IOMICA Forum

Dear all,

Attached is a discussion paper on the IOM Class Rules as they pertain to the maximum size of a vang/kicking strap. As noted in the paper, it is not an "interpretation" nor the "answer" to the question. Rather, it seeks to establish where we are now, how we got here, and where we might go in the future. Its intention is to form the basis of a structured discussion on those possibilities. I look forward to your comments, corrections, and views.

Regards

Andrew Crocker
Vice Chair Technical, IOMICA
January 2026

Thanks for bringing this discussion forward Andrew,

It's important to remember that the IOM class rules are closed rules.
If it's not specifically permitted in the class rules, then it is not allowed.

To my knowledge, this is the second time a new item/device has been introduced for the first time at an IOM WCR.
As we all know, when introducing a new fitting, device, material, etc. which is not specifically permitted by the class rules, a request for an interpretation is to be submitted to the IOMICA technical committee by the NCA of the requestor. Once the interpretation has been given, there is a grace period of 2 years to have the class rules amended if deemed appropriate.

In this particular case, the method of introduction of this device at the WCR to the class appears to have made this a controversial issue.
With a request for interpretation and a ruling before a WCR, this could all have been avoided.

To the matter at hand, the proposed rule changes did not specifically limit the area of the Vang, which in my mind is the most important criteria.
Either limit the width and length, or the specific area of the vang. Otherwise I can see a 20mm wide vang traveling the full length of the boom being attached at the aft end.

In my own private capacity,

Hi Art, thanks for your thoughts.

In referencing the definition of “closed class rules”, you raise a very interesting point.  The IOM Class Rules note at the outset that “… anything not specifically permitted by the class rules is prohibited. Individual rules may require, limit, or permit as necessary”.  Given that, consider these three examples:

• A mainsail boom.  It is specifically permitted (F.1.1(b)), and it is extensively and explicitly limited (F.4, C.8.3(b)(1)).  A builder can be in little doubt as to what is required to comply with Class Rules, provided they read them carefully,

• Headsail swivel inside a tube (this topic is the subject of the Q&A "Is it permitted to have headsail swivel inside the watertight tube?”).  The Class Rules do not "specifically permit" a "headsail swivel inside a tube” in the sense that these words do not appear anywhere in the Class Rules.  As a result, a builder contemplating such a construction would be wise to seek clarification (and did so).  The answer to the question was that the combination of Class Rules relating to a “headsail swivel” (F.4.4(a)(3), F.5.2(a)(2), C.7.5, F.2.4(c)) indeed permit such an arrangement - a headsail swivel is permitted, but the limitations do not rule out it being in a tube.  

• The vang.  It is specifically permitted (F.6.2(a)(2)) but not explicitly limited by any rule.  Where an item is explicitly permitted but not explicitly restricted, what clarification is a builder seeking?

In short, for an item that is explicitly permitted but without explicit limitation (i.e. size, surface area), there will always be room for a builder to believe that something is compliant and not requiring any clarification.   Without wishing to split English semantic hairs, the distinction needs to be made between “new” (which a vang certainly is not) and “novel” (which a large vang perhaps is).  However, understanding that an item is “novel” requires knowledge of past practices that may be achievable for a commercial builder, but problematic for a home builder.  

Regards

Andrew

Hello everyone, in my humble opinion as a boat designer, limiting the vang area on modern boats no longer makes much sense. Most of us have a cockpit that's recessed into the deck, and we try to lower the rigging's center of gravity as much as possible. Therefore, the surface area projected outside the cockpit by a large vang wouldn't, in my opinion, have a significant propulsive effect, contrary to what some might believe. Making a vang that extends to the end of the boom to increase projected surface area, as mentioned above, also wouldn't make much sense to me, since I prefer to lower the mast and have the boom just touch the deck. On more classic boats where the mast is higher and there weren't cockpits to lower the mast's center of gravity, I could understand this debate. Perhaps I'm wrong and not analyzing this issue correctly, but according to my understanding, this is my point of view...

