Anti Broaching Water Brake

Discussion in 'Hydrodynamics and Aerodynamics' started by DouglasEagleson, Nov 16, 2015.

  1. DouglasEagleson
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    DouglasEagleson Junior Member

    I have no experience with broaching except for the warning. It can make a nice medium weight sailboat plane down an inlet wave face. The boat path diverges left or right and it speeds the boat up and its bow impacts the wave ahead of the surf causing wave.

    The impact is real hard and throws every body into the water if they are on deck. If inside a true deadly impact in the cabin can occur.

    The boat ends up with a full mast parallel to the water surface and floods an open hatchway.

    So in my thinking broach control is more important than breaker control. A sailboat needs to be locked up so a small six foot high breaker is harmless. Just tie every body to the boom and let everybody surf through the breaker. Just stand-up and let the surf flow go up to your waist.

    So the trick is to literally drift thru the inlet breaker zone so no broach can occur.


    To mitigate is mandatory. Sailing downwind is ok until a certain wave face is encountered. A drogue out the rear is needed alot.

    Here is an idea. Put water brakes on the keel. Use them just like airbrakes on a glider. A button thne hydraulically open them.


    So the question is how to size the brakes. Does anybody have advice?

    Thanks Doug
     
  2. gonzo
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    gonzo Senior Member

    Broaching can happen in flat water. Some sails, like spinnakers, can increase the tendency to broach. Slowing down, by reducing sail is the proper way to control a boat. Also, attempting to enter an inlet with breakers is probably a bad idea, unless the boat can surf safely. What kind of glider has airbrakes?
     
  3. whitepointer23

    whitepointer23 Previous Member

    Most gliders use airbrakes and spoilers.
     
  4. W9GFO
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    W9GFO Senior Member

    Most gliders use spoilers and/or flaps for glide path control. A spoiler decreases lift and increases drag while an airbrake increases drag without affecting lift. Many people do use the words spoiler and airbrake interchangeably.

    I don't know of any gliders that use airbrakes in the same way that is being suggested here, a split rudder, except for the space shuttle orbiter. I do know of some hang gliders that do though. There have been at least a couple different types of keel mounted vertical stabilizers that open up to act as an airbrake and it is not uncommon for hang gliders to deploy a small drogue chute when coming in for a landing.
     
  5. JSL
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    JSL Senior Member

    I have used a sea anchor as a drogue, works fine.
     
  6. PAR
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    PAR Yacht Designer/Builder

    Running an inlet in either power or sail can be challenging and there's no real positive way of insuring you don't broach. There are other conditions where you can broach too, so the only real tool is a skilled skipper, who will feel a broach coming on or can steer a course through seas, that can cause a broach. If shooting an inlet, it can be kind of fun, steering a course "up and back" to avoid the broach or stuffing the bow, but if you have to do this for very long or the weather has broken down to the point, where you really can't see or it's at night, it can be a horrifying experience. This is when you rely on feel and experience. Most skippers "know" their boat and how it feels underway in various conditions. He'll anticipate the stern getting kicked around or skidding into a beam on situation. Simply put, it's something you learn and doing so in a small boat, close to shore in moderate conditions is a great way to learn the skills.
     
  7. DouglasEagleson
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    DouglasEagleson Junior Member

    To: PAR

    With out question the act of working to stop the broach is allowed to occur. It will be an instinctive reaction maybe. Catching it an having a true straight surfing is only one possibility. The most common is not acting until the path divergence has taken hold. At this point the rudder will always stall without capacity to turn back to the beginning path.

    A possible act is to turn around like you said and try again. Turnarounds are tempting fate in my way of thinking. I guess I need to rethink the topic some. Rudder use rules is an issue.
     
  8. whitepointer23

    whitepointer23 Previous Member

    I don't know if I am reading this right doug but you are describing loss of steerage when hull speed matches wave speed. Pushing a button to deploy flaps will do nothing as well because they are traveling at wave speed also. We have a nasty bar crossing here and i have heard of trawlers coming in with reverse engaged to keep the boat speed below wave speed for steerage.
     
  9. gonzo
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    gonzo Senior Member

    Most broaching happens when the rudder ventilates and or cavitates loosing steering.
     
  10. jehardiman
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    jehardiman Senior Member

    Won't work and in fact will make you go faster as you are deploying them in the accelerated wave orbital velocity flow that occurs when a cycloidal wave beaches (i.e why swells build on the bar, see Oceanographical Engineering by Weigel...still THE textbook to go to). To slow the boat down, you need to get drag in the part of the wave moving in the opposite direction, i.e. the following trough. And the way to do that is...

    ...or trail warps. Just be aware that the rudder will reverse as you are drug up the overtaking face and crest.
     
  11. Mr Efficiency
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    Mr Efficiency Senior Member

    I take it the "up and back" refers to turning around 180 degrees if a particularly threatening swell or set of waves is about to overtake the stern of a boat whose speed is less than that of the wave train. Never had occasion to be a part of that, which I can see could be quite nerve-wracking, but I have heard stories related of how it might need to be repeated a number of times before the bar was cleared, and required some nice judgement to execute safely. But, as you say, when things have deteriorated enough, it ceases to be an option, as in a continuous break without lulls. There is a lot to be said for planing hulls and steering props running bars.
     
  12. whitepointer23

    whitepointer23 Previous Member

    On our local bar displacement hulls broach when they achieve wave speed is what i have always been told thats why the trawlers use a burst of reverse to keep from taking off with the breakers. But maybe that works for our wave types and not others. All bars probably have different characteristics . I fully agree with mr e about planing hulls and plenty of power.
     
  13. Mr Efficiency
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    Mr Efficiency Senior Member

    That's right, you are a sitting duck in a slow boat on a bar, coming in to port, anyway. You can't position yourself where you want to be, in relation to the wave train, and if there is a dog-leg to negotiate, all harder again.
     
  14. whitepointer23

    whitepointer23 Previous Member

    Yes its hard to beat. Going out you can park in front of the break and gun it when the low wave set rolls through and coming in with power and speed you can follow the back of a wave in and be able to keep away from the greeny behind that wants to swamp the boat. We used to have a dogleg channel at lakes when i was a kid but these days there is a well maintained channel straight out.
     

  15. CT249
    Joined: May 2003
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    CT249 Senior Member

    I'd hate to be tied to the boom if a six foot breaker came aboard. That amount of water throws people around as if they were dolls. Being picked up and thrown against the cabin top, winches or boom by a wave like that is not going to be good for anyone. At least one very good sailor is believed to have died after being hit by a boom that was tied down to the deck and torn off by a breaking wave - the forces involved were high enough to break the harness which would have caused fatal internal injuries.

    I've never heard of anyone "drifting through" a bar. As others have noted, there are professionals who cross bars every working day and they don't drift, they drive.

    By the way, what yacht over 25' has been sunk by water entering the hatches during a broach?
     
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