Raceboard Design 2
June 16, 2010 · Print This Article
Raceboard Design 2 The “Skiffboard” – Conceptual Design
Last year I wrote an article on LBWS regarding Raceboard design. It outlined some design principles that I believe could improve Raceboard performance. Since writing that article, I’ve fleshed out a conceptual design and attempted to gain industry support to bring a new Raceboard concept to market. I’d like to share with LBWS my preliminary conceptual design and the feedback I’ve received from industry.
DESIGN
The overarching design objective is to the build a faster Raceboard: a ‘round-the-buoys’ sailboard conforming to the Raceboard class rules for use in 0 to 25+ knots. It would be used in a wide variety of conditions, typical of sailboat racing venues such as Sydney Harbour, and would need to be able to handle moderate-sized waves, and areas of light wind. It is an all-conditions racing board.
The overall design concept borrows heavily from the 18foot skiff designs (the pre-cursor of the Olympic Class 49er) of the early 1990s, hence the name “Skiffboard”. It has a long, sharp bow with a vertical stem and a wide, flat planning area at the stern. The design merges the bow of a displacement hull (such as the Starboard Serenity or Div 2) with the stern of a planning hull (such as a modern wide-ish slalom board).
>It would be 3.8m long, the maximum permitted length for the Raceboard class, and of a width equivalent to modern Raceboards. The diagram below shows a rough sketch of the concept:
This design as pictured above is preliminary and conceptual – it obviously requires significant refinement. However, I believe that this design concept (if refined) would provide superior all-round performance to any raceboard currently available. This superior performance would be driven by the reduction1 of the “hump” in the drag-speed curve1, as discussed in my previous article on raceboard design.
POTENTIAL PERFORMANCE
In light winds, I believe that its performance would be significantly better than existing Raceboards because of its lower form drag (due to the fine bow) – its performance should be closer to a pure displacement hull than a modern Raceboard. In moderate winds, I believe that the wave-piercing abilities of its bow would continue its out- performance of existing Raceboards – in addition, it should outperform displacement hulls because it would plane earlier.
In strong winds, I believe that its performance would be comparable to the current crop of Raceboards. It would outperform displacement hulls in strong winds because it could plane on its tail like a slalom board.
However, handling may be challenging in stronger winds. I believe it may have a propensity to nose-dive while sailing downwind in chop. This can occur with high performance designs such as skiffs and catamarans. However, I believe that handling techniques may be developed to compensate and its potential all-wind performance would be worth this compromise.
Areas where this board maybe more difficult to handle is in manoeuvring/turning (particularly tacking and bearing away). The long displacement-profile bow may be difficult to ‘push’ laterally through the water. However, I don’t believe this would be any more difficult than the Div 2 boards of the 1980s and, again, handling techniques could be developed to adjust.
DESIGN CONTEXT
All of the above comments about performance are hypotheses, but based on first- principles hydrodynamics and from my experience in developing, racing and observing Moths, 18 foot skiffs and other high performance sailboats. This design concept is unproven2 – it needs further refinement, particularly regarding the alignment of the shape to the key ‘numbers’ (rig & hull forces, weights, volumes, mast and centreboard locations etc), and then development / testing of prototypes.
I am not aware of any other truly comparable boards at the moment, although some designs have touched on this concept. This design concept varies significantly from a Div 2 board (displacement hull) because of the wide, flat planning area at the stern. It also varies significantly from the hybrid boards that were designed as potential Olympic boards because of its 3.8m length.
INDUSTRY SUPPORT
I am not approaching this as a commercial venture: I simply want to sail faster Raceboards and see the Raceboard class develop. To this end, I have contacted several of the leading sailboard manufacturers to try to make this design a reality. I have shared my design concept with them. In addition, I have even offered to co- ordinate further design / development and construction / testing of prototypes (effectively outsourcing their R&D for this board), while allowing them to retain commercialisation rights.
The feedback from the manufacturers has been positive regarding the design concept. However, they have not been interested in developing this board with me, generally stating that the Raceboard / lightwind market is too small and is considered a niche. This response is disappointing but understandable: they are operating a commercial enterprise.
While the big manufacturers may not find it attractive to invest in Raceboards, such investment might suit a niche or boutique sailboard manufacturer. I’m interested to talk to such parties and I would offer to co-ordinate further development if they’re interested.