Thanks for being open to public discussion on this controversial topic. Opening up this forum is a step in the right direction. Social media is nice for photos etc but does not offer much in terms of keeping a substantive discussion in one place.

I fear that unless we clearly define the maximum surface area of the vang and its associated mast & boom fittings, some will continue to push this particular envelope.

Regardless of opinions advanced proposing that the added projected area is inconsequential, it does exist and does add some (albeit small) area to the sail plan.

Why not attach a plate vang to the distal end of the boom, thus adding even more projected area?

The requirement for the vang to "fit" through a 20 mm ring gauge is also troublesome - what would stop someone from creating an elastomeric sheet that hung off the bottom of the vang to completely close off the gap between the deck and the lower edge of the vang, then simply roll it up to fit through the ring gauge? Is this the true purpose of a boom vang?

Why not simply limit the vang to a reasonably small attachment to the mast and a similarly reasonably small wire /turnbuckle or line/bowsie attachment to the boom as has been traditionally used for many years?

Dear

The surface area of the Viss Vang is 1739 sq mm, and can be seen at the following link: viewtopic.php?f=7&t=2111

This is a comparison with a vang that has been on the market for a long time, so I assume that it does not violate Rule F.2.3, and that our solution is therefore compliant with the rules as well.
The key question, in my view, is who determines whether Rule F.2.3 is being violated, and how the limit of Rule F.2.3 is actually defined.
To resolve this issue clearly and ensure that all existing vang designs remain legal, I would suggest the following approach:
Propose an emergency rule ( clarification/change ) that would go on the next AGM:

The vang must be able to pass through a 20 mm ring gauge with a maximum length of vang 200 mm

This would define a clear and measurable limit.


It is worth noting that sailors have already expressed their views on this matter through voting:

- at the 2024 AGM, approximately two-thirds supported a 20 mm limit, and,

- in 2025, 58% again supported the same limit.

Both votes indicate a clear majority even after IRSA attempt to block this AGM proposal again. If there is still uncertainty by some minority that is ok, but impression is now that IOM sailors either do not want a limit at all, or possibly prefer a limit greater than 20 mm.

I appreciate the effort being invested by the Technical Committee in carefully reviewing these matters, and I am confident that this thorough process will ultimately benefit the class.

Kind regards,
Zvonko Jelacic

Thanks Gabriel, Bruce, and Zvonko for your comments.

To Gabriel's point, and recognising the danger in ascribing motivation, the "bent vang" shown in Zvonko's response has the effect of allowing a boom attachment point for the vang that is further aft (further from the mast) than a straight line vang would be capable of having with a narrow cockpit (due to narrow hull) and low rigs. So the evolution can be understood as responding to the design direction that Gabriel mentions as opposed to a desire for more sail area.

Both Bruce and Zvonko are, in their own ways, arguing for a more comprehensive restriction than simply one dimension (e.g. the 20mm ring gauge). This implies a minimum of two dimensions that, in some way, control the ultimate surface area of the vang. At its most complete, Bruce's suggestion that the rules prescribe the "old faithful" vang would mean shifting to perhaps 3 dimensions - end point size (say 5mm), maximum mid point size (say, 12mm), and then length (say, 150mm). As I have noted in the discussion paper, this perhaps rules out 3D printed fittings and, given their increasing prevalence, probably penalizes the home builder more than is desirable.

Zvonko's suggestion of a 20mm x 200mm vang (ring gauge size and total length) would certainly be easy to understand and stop surface area growth. I would suggest that a 200mm length is around 50mm too much - but negotiation on size can come after agreement on the principle.

Regards

Andrew

What about the skippers?

After looking into the background on the Viss Vang component issue, I’d like to thank everyone for their time and effort in providing context on this matter. While there has been a lot of discussion, many VISS owners might be feeling a bit anxious about whether they need to change components on their rigs. Some VISS owners aren’t focused on competition, prefer to stay out of the debate, and simply want to race their IOMs with friends, while also feeling assured that they are racing within the rules.

