Sailing boats' Stability, STIX and Old Ratios

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

  1. Michail
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    Location: Chile

    Michail Junior Member

    I have stumbled upon the Flicka boats before, and I loved them. However, there are several problems with them (at least for me):

    1. I have not seen them on sale in Chile. Here, the most common boat type of this size is the microtoner.
    2. They are too heavy. They seem to be trailarable, but it is not something to be taken lightly. And they need a crane for downloading, since they have a draft of 1 m.
    3. I could not find any plans available.

    What I am looking for is a practically trailarable boat (max. empty weight 1100 - 1200 kg.) which can be launched from slip, i.e. with a launching draft of something like 60-70 cm. The only way to achieve this would be with a hoistable dagger/bulb keel. (Now such a design is obviously counterproductive for blue water sailing. However, the marina space in Chile is extremely expensive, and may cost much more than the boat itself, so that the trailarability and ease of launching is an aboslute requirement for me.).


    I did not realize that there was a weight limitation for cat A. I have downloaded the ISO 12217-2, and there indeed appears the standard clause which specifies 3000 kg, however, there is also an alternative set of conditions (6.3.2) which apparently do not specify a mass requirement for a A Cat, so in theory one could built A Cat boat of less then 3000 kg. Correct me if I am wrong, because I have just started to look through this document.

    My point is not to try to comply blindly with ISO just for the sake of it (there is no legal requirement in Chile), but only because I think that compliance with it would result in a safer boat.
     
  2. TeddyDiver
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    TeddyDiver Gollywobbler

    You think wrong. You would end up with a pig, a STIX A class pig. Better to make water tight self rightening lift keel boat, be happy with it, and not to worry too much with compliances. That is IMHO
    BR Teddy
     
  3. Guillermo
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    Guillermo Ingeniero Naval

    Michail,
    Forget about the A Class thing for such a boat. There are plenty of safe and seaworthy enough small boat designs around there. Choose the one that better suits your requirements, as Teddy says, buy it or build it and enjoy it.

    Cheers.
     
  4. chr_ramsdal
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    chr_ramsdal Junior Member

    Thank you very much Guillermo for the file you shared! I was about to make a spreadsheet like this on my own, but you saved me that job :) I´m currently drawing a yacht not unlike the Dehler 46 and other light cruisers of the similar dimensions. How to you find data like the ones you listed from existing models? I am not able to find these data for i.e. the Dehler 46 or other popular yachts.. It would be nice to have them as reference point for my own designs.

    Any suggestions on where to find this?
     
  5. Guillermo
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    Guillermo Ingeniero Naval

    Well, this is somekind of a revival for this pretty old and abandoned thread. :)
    Ramsdal, I am not active about this anymore, as I think almost all that has to be said about the STIX has been already said.

    I found data searching the web, asking some manufacturers, with the help of friends in these forums and also doing some rough guessing for those not available, which I noted up in every case.

    Good luck with your "not unlike a Dehler" boat. :)
     
  6. chr_ramsdal
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    chr_ramsdal Junior Member

    OK. Thank you for your answer, even though the thread is old and dusty. I guess the STIX calculation is still the method used today and give the values for CE classification? (..even though there are so many different opinions about the measures and how well they tell a true story about the stability.) Stability is complex, so simplification will off course impossibly be fair for all variations of hulls. I know the basics in what gives higher and lower values and can resonate how my design will be affected, and stick to STIX. :)

    Thanks again. I´ll send some emails to different manufacturer and ask them.

    I´m thinking about building a 2meter model at first, to simulate and test stability, flow, mast/keel balance and so on. Then I´ll see what happens next. I´ll post some renderings from the DelftShip model for those who wants to have a look..
     
    Last edited: Apr 22, 2015
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  7. eddygrove
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    eddygrove New Member

    Greetings,
    New to this forum I was attracted by an age old post regarding the Flicka 20 and a yacht I am investigating, the Amigo 23. It was in another thread "Seaworthiness", so old I was not even allowed to post in it when trying, but with a discussion similar to this.

    It is a specific question to Guillermo, and I do hope that you do not find it way off topic to raise it here, please excuse me if that would be the case.

    I have been interested in small seaworthy yachts for long, but still trying to understand the workings of different designs and their ratings. Reading your post about the Amigo 23 made me REALLY worried, since it is one of the finalists in my search for a small but sturdy cruiser, and since you definitely are an authority in these matters. I would be eternally grateful if you could please take the time to review your post with the very disappointing figures for the Amigo 23:
    PLEASE NOTE: this is a qoute from a different thread "Seaworthiness". (It is now closed so I am not deliberately cross-posting ;))

    What I cannot get my head around is the underlying data. It may well have been updated so that the figures at hand when you did the calculations where erroneous, but I could not tell. Looking at the sailboat data, http://sailboatdata.com/viewrecord.asp?class_id=3527 (new link, link in post is broken) I get significantly different numbers.

    E.g:
    You list a Displacement/Length Ratio of 672,57
    The Sail boat data lists a displacement/length Disp./Len. of 318.37
    I get 264,7 if I have understood the basics at all (1800 kgs/6,8 meter = 264,7) using the same formula as for the Flicka 20 in the Sail Boat data sheet (2495 kgs/6,10 m = 409)

    Please advise.
    Many thanks!
    Björn
     
  8. Guillermo
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    Guillermo Ingeniero Naval

    Björn,
    Yes, those figures for the AMIGO 23 seem to make little sense. I think I discussed this with someone else some years ago and, after working again numbers, things made much more sense.

