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Underkeel clearance and Underkeel allowance
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ihbpah
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 Posted: Thu Sep 29th, 2011 07:37 am

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SNPWG have asked us to review these two definitions.

The attached SNPWG paper provides a clear rationale behind their proposals and gives much food for thought.

Attachment: SNPWG13-14.3_UnderKeelClearance.pdf.zip (Downloaded 8 times)

JerryMills
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 Posted: Thu Sep 29th, 2011 09:31 pm

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It seems we dealt with these terms some time over the past cuple of years.  Am I mis-remembering?

Underkeel clearance - I don't see the merit in changing the first part of the definition.  The fact that the deepest/lowest part of the vessel is not always the keel is recognized in the current definition - "normally some point on the keel".  That means there are exceptions.  I think its important to retain the word "keel" in the definition of "underkeel clearance".  I'm a little ambivalent about changing "lowest" to "deepest" since they have essentially the same meaning.  I agree with the substitiution of "sea floor" for "sea bottom".

Underkeel allowance - I distinctly remember commenting on this before.  The first part of the proposed new definition is incorrect, in my opinion, in that the underkeel allowance may be specified by a Port Authority without any calculations whatsoever.  That is, they can state the underkeel allowance for our port is one meter.  It is up to the mariner to calculate his "underkeel clearance" to determine if his vessel meets the specified "underkeel allowance" for that port.   I suggest the following definition:

"The minimal underkeel clearance allowed in a given channel(s) or area to account for vessels' dynamic characteristics, sea state, chart reliability and variance from predicted height of tide."

ihbpah
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 Posted: Fri Sep 30th, 2011 06:13 am

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Jerry, what you remember is that the Chair of SNPWG sent these to you before we put them on the HDWG work programme. This is what you passed to me at the time:

Hi Steve,

Just received this e-mail regarding proposed need definitions for the IHO Dictionary.  My initial reaction is that the definition for "underkeel clearance" is fine as it is in S-32 with the exception that "sea bottom" should be changed to "sea floor".  The current definition includes "normally some point of the keel" which is sufficient in my opinion.

"Underkeel allowance" is a bit more problematic because it may have different meanings in different countries. In the US, it is prescribed by various Port Authorities and is not a calculation at all, although calculations must be done to determine if a vessel will meet the specified "underkeel allowance".  Perhaps there will be some way to combine these two slightly different, but similar concepts.

Jerry

Which is the same as you are saying now.  I like your proposal for "Underkeel allowance" but would change "minimal" to "minimum".

JerryMills
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 Posted: Fri Sep 30th, 2011 10:35 am

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I agree.

ihbpah
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 Posted: Wed Apr 18th, 2012 06:36 am

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SNPWG have made further proposals.  These together with comments from the IHB are in the attachment.

Attachment: SNPWG14 Further proposal.zip (Downloaded 10 times)

JerryMills
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 Posted: Thu Apr 19th, 2012 03:59 pm

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Underkeel clearance - In my opinion, the current S-32 definition is fine with the slight change for "sea bottom" to "sea floor".   The proposed explanation of what factors should be considered in calculating "underkeel clearance" seems better suited to the IHO Manual on Hydrography.  However, if others agree that such an explanation is of value in S-32 then I propose the following rewording of the second sentence:  "When calculating a vessel's underkeel clearance for a particular area a mariner should take into account the vessel's draught, dynamic characteristics (settlement and squat), sea state and weather forecast, reliability of the chart and variance from predicted height of tide or water level."

Underkeel allowance - I concur with the definition proposed by Steve and David with the exception that the words "static and" be inserted between "vessels'"and "dynamic".

jwootton
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 Posted: Thu Jun 21st, 2012 07:57 am

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Underkeel clearance:  I tend to agree with Jerry.  The definition should consist of only "what" the term means.  The "how", which is the suggested new wording added, in terms of how the underkeel clearance is determined, is better included in other publications such as the IHO Manual of Hydrography.  Perhaps such guidance in terms of what consitutes a definition in the Hydrographic Dictionary needs to be included in the HDWG Business Rules?

