requirements to avoid ANY hurricane (at a given speed vs warning time)

Discussion in 'Boat Design' started by black_sails, Sep 8, 2017.

  1. PAR
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    PAR Yacht Designer/Builder

    Peter has hit on it and it's not something that's easily understood. The size of a Cat 4 or 5 is something you're not going to avoid. You can run down to the left hand quadrant, but you'll still be in it for days with a big lump of sea beating the crap out of you. It's not the boat, but crew fatigue. Your body can only take so much vertical acceleration, before you just can't take it any more. Being tossed against bulkheads, headliners and soles for a few days, will leave you pretty busted up, not to mention what happens to your inner ear.
     
  2. Mr Efficiency
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    Mr Efficiency Senior Member

    Few wise souls go cruising in cyclone/hurricane season, though there is always a risk of out-of-season events, keeping well apprised of forecasts, which nowadays are quite accurate a week or more ahead, is essential, anytime.
     
  3. PAR
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    PAR Yacht Designer/Builder

    Yeah that's very true. When I was caught in the early 70's, prediction was nothing like today. It's so much better now, with near real time imagery and all available. Even with this, last week if you'd be worried about Irma and decided to slip through the Lake Okeechobee canal system to the "other side" to avoid the wrath of the storm, which appeared to be going to spank the crap out of the east coast, you'd find yourself smack dab in the middle of the worst of it, simply because it took a few days for the storm to make up its mind as to where it was actually going. Prediction is now quite good, but don't ever expect to out guess or out run mother nature. She has a nasty habit of showing how inaccurate some predictions can be.
     
  4. black_sails
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    black_sails Junior Member

    I've been reading more on related articles, and at this point i'm conceding yes it's mostly looking like the difficulty is prediction. This article was of interest to me, providing some bits of specific data such as I was looking for: The top American weather model struggled to forecast Hurricane Irma http://mashable.com/2017/09/14/hurricane-irma-weather-forecast-models-gfs-vs-european/

    Forecast models are typically evaluated by their forecast skill at different timescales, including three, four, and five days. You can see from this chart that, for example, 120 hours in advance, the official forecast was off by around 300 kilometers. The European model had an average error of just 175 kilometers at that timescale, whereas the average 120-hour error of the GFS model at 120 hours was about 475 kilometers. The models were more tightly clustered at 12- and 24-hour timescales, but with the European model still coming out on top.

    So that gives me a few starting examples - nobody even bothers to predict past five days out and it already averages 110 miles off course for the european model. Thats not trivial but it's also not the end of the world. Means if I want to avoid a 500 mile wide radius hurricane I can expect on average to chart around a 720 mile blob as the red danger zone, plus whatever safety buffer I consider appropriate. (like they keep world records concerning fastest forward speed and such but i'm curious about things like fastest changes of direction, rates of acceleration, degrees of course alteration per hour and similar have been seen as well) The safety zone can't have to be infinite I mean, even if the horizon of prediction needs to lower or I have to decide how much of a worst case scenario likely (theoretically the 'yellow margin' should start at the 'worst ever seen historically possible' and have a smooth gradient to the red 'expected average track error combined with the hurricane size', probably plus predicted size increase for instance if expected) to be concerned about, the biggest questions are when to leave, where to aim for in what direction, and how fast to go. I limited contemplation to 20 knot and up craft because i'd think that's about the minimum i'd consider having a reasonable chance of reliably crossing the nose of a trajectory and not finding that it sped up from 20mph forward speed to 40mph forward speed in the last two hours totally changing the danger zone.


    Going to peruse the added replies now and comment on each. :)
     
  5. black_sails
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    black_sails Junior Member

    No no I think there's been a misunderstanding. :) I used the example of "you either build tough or fast" as two theoretical strategies one might apply. My plan is not something machined out of solid Osmium, but actually optimizing lighter design for a specific sea state and trying to use performance at times to try and stay ahead of (speed), get away from (speed), or have the extra range (endurance) to steer a path away from ugly experiences without having to turn completely around.

    My interest in prediction is not about waiting until the last 6 hours than taking off, but wondering things like "is there any way a hurricane predicted five days out could ever arrive in TWO days" and similar. If I find out with 48 hours warning a hurricane is coming in and i've got a yacht that will maintain 20 knots for 500 plus miles straight am I a fool for leaving Miami for Rio de Janerio? What about 96 hours out? How much additional decision time does extra performance and how much flexibility does extra fuel range buy me is really what i'm asking?

    What are the "performance limits of hurricanes", i've seen the records, but how rapidly and dangerously can they change in even 1 hour, 2 hours, 6 hours, 12 hours? Have they ever gone from 30 knots forward speed due west to suddenly going 30 knots due south 2 hours later? Etc. I'm just curious because I know they're dangerous, I just don't know what the limits of plausible behavior are.

    Common sense will always dictate a captain give as wide of a berth as possible - but without experience i've no feeling for how wide that is. Under what conditions would you feel safe leaving port (in a hurricane's expected path) for a destination X miles away, Y hours in advance? Does that give a better idea of what kind of rules of thumb answers i'm groping for?
     
  6. Ike
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    Ike Senior Member

    Both models leave a lot to be desired. But that doesn't change the fact that we all know that July through September is hurricane season (sometimes extending into October). So anyone who goes cruising in that area during this period has to know they are taking a big risk, and prepare themselves for the consequences.
     
  7. black_sails
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    black_sails Junior Member

    Wow, okay that's eye opening. Yes as two examples for what i'm trying to feel out, "places you DONT want to be" because it's a high risk run to see if you can get out of the danger zone with something bearing down on your exit hole... and the issue that even if you are not in the hurricane, meaning the big 500 mile spinning diameter of death zone, if sea states are 15 foot waves well ahead of(?), or after its passing, or say to the sides, then that all affects the possibilities as well.
     
  8. PAR
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    PAR Yacht Designer/Builder

    Sea state condisions can be all over the place in open water. My last Atlantic crossing saw 30' rollers for a couple of days, there were no storms nearby. With out experenice,you can not prepare for a storm, let alone a hurricane.
     
  9. Ike
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    Ike Senior Member

  10. jorgepease
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    jorgepease Senior Member

  11. PAR
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    PAR Yacht Designer/Builder

    The simple answer is there's no such boat design, except possiably an atomic sub, that will fit these requirements.
     
  12. hoytedow
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    hoytedow Wood Butcher

    You can only run til your tanks go dry. On land it was hard finding fuel after running over 200 miles. Try finding fuel in the Gulf or Atlantic in 20 foot seas.
     
  13. philSweet
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    philSweet Senior Member

    Where are you going to go?

    [​IMG]
     
  14. hoytedow
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    hoytedow Wood Butcher

    He's on Long Island and wants to go to Connecticut.
     

  15. jorgepease
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    jorgepease Senior Member

    If that is the prediction for Irma, we didn't have 34-40 foot waves on Miami Beach or even close to that, I watched the whole thing, worst it ever got was around 10-12 foot
     
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