Seaworthiness

Discussion in 'Stability' started by Guillermo, Nov 26, 2006.

  1. Stephen Ditmore
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    Stephen Ditmore Senior Member

    Respectfully, Mike, I'm afraid I disagree.

    One can always hold the midsection constant and increase station spacing to create a hull of any length. Therefore what advocates of heavy boats are really advocating is SHORT boats. Boats that are too short for their displacement are difficult to control, being inclined to spin and broach when running down the face of a wave.

    The examples of light displacement boats I've supplied: the Wylie Wabbit, the Hobie 33, and the Deerfoot and Dashew lines of cruisers, do not involve exotic materials as far as I am aware. (I will mention, though, that any sailboat with spars made of something other than carbon fiber can lower its center of gravity and its pitching gyradius significantly by getting carbon spars).

    I've explained, from my direct experience, why I'm skeptical of "comfort factor"... yet you continue to cite it without supporting evidence or validation. Do you continue to believe that it is a meaningful measure? Why? Of what? You may be right, but show me. What's the comfort factor of a Wylie Wabbit? Might the formula have predicted the excessive pitching of the boat I was aboard? I've never been seasick on an unballasted dinghy.... its the slow, pendulum like roll & pitch of a heavy boat that fails to follow the contour of the waves in its motion that makes people nauseous, in my experience.
     
  2. rayk
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    rayk Senior Member

     
  3. rayk
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    rayk Senior Member

    Two hours mate. Less in a gale.
     

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    Last edited: Nov 29, 2006
  4. Stephen Ditmore
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    Stephen Ditmore Senior Member

    That's about 118 minutes that I'd have rather been on the Wabbit than on the "comfortable" cruiser I was sailing.
     
  5. Vega
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    Vega Senior Member

    Guillermo, what makes a boat seaworthy is not a quantity of ratios, numbers and formulas, but the way the boat handles and survives heavy seas and brings its crew safely home.

    Regarding the boats from the 40class, they are so close (by the class rules) that we can consider them, for seaworthiness evaluation, as a single boat.

    Then we can have an imaginary boat that results from the accumulated sea experience of the 25 40class boats that had raced the “Route du Rhum”. This imaginary boat has sailed 85 000 miles, 21 266 of them under severe storm conditions (Beaufort scale 11 and 12). Those 21 266 stormy miles have taken place in 50 different big storms (25 boats x 2 storms).

    This boat was not driven under normal cruising conditions, but merciless raced all the way (including storms) and it was not a crew, but a single sailor in it.

    No matter the extreme circumstances this imaginary boat has done exceptionally well, regarding seaworthiness. For 96% of the way, the boat hasn’t had any problem worth mentioning, with the exception of a broken boom (knock-down by a huge breaking wave while de skipper slept inside). This situation didn’t prevent the boat from making the long way to the nearest Port (Azores) by its own means.

    Only on one occasion has the boat met serious trouble: The skipper was sleeping inside while the boat was on autopilot doing 17 knots. The boat has surfed a huge wave and has buried itself in a freak wave coming from other direction. The boat stopped instantly and the skipper had a lot of luck in having survived the crash (several broken bones). Incredibly the boat didn’t lose the mast, but had several structural problems. The boat made some water but did not sink (it looks that the 4 closed compartments with 3m3 of closed cell foam that should warrant the boat’s unsinkability worked well). The boat floated without problem till a cargo ship was diverted to proceed to the rescue of the injured skipper.

    It is important to underline that this accident would not have happened if the boat was not driven extremely in stormy conditions. 17 knots on autopilot is crazy enough for me; 17 knots on autopilot while sleeping inside the boat is madness, unless you are a very aggressive racer. And he certainly knew that he was taking a lot of risks.

    It is important to notice, that on those 50 different extreme storms, the boat never capsized (rolled) no matter the 70k of wind and 7 meter breaking waves. The boat proved that it can be sailed safely in these extreme conditions on autopilot, with the skipper sleeping inside.

    And it is also important to say that the conditions encountered in that race where the worst ever encountered in all editions of the event.

    Guillermo, you say about one of class40 boats, comparing it with the RM 1200:

    May I point also that the average speed of all the 40class boats was of about 6.5 knots, and that is not a planning speed?