With many countries gearing up for their regatta season and several major events scheduled for the first quarter of 2026, do you think IOMICA should act quickly in making decisions regarding this Vang issue? While discussions may continue throughout the year, I believe it’s important to provide guidance to owners sooner rather than later.

In my humble opinion, it’s unfortunate that the Vang components did not meet the requirements to pass the 2025 IOMICA voting process. Taking the results at face value suggests that, as things stand, the Vang components are considered illegal.

More importantly, IOMICA should prioritise communicating through their NCAs about the technical implications for VISS owners, so they can understand the situation as soon as possible. This will allow all skippers, whether competitive or not, to make necessary changes before the racing season kicks off.

The Croatian candidate may wish to reapply to IOMICA and have another chance for members to vote in the future. However, this process will take several months, meaning current owners will need to stick with their alternative rig arrangements for the rest of 2026. So, let’s continue the debate away from the lakeside, but let’s also keep in mind the many skippers who are patiently waiting for guidance and want to race without worrying about violating class rules.

Regards
JT

Hi John - thanks for your contribution.

As to your central question - yes, I believe that IOMICA (through me) needs to make a clear statement on what is (and is not) conformant with the current class rules - preferably by way of affirming the application of the current rules. The purpose of this discussion thread is to understand whether there is a consensus on the way forward. Ultimately, any rule change that may be proposed needs to be voted on at the next World Council meeting. Without consensus, we face another defeated vote and yet more confusion.

Unfortunately, as I note in my paper, interpreting the results of the 2025 World Council vote as meaning that the "VISS vang" is illegal is only one of the plausible interpretations. It is equally plausible that it is perfectly legal. As I have noted in a previous post, there is simply no explicit limitation on the size of a vang in the class rules. Leaning on Rule F.2.3 ("normal function") is, as I note in my paper, highly subjective and leads us to where we currently sit.

My goal is to make such a statement during February 2026 - well before the IOM Worlds. Everyone's assistance in contributing to that outcome is very welcome.

Regards

Andrew

Hi All,
Firstly a big thank you for Andrew for taking on the IOMICA TC role. Owners being openly invited to contribute in finding solutions to issues, with balanced information is a welcome step forward, thank you.

I, like others have been vocal in my thoughts regarding kicker/vang sizings within these forum threads. Re-hashing, repeating or entering the same debates will not take us in the direction we need to go but my comments are there for reference.

To me the reality that neither Kicker/Vang prposals from CRO or FRA were successful shows that members are clearly divided on what is considered an acceptable size for these items. Possibly some thought the limits proposed were too lenient? Maybe some thought they were too restrictive? Maybe something else, but we know they did not pass. Arguing about margins is irrelevant at this time.

Our TC has laid out a well written paper on where we are and offers ways to go forward. I feel in his options to go forward, that his second option is one that is more in line with the ideals of closed class rules that we operate within.


2. Attempt a rule change via the AGM. For example:
a. A quantitative rule amendment – for example, the vang must pass through a 20mm ring gauge, or boom vang fitting must be no more than 100mm from the rear of the mast, or surface area must be less than 2000 sq mm.
b. A qualitative rule amendment in the form of the Marblehead or 10 Rater rules – for example “fittings must be no larger than is reasonably required for their purpose”

In supporting the above, I would suggest minor changes for following reasons

Part a.
A reduction in ring gauge size to 15mm.
It has been argued that fittings of such size are not trying to work around rules as they are set on round booms well under the 20mm maximum height. I do not believe such a fitting requires that level of height sizing for required strength to perform its role and should be reduced more in line with the boom it controls. I believe 15mm sits closer to a fair compromise between the largest sections allowed and round booms more widely used. Ideally I believe 11mm to be the optimum that should be allowed, but concede a balanced height of 15mm would allow any current units being used to be easily modified without requiring replacement or compromising strength/structure.

