MR : Winder on Cost and Performance

Merlin Rocket Cost and Performance

Guy Winder - Jan 2003

I read with considerable interest the 25th October Yachts & Yachting report on Dave Ovington’s new 59er sitting out boat. This design is interesting in that it is slightly narrower than a Tales, carries somewhat more weight being 4.8m overall but with measured sail area of 37 square metres compared to our 22.55 should have power to spare. This boat also highlights the huge discrepancy in performance/cost between Merlin and the manufacturers one designs and there may be lessons to learn from it. The 59er, ready to race costs Ł7200 inc VAT for a yardstick of 905.
Depending on the builder, a moulded Merlin, measured, ready to race, with carbon extras, Superspar carbon spars and mylar/kevlar main costs between Ł10473 and Ł13950 for a yardstick of 1024, and a good deal more with Jackson spars.

Fortunately the 59er hardly competes with Merlin as it is optimised for windward leeward racing with the huge 23sq m asymmetric taking it fast down hill, the wind strength dictating the course rather than the helm. Many of us are forced to race on restricted water and here Merlin certainly has a niche in modern dinghy racing having the versatility to be raced to its full potential on any stretch of water on any course, in all practical wind strengths.

Until we launched our all FRP boat, Merlin building had fallen to a handful of beautiful but very expensive wood boats per year.

Year	Boats Built
1999	10
2000	20
2001	11
2002	10

I believe our Merlin sold well in 2000 because it was not hugely expensive, was competitive in spite of being a 12 year old design, so we were in a period of design stability and customer confidence was high. Now we are back to change and with it uncertainty, increasing prices, and consequently falling demand.

Corrector weight

The latest development generating uncertainty is the ultra light hull with 30+ Kg of correctors. I suppose we are part responsible. Our hulls have around 10 Kg of lead and a heavy central moulding, but the laminate thickness is in line with our very durable yet light Fireball so we know that if they are looked after they will stay competitive for many years so retain their value. This movement towards ultra light hulls could damage the Class if not controlled. I am sure that if we tried really hard we could produce a hull requiring 40+ Kg of lead, then pressure would grow to push this to 45 so we would have hulls which would damage easily and may well become soft if sailed hard on rough water. This ultra light hull would require a carbon deck and centre moulding, increasing cost, and the short competitive life would reduce resale value further increasing cost of ownership. Most classes have some rule preventing the building of ultra light fragile hulls, Fireball has a maximum corrector weight of 7Kg plus minimum laminate thickness.

Reading the website forum gives an indication of the concern over any change that makes older wood boats less competitive, but this development would erode the competitiveness of the whole fleet and make wood construction definitely a thing of the past. This has got to be bad for the Class and a rule should be introduced to set a minimum inertia value.
The method for monitoring the distribution of weight in Olympic classes is by swing test and the Class has no option other than to try this. Once the minimum moment of inertia value has been set, all boats inside this value would be required to have some of their lead spread equally between bow and stern until the required inertia figure is attained. Establishing a maximum CG position from the bow does not control weight concentration as it would still be possible to concentrate weight just forward of the balance point, reducing inertia by still building ultra light ends. Basically, inertia is weight X distance to centre of rotation squared, so distance is the critical element and a hull with its weight concentrated a short distance from its CG will have less inertia than one with its weight more evenly distributed along its length even though they both have the same CG position.

Effect of weight reduction on performance

Getting back to the need to increase performance/cost and to attempt to answer some of the questions on the forum...
Frank Bethwaite (59er designer) in his “High Performance Sailing” describes the windward planing dinghy as one of the milestones in dinghy design, and having enjoyed this effortless performance regularly with Fireballs and occasionally with Merlins, feel that it might help clarify the corrector weight debate if we try to predict the weight reduction required to enable say a 140kg crew to beneficially plane our Merlin up wind. Referring again to Frank Bethwaite, he gives a guideline figure for sail carrying power expressed as a percentage of displacement as 27% for a racing dinghy to plane beneficially to windward. Sail carrying power is the side force the crew are able to apply to the rig by hiking. The greater the crew’s leverage, the more side force they are capable of generating. Similarly a lower centre of pressure on the rig, or a raised centreboard reduces rig leverage so increases the side force that crew can generate.

