Sailing boats' Stability, STIX and Old Ratios

Discussion in 'Stability' started by Guillermo, Sep 3, 2006.

  1. Guillermo
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    Guillermo Ingeniero Naval

    Claus, I don't follow you. I DID NOT say 'smaller', but 'greater' Please read again carefully. And if you take the care of working down numbers, you'll find that a 96 mm diameter opening has a GREATER area than 7200 mm2 (7238 mm2, to be precise. And two 68 mm dia. ones totalize 7263 mm2).
    And those are small openings, in my opinion, the type of a deck mushroom vent which's watertightness degree doesn't fulfill level 3 requirements.
    My understanding is that Φda1 is conceived for such types of openings. There's something similar at the rules for the openings of outboards' cables in outboard wells. But now I'm at home and do not have ISO book with me. On monday I'll check and post. I'll also check ISO 12216, were I think I'll find some extra support to this.
    Cheers.
     
  2. Vega
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    Vega Senior Member

    Sorry not having replied more promptly, as I should, because what you are doing is not right.

    You say that I have done that on other occasions, (I mean, contradicted and being "irrespetuous" to you), but obviously you are mainly saying that I have done it in this thread, otherwise it would not make any sense to say this in this thread.

    To show that I have been “irrespetous” (disrespectful ?) to you in this thread, you seem to think that it is right to quote a serial of out of contest quotations from another thread, without any information of that fact, inducing that way, people to think that I have said those things in this thread.

    Well maybe it is right by your rules of conduct, not by mine.

    I will post the entire post where I have said those “irrespetous” things to you (the quotations you make).

    I feel it is necessary, because it is the only way to put those quotations of mine in contest, and let people see what they really mean. Certainly I was not trying to insult you, only saying what I thought it was true, and explaining why.


    http://www.boatdesign.net/forums/showthread.php?t=12193&page=5&highlight=light winds (post 66)

    About being Polite…well, Guillermo, I have tried, especially in this thread.
     
  3. Guillermo
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    Guillermo Ingeniero Naval

    Paulo,
    As you've probably noticed, I was very upset with that your scorning post, and ceased answering you because I didn't want going down into that level of personal aggresion discussion. After summer I tried to be nice to you again, just for the sake of these forums, but I realize it's of no use. You came back in with the same kind of attitude. Well, I'm not available to this nonsense anymore.
     
  4. Guillermo
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    Guillermo Ingeniero Naval

    Now let's analize how STIX varies with the several input data. A kind of "what if" game. I'll use the data of the RED boat.

    Originally we had:

    Vessel Name: “RED MODEL” (LIGHT)

    INPUTS

    Overall Hull Length 11,98 m
    Length Waterline 10,57 m
    Flooded Buoyancy (Y/N) N
    Beam Waterline 3,27 m
    Beam 4,1 m
    Displacement MSC 5165 kg
    Displacement Max 6190 kg
    Height of CE above DWL 6,87 m
    Height of CLR below DWL 0,95 m
    Angle of vanishing stability 123 deg
    Downflooding angle 137 deg
    GZ at downflooding angle -0,23 m
    GZ at 90 degrees 0,58 m
    Sail Area 71,1 sq.m
    Area to flooding (Agz) 74,46 m.deg
    Area to AVS 75,56 m.deg


    RESULTS

    Base Length Factor (LBS) 11,040
    FL 1,001
    Displacement Length Factor (FDL) 0,914
    FB 2,519
    Beam Displacement Factor (FBD) 0,815
    FR 3,066
    Knockdown Recovery Factor (FKR) 1,146
    Inversion Recovery Factor (FIR) 1,010
    Dynamic Stability Factor (FDS) 1,381
    Vaw Not aplicable
    Wind Moment Factor (FWM) 1,000
    Downflooding Factor (FDF) 1,250
    Delta 0

    STIX 38,838

    DESIGN CATEGORY A
    Wave height max 7 metres
    Windspeed max. Force 10


    Now increasing LOA from 11,98 m to 13,0 m (just increasing overhangs to an oldies style one), we realize STIX (you may check it with the spreadsheet I've posted before), instead of increasing, DECREASES from 38,838 down to 38,771
    Not a big deal, you may think, but in the limits this can make a long overhangs boat not categorizable under Cat A, while an squared ends one could pass (with all it's marketing consequences).
    But it will have not only marketing consequences, but also safety ones, because surviving in rough weather conditions, in situations where a boat is heeled 90º or more, the boat with longer overhangs probably is able to defend itself better than a squared one. Rolf Eliasson states that for those conditions probably is LOA what should be doubled in the formula and not LWL.

    (To be continued...)
     
  5. Vega
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    Vega Senior Member

    Guillermo, I agree with you. There is no pleasure in replying to "scorning posts", even if a reply is needed, just to show that there was no reason for that “scorning”.

