Grimalkin IS a good design

Discussion in 'Stability' started by Mik the stick, Sep 9, 2014.

  1. Mik the stick
    Joined: Dec 2012
    Posts: 189
    Likes: 0, Points: 0, Legacy Rep: 6
    Location: Devon

    Mik the stick Senior Member

    Tansl My internet took a funny turn again so to answer another thread I'm not easily offended and appreciate all of your help. Perhaps one day Stix will not be such a problem:D
     
  2. TANSL
    Joined: Sep 2011
    Posts: 5,864
    Likes: 220, Points: 73, Legacy Rep: 300
    Location: Spain

    TANSL Senior Member

    Mik the stick, honestly, I have at no time intended to offend. I'm sorry. I can not understand how anyone would understand my previous post to be offended. Sorry, again, really. You have no obligation to know how to calculate STIX for a sailboat.
     
  3. sharpii2
    Joined: May 2004
    Posts: 1,884
    Likes: 93, Points: 48, Legacy Rep: 611
    Location: Michigan, USA

    sharpii2 Senior Member

    I think there are three things to keep in mind when discussing what happened to Grimalkin in the '79 race:

    1.) She didn't sink,
    2.) She righted herself without drowning anyone, and
    3.) She was being sailed in extreme wind conditions which were aggravated by the local sea bottom, which caused towering breakers coming from just about every direction.

    Though it may have certainly helped, I doubt a lower capsize number would have change the outcome by much.
     
  4. Mik the stick
    Joined: Dec 2012
    Posts: 189
    Likes: 0, Points: 0, Legacy Rep: 6
    Location: Devon

    Mik the stick Senior Member

    Tansl In my ongoing quest to learn about NA I found stix to be a problem because it is so involved I did not have enough data on Grimalkin to see if the boat would qualify for the fastnet race now. There are other calculations which can be done which give insight into stability. I beleive Stix is a european invention which forces American builders into complance because without a stix rating American boats cannot be sold in europe. There are several ruling bodies which cover different races. I have they all have one thing in common. Their rules read like lawyers letters.
     
  5. Mik the stick
    Joined: Dec 2012
    Posts: 189
    Likes: 0, Points: 0, Legacy Rep: 6
    Location: Devon

    Mik the stick Senior Member

    Sharpil2 I totally agree with you.
    However as the boat did capsize I wondered if it could qualify today, or be easily modified to qualify.
     
  6. TANSL
    Joined: Sep 2011
    Posts: 5,864
    Likes: 220, Points: 73, Legacy Rep: 300
    Location: Spain

    TANSL Senior Member

    Mik, I think I understand well the problems that you have to learn about NA because I had them when I was young.
    Now calculate STIX can be done only knowing how to add, subtract and multiply. The problem is that calculate some of the data involved in the STIX need to know much more.
    Sorry, really, that the potential market for American yacht builders has been adversely affected by the STIX. It seems a very clever way, although I do not defend it, of eliminating competitors.
     
  7. Mik the stick
    Joined: Dec 2012
    Posts: 189
    Likes: 0, Points: 0, Legacy Rep: 6
    Location: Devon

    Mik the stick Senior Member

    Tansl The UK is a member of the common market and while I am not pro American I have as the years roll by become anti common market for many reasons stix is just one more.

    You may be aware Dave Gerr and another member of this forum had a bit of a falling out. The result was the other guy posted the captains formula for "roll time". I think the captains formula may be better than the one Dave uses. I am inclined to use both and compare results. At this point I would like to say I have several of Dave's books and some of the westlawn PDF's he has published. Furthermore my (limited) knowledge of boats comes mostly from the pen of Dave Gerr.

    As I understand it boats rolling too quickly are very uncomfortable, roll time divided by beam in meters should be between 1 and 1.1 in the ideal boat according to Dave. Rolling too slowly is dangerous because the boat does not right itself fast enough (before the next wave hit?). I calculated the roll time for Grimalkin using both formulas. Captains formula gave 4.77sec the other gave 4.05sec.
    Ideal roll time is according to Dave 3.1sec to 3.41sec.
    Now what that means to me is 3.41 seconds is ideal 3.5 seconds is not ideal what is not clear is WHEN the roll time becomes dangerous. However I think it fair to say Grimalkin is not the best choice for ocean crossings.
     
