Swain BS_36 Stability curve

Discussion in 'Stability' started by junk2lee, Mar 9, 2011.

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  1. rwatson
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    rwatson Senior Member

    Yah beat me to it Mike.

    And may I add that the sea is perilous enough with just numbers, OR experience - that not to use both is foolish.

    If there was also any reliable data on the success of sacrificing small goats or virgins, I would suggest that as a third option.
     
  2. pdwiley
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    pdwiley Senior Member

    My reply is 'Mary Rose'.

    PDW
     
  3. pdwiley
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    pdwiley Senior Member

    Perhaps it's worth trying with politicians. That'd be a half-win regardless of outcome.

    PDW
     
  4. Jack Hickson
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    Jack Hickson New Member

    When you sail a boat hard in 25 knots of wind, and her side decks are dry, yet your calculations say they are under water, which do you believe? Experience trumps math.
    Tads post 141 gives the AVS as much higher than the majority of modern boats.
    How would Voortrecker do in the surf which the BS 36 is shown in, or pulling her off in 8 to 12 foot seas, being lifted and dropped on her keel every wave for 1/4 mile?
    If I were sailing home from Japan in the huge field of debris from the Tsunami . I would feel much safer in a BS 36, than in Wynands plywood boat , or Voortrecker.
    Friends took 52 days on that route, only the last two days without fog. The rest of the time they couldn't see the bow. How would Wynand do that trip" safely with good Seamanship" in his plywood boat?
    Heave to for 50 days?
    The yield strength of wood is very close to it's breaking strength. For steel it is 45,000 PSI ( compared to close to 1,500 for wood) which means it stretches a long way before breaking, and can bend 180 degrees , then back again, without breaking. Try that with plywood,.
     
  5. rwatson
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    rwatson Senior Member

    Very vague ... which boat? which calculations?

    You are making up an epic excuse - and if the maths actually did give a different story, either the mathematician is inept, or the load in the boat changed. It would be your job to find out which it is if you were any type of designer.

    We dont care if you think you know it all - its your prospective customers who care, and there are plenty of other boats to choose from if you dont want the business.
     
  6. pdwiley
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    pdwiley Senior Member

    I am sick & tired of hearing that claim. It's utter, utter ********. 2.4 to 3.6m seas generate 3139.2 N-m/m^2 of surface area, using 2.7m as the median value. Given a boat with a 3m beam that's just on 10,000 N-m of energy.

    In addition a 2.4-3.6m wave hitting a 1.5m or less submerged reef is a fully breaking wave so the energy *is* applied to the forward face, the wave is not in it's deep-water state where most of its energy is oscillating.

    It's been a very long time since my degree in coastal geomorphology but I do remember some of it and here's a reference to a wave energy calculator for people who want to play with numbers.

    http://www.coastal.udel.edu/faculty/rad/wavetheory.html

    Basically this claim falls into the same category as the BS claim about breaking through 100mm solid ice in a BS 31 equipped with a 20HP engine. It is total rubbish.

    PDW
     
  7. welder/fitter
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    welder/fitter Senior Member

    I believe that Tad's BS36 Preliminary Stability Curve is found on post# 104 or 105?

    Regarding healing, in terms of a "no axe to grind" experience of a new owner of a BS36, we have:
    And, from the Origamiboats site:
    While I see little value in anecdotal evidence, it seems to be what Brent best understands.

    Now, for comparison, here's an example of a stability curve for a well-known fibreglass boat:
    [​IMG]
     
  8. Dean Smith

    Dean Smith Previous Member

    Well in 20-25 knots that is not a full sail breeze(Referring to w /fitt Mikes post about those folk-- 15 is
    I think after readings from BS over a number of years(or is it decades) that most of his owners are first time owners and from the excerpt M ike just gave , these folk were no different I,ll surmise they carried full main and furling headsail and they would have been overpowered and possibly not knowing when or maybe> how to shorten up
    I have seen this with cruising folk a lot. they get the headsl in first instead of reefing main and or dumping t he traveller
    Even a very stiff boat hard on in 20 will get her rail down
    They were probably scared witless
    Yes MJ I would step aboard something I had no knowledge of you are correct too in that many yachts never encounter knock down conditions
    And you are right many of these full keel mod draft yachts have very low ballast ratio my first ever build was one such yacht , she was 18 tionne at departure and she had 3-4 tonne in full length box keel inc the steel in the keel. Only saving was her form stability Designed by a dutch NA who had never sailed a boat, a very nice man:)
    Oh and by way I had done huge amt competitive dingy sailing When my friend saw her on hard in building, he said-- she will not stand her rag, so that is what i meant you see?
    later I crewed Maxis and built many fine yachts that were designed by sailing men---- it takes time to learn
     
  9. Wynand N
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    Wynand N Retired Steelboatbuilder

    Brent, you ramble like a fool. And since Im not in the habit of arguing with fools, leave my name and boat building preference out of your arguments and stick to the matter at hand which your boat FAILED first class.

    But as a parting note and to be utterly honest with you, here are my personal views on your boats and regardless what you say, Im not responding to your dodgy arguments any further, so keep it for yourself.

    1. Your boats are extremely ugly and an insult to steel boats in general - geez, that ugly slit and corner at the bottom:eek::eek::eek

    2. Narrow boxy affair and proportionally a disaster - no matter what you do, that ugly shape is rooted in the shape of steel plate size, period

    3. Construction detail (scantling) again an insult to good boat building practices and sub standard and need I re post those famous pictures of the mast step/transverse support in your "design" taken from your marketing video to refresh your mind and newbies to the thread?

    4. Your boat failed provisional static stability calculations so patiently calculated and explained by Ad Hoc.

    4. Supply the data relevant to this thread everyone is begging of you and stop taking the heat off you discussing things not relevant.