My calculations show our Merlin now has a sail carrying power of just under 26% of displacement. If 10kg is removed from the hull, the 140 kg crew then generate just under 27%, but if the 10kg taken from the hull is added to the crew weight, they generate just under 28% of displacement. I show this because the weight sensitive Tales with 10kg less correctors will carry 10kg of extra crew weight for the same trim so we could gain significant performance increase combined with greater weight carrying ability.

We do plane beneficially up wind now when conditions are right so the figures look about right and should be proven by making controlled tests. I recently followed a Merlin in a rib and measured its speed by GPS at 6 knots in force 5-6 when displacement mode is about 4.5 knots.
The reason we occasionally windward plane now is because by de-powering the main we use less of the top to produce side force so the centre of pressure is lowered. The centre of pressure only has to be lowered by about 0.3m to increase the sail carrying power to 28% of displacement.

The Merlin mainsail profile was never intended to be that shape with all that area up high and with a top batten nearly half the foot length. 56 years ago it was not thought to be necessary to measure the ľ height of cotton sails and this loophole was exploited when dacron replaced cotton. Is our main the optimum aerodynamic shape? Why does it require so much rake to de-power it when Fireballs rig requires very little rake to de-power? Can we learn from the 59er which has main and jib area 11.5% greater than Merlin yet has no very expensive remote control over rake and bend, just simple pin adjusters. A more conventional main to the same luff and foot sizes reduces the centre of pressure height sufficient to increase sail carrying power from 26 to 27 %. The 59er has a 4.2 m2 jib which gives much low down drive and increasing the Merlin jib to 3.5 m2 with the same luff length, combined with a revised main, would increase sail carrying power to about 27.3% of displacement.

There appears to be pressure within the Class to increase performance. The weight reduction path may be more difficult to sell to the membership than a sailplan update, especially if the spinnaker change is seen to be beneficial. The argument will be how far to go. Do we want to effectively plane up wind in 3-4 when the revised rig may be too powerful to race in 5-6? Specialist independent sail design input would be required to answer all the questions before modifying a boat, such as whether the mast position needs changing and whether existing masts will have the right characteristics.
The Merlin has a definite niche in the dinghy market and this must not be lost.

Conclusion

As we know, most of the above is just pie in the sky, it cannot happen because the membership would never vote for it, and rightly so, for they fear that their boats would be outclassed by a flatter hull designed to take advantage of the increased planing requirement.
We can no longer expect significant performance increase via hull development under the present rule and significant performance increase can only come from a significant increase in power to weight ratio. Tales is 15 years old and 80% of the 2002 championship fleet were Tales or tweaked Tales so like it or not, we have pretty close to a single hullshape fleet but with an interesting variety of spars, sails and hull systems. Any action that makes this fleet obsolete would now be highly damaging to the Class and it is time to increase the restriction on hull development. In the seventies a design change required minimal tooling cost so hull development was cheap and hulls were still improving fast enough for this to be a selling point against other wood built classes. Now, we compete with moulded one designs, hull development is slow and the cost of moulds or mould mods very high. We are currently evaluating minor changes to our hull, but to modify the mould will be very expensive and I question whether current hull development still benefits the Class as a whole. I feel that the only way to introduce rig or weight change is to give the membership a guarantee that their hulls will not be made obsolete by giving them the right to vote for a freeze on hull shape development.
It may be possible to draw up a set of hull shape rules who’s tolerances encompass all designs currently in production. Another job for an independent expert.

Reading the forum shows how much owners care for the whole Merlin experience, the friendships, families, the refined boat, the highly tactical racing at venues which admirably suit its characteristics. To the outsider the slow yardstick and very high price, coupled with design and obsolescence doubts cannot help sales. Who knows, a performance hike and cost reduction through stability and we may start attracting couples from RS200 and 400 .