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Discussion Starter · #1 ·
Hey folks. This feels like a topic that should've been done to death but everything I've found on the subject's been a little fuzzy. I was reminded of it recently looking at a thread about EPIRBs..."my kayak is eleven and a half feet long, why am I thinking about EPIRB territory?" I realised.

The general consensus seems to be that for open ocean, 2km+ offshore trips you ought to be in something at least four or four and a half metres long. The only reason for this I'm clear on is that length is speed and speed gets you to safety sooner. Are there other straightforward characteristics of a long boat that help you in poor conditions? Less course correction in waves? Less likely to pitch-pole?

I hope this question's not too dumb and done :)
 

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Faster also means less effort to paddle long distances. It should also track straighter and therefore be less of a hassle. It's all about the idea that offshore fishing means long distances and often lots of trolling.
 

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I would imagine that longer/faster/less resistance would also come into play if you run into a fast current. With a shorter/slower yak you are going to burn more energy reserves sooner trying to paddle across or against said current. Yes you can take your time and slog your way thru, but by then you may have been carried quite a distance from where you wanted to be. Guess that is part of the safety aspect.

Rob
 

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Shorter boats don't tend to track as well. They are knocked off line more easily than a longer kayak. They tend to have issues with broaching on swell and wind waves earlier. Dynamic stability tends to be inferior once life starts getting bouncy and windy out on the big blue.

On the whole a longer kayak will tend to be more sea worthy.

It is all generalizations though.
 

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Discussion Starter · #5 ·
Thanks guys. So to summarise a shorter kayak:

-will cover less ground in ideal conditions
-will have the headway it can make reduced more dramatically in poor conditions
-will be more easily broached on wind waves and swell

Dru, is "dynamic stability" a summation of the last two points or is it something else?
 

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Are you sure you are not confusing with static stability? Perhaps we are crossing over essentially the same thing.

In my view dynamic stability is about stability in an active seaway. Most of the stability curves you see for kayaks (when you can get them) are actually static stability. To use your example of the circular hull, we see this tendancy in the faster racing ski's. Their static stability is hopeless. But in the right hands their dynamic stability can be awesome. Though not as good as wider slightly slower racing skis.

More in context in this discussion, issues that are covered in dynamic stability (but not in static stability) include:
x pitch
x yaw
x rolling and dynamic damping
x tracking and the effort required to get back on line

Design issues that will impact it include:
x rocker
x hull shapes that shift from displacement to planing (surfing)
x tendency to cavitate
x subjective matters like feedback to the paddler (will be different with different skill levels)
x skeg v rudder
x not sure what to call it, but the "G force" or acceleration of a shape in response to waves (the higher the primary stability the higher the acceleration)
x position and shape of skeg/rudder
x wind will tend (in swede form hulls) to make the kayak point into it; waves will tend to make the kayak broach (turn side on to the wave). design to work with, or to resist these tendencies is also dynamic stability.

I'll have a hunt through "Seaworthiness, the Forgotten Factor" tonight and see if I can find a formal definition of the two. It's about sailing not kayaks but a reasonable base for terminology.
 

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Hey Squidley, the ability to be able to travel faster can make the difference between moving forwards or going backwards in high wind. Even if you try & be careful with checking the weather forecasts, you could get caught out one day.

Everyone has to make their own choices but there is a reason that longer kayaks are preferred by the guys that are really experienced offshore kayakers. It's not just kayak fishermen either. Have a look at what sort of length sea kayaks & surf skis, (not wave skis) are.

If you start thinking about stability too, all other things being equal, a longer boat will be harder to capsize because there is more boat in the water, ie more friction & resistance to movement. I noticed this when I had a test paddle in the Stealth Pro Fisha 475. It felt "twitchier" than the 575 or my 550.

Guys like Dru will be able to give you all the ins & outs but in a nutshell, safety is the biggest reason for going for a longer kayak offshore.
 

