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shaggybaxter said..

Andrew68 said..

Out of interest why did you need the test ? Doesn't the ISO cert cover you ?

Not in Aus, which makes us a bit unique in this regard. Sailing Australia only accept an ORC stability test rating for Cat 2 and 1 races. Everywhere else in the world accepts the ISO cert. No bloody logic as to why, it just is.
Individual clubs will overrule it for a race. QCYC did for the Gladstone, and for next year Prince Alfred club got me clearance for PIttwater to Southport, bless 'em..
CYCA have not for the Hobart.

Hi Shaggy,

From my reading of the rules, Appendix S7.B.2, it is pretty clear that you need an inclination test to confirm the the ISO certificate for Cat 1. All the sister ship ORC certificates give a rating that is in fact worse the yours (about 104-110). Not promising!

Category 1 Races: ORCi Stability Index of 115 or greater, or ISO 12217-2 Design Category A except that the STIX Number shall be increased to a minimum of 35. For Category 1 races, the hydrostatics and stability demonstrating the yacht's compliance with ISO Category A shall be derived from measurement of the freeboards and righting moment of the actual yacht by a qualified source.

For Cat 2 races (pretty much everything except S2H), there is slightly different wording that suggests a measurement test is not required, or have I mis-read the interpretation ?

Category 2 Races: ORCi stability index of 110 or greater, or ISO 12217-2 Design Category A.

What am I missing ?


https://s3-ap-southeast-2.amazonaws.com/piano.revolutionise.com.au/site/dmmqegh5tpkojlb4.pdf

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shaggybaxter said..

MorningBird said..

BROWNSMTRACE said..
So the old narrow 51% ballast ratio wooden boats, if they didn't leak where more seaworthy??

More stable maybe, but seaworthiness covers much more than stability.
I do believe from a story of one that ended on Middleton Reef that they were very tender, the righting moment causing a very sharp motion.

That's interesting MB. Fusion is very stiff, so when beating to windward (non planing) in short sharp seas the motion is very sharp, violent almost. This is where the wide beam and a deep heavy keel work against me.
If I lift the keel, the motion is obviously a lot more rolly polly, but much more gentle in the oscillation.

Once the wind is abeam, or you're running, and you start planing, the motion is completely different. Even in big seas it's very smooth and stable.
Sidenote: Its interesting, I have had only one guy (complete newbie) get seasick to date. Most stomachs seem to find a stiff boat more palatable even though the action is more violent.

i agree about the sea sickness thing pagan has very high stability but being narrow and heavy rolls like a pig though never bangs off a wave gives a beautiful soft motion but does seem to encourage seasickness
when sailing on boss high performance cat extreme beam light weight more stable upside down ridiculous jerky motion at sea nearly impossible to drink out of a cup tea no seasickness

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Andrew68 said..

For similar designs, ballast is very a good indicator of righting moment. Very generally a Ballast to Displacement ratio of over 40% or a stability index over 115% is considered "stiff", however lots of other factors come into play that affect ability to resist capsize. In fact some argue that it makes very little difference at all when a wave picks up a boat and spins it upside down. Practically relates more to how much sail a boat to hold and how comfortable it rides.

A

My Currawong is 120.5 in case your interested Andrew. I presume that calculation was done with the headsail furler drum off.

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shaggybaxter said..

Yara said..

shaggybaxter said..
I'm right into this topic at the mo, as I failed a heel test that was completely at odds with my ISO cert.
It is a mind numbingly complex subject in parts, but quite fascinating even understanding the fundamentals.

It is really not that complicated in basic principle, the difficulty comes in calculating the buoyancy from the immersed hull and superstructure for each angle of heel. Would be very interesting to see details of the failed heel test and the ISO data. Do you have any pics of the test?

G'day Yara,
Here ya go, this is my stability test...only gives me an AVS of 112.
The test was 2 x 5 mtr pole with 100kgs hanging off the end, it didn't heel the boat more than two degrees. What they are actually determining is the centre of gravity, not actually the amount of righting moment, so hence the low heel angles are not a factor.
I'd perosnally be happier heeling to a bigger angle to get a more accurate result.
Or do it on a non windy day.











Aaannd......this is my ISO cert numbers, an AVS of 118.
I need an AVS of 115 for Hobart, or any Cat 1 race. So the Pogo is illegal in any Cat 1 or Cat 2 race in Aus under ORCI. The French are still wetting themselves laughing about it, as we are the only country in the world that the 12.50 does not qualify for Cat A ocean racing, or a Cat 1 race.




The issue appears to be a formula tweak in the ORCI calcs for modern beamy designs. There's an awareness at ORCI of there maybe a problem, but no action yet.

I cannot see how a simple test with a couple of degrees of heel can give you the angle of vanishing stability. In the STIX data, it looks like it was actually measured at 115.6 and they are saying it exceeds the minimum requirements.

