Opposite clockwise: Jean Genie here clearly using all of that long aft overhang – note the narrow upper girths of the mainsail which compromised the use of a thicker upper mast section to do away with runners; the clean and modern cockpit co-designed by Andrew Palfrey and builder Gavin Tappenden incorporates thoughtful Star-style handholds for today’s mini-hiked 5.5 crews; IRC-style thick fin keel with a subtle reverse taper, leading-edge ‘wedge’, large trim tab and small delta-wing endplate… but no wings or ballast bulb. Top: Steve Quigley’s own new 5.5 Metre shows a rounded stern while Hollom typically goes all-in with the board-flat approach (left). Right: Jean Genie… showing a smooth-flowing transition from bow U-sections to V-sectioned mid-body and a completely flat run aft
the water surface as possible, at the bow, and that at the stern the volume should be as near the water surface as possible. He then reasoned that the shape that best achieved this was a U-section at the bow and a V- section amidships running to a flat stern. We pretty much came to agree with this when we used a potential flow wave drag program during the Crusader America’s Cup challenge in 12 Metres. Indeed, the shape of Crusader 2 was heavily influenced by this work and she was a very fast boat. Bearing all this in mind, and as V-sections
seemed to be competitive in classes where both types of section were used, it seemed worthwhile investigating the pros and cons of the two types of section, and at the same time looking at the effect of U-shaped bow sections linked to V-shaped midsections. In the early 1990s we therefore conducted a computer experiment to try to determine the effect of sectional shape on wetted surface area and, as far as was possible, look also at the effect of sectional shape on wave drag. Boats were designed using U, V, a flat
scow section and a U to V-section à la Froude. Great care was taken to ensure that the length, displacement and meta - centric height and thus the stability of all the boats were identical. Furthermore, other parameters such as lateral area coefficient (Clat), waterplane area coefficient (Cwp) and prismatic (Cp) were held constant or, where one of them had to change in order to look at the effect of changing that para- meter, they were changed one at a time holding the other parameters constant. The results were very interesting and the
shape of Jean Genie is very much influ- enced by this work and, as mentioned, the original work on wave drag undertaken
nearly 40 years ago during the Crusader Cup challenge – using one of the earliest potential flow wave drag programs written by Dr George Gadd of the National Physical Laboratories (NPL). A visual output of the program for three
12 Metre hull forms, showing actual and computed wave shapes, is the example shown on page 52. Model 4 is Australia II, Model 13 is a development model and Model 14 is Crusader 2.
Optimisation In the brief for his new 5.5 Metre Morty specified that the boat should be optimised for true windspeeds of 8 to 18kt. He rea- soned that below 8kt sail trim and going the right way were perhaps more impor- tant than pure boatspeed, and that above 18kt boat handling became the dominant factor. This somewhat simplified the opti- misation process. With the help of Steve Quigley’s CFD
analysis, which determined canoe body drag, Tom Schnackenberg ran the data through my own VPP to obtain a full performance analysis for each boat. Firstly, we analysed boats designed to the
four candidate concepts, all fitting the same part of the rule, ie all having the same mea- sured length, displacement and sail area, to remove those variables; although it was not necessarily the fastest concept, we chose, for a number of reasons, concept one. We then looked at boats to that concept,
designed to fit various parts of the rule, and eventually settled on a boat having maximum measured length, minimum displacement and minimum sail area, in other words a boat at the bottom right of the graph on page 52. It is very dangerous, in a rule with hard
edges, to be in any corner because if there is a small inaccuracy in displacement or length the sail area might come out less than the minimum allowed and then you have nowhere to go to correct the problem other than major surgery, or the boat will not be a 5.5 Metre. We thus positioned the boat a little above minimum displacement to avoid any possible problem. The isometric of the Jean Genie hull
shape that is shown above clearly shows the progression from the U bow sections to the V-sections in the mid-body and the flat scow sections at the stern. The boat was built in a female mould
taken from a CNC-cut plug by Composite Craft of Cowes using S-Glass and foam with some finishing work by David Heritage. My VPP gave it an advantage, in the
mid-wind range, of about one minute over a two-mile windward and a two-mile lee- ward course, and this seems to have been borne out in competition. The really pleasing thing, however, is
that below 8kt true we seem to be no slower than the opposition upwind… and downwind we are still quicker. Most sporting success results from a
group effort and this is no different – largely down to Morty’s own skills in putting together a great team in which every member has contributed to that success. As a matter of interest, and as pointed
out by Morty, according to Douglas Adams’ Hitchhiker’s Guide to the Galaxy, in which the mega-computer Deep Thought, after seven and a half million years of brooding calculation, intones with ‘infinite majesty and calm’, the answer to ‘Life, the Universe and everything’ is 42. Perhaps it’s a lucky number? Dave Hollom, Yorkshire
q SEAHORSE 55
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