Length Restriction
No larger than 125mm aft of the mast
In keeping consistent with previous interpretations within the kicker body, Kicker/Vang region, I agree that the maximum length should be no greater than 100mm. The change I would add is that a kicker/vang is commonly set aft of and a with connection to a gooseneck body. Maximum permitted for this fitting is 20mm aft of the mast. There may be overlap within connection. So my suggested change allows a tollerance to be set no more than 125mm from the aft face of the mast.
It is imperitive that any rule voted on has a length restriction matched with a ring gauge limit.

b. Rule ammendments
I believe these are paramount to better reflect our rules as closed class. As a competitor, designer, manufacturer also involved in both the International Marblehead and Ten Rater classes, the clear wording in those rules as mentioned serves an important role on two fronts.

Firstly, it removes conjecture.
In the current circumstance, it is abundently clear that the presented CRO style kicker/vang is far larger than one required to perform the role of controlling mainsail leech tension. 30+ years of the IOM class would support this.

Secondly, It protects the class
Designers and manufacturers of something new are clear when creating ideas that there are boundaries. This is a closed class rule that should not be having these debates each time someone wants to push past them. For instance there is no restriction on the size of a backstay crane, mast head swivel or jib counterbalance among other fittings. Do we need to come back and debate each and every component when someone seeks to use them for any advantage, perceived or real, by making them significantly larger than what serves its purpose?

The wording change not only shifts the onus back on to the designer and manufacturer to better understand the intent of our rules, but also to request an interpretation if they are not convinced of legalities for use.

Cheers
Brad Gibson (Designer/Manufacturer)
GBR 42

I may be adding a an extra complication, but who decides what is class legal?
My understanding of the class rules is" If in doubt ask", who do you ask, and how do these decisions get broadcast to the class owners

Darin Ballington wrote: ↑

21 Jan 2026, 12:29

I may be adding a an extra complication, but who decides what is class legal?
My understanding of the class rules is" If in doubt ask", who do you ask, and how do these decisions get broadcast to the class owners

Sorry, pressed the wrong key...

If there is a new idea, or move away from the usual conventions this shouldn't appear for the 1st time at a major event. I understand the "wow" factor and commercial and competitive gains that may occur, but for the vast majority of the competitors at an event the costs to compete are coming from their own pockets and they will be reluctant to hold up the event by protesting equipment. They just talk amongst themselves and create division in the class.

It also puts the race organisers under similar pressures to avoid a competitor being sent home or taking a hacksaw to their boat.

There must be a process that can be put in place that allows a boat owner to check with IOMICA and this interpretation be given either publicly or privately but in a transparently recorded manner.

Brad Gibson wrote: ↑

21 Jan 2026, 10:34

In supporting the above, I would suggest minor changes for following reasons

Part a.
A reduction in ring gauge size to 15mm.
It has been argued that fittings of such size are not trying to work around rules as they are set on round booms well under the 20mm maximum height. I do not believe such a fitting requires that level of height sizing for required strength to perform its role and should be reduced more in line with the boom it controls. I believe 15mm sits closer to a fair compromise between the largest sections allowed and round booms more widely used. Ideally I believe 11mm to be the optimum that should be allowed, but concede a balanced height of 15mm would allow any current units being used to be easily modified without requiring replacement or compromising strength/structure.

Length Restriction
No larger than 125mm aft of the mast
In keeping consistent with previous interpretations within the kicker body, Kicker/Vang region, I agree that the maximum length should be no greater than 100mm. The change I would add is that a kicker/vang is commonly set aft of and a with connection to a gooseneck body. Maximum permitted for this fitting is 20mm aft of the mast. There may be overlap within connection. So my suggested change allows a tollerance to be set no more than 125mm from the aft face of the mast.
It is imperitive that any rule voted on has a length restriction matched with a ring gauge limit.

