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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:


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:

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.

Question details:

Is it necessary to float a Ten Rater at the time of certification control (measurement) to establish the correct placement of the waterline limit marks?


No. The true waterline length is not a measurement that is required at certification control (measurement) or at any other time unless the purpose of the measurement is to determine compliance with the certificate (equipment inspection).

What is required is placement of the waterline limit marks and measurement of the distance between them. Class rule C.4.1 shall be complied with when the boat is racing and, providing the boat complies fully with the class rules when racing, no rule is broken if the boat has not been floated at the time of initial certification control.

The requirement in the 2002 CR to have the waterline endings no more than 30 mm inboard of those limit marks no longer applies.

Question details:

Under the 2002 CR and where a hull design has plumb (vertical) ends and the waterline endings extend to the extreme ends of the hull, may the waterline limit marks be placed around the bow and/or on the transom?


No. The class rules require the waterline limit marks to be placed on the undersurface of the hull.

A waterline limit mark placed around the bow some distance up from the LWL is not on the undersurface of the hull although it may be across the centreplane of the hull. Similarly with the waterline limit mark placed on the transom. These waterline limit marks would not comply with Class Rule D.2.1.

It is suggested you add a short extension(s) to the hull, where appropriate, that may carry the required waterline limit mark(s) that are on the underside of the hull as in the diagram below.

limit mark_on_10R_vertical_bow

The 2016 CR contain different wording and this issue is effectively resolved.

Figure L.4._Variation_1gb1  Figure L.4._Variation_2gb1  

Question details:

For the purpose of initial certification control (measurement), is it possible to take the largest cross widths of two or more sails and use these to create dimensions for a ‘virtual’ sail that is recorded on the certificate?


For boats certified to the 2002 CR, no. The Ten Rater class rules I.2 and J.2 refer to the measured rig area and measured sail area of the largest rig. It follows that the largest rig and sails to be used shall be presented to the measurer and be certified.

The Ten Rater class rule does not require that the largest rig and sails be used at any event. However, alternative sails are mentioned in Section C and in order to certify those sails the measurer shall check that they fall within the profile of the largest sails (the dimensions of which are recorded on the certificate). This check cannot be made unless those largest sails are present.

For boats certified to the 2016 CR, yes. The concepts of measuring the largest suit of sails and alternative sails having to fit within the profile of those sails no longer apply. It is possible that the dimensions of 'virtual' sails could be placed on the measurement form and sails checked against those dimensions for compliance.

Question details:

  1. qa2Would a hull with an open central section of the aft overhang (fig 1), extending from the transom forward to a short distance aft of the aft waterline ending, comply with the class rules?
  2. Does the presence of a deck across the top of and joining the twin overhangs (fig 2) make any difference?
  3. Does the width of the open section (fig 3) make any difference?
  4. Does leaving the twin overhangs un-decked (i.e. each is no more than just the thin skin of the primary hull moulding) (fig 5) make any difference?


  1. No. The open section is a hollow in the surface of the hull (see definition of hollow below). Since hollows in the external surface of the hull are prohibited less than 40mm above the datum waterplane and more than 15 mm from the centreplane, the proposed feature clearly falls outside the rule D 2.4(b) and the hull does not comply with the class rules.
    Hollow is undefined in CR, ERS and RRS. The Oxford English Dictionary definition of the noun ‘hollow’ is: “a hole or depression in something”.
  2. No. The presence of a deck does not change the presence of hollows in the external surface of the hull to be tested under D 2.4 (b).
  3. Yes. D 2.4(b) (3) makes an exception for hollows within 15mm of the centreplane which are permitted. The reason for this exception is to permit the hollows that are formed by the presence of the keel and rudder where they join, or are faired into, the hull. If the hollows are entirely within this region they are permitted.
  4. No. In this arrangement the upper surface of the overhangs are “inset transom and upper surface of deck” and thereby, any concavity in that upper surface is not prohibited by D2.4(b) 5).
    The absence of a deck or any other structure apart from the hull shell does not change the presence of hollows in the external surface of the hull to be tested under D 2.4 (b).

