Question details:

Does a typical rc yacht balanced headsail boom meet the ERS definition of a boom?


The ERS definition states:

F.1.4 (b)  BOOM

A spar attached at one end to a mast spar or a hull and on which the clew of a sail is set and on which the tack and/or foot of a sail may be set. Includes its rigging, fittings and any corrector weights, but not running rigging, running rigging blocks and/or any kicking strap/strut arrangement.

The question is raised because the attachment of a typical rc yacht balanced headsail spar to the hull is not at the very end but some distance, typically 10-20% of its length, from its fore end.

For a definitive answer this question would have to be answered by seeking an interpretation from the WS ERS Working Group. There are certain problems with the ERS definition(s) relating to spars which have been made known to the ERS WG and it may be that a defnitive answer would not be made. In the meantime the following discussion is offered.

Points to consider

1     Where it is important to identify the very end of a spar the ERS has such defintions e.g. the mast top point and the mast heel point. If it were necessary to require the very end of a boom spar to be attached to the mast or hull then we can assume a 'fore end point' would be defined. It has not been and so we should not take the ERS defintion of boom to mean that the very end of the spar is the critical point.

2     Experience shows that all practical main booms are attached to the mast using a fitting with the attachment point some distance from the very end. As these booms are not attached at the very end we should be able to assume that the very end is not intended as the required attachment point.

3    Spars can be considered to have two ends and a middle. If each of these regions is 1/3 of the total length then the attachment point of a typical rc yacht headsail boom is well within the end region.

Question details:

August 2018 changes to 2018 65 Class and Marblehead class rules. Why? And why have the Ten Rater and A Class rules not been changed?


The 65, M, 10R and A class rules have certain restrictions and limitations relating to booms. In 2018 it became apparent that the ERS definition of a boom - a spar attached at one end to a mast spar or a hull and on which the clew of a sail is set .... and its fittings - meant that the class rules did not work well for swing rigged boats.

The class rules for the 65 and Marblehead class rules have been changed by the IRSA EC - effective 1st August 2018 - acting to maintain the previous common understanding of the class rules. The A Class does not permit swing rigs so the class rules need no change. One DNM has provided a proposal to change the class rules in the 10R Class and so this will pass through the formal procedure for dealing with such proposals.

Please see the related Q&A - Does a typical rc yacht balanced headsail boom meet the ERS definition of a boom?

Question details:

Is a GIZMO and its derivatives, also known as BRESMO etc, permitted in the 65 Class? This device is actuated by the sheet of a swing rig when the rig is sheeted fully in and when the sheet is winched in further so that it acts on a lever or other device that automatically adjusts other rigging.



Relevant rules


The class rules for the 65 Class are open class rules in which anything not specifically prohibited by the class rules is permitted, where individual rules require, limit, or prohibit as necessary.

(a) No more than two channels of radio control shall be used.

(b) A rudder control unit shall control the rudder only.

(c) A sheet control unit shall control the mainsail sheet and/or headsail sheet only.
(d) Except where achieved by mechanical systems, automated control of rig and/or sails and automated steering and/or navigation are prohibited.


C.8.1 (c) prohibits the use of the sheet control unit for controlling anything other than the mainsail sheet and the headsail sheet. However, C.8.1 (d) makes it clear that mechanical systems that provide automated control of the rig and/or sails are not prohibited.

Hence the GIZMO and its derivatives are permitted in the 65 Class.


The pathway for classes of boat that are not IRSA designated classes is as follows:

  • Create class rules that use the World Sailing Standard Class Rules format
  • Certify boats to these class rules
  • Create an active international class association with provision for control of the class
  • Meet the numerical requirements
  • Apply for IRSA designated class status
  • Apply to run a world championship

The process is fully documented in the IRSA Regulations, a new version of which which is currently (early 2018) in the process of being considered for adoption by the IRSA DNMs. The process would apply to any class which is not already an IRSA designated class e.g. RC Laser, DragonForce, DragonFlite, RG65, Micro Magic. 


