Correlation of hull length and speed

I’m not knowledgeable about many aspects of kayaking but am curious about the relationship between kayak length/ width and efficiency/speed. Looking at similar hull designs like the Tsunami 12.5, 14.5 and 16.5 suppose a paddler put out the same energy in all three boats. Is there a way to calculate or approximate how much faster the longer narrower boat would travel. If you have a hull 2 feet longer and 1.5 inches narrower would the speed efficiency gain be like 5% or 10% or more. I’m sure there are lots of factors to be considered but I would love to hear your opinions. Thanks

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Hah! I like this picture - needs more worms, though…

Try the longest skinniest worm first

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:clap: :clap: :clap: (at a golf clap pace)

Preachnpaddle, I have a 125, 145 a 175 Tsunami. The 145 is my preferred boat, for many reasons. It’s hard to compare them definitively, because I paddle tidal water. The 145 is the sweet spot. I hoped that the longer length would prove to be noticeably faster. It was faster, but it was also cumbersome to load and transport. Consequently, I typically took it out when I anticipated higher waves than normal. I’ll look at my logs tomorrow, but basically, I felt the the length added between .3 to .5 mph for each increase, depending on conditions.

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You really need wetted length. A more rockered boat can have the same length measurements as another but have less hull in the water at any given point.
Width also plays in there, skinnier is faster, but I am not versed in how to actually calculate this stuff.

Stop thinking “faster”. Better to think " not as slow".

mostly about the paddler power. Longer usually means more skin drag and some paddlers do better with less skin and drag as they have less power to give. That is why some canoes like the Kestrel and Peregrine are the same boat scaled up or down. Dave Curtis did that so his wife who is more petite could keep up with him.

Theoretical hull speed is nice but for many irrelevant… Oh according to John Winters scratches matter. They interfere with water flow.
I found more worms
http://www.qcckayaks.com/SpeakingGoodBoat1.aspx
http://www.qcckayaks.com/SpeakingGoodBoat2.aspx

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Nobody has brought up what water to grow what worms in.

In flatwater, rocker decreases hull speed; in blue water flat keels are slower, all other things being the same.

It is better to think of it as efficiency. How easy it is to get to and maintain, or exceed, hull speed. I have a couple of woodstrip 12 footers that are equivalent to most 14 footers. I have two 19 foot boats that blow away my 21 foot surfski in flat water, but get blown away by it in blue water.

Apples with worms, oranges without worms.

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Honestly I had no idea this was a can of worms. I’ve heard vague claims and sales speak about longer and narrower being faster and was just trying to get some knowledgeable opinions on “how much” faster. Thanks jyak for at least offering a number.

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Here’s my take: length matters only if you paddle with enough power for it to matter.

At your regular cruising speed on still water, note your bow wave. There will be other parallel waves behind it. Does the next crest back from the bow emanate from somewhere along your hull? Then you are not paddling hard enough for hull length to matter. If on the other hand the next wave is stuck to your stern, you are at hull speed. The front half of your boat is going up hill on the back side of your bow wave and the back half is surfing down the next one. They equal out; you are at hull speed. Paddle faster and the back wave detaches from the stern - you are paddling more and more uphill with less hull surfing at the back. What I really notice on my 14 footer is with every stroke the bow rises a bit then settles back down as it loses speed between strokes. If you are not seeing this then longer hull won’t do you any good; more likely it will increase surface friction and slow you down. Look instead at how streamlined the hull is, called prismatic coefficient, hull width and rocker if you want to go faster.

If OTOH you are surpassing your hull speed, increased length could help a little. How much? Hull speed is proportional to square root of length. Doing the math, going from 14 foot to 18 foot the ratio is 1.13, meaning the hull speed is 13% faster. However, that will be offset by increased weight and skin friction, so unless you have the power to overcome that you will paddle slower in an otherwise equivalent longer boat.

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Paddelite, very good article. I’ve seen that article and found several others that arrive at similar conclusions.

CraigF addresses a great point, but it doesn’t answer the original post. Mere mortals, I would not ask such questions if I were you, but the worms are wet.

Kayamedic posted a great article before I hit the send button. Pandora won’t go back in the box, and I left my supercomputer at work. Besides, many paddlers on the forum have no interest in average speed. Instead, their primary concern is control and using a large paddle to play in surf; others seek a kayak that provides a stable platform for photography; many require nothing more than a movable float to seek solitude, read a book, or socialize with a friend as they explore the changing face of their favorite lake or stream.

On the other side, there are the speed junkies with all the trappings of sleek boats and wing paddles. Speed is important to me, and I can only sit in the boat for a finite time. To go further mean going faster. The only way to answer this question is to actually paddle the same boat in different lengths, under different conditions. So despite the worms, formulas, and variables, Pandora demands blood.

Preachnpaddle, you hit on the one series of boat that I believe comes “close” to the perfect test platform. Each of the plastic models in the series are designed around the same underwater multi-chine profile. As Celia noted, the actual load-water-line is the key factor. Even with the same person paddling, the 125 Tsunami (actual overall length is 12’9"), capacity of 300 lbs, would be overloaded for my weight alone; the 145 Tsunami, capacity of 350 lbs, is technically overloaded, by my calculation, when I weighed 255 lbs, but it’s within range when I’m 230 lbs; the 175 Tsunami, capacity of 400 lbs, has a surplus that allows me to actually carry a load. Some parameters vary with model years and the bow to stern measurements, but currently, the 125 Tsunami is 26 inches wide, the 145 is 25.5" wide, and the 175 Tsunami is 24" wide.

