Arne Kverneland wrote:David,

is there a formula for this STIX number which will let an ordinary human calculate the number for his or her boat, or does one need a computer program to work it out?

Arne

Hi Arne

I know for sure that a spreadsheet exists, but i can put a hand on it. I am currently waiting for my job the latest version of all CE ISO norms concerning small recreational boats. In there are the 5 norms concerning stability that is ISO 12217. As soon as I receive it, I will let you know. The calculation itself is quite complex and require a lot of infos, some of them could only be provided by the boat designer or require you to reverse engineering your boat and have access to a hydrostatic program.

Antoine

David,

I would advise anyone thinking of a small ocean or offshore cruiser to quiz the designer about the STIX number (stability index).

I've always believed that deep drafted, long keel hulls are the most seaworthy, but am beginning to question my assumptions, especially for junk-rigged vessels.  Perhaps a shallow-draft hull with high form stability (firm bilges), retractable board and rudder but high freeboard, maybe even with the coachroof taken right out to the gunwhales, giving tremendous reserve bouyancy, provides a different kind of stability, plus the ability to slip sideways from breaking crests.  I am not talking about boats to win races here, just indulging in a purely speculative rumination about seaworthiness.  The traditional junk hull design is an excellent example of this.

Gary, I agree with you about that jib.  Kind of defeats the purpose of having junk rig, though I understand it is only intended to be used for very light drifting conditions.  Still too much bother.  I'd turbo charge the junk sail instead, make it a bit bigger and give it some camber.  The mast is in a tabernacle and can be lowered, with a watertight bulkhead aft of the mast.  I like the watertight bulkhead and can see that for some cruising grounds the tabernacle would be useful, though I probably wouldn't bother as I am not so keen on poking up inland waterways where it would come in handy to pass under fixed bridges etc. 

Which brings me to Arne's comments.  When I am sailing close inshore I often wish Arion was a faster, more weatherly boat, but once I am well away from the land I am happy to have such a strong, docile boat.  I don't care if it takes me a bit longer to get there.  The Tasman 24 was intended for ocean cruising, but with the ability to tuck into shallow waters too.  It all depends on what one wants to do with a boat.

I like sharpies, however, and would happily choose one if I was planning to cruise predominantly in shallow waters.  I am currently re-reading The Riddle of the Sands and can see the charm of such a boat for cruises of that type.  I am not too worried about standing headroom.  Comfortable sitting headroom is ok with me, as long as you can sit at the galley and chart table as well as the saloon.  I can see myself in a little sharpie with tandem centreboards.  The east coast of Australia has several waterways that would suit this type of craft well.  I built Arion for ocean sailing and still  enjoy the freedom and adventure of the open sea, though my increasingly fragile health suggests that the time is coming when an inshore boat would suit me better.  Just as long as it has a cambered junk sail!