I agree Yarra what happens if initial stability is tender as in old style yachts then picks up incredibly after that ?

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Andrew68 said..

shaggybaxter said..

Andrew68 said..

Out of interest why did you need the test ? Doesn't the ISO cert cover you ?

Not in Aus, which makes us a bit unique in this regard. Sailing Australia only accept an ORC stability test rating for Cat 2 and 1 races. Everywhere else in the world accepts the ISO cert. No bloody logic as to why, it just is.
Individual clubs will overrule it for a race. QCYC did for the Gladstone, and for next year Prince Alfred club got me clearance for PIttwater to Southport, bless 'em..
CYCA have not for the Hobart.

Hi Shaggy,

From my reading of the rules, Appendix S7.B.2, it is pretty clear that you need an inclination test to confirm the the ISO certificate for Cat 1. All the sister ship ORC certificates give a rating that is in fact worse the yours (about 104-110). Not promising!

Category 1 Races: ORCi Stability Index of 115 or greater, or ISO 12217-2 Design Category A except that the STIX Number shall be increased to a minimum of 35. For Category 1 races, the hydrostatics and stability demonstrating the yacht's compliance with ISO Category A shall be derived from measurement of the freeboards and righting moment of the actual yacht by a qualified source.

For Cat 2 races (pretty much everything except S2H), there is slighting different wording that suggests a measurement test is not required, or have I mis-read the interpretation ?

Category 2 Races: ORCi stability index of 110 or greater, or ISO 12217-2 Design Category A.

What am I missing ?


https://s3-ap-southeast-2.amazonaws.com/piano.revolutionise.com.au/site/dmmqegh5tpkojlb4.pdf

G'day Andrew,
You're not missing much at all, pretty much have it! Yep, all the 12.50's have a crap number. There's quite a few of us wider beam boats in Aus and NZ with the same issue, being an avs that doesn't gel with the boat design, and the ISO does, or appears to.
The tantalising bit is the problem may be evident already, ie: a glitch in the modelling by ORCI. They are responsive which is great, so if we prove it and fix it, it brings the numbers of both ISO and ORCI into line. I'm working on it, but its slow going, me self educating as I go.

Yep, some of the SI's show this reference you posted to an option for ISO or ORCI Cat2. I've witnessed it in SI's before, but attempts to use ISO only on a Cat2 entry were always knocked back, at least at first. The Pittwater to Southport (Cat 2) had this in the SI last year and I was knocked back (they've amended it this year to accept ISO). The Gladstone was Cat 2, is now more like a 3+, and they initially knocked me back but then accepted the ISO.
Hobart is ORCI stab only, no ISO. This is the bit at odds with all the other countries.

Regards the number used by ISO (you probably know all this), its the STIX, or Stability Index number. Under that model,
- Hobart (Cat A Ocean race) requires a STIX of 35. A higher STIX is better.
- Fusion is a STIX of 41.
- A Class 40 is a STIX of 42. (same hull mould as Fusion)

The Class 40 has the same problem as me regards ORCI, an AVS of 112 (fail), STIX of 42 (easy). And I'd bet my life on the stability of a Class 40, those things get flogged in the most punishing conditions and their's not been a prolonged inversion yet.

So the issue is the pass/fail number is markedly different between the two models. And as Sailing Aus mandates the ORCI (mebbe broken?) one, I'm focusing on working with ORCI to hopefully resolve.

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Yara said..

shaggybaxter said..

Yara said..

shaggybaxter said..
I'm right into this topic at the mo, as I failed a heel test that was completely at odds with my ISO cert.
It is a mind numbingly complex subject in parts, but quite fascinating even understanding the fundamentals.

It is really not that complicated in basic principle, the difficulty comes in calculating the buoyancy from the immersed hull and superstructure for each angle of heel. Would be very interesting to see details of the failed heel test and the ISO data. Do you have any pics of the test?

G'day Yara,
Here ya go, this is my stability test...only gives me an AVS of 112.
The test was 2 x 5 mtr pole with 100kgs hanging off the end, it didn't heel the boat more than two degrees. What they are actually determining is the centre of gravity, not actually the amount of righting moment, so hence the low heel angles are not a factor.
I'd perosnally be happier heeling to a bigger angle to get a more accurate result.
Or do it on a non windy day.











Aaannd......this is my ISO cert numbers, an AVS of 118.
I need an AVS of 115 for Hobart, or any Cat 1 race. So the Pogo is illegal in any Cat 1 or Cat 2 race in Aus under ORCI. The French are still wetting themselves laughing about it, as we are the only country in the world that the 12.50 does not qualify for Cat A ocean racing, or a Cat 1 race.