  8. TANSL
    Joined: Sep 2011
    Posts: 5,864
    Likes: 220, Points: 73, Legacy Rep: 300
    Location: Spain

    TANSL Senior Member

    It amazes me that the STIX has become a powerful business tool. I never would have approached the study of the STIX in these terms. I always thought it was something like a guarantee of the safety of a boat.
    As for the formulas you use, sorry, I can not comment, I don´t use any. When I want to know if a ship is stable enough, I reckon its stability parameters and check if it is within the rules or what similar boats have. No doubt that in a first stage of the project to handle some formula is "helping", but with an already defined, and built boat, I do not use these formulas.
    The balance period is a very approximate method for calculating the GM of a ship. The period depends on a balance of factors that vary from ship to ship, and in the same boat, depends on the ship´s displacement in each circumstance. To say that a period of balance is good or bad, I do not see it very reliable, does not allow us to know much about the stability or seaworthiness of a ship. In my opinion, it is a recipe that was given to the captain but it should be used with utmost caution. Nowadays, with so much information on board, would have to find a more accurate method to find out how a boat will withstand the onslaught of sea.
    Since then to say, by a rough estimation of the balance period, that a boat is not suitable for crossing oceans, it seems risky and very sloppy.
     
  9. Tad
    Joined: Mar 2002
    Posts: 2,303
    Likes: 184, Points: 73, Legacy Rep: 2281
    Location: Flattop Islands

    Tad Boat Designer

  10. Mik the stick
    Joined: Dec 2012
    Posts: 189
    Likes: 0, Points: 0, Legacy Rep: 6
    Location: Devon

    Mik the stick Senior Member

    Try as I might I can't work out stix for myself. I am pretty sure that The stix rating for Grimalkin is not going to be good enough for the Fastnet race these days. I think my calculations for roll time are wrong, no matter, I understand ballast on a fin keel and devices like flopper stoppers reduce roll.

    If an anti-roll device caused the roll to slow significantly over the 1.1 ratio suggested by Dave Gerr surely it would be dangerous. My logic is the device would resist and slow the roll but if sufficient roll were caused the same device would slow the return to vertical long enough to get hit by another wave and capsize. If Grimalkin had deployed flopper stoppers before she capsized they would have made it harder for the waves to right her.
     
  11. TANSL
    Joined: Sep 2011
    Posts: 5,864
    Likes: 220, Points: 73, Legacy Rep: 300
    Location: Spain

    TANSL Senior Member

    I do not know what happened to the boat Grimalkin. What I do know is that a boat not stable can capsize but does not have to sink. If the ship sank, it would probably be because some other cause was added to the roll.
    The STIX measured, in some way, the stability of a boat, not her chance of sinking.
     
  12. TeddyDiver
    Joined: Dec 2007
    Posts: 2,565
    Likes: 113, Points: 73, Legacy Rep: 1650
    Location: Finland/Norway

    TeddyDiver Gollywobbler

    The problem with Grimalkin was not the lack of stability, on the contrary, it had too much stability.. upside down, which by some criterions might be a bit of PITA.
     
    1 person likes this.
  13. TANSL
    Joined: Sep 2011
    Posts: 5,864
    Likes: 220, Points: 73, Legacy Rep: 300
    Location: Spain

    TANSL Senior Member

    So do not know what does all this history about STIX. Why are we talking about a method to "measure" the stability?. Someone is mixing things that can not be mixed.
     
  14. Mik the stick
    Joined: Dec 2012
    Posts: 189
    Likes: 0, Points: 0, Legacy Rep: 6
    Location: Devon

    Mik the stick Senior Member

    Tansl I suppose it is me doing the mixing due to my lack of understanding. To recap I'm sure almost everyone thought the Grimalkin was a good safe boat before the 79 disaster I feel that disaster does not make the design unsafe, rather race organizers moved the goal posts.

    I have found a PDF which seems to suggest the grimalkin would get a B class race certificate and the Contessa 32 would get an A. I want to study it a bit before I post it. However to quote this document a breaking wave hitting a boat beam on need only be as high as the BEAM of the boat.to capsize it. Wish I'd known that when I went to Inchgarvie island in an 8ft dingy.

    I have watched a lot of Intercepter pilot boat videos in 9-10M wave makes me think about stability.
     

  15. MikeJohns
    Joined: Aug 2004
    Posts: 3,176
    Likes: 198, Points: 63, Legacy Rep: 2054
    Location: Australia

    MikeJohns Senior Member


    The NA Kim Taylor wrote a good summary of the 98 Sydney Hobart storm (and again stressed the unsuitability of lower stability coastal racers in offshore conditions ).

    Attached is an illustration showing various craft superimposed on the commercial sailboat stability requirments in the UK. Note Grimalkin has been shown for comparisson on this plot along with the S-H rolled craft.

    There is another important factor related to LPS being the average time for the inverted craft to roll back upright. From memory at 135 degrees its 3 minutes and the time goes up as the LPS reduces. Thats what drowns short tethered or tangled or unconcious crew.
     

    Attached Files:

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.