I just tried out my two kayaks in the pool…
One is 11’1 long and 28.5" wide.
The other is 12’10" long and 25" wide.
I find the shorter/wider boat way more stable than the longer/narrower boat, which, of course, makes sense. My thoughts, however, are that I want another of the shorter/wider boat instead of the other. Am I being silly? Will I get used to the 25" wide boat? I could tip it over pretty easily, but really had to work to get the other boat to flip. The boat will be primarily used for fishing (so, stability is important) and paddling around local lakes.
Yes, stability increases.
Start by reading up a little on hull design to learn the trade-offs for various hull configurations. Generally speaking, a longer narrower hull will by tippier but faster; a shorter and wider hull will offer stability but will be slower to push through the water. A long AND wide boat will have some characteristics of both.
Consider your expected needs, and buy accordingly. For example, if you intend to toss the boat in and paddle a mile or two, then spend the morning poking around the shore while fishing, you may very well determine that the vast majority of your time in the boat will require stability, and that speed may be low on your list of priorities.
If, on the other hand, you plan to paddle many miles to get to your fishing spots, you may be willing to sacrifice a bit of stability for better speed and tracking. This article should offer some other considerations unique to fishing:
http://www.paddling.net/guidelines/showArticle.html?147
To answer your original question, I can say that stability DOES tend to increase the longer you own a particular boat. That is, you’ll become accustomed to its stability characteristics and find it easier to keep in balance. At the same time, a boat that at first seems only marginally slow will come to seem VERY slow the longer and further you paddle it. Both phenomena suggest you lean a little bit toward the narrower/faster end of the spectrum.
Good luck!
My $.02
Stick with the 25" wide one. I have progressed from 28" wide to 21.5" wide, and the narrow one now seems as stable as the other. You just have to get used to it and find your balance with it. And even though you may be primarily fishing from it, when it comes to getting to and from your fishing spots, you will come to really appreciate the increased speed of the narrower boat.
Peggy
http://paddletales.blogspot.com
Easier and easier if you gently push
– Last Updated: Jul-01-05 7:28 PM EST –
It's like learning anything else. If you are playing on the edge of your comfort zone you keep learning. I used to capsize a whole lot and still capsize quite a bit.
Sit On Tops?
Were those Sit On Top Kayaks? Either sounds pretty wide for a sit inside.
Sit on Tops generally have a higher center of gravity, so they need to be wider.
Rec Sit insides are commonly 28"
or wider.
K-DAWG, YOUR “LONGER/NARROWER” BOAT
is -in the great kayaking scheme of things actually a fairly short, fairly wide one.
Our first one was a 12’ X 30" tandem sot. Stable as the Rock of Gibralter.
Followed by 14+’ X 26" SOTs. Still “like a rock”.
We now regulalry paddle 16-6 X 22-2/3 & 17-3X22-1/2 SINKs, respectively, and now find THEM easy -these are now quite stable.
And we -well, Sally, mostly L -even manages to -on relatively flat water -move a 17’ X 21" wide specialty SOT.
Your pool foray was a static test, as well. Just sitting still in a kayak can be a test of stability, whereas when you’re paddling, quite often a boat you may wiggle around in/on at rest becomes a much smoother and more confident ride at speed.
We’re no great atheletes, we don’t have real fancy or expensive equipment, and we’re not OC competitors. We just like to paddle. And we’re no gung-ho sping chickens, either -we’re in our mid-50s -well, for a little while, at least…
If that about describes you -actually, regardless of age -then I expect your progression to more or less mirror ours.
Hang in there, get out there (with PFD and appropriate clothing for the water -and a buddy, if you can) and
PADDLE ON!!
-Frank in Miami
stability
Stability is actually not a simple concept. Just sitting there in your kayak in a pool, it may seem fairly simple, but in a lake, river, or especially an ocean, it’s not so straightforward. Factors such as width and hull shape have already been covered well by others, but what I’d like to add is the concept of dynamic versus static stability. Static stability has to do with the boat (width, hull shape, etc), wheras dynamic stability has to do with skill: how loose and relaxed you are, bracing skills, rolling ability, etc. And dynamic stability comes more into play as conditions get more challenging. Surprisingly, a kayak that is rock solid in calm water is never the choice of an experienced kayaker, because the same quality that makes it stable in flat water (a wide, flat hull) makes it unsuitable for bumpy conditions. A high performance kayak in the hands of an experienced paddler can handle serious conditions (surf zones, river currents, etc). A beginner in the same kayak may capsize even on flat water. An analogy may help. Why don’t all bicyclists ride tricycles or quads? They are more stable, aren’t they? Well, yes and no. If you are just sitting there, or going in a straight line, yes, they are more stable. But what about a tight turn at high speed? Forget it, no comparison. The 2-wheeled bicycle is much more nimble doing this. The difference is performance, and the stability in such a turn is dynamic, depending not only on the construction of the bike, but the skill of the bicyclist. So the real question is, are you willing to put in some time to gain skills and stability? Like everything worthwhile, you must put in the time.
Yes, but…
if you just want to go out and have fun, use whatever is most comfortable for you right now. You have two kayaks, and there is no reason you cannot switch back and forth. You’ll become more comfortable on the water, regardless.
Don’t beat yourself up over this.
Right On! 
rent each…
can you rent each one for a different weekend? Paddling for a couple hours will give you a better feel for the boat.
Proper outfitting
to get a good fit in your boat has a lot to do with your ability to be comfortable in a narrow boat. As some say, “you wear a boat” That means the boat should fit you like a shoe. You should have contact between your boat and your feet, thighs, hips, butt, and back. Many forget the hip shims and that is a major mistake (IMHO). You can’t really control your boat (IMHO) if you are “sloshing around” in it. It’s like running in shoes that are two sizes too big.
Here is a pretty good site with info about outfitting your boat to fit:
http://www.seakayak.ws/kayak/kayak.nsf/NavigationList/NT0000545A
Good info here
Thanks so much for your thoughts. And, I do realize that compared to other kayaks, mine are both short and wide, but I was comparing them to each other. 
They are rec boats. One is a Dagger Catalyst 12.8, and the other is a Dagger Element 11.2.
I think I may still buy the other Element my “guy” has available. I can’t beat the price ($271 brand new), and I will feel far more stable through my learning curve. After I begin using the Catalyst, I’ll have a thrid boat for guests. 
Ahhh, justification. Gotta love it.
Stability?..
…I don’t know all that many stable kayakers, let alone stable boats.
I agree with PikeaBike
I’ve got a 23" beamed artic tern and a 28" beamed perception america. I’ve given several fishermen hour long fits of ammusement with my entry and exit practices in the tern…I remember my first trip with the america…I was frozen in one spot…terrified the boat would capsize if I moved an inch.A half hour into the paddle and I began to realize I wasn’t going to flip if I moved my arse…Now,I can’t exactly say the same for the tern :o)but I expect my summer of practice in the shallows (the rotator cuff injury isn’t going to allow long haul paddles)and getting to know the boat will pay off.
Patience and faith in yourself…The skills will come and once they do the fear will take a back seat to enjoyment of one of the purest forms of enjoyment I’ve ever known.
Excellent analogy
I have been trying and trying to think of some analogy to explain why experienced kayakers (or anybody) would prefer a kayak that felt “tippier”. I has been difficult to think of an analogy, but I like yours about a tricycle vs. a bicycle.
If anyone else has any other analogies, I would love to hear them as well. It is difficult to explain to others why anyone would choose and prefer less static stability. BTW, I really liked your explanation of static vs. dynamic stability. That will help in describing things to others.
Lou