Cheers
Brad Gibson (Designer/Manufacturer)
GBR 42

Hi all,

Above mentioned proposed dimensions will put out of the class vangs which many of us are using for years, if not for decades. Maybe I was not precise with measuring the diameter of the fitting sold by one reputable supplier for years but it is close or even slightly bigger than 15 mm. Recommendation of the same supplier is to have hole on the main boom for kicking strap 130mm from the fore end of the boom, which is obviously more than 125 mm from the aft of the mast (as proposed above). I am quite sure that I am not the only one using such type of vang with this dimensions.

Do we really want to put to prohibit this type of vangs?

Regards

Robert Grubiša
CRO 68

Robert Grubisa wrote: ↑

21 Jan 2026, 16:56

Brad Gibson wrote: ↑

21 Jan 2026, 10:34

In supporting the above, I would suggest minor changes for following reasons

Part a.
A reduction in ring gauge size to 15mm.
It has been argued that fittings of such size are not trying to work around rules as they are set on round booms well under the 20mm maximum height. I do not believe such a fitting requires that level of height sizing for required strength to perform its role and should be reduced more in line with the boom it controls. I believe 15mm sits closer to a fair compromise between the largest sections allowed and round booms more widely used. Ideally I believe 11mm to be the optimum that should be allowed, but concede a balanced height of 15mm would allow any current units being used to be easily modified without requiring replacement or compromising strength/structure.

Length Restriction
No larger than 125mm aft of the mast
In keeping consistent with previous interpretations within the kicker body, Kicker/Vang region, I agree that the maximum length should be no greater than 100mm. The change I would add is that a kicker/vang is commonly set aft of and a with connection to a gooseneck body. Maximum permitted for this fitting is 20mm aft of the mast. There may be overlap within connection. So my suggested change allows a tollerance to be set no more than 125mm from the aft face of the mast.
It is imperitive that any rule voted on has a length restriction matched with a ring gauge limit.

Cheers
Brad Gibson (Designer/Manufacturer)
GBR 42

Hi all,

Above mentioned proposed dimensions will put out of the class vangs which many of us are using for years, if not for decades.
vang_210126.jpg

Maybe I was not precise with measuring the diameter of the fitting sold by one reputable supplier for years but it is close or even slightly bigger than 15 mm. Recommendation of the same supplier is to have hole on the main boom for kicking strap 130mm from the fore end of the boom, which is obviously more than 125 mm from the aft of the mast (as proposed above). I am quite sure that I am not the only one using such type of vang with this dimensions.

Do we really want to put to prohibit this type of vangs?

Regards

Robert Grubiša
CRO 68

Hi Robert,
As I have not used a kicker/vang from said providor for 20+ years, I am unaware that they were actually that large!

The only large oversized wheel example from another reputable supplier here measures 12.5mm at max wheel diameter as pictured. For reference I include a fitting used since 2007 on both my Widget and subsequent designs more suited to rigs being low in the boat without unnecessary weight.
From here my 15mm ring gauge offered would seem generous without removing anyone with existing fittings designed for their purpose and nothing more.

As to allowable positioning on the boom, like above I trust a sensible figure will be discussed and reached that better defines all limitations in staying true to a closed rule set.

Regards
Brad Gibson
GBR 42

To Darrin's post - the notion of asking for an interpretation prior to putting a new design feature into the marketplace makes sense and should quell controversy but not all agree.

Recall that two contentious developments in recent IOM history have been the issue of moulded sails and the issue of the "dual duty" plate style vang, both of which showed up at a WCR without prior consideration and/or approval.

Zvonko's suggestion of a 20mm x 200mm vang (ring gauge size and total length) would certainly be easy to understand and stop surface area growth. I would suggest that a 200mm length is around 50mm too much - but negotiation on size can come after agreement on the principle.

