Kayak length, speed and stability: observations

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Don't get too hung up on length and speed. Because, as you say, all other things aren't equal here. Longer hull at the same beam and hull shape also means increased wetted surface and more drag. It also requires more materials to build, so its heavier and that takes more energy to accelerate. 
Even ignoring that, the relationship between hull speed and length is proportional to the square root of the waterline length not the actual waterline length. Note: Waterline length not overall length. A long boat with less than it's design load sits up out of the water and has a shorter waterline length than the same boat loaded. The difference in hull speed between a 580 and a 530 would be less than a quarter of a knot or 0.5 km/h. For both boats it would be between 9 and 10 km/hr and thats a very fast pace to maintain cruising any distance. Unless you're racing you probably won't notice the difference.
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(10FEB11, John Anderson_SeaKayakForum.com )
 
John's comments are similar to my findings.
In paddling groups I have observed that paddlers left behind occasionally blame their shorter kayak for the lack of speed and them not being able to keep up. However the pace is usually around 6-7 Km/h at best.
Some paddlers are convinced that if they had a longer kayak they would be able move faster.
It would be interesting to see what would really happen if they tried the longer kayak. Chances are they would be actually slower, if they could not improve their paddling technique.
Obviously things are different if a paddler can bring his/her kayak to hull speed (maximum speed that their particular kayak can achieve). Most sea kayaks hit "the wall" at much higher speeds than at recreational paddling pace.

One must really push hard to eventually feel the kayak being unable to go any faster.
At slower speeds (Club outing pace) a shorter kayak will create less resistance and therefore be easier to paddle.
Here are some resistance stats for known sea kayaks hulls.
(Posted by: wilsoj2 on Nov-24-09 2:44 AM (EST) www.paddling.net )

Here are some drag figures for 7 boats from Sea Kayaker from 2 to 4.5 knots (2.3 to 5 mph) listed from most drag to least at each speed:
at 2 knots:
 Valley Rapier 20 = .97
Epic Edundrance 18 = .97
NDK Explorer = .94
Chatham 16 =.93
Foster Legend = .9
Avocet = .9
Nordkapp LV = .9

at 3 knots:
Valley Rapier 20 = 2.04
Epic Edundrance 18 = 2.03
Foster Legend = 2
NDK Explorer = 1.96
Chatham 16 = 1.93
Avocet = 1.92
Nordkapp LV = 1.88

 at 4 knots:
Chatham 16 = 3.89
Avocet = 3.74
Foster Legend = 3.7
NDK Explorer = 3.63
Epic Edundrance 18 = 3.55
Nordkapp LV = 3.52
Valley Rapier 20 = 3.45

 at 4.5 knots:
Chatham 16 = 5.58
Avocet = 5.4
NDK Explorer = 5.25
Nordkapp LV = 5.24
Foster Legend = 4.9
Epic Edundrance 18 = 4.73
Valley Rapier 20 = 4.45

The drag figures given are calculated assuming flat water.


It seems that the shorter kayaks have less resistance than the long ones, at recreational/Club speed.
 
I also find intriguing the emphasis put on  maneuverability and stability observations from paddlers' reports on a given kayak.
They vary incredibly.
I hear/read comments like: "the kayak is very tippy" or "the kayak is very stable" for the same very kayak.
 
So what gives? how can a person really find out what are the characteristics of a kayak?
 
I believe that stability is difficult to quantify.
Sure there are scientific measurements taken and published for most kayaks out there (Sea Kayaker Magazine being a great source) but those numbers are much harder to interpret and to come to a conclusion than the simple measurements of speed.
What one person finds stable other might find tender.

Photo: Rio Mistico Kayaks_used with permission
The biggest factor in objectively assessing a kayak's stability is the paddler's skill level.
A novice might find a narrow round hulled kayak very unstable while a proficient kayaker will pronounce it "rock solid". Needless to say that quality seat time in any kayak will increase one's skill level. It certainly did for me: here
Being able to roll also adds an incredible sense of security and a kayak that used to be regarded as tippy suddenly becomes OK. Before I could roll proficiently I would be very wary of narrow kayaks.
A paddler's weight is probably the other most deciding factor on a perceived kayak stability. I however find that more weight doesn't equate to more stable. Gear or ballast in a kayak will increase stability but a paddler's weight might not. There is a marked difference between the weight distribution between men and women; the latter being advantaged by a lower centre of gravity that in terms equates to a more stable kayak.
I notice girls having an easier time balance bracing a kayak than guys.

Being top heavy and having broad muscly shoulders does actually make it more difficult.
Last but not least: the paddling conditions.
Some crafts are excellent in calm waters but become a bit of a handful in following seas.
Regular readers of this blog will also know that I find ruddered kayak less stable in following seas where the rudder no longer can function to aid directional stability. A kayak that can be controlled by the paddler's body and paddle stroke is usually a more stable kayak, in conditions.
 
While listening to reviews is often beneficial in the quest of selecting a new kayak, some reviews/observations are so terribly subjective that give the researcher little help. What most reviewers forget is to state their weight and height.  What really can not be quantified however is the skill level of the reviewer, to then be able to draw any conclusions from the review.

