate this info, but they’re hard to come by when evaluating commercial kayaks.

I agree that hull shape has a lot to do with ease of paddling.

All else being equal, longer boats feel smoother in closely-spaced waves.

Maybe the point of the cited article is to make people examine how they paddle rather than blindly accept that longer is always faster.

Hull speed is just the speed at which you will need a drastic increase in power to accelerate above. It is strongly related to waterline length of the boat. For sea kayaks, it often falls somewhere about 5-7 knots. For a 16 foot water line boat, it should be 5.4 knots (6.2 mph).

At speeds below hull speed, the drag is more related to whetted surface and boat width. Whetted surface is related to weight of boat, paddlers, and gear. So for a given paddler at speeds well below hull speed, the only major difference is boat width. But really a 22 inch wide versus 24 inch wide boat won’t make that much difference. The 22 inch wide boat should be slightly faster, but at average cruising speed for most paddlers (3 knots), all sea kayaks have about the same drag for a given paddler.

This is all assuming flat water. When water gets a little bouncy, resistances change. As does your ability to make power and use that power toward moving the boat forward.

Ever notice that if you start out piddling aimlessly it often feels like lots of effort to get out of that mode? But if you warm up slowly yet paying some attention and THEN switch gears to a faster pace, the faster pace feels right? Works well in longer boats, not so well in short ones.

Paddle mindfully. B)

I got me a fast boat 'cuz it CAN go fast (not necessary, that it WILL go fast)

For my daily ‘stretch’, when I choose the V10, I average 4.23mph (based on 2640 total miles so far)
So, you may ask, why did I spend the bucks on an expensive surf-ski.

  1. I like the variety (on my daily paddle, I go from a highly rockered Sterling Progression (read - slow), through a selection of others, to the V10)
  2. though, 95% of the time I paddle ‘slow’, I do like to push it occasionally (especially on outgoing tide with a boost of a couple miles/hour), and the V10 has lots of ‘space’ to go faster than 4.

Canoe designers have known for decades that longer is not necessarily faster. You need the horsepower to drive a hull with lots of skin( which either translate into longer or fatter but longer is more likely to give more skin then fatter will).

This is exactly why there are different sizes of the SAME hull being made. John Winters explains this quite well in his treatise “Shape of the Canoe”.
start here. There is math
http://www.greenval.com/shape_part1.html

Thanks for the great discussion! I couldn’t contribute during the day since I was working, but I did sneak a peek at phone once or twice. I don’t want to quote this and quote that, but let me address what I can.

Width

I was talking more from a theoretical standpoint. So the width shouldn’t matter. So I guess to rephrase the original statement. If not paddled at hull speed, given two boats, of equal width, should the shorter boat be faster since it has less wetted surface?

What surprises me about this observation is that it goes completely against the common wisdom, that long boats are fast boats. I find this interesting and without significant testing, hard to prove, but it makes sense to me.

Skin boats

Skin boats are strong. They are made with ballistic nylon and 2 part polyurethane (or epoxy I guess, I’m not an expert). You should have no worries about rock gardening in a skin boat. See

https://www.youtube.com/watch?v=0JTcMMkgk2Y

where he can’t puncture it hitting it with the pointy end of a hammer, or

https://www.youtube.com/watch?v=gYyvIExWkqU

where he throws the boat around. I know I would never do any of those things with a composite boat.

As for expeditioning, well, no. Don’t. Skin boats need floatation bags. But I was only asking about speed here.

Paddler weight

interesting observation. I hadn’t thought that a heavier paddler would increase the wetted surface. So I wonder if that would be the same increase for a long boat versus a short boat. I’m not sure how to think about this.

QC boat short, not a barge

It is great to see that not all “short” boats are barges. I just sold my 13.5’ Tampico, certainly not a barge and I was said to see it drive away, but it just seems that the 14’ foots are all 24+ inches wide and all the 17’ boats are 20-22 inches wide.

I’ve seen QC boats talked about, and they always stress speed, which is cool. But then they talk about fitness, we like carrying gear. We often carry a small table and chairs for lunch, I mean lunch is important. I’m curious, does the QC have some capacity for that? Not for an expedition, but for a civilized lunch?

I can’t imagine doing 7 miles in 5 hours in any boat unless you were fishing.

We stop a lot. I look at the time stamps on some photos. Bald eagles, 30? minutes, baby ducks, 20 minutes, otters 10 minutes, neat dead tree, 20 minutes. Being stationary adds up! Oh, and there’s lunch and talking with other paddlers.

We stop a lot.

Waves

Oh yeah, certainly. I think it is pretty clear that if you are off shore you need a long boat. I would never argue that.

Hull speed is just the speed at which you will need a drastic increase in power to accelerate above. It is strongly related to waterline length of the boat.

Wow, this is the best explanation I’ve ever seen of hull speed. Thank you!

@NotThePainter said:
And where are all the fast, sleek, sexy 14 and 15 footers?

Offhand I can think of the P&H Delphin 150 (21.5" beam) and Valley Sirona LV (also 21.5). Pretty sure there are other sleek 15-footers out there.

