Kayak hull design

All other things being equal, what are the MOST and LEAST stable hull shapes? (What specific combination of chines, rocker, flare, etc.)

Things that are equal:

Novice paddler (so the kayak does the stability work)

Material (any)

Length 14’

Width 24"

Confused water with waves around 2’

Priority: Staying upright and (less important) generally on course

Not a priority: speed

I’m thinking completely round
…or egg-shaped. Ever try to balance on a floating log?

I’ve paddled deeper chine boats like the Silhouette, but once it settles off that bottom chine it stiffens up (a bit). I just had to pick which butt cheek to rest on.

Most stable for a " confused"
novice paddler:

About ten feet long, and five feet wide.

Just need a real long paddle

Jack L

wide and flat
A wide, flat bottom boat is most stable on flat water. The boat wants to stay flat against the surface of the water, so won’t want to tip over. The more you lean, sinking one side in to the water, the more that side gets submerged and its flotation tries to push it back up. Adding to this, the side you are not leaning on will start coming up out of the water, and gravity will interact with the weight of that side, trying to push it down.

But, problems occur when the water becomes not flat. Think of a boat wake coming through and hitting the kayak from the side. The boat will try to stay flat with the surface, but the surface is an angled wall. A steep enough wave and the kayak is over. In this case, a narrower and rounder bottom would be more stable, as you can let the wave roll under you without the hull having to conform with the surface.

For obvious reasons, kayak makers do
not design and offer boats which the average buyer will perceive as unstable.

On the other hand, because of what a kayak must do, makers will not offer boats for sale that are ridiculously stable, because their performance would be crappy.

It would help if you say more about what sort of kayaks you are looking at and what you plan to do with them. Whether “rec”, touring, sea, or whitewater, there are some models that are more stable and more reassuring. But don’t buy a river pig just to get stability, because you aren’t going to find many kayaks without stability.

Width and length are not in play
Assume a kayak 14’ x 24". See “Things that are equal.”

I’m interested in how you would combine ALL of the major design features of the hull, not just flat versus round bottom. There are many possible combinations of features, yielding different handling. A disadvantage of one feature can be offset by another feature that has some advantage.

Heh heh . . . perhaps not intentionally
but more than one kayak has been discontinued because the average buyer DID perceive it as unstable. And I’ve gotten rid of more than one kayak because it lacked stability.

I’m not looking for a kayak. I’m interested in the various ways of combining design features—the way they interact with each other, how one feature can overcome a disadvantage of another feature, the compromises that are made.

The 64K$ question

– Last Updated: Jun-05-14 1:15 AM EST –

You seem to be asking the 'everything' question - how does each aspect of a hull influence the final seaworthiness of the design. If we get a definitive answer, then we have the world's best naval architect on the forum.

Seriously, though, it's a great question with a million answers. You should consider reading "The Shape of the Canoe" by John Winters - it's a fantastic primer of the naval architecture principles that govern the behavior of canoe- and kayak-sized vessels, I learned a lot, highly recommended:

Fun question
Nice to see this kind of post! Higher Cp, full chine profile - meaning more square Vs round and carry this volume throughout the hull avoiding knife thin bow and stern. (Nothing good or fast about that). Yes race hulls are thin and more rounded but they are not knife edge thin in the bow relative to their overall shape.

Rocker the hull as well. The hull I describe will be stable for it’s with and playful. The best way to add a bit of potential speed is to keep the stem angle relatively steep as well as stern thus longer LWL.

At these numbers this wouldn’t be a fast kayak but would be efficient enough provided not too much weight.

Lots more to say but on iphone. Look at the sea play boats: Romany, Skerray, Chatham 16, Coaster, and many others in this category and you see common themes. I listed a few.

Questions seeking more conceptual understanding are nice.

stable - stay on course?
Flat bottom with a skeg or rudder. Seat that sits low.

Least stable a totally round bottom - high seat. Dhhhhhhh

If you’re actually shopping - Carolina 14 meets your specs close enough.

Most 14’ wide boats have enough rocker to turn easy enough and most have rudders some with skegs.

My old Phoenix “Seewun” was quite
elliptical in cross section, yet sat steady in neutral and firmed up quickly when leaned. Low rocker boat.

But I agree that if one wants to make an unsteady boat, a round cross section is the most direct way.

My '82 Noah Magma is quite flat bottomed for a boat of that vintage, and has prominent chines. It has very low initial stability. That didn’t bother Vladimir Vanha the designer, because his previous ww kayaks were round and had low initial stability. One reason the Magma does not firm up when tilted is that the sides above the chines show definite tumblehome. They slant inward.

In general, to understand initial and final stability, you have to look at what the sides of the boat are doing when the boat is tilted.

yes. good last sentence.

Name two.

easy answer
If you want a fast, stable, tracker of a boat, the answer is NC (Novice Composites). The same goes for the Eddyline Raven. There are others, but like the two mentioned, they are all over 14 feet long.

What is the hull shape of those two kayaks and how do the specific design features contribute to stability?

So far, you’ve managed to make this
a rather pointless discussion. I can’t sense that it has any reality for you.

What makes a good troll topic?