Newbie question re broaching/knockdowns

[skyflyer]

basically what is the difference? As I understand it the boat ends up on its beam ends either way? Is it a question of degree or am I missing something very basic that I should know?

Thanks in anticpation

 

[grumpy_o_g]

Neither has a formal definition but a broach is basically a loss of control due to the rudder being over-powered or ineffective for some reason. A knock-down is simply a boat being knocked down so that the sails are flat on the water. The knock-down can be due to a sudden extreme gust or a freak wave or a combination of both.

The broach is usually due to a ruddy great spinnaker driving the bows under and lifting the rudder out of the water or something similar and is normally on a broad reach. Some boats round up when heeled well over as the wide beam means the rudder gets lifted out of the water but this isn't really a full-on broach.

 

[penfold]

I think the mechanics of a broach are more like a heading gust(or just a really big gust) puts pressure on the main to the extent that the rudder stalls(as the weatherhelm/loading rises) and loses authority, then the boat will simply round up and heel over while doing so like a fat labrador after a tummytickle. This is exacerbated if the boat is rolling as at the extremes of the roll the rudder loses effect and is easier to stall. The bow burying itself points to either an unmanageably large gust, a confused and very big sea running or poor weight distrubution(unoccupied crew not being moved as far aft as possible). You don't have to be flying a spinnaker to broach, in fact it's probably easier to provoke one if you aren't. You also don't have to be going downwind; if the main trimmer and/or helm is asleep, some boats will happily broach while beating.

I would consider knock-down as a more generic term covering being hit by a massive gust; the point of sail being not relevant. I've experienced being knocked down on a Sonata while beating; an instantaneous 90 degree header resulting in an involuntary tack and the folk on the windward rail getting a bath in Lake Windermere!

 

[Deleted member 36384]

Here is an article on broaching from Wikipedia: -

http://en.wikipedia.org/wiki/Broach_(sailing)

Its good enough to think of broaching as downwind sailing event and a knockdown as an upwind sailing event.

When broaching the risk of a gybe when broad reaching or running is high, although uncontrolled luffing up is most likely.

When knocked down the yacht may luff up but that is not necessarily a guaranteed response, she may just loose a lot of her forward velocity and be pinned right over on her ear with water threatening to breach the cockpit coaming.

 

[flaming]

Broaching is the helm's fault. Sometimes with an assist from the trimmers.

A knockdown is Mother Nature's fault. Usually involving big breaking waves.

 

[jakeroyd]

The other posters are quire right but as a newbie you will want to avoid going out in conditions where either could happen.
I have never been knocked down but have suffered a couple of near complete broaches in my many years of sailing.
However I only sail in good conditions.
Of couse you can never say never but I think if you pick your conditions then as your experience grows you will know learn not to worry unduly about these two issues.

 

[Lakesailor]

The good news is the boat will sit up again.

 

[FullCircle]

Broaching is the helm's fault. Sometimes with an assist from the trimmers.

A knockdown is Mother Nature's fault. Usually involving big breaking waves.

Nonsense. The helm is ALWAYS right. Its the trimmers, and possibly the boat designer too, in the case of 70s IOR boats.
The answer is to fit a water ski to the end of the pole and another to the end of the boom.

 

[alant]

basically what is the difference? As I understand it the boat ends up on its beam ends either way? Is it a question of degree or am I missing something very basic that I should know?

Thanks in anticpation

Broach is a bit like the boat doing a forward roll.

 

[Lakesailor]

Not entirely relevant, but watch the last boat after the dismasting

Aand this boat seems to be stuck in it's broach. Funny that, you'd imagine the sails would depower when almost horizontal.

​

 

[flaming]

Nonsense. The helm is ALWAYS right. Its the trimmers, and possibly the boat designer too,

I'm allowed to blame the helm, cos that's me!

 

[snowleopard]

A knockdown can be caused in several ways - flattened by a squall, rolled by a breaking wave or indeed a broach. The meaning is an event causing the mast to get close to or in the water.

A broach is a specific event where rudder control is lost and the boat rounds up sharply to windward, generally causing serious heeling. The easiest way to avoid a broach is to carry less canvas.

 

[30boat]

In a knockdown the mast is likely to touch the water while in a broach it usually stays clear.As said before a broach is usually induced by carrying too much sail and reducing the sail area is the most effective way of preventing it.A knockdown is normally caused by a wave of the right size or,as happened to me,by running into a ship.In my defense it was dark and they had no lights.

 

[skyflyer]

so far so good...

I think the definition of knockdown has been agreed but on that of broaching...

Even in realtively benign conditions I have experienced a following sea on a broad reach where the waves will pick the stern up and the boat will tend to slide down the wave rounding up into wind. I have learnt to anticipate that and nudge the helm to counteract the tendency just before it happens and thus steer a straight course.

Is it the case that a broach is the result of getting that wrong, ie poor helming or are posters saying that a broach occurs when the wind/sea over-canvassing etc is such that no helmsman could prevent it?

I know its semantics but I am aware that most yachts will round up into wind in a gust (hence weather helm etc) and am trying to get the distinction in my mind between that and a full-on broach!

 

[30boat]

I know its semantics but I am aware that most yachts will round up into wind in a gust (hence weather helm etc) and am trying to get the distinction in my mind between that and a full-on broach!

Some boats will never do a full broach and some are only to eager.Traditionally shaped boats will only heel and accelerate while more modern designs will heel and as they do their broad after sections will lift the rudder enough out of the water to make it ineffective and then round up.
It's all to do with hull shape and rudder effectiveness.My Westerly Fulmar(which,just to confuse things, is not all that narrow in the stern) is very resistant to broaching while a friends Bavaria 30 would broach and tack at the slightest provocation.

 

[KellysEye]

>Broaching is the helm's fault. Sometimes with an assist from the trimmers.
A knockdown is Mother Nature's fault. Usually involving big breaking waves.

I'd add to that rudder too small. To me a knockdown is a breaking wave because the boat often does a 360 degree roll. Wind doesn't do that. To avoid it don't reach in breaking waves the height of your beam. I do mean breaking not cresting, there is a big and dangerous difference.

 

[GruffT]

Lakesailor, a most excellent example of a round up and a round down, 2 variations on the theme of the broach. I can testify that the latter is much more dramatic!

 

[snowleopard]

I know its semantics but I am aware that most yachts will round up into wind in a gust (hence weather helm etc) and am trying to get the distinction in my mind between that and a full-on broach!

Simply a question of degree. A broach may be a slight inconvenience or a major disaster.

'Most boats' don't necessarily round up in a gust. The tendency is much more pronounced in boats with a broad beam and a wide stern, in fact AWBs are far more prone to broach than narrower more traditional boats and of course multis rarely suffer.

 

[GruffT]

of course multis rarely suffer.

Dosn't a broach in a multi have a different name... ;-)

Broaching a multi reminds me of talking to a chap on a narrow ridge in the mountains of North Wales...

"How often do people fall off here?" I asked,

"Just the once" was his reply.

 

[doris]

I'm allowed to blame the helm, cos that's me!

Funny. I thought the foredeck bloke was blamed for eveything. Hardly ever his actual fault but blame carrying is part of his job function.