    I would find these comments amusing, if they would not contribute to the misinformation of less informed members of this forum.

    You know Guillermo, it is the sea that informs about the seaworthiness of a boat, not the ratios or your calculations. This boat has proven its seaworthiness in the most demanding sea conditions, and it is obviously a very seaworthy boat.

    I think you should adapt your numbers and ratios to the reality and not the reality to your numbers and ratios.

    I agree completely with Crag Cay when he says:

    Regards
     
  6. longliner45
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    longliner45 Senior Member

    structure make a boat seaworthy,,, and basic design,,ballest and materials,,,,,first of all ,,what is this about someone putting a boat on auto pilot and taking a nap in heavy wheather,,,,,,I say bullcrap...if its rough out ,,your but is up and on high alert.,,,even if you want to sleep ,your *** is being throne about ,,the cans of food are all over the wheel house ,,water has washed the lables off of them ,,your tools are put away ,,,so noone gets knocked upside the head.I can attest to this from experiance ,,not no weekend andventure gone bad.I have come home many times with all my fishing gear in splinters on deck.. and the boat seemingly sandblasted clean.like I have stated early on ,,,I would rather fight mike tyson ,or let 2 guys beat me with a bat ,than to ride another hurricane out.I would probably come out ahead.one hurrican I remember well was hurrican juan ,,I spent 44 hrs at the wheel, the only relief was holding onto the helm,,this was in the fishing vessel broadbill, (a 31 ft jc hull)fisherman and sailors have much in common....the storys ,,,,,,,,and fish get bigger and bigger,,,,,longliner
     
  7. Mikey
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    Mikey Senior Member

    Matt, that does not always show the true picture though.

    Make a design brief for a yacht with a LWL / BWL of 5.5 to 6 and you can build it very sturdily indeed and still get a displacement/lenght ratio of 100. Light for its length, yes, but not lightly built.

    But then you would have problems keeping WSA low and still have enough lateral plane area to provide adequate damping

    Mikey
     
  8. MikeJohns
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    MikeJohns Senior Member

    Stephen , no problem........by the way it's cite isn't it?:)

    We need a better yardstick. Boats like your Wabbit are engineless day sailors, they have enough displacment to carry their scantlings and their crew.
    Now scale down a cruising boats load (including engineering) and add it to this day sailor and she likely becomes a very heavy displacment craft indeed with totally different characteristics, as for your "comfortable" cruiser what was she? what were her ratios? what were her stores tankage and equipment aboard on the day? There are too many variables for your experience that day to be as you say "supporting evidence or validation"

    As for heavy and short; This is an amotional appeal ? :confused: I am sure you know full well that Cp can be the same regardless of displacement. In fact reasonably narrow deep and long is arguably one of the more seaworthy hullforms (Marchaj). What I think you are really saying is that lwl/lod is much closer to 1 in modern vessels compared with the older long overhang vessels of the past. We can as I said before design contemporary heavy boats with much better characteristics than they may have exhibited in the past eg finer entry inherant long damping flatter aft sections etc.

    I was hoping not to turn this into an enginnering treatise. But I'd be interested in what you think of Marchaj's and Renilsons research in this area if you've read them, or if you were aware of any other papers or research to the contrary.

    I would also like to define what I call heavy as a DL of around 300-350. Which is heavy by todays standards ( but not many old boats which could be over 400) .
    ---------------------
    An example

    Lets consider two 40 foot boats, one 7 tons and one 15 tons:

    To both vessels add a genset, 2 tons of fuel and water, provisions for a crew of 4 a radome, lifreaft a dinghy or two and their motors , 2 sets of ground tackle and a some spare sails. (say 3 tons all up)

    The lighter weight is now floating a foot down on her lines, her loaded DL has become heavy and her hullform is not beneficial to perform well with this load at sea ie Cp is now detrimental, in addition she now has a very compromised stability since her shallow hullform denies sensible stowage and mounting of much of the gear. GM is now so low that the boat cannot stand up to the canvas she so desperately needs. (You should try this exercise on one of your W&M spreadsheets).

