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Au Class Concept
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LAST UPDATED 4 th Feb 2006

WHY
 SOME THEORIES
 THE DEVELOPMENT PATH
THE NEXT LEVEL

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WHY

The Au maxi concept basically started with a desire to be able to sail large scale models,born out of the same dream I had each year when I watched the Sydney to Hobart race.
They create a spectacle all thier own.
I started model sailing way back in the 80's with EC 12's at Narrabean Lake,Northern Beaches EC 12 Sailing Club,and enjoyed the class of yacht as they had a full sail area and looked more like the real yachts than any other class of model.
Sure,they had a downside due to thier sail area and that challenge was accepted.

Lost the interest when the 1990 Rules came out,plus a couple of other issues. A number of years back I came back to model sailing with A class yachts at Sydney A Radio Yachting club at Woodcroft Lake,became a club measurer and built a Super Nova with a fully working spinaker.The yacht had many hardware operating problems but I knew what I had to do to improve the whole settup,and I was confident I could get it all to work successfully with a new hull capable of carrying the extra hardware weight and delivering a better sail area.

As an A class measurer,I developed a good working knowledge of how the rating formula actually worked,and what a basic hull needed to gain a reasonable sized sail area,but they still wouldn't and did not look like real boats.
There's a bit of a difference between a model yacht and a model of a yacht,and I wanted the latter.The spinaker dream for an A class yacht died.
I liked the size of the A's,but in order to build a 'Maxi' model within the class required a few rules to be changed,specifically,the dropping of the Quater Beam rule,plus some changes to the deck restrictions limiting the construction of scale like decks,and they still wouldn't have the sail area.
So Bob Jones and myself decided to start from scratch with a new class-Au Maxi's.

The main criteria was scale models of Maxi's with all their colour and advertising,looking and sailing like the real thing.

Just for the hell of it,I stuck a huge sail area on the old Super Nova,and it handled it well.

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SOME THEORIES

Knowing full well that a scale Maxi with a scale sail plan would be way over canvassed when the wind picked up,I realised these were not going to be easy yachts to sail,and would probably require reductions in sail area from about 6 to 8 knots of wind.
I've since roughly figured that the ratio of wind speed to boat size between full size maxi's and a 2 metre maxi model is perhaps about 3:1,and maybe even closer to 4:1.
In perspective,when a model is sailing in 5 Knots,that is equivalent to the full size in about 15 knots,or more.Taking that to the other end of the spectrum,a model sailing in 15 knots is the equivalent of the full size in 45 knots,and maybe as high as 60 knots,at which it's most likely on it's 3 rd mainsail reef and a small jib.
Without a reduction in sail area,the model is laying flat on the water.
One obvious factor that any scale model yacht is lacking over it's full size prototype is moveable ballast,all those crew members sitting along the windward railing,hence making the model even 'tenderer' than the prototype.
A factor taken into account with the wind to boat ratio THEORY.

So we have model yachts with a large lead bulb hanging at the bottom of a keel foil to provide a sufficient righting moment for them to sail.
To get a scale model Maxi to sail in stronger breezes with a full sail plan would require a massive increase in righting moment,meaning a much heavier lead bulb or a much deeper foil.The resulting heavier yacht sits much deeper in the water detracting very much from it's prototype in the way it looks on the water,though it's then stiff enough to handle the stronger winds,but too stiff in lighter breezes,and is pushing a whole lot more 'drag' through the water,further detracting from light wind performance.
Also,the Maxi hulls have long finely angled lines in thier foreward sections combined with shallow 'rockers',thereby not displacing as much as the traditional A class of model yacht,causing them to dive by the bow as an in part result of all the extra drag induced by larger heavier foils and bulbs,plus the huge sails pushing from the top.

Now we have a 2 metre model that's about 2.6 metres high with a huge sail area and weighing in at 20 kg or more,an awefull lot of boat to manhandle and launch/retrieve in a bit of a breeze.
I for one was not too interested in a model requiring me to walk into the water up to my waist for launching.

Then along comes the invention of canting keels on the Maxi yachts,and the whole concept of scale Maxi's gets a little more interesting.

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THE DEVELOPMENT PATH

Where to start ?
I need drawings of Maxi's ?
How difficult will it be to get any drawings ?
Do I design my own ?

Scouring the internet I found a reasonable range of usefull photos of the then maxi's,Alpha Romeo,Scandia,Zana and Nicorette.
The Nicorette site had a lot of info on the yachts specs,but most importantly,it had a few drawings of hull stations (cross sections) plus detailed plan and profile views.
I'd found my new model yacht project.

