The size of a vang/kicking strap ... discussion

[Jerry Brower]

Myself being one known too many times to have wrench in hand and aimed squarely at The Mix, I offer this boom vang cam plate design that could possibly be older than the IOM class. It definitely fits well within the build on the kitchen table at minimal cost philosophy that spawned the IOM class. I wonder how this configuration would fit through the ring gauge restrictions suggested for previous rule suggestions. As an aside, note the clear window of cellulose acetate used to likely increase sail area. The transparent plate tied below the main boom is nearly invisible to all but the most diligent observer.

[Zvonko]

Cool design

Should be OK now, now that multiple attachment points are allowed.

[Andrew Crocker]

Hi Jerry, thanks for this. I assume it did not pass the ring gauge test when that was a part of the rules in 2024? Something else to think about for sure.

Andrew

[Olivier Cohen]

Sorry Andrew, not the end yet, I would like to add my 2 cents here on my personal view, not as VC event.

The concern for most people about "Viss vangs" is its projected surface downwind as highlighted by Bob Lewis.

If we want to reduce the surface, why not just ask for holes or cuttings ?
I let you write it properly, but it could be something like :

"If surface of vang is bigger than what is needed for its purpose, its surface should be limited by cutting holes inside or on the edges"

[Jeff Kay]

If you take a step back from all of this and reflect. I’m struggling to see the logic of bending over backwards to make the Viss type legal while the potter type one was forced to be modified.
Seems inconsistent.
Jeff IRL 3/43

[Zvonko]

Vang on the Viss was and is legal.
Now there is a discussion about whether someone can be made bigger or if we need to limit it.

The Porter one was not a vang, it was and still is a vang fitting. It was not legal at the start and later became legal with a size limit.

[Jeff Kay]

Hi Zvonko
Good to hear from you.

I don’t think that’s factually correct. The potter one was legal initially. I actually still have one here.

I think you can go around in circles with the history of it but I struggle to see the fundamental difference - they’re both gooseneck / kickers that appear to have excess area.

Why not go back to the simple metal rod with thumb adjustment that everyone used and remove the unnecessary complication. And make a rule that achieves that rather than splitting hairs over what each word was defined as historically.

Just my thoughts.

Jeff

[Andrew Crocker]

Thanks to Jeff, Olivier, and Zvonko for the comments.

A few people have expressed the view, as Jeff has, that things would be much simpler if the vang style was restricted to the “… simple metal rod with thumb adjustment …”. However, Class Rules F.2.5 and F.6.1 respectively permit that “Construction techniques for forming rigs are unrestricted” and “Materials of running rigging are unrestricted” which means that anything goes when it comes to vang style. While it is quite possible to imagine a new Class Rule that limits the style of vang to the “… simple metal rod with thumb adjustment …”, such a rule would not be in character with the rest of the Class Rules which are simply not that prescriptive when it comes to fittings.

Olivier’s comment on using holes to reduce the projected surface area brings us back to the question of using surface area as a limiting element in the rules. This would allow maximum flexibility and handle features such as holes very well. However, the consensus is that the use of surface area as a limiting measurement has no precedent in the Class Rules and that measurers would struggle with the additional complexity. As a result, the best we can do is utilise two measurements to define surface area and this rules out allowing for holes and so forth to reduce area. Unfortunately, to keep existing (and very non-controversial) vangs compliant, the dimensions will need to be permissive if that is to be the approach. I continue to believe that only a defined surface area can be truly effective but acknowledge that is not a supported view.

As to the past and the Potter gooseneck. I was not a part of what happened 10 years ago, and I am therefore dependent on anecdotes and contemporaneous accounts to flesh out the actual Interpretation (2015-IOM-1) and subsequent rule change (F.2.4(d)). Additionally, as Jeff has done, several people have communicated to me (both within this forum and privately) their frustration with the apparent differences in approach between then (restrictive) and now (permissive). However, the Interpretation and its aftermath are instructive in this regard.

The devices that triggered Interpretation 2015-IOM-1 are shown at the top of the attached image (2015-IOM-1 Subject). Both devices were determined to be not permitted – both because of size but, in the case of the combined gooseneck and vang fitting, because it was interpreted that the Class Rules did not allow this arrangement.

The narratives following the issuing of Interpretation 2015-IOM-1 indicate that the ruling caused a range of existing gooseneck fittings to become non-compliant - examples of which are shown at the bottom of the attached image (2015-IOM-1 Collateral Damage, taken from the IRSA proposal for Class Rule F.2.f(d)) and the Potter gooseneck was one of those impacted. The Emergency Rule change was implemented (Class Rule F.2.4(d)) that essentially negated Interpretation 2015-IOM-1 and again permitted these fittings (provided they complied with the 20mm dimension specified).

