Same stability for deep and shallow draft???

[GTom]

I found a list of STIX values here, within some interesting pieces:

(Bene) oceanis 373 Deep (1.85m) draft: stix 36, AVS 132 degrees
(Bene) oceanis 373 Shallow (1.45m) draft: stix 36, AVS 132 degrees

(Bene) oceanis 393 Deep (1.9m) draft: stix 43, AVS No data
(Bene) oceanis 393 Shallow (1.5m) draft: stix 43, AVS No data

How is this possible?? The ballast weight, shape and material are identical, hulls are identical...

[a64pilot]

I know nothing about Bene's, but do the deep draft boats have a taller mast?

[barnakiel]

A taller mast may/will dictate the dynamic behaviour.

But for a static behaviour (heel degrees / kilograms at boom's end, etc) the ballast or the structure would have to have different distributions.

Can you PLS bring forward the STIX formula? Maybe simply it does not use ballast as a factor?

b.

[GTom]

Originally Posted by barnakiel

A taller mast may/will dictate the dynamic behaviour.

But for a static behaviour (heel degrees / kilograms at boom's end, etc) the ballast or the structure would have to have different distributions.

Can you PLS bring forward the STIX formula? Maybe simply it does not use ballast as a factor?

The STIX-calculation is quite complex, it does include dynamic and static factors:

The 7 factors used to further specify the stability index are:

FDS: Dynamic Stability Factor
FIR: Inversion Recovery Factor
FKR: Knockdown Recovery Factor
FDB: Beam-Displacement ratio Factor
FDL: Displacement-Length ratio Factor
FWM: Wind Moment Factor
FDF: Downflooding Factor

The final formula to calculate the STIX is:

STIX = ( 7 + 2.25LBS) x (FDS x FIR x FKR x FCB x FDL x FWM x FDF)0,5 + Q

where Q is 5 for unsinkable boats and 0 otherwise.

Haven't checked mast lengths though...

[Stumble]

Originally Posted by GTom

I found a list of STIX values here, within some interesting pieces:

(Bene) oceanis 373 Deep (1.85m) draft: stix 36, AVS 132 degrees
(Bene) oceanis 373 Shallow (1.45m) draft: stix 36, AVS 132 degrees

(Bene) oceanis 393 Deep (1.9m) draft: stix 43, AVS No data
(Bene) oceanis 393 Shallow (1.5m) draft: stix 43, AVS No data

How is this possible?? The ballast weight, shape and material are identical, hulls are identical...

I don't know where you are getting the data that the ballast weight is the same for the deep and shallow draft vessels, but I highly, highly doubt it. Typically to get a shoal keel you cut the bottom off and make a heavier keel, with the weight increasing enough to keep the same RM thus keeping the same AVS.

[GTom]

True, I haven't found ballast weight data for the shallow vs deep version.

[roverhi]

Most of the shallow keel boats have much of their weight near the bottom as in a Scheel or winged keel. A deep keel, unless it's got a a bulb at the bottom, distributes it's weight over a greater length so the effective force of the keels moment arm on righting is not a lot different.

[barnakiel]

I am sorry, but we need to know:

"...

FDS: Dynamic Stability Factor
FIR: Inversion Recovery Factor
FKR: Knockdown Recovery Factor
FDB: Beam-Displacement ratio Factor
FDL: Displacement-Length ratio Factor
FWM: Wind Moment Factor
FDF: Downflooding Factor

..."

E.g. ow is FDS calculated? etc.

Saying STIX is say A x B while not defining formulas for A i B is not knowing STIX.

Can someone point us to a place on the net where STIX formula is defined.

For it sounds as if STIX is just another piece of CE idiocy jumbo mumbo pseudo language that nobody knows. E.g. Wiki does not seem to contain proper STIX definition and formula while it does contain things like Black Schoeles options pricing model. How come.

If STIX allows for ballast in the way AVS does, then same ballast just shallower DOES NOT affect the STIX (whatever) number. (Unless one actually adds / subtracts the ballast stub/bilge depth in the process, which in turn renders the AVS formula useless.)