The issue appears to be a formula tweak in the ORCI calcs for modern beamy designs. There's an awareness at ORCI of there maybe a problem, but no action yet.

I cannot see how a simple test with a couple of degrees of heel can give you the angle of vanishing stability. In the STIX data, it looks like it was actually measured at 115.6 and they are saying it exceeds the minimum requirements.

Yeah, and to &*+$ with your head more, the following is how ISO measure for STIX. It appears to me exactly the same as how ORCI measure.

It hurts.

---------------------

1. Waterline Beam, BWL
By inspection, establish an approximate BMAX station and hang a plumb bob over each side. Measure BMAX and insets from the plumb lines to the local waterline beam. By subtraction from BMAX, BWL can be found.
2. Freeboard at BMAX station (IOR FMD)
Measure freeboards both sides.
3. Canoe Body Depth (IOR CMD, Centre Mid Depth)
This will normally be found from the designer supplied line plans or other data.
4. Waterline Length, LWP (IOR L)
Measure as for IRC, subtracting forward and aft overhangs from LOA.

The inclining is carried out exactly as for an IRM/IMS inclination, with the exception that the only freeboards required are those at the BMAX station (2. above). The boat may be in either empty condition be in 'light' sailing trim with all gear and equipment necessary to race the boat. If in the light condition, water tanks must be empty, but small quantities of diesel are acceptable. Any in-mast or headstay furling sails should be hoisted and furled. Otherwise, the mainsail should be on the boom and other sails stowed below. The condition must be declared on the input sheet. Environmental conditions are critical. There must be no current and an absolute maximum of 10 knots of wind, preferably less.

--------------------

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BROWNSMTRACE said..
Being mathematically challenged could any one explain how to work out limit of stability for my yacht in plain English please.
My eyes glaze over with x times y divided by z

Browny,
good thread. I can't explain the whole calc sorry. This is what ISO say about calculating the STIX number;

STIX is the product of a number of different safety/stability related features. These are: Length, Dynamic Stability, Inversion Recovery, Knockdown Recovery, Displacement Length, Beam Displacement, Wind Moment, Downflooding, and Reserve Buoyancy.

Who needs sleep anyway?

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shaggybaxter said..
Hey Lydia,
According to the stab test results, I have a sink rate of 29.2 kgs per mm of freeboard.
What is say a Sydney 38, do you know offhand?
Interested in comparison of the two hull shapes, I dunno if that looks right.

S
For a sistership which slightly heaver than mine
sink rate 21.16 kg with a wetted area of 27.94m2

My feeling is that there is a problem with the ORCi stability calculation for very wide shallow boats as many are not getting consistent numbers.

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lydia said..
My feeling is that there is a problem with the ORCi stability calculation for very wide shallow boats as many are not getting consistent numbers.

There is not very many Class 40 entries in the ORCi certificate library. I wonder how the Melbourne Osaka boats Class 40's got in ? They don't seem to have certificates in the system.

A

Select to expand quote

shaggybaxter said..

BROWNSMTRACE said..
Being mathematically challenged could any one explain how to work out limit of stability for my yacht in plain English please.
My eyes glaze over with x times y divided by z

Browny,
good thread. I can't explain the whole calc sorry. This is what ISO say about calculating the STIX number;

STIX is the product of a number of different safety/stability related features. These are: Length, Dynamic Stability, Inversion Recovery, Knockdown Recovery, Displacement Length, Beam Displacement, Wind Moment, Downflooding, and Reserve Buoyancy.

Who needs sleep anyway?

The ORC admit that their test is BS.
This is their explanation www.orc.org/rules/Stability and Hydrostatics Datasheet Explanation.pdf
All good until you get to the end, where they tell you what they do not take into account. They ignore some pretty important factors, such as the bouyancy from a coachhouse. When you are talking about angles beyond 90 degrees, these things make a difference.

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Andrew68 said..

lydia said..
My feeling is that there is a problem with the ORCi stability calculation for very wide shallow boats as many are not getting consistent numbers.

There is not very many Class 40 entries in the ORCi certificate library. I wonder how the Melbourne Osaka boats Class 40's got in ? They don't seem to have certificates in the system.

A

If you look under the vendor name Andrew you find some. Pogo 40 is a class 40 for example.

so do all these righting calcs take sails in the water into consideration ?

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SandS said..
so do all these righting calcs take sails in the water into consideration ?

That probably throws a spanner in the works.
Like putting the float on the top of a Hobie cat mast.
or a radome that floats put high up on the mast

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Andrew68 said..

lydia said..
My feeling is that there is a problem with the ORCi stability calculation for very wide shallow boats as many are not getting consistent numbers.

There is not very many Class 40 entries in the ORCi certificate library. I wonder how the Melbourne Osaka boats Class 40's got in ? They don't seem to have certificates in the system.

A

Not racing with orc I. Certificates