Alternatively, perhaps an individual will take these design concepts, and build and race a board competitively. Unfortunately, the Raceboard class production rule discourages such innovation.
The Author
Richard Reatti (AKA ‘yagon’) is an avid sailor of Raceboards at Dobroyd Aquatic Club in Sydney, Australia. His sailing background includes extensive racing of skiff Moths and 18 foot skiffs, achieving top 5 placings in their respective world championships and he was the world junior champion in the Moth class. He is also an engineer specialising in fluid dynamics.
Richard can be contacted at: richard @ reatti.com.au
(1) I expect that eliminating the hump in the curve will not be possible for a craft as small as a sailboard, but I believe that this design will reduce the hump significantly.
(2) Unproven in sailboards, however, this design concept has been proven in dinghies such as: Moths, 18 Foot Skiffs, 49ers, 29ers and others.
The idea of one race-board used world wide is a good one. In many respects Open Class racing helped lead to the demise of windsurfing in the 1980’s. The battle was between designs, and the average recreational sailors interests were forgotten.
The current Olympic Board class has not seemed to satisfy the general public as it is way too expensive to be a generally accepted recreational and/or raceboard, is cumbersome to cart around, and somewhat difficult to master sailing it.
Any successful raceboard must also be a successful all-around recreational board or it will never prosper. And it will never help the sport to start to grow again. The “race” performance of the board, so long as it is relatively efficient and a pleasure to sail in 2-20 knots, is secondary to it’s general appeal to consumers to sail in 2-20 knots.
I repeat: The race performance is secondary to general appeal (durable, lightweight, easy to transport and store, affordable.)
One very good thing is that there is only one board manufacturer now.
Why is this good?
One entity or any combination of entities can combine funds to have a mold made at that facility, where mold building costs are relatively low anyway.
Then that mold, with only ONE layup that is “middle-of-the-road to lesser expensive” can be built for whomever wants to buy from it. Any manufacturer can draw from it and put whatever name and graphics they want on it. Clubs and fleets can even buy directly if they can put the purchase together.
The rig is another issue that should be delt with at the different club, national and international levels.
This is an opportunity for the entire windsurfing community to act together for the advancement of the sport instead of segmenting it by continually coming up with incrimental improvements that chase people away from investing in racing.
What a great article and thanks Paul for your views and comment on the article. In response to the comment from Paul I make the following points.
Paul noted that “the current Olympic board (RSX) has not satisfied the general public”. It should be made clear that this is not a raceboard. It is a hybrid board that has not satisfied the public as it has a narrow wind range where it performs well. That is to say that it is very average in light winds and a lot of the public sail in light wind at their local club. In short it is not a good club board.
While I to some extent agree with the advantages to there being one manufacture, I draw your attention to the following article on LBWS that notes some negative issues with this.
http://www.lbwindsurfing.com/opinion/ensuring-supply-of-longboards/
Cheers
Pat
Hi Richard,
The problem with the currentCobra system is that the technology used of pre-expanded oversized polystyrene cores that then shrink prior to use in the final build of EPS cored boards require not one but two different sized moulds to be built for each model. This is obviously an expensive commitment for a small run of product.
Many years ago (in the late 1970’s the Sailboard Brand in Germany produced a model “Porsche Design” not so different to your sketch although the bow was less vertical.
It had too much wetted surface in the tail to be quick in light wind ,in displacement,and only worked well in more than 10 knots when on a plane. The “sailboard Sport” a much cheaper model was quicker in most conditions
I would be very interested to know your proposed centre rocker line
offsets to see how they compare to D2.
The only reason D2 was so unstable in a blow was the stupid “Half height” measurement system together with the desire for minimum wetted surface for light wind sailing produced the semi-cylindrical hull form.
On the positive side the construction was from single moulds and there are still lots of minimum weight Lechners around .
As a matter of Fact the last batch of Lechner A 390 boards built for the Barcelona Olympics by “Bridgestone” were in fact sub -contracted to COBRA.
I have been windsurfing since 19 74 and building prototypes since 1978 but old age and infirmity has kept me off the water for the past year.
Peter E
Apart from the nose section, looks similar to the Expedition Windsurfer.
http://adventurewindsurfing.blogspot.com/
It would be worthwhile talking to this guy about the design/ construction.
