Centreboards

[tonyquoll]

It was interesting looking at the variety of centreboards at the Internationals, and seeing how they went.

Ben Deed's borrowed "People Eater" appeared to carry Fay boards with the spoon shape. These seem to have a NACA section of maybe 5 or 6% thickness to chord length, and a side-on area of around (0.3m x 0.5m) 0.15m sq when fully extended.

Ian Marcovitch and Greg Williams both had the skinny planks (sorry don't know the correct title), which are about 12mm thick x 120mm wide; a 10% ratio. The shape is not convex on the trailing edge, but flat or concave. The area was around (0.12 x 0.6) 0.075m sq; half that of the Fay boards.

Ian also seemed to have modified the shape at the top, so that the board would rake more on reaches and less on works, keeping the centre of effort around the same spot. Seems like a good strategy to minimise weather helm.

It seems the skinny boards are faster, with less drag at planing speeds, but are not so good at low speed. The lack of cross-sectional area means there's not much to hold the boat on line until it gets up speed. It seemed the lack of ability to take off from the start led to top sailors being buried in the fleet, with the lost time costing them dearly by the series end.

My own boards were 220mm wide x 20mm thick (9%) x 1m long, basically like the skinny planks except twice as big. Side-on area is about the same as Fay boards at 0.15m sq. In the light air my big boards were ace; never stalling and the boat was easy to tack & bear off from irons. They also sing whale-songs at speed, but that's the fat trailing edge. They're F20 hardwood with polyester coating (no cloth), which allows me to keep shaping & testing & also kept the cost down ($30 each in materials). They were given a fair strength test at Batemans Bay Anzac Regatta, with 25knot gusts, 2m swell & 1m chop to throw the boat around. All good.

When I'm happy that I've got the right size & shape, I'm hoping to crack moulds off the heavy wooden foils & make nice carbon-copies.

I'm thinking of thinning them down more; maybe 170mm x 14mm; 8%. This ought to reduce drag by reducing the frontal ara, while keeping a fair side-on area (0.12m sq). Incorporating Ian's genius raking method seems like a good idea; if no-one minds?

Has anyone trialed these mid-sized boards before? How'd they go?

Tony Hastings

tonyquoll@yahoo.com

PT 2128 "Pelikinetic"

[tom]

Good discussion, thanks Tony.

I also started off with a set of Fay c/boards, elliptical shape.

I then had a set of boards made that are 200mm by 20mm, rectangular boards, basic NACA0012 section. The length protruding from the bottom of the hull when fully down is 650mm.

I found upwind performance was improved a little, and didn't really notice any difference in "holding" the boat or accellerating from the line.

I can't really comment on how it affected light weather performance, because not long after i changed to the boards i stopped sailing for a while, and put on 15kg's.. So i'm now not as competitive in the light as i once was.. Wish i could blame the boards!

I also have the top of the board shaped so i can alter the rake of the boards, but i use this more on light days to reduce rake.. Not sure about altering rake on a reach, i tend to raise the boards if the steering feels heavy.

If i had to make a change i would make the boards shorter (which i will probably do before next season). I mostly run with the leeward board half up going upwind. (the windier it gets, the more board i pull)

Good on you for making your own boards, i'd like to try some narrower boards than the ones i have, just too much of a numpty to make a decent set.

Also at 12mm thick i'd imagine there is significant flexing going on, i don't think i'm brave enough to go that thin!

Another thing i noticed when i was using the Fay foils, is that it was VERY noticeable when i let them get badly scored, that the performance dropped off.. I think that c/board finish and fairness is one of the most critical areas of performance in the PT.

[tonyquoll]

Thanks Tom

Did the boards you had made have a square, eliptical or rounded tip? Any thoughts on that?

The skinny boards are carbon-fibre, made in 2 halves from female moulds. Not sure who makes them or how many layers of carbon are used, or if it's a composite layer.

