… Sabre does not promote its Stability Index much (as does Island Packet and others) but I exchanged some email a while back with Sabre hull designer Jim Taylor and convinced him to buy the software to do the STIX analysis on Sabre hulls. I'm looking at his email now and the STIX for the S-426 checks in at 43.4 well above the Island Packet 370 at 43 which is generally acknowledged as an offshore capable vessel.
Euro rating of A ocean requires STIX of 32 as a minimum and is more achievable by productions builders, and STIX of 40 is more often regarded as bluewater suitable by many.
And US Sailing Stability Index for the Sabre 426 is above 123 which exceeds the 115 minimum allowed for entry in the Bermuda Race and which is also quite high for any production boat….
STIX is not very good to compare stability of two different sized boats. One of the main factors in the STIX formula is the length of the boat, so bigger boats will tend to have always a better STIX.
Many European production boats with around 40ft and some with less have a STIX over 40:
Southerly 110 – STIX 55; Jeanneau Sun Odyssey 43 – STIX 44
Swan 44 – STIX 57; Benetau 393 – STIX 43
; Najad 380 – STIX 43; Regina 35 – STIX 43; Elan 37 – STIX 40; Dehler 39 – STIX 42; Benetau First 44.7 – STIX 46
I don’t post more because most of the designers find it a not very useful tool to access boat stability and they don’t publicize it. So I would not give STIX number too much value. It tends to favor some boats in detriment of others without any reason connected with the boat real seaworthiness and stability.
It was popular in Europe on the first years till it was clear that it not a very good measure of boat stability.
A stability curve will give you more information about the boat static stability and some other indicators will give good clues about the dynamic, stability being freeboard one of the more important (a big freeboard is bad for dynamic stability).
About what you call US sailing stability index I am a bit at loss with it. I can see that it relays heavily on the boat LPS, but I don’t know what it means MB and DSPM (displacement?) to find the CI or LSMO for finding the SI. Does anybody know?
… Most productions boats, Catalina, Hunter, IP, Bene, Jenneau etc all use a pan or grid system that bonds the hull to the grid thus giving structural stability to the hull. On impact from a submerged object, it is possible that the impact will cause the grid adhesive bond to separate from the hull thus compromising the strength of the vessel. A boat built like Morris, Sabre or others that do not use structural pans will more likely flex and the overall bonds of the bulkheads which are glassed into the hull will not compromise the vessel. …
Those grid systems are not bonded to the hull, but fiberglassed to it till they become a part of the boat. I cannot see how they would become lose (if the boat is properly made).
Far more important is a lead keel and a steel grid (ideally stainless steel) fiberglassed to the hull, not because the other kind of grids don’t work perfectly but because the problem is not on the distribution of the forces or its fixation to the hull, but on the link between the Keel bolts and the fiberglass (cutting force). If the steel bolt keels are fixed to a strong steel grid, that fixation is incomparably stronger.
There are several top range boats that use this system.