Ethan Allen capsize: Lake George

Yes, you can change a vessel to improve stability, which, as I've said, is primarily associated with waterline beam and low center of gravity. Whatever its stability, though, there will always need to be a maximum passenger capacity, and a way of determining said capacity.

 

I agree with you Stephen, but there are a lot of countries where passenger boats or vessels are overloading in such manner that only with the help of the Lord they arrive safe at destination...

I suppose that in States such dramatic accidents are very rare...

 

I'm aware of that, Ranchi, but thanks for mentioning it. The U.S. is at its best when it leads by example (not by preaching). If the U.S., Europe, and not insignificantly Australia, which is putting a very serious effort into good regulation, can set a standard, then our profession can point to that standard as a way to make the sea safer for everyone.

 

How many present, small cruise boats, under 100', would pass a test that required. Full load, all on 1 side, at maximum speed, with moderate chop and cutting the wheel very quickly to a full rudder. I see no difference in safety on a Queen Mary or a small cruise ship, do you?

 

Cyclops, to satisfy the stability test you need only to know where find a lot of dwarfs....

 

Probably all working in the vessel safety division with a very low overhead.

 

Proposed new Australian Stability Standard

Dear Participants in boatdesign.net,

I have been reading the messages about the capsize of the Ethan Allen. My organization (the National Marine Safety Committee) is reviewing intact stability standards for domestic commercial vessels in Australia.

A draft of the new standard has been prepared and is currently available for public comment. It can be viewed at http://www.nmsc.gov.au/yoursay_2.htm.

A test based on the US Category T test has been used by Australian jurisdictions for 25 years quite successfully. However, as part of the review process, the Category T test has been removed.

This section has not been my project, so I am not yet aware of the rationale behind the change. That should be explained in a Regulatory Impact Statement that will be posted on our website this week.

Some changes have been proposed for Category S which also would have relevance to Category T if that were retained. These include raising the assumed weight of passengers from the current equivalent to 46kg (for Category S) to 75 kg per person for all classes of service.

In an earlier draft that retained Category T, it was proposed to calculate the passenger moment on the basis of lateral centre of gravity rather than B/6, assuming a distribution of 4 persons per m2 in the worst lateral location.

One reason why the simplified criteria are being reviewed is that, as an alternative to simplified criteria, stability may be calculated using comprehensive stability criteria (i.e. Rahola-IMO type criteria). However, the anomaly arose that a vessel would frequently pass the simplified criteria and fail the comprehensive criteria. This is inconsistent with logic. Comprehensive criteria should be the better measure of the vessel's characteristics and, if anything, the margin of safety should be built into the simplified criteria. The result of this anomaly has been that simplified criteria is often preferred BECAUSE IT WAS EASIER FOR THE VESSEL TO PASS than the comprehensive criteria. My understanding of simplified criteria is that they are intended to reduce the cost of measuring compliance, rather than the cost of achieving compliance. An analysis of the reason for the anomaly showed that the assumed passenger heeling moments were frequently very different, those for Category S and T being much less.

The proposed change to Category S means that the passenger moments are calculated in the same way for both simplified and comprehensive criteria, meaning that we are at least comparing apples with applies.

Participants in this website are welcome to comment on the draft stability standard and the regulatory impact statement. The cut-off date for comment is 10 January 2006.

Regards
Mori Flapan

 

I've taken a look at the standard above, and one comment I have is that it's unclear that you go to "Draft Document C6B" Chapter 5 first to calculate heeling moments before going to "Draft Document C6A" Chapter 6, the simplified stability test. This should be corrected both in the flow chart at the beginning of each document, and by referencing the appropriate C6B chapter in C6A, wherever heeling moments are called for.

Even though I'm not an Australian citizen I plan to submit a comment form before January 10 with this and other observations. Please understand that I wish to be constructive, not critical. As I've said:

Bravo, Australia!
(see also http://www.boatdesign.net/forums/showthread.php?t=9231)

 

Dear Stephen

Thank you for your input. Comments on the draft standard from yourself and any other participants to this forum are most welcome, notwithstanding that the person might be located outside Australia. There is no technical reason why safety should differ across borders. Variations in safety outcomes between countries are largely the result of differences in community expectations, politics and economics.