Greg Williams demonstrated how incredibly strong and stiff these carbon foils are when he dropped off a wave at the nationals, and the foil slammed sideways - through the plywood!

Ron Wiggins told me about some blades he made out of balsa core & kevlar covering, which were very disappointing as they were too flexible.

Possibly a hybrid cloth would be ideal, such as seen at: http://www.meury.com.au/ProductDisplay.asp?PID=52

Some related info; I learned from Mike Wold that Araldite is water soluble! So THAT's why my centreboard handles keep falling off. Epoxies aint epoxies...

Cheers

Tony

[tom]

I didn't make the boards, i had them made..

They have a square bottom, although as i'm looking to shorten them i would like to try to change this to an elliptical bottom (not quite sure how i'm going to accurately do this) My feelings on this are that it will help the weed fall off more easily. (as a bonus it may have less drag)

As for flexibility, i think the carbon fay boards are too stiff. In the chop my rig used to shudder through the waves, and with the timber boards i use now it doesn't do that..

ps. I didn't know about araldite being water soluble either, i wonder how many people learned that lesson the hard way?

I'm not sure about the hybrid cloth for foils.. All the high performance foils (moth's I14 etc..) i've seen use straight carbon with timber stringers or foam cores.

[This message has been edited by tom (edited 02 May 2009).]

[tonyquoll]

Thanks Tom,

Eliptical boards had the most drag and least lift of boards I've tried. In applications like Spitfire wings, they worked a treat because they can generate lift from a wide variety of lateral attack angles. Great when maximum manouverability is required.

On our cats, this angle only changes when the boat pitches up and down in waves, so probably wont go much past 10 degrees.

The other factor in tip shape is that water will take the easiest path, so it may travel down the blade from the leading edge to the bottom if there's less drag there than going to the rear edge. This would creat tip turbulance on square blades.

I go for rounded tips; most of the board has parrellel edges, but the tip is rounded so that the water will travel over a wing-shape at pitch angles of upto 30degrees. Also helps guide the thing down the slot.

To get a faired curve, bend a thin strip of plastic and trace along its edge. I used a very thin sail batten & "Sharpie" marker, before getting out the jigsaw and angle-grinder (with sanding disc).

When trying to re-shape old blades, I found it hard to restore a flat, smooth surface after I'd sanded through laminated fibreglass. For this reason I'd suggest cut the tops off the blades to make them shorter instead.

Disclaimer: not claiming to be any kind of expert here, just expressing my views.

Tony

[tom]

Cheers Tony,

It's always great to have discussion about the way the boat works.

I'm hoping to get out and about with the boat a bit more next season, so i'd like to get it as good as i can. Like i said before, from what i have experienced the boards are critical to the speed of the boat.

I'm interested in your thoughts that an elliptical shape isn't really suited to the PT, i have noticed that a lot of the newer foils on other classes have a straight leading edge, and a curved trailing edge.

Thanks for your input.

[knobblyoldjimbo]

One cure for howling blades is to chamfer the trailing edge. They say 60 degrees. This means that the flow over one side always "wins" and thus reduces the turbulence that causes the noise. There's no discernible impact on lift.

I had this problem with a Careel 18 rudder (I know nothing like your babes but principle is the same). I bogged on marine epoxy (which isn't water soluble!) into a rough 45 degree chamfer. Stopped the howl and made no difference to steerage or speed.

KO

[tonyquoll]

I’ve decided that the optimum width (chord length) of the blade is directly tied to mast rake. A narrower blade allows more rake of both centreboard & mast, but there are many factors to consider:

- more rake generates more vertical lift = more speed

- more rake can generate more weather helm, which drives the rudders harder and can generate more lift, at the expense of more drag

- more rake greatly increases the chance of getting stuck in irons

- due to limits on sail dimensions and mast height, rake is limited by going ‘block-to-block’ above the traveller.