Have a look at a Naish Glide 14 SUP…
http://www.naishsurfing.com/en/boards/glide_1.html
Apparently you can sail it…
http://www.windsurfcanada.com/index.cfm?fuseaction=journals.view&journalid=1305
Looks fairly similar to your thoughts!
Railing a traditional raceboard solves a few of the drag problems you mention. Scow sailing is a good model for raceboard windsurfing. They use all sorts of heeling angles to reduce drag created by the barge-like hull. By either railing when beating or flat for planing scows are fantastically efficient for their tremendous simplicity.
A wide stern creates tremendous drag in displacement, aren’t skiffs intentionally heeled when going upwind to address this? The bow shape of your design will create extra aero drag that will reduce upwind planing angle, though that isn’t really a priority with a raceboard anyway. Your design has merit but I think enhancing the railing ability of a more traditional raceboard with a more traditional oval-outline board shape will reap greater rewards.
Hi Richard.
An interesting reprise of an old idea.
Raceboards like this tend to be quick in light winds but are horrific in strong winds and chop.
The reason is that they reverse foot steer. that is that they steer away from the immersed edge. They even make a Div 2 sailor weep!!!
Also are very unstable in the tack due to being much narrower in the bow even that a normal div2 board.
I unfortunately speak from first hand knowledge!
In 1984 I had a Div 2 board based on one of my ‘Demon King’ design moth hulls. It had reduced freeboard and 350mm of extra length added on to the stern. The shape was very similar to your drawing.
The thing was fast enough to win a UK’s regional championship that year but it was an exercise in misery.
I built a tunnel hulled (scow) hull the next year which was faster in almost all conditions and also really nice to sail. This was good enough to win the UK national champs.
The main advantage these fine bowed hulls have in a normal sailboat is that the fine bow reduces drag when pitching into waves.
With a windsurfer the angular momentum of the rig in pitch is decoupled from the hull. This means that the hull pitches far less into waves and therefore the fine entry is less advantage.
Personally I think that the top custom Div 1 boards of the late 1980’s were the fastest and nicest to sail all round racing windsurfers ever.
The Raceboard rules were framed to outlaw these boards for a reason!
Mistral , F2 and Fanatic despaired of making anything that could match them and had the bureaucrats of the time in their pockets.
A Sabre 3 or a Tunnelhull D1 would make mincemeat of any of the current Raceboards in any wind condition.
Other than the Moth the only other hull of similar proportions to a board is the 10sqm Canoe. Just a thought, are there any elements in their hull design that could be used for boards?
Thanks for all the feedback. Apologies that I haven’t responded earlier, but I’ve been distracted while I move house, including co-ordination of some renovations. I’ll repsond to each comment in an individual post.
Paul Julien – the one design versus development class is an ongoing debate. I agree with many of your points, particularly regarding the need for one design classes to develop broad general appeal. However, I also think there is a role for development classes to encourage progress in design and development, even if they will never attract the numbers that a good one design class will generate.
Personally, I am passionate about development classes – perhaps its the engineer in me, but I enjoy the design and development process. I’ve had the good fortune to be involved at a high level in 2 of the most progressive development classes: Moths and 18 footers.
The very open class rules of the Moths enabled the development of the the foiling Moth – a paradigm shift in recreational sailing that has lifted the profile of the entire sport.
Likewise, the open class rules of the 18 foot skiffs led to the development of the 49er – one of the most exciting and high performance one design / olympic class available.
Peter – thanks again for your thoughts. Your seasoned perspective is highly valued.
Regarding your comments on the wetted surface area – my conceptual design has greater surface area than a D2, but probably similar to the current raceboards. I think a D2 would outperform this concept in light (non-planing) winds.
Regarding the rocker line – I have not yet defined the detailed parameters of the design – that is the next step in the process that I hope to do with the help of one of Australia’s leading sailboat designers. I imagine that the rocker would be like a Moth – fairly low.
Re the stability of the D2 in strong winds – my design is really a D2, but with a wide flat planing area at the back of the board instead of the semi-circular cross section. I think it would plane more readily and be much more stable than a D2 in such conditions.
Dan – I really like the expedition windsurfer and agree that it is similar to the ’skiffboard’. I couldn’t believe it when I saw it. I’d like to know more about its sailing performance.
I would note that its design focus is very different: cruising versus racing. Accordingly, many of the detailed design features would be different.