Underkeel allowance:  I have concerns over the proposed new definition.  The words "specified by a relevant authority"  and "given channel or port area" imply that this term is only relevant when a vessel is in a particular area and subject to particular regulation, when the master of a vessel may have a pre-determined underkeel allowance that they have calculated for the entirety of a voyage (in terms of ECDIS use the "safety depth" that they manually apply to their ECDIS).  I would therefore prefer something similar to "the estimated, or specified (by a relevant authority), minimum UNDERKEEL CLEARANCE accounting for a vessels' static and dynamic characteristics; SEA STATE; CHART reliability; and variance from predicted HEIGHT of TIDE". 

Maria Alejandra
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 Posted: Thu Oct 4th, 2012 02:29 pm

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A dictionary gives a list of words and explains "What they mean" , not "the how".  What constitutes a definition may be included in the HDWG Business Rules. But you really believe it is necessary?

Jean Laporte
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 Posted: Thu Aug 15th, 2013 08:36 pm

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We have a double issue to tackle:

1. In addition to defining what the terms mean, should the HD provide explanations on how they are calculated?
In consideration of Jerry Mills’, Jeff Wooton’s and Maria Alejandra’s reservations and the enormous task awaiting us if we decide to revise the entire HD by making it more comprehensive, I would tend to stay on the conservative side and, when the case occurs, send our findings to the C-13 editors with a request to have these included into their next issue.

2. Can the HDWG agree on the latest definitions (without some of the explanations) suggested by Steve Shipman and David Wyatt?
Here again, I would tend to say YES, especially after looking at Jeff Wootton’s additional generalisation suggested in his June 21st 2012 posting.

With the Secretary agreement, the HDWG report to HSSC5 could then be drafted as follows:

Task B9: Underkeel clearance/allowance

 The new definitions of  "Underkeel clearance" and "Underkeel allowance" proposed by the SNPWG are accepted with minor changes underlining the fact that the HD provides definitions for terms, not explanations of how the terms should be calculated.

Subject closed


*****



The HD could then be modified as follows:

S-32 New English definition

Underkeel clearance
The distance between the lowest point of the ship's hull, normally some point on the keel, and the SEA FLOOR.

Underkeel allowance
The minimum UNDERKEEL CLEARANCE estimated, or specified by a relevant authority, to account for vessels' static and dynamic characteristics, SEA STATE, CHART reliability, and variance from predicted HEIGHT of TIDE.
 
S-32 New French definition

Profondeur d’eau sous quille
Distance entre le point le plus bas de la coque d'un NAVIRE, en général un des points de sa quille, et le FOND DE LA MER.

(No change required, the term “Fond de la mer” being an acceptable translation for « sea floor » at this stage).

Pied de pilote
Valeur minimale estimée, ou spécifiée par une autorité qualifiée, de la PROFONDEUR D'EAU SOUS QUILLE, définie en tenant compte des caractéristiques statiques et dynamiques du NAVIRE, de l'ÉTAT DE LA MER, de la fiabilité des cartes et des variations de la MARÉE PRÉDITE.

S-32 New Spanish definition

(to be completed)

ihbpah
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 Posted: Tue Aug 20th, 2013 09:50 am

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I agree with the proposed definition for Underkeel clearance; I would add for Underkeel allowance:  after 'or specified by a relevant authority' add 'for for a defined area or vessel type'

Jean Laporte
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 Posted: Tue Aug 20th, 2013 09:37 pm

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Thanks David, this is a significant improvement.

The English definition then becomes:

Underkeel allowance
The minimum UNDERKEEL CLEARANCE estimated, or specified by a relevant authority for a defined area or vessel type, to account for vessels' static and dynamic characteristics, SEA STATE, CHART reliability, and variance from predicted HEIGHT of TIDE.


and in French:

Pied de pilote
Valeur minimale estimée, ou spécifiée par une autorité qualifiée, de la PROFONDEUR D'EAU SOUS QUILLE pour un type de navire et une zone donnée, définie en tenant compte des caractéristiques statiques et dynamiques du NAVIRE, de l'ÉTAT DE LA MER, de la fiabilité des cartes et des variations de la MARÉE PRÉDITE.


jwootton
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 Posted: Tue Sep 3rd, 2013 06:10 am

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I agree with the proposed revised definitions.


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