Newbie question re broaching/knockdowns

[georgeo]

whilst we are on the subject, could somebody explain exactly what a 'Chinese' gybe is. Am I correct in thinking it is the situation where after an inadvertent gybe and broach, the boat is pinned down by the wind filling main/spinnaker etc?

 

[fergie_mac66]

i have always though of a broach as being when the stern of the boat goes uncontrollably faster than the bow ..perhaps down a big wave

 

[KellysEye]

>i have always though of a broach as being when the stern of the boat goes uncontrollably faster than the bow ..perhaps down a big wave

Yes, if the boat starts to surf the rudder is moving at the same speed as the wave thus it it has no control and a broach can happen. If you study waves none are exactly the same, it just needs one wave to come in at the wrong angle. The problem is exacerbated if there is an angled swell running.

On the subject of Chinese gybes there a fantastic piece of film here: http://www.youtube.com/watch?v=d89-0-lp7yI

 

[alant]

i have always though of a broach as being when the stern of the boat goes uncontrollably faster than the bow ..perhaps down a big wave

Like wot i said "Broach is a bit like the boat doing a forward roll."

 

[GruffT]

whilst we are on the subject, could somebody explain exactly what a 'Chinese' gybe is.

Right - i'll try and get this right but I'm sure I'll be corrected if i'm wrong...

Chinese gybe - aka round down :
1) the bow tries to push down (due to wave motion / too much headsail, rolling action & hull form etc) and wins the battle vs the rudder.
2) Boat slews down wind (hence round down rather than up), pushes through the gybe and the boat goes sideways and flatter than you might like. Not much to be done at this stage.
3) At this point the main is now pointing at the sky, gravity & breeze decide to take over so it crash gybes over, leaving you with both main and foresail in the water (which was previously the windward side).
4) Cunningly you sit there until you depower / drop the foresail and do likewise for the main. At this point you hope your companionway is high enough or you've the washboards in. You also notice that if you've got a kite up, the pole is underwater and doing a damn good job at trying to push it's way through the shrouds.
5) Best get that kite down quick.

Round up is much less interesting. Main wins the battle with the rudder, boat luffs up dramatically. Depower and off you go again. Yeee haaaa.

Great example in post 10. Top one is round up, bottom one is round down.

Ironically, the boat seems to lean the wrong way going into a round down as often it's rolling and the consequential impact of the hull form that does for you. The rolling setup by having the leeches too open on the headsail while running deep. Can happen under kite or white sails.

 

[scottie]

Chinese gybe is when you end up with the gaff and boom both vertical but on either side of the mast and as such can only happen when gaff rigged.

 

[georgeo]

Right - i'll try and get this right but I'm sure I'll be corrected if i'm wrong...

Thankyou for that very clear explanation.........I have not heard the term 'round down' before but it is very apt!

 

[agurney]

Hmm. My understanding is that it could happen on a bermudan rig if there wasn't a kicker/vang. The boom could raise up during the gybe with unfortunate consequences when gravity regained control. Looks like I'm in the minority though.

 

[fergie_mac66]

Chinese gybe is when you end up with the gaff and boom both vertical but on either side of the mast and as such can only happen when gaff rigged.

+1 not nes' to be fully vertical depends on sail and reefs in sail very disconcerting to say the least !when you find gaff and boom on different side of mast . I had one in light winds(fortunately) on my gunter westerly when the peak halyard slipped out of a clutch

 

[fergie_mac66]

Hmm. My understanding is that it could happen on a bermudan rig if there wasn't a kicker/vang. The boom could raise up during the gybe with unfortunate consequences when gravity regained control. Looks like I'm in the minority though.

guess it could specially on a fully battened main with a lot of roach

 

[snowleopard]

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

That is a fair illustration of the difference between a broach and a knockdown - mulltis generally don't broach but a knockdown is pretty scary.

 

[sighmoon]

Yes, if the boat starts to surf the rudder is moving at the same speed as the wave thus it it has no control and a broach can happen.

I can only imagine that happening in a monster breaking wave (the like of which I hope I never meet), otherwise surfing gives the boat more speed through the water, and so the rudder has more control.

Hmm. My understanding is that it could happen on a bermudan rig if there wasn't a kicker/vang. The boom could raise up during the gybe with unfortunate consequences when gravity regained control. Looks like I'm in the minority though.

I used to let the kicker off a lot downwind in the last boat (current boat has a strut, so I can't), under the assumption that it would lesson the odds of an acidental gybe, and take some of the sting out of it when it did, as the bottom the sail gybes before the top.

 

[grumpy_o_g]

Hmm. My understanding is that it could happen on a bermudan rig if there wasn't a kicker/vang. The boom could raise up during the gybe with unfortunate consequences when gravity regained control. Looks like I'm in the minority though.

I have err.. let's just call it empirical evidence that would tend to confirm that.

 

[skyflyer]

great replies folks - thanks - I never imagined when posting the original question that there would be so many variations on a theme! Reminds me of the old saying,"ask six sailors for advice and you will get at least seven different answers"!

However I am now much better informed - thanks

 

[E39mad]

Both can be "brown trouser" moments esp with the spinaker up.

Have broached a few times but never Chinese gybed although seen a few including a spectacular Swan 51 "Pacer" in the RTIR many moons ago (IOR shaped hulls again)

With the kite up in a blow you have to keep control of the spinaker pole (ie the downhawl is on very hard once the pole is up to the correct height) - classic error in a blow is to bring the pole too far aft downwind and/or letting too much spinaker sheet out which causes the centre of effort to go to far over to windward and control can be lost very easily and can be the beginning of a Chinese gybe.

 

[KellysEye]

>Like wot i said "Broach is a bit like the boat doing a forward roll''

That's a pitchpole, sailing downwind in big seas and digging the bows in. Here is a famous picture: http://johnvigor.blogspot.com/2011/05/picture-perfect-pitchpole.html

 

[mjcoon]

Yes, if the boat starts to surf the rudder is moving at the same speed as the wave thus it it has no control and a broach can happen. If you study waves none are exactly the same, it just needs one wave to come in at the wrong angle.

If you study waves you know that the water moves in a circular motion; the water does not travel at the speed of the wave.

Thus the boat and rudder are still moving through the water even if surfing, and the rudder could be fully functional. However there may be all sorts of other effects caused by a breaking wave, hull shape, angle of heel and so forth, which result in loss of control. But not lack of speed through the water...

Mike.

 

[KellysEye]

>If you study waves you know that the water moves in a circular motion; the water does not travel at the speed of the wave. Thus the boat and rudder are still moving through the water even if surfing, and the rudder could be fully functional.

Yes that true. However when I've surfed in AWB's I've stayed on top of the wave not gone down the front, thus the boat speed is the same as the wave and, as I said, the rudder doesn't work. I proved that by turning the wheel with no effect.

 

[30boat]

If you study waves you know that the water moves in a circular motion; the water does not travel at the speed of the wave.

Thus the boat and rudder are still moving through the water even if surfing, and the rudder could be fully functional. However there may be all sorts of other effects caused by a breaking wave, hull shape, angle of heel and so forth, which result in loss of control. But not lack of speed through the water...

Mike.

When the wave overtakes the boat there is no steerage for a while.

 

[mjcoon]

When the wave overtakes the boat there is no steerage for a while.

Ah, well, that is the down-side (or up-hill side!) of surfing. There may not be enough drive to counteract gravity on the wave slope, or to keep up with the waves. But it still isn't anything to do directly with the speed of the wave.

Mike.