Just for info, this is from Worlds 2009
With the mainsheet post positioned at 195 mm from the mast on the Pikanto, the vang attachment point ends up roughly 180 mm from the mast. Consequently, the overall Vang length becomes even longer.
https://www.yachtsandyachting.com/news/ ... n-Barbados

Thanks to Brad, Darin, Robert, Bruce, and Zvonko for the contributions to the discussion.

Darin's question as who determines "class legal" is answered in the IOMICA Constitution - the short answer being the Executive Committee of IOMICA. The longer answer, of course, involves the Technical Committee of IOMICA responding to requests from IOM builders/owners with either clarification, interpretations (which are binding), or proposed rule changes, that are then ratified (or not) by the Executive Committee of IOMICA and then, for rules changes, ultimately voted on by IOM Owners. So, in a sense, the final answer is that IOM Owners determine what is "class legal" by determining what the class rules are. The role of the Technical Committee is often to closely read and parse those rules in responding to queries. As I noted in a previous post, things may not be explicitly permitted but, by a combination of rules, are actually allowed. Having said all that, the interpretation of rules at an event is laid out in Class Rule A.7.2 or, in more extreme cases, in the "Deviations outside of tolerances" section of the Introduction to the Class Rules. I think we can all agree that noone wants to be the person to whom those rules are applied, as Darin has rightly pointed out.

Darin and Bruce also note the "if in doubt ask" principle - and that certainly is the basis of many requests received for clarification. However, the corollary to that principle is "if there is no doubt, then don't ask". As I noted in a previous post, where an item is explicitly permitted but not explicitly limited, builders (whether commercial or home) may believe that there is no doubt and, therefore, no reason to seek clarification. The desire to explicitly limit the size of a vang would take away that ambiguity. However, as Brad notes, that leaves many, many fittings that are simply permitted but in no way restricted with the potential for future difficulties.

For all that, there does appear some coalescing around the notion of a "two dimension" rule for the size of a vang - ring gauge + length in some way. However, as Robert and Zvonko have noted, those two dimensions could be problematic for a range of existing vangs that would, in the normal course of events, raise no eyebrows at all. In reality, what we are trying to control is surface area - so a surface area restriction makes more sense and would not cause as many problems (if any) for the examples that Robert and Zvonko cite. However, finding a calculation for surface area that is easy to implement for measurers may be very difficult indeed. So we are between a rock and hard place - more thought indeed.

Thanks again for the interesting contributions.

Regards

Andrew

Andrew Crocker wrote: ↑

21 Jan 2026, 22:31

....snip....
For all that, there does appear some coalescing around the notion of a "two dimension" rule for the size of a vang - ring gauge + length in some way. However, as Robert and Zvonko have noted, those two dimensions could be problematic for a range of existing vangs that would, in the normal course of events, raise no eyebrows at all. In reality, what we are trying to control is surface area - so a surface area restriction makes more sense and would not cause as many problems (if any) for the examples that Robert and Zvonko cite. However, finding a calculation for surface area that is easy to implement for measurers may be very difficult indeed. So we are between a rock and hard place - more thought indeed.

Thanks again for the interesting contributions.

Regards

Andrew

For many years the kicking strap has been a simple SS wire hooked into a hole in the underside of the boom with a threaded adjuster.
For some reason builders and designers felt the need to use a CF plate instead.
If the claim is the CF plate is not intended to enhance sail area, then why use it?
There must be some benefit to the CF plate vang that makes the wire vang obsolete now.

Also, as per the class rules, the vang can only work in tension and not compression.
Does this mean that if the sail is detached from the boom at the clew the boom should fall to the deck?
If not, then is the CF vang supporting the boom using compression?
How is this restriction determined when a boat and rig are being measured for a certificate?

In my own private capacity.

Hi Art,

The question of a vang being in compression did arise at the 2024 Worlds. During pre-event measurement, the vang was checked to ensure that there was "play" in the adjuster such that the boom could move in the downward direction indicating no compression. It was the adjustment mechanism that determined this and not the overall design of the vang - C/F plate or otherwise.