My experimentation has found that:

- ‘velocity made good’ to windward is best when there is only a small amount of weather helm; balancing the boat for speed not pointing ability

- increased mast rake requires a lot more body movement around the boat when tacking, almost like tacking a windsurfer; stay forwards when going into the tack, wait until the boat has passed head to wind, then dive over the other side and sit all the way back until the boat has swung around, to below normal angle to windward. Then slowly sheet in and move forwards while building up speed

- wider blades work better at low speeds, with side-on area the main factor until there’s enough speed to generate hydrodynamic lift

Based on all that, my next pair will be 180mm wide x 14mm thick (8%) x 1m long. I’ll go for the NACA parabolic ellipse leading edge & flat sided trailing edges, possible a little ‘tad-pole’ shaped with slight concave sections near the trailing edge. Thanks for the idea on chamfered trailing edges, but I’ll aim for razor-sharp.

On materials, carbon-fibre is the ultimate, with the best strength to weight ratio. This page describes the material very well:

http://www.boats.com/news-reviews/article/shifts-in-fiberglass

Weights of a pair of centreboards are something like:

- carbon fibre;1.5kg

- polyester coated hardwood; 3kg

- fibreglass coth wrapped cedar & pine laminate; 4kg

The heaviest pair I have are 5kg, which are fibreglass wrapped laminate boards of massive old-style dimensions (300mm wide x 19mm thick). The difference between cedar & hardwood was about 0.5kg, with the fibreglass coating the main weight factor.

To keep costs down I’m looking at fibreglass cloth wrapped timber. It’ll depend on what I can get. The cypress slabs in the neighbour’s shed are looking attractive!

The volume of the slot which the centreboard passes through is about 3 litres. The water which fills this slot when sailing gets moved around with the boat, effectively adding to the boats mass & slowing it down. Therefore making a tube which your boards neatly slide through, instead of the big open slot, will save more effective mass than any type of centreboard construction.

Ideally I’d buy enough carbon fibre to make 2 new boards & then mould cases to slide them through, complete with pulley inserts to pull them up & down from across the boat. In reality it might be Styrofoam packing with waterproof carpet on plywood facing strips.

Any thoughts on all this?

[tom]

Hi Tony,

I have to say i don't know how you manage to NOT give yourself a headache!! lol.

My sail is close to maximum size, and this prevents me running what i would call "excess" mast rake. I run as much rake as i can, ie: mainsheet blockbound when downhaul and vang and main are full-on.

I'm not great on theory, but the reason i run maximum rake is that the mainsheet pulls straight down the leech when using a lot of rake, but if the mast is more vertical you pull really hard on the mainy and it just seems to stretch out the guts of the sail and doesn't depower as easily.

To fit my boards to the case, i got some marine carpet, and cut out a 100mm strip the length of the case. I held the c/board parallel to the ground, draped the carpet over the leading edge and laid 3 strips of 3inch f/glass tape over the whole assembly.. When it was set i took the curved carpet assembly and glued it into the front of the case at the correct angle with liquid nails.

This has the advantage of holding the entire length of the board so there isn't a pressure point at the bottom or top of the case..

I made a similar tab of carpet at the trailing edge of the case.

I haven't got around to filling in the sides yet, was trying to use urethane but it kept peeling out so i'll go with the traditional "bog" for this season.

Good luck with making your boards!

Cheers. Tom.

[tonyquoll]

Thanks for that Tom; I like your idea for the centreboard case & have added to my list of winter upgrades.

Today Max (1464 "Why Worry?") & I had great fun blasting around in 14-17 knots wind, trying for top speed. The goal is to get over 30km/h recorded on the Etrex GPS. 29.1 km/h with a full sail twisting a bit, broad reach with the nose at the point of diving in peak gusts. 29.5 with a flatter sail, hiking backwards with a leg over the rear beam, but couldn't go any faster.