    But may I remind you that in this thread it was you the only one who made scorning comments:

    I hope that this disagreeable matter is finished, because I would like very much to have time to post about the subject of this thread: The STIX numbers.

    No hard feelings,

    Vega (Paulo)
     
  6. Guillermo
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    Guillermo Ingeniero Naval

    Thanks, Paulo.
    I recognize I overreacted. Let's go boating again.
    Cheers.
     
  7. Guillermo
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    Guillermo Ingeniero Naval

    Claus,
    6.4.8 states that Φd shall be taken as the least of the following: Φdc, Φdh and Φda1. This last I've already posted what it is. The other two:

    Φdc: Downflooding angle to cockpits that are not quick draining according to ISO 11812
    Φdh: Downflooding angle to any main access hatchway.

    Degree of watertightness 3 is "protection against splashing water", as known.

    This, united to the relatively small area required, is what makes me think Φda1 relates to small openings. But I may be wrong, of course. In my opinion the sense seems to be this one, but I agree with you that redaction is not clear enough.

    By a quick look I have not find a clue neither in ISO 12216 nor in ISO 11812

    I would love to know other people's opinion or firm knowledge on this. Anybody?

    On my side, I'll put the question to a Notified Body, to find out how they understand this. If I get an answer, I'll post it here.

    Cheers.
     
  8. Vega
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    Vega Senior Member

    Guillermo, I am relieved. I believe that both of us "fervemos em pouca água" (and I really don't know how to put this in English), so I believe that that the guilt in what concerns overreacting, is not only yours. I guess that in what concerns temper, we are not very different. :p

    Cheers

    Paulo
     
  9. Guillermo
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    Guillermo Ingeniero Naval

    Oceanis Clipper 44 CC data?

    I would very much appreciate if somebody could provide accurate info on the Beneteau OCEANIS CLIPPER 44 CC. I've been sailing one of those for several days in the open waters of the Canary islands and I would like to analize her numbers against my sailing experience. Specifically, stability data and curves will be most appreciated.

    A first glance to numbers, as provided at http://www.beneteau-owners.com/
    and http://www.beneteauusa.com/sail/previous/center/44cc_intro.php
    but using I,J,P,E from the Oceanis 440, gives the following:

    Lh = 13,2 m
    Lwl = 11,2 m
    Bmax = 4,25 m
    Bwl = 3,83 m (as 0.9 Bmax)
    Draught = 1,75 m
    HD = 0,75 m (guess)
    Disp = 12598 kg (full load, 6 crew)
    Ballast = 3100 kg
    Sail area = 75,7 m2
    Power = 72 HP

    Length/Beam Ratio L/B = 2,87
    Ballast/Disp Ratio W/Disp = 0,25
    Displacement/Length Ratio D/L = 250,11
    Sail Area/Disp. Ratio SA/D = 14,21
    Power/ Disp. Ratio HP/D = 2,59 HP/ton
    Hull speed HSPD = 8,12 Kn
    Potential Maximum Speed PMS = 8,23 Kn
    Velocity Ratio VR = 1,01
    Capsize Safety Factor CSF = 1,84
    Motion Comfort Ratio MCR = 32,91
    Heft Ratio HF = 1,03
    Angle of Vanishing Stability AVS = 116 º
    Roll Period T = 3,23 Sec
    Roll Acceleration Acc = 0,11 G's
    Stability Index SI = 0,76


    As per a first estimative, the STIX should be around 60, so well into the A Category. As said, more accurate info will be greatly appreciated.
    Thanks in advance.
     
  10. Vega
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    Vega Senior Member

    ISO 12217 STIX: 34

    AVS: 110

    I don't know if I can find a RM curve. The Avs and the STiX are on the low side.

    Cheers
     
  11. Guillermo
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    Guillermo Ingeniero Naval

    Thanks, Paulo.
    Those STIX and AVS seem to be too low for such a boat. Did you get them from the manufacturer/designer?
     
  12. Vega
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    Vega Senior Member

    Yes the data is provided by the manufacturer and I also think that those numbers are low for a 44ft boat.

    Unfortunately it is not the only case:

    BAVARIA 42 ISO 12217 STIX: 36
    BENETEAU CYCLADES 43 STIX: 36
    DISCOVERY 55 STIX: 37
    BENETEAU 50 AVS 109 ; ISO 12217 STIX: 41

    To have a STIX of 60 in the 45ft range you would have to look at another kind of boats, for instance to the Malo 45 (STIX: 62).

    Cheers.
     
  13. Guillermo
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    Guillermo Ingeniero Naval

    This supports my understanding that a lot of pressure was done from manufacturers when the stablishing of the STIX thing. Many boats nowadays categorized as being "A", do not fullfill the requiremnts for proper blue water cruising, as I understand it.