As I speculated elsewhere in this thread, the large C/F vang shaped like an ice-hockey stick could be a response to the need to clear cockpits in narrow hulls. The alternative is an attachment point for the vang that is very close to the mast which, presumably, has an impact on the force that the vang is able to exert under load.

Regards

Andrew

Hi All

Regarding production, in my case, it is easier to manufacture a VISS vang than a standard wire with a threaded adjuster.
For the VISS vang, you need 2D laser cutting ( or it all can even be cut by hand ), plus a small amount of epoxy and carbon fiber.
For the wire-and-threaded-adjuster solution, you need 3D machining, which, for example, I do not have good local access to.

For all that, there does appear some coalescing around the notion of a "two dimension" rule for the size of a vang - ring gauge + length in some way. However, as Robert and Zvonko have noted, those two dimensions could be problematic for a range of existing vangs that would, in the normal course of events, raise no eyebrows at all. In reality, what we are trying to control is surface area - so a surface area restriction makes more sense and would not cause as many problems (if any) for the examples that Robert and Zvonko cite. However, finding a calculation for surface area that is easy to implement for measurers may be very difficult indeed. So we are between a rock and hard place - more thought indeed.

Maybe we could define a surface area limit of 4,000 sq mm, which is why I suggested a 20 mm ring gauge with a maximum length of 200 mm.

The real challenge is how such a limit can be measured, especially as future designs enabled by new technologies are unlikely to become simpler in shape.

In my opinion, the class should leave room for, and actively encourage, innovation and progress, rather than criticize or restrict solutions simply because they are slightly different. In my own experience, molded sails have made access to sails easier and significantly reduced waiting times, while the vang addresses the practical issue of very small vangs that are difficult to use, particularly for sailors with larger fingers and hands.

Honestly, I do not see why this topic has generated so much debate. If someone likes the concept, they are free to adopt a similar solution; if not, they can continue with their preferred setup. None of these developments has made older boats non-competitive, unlike changes such as cockpit design when they were first introduced.

Regards

Zvonko

Hi Zvonko, thanks as always for the contribution.

If I may reinforce one point that you make (leaving open views on the dimensional aspects) and wax slightly philosophical ...

While the IOM Class Rules are "closed class rules" (in accordance with ERS C.2 which only gives two choices - "closed" and "open"), it is very clearly not the intention that they define a "one design class".  This may seem very "off-base", but compare the IOM Class Rules with the International 420 Class Rules as an example.  The International 420 Class Rules are "closed class rules" (A.1.1) but then explicitly state that the purpose is to define a "one design class" (A.1.2).  If you search those class rules for the word "unrestricted", you will find no instances - the class rules are highly prescriptive in line with the "one design class" purpose - ".. to ensure that all boats are as alike as possible ...".

The IOM Class Rules, on the other hand, do not use the words "one design". Search for the word "unrestricted" and you will find 11 instances.  The IOM Class Rules afford the designer significant opportunity to express themselves - as the plethora of hull and hull appendage forms indicate - but within a series of constraints - some very well specified, others not so.  Rigs represent the one part of the rules where the constraints are most carefully defined and so I am not surprised that the vang form (as a part of the rig) generates debate as it seems to run counter to the generally prescriptive nature of those rules.  Major hull design transitions from, say, the TS2 to the BritPop, to the Venti, Viss, and V12 (to name but a few), on the other hand, attract exactly zero comment.

I believe that most want the IOM class to continue to be dynamic and innovative within the constraints that the rules provide - I look forward to the next hull evolution and the price that I will have to pay for adoption  But, there are constraints and they need to be observed - many IOM owners take this aspect very seriously indeed and that needs to be respected.  Finding our way through the occasional controversy that they generate is a necessary process.