If you put the 140 Tsunami in the mix, the overall length is 14’ long, 25.5" wide (2007 model was 24" wide), capacity 325 lbs. My sister uses one and I bought one for my grand daughter, but have not paddled it, because it’s too narrow for comfortable foot placement. I also have another model, the Tsunami SP, at 12’ long, 21" wide, capacity 180 lbs, for another grand daughter. Although these models follow the same design, the paddler who fits one of these models would be uncomfortable switching between some of the other models, and I haven’t paddled them.

My experience, alternating between the 3 models you mentioned, is consistent with the article PaddleLite posted. The increased length added about 10% to the speed with each increase in length. I stopped using the 175 because it’s just too heavy to lug around with my bad knees and shoulder. I also didn’t think the added length was worth the effort of fighting the way wind and current often made it harder to handle without the rudder. It also felt like it was riding to high without a load. Regarding maximum speeds, I could hit close to the same maximum spikes in each of the three boats, despite hull speed. On trips around 8 miles, I felt that I had the stamina to push even the 125 to the limit. Past 16 miles, the 145 and 175 had an advantage.

I have no experience with the pro series of Tsunami, but from what I’ve seen by looking them over, those models are in an entirely different performance category.

Anyone interested in the my impression of where each of the models excel, I’m glad to entertain questions.

Length equals speed in a general sense.
Kayaks keep getting shorter.
I have always liked big boats. There is a practical limit to how narrow a beam a good touring boat has, somewhere in the 24-25 inch range.

Kevburg, wish I could have explained it as precisely. I consider myself to be a strong paddler and thought the 175 Tsunami longer hull and 1.5 inch narrower beam would take off like a rocket. Apparenty, I didn’t have enough ass to take advantage of it.

I often swap paddles and boats with a partners to give them experience with other equipment. When I bought my 145 Tsunami, I let my older sister try it, while I used my 125 Tsunami. Despite the length difference, I could outpace her in every way. She used it a total of about a half dozen trips, and complained endlessly about every aspect of the boat. I finally took her to a shop so she could try a 140 Tsunami. She loved it and insisted on buying it with her own money; she complains about my 145 to this days.

There’s a twist. She’s near equal to me at cruising speed using her 2007 (24 inch), 140 Tsunami, when I’m in my 145 Tsunami. However, paddling into a 15 mph wind with 18 to 24 inch waves, I need to shift into force-of -will mode to hang with her. Still another twist. Under normal conditions, I can “power” away from her at will, but when we hear thunder, she takes off like a bolt of lightning. If I stop for a quick drink of water, it take maximum effort to catch her. Theories and formulas are grand, but there nothing like swinging a blade and pushing the envelope with another person. Perception alone is inadequate. She often remarks about how fast it feels we’re going. The GPS puts it in proper perspective every time.

Another twist: I often trade off boats and paddles to give a partner the experience to try different equipment. On half a dozen trips, she used my new 145 Tsunami and hated everything about it. I reverted to the 125 Tsunami and could outpace her in every way. Her main complaint was the width and hight of the cockpit and deck. We went to a shop so she could test the 140 Tsunami and she fell in love with it. She complains about the 145 to this day.

Preachnpaddle. I’m curious why you specified the three Tsunami models in particular.

Whenever folks talk about canoe/kayak speed I always wonder whether they mean a short all out sprint or a long paddle or ?

Since shorter boats have less skin friction they require less effort than longer boats at low speeds before the hull shape dominates drag…so in principle if a paddler could put out the same energy the 12.5 would be fastest up until a speed where skin friction plus form drag is lower on the 14.5, then the 14.5 is fastest (most efficient) until the skin plus form drag on the 16.5 is lower.

I recently bought a used 16 foot solo canoe (Bell Magic). I like it but it didn’t feel any faster than my 15 foot Bell Merlin II. Both boats have the same capacity (160-280 ideal load) and both have a 25.5 inch waterline width. Even though the 16 footer has a higher theoretical hull speed (6.2 vs 6.0) for me the 15 footer is more efficient at all speeds right up to the 5.7 I could do in both canoes. Plus the 15 footer is more effortless in the normal 3-4.5 mph range.

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Back to Pungos.
As we’ve aged and paddled, my female paddling partner has gotten faster to the point of leaving me. She is 15 years younger and in good shape.
She in the P140 and me in the Tarpon 160.
So, I put her in the Pungo 120 and me in the 140, thinking it would make the difference.
She still left me without even trying.
The motor is the major factor as already stated.

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If you want the fastest boat, check out what professional racers are consistently winning in for various classes of boats. . Many of these people are making a significant amount of their income from racing and the top competitors are closely matched in ability. They and their coaches have spent more time trying boats and poring over all of the theoretical aspects of boats than we ever will. There may be more than one boat in each class that may be nearly identical in performance and it may change according to conditions. Theories are one thing but results are another.

I’m not a racer and fast enough is good enough for me.

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