The 2002 CR have the same effect.

Question details:

  1. Is a spar that is attached to the hull and extending from the mast and along the foredeck a part of the rig for measurement purposes and should it be included in the certified rig area?
  2. Is a spar that is attached to the mast of a swing rig and extending forward to support a spar to which the tack and/or clew of a headsail is attached to be included in the certified rig area?


  1. If the item is part of the rig (if it is removed when the rig is removed from the hull, then it is a part of the rig rather than a part of the hull) then it shall comply with the class rules for the rig.

       The relevant class rule is J.1 (a):

One spar, not being a mast spar, with a spar cross section not exceeding 22 mm is permitted to extend the tack and/or clew of each sail without being included in the certified rig area.

The spar described does not extend the tack and/or clew of a headsail so its area shall be included in the certified rig area.

  2. Same answer as Q1 – see 1. above.


Revised on 11.11.2018. to be in accordance with Ten Rater Class Rules - Effective 1st November 2018

Question details:

Who issues a certificate for Marblehehad and 10R 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:

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:

Where the deck is irregularly shaped near the mast, where is the correct place for the deck limit mark?


The IOM 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 shall be displayed on the hull centreplane near to the mast position. The mark shall be a minimum of 5 mm in diameter.

It is for the owner to decide where to place the mark.

Once the mark is placed the measurer can carry out his measurements.

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

Question details:

When a boat with a reverse sloping transom (retrousee transom) has a waterline limit mark placed at the waterline, but where the transom/stern of the boat extends beyond the limit mark under the water, what is the correct treatment under the class rules?


The class rule C.4.1 (c) requires that no part of the underwater hull extends beyond the waterline limit marks.

C.4.1 (c)   submerged parts of the hull shall not extend beyond the inboard edges of the waterline limit marks.

In the case described a part of the underwater hull does extend beyond the waterline limit mark (which is correctly placed). The boat does not comply with C.4.1 (c) and therefore is not eligible to compete in competition.

The owner needs to find some way to place the limit mark so that the boat complies with the class rules.


Question details:

Why is the waterline length not required to be checked at certification control (measurement)?


Prior to the 1994 version of the class rules it was required to determine the waterline endings, measure the length between them and use that figure to determine the rating. The waterline endings were not marked with limit marks and no data was recorded that might determine those points. According to the certificate any alterations to the boat that affected the rating would invalidate the certificate.

However it was commonplace for owners to alter the fittings, mast position, spars, sails, on board rc equipment etc and not repeat the measurement process. Note that even a weight reduction would alter the rating thus rendering the certificate invalid.

In 1994 the requirement to add limit marks was introduced and it became permitted for the first time to alter the boat without the certificate becoming invalid. 

The purposes of this change:

  • to permit owners to freely modify their boats (which they did anyway) but for the first time within the class rules
  • with suitable equipment the measurer (certification measurer or equipment inspector at an event) can easily dry measure between the marks to establish the rated waterline length
  • with a tank, or any piece of calm water, the owner/measurer/sailor can float the boat and establish that the waterline endings are inside the limit marks without the need to precisely determine the waterline ending positions
  • there is the possibility that other sailors can judge whether a boat is floating to its marks or not

The new freedom granted to the owners was balanced by their new responsibility to ensure that their boat complies with the class rules and certificate when competing at an event. It follows that equipment inspection at an event (always difficult when flotation has to be checked) is the only way to monitor correct compliance with the class rules. But there is nothing new about this - it has always been so.

Should a boat be found to float with the waterline endings beyond the limit marks at an event the responsibility lies clearly and solely with the owner for failing to ensure it floats correctly. Altering the boat and failing to take steps to ensure continued compliance with the class rules might be taken as a breach of RRS 69 by a jury.

The 2016 CR have followed the same logic but have introduced some further safeguards. Boat weight is determined at certification control and is recorded on the certificate. At an event the boat may not weigh more than 0.05 kg more than this figure. The waterline limit marks shall be long enough to be visible when afloat.

Question details:

Why are boat weights and lengths not required to be checked at certification control (measurement)?


