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Displacement Hull Draft

Discussion in 'General Trawler Discussion' started by clnewman, Feb 14, 2007.

  1. clnewman

    clnewman New Member

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    I'm no nautical design engineer, and I'm hoping one of you designers that peruses this forum can answer these questions for me:

    1. Would a draft of 4.92 ft. (1.50m) be unusually shallow for a full displacement hull displacing 83,725 pounds?

    2. Is this light for a vessel with a LOA of 63.25 ft., LWL of 57.50 ft and a beam of 17.17 ft.?

    3. Assuming a rounded bilge bottom, could one expect unusual pitch/roll characteristics, with no bulbous bow, but equipped with active stabilization?

    4. How about roll when anchored, w/o flopper stoppers?

    If you need more data to give an informed answer, drop me an email.

    Thanks,

    Chuck
  2. Loren Schweizer

    Loren Schweizer YF Associate Writer

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    1) No
    2) Yes
    3) No
    4) Yes

    Seriously.
  3. AMG

    AMG YF Moderator

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    On nr 3 and 4, it also has something to do what is above, how many decks and in what material...
  4. clnewman

    clnewman New Member

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    Here's a rendering of the profile:

    [​IMG]

    I apologize in advance if I shouldn't have posted the rendering here. Thought it would help.

    We've just entered into a (very) preliminary discussion re: a possible build of this, and the shallow draft (compared to the draft of similar sized displacement vessels I've come across) sticks in my head as a potential issue. However, the price is definitely right, so it's worth looking into further.

    It's supposed to be all FRP construction. I don't have comprehensive specs yet, so I don't know about the overlays, thicknesses, etc. They're supposed to be coming today.

    We can always add flopper stopper booms (perhaps just 1, not sure) during the build process.

    The light weight also gives me concerns about righting ability in the event of a knockdown. From my understanding, there's only 1500# of ballast in the keel.
  5. AMG

    AMG YF Moderator

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    The righting ability should be no problem, as long as there is no water intrusion.

    For stability a couple of bilge keels could help.

    When I look at the stern extension it appear as this boat is designed to have a bulbous bow? But whatever, S&S use to know what they are doing, so there is no reason for concern I think.
  6. clnewman

    clnewman New Member

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    S&S does have a good reputation, so am assuming all is well with the design. I just received a profile drawing of the vessel, and it shows a bulbous bow. My mistake before.

    I discussed bilge keels with the designer, and he says there are no current plans to implement them. Hull #1 is just out of the mold. If we buy, we'd be hull #2 or #3. Unfortunately, there won't be time to have a sea trial on #1 before #2 goes into production.

    The builder is Queenship, in a yard in Zhuhai, China. Apparently they're now OK financially. Does anybody have any recent feedback (good or bad) on them?
  7. AMG

    AMG YF Moderator

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    About bilge keels, on a GRP yacht they are not as easy to fit as on a metal hull so I should probably not try. There must be a center keel anyway which also helps at rest. Another option that you can retrofit is a mast with a small sail if you should experience too much rolling. It could actually be removable and stored on deck.

    My experience with Far East production is that they are using a little too much material, making the yachts heavy. But with a displacement yacht this may be just favorable.
  8. clnewman

    clnewman New Member

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    A stay sail is indeed an option, as are downrigger booms that not only handle flopper stoppers at anchor, but paravanes while underway.

    As far as too much material goes, this vessel only displaces around 42 tons, so I don't think they're using too much material. If anything, perhaps not enough. Am still awaiting hull material/construction specs.
  9. AMG

    AMG YF Moderator

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    If it isn´t built yet, you don´t know the final displacement...;)

    About paravanes, maybe useful at rest, but underway I wouldn´t use them on a pleasure yacht. I have heard horror stories on incidents when they must be recovered in heavy weather, they can both hurt yourself and crash through portholes or windows...:eek:
  10. clnewman

    clnewman New Member

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    This is true... all specs are estimates. However, I was quoting their preliminary "estimate" for (lightship) displacement. That said, the quoted 4.92' draft is a lightship estimate, too. However, with the hull design as it is, more draft due to higher displacement means less freeboard. A Catch-22, yes?

    I saw The Perfect Storm, too... and have no desire to have paravanes come crashing into my pilothouse :eek: That would ruin my entire day.

  11. Loren Schweizer

    Loren Schweizer YF Associate Writer

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    I am 100% with Lars-- flopper stoppers will, at the very least, remove meat from your hands, if not whole fingers, over time.

    They are, in this modern age of bow thrusters and the like, an anachronism and a royal pain in the @ss to deploy--usually when it has already gotten snotty.