Joe – re the Naish glide and other racing SUPs – I really like the fine bow, but they lack the broad tail of the ’skiffboard’. I’d be interested to hear about their sailing performance.
Wildblue – thanks for your comments. This is a really good point to raise.
I agree that scow sailing is a good model for raceboards (and also formula/hybrid boards). They have fantastic performance in stronger winds. In lighter winds, they heel the scow to reduce wetted area. This is quite effective, but can also increase wave impact drag.
I am fortunate that I was sailing Moths in the mid to late 1980s, when Skiff Moths ‘evolved’. At that time, critics of the skiff said that they would be faster in light winds, but only for a small number of elite helmsman. In strong winds, they hypothesised, they would never compete with the planing ability of the scows.
They were right initially – skiffs smashed the scows in light winds because of the reduced drag from smaller wetted area and lower wave impact drag. But in stronger winds, the skiffs were challenging to sail and the scows were easily competitive. There were only a handful of helmsmen sailing skiffs.
This continued as the skiffs became narrower and the helmsmen because better. Then Steve Shimeld, sailing a skiff, won the world titles in South Australia in extremely windy conditions. His handling abilities proved that skiffs, if well handled, could beat the scows in stronger winds. This was a turning point in the development of Moths – a similarly important turning point to when the foiling Moth first won the world titles.
I believe that a ’skiffboard’, although challenging to handle, could deliver similarly superior performance to existing raceboards – if the appropriate handling techniques were developed.
Wildblue – to address your other comments:
Regarding heeling of skiffs – this is only done in light winds to reduce wetted surface area (refer to Bethwaite’s book: High Performance sailing), not once you are fully powered up. When fully powered up, the skiff is generally sailed flat.
Regarding extra aero drag – I agree that aerodynamic drag will increase, but I believe that the benefits of the fine bow will outweight any negative effect.
Regarding railing – I’m interested in your thoughts on how the railing ability of a board might be enhanced. Can you expand on this?
Sean – Thanks for your feedback. I’d really like to see photos of your 1980s designs – can you post them to the forum?
Regarding your comment of angular momentum – I absolutely agree that the decoupling of the rig and board reduces angular momentum. The technique most racers will be familiar with is to keep the rig and your body stationary, and let the board float up and over the waves – a technique impossible to replicate in a sailboat. However, I still believe that there is merit in a fine entry – and that a fine entry is worth pursuing.
Does anyone know where I can get my hands on a Sabre 3 or Tunnelhull D1?
River – I’m a huge fan of the international canoe. Their hull shape shares many similarities with Moths and the ’skiff board’. They too require expert handling and can be prone to nose diving, although they can have the benefit of the upward lift on the bowsprit when sailing downwind. I’ll try to post some photos later.
I made some boards that style around 1985, I tried several widths 60 up to 80 cm.
[img]http://img5.imageshack.us/img5/4321/numrisation00334.jpg[/img]
The best all-wind-machine I ever sailed, progressive planing mode, remaining quite horizontal, affording easily 100 cm centerboard,
Upwind in light conditions the flat back is mostly lifted out of the water,
About 4.20m long, thicker than a div2
Hi Sean
Its a long time since we last raced at Axebridge!!
Are you still in new Zealand?
As one of the”beaureaucrats” and the measurer who drafted the original Raceboard Rules I can assure you that the big brands had zero input in the process.
The prime movers were the FFV (French Federation) who did a lot of testing in Brittany and produced a list of suitable production hulls of fairly equal performance in most conditions.
D1 did not exist in France as a racing category and they needed an alternative to D2 to promote to their club sailors.
As a D1 hull builder/designer I was fully aware that the exclusion of all the “specials” (including my own) as well as the Mistral superlight was essential as they were all too fast for the new class in lighter conditions. Limiting the rise of floor and beams to lock in the flat planing shape that suited the volume production system was essential for what was supposed to be a “production class” available in shops to all and easy to sail.
The really good guys had D2 and then Lechner and the weekend sailors who could not handle those in a blow needed a class they could cope with if they were to stay in the sport.
Hi Yagon The increase in potential length of the centreboard in the current rules offers the best opportutity.
As you “rail ” the board you are creating half of a Vee Foil and moving your weight astern increases the angle of attack and hence the vertical lift effect. A longer high aspect ratio foil has more lift at lower speeds for the same surface area than a low aspect ratio foil,just look at gliders wings and how different current hang gliders are from the early “Deltas”.
