Does having your skeg down make you more/less vulnerable to capsizing in waves?

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Does having your skeg down make you more/less vulnerable to capsizing in waves?

Post by leighv »

Here's something I have been wondering about lately and can't find an answer - I don't use my skeg much, but when the wind is really blowing strong I'll sometimes deploy it. Bearing in mind that strong wind often means strong waves too, I was wondering whether having the skeg down can make you more vulnerable to being tipped by a wave, because it's an additional surface that could take a hit, especially from a wave approaching from the side? Or would it not affect vulnerability at all? Is it too small a surface to make a difference?

Curious to hear your thoughts.
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Re: Does having your skeg down make you more/less vulnerable to capsizing in waves?

Post by Owen »

Doesn't make any difference, where your weight is and which way you brace is what matters.
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Re: Does having your skeg down make you more/less vulnerable to capsizing in waves?

Post by seawolf856 »

I don't have a degree in hydrodynamics but although the skeg will definitely prevent a kayak from weather cocking (turning into the wind) - proving that hydrodynamic forces are at play with the skeg down, I have enough real life experience to comment that if the waves are big enough to capsize you if hit from the side, the skeg being up or down will make little or no difference. Hours of capsize and rolling practice have also shown that there is little or no difference rolling up with the skeg down so again I would say that the drag created by the skeg being down when you take a big sideways hit will not be enough in itself to cause a capsize, or indeed prevent one.
There are always alternative answers and opinions when you ask a question about sea kayaking and there is NEVER one right or wrong answer, that's why this forum is so entertaining and educational, so before changing the way you use your skeg, lets see what others have to say.
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Re: Does having your skeg down make you more/less vulnerable to capsizing in waves?

Post by MikeB »

Look at it from a different perspective. If having the skeg down prevents the boat being weathercocked when you want to be either crosswind, or downwind, then the chance of retaining control is probably higher.

But the surface area involved is so small that it wouldn't contribute to instability. Or indeed lack of stability in the context you outline. Good question though!
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Re: Does having your skeg down make you more/less vulnerable to capsizing in waves?

Post by Chris Bolton »

My initial thought was that if you're knocked sideways it might act to trip the boat up, but not much - on reflection, it's the movement of the wave that pushes you sideways, and so the water the skeg is in will be going sideways as well, possibly faster than you. I don't remember ever having noticed an effect either.
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Re: Does having your skeg down make you more/less vulnerable to capsizing in waves?

Post by nickcrowhurst »

This is an important issue for vessels with much larger underwater appendages in proportion to their underwater profile. For example, in our National 12 foot racing sailing dinghy, the centreboard is huge in comparison to the area of the immersed hull, and it's the lowered centreboard that is the culprit in many capsizes, as it stops the sideways slipping of the hull (leeway) when the wind and waves are from the beam. The dinghy simply trips over its centreboard. In ocean-going sailing yachts, a deep, narrow and heavy keel has the same effect in survival conditions. In competitive races, that's a risk one takes for the sake of speed around the course.
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Re: Does having your skeg down make you more/less vulnerable to capsizing in waves?

Post by mrcharly »

Don't have experience of a skeg, but I do paddle boats with rudders.

They can contribute to the risk of a broach, if a following wave sweeps under you. Catches on the rudder and pushes stern around.

If I were paddling a boat with a skeg, I'd raise it when going downwind.
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Re: Does having your skeg down make you more/less vulnerable to capsizing in waves?

Post by Chris Bolton »

If I were paddling a boat with a skeg, I'd raise it when going downwind.
I understand why you say that, but it would defeat the purpose of a skeg which is to balance the boat going downwind. I usually put the skeg down going downwind, unless the waves are big enough to surf (deliberately or otherwise) when I might raise it. At that point I may be using stern rudders and steering by pushing the stern sideways, which the skeg would hinder.
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Re: Does having your skeg down make you more/less vulnerable to capsizing in waves?

