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:

To what extent are hollows permitted in the profile of a Marblehead hull?


The relevant rule is D.2.3 (b) (2).


(b)         Except for the trunking for hull appendages, the hull shall not have:

(2)         hollows in the plan view and/or the profile under the datum waterplane that exceed 3 mm,

The drawing shows a hollow in the profile under the datum waterplane. There is a difference between the true waterline (waterplane) and the datum waterplane referred to in the class rules. The class rules use a length restriction gauge of a specified design to determine the datum waterplane.

The drawing shows a hull with a hollow in the profile at the stern. It also shows the length restriction gauge and the datum waterplane. The hollow found when a straight edge is placed to touch the hull at A and D is greater than 3 mm. However D.2.3 (b) (2) applies to hollows under the datum waterplane. When a straight edge is placed touching the hull at B and C, the hollow is less than or equal to 3 mm. The hull, therefore, complies with D.2.3 (b) (2).

Question details:

How large can the sail maker label be on sails? Or the manufacturer label on other items of equipment? The class rules do not restrict this?


The relevant rules are contrained in the World Sailing Advertising Code, also known as Regulation 20.

Clause 20.7.1 states that the display of manufacturer's and sailmaker's marks is permitted at all times as detailed in Table 2 but not in areas that area reserved for Event Advertising. For radio controlled boats the area reserved for Event Advertising is 40% of the hull length on each side of the hull from the foremost point on the hull. No Event Advertising is permitted on the boom(s), backstay or sails.

20.7.2 tells us a manufacturer's mark may include the name, logo or other identification marks of the designer or manufacturer of the equipment.

20.7.3 tells us that a sailmaker's mark may include the name, logo or other identification marks of a sailmaker or of the sail cloth manufacturer or the pattern or model of the sail.

Table 2 – Manufacturer’s and Sailmaker’s Marks

Radio-controlled boat

Hull  - On each side of the hull, and may include the name or mark of the designer or builder - One mark to fit within a rectangle measuring 15% of hull length x 150mm                     

Spars and Equipment - On each side of spars and on each side of other equipment - One mark not exceeding 50mm length                    

Sails - On each side of sails and kites - One mark to fit within a 50mm diameter circle






Question details:

Template to assist measurement of Marblehead sails and rigs


Daniel Kohler (FRA) was seen using this simple but useful template at the 2016 Marblehead Championship in France. The design is by Michel Brun (do you have a CAD file please, Michel, that we can add as a download?).

It seemed to be laser cut or CNC cut from aluminium alloy. The dimensions of the cuts outs etc are used as follows:

900 mm radius - control of upper and lower regions of leech

105 mm - maximum batten length

40 mm - top width of pocket luff mainsails, mast spar cross section below lower point, combined boom spar cross section where two boom spars are joined, boom spar cross section within 100 mm of one end

25 mm - top width of mainsail that has a luff rope

20 mm - mast spar cross section above lower point, headboard width and top width for mainsail

13 mm - minimum bumper length

3 mm - minimum limit mark width

PLEASE NOTE - The 40 x 40 and 20 x 20 cut outs DO NOT imply that the mast and/or boom may be square sections in those regions. The class rules make it clear that the limit is on any cross section - a 40 mm diameter or 20 mm diameter are effectively the maximum sections permitted.  

M Measurement Jig    P1040043s

Question details:

Is there a size limit for primary and/or secondary reinforcement on Marblehead Class sails? Is the material used for primary and/or secondary reinforcement restricted in any way?


Primary or secondary reinforcement used on Marblehead Class sails is un-restricted in size.

Class Rule G.2.5 (a) requires sails to be soft sails.

ERS G.1.4 (c) defines a soft sail as one where the body of the sail is capable of being folded flat in any direction without damaging the ply other than by creasing.

ERS G.1.4 (a) tells us the body of the sail is the sail excluding areas where parts are added e.g. (ERS G.1.1) sail reinforcements.

Therefore sail reinforcements do not have to comply with the soft sail test.

ERS G.6.1 tells us that primary reinforcement is an unrestricted number of additional layers of ply of permitted material and that secondary reinforcement is not more than two layers of ply of permitted material not thicker than the body of the sail. As there are no restrictions on size the maker is free to use any reinforcement that complies with the restriction on primary reinforcement.

The only requirement is that reinforcement consists of ply of permitted material (there are no restrictions so any material is permitted subject to it being a ply).

