Seaworthiness

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

  1. Crag Cay
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    Crag Cay Senior Member

    "........a bigger displacement seems more desirable".

    To You!

    Another example of why you can't separate personal preference from the notion of seaworthiness. ANY boat that returns its crew safely back to port is seaworthy. If you didn't enjoy the experience, then that boat is not seaworthy - for you. I know folk who wouldn't go to sea in a minesweeper as they were 'too small for the open sea'. But then some weren't happy on destroyers either. Still made Captain, though.

    A lot of the preferences shown go back to 'confidence'. People are prepared to trade off all sorts of other characteristics, including performance, to get themselves a boat that inspires confidence in them. For some this means full keels, steel hulls, no through hulls, covers for all ports, drogues, trisails, oil dispensers, etc, etc. Some would say all that is prudent, others 'overly cautious'. It's up to you.

    But for those who are happy in light displacement, or multihulls, or swinging keels, or powerboats, then that is great. Realistically the chance of coming to harm at sea in a well found vessel of any sort is pretty slim. Once you arrive safely at the marina in your car and head down to the boat, the most risky part of your trip is over. (Peeing over the side and dinghy rides ashore, excepted).

    And seaworthiness has other components, apart from the vessel. As Marchaj says, seamanship (as well as the the weather and luck) plays a part. Again, we must consider these as a whole. Although seamanship cannot completely compensate for all the shortcomings of a particular vessel, neither can a particular vessel entirely compensate for poor seamanship. However a lack of confidence in their own ability is why many go looking for a 'safe cruising boat'. In particular, as a designer of steel cruising vessels, I've noticed that potential buyers (or their wives) are looking for this perceived safety of a steel hull to prop up their own inadequacies as sailors. As a result, I have calculated that a lower proportion of steel boats ever do the trips for which they were bought, compared to other cruising boats types.

    Pick the boat that suits your needs, but be careful not to project your own preferences as being 'the only way to skin a cat'. Other boat / sailor combinations may be just as seaworthy, just less attractive to you.
     
  2. rayk
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    rayk Senior Member

    I meant self detaching keels :D
    Not very seaworthy.

    High tech keels on cruising boats...thankfully still rare.

    Why doesnt some one make a series of documentaries about famous cruisers or classic cruising grounds that can be aired simultaneously during ROTW and TransAt races? A nice contrast.

    Might remind us of the benefits of conservative engineering and design.

    Hats off to the guys on the racers any way. Southern Ocean looks pretty wild.
     
  3. Stephen Ditmore
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    Stephen Ditmore Senior Member

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  4. MikeJohns
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    MikeJohns Senior Member

    Sounds like the IOR boats, but directly downwind tests all hull-forms and most of us avoid it at sea like the plague. Sailing by the lee helps this but I think we are always better tacking downwind for vessel and crew.

    We recently completed the re-pwer and re-designed of rudder for a real oldie from 1905 (60 footer). On extended sea trials (a jolly) in weather which sank another boat and drowned two we were so safe as to be without harnesses. This vessel tracked downwind so well that we simply lashed the helm. on releasing the helm it was found to be empty of hyd oil and spinning freely as was the interior helm. We hove to and rounded up with the mizzen and re-filled the steering and tightened the offending coupling and bled the lot. It was an anxious moment as the seas were not small, but I have never been on a more seaworthy sailing vessel . My own preferences are for a better light air performance but that vessel was a real eye opener.




    Cheers
     

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  5. Guillermo
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    Guillermo Ingeniero Naval

    We cannot compare stability in planning conditions, when high hydrodynamic lifts are in charge, with stability when there's no lift at all. Two totally different things. But the question, from my point of view, is that even when in no lift conditions (be it a light or heavy one), a cruising boat said to be oceanic must be intrinsicly safe, no matter what her crew abilities are. This is most relevant for what concerns to B2 knockdowns, the worst thing that can happen when you are in the middle of nowhere in a storm.
    Beamy, light and fast boats are not safe by any means under this point of view, although they may be able to run out of trouble 9 out of 10 times. The problem is when that 1/10th possibility (or 1/100th) arises and you are knocked down, i.e. And things will get really interesting if the mast breaks in the process.
    Have a look at the RM 1200 and POGO 40 numbers I posted at the STIX thread.
    (And this doesn't mean I'm saying all heavy and narrow boats are intrisicly safe, take notice! ;) )

    Cheers.
     