    The heavy 40 footer displaces those 15m^3 of water her volume is able to absorb engineering tankage and emergency ground tackle at a vertical position that often has a neutral or even positive effect on her stability, in addition she is designed to operate close to this displacement, her GM remains the same and she will be faster and far more seaworthy than her cousin above.



    Cheers
     
  9. rayk
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    rayk Senior Member


    Syndicate boss:So, can you sail this thing?

    Crew:Yup.

    Designer:Dont touch anything, you can remember that right?

    Crew:Yup.

    Syndicate boss:You got your sleeping pills?

    Crew:Yup.

    Comms guy:Ill send you an email when you have to do something like
    putting numbers in the computer.

    Crew:Yup. ...hey can I do the sails?

    Syndicate boss:Yes. Put them up at the start and pull them down at the
    finish of each leg.

    Crew:What about really windy days?

    Designer:Dont stop whatever you do because the boat isnt des....!

    Syndicate boss:....isnt going to win if you start worrying like that!

    Comms guy:Its okay, if anything goes wrong the boat will eventually flip
    over and the emergency antennaes located in the keel and
    rudders will transmit.

    Designer:Yes yes its a safety thing I noticed, the keel and rudders
    never detach at the same time, because the forces inv...

    Syndicate boss:Moving right along, just remember if you get picked up
    by the rescuer tell them you were asleep travelling at 25kn
    under spinnaker trying to reach the next storm when a
    rouge wave did you in somehow. The media like that.

    Crew:You guys arent gonna blame me if something happens are
    ya?

    Syndicate boss:No. We are all in the same boat. Its no ones fault. No one
    knows what the ocean is going to do.

    Crew:I gotta go guys everyone else is getting ready!

    Comms guy:If you cant reach us at the commcentre just take a
    sleeping pill and try again when you wake up!

    Syndicate boss:If you run out of pills I had computer battleships installed
    on the laptop!

    Designer:Dont touch anything! Good luck!
     
    Last edited: Nov 30, 2006
  10. Mikey
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    Mikey Senior Member

    Good one, rayk!
     
  11. Guillermo
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    Guillermo Ingeniero Naval

    Here you go again.
    I would appreciate if you from time to time (at least) use numbers to support your many times surprising statements, instead of disqualifying those you do not agree with.
    The reluctancy in the using of numbers and keeping on with disqualifications and magazine-based marina-cafe style discussions, only reflects lack of knowledge and an excess of ego, I'm afraid.
    Cheers.
     
  12. fcfc
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    fcfc Senior Member

    Is your problem of seaworthiness a REAL problem ?

    From all the deads and injured while leisure boating in your country, (not in race, not professional sailors), how many happened from a capsize with a correctly trained crew and correctely maintened boat, even with the minimal certification for the encountered weather ? What percentage does it makes?

    I fear people get burned while cooking at anchor, crushed while trying to stop a boat against a wharf, killed while grouding dur to bad navigation etc ...

    Capsize is a very psychological and emotional issue, but has nothing to see with real life accidents. A bit like being hit by a meteorit.
    That DOES happen and makes big headlines. But it is not the MAIN cause of accidents.
     
  13. Guillermo
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    Guillermo Ingeniero Naval

    What do you want fcfc?
    That these forums should not discuss seaworthiness....? That I should not discuss seaworthiness...? That seaworthiness is not a relevant matter anymore?
    I don't understand the meaning of your post.
     
  14. Crag Cay
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    Crag Cay Senior Member

    This is the key question. And if we were to do a valid 'risk assessment' there would obviously be a significant risk to some sailors in some situations.

    But would it be significant enough, or prevalent enough, to warrant all the passion and debate that this topic causes? To answer this we probably have to look at the work of Peter Sandman. He added an extra 'variable' to the normal risk evaluation formula of 'hazard x likelihood x consequence'. His addition was the idea of a 'fear or outrage quotient'.

    His theory is that our assessment of risk can become distorted when the hazard identified is either scary (often through a lack of control over it) or outrageous (either because of the hideousness of the death or the 'freakishness' of that death). This is why parents do everything to protect their children against paedophiles (low risk / high outrage) but are happy to have them ride in the car without a seat belt (higher risk/low outrage).