As a matter of fact all the good D 1 sails (limited to 6metres if fully battened) were high aspect ratio ,using booms down to 1300mm
on luffs over 5000mm, both Sean Cox and Mac McRea were sailmakers specialised in these in the Uk.
Regards to all
Peter E
.
Dronist – I love that board. The bow is exactly what I have in mind. For the stern though, I’d cut the back 1/3 of the board off, then stretch the front 2/3s to the full 3.8m length (moving the straps and centreboard accordingly) – giving the wide planing surface at the stern. Good to hear that it performed well.
Peter – I agree with your comment on centreboards and high aspect ratios. Last year I contacted Sean about building a full 5m luff length VG5 for my racing.
However, one thing that has me puzzled is the length of centreboard used in Raceboards compared to other high performance sailcraft (eg a 49er centreboard is proportionally much smaller). Based on some back-of-the-envelope calcs, the lateral load of a centreboard in a Raceboard simply shouldn’t need such a large board. However, experience suggests that bigger is better.
For interest, the skiff-hull design has also been adopted in other areas of high performance sailing. See video below:
http://www.youtube.com/watch?v=uLfekPLvUvE
Hi. Richard.
I’ve sent some photos to your Email. Most of the old photos of the Div1 era are before digital cameras and stuck in a box somewhere.
The change in the Raceboard rule allowing 850mm centerboards rather than the usual 700mm is another example of a stupid pointless random rule change that just makes older equipment out of date.
850 rather than 700 is enough to make a small difference in light wind racing. A Raceboard with an 850 centerboard will point about 1.5deg higher and go 3% faster than one with a 700mm board.
Against this the board is really nasty to sail on the rail, the extra 150mm makes it much more twitchy. More importantly the centerboard slot is 150mm longer. Most manufacturers (especially the most common one) have real trouble making even a 700mm slot light and strong.
So you make the board an overweight weak dog for a performance gain that will only be noticed in the closest of competitive racing WTF.
You don’t need the beam of the hull at the back for a windsurfer. The low overall weight/length ratio and the very high movable-balast/weight ratio means the board can be easily trimmed in planing transition.
Yachts and dinghies have the wide stern because they squat during transition to planing and a wide stern stops this. They also spend a lot of time in the planing transition region.
Another reason windsurfers don’t need a large planing surface is that a good proportion of the weight is supported by the rig. When planing properly even a longboard only needs a planing area of the order of a couple of square feet.
Sounds like fun!
All this technical debate should be used for progress,…faster windsurfers!
Along the lines of the original design, why not have the skiff bow, a flat mid section (for the transition, and a scow (reverse concave) style in the stern?
I would see the scow section tucking all the way under, similar to the fins on the front of a manta ray.
Now, saying all this, the concave I would use would be quite dramatic in this tail section, allowing air to be funnelled from the planing section out the tail (manta) section, both compressing the air (inducing earlier planing), and acting as fins. this would also allow for some greater outline to use for carving, as well as a big flat middle section to stand on whilst tacking/ going upwind??? random thoughts really, but it would go fast, and turn in all conditions!
I meant to say rocker in the tail section would be dramatic.
As Peter said. Just like the “Porsche Design.”
Please note that I’ve created a thread for posting of photos of raceboard designs:
http://www.lbwindsurfing.com/forum/viewtopic.php?f=2&t=1015&p=2846#p2846
Hi again
I was at the Kona Euros in Brittany last month and had several conversations with Patrice Belbeoch of Exocet on possible longboard developments. Apparently he is thinking about maybe
using “twinzers” in order to get the longer cb blades further back.or more to the point no further forward in the hull.
He had a prototype on the beach with an 850 cb in a 3500 round nose hull under evaluation .
There is nothing new under the sun. it is a shame i don’t have any photos of Bob Jones on a Proton which was a custom board that, if my memory serves me correctly, was made and sailed by Nick and Ali Highton (sp). Nick was a RN helicopter pilot. The Proton was almost exactly as you have drawn/described. Sean will remember better than I. I think it was an even better concept than the Sabre he and Bruce Keeping were building back then. (Bruce is keeping well btw Sean) These boards would (and did) destroy production boards but were unreliable. Memories! Stlll, for 100kg sailors like me, LBs can’t match the excitement and performance of FW which is the way I went.
good luck.