I have a 14-foot, 22.5" wide kayak which is most definitely not a barge. It doesn’t come up to speed as fast as my 17-foot (21") boat nor does it have the same long glide. It’s also much wetter in waves and chop but I can turn it much more quickly than the long boat. On the other hand, I can paddle the long boat faster with less effort.

When I joined this community as a clueless paddler, I didn’t understand why so many have more than one boat. Now I do.

@kayamedic said:
Canoe designers have known for decades that longer is not necessarily faster. John Winters explains this quite well in his treatise “Shape of the Canoe”.
http://www.greenval.com/shape_part1.html

This set of articles is highly recommended — it’s telling that Winters, primarily a canoe designer, has provided some excellent kayaks of moderate length. I once had the Q400 on my car roof at an angle that hid the deck, and it looked very much like someone had mistakenly loaded a white canoe onto my car.

I think QCC boats are no longer available, but Winters has designed at least some of the Delta Kayaks lineup, the touring hulls, I believe. The Delta 15.5 GT looks pretty similar to the Q400. Speaking of fast, medium-length hulls, Placid Boat Works pack canoes come to mind, which I really have to try someday soon.

If not paddled at hull speed, given two boats, of equal width, should the shorter boat be faster since it has less wetted surface area<

I’m not a naval architect by any means, but am just thinking about this intuitively. With that said, I question the premise that the shorter boat of equal width has less wetted surface area. The two boats have to displace the same amount of water assuming that the weight of the boat, paddler and equipment is the same (the shorter boat would weigh a little less but I suspect that the difference would be minor relative to the other contributors to weight - especially the paddler [at least in my case]). So the shorter boat (of equal width) would sit deeper in the water which would increase it’s wetted surface area. This might be offset somewhat by the fact that the (wetted surface area)-to-(water displaced) ratio is going to be higher for the long skinny boat. (The underwater profile of a floating sphere would have the lowest [wetted surface area]-to-[water displaced] ratio) but I’m guessing a hull thus shaped would paddle quite slowly.

Although drag (generated by friction between the hull and the water) will slow the boats, I would guess that more of the resistance to driving the boat through the water is generated by the pointy end pushing water out of the way. A long skinny boat would increase drag but reduce the amount of water being pushed aside (proportional to the cross section of the boat with the most area) relative to a short but wider boat (wider so that the total volume of water displaced is equal). That is, the long skinny boat is continuously punching a smaller hole in the water through which the rest of the hull can then pass with minimal resistance, compared to the shorter but wider boat. As an extreme illustration, and putting ergonomics aside for the moment, imagine paddling a kayak sideways (vs forwards). It wouldn’t go very fast even though the water displaced and wetted surface area are the same irrespective of which direction it is paddled.

@Rookie said:
Offhand I can think of the P&H Delphin 150 (21.5" beam) and Valley Sirona LV (also 21.5). Pretty sure there are other sleek 15-footers out there.

The Sirona looks pretty interesting to me, thanks for the tip!

When I joined this community as a clueless paddler, I didn’t understand why so many have more than one boat. Now I do.

LOL, just yesterday I watched my first ever boat drive away with the new owner. Now I’m down to only 2 and might buy one this weekend! So true, so true…

@Monkeyhead said:

I’m not a naval architect by any means, but am just thinking about this intuitively. With that said, I question the premise that the shorter boat of equal width has less wetted surface area. The two boats have to displace the same amount of water assuming that the weight of the boat, paddler and equipment is the same (the shorter boat would weigh a little less but I suspect that the difference would be minor relative to the other contributors to weight - especially the paddler [at least in my case]). So the shorter boat (of equal width) would sit deeper in the water which would increase it’s wetted surface area.

That’s it in a nutshell, thanks! and let me quote from the Valley Sirona page

Valley said
The shorter a kayak is, all other things being equal, the more it will be affected by variations in load. This is because the smaller the footprint, the more it needs to sink into the water, to support a given displacement

That is, the long skinny boat is continuously punching a smaller hole in the water through which the rest of the hull can then pass with minimal resistance, compared to the shorter but wider boat. As an extreme illustration, and putting ergonomics aside for the moment, imagine paddling a kayak sideways (vs forwards). It wouldn’t go very fast even though the water displaced and wetted surface area are the same irrespective of which direction it is paddled.

Great visualization, thanks!

As above and why I asked my question, the full hull design matters in the end. Can’t have a useful discussion without bringing in more factors. I have the boats that go to this hanging in the basement.

Skinnier shorter boats are not super new. My old Vela comes in at 14’6" long and 21" wide. It is an old boat design and anything but a barge. It also accelerates fast in a sprint but sets up a bow wake at speeds where my husband’s much longer Aquanaut would still be easily accelerating.

But I am a small paddler, though less small than a couple of decades ago, and I cannot provide the engine to move the Aquanaut like my husband could. So the boat’s higher hull speed is useless to me. Inversely, even if he could have fit into the Vela he would sink it below the optimal waterline. So he would have been pushing water sooner than me.

Just found the Valley Gemini, 14’10" by 21"

And yes Celia, full design does matter. We can talk all we want, and hey, I started it, but in the end, you’re in the water in a real boat, not at your keyboard.

Is the bow wake the sign that you’re at hull speed?