    The outrage quotient associated with 'being rolled at sea' is born of our lack of control. By definition we are in 'survival mode' when conditions have got that bad and we are programed as humans to treat such circumstances with a degree of fear. However the degree of fear varies from person to person and so the 'outrage quotient' we (probably subconsciously) apply to out own risk assessment varies and hence our perception of the risk level involved. Whilst for some, this may skew them to being overly cautious, in others it may even lead to recklessness.

    In sailing, the other problem that applies a distortion to an objective evaluation of this risk is the 'freakish nature' of any deaths when viewed from society's norms. Drowning yourself alone in the southern ocean is a 'freaky' way to die in most non sailors' eyes. Therefore those who risk doing it are subject to societies 'outrage'. Fingers are wagged, pompous editorials written, whilst the millions who smoke and drink themselves to death, still do so without a murmur in many European countries, for example.

    On a micro scale we also have the outrage factor working within the sailing world itself. Multihulls, in particular suffer from what could be described as our '********** status'. When these capsize it reinforces what, deep down, we all belive we know about them, whereas problems with ordinary monohulls are more likely to be dismissed as 'simply unfortunate accidents'. And even less 'outrageous events' (such as drowning by falling overboard, wrecking due to engine malfunction or fouled prop, severe head injuries from the boom, etc,) which fill the rescue services call out logs, are just problems 'that happen at sea'.

    At the recent Kendal Mountain Film Festival, there was a round table discussion that focussed on 'The Risks and Rewards in Adventure'. Although it naturally focused on the mountain environment, sailing and even the 'Timothy Treadwell Bear Man' saga were considered. The 'outrage quotient' was seen as a valuable insight when accounting for the variations in any risk assessments. So to be truly objective, our risk assessment of seaworthiness must be without the outrage quotient and deal solely with examples of failure that were due entirely to the nature of the vessel.
     

  15. MikeJohns
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    MikeJohns Senior Member

    Crag and all


    I agree and this is a sensible post, but surely we as a group of designers (not as society as a whole) should be able to have a good debate on this issue and try and identify objectively some of the key issues that make a vessel either intrinsically safe or unsafe.

    The non-technical sailors do need some protection from an industry that sometimes pushes unsafe boats onto people who are not in any position to know better.

    Those of us that work with commercial vessels see a much higher standard demanded of design and seaworthiness, and to good measure. If we deem a vessel too unsafe for an unsuspecting public and refused survey because of safety and strength issues, shouldn't that be a good indicator that it is not a very safe design?

    As a pro engineer I am particularly culpable if my design or assessment leads to injury, far more so according to the courts than a less qualified “designer".


    If the risk assessment says "event probable and likelihood of death High" then its off .......period. This goes for every other field be it a commercial marine vessel an aircraft, car truck or bridge and an engineer has to certify these and carry the can if they fail.




    Lets take one example of what constitutes an un-seaworthy vessel the Limit of Positive Stability (LPS)

    In Australia we require that that any commercial boat have a specific LPS but we do nothing to educate the public and advertisers sell boats as suitable for offshore with abysmal LPS’s well below certification standards. That the boats are fast responsive and exhilarating doesn't stop them becoming death traps in heavy weather for people who know little of these issues.

    The limit of positive stability is not just where the boat turns turtle, it also is strongly indicative of the expected inversion time, although using LPS the predicted time is usually a bit optimistic and it takes longer for the vessel to right.
    Recent analysis of inversions suggest that an LPS of 120 degrees takes approx 4 minutes to self right. but it can be far worse.
    In the 1992 Japan Guam race a yacht with a LPS of 114 remained inverted for 45 minutes killing 6 of its crew.
    In the 98 Sydney-Hobart we see B52 (LPS 119) inverted for 4 minutes. BP Niad (LPS 105) inverted for 4 minutes drowning one crewman and nearly a second.



    I don’t have the time to research the other poor sods who have died this way although I am aware of several others.

    If it takes an LPS of 135 degrees to guarantee that the vessel rights before the crew drowns then that should be our first demand of seaworthiness for any vessel venturing offshore.

    In fact the Fastnet was the lesson on LPS limits and the lessons from the 98 Sydney-Hobart had already been taught long before but were ignored.


    How many deaths are acceptable from deficiencies in a vehicles design? Remember this is human life we are talking about, not a point scoring debate.
     
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