It used to be normal for class rules to require all equipment to be checked for compliance with the class rules. It was also normal for the certificate or class rules to state that alterations would invalidate the certificate. Yet it was commonplace for owners to make alterations to their boat/equipment without returning to the measurer to have it re-checked. This made it tedious for scrupulous owners to enjoy the freedom to develop their boats in the same way that less scrupulous owners did.

Clearly, when a boat competes at an event it is important that it complies with the class rules in all aspects. However at certification control (measurement) it makes no sense to check the overall length or draught of a boat because those dimensions necessarily depend on the weight of the boat and its flotation which are in turn affected by the weight and placement of removable items (rudder, fin, ballast, rc equipment). By removing those checks from certification control a tank and accurate scales are not required before a certificate can be issued. Only at an event when those items are in place need, and can, those dimensions be checked. If a tank and accurate scales are available at certification control measurers are encouraged to monitor those checks if owners wish. But owners need to be made aware of their continuing responsibilities after the certificate has been issued.

The freedom granted to the owners to alter equipment is balanced by their responsibility to ensure that their boat complies with the class rules when competing at an event. It follows that equipment inspection at an event (always difficult when flotation has to be checked) is the only way to monitor correct compliance with the class rules. At an event a tank can be used to check all the boats, far more efficient than at each boat's certification control. 

Should a boat be found not to comply with the weight and dimensional limits the responsibility lies clearly and solely with the owner for failing to ensure compliance. Altering the boat and failing to take steps to ensure continued compliance with the class rules might be taken as a breach of RRS 69 by a jury.


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:


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:

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.


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:

Does an alternative sail have to fit within the profile of the 'largest' measured sail?

The 2002 class rules C.8.1 Limitations stated: "The profile of each alternative sail shall fall within the profile of the sails recorded on the certificate."

Is this no longer a requirement in the 2016 class rules?




Diff Profilesgb1No. Under the 2002 class rules it is required that 'alternative' sails shall fall within the profile of the sails recorded on the certificate. The 2016 class rules do not require this.

Sail makers will be aware that sails are 3D objects and small changes to the inbuilt shape at the seams will have an effect on the profile of the sail. Although apparently simple in its requirements, the 2002 class rule creates several problems. Unless the sailmaker knows the leech length of a sail he is replacing he is unable to make a sail of the same profile (even if it is a purely 2D object). Even 1 mm more, or 1 mm less, leech length or luff curve results in the profile of the replacement sail not matching the original. It is not smart to have a class rule that does not allow the owner to replace his equipment and easily meet the class rules. Further, unless the sails measured and recorded on the certificate are retained by the owner when he has replacement sails they, and the other 'alternative' sails cannot be checked according to the class rules.

The 2016 class rules no longer require alternative sails to fall within the profile of the sails recorded on the certificate but treat the issue in a slightly different way that solves the problems mentioned above and gives other benefits. How?

The way in which the 'largest' sail is placed on the measurement grid has been revised marginally - the head and tack are placed on a line perpendicular to the transverse grid lines with the clew placed on a grid line. At and above the clew the cross widths are taken as usual (but at 200 mm intervals instead). Below the clew the depths are taken at 50 mm intervals. The dimensions are recorded on the certificate.

'Alternative' sails are checked by placing them on the grid in the same way and checking that their dimensions (measured in the same way) are equal to or less than the certificate dimensions.

There is no requirement for these 'alternative' sails to fall within the profile of the 'largest'. This introduces freedom to have sails made with different luff curves (or fullness/camber for example) but which comply with the certificate. Any width added at the luff needs to be removed at the leech. Provided the cross widths measured at all grid lines remain less than or equal to the certifiate values, the sail complies. See the diagram above.

The sail maker has all the information he needs to make sails that comply with the class rules as extended by the boat's certificate without asking for more. At equipment inspection there need be no difficulty in establishing a sail's compliance under the 2016 class rules.

This freedom exists for boats with certificates to the 2016 class rules only. Boats measured to the 2002 class rules and any new sails made for them shall continue to comply with those class rules. 



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.