Question details:

Why should a different gauge used for draught restriction than for length restriction (relevant to Marblehead, RG65 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 RG65 and NANO class rules.


Question details:

Will there be a method of producing a certificate/sail measurement for the provisional 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).

Currently some edits are being made to the 10R certificate/sail measurement software that will give more useful information to the measurer, certification aithority and sail maker. When these have been refined and tested the certificate will be released and the same material will be used for the provisional IRSA RG65.

Question details:

What steps were taken to consult RG65 ICA and others before release of the provisional class rules?


Log of actions over the last 15 months up to March 2017 concerning the dialog between the RG65 ICA, others and IRSA :

Dec 2015             Based on the interest of some National Members the IRSA TC develops a first rule to discuss within the Technical Committee of IRSA

Feb 2016             First contact of IRSA TC with Fredo Vollmer (RG65 ICA Chairman) by Gerd Mentges (Vice Chairman TC) and explaining the wish of IRSA to develop the RG65 class in a way that is acceptable for both IRSA and ICA. IRSA explained that this action is in no way an unfriendly act but an action which IRSA wants to make in conjunction with the RG65 ICA.

March 2016         First draft of a rule text send to Fredo Vollmer

March 2016         First draft send to the RG65 representative of USA

March 2016         First draft send to the German representative of RG65 ICA

May 2016             Discussion of the text (input from different parties, amongst others Fredo Vollmer, Earl Bobert, Graham Bantock)

June 2016            Sketches with possible faults using the current RG65 sail measurement rule send to Earl Bobert (USA)

June 2016            Survey from Fredo Vollmer send to all RG ICA countriesr recommending rejection of IRSA approach. Results in rejection of IRSA approach

June 2016            Advantages for the RG65 sailors sent to Fredo. Answer to his question concerning possible cost - there is no fee to be paid to IRSA

July 2016             IRSA did not give up the attempt of working together and sent a proposal to Fredo Vollmer for an official working group of IRSA and RG65 representatives

Sept 2016            Answer from Fredo Vollmer with some questions concerning the proposal and reply from Gerd Mentges

Oct. 2016             IRSA proposal for a personal meeting with Fredo Vollmer and ICA representatives to improve any cooperation.

Oct. 2016             Skype meeting Fredo Vollmer with Harry Drenth (RG representative for the Netherlands). Harry repeated the proposal for a meeting.

Nov 2016             Skype meeting Fredo Vollmer with Gerd Mentges. Announcement of publishing a "provisional rule” to progress the discussion and for public information.

Nov 2016             Gerd Mentges sent a DSV (German national WS and IRSA member) proposal for organization of a collaboration between a national RG community and an IRSA national member to Fredo Vollmer. 

This proposal shows opportunities of sailing together even if someone is not a member of the national organization.

Fredo Vollmer found this being a very good solution and mentions to translate it and send it to all RG national representatives.

Dec 2016             Transmission of the accompanying text to the provisional rule to Fredo Vollmer with the request to comment on it.

Jan 2017              Fredo Vollmer answers that the RG ICA has a lot of experts to take part in the proposed working group.

March 17             IRSA is still waiting for nominations of RG ICA representatives for the proposed working group.

March 17             Provisional RG65 class rule posted on IRSA website



IRSA would like to see the RG65 class form a class committee within the IRSA structure. Although currently organised on a regional structure of representation, IRSA is in the process of re-structuring into a class based organisation. When any class committee becames self-sufficient, IRSA policy is that it should split off to become an independent ICA in the same way as IOMICA. 


That pathway would be: 

  • Use the revised class rules 
  • Achieve sufficient registered boats in sufficient countries and continents 
  • Apply to IRSA for International Status 
  • Apply to hold a world championship. 


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


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.  


Briefly: 

  • The class rules would be written in the WS SCR format using terms defined in the ERS. 
  • The sail measurement system would be specified 
  • Ballast materials denser than lead would be prohibited 
  • A draught limit would be introduced 
  • Sail marks rules would be rationalised with those in Appendix E of the RRS 
  • The rules for racing will be specified as the RRS. 
  • Changing the fin/ballast unit after each day’s racing could either be facilitated by the class rules or, alternatively, prohibited. 
  • Measurement and certification of boats would be by independent official measurers 
  • Each national association would keep a register of officially certified boats


An issue that would prevent the RG65 achieving international status is the tradition that the boats are measured by the owners with no independent checking. A complicating factor here is a lack of a prescribed system for measuring sail area.

Another tradition in the class, that of being able to replace the fin/ballast unit after each day’s racing, is not permitted either by the current class rules or the Racing Rules of Sailing.

The current lack of restriction on the material used for the ballast means that Tungsten (also known as Wolfram) and other exotic high density materials are permitted. The unwelcome cost implications of this in the long term are clear.

The concept of having only three rigs in the class is a sound principle that works well in the IOM class. Whereas the IOM class has several safeguards to keep cost down (no exotic materials in the hull, minimum hull weight, wood or aluminium spars only, one design sails) there are no such restrictions in the RG65 class and construction costs are higher than they would be otherwise. It is probably too late to introduce some of these concepts into the RG65 class – as “the horse has already bolted”. But there are some things that can easily be achieved that will help keep the class popular in the long term and restrict escalation of costs. 


Class rules written using the WS SCR format ensure that as far as possible the language used and the 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.

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


To gain international class status 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.

Whereas the numerical requirements are met, it is clear the requirement for WS SCR format class rules is not.


The 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.

It is consistent with IRSA’s constitutional object to develop the sport of rc sailing throughout the world to lend support to any class that is popular internationally.

Given the opportunity to hold world championships the class would inevitably attract greater numbers of participants and the level of competition in the class would increase enormously. It is essential that robust class rules are in place before that happens so that continued participation in the class does not become prohibitively expensive.  

Wtih well designed and managed class rules there is no reason why the class cannot become an international class and hold a world championship in the near future leading to even greater numbers being attarcted to the class - for this reason IRSA is interested in the class. 


Not as it exists at present.

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 championships in the rc international classes. WS protects the right to call a sailing event a world 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 international 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 the RG65 class may hold any event titled ‘world championship’ it has to have international class status given by IRSA.

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.