Max did well, almost matching my speed. Over about 2 km leg he'd lose only 50m, mostly from slower acceleration rather than top speed. It shows what little difference all the work on foils, hull drag & rig upgrades have made. Old Why Worry still has stubby little rudder blades and very blunt, full size centreboards, though we've smoothed most of the dags on the hull. His advantage is more power, with heavier body weight & hull weight.

No headaches, but the eyes were stinging in the spray!

[tom]

Sounds like fun Tony!

I think you'll find that there is not too much difference in outright speed between a lot of the PT's.

I have managed to find myself at the front of the nationals fleet on a number of occasions, and i find that what slows me down is my ability to adjust to a change in conditions, or some slow manoevering.

The top skippers are right on top of adjusting their sails to suit the conditions, but i doubt their max. speed is any better than the mid-fleet boats.

Getting back to fitting the c/boards to the case, initially i wanted to make a sleeve of marine carpet that went right around the board, but there isn't enough room in the case for it.. If your case is really big this might be an option? I really didn't want to bog around my board because last time i did that i ended up with gouges from sand that got caught in there.

If you come up with an idea for sealing the case to the board i'd love to hear it.. At the moment the only other thing i'm thinking of is a gasket made of 3M clear tape with a slot cut in it.

I like the idea of using a GPS to track boat performance. At our recent state titles one boat was dominant on a particular point of sail. I am determined to find a setting for my Alegayter sail that improves my speed in that area, and at the moment my only method is to wait for similar conditions to occur in a race situation, and try something different. I guess with a GPS i could just wait for the right wind-speed, and then try different settings?!

I'm pretty keen to get back into the top ten at the nationals in SA this year, so i have to pull my finger out..

[tonyquoll]

Winning:

Agree with you that there’s a lot more to finishing at the front than outright boat speed. However, the PT fleet is so competitive that to win, everything must be perfect; the hardware, the tuning, the start, the tacking & gybing and mostly the tactics. In one race at the Nationals I dropped back from 6th at the first mark to 20th at the end, purely due to lack of speed. I’m hoping to keep improving the boat, so that if I sail well, I get a good result. Improving from 33rd at the Nationals to 22nd at the Internationals shows I’m on track. Also agree with you about sail trim; it was setting the sail too full in very light winds that cost me a lot of places.

_________________________________

GPS use:

One morning while racing was postponed as we waited for wind, I went out with the GPS and tested a variety of sail settings. I found that the full sail I had been setting moved me at 3.5km/h, while a much flatter sail got upto 5km/h. A 40% increase in speed! The real lesson though was memorising what the tell-tales were doing when the sail performed at its best, and then continuing to trim the sail to achieve that flow.

The Etrex is OK, because it’s cheap and waterproof, but it’s near impossible to read while sailing as the numbers are tiny. Possibly a car-navigation type would have a larger and more useful display, and could be waterproofed in a zip-lock bag.

____________________________________

Centreboard slots

Boats such as the Nacra appear to have carpet in a sleeve all around the top of the centreboard case, a gap through the middle and a hard moulding at the bottom. I guess the idea is to minimise friction (to get the blade up & down) while holding the blade firmly.

Using something flexible to seal the case, such as Sikaflex (Polyurethane), increases the problem high friction coefficient holding the blade. This can be mitigated by reducing the contact area, with a thin lip, and by roughing up the surface.

Polyester based filler (bog) has lower friction coefficient, so there isn’t the same problem, but I’ve found it chips and cracks easily.

On both my Sailfish & Moth I had a strip of fibreglass tape, set in place and stiffened with polyester resin, with a slot cut in it. I’ve seen a photo of this done on a Kiwi Paper Tiger. I’m guessing the issue there is that it is flexible, so not as effective as properly shaped bog.

_______________________________________

Forum

Thanks for the feedback and discussion here. From now on I’ll be supporting the new PT website by posting discussions to the forums at

http://www.papertigercatamaran.org/

Cheers

Tony

[Dave]

Great discussion guys.