ERS G.1.4 (b) defines a ply as a sheet of sail material (which may be made up of a number of layers).

Provided the reinforcement is made up of sail material it is compliant with the Marblehead class rules.




Question details:

Is it permitted to use deck spreaders?

These are sometimes referred to as outriggers and can be seen on IMOCA 60 Class boats. The inboard end is close to or on the deck and they have standing rigging going down from the outboard end to the hull and standing rigging going up to support the mast.


A deck spreader is defined in the ERS F1.4 (c)(iii) as a hull spar extending transversely to attach standing rigging. A hull spar is defined in ERS F.1.4 (c) as a spar attached to the hull. The spars permitted on a Marblehead rig are limited to one mast spar, one headsail luff spar and four boom spars.

A deck spreader is not permitted.

If the spreader is attached only to the mast, and not to the deck, then it no longer falls within the definition of a deck spreader. Instead it is a spreader defined in ERS F.1.5 as equipment used to brace a spar, attached at one end to the spar and the other end to rigging and working in compression when in use. It is effectively the same as any other spreader, normally placed higher up the mast.

A spreader, if not attached to the hull, is permitted.

Question details:

Does the Certification Authority have to use an official stamp in the relevant place when issuing a certificate?


There is no prescribed requirement for the size or style of ‘official stamp’. At an event the person inspecting the official stamp on a certificate has no means of knowing if it is the correct one or not. The important thing is that the issuing Certification Authority will recognise it at some future stage should the certificate be referred back to it for any reason.

Any size or style of official stamp will suffice providing the CA is happy that it can recognise it as authentic at a later stage.

Question details:

What has happened to the previous interpretations? There were many interpretations to the previous versions of the Marblehead, Ten Rater and A Class Rules. Where are they now?


IRSA regulations restrict the life of an interpetation to two years - after that time any interpretation ceases to be valid. The reason for this is that it is expected that the class rules will be changed during the two year period to make the interpretation unnecessary.

Where the new class rules require equipment to comply with the current class rules, if the class rules incorporate the effect of the earlier interpretation(s), then clearly the intrerpretation(s) is no longer needed. This explains why some interpetations are no longer needed and have been removed.

Where the new class rules permit equipment to comply with earlier versions of the class rules (usually known as 'grandfathering') then the earlier interpretation, although expired, remains relevant and is retained for information. A few such interpretations are retained.

Many other interpretations that were issued in the period before 2014 have been revised and are presented here in the form of Q&As (see Q&A on the difference between an interpretation and a Q&A). Again, this explains why many earlier interpetations are no longer needed and have been removed.

Question details:

Under the 2002 CR was it permitted to use a 'square' boom spar cross section 20 mm wide x 20 mm deep?


The 2002 CR restricted the boom spar cross section to 20 mm. The ERS definitions referred to vertical boom spar cross section and transverse boom spar cross section which led to the unfounded belief that the Marblehead boom spars were restricted in a vertical sense and a transverse sense thus permitting 20 mm 'square' section boom spars. As the term boom spar cross section was not itself defined in the ERS - the class rules effectively permitted a maximum boom spar cross section equal to a 20 mm diameter circle. A square section could be used but would have a maximum side of 14.1 mm.

The 2016 CR revert to the term 'cross section' and a diagram indicates how the limit is applied.

Boats in the class shall have rigs that comply with the 2016 CR even if initially certified before the 2016 CR came into effect.


Starting in around February 2015, class rule changes were introduced and discussed within the IRSA Technical Committee. The proposed rule changes were circulated to IRSA Designated National Members (DNMs) around December 2015 and January 2016. A number of DNMs responded with comments, and these were addressed by the TC Chairman. The proposed revised class rules were then brought to the Executive Committee by the TC Chairman in March 2016, which the EC formally voted on and approved. The rules, and an explanation of the changes, were published in April 2016, and came into effect in July 2016 after minor errors were found and edits made. This is the process which has been used in the previous decades of rule changes by the IMYRU, ISAF-RSD, and now IRSA.  


It is inevitable that a new set of class rules may have a rule which is thought to be in error or in need of amendment. Suggest a rule change to your DNM. If it agrees, or if you are the DNM, send it to the TC Chairman for further discussion. Please read carefully our regulations and Q&A to avoid unnecessary work before you send any suggestions to the TC. Proposals for rule changes should be based on meaningful technical evidence and not on loud repetitions.  

Question details:

Use of boats with certificates issued by sources other than IRSA affiliated bodies?