Regards

Andrew

Andrew Crocker wrote: ↑

21 Jan 2026, 22:31

For all that, there does appear some coalescing around the notion of a "two dimension" rule for the size of a vang - ring gauge + length in some way. However, as Robert and Zvonko have noted, those two dimensions could be problematic for a range of existing vangs that would, in the normal course of events, raise no eyebrows at all. In reality, what we are trying to control is surface area - so a surface area restriction makes more sense and would not cause as many problems (if any) for the examples that Robert and Zvonko cite. However, finding a calculation for surface area that is easy to implement for measurers may be very difficult indeed. So we are between a rock and hard place - more thought indeed.

Some possible options to move forward

- A Kicker/Vang with an area body size greater than …… shall be set no further than ……. from the aft face of the mast. This could effectively control those looking to build a fitting beyond its purpose.

- A body size shall be no greater than ……mm squared, less fixings (no greater than 4mm in diameter) placed along a load line axis when used under tension. Restricts body size looking for purpose other than required while allowing fixings such as wire, threaded adjustment etc up to a diameter of 4mm

- We ammend the rules to better define a fitting in line with closed class rules as suggested ‘fittings must be no larger than required for their purpose’

The class has always allowed innovation within a closed rule set that invites a challenge for any designer or builder from amateur through to professional. The greater majority accept this, acknowledging it is the rule set that has kept old boats competitive while encouraging new ideas in design, rigging setup and so on.
The only thing that threatens us is most often led by manufacturer interest to continually push boundaries beyond rules written, near always leading to added or unwarranted expense. When done in a way that circumvents clearly stated class outlines of first seeking clear approval through official interpretation, it goes beyond class interests and into self interest, performance, business or otherwise.

It is all well and good on one hand to suggest a quentioned component can be made rapidly or inexpensively. The available propriety or pricepoint more often than not reflects the real story behind the original intent of such ‘innovation’.

Regards
Brad Gibson
GBR 42

I honestly find the 20mm dimensions very limiting regarding the fitting that attaches to the mast. I developed my own designs for 3D printing; I'm not looking to increase the surface area of ​​this part, which is largely enclosed within the cockpit and provides absolutely no extra propulsion, either downwind or upwind.

And now I realize that perhaps I misinterpreted the 20mm rule for the fitting attached to the mast (I understood that the rotating parts shouldn't exceed 20mm from the center of rotation).

The fact that I made a piece that wraps around the mast to give the 3D-printed part more strength, and combined it with the mast foot and a ring where the mainsail's Cunningham passes through might mean that this piece doesn't comply with the 20mm rule.

I'm referring to the fitting that attaches to the mast, not to the rotating parts. I'm having trouble interpreting this part of the rules, but if the part of the vang that's fixed to the mast isn't exposed and doesn't rotate, then could it exceed 20mm? It's all very confusing for me with the translator.

In any case, that 20mm limitation is problematic for making strong 3D printed parts that are accessible to a wider audience. But I'll adapt if necessary!

I never designed my vang system intending to break the rules, but now I have doubts...

When designing the parts in 3D, I mainly focus on their strength and the surface area I might gain or lose I think it's really ridiculous... as you rightly say, the differences in sail manufacturing between the maximum and minimum dimensions are much more important and are found in an area where they are actually useful.

I still think the vang's surface area limitations, given its location on the boat, are irrelevant in both modern and older boats. Even with a "VISS"-type kicking strap, most of its surface area would be inside the cockpit, contributing very little to no "propulsive surface."

As a designer, if I wanted to gain extra propulsive surface area at the stern, I might consider a higher deck to project more surface area into the wind. We could gain significantly more surface area than with a simple vang fitting, but even then, I still don't think that's the right approach.

In short, as you may have guessed, I believe the vang's surface area and the system used to regulate its tension shouldn't be restricted. This would allow for the easy creation of functional and robust 3D-printed parts, making the class more accessible to a wider audience.

If I had to vote, I would vote for this:

b.A qualitative rule amendment in the form of the Marblehead or 10 Rater rules – for example, “fittings must be no larger than is reasonably required for their purpose.”

Thank you all for reading, and I hope you understand my point of view.

Gabriel Le Duc