As the custodian of the Paper Tiger website, which does have its own forum, I wouldn't like to think we abandoned this site altogether. I know having two forums can be painful, but I really enjoy the interaction of the various classes on this one.

Also, keep in mind that people may discover this one first and ask questions here, so it's worth checking in regularly here.

I would like to thank catsailor.net for providing this very good forum for all the classes.

I will continue to use it for both PT and general information as well as using the PT website.

Regards,

Dave Stumbles

Secretary

Paper Tiger Catamaran International Association

www.papertigercatamaran.org

+61 (0) 400 476 449

[tom]

I only recently became aware that the rules for the centreboard cases on the PT are pretty flexible. The trailing edge is controlled, and the width of the case is controlled, but you can rake the whole case as far forward as you wish...

Apparently it is clearly visible on the Markovitchs' and Williams' boats that the top of the centreboard case is a lot closer to the front beam.

With the narrow section board, the effective chord is made wider the more it is raked. It would be interesting to measure the chord parallel to the waterline of these boats?

I gather at some stage you will start to get ventilation which will limit the rake of the board, so it will be interesting to see where things end up.

Might need to get the grinder out and "move" the front of my centreboard case!

[tonyquoll]

Wow, had to think about that one! Scaling off Neil's great photos (at http://photos.papertigercatamaran.org/), Ian Marco's blade are at about 64 degrees rake, which increases the chord length from about 120mm to 133.5mm. I keep saying "about" because none of these are properly measured lengths.

The Class Rules say:

6-CENTRECASES

1. Centrecases: rear of slot to be 1390mm + or - 15mm along the keel from outside of transom.

2. Maximum dimensions of centrecase slot measured at deck level shall be 25mm x 310mm and at keel level 25mm x 305mm. Recesses for centreboard stops are permitted providing they do not exceed 40mm in depth from deck level.

3. Centrecase must not be fitted with any device or means for angling centreboard to port or starboard.

So that prescribes where the slot is on the bottom of the boat, and the maximum size of the entry slots, but not the rake of the case. Still seems to me maximum rake is limited by getting stuck in irons, going block-to-block, and generating too much flow down the leading edge.

What about pushing the rule on “angling” the centreboards? Say they’re fixed at a constant angle, but the blades is curved so that the tips point towards each other. This provides vertical lift, like a hydrofoil. There’s some discussion about this in A-class cats. See photo here: http://photos.catsailor.org/A_Class_worlds_design_details_2009/slides /Nikita%20curved%20centreboards.html

To go with it, the rules would seem to allow foils on the rudder blades, like 16 foot skiffs have. I was amazed at the size of these things; the cross-foil is as big as the rudder blade itself. Apparently they help stop nosediving, and also help provide lift to get the boat up and planing. Some say there’s little additional drag; it’s all good.

The rules don’t seem to prohibit it:

7-CENTREBOARDS AND RUDDERS

1. No restriction on centreboards and rudders shall apply other than maximum centrecase dimensions as in rule 6(2) above.

2. The centreplane of each hull, its centreboard case and its rudderstocks (in the fore and aft position) shall coincide.

In reading about NACA sections, I learned they were mostly developed in the early days of powered flight, bi-plane era, when air-speeds were around 300km/h. The relationship of the wing to air at that speed is comparable to our foils to water at 30km/h. These days the most high-tech thing designed for 300km/h are Formula 1 cars. The F1’s primary aero function is downforce. Great illustrations at: http://www.formula1.com/news/technical/

They have a lot of fins to maintain laminar flow, and to guide the flow of air off the back of the car. Makes me wonder if we should have fairing on the rudder boxes to effectively extend the hull’s planing surfaces & reduce wake.

The F1’s are tightly limited by rules, and protests followed the use of flexible and adjustable flaps, which stood up in corners, with more curve producing more downforce, and flattened out on the straights, reducing frontal area and drag.