    Get some active fin stabs and pay close attention to the square footage recommendation; if in doubt, get the next size up.
  12. clnewman

    clnewman New Member

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    Am not too concerned about active stabilization... the vessel comes with Wesmar RS9000s with 9 sq. ft. fins... so am good to go there.

    My original thought was the use of flopper stopper discs (as opposed to paravanes) for use while anchored/moored.
  13. JWY

    JWY Senior Member

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    Am chiming in here a bit late, but agree with the comments already posted: negative on added bilge keels on fiberglass, negative on flopper stoppers even the discs at anchor (go with an "at anchor" active fin stabilization system).

    The righting ability of the vessel may be affected by any flexing in the hull at the time of rollover as relates particularly to the windows which may relate to AMG's comments about water intrusion. A staysail that would be large enough to be effective, along with the mast, adds significant weight on the upper deck and combined with davit,dinghy & engine may created a different roll issue.

    Although it has "rounded bilge bottom", is there any mention of chines?

    Judy
  14. cranky

    cranky New Member

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    Active stabilisers require lots of energy therfore one would need a generator running to provided hydrolic power 24/7 On a 60 ft displacent vessel it should be possible to be at anchor for 12 hours running on batteries alone ( assuming one uses the correct equipment ) In this case flopper stoppers are the best option.

    Yes deploying and handeling flopper stopers can be dangerous to the careless or inexperianced but they do work, even better when underway.
  15. Loren Schweizer

    Loren Schweizer YF Associate Writer

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    Hate to disagree, cranky, but stabs actually require very little power, at least in running mode ( 8 kts ).
  16. yotphix

    yotphix New Member

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    mucking around with heavy swingy things on deck in any sort of a seaway is dangerous to anyone. It is merely less dangerous to careful and experienced people. Then again, I suppose you could argue that yachting is inherently dangerous! Running a yacht that size on batteries alone presupposes that you are not running AC or electric rangetops or clothes dryers. Different strokes I suppose!
  17. cranky

    cranky New Member

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    POWER REQUIRMENT FOR STABILISERS.

    Yes the control package uses very little power, maybe 2 amps but the hydrolic package uses a lot, on a 60 ft vessel you would have to pump 5 to 8 gallons a minute at 1500 psi or so, most of us don't think about it because the hydrolic pump is monted on a main or generator. Fine if you want to run that way but on a small vessel there is the option when you want to go to bed to shut down everything.

    In many parts of the world one does not really need air conditioning, it is quite pleasant if you just open a porthole, lots of people still do that, My boss does it just about every night.

    The point I was making is that flopper stoppers do work and work well, for some people they are the right choice.
  18. Loren Schweizer

    Loren Schweizer YF Associate Writer

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    Cranky, you make a good point.
    I dug through my notes and found from real-life that a 77' expedition vessel @ approx. 115 tons displ. running at 8 knots requires approx. 6 HP to run her Wesmar 12 sq. footers.
    I guess that'd equate to about an 8 KW genset; maybe a gal.per hr. burn, or less, and inside a hushbox, not too onerous.

    Flopperstoppers-- God Bless.
  19. tri - star

    tri - star New Member

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    S & S have been around a long time - so I don't think that dismissing their design out right - just because the
    " guesstimated " weight seems too light - is reasonable.

    Perhaps, due to their long experience, they are going for less weight in the design phase.
    Because, as mentioned above by AMG:
    - Asian built yachts, often gain weight during construction.
    And definately, yachts will do so after a couple of seasons of cruising.

    So the court is out on the actual displ., until one or two, vessels are in service.
    To be seen floating, well above their designed water lines
    - or below them !

    To be fair, to S & S - if displ. is an issue. Tell them.
    The easiest thing for designers and builders to do
    - is add weight.
    Usualy, we are working very hard to save a few lbs! Here and there.

    I'd be far more concerned; as to how seaworthy the design is and how easily driven.

    After all; there's always; the option of pouring concrete down below.
    - To stiffen things up !
  20. clnewman

    clnewman New Member

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    I wasn't questioning S&S' experience. Also, my issue wasn't entirely one of weight, but the draft for a vessel of that size (<5' [1.5m]). That's less draft than my 64' semi-planing hull M/Y, which displaces less.

    Hull #1 of this (the S&S) vessel in under construction now, with hull #2 to follow. Would you buy hull #1/2 sight unseen with those spec draft/weight specs? How do they fix an FRP hull if it handles like like a pig or rolls all over?

    I guess my point is to not publish a spec like that if you really don't know (or can VERY closely approximate) what it's going to be. Of course, we won't know until it's in the water... but not on my nickel.