  6. Mikey
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    Mikey Senior Member

    Guillermo, Thanks for that, totally agree.

    So who will agree on this; To have to rely on speed to be seaworthy is an unacceptable characteristic in an ocean cruising boat

    In “Seaworthiness, the forgotten factor”, Marchaj let’s us know how important roll damping is, and he even questions the competence of the members of the inquiry into the founding of a fishing boat for not seeing the connection.

    Beamy shallow sailing yachts with high aspect ratio foils, light rigs and small lateral plane area will by definition have low roll damping and low inertia – Both are characteristics that I would call undesirable for cruising yachts.

    Mikey
     
    Last edited: Nov 29, 2006
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  7. rayk
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    rayk Senior Member

    I agree. These mordern racers are designed like a car with no brakes. Only skilled drivers can handle them. If they crash its obviously the fault of the design and engineering.
    These boats drive the crews really, no other options.
     
  8. Frosty

    Frosty Previous Member

    There seems to be too much emphasis on the boat here. A boat can not cross the ocean on her own, a good boat can not cross the ocean with a bad crew, A bad boat can cross the ocean with a good crew.

    You cross an ocean by her good grace. I would go so far as to say that no boat is seaworthy, there are some better than others.

    a seaworthy boat would be a steel sphere but in which life would be intollerable.
     
  9. rayk
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    rayk Senior Member

    A seaworthy boat could be a bathtub if the crew is expected to paddle and bail the whole passage, with an appropriate level of external assistance on standby if an insurmountable problem arrises.

    The earliest ROTW entrants are an excellent example of the best in cruising design. I am thinking of Dick Mcbrides City of Dunedin(anyone got more info?). The crews placed great emphasis on self rescue before speed.

    I think self rescue is non negotiable in a sea worthy design. It was a requirement for the earliest competitors without a death wish. They sailed the same Southern Ocean as todays competitors, only without the extensive external support network.
     
    Last edited: Nov 29, 2006
  10. MikeJohns
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    MikeJohns Senior Member

    Crag

    We want a hullform that returns us to port in one piece and will do so repeatedly in all weathers for years of reliable service. Strength and durability don't equate well with light scantlings.


    As an engineer I carry out many insurance reports on damaged vessels I see a lot of damaged boats that simply experienced bad weather while coastal sailing , ripped out and fatigued chainplates sheet winches runners attachments pulled out or right through decks, Bollards that ripped out under load, most on modern foam cored production yachts with very high price tags and very little displacement. We see a lot of damaged rudders, particularly spade types after dragging anchor, and lately a couple of severe hull damage from grounding of strut bulb configurations that are irrepairable.

    Weight allows factors of safety which are just not possible in lighweight vesssels. Most cruisers are uninsured and with a substantial investment in the vessel they are far better off with a boat that can take a prolonged grounding on a coral outcrop or a rocky shore and be pulled off. Bumps knocks and even groundings are very common when cruising extensively in coral infested waters, usually at no great fault of the crew either.
    If for example a well placed anchor is dislodged by another boat dragging down and you end up bumping on the reef at 2am (this happened to me) it is the strength of your vessel that prevents serious damage.

    Cruising in the Pacific you will find around half the boats are steel and most are medium heavy to heavy displacment the majority of the steel boats are home built from designers like Colvin and Roberts.

    They do not have such vessels as you suggest to prop up their own inadequacies as sailors but on the contrary because they are prudent and experienced cruising seamen.

