Hull speed – paddling out of a hole?

I took an Enlightened T16 out for its maiden voyage (at least with me) yesterday and experienced something new. I wanted to find the top speed that I could reach, and as I reached 6.5 to 6.7 mph it felt as if I was pushing the bow up over a swell. When I was learning to sail a keelboat I remember someone telling me that hull speed was being caught in a hole of our own creation – that is a hole created by our own wake and determined by the length of the hull. I have heard other paddlers talk about “hitting the wall,” but had not imagined it quite like that. My other boat is a Prijon Kodiak, and I have not had that experience. Maybe I just haven’t paddled it hard enough yet. Has anyone else experienced getting caught in a hole of their own creation?

Paddling out of a hole at speed?
At higher speeds (higher being a relative term), kayaks tend to “squat”.

This is because the hull’s waves upset its trim (bow up, stern down) The better designed hulls can get “wave cancellation” meaning a boat can surf its own waves. This is typically racing type hulls, with the Epic Endurance being well known for wave cancellation at lower speeds, like about 6.5-7 mph. I don’t get the impression that “average” sea kayaks can be brought to this state. The tendency to squat can be dealt with by adjusting trim - if you have a seat that slides forward to drop the bow down. This has worked for me in a Knysna Stiletto, and Nelo Razor, or the Endurance. Having just acquired an Epic 18x, I’m figuring out that hull now.

My terminology above may be off a bit, but this seems to be true for boats that I’ve paddled, especially the ones 18 ft or less. The longer 21 ft boats don’t squat as much, but they seem to build up skin friction, not the wave making type resistance of a “sea kayak”. (A boat’s resistance in the water is the sum of skin friction plus wave making resistance). Shorter hulls tend to have less wetted surface (friction) but more wavemaking resistance at higher speeds. A longer hull tends to be more wetted surface (skin friction), but less wake making drag.

Hope this helps - there are doubtless more technically conversant folks than myself out there who understand this better and can shed more light on the issues.

Good Time To read this Again
John Winters wrote a great article on how the term “hull speed” relates to kayaks - it doesn’t.

In this article he simply and eloquently describes the physics of wave-related drag including “squatting” as someone said above and also “wave cancellation” which may have been defined a little unclearly above. Anyway, this is one of the most important lessons for anyone interested in how kayak’s work. If you like this stuff, then you should seek out Mr. Winters other kayak design related articles. I would also recommend Ross Garrets book, The Symmetry of Sailing, if you want to learn even more about how boats work.

Good posts above
Directed at factual understanding of hydrodynamics. Winters stuff is clearly accurate.

The hole sensation / squat is what happens when the hull creates a wave period equal to that of it’s LWL (wave of translation). This is realistically the point at which exponential amounts of power are required to increase speed. Hugely powered tug boats will actually sink their decks at full throttle empty operation as they’ll push such a large bow wave and literally sink the sterns. An extreme example, but same principle.

Race hulls are designed to be as efficient as possible and balance Frictional and Residual resistance. There comes a point where Frictional resistance gets to be too great, even on a very skinny, round cross section hull.

Most sea touring yaks are not designed with flat out speed in mind.

The often discussed Froud’s formula for hull speed is not so applicable to kayaks as it was derived from larger displacement hulled craft. Sq. root LWL x 1.34.

It’s a guideline only and applicable as such to rec. and general touring boats as a “rough” guide only. Not really applicable to race hulls.

Thanks for the info and link to Winters
The Winters article was interesting. I’d like to see it with the figures to illustrate what he is talking about. Sounds like I need to find the book.

Check out Sea Kayaker web site
They did some extensive tank testing of hulls some years back and have drag data on a number of touring kayaks. Their explanations are also good. Also Mariner kayaks has good info. BTW, with a displacement hull you never paddle out of the hole…you just make a deeper hole.

That is until a big wave hits you from behind and liberates you from displacement.

Yep Figures & Formulas Missing
I’m not sure why the figures and formulas are missing in that version of the Winter’s article. If you Google for “John Winters Kayak” you will find some other sites that his articles, maybe with figures and formulas.

The website for Enlightened Kayak also has his articles I think.

Winters book
It’s called “The Shape of the Canoe.” It used to be available only as a book-on-CD (not on paper, not as web pages). Not sure of the status now.

He has similar writings available on various web pages, but I found the book worth purchasing.

– Mark

"…and liberates you from displacement."
Great turn of phrase!