Is it possible to enter an event described in the NoR and SIs as for boats of an international class (IOM,. M, 10R or A Class) with a certificate other than an IRSA certificate issued by a body affiliated to IRSA?



The IRSA international classes are distinct from classes using the same name but which are not administered (ultimately) by IRSA. For example the Naviga administered One Metre, Marblehead and Ten Rater classes are different classes and the certificates issued under those rules are not valid for IRSA events (world or continental championships) or events normally organised by IRSA affiliated bodies. The same is true for the Marblehead class administered by the American Model Yachting Association which uses class rules different to the international class rules.

The owner of a boat in one of those classes can obtain a certificate for the international class after having his boat measured to the IRSA class rule. To do this he should find an official measurer (please see the Equipment Rules of Sailing) and then contact his certification authority (normally the body in his country that administer rc sailing and is affiliated to IRSA). If he is a member of a body affiliated to his World Sailing Member National Authority (the body responsible for the administration of SAILING in his country) he will then be eligible to take part in events for the international class.

Question details:

A Ten Rater has its largest sails measured for the purpose of establishing its rating. Those sail sizes are entered on the measurement form and are recorded on the certificate. The same is true for an A Class boat and for a Marblehead (usually the largest of A rig, of B rig and of C rig). Is it necessary to have smaller sails measured and certified?



The smaller sails are measured to ensure they are indeed smaller and that they meet the other requirements and restrictions. Then they are certified (usually by the measurer signing the sails) to show that this porocess has bene completed satisfactorily.

Question details:

At what point, on change of ownership, does the certificate become invalid?


The certificate becomes invalid upon a change of ownership. The change of ownership is the important criterion – not the signing of the certificate by the new owner – not the issue of the new certificate in the new owner’s name.

However, while the concept of ownership is normally well understood between any two people it may be that the law of the land becomes relevant in particular cases and this may vary depending on the contract involved and where the ‘transaction’ takes place.

The view is that IRSA class rules are not intended to, nor do they, shed any light on ownership or when it changes hands.

Question details:

When the foot of a double luff sail falls below the lower limit mark, does it comply with the class rules?


The class rules (Marblehead and A Class) require that the tack point shall not be set below the upper edge of the lower limit mark. The tack point is normally aft of the mast spar but on a double luff sail (specifically a pocket luff sail) it may be forward of the mast spar. In this case it may be that the foot of the sail overlaps the lower limit mark (as shown on the diagram). There is no requirement in either class rule that the foot of the sail shall be above the lower limit mark.

A sail set as shown in the diagram complies with the class rules.

tack point_and_lower_limit_mark

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.

Question details:

Section C of the class rules requires the hull registration number to be displayed legibly on the external surface of the hull with a minimum height of 20 mm.

Section D of the class rules requires the hull registration number to be permanently marked on a non-removable part of the hull surface.

Can a single set of hull registration numbers satisfy both rules?


Yes. Providing the hull registration number digits are of minimum height 20 mm, are clearly legible, are easily visible, are painted, engraved, bonded in or moulded in, and are on a non-removable part of the hull then both rules are satisfied by a single set of numbers.

However, it is often more convenient and attractive to use vinyl numbers on the deck to satisfy the Section C rule and some more convenient method on an inside area to satisfy the Section D rule.

Bear in mind the purpose of the rules: the Section C rule is for the benefit of the race committee and other competiors at an event to help identify a boat when it does not have it's rig in place; the Section D rule is to permanently and uniquely identify a boat so that it may be grandfathered, if needed, at a later date. In 50+ year's time the number will also add value and interest to any boat that has survived that long.

Question details:

A recent ruling for the IOM class says the certification authority for the hull is the DNM of the country where the owner is resident.  Does this apply to the M, 10R, and A Classes too?



The IOM, Marblehead, Ten Rater and A Class class rules indicate the certification measurement forms (measurement forms) are sent to the certification authority in the country where the hull is to be registered. This seems to give the owner some choice over where his hull is to be registered.  However, ERS C.3.1 defines the certification authority as 'the MNA of the owner'. Where the term certification authority is used it shall be understood to be the certification authority in the country where the owner is resident or in the country of which the owner is a national. This is normally the DNM (Delegated National Member for radio sailing) in the country.

Question details:

Who issues a certificate for any of the IRSA classes?






The certification authority issues the certificate. As of 1st July 2016 all the IRSA classes have the same administrative section. It is A.9 that indicates it is the certification authority that issues a certificate.