    Another big problem with lighweight cruising designs is the loss of stability with the gear that accumulates that the designer never allowed for.

    We discussed some of this in D'Artois "Ideal cruiser" thread a while back.
     
  11. Milan
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    Milan Senior Member

    This divide in "heavy displacement" and "light displacement" camps is a bit misleading. "Heavy" or "light" is relative, usually in relation to the water line length. It's perfectly possible to build heavy displ / WL length ratio boat, (short, wide and deep), with a very flimsy scantlings, or to build very strong, build as a tank, indestructible, light displ. boat, (long, narrow and shallow).
     
  12. marshmat
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    marshmat Senior Member

    I think we usually refer to "heavy" and "light" being an expression of displacement/length ratio, rather than of actual size....

    I certainly agree that in the case of a cruising boat, seaworthiness requires that the boat keep her crew alive and safe in bad conditions with no effort on their part.... such boats usually sail with small crews, and especially if someone is injured there will be nobody to focus all their effort on the boat.
     
  13. Guillermo
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    Guillermo Ingeniero Naval

    I'd say: "To have to rely only on speed to be seaworthy is an unacceptable characteristic in an ocean cruising boat"

    Cheers.

    P.S.: I'd dare to recommend to the ones who have not done it yet, the reading of Marchaj's book. Most formative.
     
  14. Vega
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    Vega Senior Member

    Yes, you are right about the importance of good communications and accurate weather reports. Without good communications and weather routing Philip Sharp would have never won that race. How the hell would he know where to find the very strong winds that have given him the victory?
     

  15. MikeJohns
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    MikeJohns Senior Member

    Milan
    The easiest way to get sea-kindliness is with displacement and displacement allows many other benefits to the cruiser, I said before strength and weight are on opposite sides of the coin, this is a hard engineering fact. If you want a super strong lightweight you need very expensive materials.

    Cheers


    To all

    You can have a light weight with very high stability and roll inertia with a long strut and a big bulb but vertical acceleration will still be high. Open 60 hull-forms are not comfortable to be aboard at sea, they slam and jerk with their high metacentric height and big water-plane area. In waves and little wind they wallow miserably and it is very hard to keep your feet. With the open 60 hull-form would it be fair to say that the open 50's on their inversion statistics were too small but that 60 feet seems to be the minimum for this configuration?

    Comfort
    How many designers are even aware of the comfort factor?

    Comfort factor seems to have gone out of the window with boats like the Pogo 40. Consider what you would design if your brief was comfort as the main factor. Say a comfort factor of 60, a larger volume cruising hull with a safety factor of at least 3 on the rig with reasonable performance, running through the options you will quickly see how the boat takes shape and it's not a modern hull-form, now add sufficient lateral area without compromising cruising draft and the hull starts to look pretty traditional.

    The helm
    On a long trip the most wearying of chores is the helm. Some boats are very hard to steer many oldies developed enough weather helm to just about snap the tiller at times others ran on rails. Modern ocean racing boats like the open 60 form are a joy to steer when well trimmed reacting instantly to the wheel and I find it very similar to driving a car. But my first windward stint on the helm on one of these I took my eyes off the horizon for 2 seconds to receive a well earned bit of cake and I was off course by 15 degrees. You cannot lash the helm or wander fwd to untangle a sheet without either stopping or using an auto-helm. None of our modern solo racers would be able to achieve their feats without high levels of technology. If the electrical power system fails they are out of the running.

    This adds another point, that dependence on high levels of technology for seaworthiness.


    Theres a famous quote which says sailors fit one of 4 profiles they are either Dead, Retired, Pessimists or Novices.
    Direct offshore experience is the best qualification for any offshore designer. Unfortunately many current designers and marketers only have coastal racing experience. Consequently we end up with Pogo 40’s marina to marina, semi sheltered, weather window boats with inadequate vanishing stability and abysmal comfort ratio.

    IMHO
     
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