Question details:

Why should a different gauge used for draught restriction than for length restriction (relevant to Marblehead, 65 and Nano class)?


Use of the length restriction gauge adapted to also restrict the draught of the Marblehead class was proposed when the draught limit was introduced in that class (late 1990s).

The conclusion at the time was that use of a combined gauge would have major disadvantages –

  • it would not restrict the draught of a boat as accurately/effectively as a transverse draught restriction gauge does
  • it would be easy to get more draught by lowering the bow and stern of the boat into the water
  • it would tend to encourage boats that were not manoeuvrable

The following notes expand on this. In the time leading up to the Marblehead rule change the major section, relative to the true waterplane, of all available M designs were placed on a single piece of paper#. There was a spot on the 'hulls' about 50 mm off the centreline that all the sections passed through with a + or - 3 mm variation. This + or – 3 mm range is a very small variation from the average value being + or - 0.5% of the overall draught figure.

The bow and stern profiles of the same designs were all plotted, relative to the true waterplane, in the same way and there was a large vertical range at the 'measurement points' created by the ledges in the length restriction gauge. A + or - 10 mm range, or more, was found.

This test indicates that, in a mature class, the transverse draught restriction gauge is approximately three times better/more effective for controlling draught than the length restriction gauge.

It was also considered how the different restriction methods could be exploited to gain additional draught.

Using the transverse draught restriction gauge

The section shape of a hull near midships could be altered to increase draught marginally. However the change that is necessary would have the following effects:

  • increased wetted surface area
  • increased form drag (due to distorted section shape)
  • decreased prismatic coefficient (or beam, or waterline length) for the same displacement

These effects were all counterproductive and would tend to discourage such changes or negate them if tried.

Using the length restriction gauge

The bow and stern profile of a hull could be altered to increase draught markedly. The change would have the following effects:

  • longer waterline length (if not already maximised)
  • increased prismatic coefficient (or decreased beam or decreased hull depth)
  • marginally increased wetted surface area for same displacement
  • decreased manoeuvrability

The first and second might be viewed as positively useful. The third of these effects was the only one that directly adversely affected straight line speed but was marginal in size. The fourth, which may not be considered as a problem, was probably the most serious negative factor.

Based on the data and brief analysis above the conclusion at the time was that the transverse draught restriction gauge would be the better choice for the following reasons:

  • It controlled draught several times better than a combined gauge
  • With a transverse gauge any exploitation of section shape could give marginally increased draught but created three disincentives and no clear benefit
  • With a combined gauge any exploitation of profile shape could give a marked increase in draught, had two potential benefits and only one negative factor which might not be recognised as such.
  • It would be unwise to use a draught restriction system that might encourage designs of boats that were not manoeuvrable.
  • Dedicated length and draught restriction gauges are smaller, easier to handle and transport than a combined gauge

For the same reasons the Marblehead system is proposed for the 65 and NANO class rules.


Question details:

Is there be a method of producing a certificate/sail measurement for the provisional IRSA 65 Class?



The sail measurement system is identical in concept to the 2016 10 Rater measurement system that has many advantages compared to the previous 10R system.

Apart from being very simple to use it produces very repeatable results and is not type forming (does not tend to encourage one partcular sail profile shape).

The 10R certificate/sail measurement software has recently been developed to give more useful information to the measurer, certification authority and sail maker. The same advantages are incorporated into the 65 Class certificate.

NB        In the IRSA 65 Class rules there is no requirement for a boat to have a certificate - compliance is to be established by equipment inspection at an event only. Each rig (spars, fittings, rigging and one or two sails) shall have its own certificate. Owners may have as many such rigs as they choose and use whichever three rigs they wish to during an event.

Question details:

What steps were taken to consult with RG65 ICA and others before release of the provisional IRSA 65 Class rules?


In December 2015, the IRSA TC started the development of a discussion rules document for 65cm long monohulls. This was based on interest from some of the IRSA National Members and in recognition that the current RG65 Class rules were not in a format acceptable to run an approved Championship.

The IRSA TC aimed to give to the RG65 community a set of rules that would suit the class and also be in an acceptable WS format.