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Salty Dog said:
Hey Squidley, the ability to be able to travel faster can make the difference between moving forwards or going backwards in high wind.
A truism. But as allways other matters can also impact and even take over. Windage and your yaks exposure to it, how the yak reacts to it (turns into or down from the wind) any dynamic differences. Ie does the yak react the same in wind as in no wind (not likely).

The definitions promised, I have to redact and paraphrase unfortunately:

Static stability
The property of a boat by which the action of the buoyancy and weight forces tends to restore its original position if it's equilibrium has been disturbed. the author (CA Marchaj) also defines it as meta centric stability. I'm not totally in agreement, meta centric stability is probably the predominant measure of static stability, but initial stability and (angle of) vanishing stability are also static measures. They are roughly analogous to primary stability and secondary stability in kayak design.

As Tonystott pointed out, these measures are about the centre of gravity compared to the centre of buoyancy. So define the angle of roll where the boat won't recover but will capsize - is a test tank not in a seaway. The paddlers weight and shape also impacts this.

Dynamic Stability
The property of a vessel which causes it to maintain its steadiness or stability only through reasons of motion. It is dynamic stability that we consider the motion of a boat, regarded as a system, taking into account all the forces which effect the boats behavior; that is to say, not only the forces considered under static stability above, ie buoyancy and weight, but also including inertia and damping forces and taking into account input from the waves and wind
 

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Of course the technical stuff isn't necessarily Intuitive. All it means Squidley is that a shorter yak is, on the whole, going to get knocked around by the conditions more.
 

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dru said:
Of course the technical stuff isn't necessarily Intuitive. All it means Squidley is that a shorter yak is, on the whole, going to get knocked around by the conditions more.
And if you're Carnster or a Safa, you can paddle it to Noumea and back in a day, (with a behemoth on the deck). Being fit is also a big factor. :)
 

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Discussion Starter · #11 ·
Thanks again guys :) You make this a pretty good forum. I think you might've helped me assess risks a bit better.

I wonder if a forward mounted "skeg" would aid tracking in rough water
 

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Squidley said:
Thanks again guys :) You make this a pretty good forum. I think you might've helped me assess risks a bit better.

I wonder if a forward mounted "skeg" would aid tracking in rough water
Skills training with a qualified instructor will change everything for you Squidley. If you can afford it, pay the money, and reap the rewards.
 

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Squidley said:
Thanks again guys :) You make this a pretty good forum. I think you might've helped me assess risks a bit better.

I wonder if a forward mounted "skeg" would aid tracking in rough water
More generalisations, but most sea kayaks tend to be Swede-form. Ie more volume in the tail. This means that the wind hits the tail more than the nose and tends to steer the kayak into the wind.

In this arrangement designers put the skeg on the tail to counter that movement. If the skeg is adjustable, more skeg will keep you broadside, withdraw the skeg and you point into the wind again. It's not exactly steering, but you can set a skeg to hold the line you want.

All a skeg on the nose will do is make it really hard to turn anywhere but into the wind.

Rules change with fish form, or most of the volume forward. But on the whole, skeg to the tail.
 

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To technical guys i thought kayaking was for fun and fishing /fitness not a science lesson sorry but imo you have made it sound incredibly boring and way to scientific :?
 

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Discussion Starter · #16 ·
The essential info is that a yak far under 4m is going to be slower, and affected more drastically by rough weather. Some of the stuff about dynamic stability is over my head too but no one needs to apologise for providing it.
 

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Sure, i agree partially but i was giving my opinion and not looking for an apology at all its not offensive or biased or anything like that ,just boring...
 

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Squidley said:
The essential info is that a yak far under 4m is going to be slower, and affected more drastically by rough weather. Some of the stuff about dynamic stability is over my head too but no one needs to apologise for providing it.
Bugger. Found out. Had to happen sooner or later. Squid, succinctly put. [screaming urge for caveats and more info being forcfully overridden.] It's all good. Honest. I'm OK.
 

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Thanks for taking the time Dru - interesting to learn about hull shapes.

Thanks for your input too norevo - your contribution is not boring at all (I don't care what they say ;-) )
 
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