Performance

16/07/2012 11:49:08
John langman
I note that amongst the easily available literature there appears to be no detailed study of the total power in (lbs, Kilos) delivered by a sail plan. Unlike the unrestricted classes like the 18 foot skiff or in classes where sail area is substantially larger than an unrestricted class the restricted classes have little opportunity to increase sail area or righting moments above that noted in the class rules.As a Merlin Rocket sailor of many years I have observed (and sailed) a number of different hull designs and with the exception of the change from a full triangle sail to a battened roach design sail area has remained fixed since inception.

Hull design has changed radically, however in the last few years arguably it has stagnated to the point of seizure in class development except for minute changes delivering a minute percentage advance in boat speed. For the Round The Buoys Sailor (RTB) the choice is stark, reach for the cheque book or drift to the back of the fleet.

A solution to some of the issues strikes me as a more measured approach to understanding sail performance and being able to put numbers in Lbs or Kilos to the forward driving force that the rig delivers without the hull and its appendages. It strikes me that if this was better understood the RTB sailor would be able to assess whether his rig was capable of delivering the performance needed to compete and under what conditions, or whether he genuinely had a need to upgrade his hull/sail options/design (given that the hull shapes of the last 15 years have converged into near seamless identikits-not that the designers would agree-:)

In a class(ess) where the sail area and shape is fixed by the class rules then a clear value of the rigs delivery ability is missing from all the research literature. Clearly the delivered power of the rig in situ will be subject to all the normal sailing caveats of hydrodynamics, but how can you make an objective assessment of capability if you have no data on delivered power. Whilst towing tests tells you a lot about hull dynamics it tells you nothing about restricted sail area classes ability to deliver full power to the hull and its appendages under the full control of the crew. Clearly in a restricted class the ability to cram on more sail is by definition restricted, so where are the numbers?

16/07/2012 13:22:32
Joker
Are they above QWERTYUIOP?

16/07/2012 16:42:09
Richard
Check out Sail Performance: Techniques to Maximize Sail Power by Marchaj.

TML

http://www.amazon.com/Sail-Performance-Techniques-Maximize-Power/dp/0070402507
17/07/2012 09:38:24
Andrew M
I suggest the problem in supplying the numbers is in getting properly controlled conditions in which to measure the power delivered by the rig.  Access to wind tunnels that will fit a Merlin mast with room round it to properly simulate open air conditions will be expensive and the differences in power between similar properly functioning rigs will be small, so just setting it up in the open and waiting for the wind to blow will not really give the consistent accurate results needed.  Towing tests by contrast are pretty easy.  What has happened is that after rule changes e.g. to the spinnaker, the shapes have changed and then stabilised to a consensus that is a workable compromise.  There probably won't be a big change unless there is another rule change on materials or battens or whatever.  The differences in power, as always, will matter at the sharp end where a couple of boatlenghts up a beat make a big difference, but for the middle of the fleet getting your tacks better & spotting the shifts is the big one.  Someone told me that GPS plotting of sailing races generally showed the winner was not the quickest (speeds usually very similar) but the boat that sailed the shortest distance.

19/07/2012 16:48:02
John langman
Read marchai! amongst others, does not answer the above questions

19/07/2012 17:00:33
John langman
The newer hull designs appear to have at last seen the need to cater for heavier crew/helm combos, for too long it seems we have designed to weight where that combo is for lighter people, we even have swinging tilting rig technology (and how much does that engineering solution cost in sterling on top of the boat cost) I want a hull that accepts what ever power the wind delivers and sit it out with us bigger blokes. I want the hull to accept all the power the rig can deliver. I dont want de-powering systems I want effiency in delivery to hull, and carrying capability in the hull. Towing test info seems unavailable for MRs, power numbers for rig delivery similarly are absent, we see major advances in new classes where they cram on as musch as they can and put guys on trapezes to control the power. A modern suit of MR sails delivers in most wind strengths a real fistful of power. The hull design should aim to deliver this to forward speed. Again without the numbers we are all best guessing. It is true and has been said sfor 30 years+ that the most frequent winners are either the ones out on a limb or those canny enuff to sail the shortest route.