The document went through several iterations based on feedback from the RG65 ICA representatives and other stakeholders in the ensuing months until a dedicated working party was set up within the IRSA website to accelerate the development of the class rules.

The forum included three delegates from the RG65 ICA and three from the IRSA along with a large observer base from stakeholders and interested parties from around the world. The observers were allowed to introduce ideas through any of the delegates present.

This working party ran from March 2017 to December 2017. Each part of the draft rules was analysed and discussed. This resulted in a document called the 65 Class rules which has since been approved by the IRSA EC and is now published on the IRSA site under Classes.

It needs to be noted that the RG65 ICA has requested that these 65 Class rules should not be confused with the current RG65 Class rules under their care.

The 65 Class rules are, in a sense, a “generic” set of rules that could help any class of this size to develop and run a “Championship Event”


Where no ICA structure exists for an IRSA class, the IRSA sets up a class committee within the association and works towards growing this committee to the point where it can stand alone as an ICA.  Of course there is always the opportunity for a non IRSA association to take up that role.


As the IRSA 65 Class has provisional IRSA status the pathway is now straightforward: 

  • Apply to IRSA to hold a world championship 
  • Run the world championship

Boats will be eligible for the event only if their certification complies with the IRSA 65 Class rules. There is no prohibition on boats complying with and being certified to the IRSA 65 Class rules and, at the same time, complying with and being certified to the RG65 Class rules.

Question details:

Could the owners of boats that are not yet an IRSA designated class create their own class rules to the World Sailing Standard Class Rules format (as a precursor to applying for IRSA status and a world championship)?


Of course, but it may take longer to arrive at a result that is satisfactory to IRSA. 

This would apply to any class which is not already an IRSA designated class e.g. RC Laser, DragonForce, DragonFlite, RG65, Micro Magic.


The draught limit is to ensure all boats at an event can be guaranteed to be able to sail. From an IRSA point of view it is imperative that the race committee of an IRSA event does not find itself embarrassed because some competitors with class rule compliant boats cannot compete.  


You can find the provisional IRSA 65 Class rules under the relevant sections of this website (look under Documents and/or Classes).

In creating the IRSA 65 class rules, based on the RG65 class rules, the guiding principles have been:

  • The class rules are written in the WS SCR format using terms defined in the ERS. 
  • The sail measurement system is specified 
  • Ballast materials denser than lead are prohibited 
  • A draught limit is introduced 
  • Sail marks rules are rationalised with those in Appendix E of the RRS 
  • The rules for racing are specified as the RRS. 
  • Changing the fin/ballast unit after each day’s racing is prohibited. 
  • Measurement and certification of boats is by independent official measurers 



The major differences are:

In the IRSA 65 Class rules

  • The class rules are written in the WS SCR format using terms defined in the ERS.
  • The sail measurement system is specified
  • Ballast materials denser than lead are prohibited
  • A draught limit is introduced
  • Sail marks rules are rationalised with those in Appendix E of the RRS
  • The rules for racing are specified as the RRS
  • Changing the fin/ballast unit after each day’s racing is prohibited
  • Measurement and certification of boats is by independent official measurers


Class rules written using the WS SCR format ensure that as far as possible the language used and the certification (measurement) methods employed by the class rules are harmonised across the classes. Designers, builders, sail makers and measurers can then be confident of having a common understanding of class rules. This makes it easier for manufacturers of equipment to create products that are less likely to be found to be non-compliant by measurers.

Commonly used words like ‘boat’, ‘hull’, ‘hull appendage’ and a vast number of other similar boat part names, when printed in bold text as here, are all very precisely defined in the Equipment Rules of Sailing (ERS). The ERS is a stand-alone document available as a download from the WS and IRSA websites. 


To gain IRSA designation some straightforward, but important, standards have to be achieved. 

  • The class has to have a certain number of boats across a certain number of continents and countries. 
  • The class rules have to be written to a common standard, the WS Standard Class Rules (SCR) format.

