Primary stability considerations in kayaks

messabout,

yes, that is true. The problem is that as you add more length, the water line does change, so the righting moment curve may also change since what the water "sees" changes as you add length with the same displacement and same hull shape. It most likely will increase, but it is possible it could also become more tender depending on rocker and hull shape at the new water line.

If you had the water line the same, and increase length (which means increased displacement), the stablity will increase with most normal hull shapes.

 

Sorry --you got me there.

 

Sorry I miss typed, not water line length, but water level on the side of the hull. IOW, keel same depth in water. Being longer it would mean it would displace more.

 

Hippo:

Oh dear - the guys did get excited didn’t they? You’re always gonna get into theory in the forum but the following is from experience - photography as well as paddling. Hopefully I’m not too late . . .

Stability in a small boat is all about feel: I doubt you want to calculate hydrostatics for a boat when you can just try one out. Besides, most commercially available kayaks, canoes, kits and designs have been analyzed to death in some magazine and manufacturers' data is generally available - search the web. But don’t buy a boat you haven’t tried: a dealer located on the waterside will happily let you try out boats - that’s why he pays the extra bucks for the location. Try out the motions you will need when photographing especially over your shoulder and off to the side.

For photography you need equipment storage, lots of primary stability and agility. Most typical kayakers want speed, secondary stability and low resistance. You will likely sit fairly high and turn often and on occasion move quickly to capture a rare target. Weight may be a factor too - how far will you have to carry it?

Alan’s advice was spot on but I suggest even shorter maybe 12' - or even shorter if you are gunk-holing in narrow streams. Great speed is counter-productive for photography, stopping and spinning a skinny boat can be noisy and time-consuming, the last thing you want when you spot something rare.

You don’t want either a flat bottom with really hard chines or a rounded bottom; flat bottoms often have a sudden transition from rock solid to whoops ‘n wet and round bottoms are tippy. An almost flat bottom with rounded bilges is the ticket. It just happens than all the beginners kayaks meet your all requirements except one, the storage, and are cheaper than building. Look for short, beamy, round bilges, almost flat bottom, and cheap! Pick one with a large cockpit and bungy cords on the decks, not hatches which are virtually inaccessible on the water. It would be nice if it had enough space under the foredeck (assuming a kayak) so you can slide down low and drift with the wind like a log - some waterfowl are very shy - but check the seat doesn't crucify you!

One or two grooves down the bottom is a good idea: it’s for stiffness but they work like chines dampening out rolling motion faster than a smooth bottom. You won’t notice the additional drag unless you are really working hard which will scare off your subjects . . .

I recommend a rudder - I don’t usually say that but the ability to coast in a curve while you grab the camera to capture something you just passed is priceless. Make sure you can adjust the pedals easily!

If you’re building, a canoe is the best bet - easier to build, lighter and more storage. Commercial ones are mostly too long and tippy and designed for a single paddle - a double paddle provides far more agility especially if you have half your liquid assets tied up in the camera on your lap.

Some folk will suggest a sit-on-top canoe and they are usually super-stable, but the short ones waste a lot of paddling energy and there is nothing to stop your equipment going overboard.

I use 3 boats mostly, a 9-1/2' x 30" kayak (A), a 13' x 24" kayak (B) and a homemade 11-1/2' canoe - all use double paddles. Kayak A is rock solid and is used when I really don’t want to get wet, when the water is near freezing for example. Kayak B is supposed to be a racing design and is fast but takes too much effort, at moderate speed the canoe is quicker and easier and it gets the most use, I can toss spare clothing, water bottles, safety equipment, cameras, but no beer - too visible! The nice thing about kayak A is I can toss it into my minivan which saves time.

Since you’ll probably end up with a kayak, fit a paddle clip so you will have two hands free for the camera. Oh yes, the paddle: shorter than usual for you, a long one is more likely to bang on the boat while your storing it, and may frighten off the subject. A short single-blade paddle may be useful for creeping up on a subject using the slow but silent Indian stroke: I can vouch that it works and the rudder will be useful here. Tie it on with a cord so you can just let it float along behind while you grab the camera.

Good Luck!

 

I may not be good for much, but I can usually be counted on to stir up trouble

@AK, I'm defiantly building, mostly because I enjoy building boats.

Much of the rest of your advice is the same as I give people, especially about never buying a boat you haven't paddled, but in this case it doesn't apply too well. Some of the problem has been solved just by spending time in the Raptor and getting used to how she moves. I took her out in the surf at Neah Bay a couple of weeks ago and dumped her a couple of times and she handles better than I thought. I'm also compromising by using a waterproof point and shoot camera for some of my shots since I only have to take one hand off the paddle.

My next project is going to be a 9 foot x 25" 'yak for my more normally sized friends, most of whom have little or nor paddling experience. Worklog coming soon (I hope).

 

You guys still around?

Believe it or not, I'm still trying to nail down an answer to this question and as I was googling this thread popped up in the results.