    Lastly, if you like steel, please do so. What I like, has bugger-all to do with you or others and has no relevance to this thread. I did told you a few times now to keep my name and building material preference out of your silly argument to detract from the real issue at hand, instead you are trying to discredit me and in so much insulted me by stating Im having poor judgement problems.
    If you like steel and potential rust traps, be my quest, however, look around you, the sailing world are much bigger than the few steel boats around.
    However, Im not asking again and should you keep at it one more time, you will me no choice of flagging this issue with the moderator.
     
  10. Dean Smith

    Dean Smith Previous Member

    Smile Wynand
    yes years ago when I called his boats crap I lost so many points
    Even though I build metal not so pig headed to think they are IT!! In fact unless they are designed built extremely well they are a bloody liability ,
    and IF i were just tooling around and not on coral or surfing down big ocean waves I would choose tupperware or timber
     
  11. rwatson
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    rwatson Senior Member

    Yes, I remember that now. I think he ran into trouble with getting 'proper' plans and specs in order to finish the analysis.

    Given the lack of proper hull studies for the boats, each plan is probably just cobbled together with the current 'experience' that BS is currently re-living.

    It appears from some sources you quote, that the studies may not be as far off reality as the designer would like.
     
  12. HReeve
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    HReeve Junior Member

    I love that the only past performance which you accept as "proof" of a design, is the performance you quote, then you dismiss what others offer.

    There are plenty of examples of well-built, good sailing, plywood boats.

    Ragtime

    [​IMG]

    and of course, the quintessential PNW boat, one of which can be found in just about any marina in the area, the Thunderbird.
     
  13. Jack Hickson
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    Jack Hickson New Member

    Tad's post 141 gives the BS 36 an AVS over 160 degrees, after the mistakes in his previous calculations were pointed out to him.
    It would be even higher, if he calculated the center of gravity of the interior and its contents below the waterline, and the tankage under the floor, where they are, instead if halfway up, where they are not.
    The AVS of over 160 degrees for the Contessa, makes my point about more traditional beam lenght ratios and deck shapes having a positive affect on AVS.
    MOM was not built to the design. The Winnabago pilot house with the super heavy 5/8th glass picture windows were entirely his modification. That definitely affected stability negatively. The guy he hired, had, as a main objective , maximizing the number of paid hours for himself in the project. He bought a lot of new gear, incuding , for example , trendy blocks, which he was told how to build for a couple of bucks each.
    His landlord, a very experienced BS 36 cruiser, who had got one sailing and on her way to Japan for $17k, said he never saw anyone spend so much money so freely and unimaginatively.
    There are no "Huge Waves " in Georgia Strait. Given it's limited fetch, the highest they can get in any winds, is around 8 feet. Such an unreliable source of dis-information, explains your misconceptions.
    I have lived under a plywood deck , long enough for one lifetime. I remember a cold molded plywood boat in New Caledonia, which was on her way from Brisbane , beating to Fiji. Built in 1905, she was as strong as the day she was built , definitely the strongest way to build a wooden boat, but less than a tenth the strength of a BS 36. Like all older wooden decks, the crew said sailing her was like living under a garden sprinkler. My experience with a plywood deck was the same . I remember seeing solid ice lining the underside of the deck, with the stove going full bore. Not much of an insulator. For folks like Wynand, who cruise only in sub tropical regions, the inabilty to insulate wood, without incuring dry rot problems, is not an issue, but for us northern cruisers, sprayfoam is mandatory. Unlike steel, rot begins deep inside the material, where it can advance to dangerous porportions, before warning the skipper.
    I know some of the best and most meticulous wood workers, who have built their own wooden decks with the utmost of skill and care. All have leaked eventually, regardless of how meticulous and epoxied their efforts.
    Take a sledgehamer to the middle of a piece of 3/16th plate, then a piece of plywood, then try to tell anyone watching, that they are the same strength and toughness. Better yet , make bets with them that the steel will be holed first.

    Junklee . Would you mind posting those pictures of the BS 36 in the surf, here, again?

    Wynand . If the sight of chines above the waterline are so much more attractive than a hull with no chines visible, then why do guys like you go to so much trouble and expense trying to eliminate them, in radiused chine and round bilged hulls? One would think you would want to add chines to round bilged hulls, to make them more attractive ,according to your theory.

    Pearl Song, sailed by Will Newcomb, a BS 36 with a much heavier box section wooden mast than the steel ones, covered 1006 miles in six days leaving Cabo, beating into a strong NW wind . Then he broke the top 1/3rd off ,but still beat the Gazzelle , which had left the same time as him, to Hilo by several days. The steel mast weighs about the same as the 8 1/2 inch by 5 1/2 inch fir box sections commonly used on boats this size. Being able to weld tangs on , instead of having to bolt them on, also saves some weight.
     
  14. Nurb
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    Nurb Junior Member

    The problem seems to be a lot of assumptions needing to be made due to incomplete data available and no two boats exactly alike. An inclining test and real-world numbers would help this discussion.
     

  15. welder/fitter
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    welder/fitter Senior Member

    Brent, the primary purpose of the Contessa/half-tonner graph was to point out the difference in righting arms. (Those are the numbers on the left side of the graph which run vertically & increase as they ascend.)

    So, which 36 footers have been built entirely to your design? If Haidan's was, perhaps, he'd volunteer his for an inclining test, as the info. would be of value to you and him. I'd even be willing to pay him a few bucks to spend a day or two in Silva Bay.

    Yes, if one were to leave their BS36 at the dock, most wouldn't have a clue about the existence of the chine. But, on even a bit of a heel...
     
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