It follows that our foils would be better if we curved them more when we want more lift, such as curving the rudders when tacking, and thinning them down when going straight. The Moths have adjustable hydrofoils, which adjust the amount of lift. Why not have ailerons that adjust the curve?

I’ve a design for cam-operated rudder blades, which form a curved profile as the box is turned relative to the transom. However it’d require carbon-fibre moulding to build and test – out of my price range! The centreboards could be easier; imagine 6 long strips glued together with Sikaflex, and a case that is curved on inside (nearest the tramp) and flat on the outside. Your leeward board would be pushed hard against the curve and form that shape, while the windward board would go flat. In situations of less side-force, the board would naturally straighten out.

Ever seen anything like that?

Cheers, Tony.

[This message has been edited by tonyquoll (edited 02 June 2009).]

[knobblyoldjimbo]

Just another tuppence. The i14's which aren't allowed hydrofoils do have big horizontal fins on their rudders. Does two things apparently, one is adjusting the up/downforce so they don't nosedive but the other more intriging thing is that apparently they trick the boat into thinking it has a longer waterline length.

There's also a thread on Sailing Anarchy (dinghy's) about a National 12 winner (English development class) which as a similar arangement.

Can't really see that working on a cat but would like to see it.

[tom]

Jimbo, those skiff guys are insane! It's already outside the rules to have a 'T' foil on the rudder, as it would go outside the max. width of the boat. As far as i can see there is nothing stopping an 'L' foil which would have a similar effect.

I think that would be great to minimise hobbyhorsing in the PT's. But in my opinion isn't in the spirit of the rules and i would hope that anyone going to implement it should clear it first with the inter. measurer. (actually i think anything outside of what is currently in use should be cleared before use)

The great thing about the PT is an old boat can be competitive, but there is still room for innovation. I am worried about the trend of the centreboard case "migrating" towards the front beam.

Tony, the 5o5's are one class that have used "bendy" foils on their boats. The A's have boards that are permanently curved, and i would imagine this is an advantage. There is a rule in the PT class rules that states that the centreboard cases shall be in the same plane as the centre-line of the hulls. In my opinion putting a curved board is outside the spirit and intention of the foil rules for PT's.

On that theme, i think the spirit and intent are the most important part of the rules.. If the majority of the fleet agree on a certain interpretation of the rules, then that is what should be applied.. No matter what wording you use, there will always be someone that can find an "interpretation" that is not what was originally intended.

It's a fine line between encouraging innovation, and alienating a large proportion of the fleet.

Cheers!

[tonyquoll]

Hi,

Those are great intentions and sentiments, and I agree if I were to design a radical new rudder system that it would ideally be affordable and available to others. The rule on maximum width is Rule 2.4, under the heading “hulls”. Cant see how that would apply to T-foil rudders.

My experience in PTs has differed from the ideals Tom describes.

Neither Sate or National / International measurer replied to my query about these ideas (sent 6 months ago). Informally one said that he took on the voluntary role to help sailors compete in the class, but doesn’t really like or want to be involved in disputes and rulings about what is allowed.

My boat (2128 Pelikinetic) was minimum weight and competitive 25 years ago, but when restored and put in the fleet was much slower than new boats. Upgrades required included:

- newer sail; (they are bigger now than they used to be).

- new mast (more streamlined section),

- swivelling cam-cleats (allows downhaul adjustment from the side stays)

- other cam-cleats (to adjust vang & outhaul)

- updated rudder box, with swing-up/down remote control

- updated rudder blade with different cross-section & overall size

- updated centreboards, with increased rake

These were all good things that made the boat much faster, I now average 18km/h upwind in 15 knots, increased from averaging13 to14km/h. I wasn’t impressed at all with snobs who called me a beginner because I finished at the back of the pack on my old boat. I can cite two examples of PT sailors who have sold their boats after being discouraged, and recall one skipper saying “what’s the point?” and leaving a titles series early after his older boat kept getting passed all over the course. It doesn’t help anyone to pretend that old boats are just as fast as newer ones. It was very satisfying to beat certain people in the Internationals once I’d made a few upgrades; I guess that’s the flip-side of sledging.