These requirements would apply to any class which is not already an IRSA designated class e.g. RC Laser, DragonForce, DragonFlite, RG65, Micro Magic. Whereas the numerical requirements may be met in all or most of these cases (please see the IRSA Regulations for these), the requirement for WS SCR format class rules is not.


The RG65 class appeals to a large number of builders because they can exploit exotic construction methods without the problems associated with larger scale building projects. Construction can be as convenient as on a kitchen table. Sail making can be accomplished in a relatively small space. The class is a ‘development’ or ‘open’ class so builders have freedom to improve performance that is deliberately blocked in ‘one design’ or ‘closed’ classes.

The boat with all its rigs will comfortably fit into a well designed pack not much bigger than a box used to transport an IOM hull. The prospect of travelling by public transport, as well as by plane without having to pay for excess baggage, is a realistic one. The restriction on the number of rigs serves to restrict cost and complexity, and the boats can be sailed in a space as small as an Olympic swimming pool. A well set up RG65 performs remarkably well, so it is easy to see why the class is popular.

While the RG65 class rules do not meet the required standards for the class to become an IRSA designated class it is not possible for the class to hold a world or continental championship. However, it is consistent with IRSA’s constitutional object to develop the sport of rc sailing throughout the world to lend support to the sailors of any class that is popular internationally. For this reason the provisional IRSA 65 class rules have been created.

Creating a provisional IRSA 65 Class opens up the possibility of world and continental championships. Robust class rules are now in place so that continued participation in the class is not adversely affected by escalating costs. In this way it is believed the class will attract greater numbers of participants and the level of competition in the class will increase enormously. For these reasons IRSA is interested in assisting the class. 


No. Such an event would be defined by World Sailing as a prohibited event.

Some time back WS delegated responsibility for the international administration of radio sailing to IRSA and it is through this affiliation that IRSA is able to grant the right to run WORLD and continental championships in the rc international classes. WS protects the right to call a sailing event a world or continental championship – claiming an event is one when it is not sanctioned by WS or IRSA is a breach of the WS rules and can result in competitors being excluded from legitimate sailing events.

IRSA is the international class association for the Marblehead, Ten Rater and A Classes. The International One Metre has its own independent international class association, IOMICA, that is responsible for the administration of the IOM class and which is affiliated to IRSA. All these classes hold world championships from time to time and the events are run under the guidance of IRSA’s & IOMICA’s regulations using the well known Appendix E of the Racing Rules of Sailing (RRS).

In order that any class may hold any event titled ‘world championship’ or '(continental) championship' it has to have IRSA designated status. However, the classes that are not already IRSA designated classes e.g. RC Laser, DragonForce, DragonFlite, RG65, Micro Magic, have a clear pathway to follow (see IRSA Regulations) if they wish to pursue the goal or holding world or continental championships.


Question details:

What is the difference between a Q&A and a Class Rules Interpretation?


An interpretation is requested when it is not clear (to a designer, builder, measurer, class association or certification authority) how a class rule shall be interpreted. When an interpretation is issued it should be kept in mind that the interpretation is valid until the class rules are changed or for two years maximum only. The purpose of this last rule is that two years gives sufficient time to consider if the effect of the interpretation is a) desirable or b) undesirable. Depending on the decision or choice (a or b, by the IRSA TC or the class depending on whether there is an independent class organisation or not) the class rules can be revised accordingly.

Thus, when drafting any interpretation, it should be kept in mind how the class rules should/could be revised to make the original interpretation request redundant.

It follows that, if no revised class rule can be written, there is no need to issue an interpretation. Where no interpretation is required, but only an explanation of the effect of the class rules, it follows that it would be appropriate to deal with the original request by issuing a Q&A to be published on the IRSA website and elsewhere as appropriate.

This is the guiding principle used by the IRSA Technical Committee when considering any question about the class rules whether it is a formal request for an interpretation or not.



The ERS is a document maintained by the ISAF which is a revised on the same 4 year cycle as the Racing Rules of Sailing. The current version may be found on the ISAF website and there are several versions in translation listed there too.