to windward in a storm

Discussion in 'Hydrodynamics and Aerodynamics' started by Jamie Kennedy, Feb 9, 2016.

  1. Jamie Kennedy
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    Jamie Kennedy Senior Member

    Has there been CFD analysis on extreme wind and wave conditions, like a folkboat or much smaller micro-cruiser designed to be able to go to windward or hold her own hove to in say 6-12m waves and 40+ knots of wind. Can you combine wave dynamics with CFD in a meaningful way? What are the limitations. What is known about wind speed and turbulence down in the trough and up on the crests? Also, the effects of surface currents. Is it beyond the ability of CFD to model in a meaningful way? The objective would be to investigate the dynamics in storm conditions, when you are trying to weather a storm without losing distance to leeward, off a lee shore or just trying to get some rest. Also to better understand whether a boat needs to be 14 feet long or 28 feet long etc. Context would be a solo transatlantic crossing in a small boat, in a modest boat easy to build and maintain yourself without exotic materials. I understand at some point you need to put out a drogue and go the other way, but I am curious what the limits might be on being able to go to windward or at least hold your own.

    Also, wondering if a small remote control model might be a reasonable simulation. Would a 1/4 scale model be valid. Say a 4 foot boat in a 6 foot sea simulating a 16 foot boat in a 24 foot sea. How would you tweek the sail area and righting moments? How would the wind speed scale?
     
  2. gonzo
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    gonzo Senior Member

    You won't be pointing high, but can definitely keep off a lee shore. However, on a smaller boat, you will have little or no speed in the trough of the waves. I have been solo on a 25 footer where it would almost stand on the stern and then pick up a little speed on the wave tops. It rolled over too. However, I push my boats hard.
     
  3. Jamie Kennedy
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    Jamie Kennedy Senior Member

    I've been thinking it might be fun to build something small like Paradox, and use it like a half scale model. Would a 12 foot boat in a 12 foot sea, and 35 knots of wind; be comparable to a 24 foot boat in a 24 foot sea and say 50 knots of wind? That's kind of what I'm thinking. The Bay of Fundy is where I would like to try this out, but in late summer and fall when the water is warmer.
     
  4. CT249
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    CT249 Senior Member

    Model yacht guys would have worked the scaling issues out. From what I recall, some things scale up very well and others don't. As early as the 1850s they worked out that the performance of models in rough water can be very different to the performance of full-size boats.

    The other thing is what sailor and boat we are talking about. Does it have a cheap roller-furling jib or a kevlar/carbon #4? And who is sailing it? The difference in skill becomes vast in such conditions. Just watch any dinghy race in strong winds and you will see some people who cannot finish, and some people who will never look like capsizing.As an analogy, put Tom Slingsby in a Laser and he'll keep away from a lee shore in 40 knots, but put a good club racer or a beginner in the same boat and the same place and it would be a different story.
     

  5. Jamie Kennedy
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    Jamie Kennedy Senior Member

    well said
     
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