If curved centreboards were legal and faster, they would not cost much more than the carbon-fibre boards in use today. I can’t see how anyone could complain that these would not be in the spirit of the rules; did they consider that when gaining an advantage over the old wooden boards by upgrading to carbon-fibre?

[Dave]

G'day Tony,

It was very disappointing to read your posting. Firstly, it is disappointing to hear that people didn't reply to your queries. I'm not sure how you went about this or who you dealt with, but I would like to think that most people in the class would reply or pass it on to someone who knew the answer if they didn't.

Certainly my experience in the PT fleet has been that nearly everyone is very helpful and many of the top sailors have given incredible amounts of time to unselfishly help others. There were many examples of this at Easter during the Internationals, such as Ian Marcovitch doing informal "classes" on sail trim and Garry Williams spending every spare minute between two of the races getting someone else's boat repaired so they could continue the series.

I have definitely never seen anyone talking or acting like a "snob" towards people further down the fleet. While I still think the PT is one of the nicest boats to sail, the main reason I have stayed in the class for over twenty years is because of the people. I have found that right throughout the fleet they are a really great group of people and, as mentioned, very helpful.

I was also disappointed to hear that a measurer did not really want to fill the role. While it is often not easy to get people into committee positions, I have found that most are willing to fulfil the duties of the role they have taken on. The role of Measurer can be difficult at times, but there is normally a process that is followed to resolve issues. Possibly the person in question was not fully aware of the process. I think it is a shame if they have found themselves in a role that they just don't want to be in.

Again, I'm not sure who you dealt with, and I don't want to name people here anyway, but the State and National Measurers are not there to resolve disputes. Disputes, clarifications and interpretations are escalated to the International Measurers to be resolved. We had a situation in Australia until recently where we had a caretaker in the role of International Measurer for some time while he was also National Measurer. This has now been resolved.

The Paper Tiger Class Rules state "Interpretation or clarification of the Class Rules shall be requested in writing from the Chief Measurer." We actually have two International Measurers (one each from the two main countries), but a request made to one of them will be discussed by both of them and the International Committee if required. As International Secretary, I can certainly pass these requests on to them and, if so, would guarantee that you would get a reply.

In regard to sail size, the only differences since the class began are in the way they are measured. Some years back, Australia agreed to measure the sails using the ISAF procedure that New Zealand had always used. This meant a very small difference in one or two measurements that was so small (millimetres) that it made no difference. Essentially, the sails are the same size they were when the class was designed.

I can state categorically that the age of a Paper Tiger is not a determining factor in its performance. If the boat has not been looked after and is heavy or soft or has other issues, then sure, it will struggle, as it would in any class. But a well looked after old boat can be just as competitive as a new one. The prerequisite is that the boat is close to weight, reasonably stiff and the hulls are sound. Plenty of old boats still fit this description. The 2006 Internationals were won by a 25 year old plywood boat. Several competitive boats in the New Zealand fleet, including the one that finished second in their last Nationals, are 35 years old!

Sure, they have modern sails, masts and fittings (systems), but they are still old boats. I can't think of any class where a 25-year-old sail is going to be competitive. And as Paper Tiger masts are only about $300, it's not a major investment to upgrade. No class is immune from older boats struggling to be competitive, but I firmly believe that the Paper Tiger is one where this is as close to a reality as possible.

It is unrealistic to expect that someone (especially someone who has not sailed Paper Tigers before) can purchase a 25-year-old boat that has been sitting under a tarp in someone's backyard for 15 years and then simply turn up to a Nationals and be competitive. Someone who has not sailed PTs before would be doing well to be competitive straight away on a brand new boat. It takes time to learn the various nuances of a class (again, this would apply to many classes). And of course the boat that hasn't been touched for 15 years will have things that are less than helpful, like corroded parts, friction issues on blocks, dilapidated sail cloth and stitching, stiff ropes, twisted battens, etc.

