Overview - comments by "Petrol " designer John Lewis
INTRODUCTION TO PLANKING by Paul Heys
For those who are interested in model yachting and who wish to sail for fun or in competition, the 6 Metre Class has a lot to be said for it.
It was when putting together a specification for a non-class model for sport sailing that I found my ideals for such a yacht are very largely met by the 6 Metre rule.
The Class Rule produces a yacht that is not too long to transport easily, but large enough to look significant when on the water. There is enough displacement to make for realistic action when afloat and stability to carry the adequate sail area. The yacht can look like what most people perceive as a yacht.
The rule itself which has been in existence for many years was at one time considered to be complicated, and the models difficult to measure. All things are relative and today neither the rule nor the measurement should present difficulty for the average yachtsman. Of course if you are building and sailing for fun, then the niceties of the rule may be ignored and one can enjoy a beautiful model with a classic pedigree. On the other hand, if the model is built so that it is within class rules and is registered as such, then the value of the model must be enhanced.
A perfectly satisfactory and competitive yacht can be built in wood and although the question of ballast ratio should not be ignored. It is not vital however, to use 'exotic' materials. I suppose it was inevitable that with the Class resurging into radio racing popularity that the top boats and skippers will be using expensive composite materials. This does not however have to spoil the enjoyment or validity of the Class for fun sailing.
For the design of Petrel, l have opted for a relatively short hull which makes for ease of transport and enhanced handling when radio racing. The water-line length is longish without being excessive, thus giving a minimum displacement which should provide enough stability to cope with the large sail area. Therefore the natural displacement speed will be fully competitive.
It is in the design of the overhangs where the subtlety of the 6 Metre rule appears. Make the ends full and wide, the measured length increases and the sail area is reduced. This is intended to discourage the design of hulls of scow form which increase their sailing length, thus potential speed on heeling.
On the other hand there is a minimum fullness requirement which prevents hulls being too sharp and thus losing sea worthiness. Petrel is designed with an amount of fullness only just over the rule minimum and thus the allowed sail area is distinctly greater than the average 6 Metre of 41 inch (1042 cm) LWL. Performance should be extremely good in light to medium winds and only marginally slower in strong winds compared with the longest and heaviest designs in the fleet. Ideal for radio control competitions or for pure enjoyment on all types of sailing waters.
Points to watch during construction are;-
(1) No hollow must be seen in the hull surface between the LWL and sheer line and to assist the builder additional cross-sections are shown fore and aft of section 10.
(2) The designed displacement is very close to the rule minimum so do not over estimate the final thickness of your planking when cutting the shadows.
(3) Take care that tumblehome does not exceed 2% of the extreme beam. This should not really be a difficulty if normal care is taken.
The stern fairing to the rudder post, or bustle, is not extreme but I have shown a radius to the profile immediately above the rudder. This enables the bustle to be faired out nicely rather than ending in a sharp angle. It does not make construction easier, but it must be the better way of finishing off the lines and is certainly most elegant. Some of my recent 6 Metre designs have incorporated a 'bustle' type of bow which does have theoretical advantages, but it is difficult to build satisfactorily. I think it is unreasonable for a published design to be only suitable for the skilled builder when the advantage in terms of performance may only be marginal.
Petrel should look good both on and off the water and hopefully will also be a good performer.
Web Masters comments.
The publication in Radio Control Boat Modeller (Jan/Feb. 1991 editions) of the Petrel design by John Lewis, coincided with a resurgence of interest in this class of model yachting which was long overdue, but I must admit to some bias on this point! The plan was available from Radio Control Boat Modeller Plans Service, Argus House, Boundary Way, Hemel Hempstead, Herts, HP2 7ST. Plan Number BM1445. Regretably the magazine was absorbed into Model Boats, and the Company has been bought and sold a couple of times since. Magicallia ltd are understood to be the present owners.
Having built a Revival design by Graham Bantock, and planked the hull of another Lewis design Tern, I was keen to build a different design for the coming Nationals and Match Racing series. The Petrel design has to my mind the two main ingredients for any boat, ie. attractive lines and that certain something to make me want to build and own one. So the decision having been made, the next step of actually constructing the boat was comparatively easy, as I hope to prove.
My aim in building was to produce a boat that would stand the rigours of a competitive racing life, possibly for several years, and constructed to a standard of finish that I could live with. I hasten to add that I am an average modeller who is still learning. But then you always do. If you want to see what a true artist/craftsman is capable of, then John Gale's yachts stand out, but do not be put off if your results do not reach such levels, because most of us can only aspire to such standards. But then, practice does make perfect. And. John has built more than his fair share.
If you would like your Six Metre added to the boatography contact the webmaster with a picture and details.