    After logging 300+ miles in the Canary islands with the Oceanis 44 CC, in open waters and nice weather conditions, I have to say she has quite uncomfortable movements. Measured rolling period aboard is around 3 seconds, which agrees quite well with the estimated one. An this for a boat with a 4,25 m breadth.
    Sleeping in the forward bunks and even in the cockpit is quite uncomfortable even with the slightest chopping/swell, both at sea or at anchor. And this for a very heavy full load cruising condition (My friend carries a lot of gear aboard, we had full tanks and and we were 5 big boys), so probably being the boat close to a 13 tonnnes displacement.
    If we work numbers for what Mmsc could be (around 10842 kg), we get:

    Ballast/Disp Ratio W/Disp = 0,29
    Displacement/Length Ratio D/L = 215,25
    Sail Area/Disp. Ratio SA/D = 15,7
    Motion Comfort Ratio MCR = 28,33
    Heft Ratio HF = 0,89
    Roll Period T = 2,84 Sec
    Roll Acceleration Acc = 0,15 G's
    Stability Index SI = 0,67

    So even worse than the ones I posted previously.

    Further on, the steering system is not enough safe, in my opinion, with the autopilot disengaging the wheel. The keel configuration (low draught, winged) and the assimetrical hull lines when heeled, make for an excessive leeward walking. The low freeboard at the bow, along with the assimetrical heeled hull, makes the bow very wet, embarking green water on the forward deck when beating to winward, even with as low as 0,7-1 m waves.

    It's amazing a boat this size and configuration can have an STIX as low as 34. In my humble opinion it should have been categorized as "B" at its most. I agree with Eliasson's statement about being 40 a much better lower limit for Category A. By the list you have posted, only the Beneteau 50' would have fulfilled the requirement (!). I also agree with him it makes not sense to favour plumb bows. A well conceived reserve of buoyancy forwards is important. Interesting to realize now that freeboard at the bows is not taken into account to stablish the STIX number, which is supposed to give a clue to the seaworthiness of a boat.

    Being totally honest, I think most of this kind of boats should be categorized as 'C'. Nice weather coastal cruising 25 miles away from land (What some EU countries legislation allows for this category) is quite enough for them.
     
    Last edited: Oct 22, 2006
  14. Vega
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    Vega Senior Member

    Guillermo I was waiting for someone to reply, not wanting to turn this into a dialogue...but as no one has posted, I would like to comment on your statements.

    I agree with you, without going to the point of saying that this boat should be classified as class C.

    I have already said that for me, one thing is seaworthiness, other is comfort and the two are not necessarily linked.

    For example, take a look at the STIX ,AVS, and seaworthiness of these very sporty and uncomfortable cruiser-racers:

    Elan 45 : Stix 44, AVS 124 ;

    Beneteau First 44.7 : Stix 41, Avs 130

    X-Yachts IMX-45 : Stix 46, Avs 124

    X-Yacht IMX-40 : Stix 47 Avs 132

    J 133: Stix 46, Avs 130

    Why does the Beneteau Oceanis 44 cc have such low numbers on seaworthiness? The Oceanis 411 is smaller and has a higher Stix (37). At first sight, that doesn’t seem to make much sense.

    You know, some years ago, when Bavaria 40 Ocean came out in the market I was interested in it. It looked like an Oceangoing boat (very much alike the Halberg-Rassy 40), so I got some detailed information only to be vastly disappointed. That boat had the same hull as the “normal 40”, the same ballast, only the interior and upper deck were different.

    As the boat had more freeboard and more weight up, it would have a higher center of gravity, compared with the “normal version” and it would not be more seaworthy, but less. Ridiculous!:rolleyes:

    I think that with the Oceanis 44cc it happens exactly the same.

    This time, about comfort, in what regards the Oceanis 44 cc, I fully agree with you. That boat is sold under the image of a comfortable oceangoing cruiser, so it should be comfortable and seaworthy. It is like selling a car that looks like a Mercedes, has the safety of a cheap Fiat and it is as uncomfortable as a Ferrari.:p

    Cheers
     

  15. luso
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    luso New Member

    Hello,
    You guys are very knowledgable.So I wonder if you could help us. We have a 48' schooner metal hull made by Carof design in 87. I believe the model name is Lex Erterna. We could never find any information about her estability and I 'm very curious about it.We've been refiting her for the past 6 years. We are getting close to being ready to leave port and sail around for awhile. I am always wondering about her limits of estability. Would she flip back? How long would that process take? How far can she heel? Maybe you could help us answer these questions? Here goes some info on her:
    Hull 48'
    loa 42'
    beam 14.5'.
    hard-chine,
    deadwood cut away type of keel,
    freeboard 5',5"
    displacement 30.000[I believe in metric]
    We would appreciate very much any info you could give us
    thank you, Luso
     
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