In regard to the curved centreboards, I can't find a rule that prohibits them. The main rules that cover them are:

"1. No restriction on centreboards and rudders shall apply other than maximum

centrecase dimensions as in rule 6(2) above.

2. The centreplane of each hull, its centreboard case and its rudderstocks (in the fore

and aft position) shall coincide."

The first three paragraphs of the class rules are:

"The Paper Tiger catamaran is a one-design class. Boats shall conform to the general requirements and outlines shown on the plans except as modified by these Class Rules.

In accordance with the ISAF Equipment Rules of Sailing, these Class Rules fall under the definition of clause C.3.2 “Open Class Rules” which state:

“Class rules where anything not specifically prohibited by the class rules is permitted”"

However, as with anything, if there were any doubt, I would certainly run it past the International Measurers. As stated earlier, if you forward your request to me, I will guarantee that they get it and that you get a reply.

Also, as always, I am able to put people in touch with whoever is needed to answer their questions about the Paper Tiger class, whether it be in regard to measurement, performance, tuning, rigging, building, fitting out, buying, selling, race management, or whatever, and I do so on an almost daily basis. Please give me the opportunity to help you if you are not getting satisfaction elsewhere. I am here to help!

Regards,

Dave Stumbles

Secretary

Paper Tiger Catamaran International Association

www.papertigercatamaran.org

[tonyquoll]

Good one Dave,

Measurement of sails may not have changed, but I own sails made in the early 70's, late 70's, early 80's and mid-90's. When you lay them on top of each other, they were clearly made progressively larger, especially at the top of the leech. During measurement at the Internationals, my mid-90's Williams sail was easily under-size, while brand-new sails were right at the maximum dimensions.

Not saying that's a bad thing; just that current spec boats are definitely faster than old ones. When I say 'boat', I don’t mean just the hulls, but the entire complete assembly of parts. As stated above, the majority of components on my 25+ year old boat had to be upgraded to make it competitive.

I agree with you that Paper Tigers strike an excellent balance in the rules, allowing development while staying affordable. My example demonstrates that; buying a $200 wreck and piece by piece upgrading it to a good competitive boat. The total cost is now around $1400, which is cheaper than most classes.

The theme of this discussion started with centerboards, which seems to be an area that further development is possible. I followed Tom’s leads and read about 505 centerboards; they evolved into long, high-aspect ratio boards. Experiments in allowing them to twist to ‘depower’ weren’t adopted. The rake is adjusted between light winds & strong winds.

In Mallacoota these days, when its nice & warm the lake is glassy & still, and the only time there’s wind it’s 5 degrees and raining. Therefore the boat is back in the driveway and it’s time for mods & repairs, with upgrades planned:

- manufacture new high-aspect centerboards; 180mm wide x 14mm thick x 1m long

- manufacture new rudder blades; 190mm wide x 19mm thick x 750m long

- add cedar strips to the gunwales, to upgrade the old hull to the newer idea of 40mm wide curved bits under your legs (up from 20mm)

- add an insert or modify the centerboard cases to exclude all the water

- patch up all the cracks & leaks

- patch up the fraying bolt ropes in the sail

Cant wait till next season!

[tonyquoll]

Check out these S-shaped centreboards, used on America's cup challenger, Alinghi:

http://www.boatdesign.net/forums/attachments/multihulls/33360d1248122156-foiler-americas-cup-alinghi-sa.jpg

There's an article comparing the Alinghi cat with BMW trimaran in this Month's "Australian Sailing Magazine" (October 2009). Both boats have curved centreboards that provide vertical lift. In one photo (p.8 bottom right) the all 3 trimaran hulls are out of the water.