1958
By 1958 the IFA had gained some experience in the way to treat the IYRU and got most of the proposals approved. The rule about the fully lowered centreboard was approved with 700 mm from the bottom of the hull and not to the keel bands. The rules about the mast were rephrased. A rake of 50/1000 was recommended, but the rake was not to be adjusted. The mast had to be made of spruce upward from a point maximum 1500 mm above the top of the keel.

The most important change concerned the material of the sail. The limitation to cotton was abandoned and replaced by the requirement to use woven cloth of even thickness. To improve the visibility one transparent panel not exceeding 0.279 m 2 was permitted. There the IYRU, headquartered in London, managed to introduce a non-metric measurement into the Finn rules, because the odd 0.279 m 2 is 3 sq feet. Finally a new buoyancy rule was introduced, requiring 200 kg of buoyancy. Tanks were allowed and bags could be included in the weight measurement.

Most important for 1958 was, that the IYRU approved in principle the suggestion of the IFA to allow plastic construction for the hull. For the final approval the IYRU requested a major revision of the rules. In Switzerland and Germany some experiments with Finns in plastic construction had been initiated by enterprising boat builders in 1958, in order to keep the Finn Dinghy up to date. Within the IFA as well, strong forces attempted to avoid that the Class be outmoded by new boats built to more modern construction methods. However the President Henri Leten, the Secretary Richard Murray and Rickard Sarby as the leading forces of the Technical Committee had to consider the existing wooden boats and had to take care that they remain competitive. Murray asked for suggestions for a new set of rules, in which the important regulations which make the boat what it is remain unchanged, while the details of the wooden construction became optional. Murray in addition attempted to draft a special brochure 'Instructions to Measurers', however it took several years before these were published.

1959
By March 1959 Richard Murray sent out a new set of suggested rules to the National Finn Associations and the members of the Technical Committee. At the AGM in August 1959 at Copenhagen these rules were discussed in detail. A revised version was handed in to the IYRU in time and generally approved at the November 1959 IYRU meeting. The driving force behind this process was the Secretary of the IFA, Richard Murray from the UK. In order to keep the deadlines he partly exceeded his authority but got away with it. Sometimes you have to ignore the rules of democracy and fall back upon authoritarianism in order to get things done. Murray was aware of this and apologised after the fact, but the final approval of the new rules by the IYRU justified his excess of competence.

The new rules of 1959 had 4 Sections. Section I stated the objective of the rules as the establishment of a One-Design-Class in all matters which affect the speed of the boat, but in which the material and details of construction are left optional. The rules of Section II were obligatory and are the hard core of the new edition. Section III referred to the conventional method of carvel construction and did not need to be followed. Section III became rather short and was intended to serve as a guide for amateur builders who wanted to play it safe and build a conventional boat without the danger of not passing measurement. Section IV concerned the measurement and certificates.

Aside of a complete rearrangement of the rales in four sections, the 1959 edition also included a number of substantial changes. The keel line was defined by distance from a theoretical base line. The measures differed slightly from those presently in force and the method of taking these measures had to be redefined some years later. The stem profile had to be controlled by a template. The appearance of the Finn was changed by the new rule to allow the side decks to be rounded in. This made the boat more comfortable, more modern looking, and allowed for a better construction of buoyancy tanks both in wood and in plastic. Most important was that the material of the hull was optional, thus plastic or any other method was allowed. This regulation was restricted again in the following years excluding sandwich and similar methods.

In order to keep the One-Design character of the Finn for all methods of construction a very important rule about the Centre of Gravity was introduced. When balanced on one gunwale, the hull had to lean with the upper gunwale against a vertical surface maximum 500 mm from the resting point. The position of the mast hole was controlled by measuring from the front of the stemband to the forward side of the mast hole. This was easy to control but gave a tolerance of 30 mm to the position of the mast.

1960
By January 1960 these rules as approved by the IYRU in November 1959 became effective and were printed together with a short history and description of the Finn, the Association Rules of the International Finn Association, the Rules for the Finn Gold Cup and a clean drawing of the new regulations. On the basis of these new printed rules some countries developed Measurement Forms in their local language, listing the correct measurement and empty spaces for the actual measurement and possible remarks.

At about that time the first doubts about the reliability of the template measurement to control the shape of the hull cropped up. Some boats measured once and did not measure the next time. Templates were made locally from a table of offsets and the definition of the stations was rather vague. At the end of 1960 for the first time it was made clear, that the floorboards must not form the top of a double bottom. The height of the floorboards was limited by minimum distances to the sheer line.

However there were bigger problems casting their shadows over the Finn Class in 1961. At the Gold Cup in Travemunde the first three boats were made of GRP Glass-Reinforced Plastic. About 2000 owners of older wooden boats were afraid that the rule changes of 1959/60 had outmoded their dinghies. Even more disquieting than the victory of the old champion Andre Nelis was the third position of an unknown sailor from the United States, Fred H. Miller Jr., who finished third. After the Gold Cup Fred Miller sold his magic boat, about which he had told many fantastic stories, to Arne Akerson of Sweden.

1962
At the measurement for the Gold Cup 1962 in Tonsberg, Norway, some hidden lead was found in the bottom of that magic boat, which was against the rules. The Finn Class was in danger of falling apart. The new rales had turned out to be too weak to ensure the One- Design character of the Finn Class. The IYRU threatened to withdraw the international and the Olympic status. Many of the owners of wooden boats were disillusioned, and those of plastic boats considering to hide some lead themselves, only did not know how much and where. Builders outside of Europe were especially confused and did not know how to build a fast boat that was also legal. Therefore a new Technical Committee was elected at the AGM in Tonsberg to redraft the rules and plans for submission to the IYRU in November 1963. For the time being a few changes were proposed to the IYRU November 1962 meeting in order to solve the most pressing problems.

Most important in the rale changes of 1962 was the requirement to keep the distribution of weight in the hull as near as possible to that of a normal carvel planked boat. In reinforced plastic boats the structural panels had to be made of single skin plastic material with normal reinforcement of glass. Sandwich constructions or trapped air-cells were not allowed. In addition to the older control of the centre of gravity athwart a second control was introduced longitudinally. Supported at station 3 the boat had to have a bow-weight of 21 kg mm.

For an improvement of the unsatisfactory situation with the hull measurement, it was decided to define the stations by measuring along the keel and the rubbing strake from the transom. Later this method proved to be wrong by 9 mm with perfectly legal boats compared with a theoretical definition of the plane of station 8 and was abandoned again. The definition of the keel line was slightly changed to be measured to the flat under the keel band and not to the theoretical point, where the sections meet.

The driving force in the newly elected Technical Committee was Richard Creagh- Osborne from the UK as the Chairman, with Rickard Sarby from Sweden and Ole With from Norway as members.

1963
All through 1962 and 1963 the new Technical Committee worked hard to submit the following for ratification in November 1963 to the IYRU: a set of rules, a standard measurement form, a set of instructions to measurers, modified plans to assist builders in plastic materials, and a statement of which rules are to apply retrospectively and which are only for new boats. For the information of builders, measurers and boat owners a revised version of the rules as approved in November 1962 by the IYRU was published by the IFA early 1963. Compared with the printed version of 1960, most significant is the statement in Section 1 that builders are not to attempt to get round the spirit or the letter of the. rales, to produce boats which are intended to be basically faster than those originally built of conventional carvel timber construction. Furthermore, the rules read that it is the sole responsibility of the owner of the boat that it complies with the plans and rales of the Class at any time.