19/07/2012 21:50:39
Andy Hay - Business as Usual
Not Marchaj (too old school), try Frank Bethwaite who explains it all in laymans terms (well except the bit on wind in his first book which lost me). In his second book he talks about three critical ratios, the parameters of which are fixed in the Merlin Rocket, i.e. all up weight weight, sail area, leverage (aka hull beam), position of centres of effort, etc. Guy Winder did some rudimentary calculations (available elsewhere on this web site to MROA members) that looked at some of these ratios. Interesting reading.

Whilst the Merlin hull design has stabilised - and I am so thankful that people are now playing with shapes again - the rig offers a multitude of posibilities. Twin spreader skiff rigs with uber flexible topmasts (49'er, et al) is one route. 130mm chord wing masts offer an alternative. Both would offer the opportunity to generate more power from the rig. But those whom have played with these things (Peter Scott with Wing & a Prayer being one exception, I am sure there are others) have done so with existing hull shapes, mast positions and centreboard locations. If you wanted to take a completely new approach, you need to take a leaf from Jo Richards N12 and start from scratch. Looking forward to the full write up about the Superfast Jellyfish and the thoughts behind this design. Wing masts would probably need the centreboard leading edge almost under the mast, so you either bring the rig aft or board forward, either are big risk items. If you are spending £15K on a new boat are you willing to risk it and the resale value? Or build one from scratch? This is the crux of the development hiatus that we have seen for the last 20 years for hulls. Here's to a brave new riskier era ...

Developing numbers for this is possible for those with the time, inclination and computer equipment - there probably is a university thesis here or at least a doctorate. Has Ellie graduated yet?

Don't forget that the clinker hull throws a further curve ball into the mix. My hydrostatics software likes smooth forms. It does not deal very well with flow attachment around the lands if I round the plank corners (lower resistance & surface area) or flow seperation if I sharpen them to a true square corner.

An old mate of mine once remarked that if you want to make heavy weights competitive; INCREASE hull weight. Not sure you would get many takers for that at an AGM.

21/07/2012 20:57:12
John langman
Have also read Bethwaite, (recently) and sent email on subject and got nil response (oh surprise) we need to get our heads round the simple facts, we do NOT have enuff solid numbers, in this day and age, when I can plonk down under my desktop for sub £1000 the same computing power that 15 years ago would fill a small room and cost 30million, we are not addressing the science in a measured methodical way, empirical will do fine, but logical is essential. 
I want to stir some action out of probably the most interesting class sailing today,clinker hulls (perhaps a throwback but nevertheless stimulating and fascinating)in the mix makes life interesting. We all are aware of skiff type machines that cram on inhuman amounts of sail or developments in AC catamarans that literally fly. However if we are to push the acceptance of MRs as fascinating sailing machines we need to speak from an authoritative base backed by solid knowledge as well as experience. It has recently been proven that the assumptions about rig power and hull interactions that have been accepted fact for the last 10 to 20 years are NOT valid. so we are back to basics attempting to identify solid repeatable data from hearsay.The hydrostatic equations used for most calculations over the last decades are now deeply suspect.
It is good to see new hull shapes, if we are hostages to past designs we would all sail NSM, without the fundamental data what rig power is deliverable with what technology then yes gambling of 15K will only be for the brave or rash. There are some certainties in all this mix and we need to maintain them and the conditions under which they are specified. A key observation I have is that very few MRs are designed with modern CAD systems most seem to be by eye and then transferred to CAD. For a minimum we need hull designs to be routinely drawn on CAD, we then start to move to measurable repeatable designs and an era of solid fact based measurements. ( first to say oh down with the devil for destroying the mystique gets to give out the pens:)

24/07/2012 10:38:35
John langman
Are they above QWERTYUIOP? Actually NO! since I use a scientific kbd they are transcendental functions

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