Public comment received on our draft standards is collated and reviewed by a reference group comprising both industry and government representatives. The members of the reference group are chosen for their expertise in the content of the particular standard and hopefully bring to the process an understanding of Australian community expectations and economic considerations. They make recommendations for changes to the draft to the National Marine Safety Committee, which comprises the chief executives of the various Australian Marine Authorities. The NMSC's function includes an awareness of political objectives and issues. So persons making public comment from outside the Australian arena need not be concerned that they might be remote from such issues. Public comment that provides good technical input and logic will make its mark.

Members of this forum might be interested in a presentation that was made at the Interferry 2005 Conference that was held in Greece in October. A White Paper has been prepared by the DnV Passenger Vessel and High Speed Craft working group on behalf of Interferry proposing the development of an international standard for domestic ferries. The White Paper will be submitted to IMO for its consideration. Details of the presentation can be viewed at:

http://www.interferryconference.com/confpapers/ThunesPpt.pps

Best regards

Mori Flapan

 

Interesting to note a local (Falmouth, Cornwall -some would say England, but the locals wouldn't!) ferry firm has decided to retest it's vessels as passenger size has increased over the last few years!

How?

by getting a lot of 'Large' (fat) people to go out in the ships, at a given time a large proportion of them will all go to one side then rush over to the other whilst the helm is put hard over! confident or what! Obviously there will be rescue boats standing by, but what a resounding way to test - proves beyond doubt that the vessel is stable (if not a lot of people will get wet!)

Thats the way to do it! None of yer silly bloody calculations! do it properly!

 

Bless that ferry company and talk it up for them doing the test. Sink or swim, they deserve some Free TV coverage.--------In the USN all destroyers get the same test. Entire crew runs back and forth to check the maximum roll angle. It takes a long time to get her rolling.

 

I'll post the math to justify this later, but a roll period test is a good quick test. In general any boat for which the roll period, over and back, in seconds, is more than 1/3 the beam in feet, in any loading condition, is not stable enough to carry passengers for hire. This might need to be modified a little for boats with large keels or skegs that dampen the roll, but it's still a pretty good rule of thumb.

 

I can give the roll period of the DD 519 DALY at 45 knots. Full port rudder applied from amidship by a sticking servo drive. took 3 seconds. Crew swept off, guns ripped out of their locking pins. And most important Saltwater was found later inside the stacks and the smaller safety stacks. It proves that almost any ship can self destruct. If the cold seawater had made it all the way down the safety stacks we would have vaporized in a massive steam explosion. Our original steam chests were replaced in WWII after a Kamikaze attack and replaced with those from a light cruiser. ----------------------------------------------Small, very fast destroyer on steroids.

 

Scuse my higgerance

Please realise- my genuine interest in this subject and the entire thread. I'm trying really hard to understand all this stability stuff.

Is it just me or does that quote above sound 'wrong'?.

If the roll period is shorter (i.e the boats stiffer, or rights faster doesn't that mean it's MORE inherrantly stable - ergo has more weight below the metacentric height, and less above?)

Should the quote read:-

A long roll period - surely means that the vessel is less stable, ie takes longer to right itself, or has a shorter righting lever? (Gz?)

And isn't the boat with a longer righting lever (Gz?), which rights itself more quickly (is more stable) the one that SHOULD be carrying the passengers?

Confuzzled!

Likely as not I got the bull by the **** - feel free to correct me.

Many thanks in advance.

(Source - Most of trouty's school teachers...who ALL had the ability to look at the ceiling while saying this and do this!)

Ya gets used to it after a while!

Cheers!

 

"How many present, small cruise boats, under 100', would pass a test that required. Full load, all on 1 side, at maximum speed, with moderate chop and cutting the wheel very quickly to a full rudder. I see no difference in safety on a Queen Mary or a small cruise ship, do you?"

None are tested to,


When we got boats thru the USCG inspection process the loads were water drums (or sand bags) lined up on a rail.

Basically the vessel could loose 1/2 the freeboard , and that weight was the pax load.
Any portholes or openings need a metal hatch cover or the freeboard only counts to the lower lip of the lowest hole.Sub T

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