Sea kayak grab handles

source *: http://www.kayaking.com.au/brochurefiles/Ocean.pdf
A sea kayak to be safe must have grab handles.

Just like its perimeter lines, the grab handles are used to hold onto the kayak when out of the boat.

While perimeter lines are essential to perform an assisted rescue and vital for hanging onto your vessel in rough waters, the grab handles perform also other duties.

They are needed in towing situations but most often are used by the paddler in a wet exit in the surf zone.

When paddling in ocean conditions chances are you might need to land on a beach where surf is encountered. Most paddlers have been dumped at some stage out of their kayak (some more than others) and probably had to hang onto the boat to prevent their vessel being smashed onto shore by the following waves.

The best location to hold onto your kayak is the bow or stern where you can point the vessel into the incoming force of the wave and minimize the impact (less surface area).

Unfortunately not all kayaks have stern grab handles because of rudders.

The waves don't even have to be that big to surf your kayak away from you if not held tight.

Often the wave will twist your kayak when you hanging onto it by the grab handle.

Most likely you will have your full hand holding onto the grab handle trying to stay together with your kayak.

Let's analyze the different types of handle, their merit, shortcomings and potential dangerous features.

(Explanations to comments at the bottom)

Eco Bezhig:

-great carry handle

-no grab handle

not safe in the surf zone (1)

Mirage grab/carry handle:

-average carry handle (too small)

- dangerous as grab handle in the surf (2)

Guillemont Petrel custom made kayak and handles:

- good anchor for towing

- dangerous handle in the surf (3)

Raider grab and carry handle:

- OK carry handle

- dangerous grab handle in surf (4)

Impex grab handle:

-very good handle for surf (5)

-carry handle is separate (same as Eco Bezhig)

SeaBird carry handle and grab handle (retrofit)

- good carry handle

- excellent grab handle for surf (6)

Valley (VCP) grab/carry handle:

- average carry handle (too small)

- very good surf handle (7)

SKUK (Nigel Dennis)

-one word: brilliant

The simplest design seems to be the best.

There is no chance to get your fingers caught or your wrist injured in the surf.

The stern handle is offset (handle of left) to balance the kayak when carried.

While this handle might look like the obvious solution it took the genius of Nigel Dennis to perfect this simple design.

.

By dangerous I mean:

if the kayak is held by this handle chances are that your wrist or fingers will be injured if the kayak twists/rolls.

Analysis by numbers:

(1) this kayak has no grab handle, only a carry handle. Holding the kayak in the surf by the grab handle there is a good chance of injuring/braking your wrist when the kayak gets rolled by the wave

(2) this grab handle allows for fingers to be slipped between the two ropes of the handle. Documented cases of severed fingers are the result of this type of handle. If the kayak is rolled by the wave possible wrist injury.

(3) this handle is excellent for towing (low centre of gravity that lifts the bow under tow) but is even more dangerous than handle (2). Not be used in surf at all as grab handle.

(4) this handle is soft on the hand for carrying an unloaded kayak but has similar potential of injury as handle (2). Just slightly better because the ropes join at the handle and less of chance of having fingers caught between the lines. Still potential wrist injury when boat rolls.

(5) this handle uses bungee cord as shock absorption when the waves yanks on your holding hand. The cords might still allow finger insertion however the bungee would be softer and less damaging. Not perfect but better than others.

(6) the SeaBird Desisg kayak came only with carry handle (bad); I retrofitted a decent grab handle by drilling the bow and threaded some heavy duty bungee cord. The bungees also have a sleeve that prevents the fingers being inserted between the two lines. Very safe grab handle.

(7) Valley has addressed the risk of severed fingers by sleeving the grab handle lines however the handles are a bit undersized for carrying an empty kayak.

After a few near misses with some of the types of handle described above I now will not hang onto a kayak in the surf that potentially will injure me.

There are some other handles that I have not reviewed yet but I might add them as I will have more photographs to post.

* used under COPYRIGHT ACT 1968 - SECT 41

PS 17JUN. It appears that my observations on the above grab handles have stirred some emotions from loyal kayak owners and manufacturers.
It seems that maybe one kayak manufacturer is prepared to redesign the grab handle on his kayaks.
However, today I had a strange call from a kayak instructor.
He sternly warned me against possible lawsuits from the "offended" kayak manufacturers. I am grateful to him for his concerns for my wellbeing however before posting the above I consulted with my legal advisor and cleared some points.
What I don't share with my concerned instructor is the fear that some individuals have towards manufacturers.
While I can't see any slandering in my review, just observations, I do understand that individuals might have been challenged with their design rationale.
My question is: how would a consumer truly find a non bias review?
I have tried a few times myself but the ones available on forums are often "doctored" or deleted. It seems that is not uncommon to have forum administrators not display an unfavourable review with the fear that an advertiser/sponsor might cancel their support.
I have also noticed that true unbiased reviews are only possible from users that have no ulterior motives.
Come on, how often have you read a review on a website that was just reeking of commission?
Unfortunately there are very few sources out there that are fully independent from any commercial agenda that will give you an honest opinion.
While some might advocate for "if you ain't got nothing nice to say, say nothing at all", I rather believe in an informed consumer.