Post by rockhopper »

Would having the skeg down sideways in a wave not actually help the boat to rotate around the skeg and therefore turn it to face the direction the waves are going...I am sure sometimes when messing around in waves this is exactly what has happened. I imagine that with such a relatively small area the skeg presents it would act more as a pivot on the length of the boat rather than a pivot on the circumference/rotation of the boat (does that make sense ??).

Rog.
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Re: Does having your skeg down make you more/less vulnerable to capsizing in waves?

Post by Chris Bolton »

Would having the skeg down sideways in a wave not actually help the boat to rotate around the skeg and therefore turn it to face the direction the waves are going
It might, but as I posted above, I think the wave at skeg depth is moving the same as at the surface, so the skeg isn't being held when the boat moves sideways when push by a wave, only in wind. However, whether it does or not, if I wanted to be pointing downwave, I'd point the boat that way myself. If I'm side on to a wave, it's because that's the direction I want to go in - perhaps because I'm paddling parallel to the shore and the waves are breaking further in, or that I'm making a crossing.
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Re: Does having your skeg down make you more/less vulnerable to capsizing in waves?

Post by Ceegee »

A lot of comments about broaching, weathercocking etc are missing the point that a skeg is ADJUSTABLE.
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Re: Does having your skeg down make you more/less vulnerable to capsizing in waves?

Post by MikeB »

Ceegee wrote:
Sun Nov 27, 2022 9:48 am
A lot of comments about broaching, weathercocking etc are missing the point that a skeg is ADJUSTABLE.
Aye - but I think the OP is wondering whether the skeg blade acts as a lever, a lever that will tip the boat. I may be wrong, but that's my interpretation.
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Re: Does having your skeg down make you more/less vulnerable to capsizing in waves?

Post by Franky »

Imagine if a skeg were the size, relative to the boat, of a keel on a ship - basically it would then *be* a keel. So shouldn't it stablise the boat? Or would its position at the stern complicate things?

If the underwater current is more or less uniform, a skeg/keel won't act as a lever - it will be more like a sail, causing the boat to move sideways (or rotate horizontally in the case of the skeg, since it's at the back of the boat). Only if there is a powerful opposing force above the centre of gravity, such as a strong wind, will pressure on the skeg cause the boat to overturn.

I suppose another situation in which a kayak with an (improbably large) skeg might overturn is if there is an underwater current a lot stronger than the surface current. But the skeg would have to be several inches high!
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Re: Does having your skeg down make you more/less vulnerable to capsizing in waves?

Post by pathbrae »

Imagine if a skeg were the size, relative to the boat, of a keel on a ship - basically it would then *be* a keel. So shouldn't it stablise the boat? Or would its position at the stern complicate things?
A yacht keel works by having enough mass to balance the weight of the boat and it's mast and sails and the force of the wind against it. The shape of the keel and the hull both resist (but never completely remove) being blown sideways. As a yacht heels further over on the wind the counterbalance effect of the keel becomes greater until a state of equlibrium is found.
Yachts don't capsise on the wind alone (but can be blown flat and recover) A capsize is almost always due to wave action, either on its own or combined with wind gusts.
Dingy centre boards, on the other hand, have very little mass so don't act to right the boat, which can be capsised by a wind gust or wave action or both.

A skeg on a kayak is a fraction the size or weight of either of these devices.
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Re: Does having your skeg down make you more/less vulnerable to capsizing in waves?

Post by Franky »

pathbrae wrote:
Tue Nov 29, 2022 6:28 pm
A skeg on a kayak is a fraction the size or weight of either of these devices.
I know. I was just wondering if, given its similarity in shape, its effect would be to stablise the boat in a similar way, even if by a barely consequential amount.
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Re: Does having your skeg down make you more/less vulnerable to capsizing in waves?

Post by pathbrae »

Franky wrote:
Tue Nov 29, 2022 10:56 pm
pathbrae wrote:
Tue Nov 29, 2022 6:28 pm
A skeg on a kayak is a fraction the size or weight of either of these devices.
I know. I was just wondering if, given its similarity in shape, its effect would be to stablise the boat in a similar way, even if by a barely consequential amount.
I doubt if it would have any noticable effect. (which doesn't mean it wouldn't be measurable)
Something the size of a dingy centreboard would have some effect - but being so near the stern I'm not sure what that would be.
Hanging a bucket of concrete from the mid-point of the hull would replicate a keel though.
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Re: Does having your skeg down make you more/less vulnerable to capsizing in waves?

