Seaworthiness

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

  1. rayk
    Joined: Nov 2006
    Posts: 297
    Likes: 15, Points: 0, Legacy Rep: 146
    Location: Queenstown, NewZealand.

    rayk Senior Member

    As for 30ft cruising boat vs 900lb 24fter, daysailing for tin or a $100 bar tab, horses for courses I think.
    Round two should be a race to Tahiti.
     
  2. longliner45
    Joined: Dec 2005
    Posts: 1,629
    Likes: 73, Points: 0, Legacy Rep: 505
    Location: Ohio

    longliner45 Senior Member

    put the saki down ,,,your starting to make too much sence,,,,,longliner
     
  3. rayk
    Joined: Nov 2006
    Posts: 297
    Likes: 15, Points: 0, Legacy Rep: 146
    Location: Queenstown, NewZealand.

    rayk Senior Member

    If you tell the designer youre going to stack fish bins six high in the deck and run for home in the teeth of a howling gale, retiring in 7 years a wealthy man; I expect he will draw you some thing seaworthy.

    And if you ask the designer wether one of his existing boats is capable, the slightest hesitation is your answer. The onus is on the skipper to scale down expectations until the designer is nodding enthusiastically. The boat has become seaworthy.
     
  4. longliner45
    Joined: Dec 2005
    Posts: 1,629
    Likes: 73, Points: 0, Legacy Rep: 505
    Location: Ohio

    longliner45 Senior Member

    rayk ;wasnt putting you down man.but boats are desinged,for purposes. you can buy a nice daysailor lets say 50 ft ,,but you dont want to cross the ocean in it,,,eveything has its limit of design, if it fulfills that spectrum ,,it is seaworthy according ,,to it.buy the way Ill trade you a jar of some good kentucky moonshine for some good saki.....longliner
     
  5. MikeJohns
    Joined: Aug 2004
    Posts: 3,173
    Likes: 198, Points: 63, Legacy Rep: 2054
    Location: Australia

    MikeJohns Senior Member

    Stephen


    I think that to really judge the benefits of heavier boats you would need a broader exposure to the type than you have had the opportunity to experience so far. They are as varied in their design as any other craft and can be a real joy to be aboard at times. After my own experiences and vessels over the years I find heavy displacement can provide both performance and a far greater level of comfort.


    Pitching is a problem with small heavy boats I agree. Although they can be designed with varying degrees of inherent pitch damping but size is important when it comes to characteristic pitch frequencies and smaller boats will always be at a disadvantage. You may have been on a particularly bad specimen with bluff bows and equal fore-n-aft areas, (but I’m sure you know all this anyway). Had the waterline been 5 feet longer you may have had a completely different revelation :)

    It is always interesting to watch the longitudinal damping time of boats aligned into oncoming ferry wakes, the last one to stop will always be the round bilged double ender, particularly the small heavy double ender that will sit there rocking away ages after all the others. Every skipper needs to know enough to avoid the shortcomings of their vessel.


    The Dashews are certainly experienced passage-makers, but look at the size of their vessels, even then by their own admission they find the fast passages a little tiring at times. They are also consummate marketers of their product which is now the even faster higher tech Beowolf rather than the Sundeer, to me they do seem a little manic at times and they are trying to appeal to a target market. They push their boats to the limits and exhilarating as it may be I would not keep my family aboard slamming across oceans at breakneck speed.


    The modern skimming dishes are very good at reducing pitching but other attributes can be very poor when applied to smaller vessels eg the mini transat has been a debacle at times with decimated fleets and survival down to luck rather than skill due to the inherent un-seaworthiness of a hullform that works for 60 footers but not for the minis.

    I'm with you that narrow light boats are certainly more seaworthy than beamy light boats but a heavier boat if it has the right characteristics will (all things being equal) be more comfortable. Vertical acceleration is governed by mass to water-plane area and is the most debilitating motion. The heavier the boat for a given water-plane area the lower the acceleration, in addition the heavier boat has a far greater the roll and pitch inertia ……… yes a high pitch inertia translates to a greater moment to damp when the vessel does pitch so we need to design for that.


    I think pitch inertia helps heavy boats cut through the waves while lightweights tend to pitch more, the opposite of your experience, but it does depend on the vessel its size and the sea state and the course held.

    Unfortunately many modern yacht designers particularly in the USA seem to have a very prejudiced opinion when it comes to the merits of more robust displacement despite a rich heritage of successful heavy cruising boats from very professional design offices in the past.


    Probably this is a cultural influence and designers buying into a marketing atmosphere of light weight go-fasts, and the fact that light boats use less material and are consequently a more economic proposition for hard pressed yards.

    IMHO
     
  6. Vega
    Joined: Apr 2005
    Posts: 1,606
    Likes: 26, Points: 58, Legacy Rep: 132
    Location: Portugal

    Vega Senior Member

    I think we can see in these two videos what you mean.

    The two boats seem to be about the same size. The old heavyweight and modern light boats have complete different ways of handling heavy weather.
    On the first video you can see a nice oldie bobbing around in bad weather.
    On the second (the little advertise to the Ocean's twenty DVD) we can see an open 60 sailing on heavy weather.

    You can take your pick, but the Mono 60 is much more stable than the oldie. I would feel a lot safer going to the mast in the open 60, than in the Oldie. In the open 60 I can predict the boats movement, on the oldie I would never know.
    It seems to me that the Mono 60 has a much more comfortable motion.

    And let’s not forget the Mono 60 is racing. Some knots slower and the motion would be a lot more comfortable.