Interpretation 2015-IOM-1 and its subsequent difficulties demonstrate the need to consider the practical realities of the IOM class in finding an appropriate balance between restrictive and permissive perspectives. This continues to be the objective of the current process.

Regards

Andrew

[Andrew Crocker]

Hi all,

Apologies for the delay in finalising this discussion.

Thank you again to all those that have contributed to this discussion. It has been a journey and considerable effort has been made to find a resolution. However, this journey appears to have simply taken us back to where we all started. For those who value the destination over the journey, this is going to be very frustrating.

We do know from the conversation in this forum that there has been a consensus that some control over the size of a vang would be preferred. Additionally, there is a level of consensus (although not unanimity) that the critical factor is the surface area of the vang. However, there is virtual unanimity that requiring Measurers to determine the surface area of a vang would be impractical and therefore cannot be used in the Class Rules as the limiting dimension. Other potential limiting dimensions (ring gauge, boom attachment point) have been questioned due to either unintended consequences to existing (complying) vangs, or the perception of insufficient control over size.

As a result, there is no consensus on the limiting dimension to be used for a vang – certainly not enough to run the risk of enacting an emergency rule change that is then overturned at the next AGM with the resultant confusion that would be caused. In any event, at this point the size of a vang is hardly an emergency. There is no evidence of either a vang size arms race, or any distortion of major regatta results that would warrant regarding this question as requiring emergency action. The fact is that we have lived with this situation for 2 years now without any negative impacts (other than blood pressure).

As an alternative approach, an Interpretation was proposed by the Technical Committee on the size of a vang (and other rig items) that established the principle of rig items being no larger than is reasonably required for their function, and its application to the Viss vang. However, this was not ratified by the IOM ICA Executive as required under the IOM ICA Constitution leaving that avenue similarly fruitless.

Without a rule change or interpretation regarding the size of a vang, we are left with the position that, based on a “written law” view, the Class Rules do not restrict the size of a vang (or any other non-dimensioned rig item). A Q&A has been prepared on that basis and is attached for information. It will be posted to the normal place on the IOM ICA website.

None of this precludes an NCA from proposing a rule change to the next AGM that does control the size of a vang – even to the point of taking the class back to the “wire and adjuster” style advocated by some contributors to this discussion (although the revised Class Rules’ definition of a vang may make that challenging to enact).

Thanks again for the considerable interest in this topic.

Regards

Andrew Crocker
VC Technical IOM ICA

[Zvonko]

Hi All

It is unfortunate that the IOM ICA Executive did not ratify the proposed new interpretation.

Just to be clear: the VISS vang is fully compliant with the current Class Rules.

Based on the “written law” position outlined above, it could technically be made even larger. However, as I have already stated earlier in this discussion, there is no intention on my part to increase its size further in coming years.

Regards
Zvonko Jelacic

[Bruce Andersen]

In my private capacity I offer the following:

Since IOMICA has not specifically addressed the plate vang issue in the newest edition of the IOM Class Rules, one must refer back to IOM Class Rule F.2.3 which states:

"The function of items shall be limited to what is normally provided by items of their type."

and ERS F.1.7.b(xi) which defines a vang:

"Equipment connected to the boom and used to control the angle between the mast and the boom. The term includes Gnav variations."

which is further modified by ERS F.1.6 that specifies:

Any equipment attached and/or connected at one or both ends to spars, sails or other rigging and capable of working in tension only. Includes associated fittings which are not permanently fixed to a hull, spar or spreader.

which seems to eliminate compression vangs although there appears to be a conflict between the ERS definition of Rigging and its definition of Vang - the former prohibits GNAV while the latter permits GNAV.

Since wire/turnbuckle vangs are installed on thousands of IOM's, control the angle between the mast and the boom effectively, and essentially never fail, what is the reason that they need to be changed to a large plate of carbon fiber that, in addition to what is normally provided by items of their type, decreases airflow between boom and deck and adds unmeasured projected area to the sailplan?

[Andrew Crocker]

A couple of things.

1. There is a "Q&A" on vangs acting in compression (https://www.iomclass.org/iom-questions-and-answers/) - I have included the original text as an attachment for those that have not seen it.

2. The 2026 revision of the IOM Class Rules (currently with IRSA awaiting approval) adopts the full text of USA Resolution 2025-2 that has the definition of a vang (now under IOM Class Rule A.1.4) as "Equipment connected to the boom and used to control the angle between the mast and the boom." - that is, removing the "Gnav" reference that is a part of the ERS definition.

Regards,

Andrew