Height of Wave/Capsize question
- Thread starter Razorfish
- Start date
snowleopard
Active member
that link is popping up everywhere! the 'rule' postulated in Adlard Coles' Heavy Weather Sailing is that a breaking wave whose height is greater than the yacht's beam will cause a capsize.
mine's 23 ft, what's yours? /forums/images/graemlins/wink.gif
mine's 23 ft, what's yours? /forums/images/graemlins/wink.gif
Spyro
Well-known member
Don't think its the wave height that matters, the problem here is these waves were coming into shallow water and becoming very steep and breaking. In the southern ocean yachts are regularly surfing on 30ft waves and not capsizing
Razorfish
Member
whoops, so it is and was posted here earlier this week I have just noticed. Sorry.
Peppermint
New member
Re: Not height. Profile
Steep to and breaking waves are the dangerous ones. A breaking wave is not only a dynamic problem. As it curls over and slams down on you it will be damaging but it has another trick too. Breaking waves foam. This foam is less dense than the water around it. It's less bouyant and gives less grip to control surfaces.
Another componant in heavy weather capsize is the Human element. Heavy weather is exhausting and quite scary. My preference for getting through it is active rather than passive. Mainly as a result of boat type. So accurate helming is important. Inaccurate helming can lead to some spectacular wipe outs.
Steep to and breaking waves are the dangerous ones. A breaking wave is not only a dynamic problem. As it curls over and slams down on you it will be damaging but it has another trick too. Breaking waves foam. This foam is less dense than the water around it. It's less bouyant and gives less grip to control surfaces.
Another componant in heavy weather capsize is the Human element. Heavy weather is exhausting and quite scary. My preference for getting through it is active rather than passive. Mainly as a result of boat type. So accurate helming is important. Inaccurate helming can lead to some spectacular wipe outs.
snowleopard
Active member
The capsize only happens if the wave is (a) breaking and (b) hits you on the beam. When that happens, boats do capsize in the southern ocean. Spirit of Birmingham was rolled several times under these circumstances. Tzu Hang capsized over the bow in extreme seas.
Spyro
Well-known member
[ QUOTE ]
The capsize only happens if the wave is (a) breaking and (b) hits you on the beam. When that happens, boats do capsize in the southern ocean. Spirit of Birmingham was rolled several times under these circumstances. Tzu Hang capsized over the bow in extreme seas.
[/ QUOTE ]
I do know that boats do and have capsized in the southern ocean I was referring to the original post which asked how big a wave has to be to capsize a boat. I was giving an example that you can sail in huge waves and not capsize.
I presume if Tzu Hang capsized over the bow then she was not hit on the beam?
The capsize only happens if the wave is (a) breaking and (b) hits you on the beam. When that happens, boats do capsize in the southern ocean. Spirit of Birmingham was rolled several times under these circumstances. Tzu Hang capsized over the bow in extreme seas.
[/ QUOTE ]
I do know that boats do and have capsized in the southern ocean I was referring to the original post which asked how big a wave has to be to capsize a boat. I was giving an example that you can sail in huge waves and not capsize.
I presume if Tzu Hang capsized over the bow then she was not hit on the beam?
Its_Only_Money
New member
"Capsize over the bow"
Is that the same as a pitch-pole???
Is that the same as a pitch-pole???
kandoma
New member
I would call the "wave" under the Golden Bridge not a wave but ground swell and has nothing to do what you encouter in the open sea. Even freighters break up in such a groundswell.
The following is only valid when running:
Big waves do not consist of solid water in the upper part of the wave but are intermingled with a lot of air bubbles. The rudder starts to suck in air and looses more and more steering power. Running under autopilot, you will notice bigger and bigger moves of the rudder up to the point, where the boat does not manage to get back on course on time for the next big wave coming in and the boat may capsize. You do not have to go to the southern ocean to encounter such conditions. The carribean sea at the height of the trade wind season has such waves. The reason is not bad weather, but low airpressure over the landmass of South America and high pressure over the carribean sea. The isobares get compressed and the corresponding wind in the 40+ knot range blowing for several weeks create some nice, bubbly waves.
Ahh, by the way, ticking over the engine (1200 rpms) in such a situation slows down the boat and the rudder bites much better, because there is some activ waterflow around the rudder generated by the propeller. It really slows down the boat.
(This method is copyright protected by Jonathan Seagull...)
Read "Seaworthiness, the forgotten factor" Its all in there.
Peter
The following is only valid when running:
Big waves do not consist of solid water in the upper part of the wave but are intermingled with a lot of air bubbles. The rudder starts to suck in air and looses more and more steering power. Running under autopilot, you will notice bigger and bigger moves of the rudder up to the point, where the boat does not manage to get back on course on time for the next big wave coming in and the boat may capsize. You do not have to go to the southern ocean to encounter such conditions. The carribean sea at the height of the trade wind season has such waves. The reason is not bad weather, but low airpressure over the landmass of South America and high pressure over the carribean sea. The isobares get compressed and the corresponding wind in the 40+ knot range blowing for several weeks create some nice, bubbly waves.
Ahh, by the way, ticking over the engine (1200 rpms) in such a situation slows down the boat and the rudder bites much better, because there is some activ waterflow around the rudder generated by the propeller. It really slows down the boat.
(This method is copyright protected by Jonathan Seagull...)
Read "Seaworthiness, the forgotten factor" Its all in there.
Peter
snowleopard
Active member
yes, just so.
in a planing boat it can happen by overtaking the wave in front and tripping over the bow. a heavier boat can be pitchpoled by a very large breaking wave from behind. accounts speak of a sound 'like an express train' coming up from behind.
in a planing boat it can happen by overtaking the wave in front and tripping over the bow. a heavier boat can be pitchpoled by a very large breaking wave from behind. accounts speak of a sound 'like an express train' coming up from behind.