Post by Chris Bolton »

The keel on a yacht has two functions; stabilise it by providing mass well below the C of G, and reduce sideways movement due to wind pressure on the sails. On a dinghy, the centreboard does just the latter. A dinghy has mass high up, in the mast and rigging, goes faster than a kayak, turns more sharply and the centreboard has much more area than the skeg; if you turn a dinghy sharply, it can trip over the centreboard. To transfer that to a kayak, which doesn't have high up mass, if you were surfing fast down a wave in a kayak, and you turned sharply but forgot to edge into the wave, the skeg might catch a tiny bit, but if you didn't edge into the wave you're probably going to capsize anyway.
A lot of comments about broaching, weathercocking etc are missing the point that a skeg is ADJUSTABLE
The OP asked about the consequences of having the skeg down, so what happens if it's up or partly up is a different question.
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Re: Does having your skeg down make you more/less vulnerable to capsizing in waves?

Post by Jim »

A very complex subject, which we are not likely to gain a full understanding of...

Unless it is breaking, the water in a wave mostly moves up and down, not side to side. So it won't push on the skeg in any way that affects stability.

A side wind occurring at the same time will try to tip you over a skeg (or rudder), but I can't say I've ever felt it as a noticeable problem, even without a skeg a strong side wind will try and push you over.

Wave rolling is due to ending up sideway of a wave slope, so you tend to tip downhill.

One way we damp rolling on ships is to use bilge/bar keels that run 50-75% the length of the ship and stick out from the bilge radius, but usually no further than a square corner would. Wind action or a wave profile can still roll the ship, but first it has to push the water over the bar keel, which takes time, thus slowing the roll so the ship rolls less before the tipping force is removed, or reverses or whatever - under a steady force it would eventually reach the same list, but it is surprisingly effective against transient/dynamic forces like wind and waves, and very much cheaper than active roll stabilisation (like the sensor controlled fins you will find on many modern passenger ships).
A kayak skeg is not big enough to contribute significant roll damping, but it probably does a tiny little bit.

Sailing vessels have huge overturning moments from the propulsion, and these are largely controlled by ballast rather than hydrodynamics* - in a dinghy the crew move their CG further outboard as the boat heels, on a racing yacht crew members not actively doing anything else sit along the windward side to contribute whatever anti-heeling moment they can, but usually most of the ballast is in the keel because it helps to get it low. Some yachts use pumped water ballast to avoid too much weight in the keel. The keel itself is to resist leeway (sliding sideways through the water) and because its centre of effort is below the roll centroid it does actually add to the overturning moment, but only because of the wind, not due to waves.
* sailing hydrofoils are another matter, the V configuration of the foils means they can provide righting moments, and will be self stabilising at foiling speed. As the V tilts over, the downhill side generates more lift and the uphill side less lift, so they tend to restore themselves - I have no idea exactly how much a sailing hydrofoil manages that, but certainly motor hydrofoils can be a very steady ride.

But the short answer to the original question, is neither.
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Re: Does having your skeg down make you more/less vulnerable to capsizing in waves?

Post by john.ruston »

pathbrae wrote:
Wed Nov 30, 2022 5:45 pm
Franky wrote:
Tue Nov 29, 2022 10:56 pm
pathbrae wrote:
Tue Nov 29, 2022 6:28 pm
A skeg on a kayak is a fraction the size or weight of either of these devices.
I know. I was just wondering if, given its similarity in shape, its effect would be to stablise the boat in a similar way, even if by a barely consequential amount.
I doubt if it would have any noticable effect. (which doesn't mean it wouldn't be measurable)

Hanging a bucket of concrete from the mid-point of the hull would replicate a keel though.

Providing the 'suspension' was rigid (?)
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