As I began building the moulding plugs for the hull,decks and keel bulb,we started putting together the rules for this new model class,the Au Maxi's.The draft of which is in the Au Maxi Rules section.

Settling then on an LOA of 1700 mm to keep it about the same as an average A class,mast height same as well for ease of transport in the average car,then turned my attention to the sails.
She has a huge set of sails with a very full mainsail leach,way outside of the normal backstay.The prototype like most has running backstays.
So for this yacht I'm going to need to develop some new control systems,and the list started to grow:
* running backstays
* loose footed headsail
* port/starboard headsail throw
* mainsail runner
* adjustable slot
* in mainboom mainsail outhaul
* in mainboom adjustable leach
* variable depth keel
The AU Maxi 'how to' section will detail some of these functions.

Basically,she's a model that will not self tack,requiring that the P/S switch is thrown when tacking or jibing to put the running backstays to the windwward side and the headsail to the leeward side,and at this stage, also pulling the mainsail runner to windward.This function was later dropped in favour of a centre fixed position.

After a lot of experimenting,a lot of pulley blocks,and 4 RMG Winches,the system worked reasonably well.
The hull turned out very much heavier than planned,a whole lot of filler was needed with the internal structure,particularly as I'd decided to also incorporate water ballast tanks.Another function that was later dropped.She now had a huge air box the full hull length,at least she wont sink.
The deck is made of many section and all are removable for unrestricted access to the control systems,though she ships water because my deck edge seals are badly designed.
Other design and building errors became apparent.
The foreward 'rocker' was too flat,not displacing enough,and she balanced rearward of where she should.
I didn't know enough about these aspects and set about digging up information and figuring it out.The relationships between CB,CG,CLR and CE,these are all theorised and detailed in the main 'how to' section.

Out on the water at Woodcroft,the huge sail area drove her along in 'nothing' of a breeze,but she developed a nasty habit of often 'turning turtle' in shifting very light breezes.Retro fitting a foreward Cunard quickly cured that,which is caused by a combo of the huge sail area,particularly the headsail,and a very narrow corded keel foil of only 80 mm.
The single most difficult aspect of sailing her was having the P/S on the correct side for the wind direction and where I wanted to point her,other than that she was good,for the first development Au Maxi on the water anyway.

Then I made the switch from the light shifting winds of Woodcroft out to Chipping Norton Lake,and quickly started to realise that's there's a whole lot more to building and sailing these monsters.The wind out there is not only a little stronger and consistant in direction,but it's coming across an expanse of water with a good deal more 'punch' to it.
Even with my keel set on it's deepest setting,she just had way too much sail area.Adding to some hull errors realised,the flat foreward rocker and her CG some 80 mm further back than it should be.
I planned to re-build her,and correct all these things,make her lighter,but for now I'll keep sailing her and learn all I can,as frustrating as it was at times.

I had made 3 mainsails for her,and the smallest worked pretty good though the mainboom dragged in the water and was killing her performance.I could'nt 'reef' the mainsail as I had a 'jackline' mast,and the mainsail was still way too tall even though it was much shorter on the foot.
By this stage I had removed the running backstays in favor of a fixed adjustable backstay and was no longer using the #1 mainsail.

What had I learnt?
* get the hull shape correct and ensure right from 'plug stage' that the CB,CG and CLR are correct so the hull will 'drive' through the 'point' that it should
* the mainsail has to have at least 3 reefs in it,lowering it to at least 1/2 full hgt
* design better deck sealing
* build a lighter hull
* engineer the internal structure and control systems a lot better

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THE NEXT LEVEL

I took my model of Nicorette over to show the boys at SP Systems where I source all my epoxy/carbon fibre supplies,the next day I'm meeting with owner/skipper Ludde Ingvall,with model of course.
He's impressed that I've built the model,and even more that I built it from a few cross section drawings and a bunch of photos.
He shows me drawings of the new 90 ft 2004 Nicorette whose hull was being built at Boatspeed and will be completed at Woolwich Docks in the Sawtooth building by his people,The Bigboat Racing team.

He gives me the drawing and asks if I'd like to build a static model for him and be part of the team at Woolwich Docks.Great sailing site down there,good water,lousy access,and virtually no passing public.
I eventually declined on the building of his model,but the relationship still developed and I had full access to all that was taking place at Woolwich and followed the project through to official launch.

My new model,300 mm longer,at least 500 mm taller,square hull with a very flat rocker - and a canting keel,and it won the SH first time out.

It's all in the 'projects' section of Au Maxi,and I will be building Ludde a static model in appreciation of his support and friendship.

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