The term 'certification authority' is defined in the ERS as:

For the hull: the ISAF, the MNA of the owner or their delegates.

For other items: the ISAF, the MNA of the country where the certification shall take place, or their delegates.

The members of IRSA are the bodies to which the administration of RC sailing has been delegated (if not the MNA of the country itself) and which are known as the DNMs. So, for the hull it is the IRSA DNM of the owner.

For other items it will usually be the same but it could be the MNA or delegate of MNA in another country where the emasurement took place. This would apply where, for example, sails were certified in house by a sailmaker who had been delegated the authority to do that.

See also the related Q&A concerning who is the certification authority, or DNM, for an owner.

Question details:

Where there are multiple deck limit marks, how should the measurer chose which one to measure to?


The Marblehead class rules do not seek to restrict the shape of the deck near the mast. It would be complex to do so and the point to which rig height is measured is taken to be relatively non-critical.

A deck limit mark for each rig/sail group shall be displayed on the hull centreplane near to the relevant mast position. The limit marks shall be a minimum of 5 mm in diameter.

It is for the owner to decide where to place each limit mark. If there is any lack of clarity regarding which limit mark applies to a rig/sail group the owner should be asked to identify the limit mark(s) accordingly.

Once the limit marks are identified the official measurer can carry out his measurements.

Equipment inspectors (event measurers) carrying out pre-race checks may wish to make deck limit marks 'permanent' by signing over the top.

Question details:

Is a rotating mast head fitting (approx. 10 x 20 mm) that supports the head of the mainsail permitted?


If the size is no bigger than is necessary, yes.

The 2016 CR require rigs to comply with the 2016 CR. The rule relevant to the design of rig fittings has changed marginally. A rotating fitting or a fitting attached to a rotating spar shall be no bigger than is necessary.

Question details:

Is it permitted to have a hull with a beam less than 100 mm?



For a hull certified to the 2002 CR, if the maximum beam of the hull is less than 100 mm it will not be possible to use the depth gauge in the prescribed way to test compliance with C.5.2.

If the hull beam is 100 mm or more it will be able to meet class rule C.5.2 but this may impose restrictions on the design of the hull appendages, as on a 100 mm wide hull the gauge may touch the hull at only one section and will have to rotate about a single point of contact.

For a hull certified under the 2016 CR, D.2.4 specifiies a minimum hull beam of 100 mm.

Question details:

What sail identification marks shall be displayed when a hull holds a certificate in more than one class.


When a boat races it shall carry the appropriate sail identification marks for that class. Providing they do not affect the legibility of the marks, alternative class insignia may remain on the sails.


No. C.6.3 prevents the movement, articulation, retraction or extension of hull appendages (including the ballast). Additionally RRS 51, which is not excluded by Appendix E of the RRS, states that movable ballast ‘for the purpose of changing trim or stability’ is not allowed.

1994 CR 4.1.1 prevents movement of the ballast fore and aft and canting keels per se are not prohibited. However, when a race is un using the RRS and RRS 51 is not cancelled the effect is the same.

The same logic applies to the other classes too.

Question details:

Can a boat with a certificate in one class also hold a valid certificate in another class?


There is no rule in any of the International One Metre, Marblehead, Ten Rater or A Class class rules which prevents a boat from having a valid certificate for another class.

Question details:

Where a mainsail has a pocket luff over only a part of the luff, how are the luff perpendicular, quarter width, half width, three-quarter width and head width to be taken?


qa3The ERS G.1.4 (g) defines a double luff sail as “….a sail with more than one luff or a sail passing round a spar and attached back on itself.”

The sail does pass round the spar and attaches back on itself so it is a double luff sail and shall be measured as prescribed even where the double luff is not present. The class rule G.2.4 (b)(1) prescribes that the luff perpendicular and cross widths shall be taken to the luff, or to the fore edge of the spar, whichever gives the greater dimension.

The ERS G.4.2 shows how the head point of the mainsail is found at the intersection of the luff, extended as necessary, and the line through the highest point of the sail at 90 degrees to the luff. When the luff is extended in this way, the head point will be a point at the forward edge of the mast spar.

Where the sail has a series of short luff sleeves, each like a double luff, in total no more than 10% of the luff in length and no one of them more than twice as long as the shortest, then the sail ceases to be a pocket luff sail. The widths shall all be taken to the luff excluding the luff sleeves which are discontinuous attachments. Class rule G.2.4 (b)(5) refers.