Pierrot
N/A
[ QUOTE ]
I do know that boats do and have capsized in the southern ocean I was referring to the original post which asked how big a wave has to be to capsize a boat. I was giving an example that you can sail in huge waves and not capsize.
[/ QUOTE ]
It is breaking waves that capsize boats (as in the above sequence).
The Wolfram institute did a lot of research into this in the wake of the 79 Fastnet tragedy. Their findings is that most monohulls can be capsized by a breaking wave equal to the beam.
I do know that boats do and have capsized in the southern ocean I was referring to the original post which asked how big a wave has to be to capsize a boat. I was giving an example that you can sail in huge waves and not capsize.
[/ QUOTE ]
It is breaking waves that capsize boats (as in the above sequence).
The Wolfram institute did a lot of research into this in the wake of the 79 Fastnet tragedy. Their findings is that most monohulls can be capsized by a breaking wave equal to the beam.
ongolo
New member
Bit more than half what you got
ongolo
ongolo
graham
Well-known member
Re: No simple formula
I dont believe its as simple as wave height/beam.The steepness of the wave and speed the boat is doing must be factors.
A boat surfing at great speed then broaching must be more at risk due to inertia than one towing a drogue or whatever other means of slowing the boat down and preventing a beam on situation.
I dont believe its as simple as wave height/beam.The steepness of the wave and speed the boat is doing must be factors.
A boat surfing at great speed then broaching must be more at risk due to inertia than one towing a drogue or whatever other means of slowing the boat down and preventing a beam on situation.
ashanta
New member
That doesn't make sense at all! Many of us have sailed in sea conditions with waves higher than the length of our beam (Mine is only 9.5') The conditions in the pictures that have been published all over the place on this yacht in SF is being caused by shaoling waters and the boat is floundering due to the breaking waters. The yachtsman should not have been there. The wind was behind the vessel and he had full main driving it and I assume the tide was ebbing and if anyone has left Salcome on the ebb with a strong s to se wind would appreciate. I think I dropped 15 foot or more into a trough and i thought my keel would smash on the bar. Fortunately it didn't. Out at sea the waves behave differently and the deeper the water the more of a high swell occurs and only when the wind gets up really high does the wave tops breaks. 10 foot waves are only approx 3mtrs and if you look at the beuoforts scale you can see what I mean. I think this guy was a racer and caught out?
Regards.
peter.
Regards.
peter.
fireball
New member
It isn't just a simple matter of wave height or steepness - it also depends on length of vessel and how you helm through it - or try too ...
I have brought sailing dinghies through breakers with great success purely by surfing down the waves, a couple of pumps on the sails and comming down the wave front "surfer style" will get the boat up on the plane (if it isn't already) and you take off - into the trough and usually sit and wait for the wave to catch you up again!!
With a larger boat it is different as you generally can't get up on the plane (not so cats and tris!) quick enough and what tends to happen is that the nose digs in (where is your CofG when your heading down a wave?) and the wave tries to accelerate the boat - pushing the stern round - once your nearly beam on - over you go!
not something I intend to prove in my yacht ... quite happy to wipeout in the dinghy though! /forums/images/graemlins/smile.gif
I have brought sailing dinghies through breakers with great success purely by surfing down the waves, a couple of pumps on the sails and comming down the wave front "surfer style" will get the boat up on the plane (if it isn't already) and you take off - into the trough and usually sit and wait for the wave to catch you up again!!
With a larger boat it is different as you generally can't get up on the plane (not so cats and tris!) quick enough and what tends to happen is that the nose digs in (where is your CofG when your heading down a wave?) and the wave tries to accelerate the boat - pushing the stern round - once your nearly beam on - over you go!
not something I intend to prove in my yacht ... quite happy to wipeout in the dinghy though! /forums/images/graemlins/smile.gif
William_H
Well-known member
The Australian Surf Lifesavers with their open rowed surf boat make a habit and sport of bringing these boats through shallow breaking waves. Yes sure they do capsize but not if they can keep the stern to the waves. (which are certainly higher than the beam of the boat.) You must have seen pictures.
I was very impressed by the yacht in SF bay. I wonder if a drogue and perhaps with mainsail down he may have been able to keep the stern to the breaking wave and if then the main hatch was sealed and he could hang on in the cockpit the boat could have survived the wave. More comments please. olewill
I was very impressed by the yacht in SF bay. I wonder if a drogue and perhaps with mainsail down he may have been able to keep the stern to the breaking wave and if then the main hatch was sealed and he could hang on in the cockpit the boat could have survived the wave. More comments please. olewill
ChrisE
Active member
But if you flip, Chris, you'll stay flipped, whereas we'll bob up again, pump out the bilges and ten minutes later we'll be eating cucumber sandwiches on the foredeck!
fireball
New member
[ QUOTE ]
eating cucumber sandwiches on the foredeck!
[/ QUOTE ]
Cos that'll be the only bit of the boat out of the water!! /forums/images/graemlins/tongue.gif
eating cucumber sandwiches on the foredeck!
[/ QUOTE ]
Cos that'll be the only bit of the boat out of the water!! /forums/images/graemlins/tongue.gif
Pisces
New member
I would have thought that tripping over the keel would be part of the effect in breaking waves on shore. The bottom of the wave is moving more slowly than the top (else it wouldnt break!). So presumably the keel depth, shape and design would make a difference here -
The question is - Should I lift my keel in running down large swells?
The question is - Should I lift my keel in running down large swells?
coco
New member
To answer to the first poster, I have read somewhere that danger to be capsized starts when the breaking waves reach a height of half the length of the boat and capsize is almost certain at 2/3 of the length. I do not remember exactly, but I believe this was found through tests run at Southhampton University.