    I will try to search in the deepness of my files, find out and post again here.
    Best wishes,
    Guillermo.
     
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  9. eddygrove
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    eddygrove New Member

    Thank you so much Guillermo for your reply. That was fast!

    I am looking forward to any input from you on the Amigo 23.

    I used the calulator at http://www.tomdove.com/sailcalc/sailcalc.html and got the figures below. I had to enter the Amigo data myself since it is too unknown to be in the database. Figures are not as extensive as yours, and then there is STIX which I have not yet looked into. Would you say that the Tom Dove calculator is reliable? It's a neat tool.

    Again, I really appreciate that you took your time to answer.

    boatName=Amigo 23
    LOA=22.31
    LWL=17.72
    beam=7.55
    displacement=3968.28
    sailArea=247.57
    displacementToLWL=318
    speed=5.64
    sailAreaToDisplacement=15.8
    LWLToBeam=2.35
    motionComfort=21.58
    capsizeRatio=1.91
    category=cruiser
    ppi=478

    boatName=Flicka 20
    LOA=20
    LWL=18.17
    beam=8
    displacement=6000
    sailArea=250
    displacementToLWL=447
    speed=5.71
    sailAreaToDisplacement=12.11
    LWLToBeam=2.27
    motionComfort=30.82
    capsizeRatio=1.76
    category=cruiser
    ppi=519
    description=Sail Area to Displacement: The sail area is the total of the main sail and the area of the front triangle. I cannot be sure that this datum was entered correctly for each listed boat. A racing boat typically has large sail area and low displacement. A number less than 13 probably indicates that the boat is a motorsailer. High performance boats would be around 18 or higher.​
     
  10. Guillermo
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    Guillermo Ingeniero Naval

    Tom Dove's "Carl's Calculator" is a pretty fine one and you can totally trust it.
    When calculating numers for AMIGO 23 in that my old post I probably took some wrong data figures.

    Unluckily I have lost an old correspondence with someone in Spain who wanted to amateurly build the Amigo 23. I don't remember what happened with that, but I remember the guy was very happy having chosen this particular boat to build.

    Cheers!
     
  11. eddygrove
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    eddygrove New Member

    Thanks,

    In the "Carl's Calculator" draft is not taken into account.
    Wouldn't that substantially affect the stability and motion of a hull, not to mention sailing properties and ability to seek safe harbour?

    I have not fully understood all the parameters of the STIX formula, but it definitely seems more thorough since it encompasses draft in the AVS value.

    A German boatmaker has taken up production of the Amigo 23 again, under the name of Västbris 23. That is what the smallest vessel in the Amigo series from Carl Andersson's pen was called, Västbris 20.

    http://www.bootswerft-funger.de/geschichte.html
     
  12. Guillermo
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    Guillermo Ingeniero Naval

    The parameters we get in the Calculator are neither intended to evaluate stability nor the winward sailing ability. They are just a clue to some basic characteristics of the boat and its behaviour at sea, regarding its movements (comfort), ability to move under sail (power), ability to recover from a capsize and little more.

    STIX is a good clue to stability, ability to recover form a knock down, etc, etc, but we should be cautious to not take as a "seaworthiness figure". It says nothing either about the winward ability, structural strength, and other relevant things to take into account when judging a boat. Not to talk about crew seamanship, of course. ;)
     
  13. mlorch
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    mlorch New Member

    Novice and Stability

    What a great forum, thanks everyone for exchanging thoughts here. I'm pretty new to owning a sailboat and have bought a Bavaria Cruiser 45 last year, mainly to do coastal cruising with the family (2 kids). I did not realize the big difference between the different stability aspects until I started to read this forum etc.
    I think I'm going to be happy anyway with the boat for that purpose. Now, one question I could not really answer for myself is the comparison of the AVS in a mono versus a cat. Basically the AVS for a cat is very low, but initial stability and righting arm are huge. In other words there would be a relationship to the importance of AVS based on beam width. The wider the floating body, the less relevant becomes AVS for overall stability. So, with the newer production boats like my Cruiser 45, which has only an AVS of 113,5, but probably a higher righting arm due to the beam width.
    Is there some sort of graph or chart that talks about that relationship of beam width versus meaningful AVS?
     
  14. TeddyDiver
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    TeddyDiver Gollywobbler

    Not any simple one. As you have propably noted after reading in BDnet there are too many chararacteristic in the play. But generally speaking, the wider the beam (compared to everything else) the closer to AVS 90deg.

    BR Teddy
     

  15. Propaganda 2
    Joined: Jun 2016
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    Location: Belgium

    Propaganda 2 New Member

    Hi all !

    Just a newbie on the forum... I'm the "proud" owner of a Beneteau First Class 12 (a one ton IOR hull design, dating back from 1987) which I've been refitting extensively out of love really... I intend to participate to the "Transquadra" ocean crossing regatta next year. The "only" problem is that I need to provide them with a Cat A STiX calculation which this good old cruiser is not capable of... since I have started works for quite some time and invested stupid amount of money to get her fitted, I am stuck in a "head in the bag" approach and will need to fix this or simply give up the race...

    I'm looking for some guidance on how to get the numbers right. I have some 400 pounds of lead that I can put in the keel bulb (the boat structure has been upgraded and can stand the load). I'm also thinking of putting up a carbon mast (a 60 Kg saving versus the current rig)..

    Anyone can help ?

    Thx !

    B.
     
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