PLS link me to a full STIX formula and I will reflect on the whys and hows.

Cheers,
b.

[hamburking]

Hunter used to make deep draft and shoal draft versions of the same boats (in the late 80s?). I read that they conducted a series of match races, with identical deep draft and shallow draft boats competing against each other. They also swapped crews and skippers to eliminate that from the equation.

What they found was that the shallow draft versions, with their winged bulb keels, performed either the same or better than the deep keel versions. So the winged keel became standard equipment.

FWIW, the winged keel gained notoriety at the 1983 America's Cup, and was attributed for the win. So winged keel production boats were quick to follow.

The water is thin and the bottom mostly rock here in the 1000 islands region, which is my home cruising area, so I appreciate shallow draft AND good sailing performance. However, the first time I put my winged keel Hunter (1994 Legend) into a mud/clay bottom, I came to appreciate how much that keel also resembles a bruce anchor.

[barnakiel]

OK

I have found this:

http://www.boatdesign.net/forums/att...formula-r3.xls

Gimme some time to open the link and read the sheet thru.

b.

[GTom]

Originally Posted by barnakiel

I am sorry, but we need to know:
...
Cheers,
b.

Knowing the formulae wont do much good for us if we don't know all parameters required

[Ardbeg]

My 2 cents worth. Do not know about the formulas however I will tell you I had a 2006 Hunter 33 with a shallow winged keel. I found the boat very tippy and the wind pushed it off course. ( Made it slide).

I now have a 2011 Catalina 375 with deep keel ( 7 foot draft when tanks full). This boat points better to the wind and digs in to the water. No slip what so ever. I regularly sail back and forth across Lake Ontario. I will never go back to a winged keel on a production boat. I think the winged keels on racing boats were deep whereas the winged keels on production boats are shallow.

[boatman61]

Could be in the bulb keel..

BENETEAU 373 sailboat specifications and details on sailboatdata.com

And the wing keel..

BENETEAU 393 sailboat specifications and details on sailboatdata.com

[thomm225]

Here's one AVS Formula: (Limit of Positive Stability)

http://files.sailberkeley.com/Sailin...ty_angle_2.htm

Angle of Vanishing Stability

From the link above:

This formula does not fully take into account the vertical position of the center of gravity (VCG). The VCG can be lowered by a longer keel or by having more ballast (weight of the keel) at the end of the keel. However, according to Adlard Coles' "Heavy Weather Sailing" thirtieth anniversary edition, "The effects of large movements of the VCG on the propensity to capsize was surprising small". Nevertheless, a low VCG will greatly help the boat in righting itself once it has capsized. Thus, boats with a long lead keel or a lead bulb at the end of the keel may have a higher angle of vanishing stability than that predicted by the formula.

A caveat regarding stability predictions: One of the greatest sailing disasters in recent maritime history, the 1998 Sydney-Hobart Race, offered a number or lessons regarding the performance of sailboats and crews in heavy weather conditions. The 1998 Sydney to Hobart Race Review Committee report, summarized by Peter Bush, the committee chair, reported the following as one of the significant findings: "There is no evidence that any particular style or design of boat fared better or worse in the conditions. The age of yacht, age of design, construction method, construction material, high or low stability, heavy or light displacement, or rig type were not determining factors. Whether or not a yacht was hit by an extreme wave was a matter of chance." (Ref: Rob Mundle in Fatal Storm, Publisher's Afterward p 249. International Marine/McGraw-Hill Camden, Maine.)

According to Andrew Claughton in Heavy Weather Sailing 30th ed. p 21 "This (the test data presented in the chapter) suggests that alterations in form (of a sailboat) that improves capsize resistance may be rendered ineffective by a relatively small increase in breaking wave height."

[Cadence]

Originally Posted by a64pilot

I know nothing about Bene's, but do the deep draft boats have a taller mast?

I feel you are right. The amount of sail may be the same, maybe a longer boom, or maybe not sailing as fast. Every thing is a compromise.