    Regards

    http://video.yahoo.com/video/play?&...44e5d429833c3f66&rurl=www.biology.ualberta.ca

    http://www.courseaularge.com/index.php?T=depeches&I=6003
     
  7. MikeJohns
    Joined: Aug 2004
    Posts: 3,173
    Likes: 198, Points: 63, Legacy Rep: 2054
    Location: Australia

    MikeJohns Senior Member

    Vega

    An open 60 is a completely different ballgame and it's no cruising hullform either, scale it down to a mini and you have a very unseaworthy hullform.

    The current open 60 type develops a lot of dynamic stability from its foreward movement and if it slowed down it could become more uncomfortable, surging sideways and following the water surface contour . You get some of the worst rig stresses on thes sorts of boats in sloppy leftover seas with little or no wind and it would be worth watching videos of these sorts of boats in those conditions alongside your "oldie". Also a well designed "Newie" of heavy displacement is a different kettle of fish.

    Cheers
     
  8. rayk
    Joined: Nov 2006
    Posts: 297
    Likes: 15, Points: 0, Legacy Rep: 146
    Location: Queenstown, NewZealand.

    rayk Senior Member

    Re the oldie. A crew of 6-8 would get that old tub flying again. An old cruiser racer was thrrashed like any modern racer. A racing crew didnt lie around the saloon drinking peppermint tea when it was windy.
    How is the Open 60 going to cope with a family as sole crew? Go to the mast and take another reef out with your eleven year old daughter at the helm.

    A seaworthy boat can be sailed as hard as you can handle it and be exciting enough. Active sailing is not the sole domain of modern design.
    Todays ocean racing boats evolved from these racer cruisers as designers slowly chipped away at attributes that slowed the boat down. There was a thresh hold. Crew took greater risks to win as technology provided a faster and more reliable external safety net. Most modern racing sailboats would have sailed off to oblivion 50 years ago without the supporting technology of today.
    Remove all the comms from these minis at the start of the race and watch the crews faces turn to stone. The boat is just as seaworthy. Communications technology is nurturing these bold sailors not safe design.

    A seaworthy boat can make a safe passage without hourly weather routing and foreign navies on stand by.
     
  9. Vega
    Joined: Apr 2005
    Posts: 1,606
    Likes: 26, Points: 58, Legacy Rep: 132
    Location: Portugal

    Vega Senior Member

    I don't understand what you mean.

    Yes, it is true that you need a crew to race that oldie.

    No, you don't need a crew to race the 60 open. They are solo boats, one sailor is enough.
    They sleep with the autopilot on, in stormy conditions, with the boat doing 15k.
     
  10. rayk
    Joined: Nov 2006
    Posts: 297
    Likes: 15, Points: 0, Legacy Rep: 146
    Location: Queenstown, NewZealand.

    rayk Senior Member

    Good shot Vega :eek:
    How about this amazing guy getting 5 more knots out of the oldie by himself and having a kip. He will need one of those big expensive racing autopilots to get a good sleep.
    Seaworthiness and performance arent mutually exclusive attributes.

    Any way a boat that inverts and stays that way just reinforces the choice of most people for a boat with better positive stability attributes.
    Being rescued is a poor design crutch.
     
  11. Vega
    Joined: Apr 2005
    Posts: 1,606
    Likes: 26, Points: 58, Legacy Rep: 132
    Location: Portugal

    Vega Senior Member

    What boat are you talking about?
     
  12. rayk
    Joined: Nov 2006
    Posts: 297
    Likes: 15, Points: 0, Legacy Rep: 146
    Location: Queenstown, NewZealand.

    rayk Senior Member

    Modern racing monohulls, with detatchable keels.
     
  13. Stephen Ditmore
    Joined: Jun 2001
    Posts: 1,388
    Likes: 44, Points: 58, Legacy Rep: 699
    Location: Smithtown, New York, USA

    Stephen Ditmore Senior Member

    Point well taken, but there were other medium displacement boats between 30 and 40 feet racing, some of which were in racing trim. While the boat on which I was a guest was the worst case, other boats were also pitching badly. As I recall the Wabbits, the smallest boats racing, finished first and second, with only one or two other boats anywhere near them.

    Mike, I don't know about Americans being prejudiced against heavy. Seems to me there are plenty of heavy boats around, and I think some are fine vessels. When pushed to travel at hull speed downwind they seem to roll and need constant correction on the helm to travel in a straight line, so I think the truth should be told when it comes to issues of directional stability, and I think comparisons should be made at equal speeds (not comparing a boat going slow to a boat going fast). I've had some wonderful experiences aboard traditional designs, too. I remember well sailing a Wianno Senior as it charged along to windward like a freight train. The type has its merits.... I'm just saying I'm skeptical of formulae that predict heavy displacement boats will always have a more comfortable motion. It runs contrary to my experience.
     
  14. rayk
    Joined: Nov 2006
    Posts: 297
    Likes: 15, Points: 0, Legacy Rep: 146
    Location: Queenstown, NewZealand.

    rayk Senior Member

    I see your point. The light sporty boats had the most fun and demonstrated performance.
    The wabbits can accelerate in your given conditions. But without enough wind even wabbits are gonna have a crap day pitching rolling and heaving in the swell.
    If there is enough wind to knock down the wabbits, the cruisers will have enough to get moving and enjoy themselves.
    The achilles heel of cruising boats in light weather is displacement and sail area. When the wind picks up, its waterline length. When its howling a bigger displacement seems more desireable.
     

  15. Vega
    Joined: Apr 2005
    Posts: 1,606
    Likes: 26, Points: 58, Legacy Rep: 132
    Location: Portugal

    Vega Senior Member

    Detachable keels are bulbed keels or canting keels?

    Anyway, it makes no sense, they are all different. Why do you think they will have more difficulty to return to the upright position than a good ocean cruiser like the Najad 44 or the Hallberg-Rassy 40? Or do you mean they will stay inverted, no matter what?
     
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.