Rules and Measurements
Design and Construction of a Cherub
The design of Cherub hulls has changed significantly over the years as designers have strived to search for the best hull shape to suit particular crews and particular local conditions. The design rules for the class allow for significant differences in hull shape while maintaining the basic performance parameters of the class.
The most successful design among recent boats is the Matthews design developed by the Matthews brothers Mark and Brendan from Brisbane. Many other successful designs are also prominent in fleets across Australia.
Most modern Cherubs share some key measurements. Most are minimum beam at the chines at the 6ft station, close to minimum beam at the transom and as close as possible to the maximum beam at deck or sheerline level. These features make the hulls narrow while maintaining deck width to give righting leverage for the crew.
One measurement that the designers have tried to vary is the depth from the chines and the bottom of the boat at the 6ft station.
In the 1980s and 1990s the Foreign Affair design kept the chines as high up as possible to try to keep them clear of the water when sailing to windward. This was done by putting the maximum amount of hull shape or buoyancy as low as possible in the hull. The various versions of the O’Mahoney designs conceptually similar to Foreign Affair but tend to have more rounded sections towards the bow. Boats built to these designs are still very competitive in club racing.
By contrast the Matthews boats built in the past few years have much lower chines minimizing the distance between the chine and the bottom of the boat at the 6ft station. This gives the hull much flatter sections in the area of the centre case and aft toward the transom. These flat sections are very effective at creating dynamic lift, inducing planning early and shedding water when planning at high speed. In practice this seams to give the Matthews design an advantage on the high speed reaches that make up so much of modern Cherub races. The design penalty is going to windward when the Foreign Affair and O’Mahoney designs, despite their age, may have an advantage particularly in lighter winds. Screamin’ Seamen, a modified O’Mahoney hull, is still one of the fastest Cherubs going to windward in light air.
The low chines also mean that a Matthew’s hull needs to be sailed to windward as flat as possible to avoid the drag caused by the chines. The other feature of the Matthews hull is the very straight lines of the chines which give the boats the distance knuckle look at the halfway measurement point. This means that both the bow and stern are very fine making them sensitive to fore and aft trim by the crew. Good crew work is required to avoid nose diving when sailing downwind in short waves and a strong breezes.
Alternatively, the current Bartley hull shape came about as an apprentice lofting project after Andrew Stephenson and Kirk Mitchell had built their first cherub from a Matthews shell. The lines were lofted to 1⁄4 scale, waterlines cleaned up and hollows removed. The keel line was straightened aft of the fin case, the chines raised and reduced in beam at the transom. These changes aimed to improve the boat in lighter winds, safer down wind and easier through chop. Andrew modified the jig for his second build, changing the bow entry slightly and moving the mast and fin case further aft. This helped get the boat on the plane earlier.
While these design points are of interest it is still the best crews and the best rigs and sails that win races.
Many Australian sailmakers have put time into refining sails for the Cherub class. Several of Australia’s top young sailmakers currently race Cherubs.
At a recent National championships, sails from eleven different sailmakers were carried by boats that finished in the top ten places.
A number of larger lofts have also developed successful Cherub sails. Quantum in Melbourne and UK Hasley in Fremantle are among these.
The flexibility of the ‘restricted’ design rules for sails allows Cherub sailors to work with their local sail loft to design sails to suite their own particular rig characteristics. The class rules allow only one set of sails to be used in a given championship event. This keeps the cost of new sails reasonable and affordable.
Modern composite construction methods have made it possible to build your own Cherub at home, either from scratch using a jig or by buying a hull shell and finishing it with frames, floors and decks. It is not an easy task but it is a manageable one. More than half the boats in the current Cherub fleet were fully or partially built by their original owners.
Hull shells for the very successful Matthews design are available in full carbon fibre construction from the Matthews brothers in Brisbane. For details and prices call Brendan Matthews on (07) 3274 5751.
More information on the Matthews boats can be found here.
The majority of new Cherubs are now being built with full carbon fibre composite construction using ambient temperature epoxies and closed cell foam.
A number of construction jigs are available for successful designs such as The Lairy Canary. For information on how to acquire an existing jig contact firstname.lastname@example.org
Technical assistance is available from experienced Cherub builders in each Australian state who are able to provide advice on design and construction and on details such as materials and lay-up design. For technical advice contact email@example.com
Building your own one off design is also quite feasible and a very rewarding experience.