Raceboard Design
July 24, 2009 · Print This Article
A recent thread in the forum prompted me to think about the future of raceboard design and articulate my emerging opinion on this topic.
Raceboard Designs
The IMCO was originally designed for a minimum wind strength of 15 knots (ie not really in displacement mode). It was the best course-racing, high-wind (planning) design at the time of its creation (pre the wide tail revolution). Even today in high winds (>20 knots), it is a very competitive design compared to the modern high volume raceboards. The IMCO “works” in light winds, but it was never really designed for such conditions.
The IMCO offers great one-design course racing across the wind range, but its original mandate (>15 knots) and its dated design limits its application for heavyweights and delays the onset of planning. A great board, but it needed to be replaced as the Olympic board, especially in today’s media / spectacle driven world, which gravitates towards fast planning action.
When Formula boards evolved, they offered spectacular planning racing (albeit a different type of racing to traditional IMCO/Raceboard racing) in relatively low winds (>8 knots), although they are not all-wind, real-world racing boards. It was not surprising that the Olympics wanted to get a piece of this exciting action, although they needed a board for all conditions. In the end they adopted the RSX, which is (in my view) a formula board with a centreboard.
The RSX’ attempt to bridge the gap between planning and displacement was skewed to the planning end of the spectrum to the massive compromise of displacement sailing. The current proposed next Olympic designs are for even larger formula boards that can plane in ~6 knots, but these are still not all-wind real-world boards because they are pigs in displacement mode.
Displacement-focused designs, such as the Lechner and Serenity, offer outstanding performance in light winds. However, they too are not all-wind real-world boards and do not offer the spectacular high wind performance of a planning design.
Raceboard designs after the IMCO (eg Pan-Am, Phantom) did not have the 15 knot minimum wind strength, and thus had high volume rails and tail, making them better all-wind boards and better suited to heavyweight sailors. However, they are variations of the IMCO concept and have not yet (in my view) adopted some of the design insights of the wide-tail revolution of the past 10 years. At the moment, I believe that they are the best available compromise between displacement and planning sailing.
The Dream Raceboard
The approach I’d like to see for future raceboard designs and future Olympic designs is to start with a true all-wind course racing board, then improve its planning abilities in lower wind strengths through wider tails and bigger rails. In addition, I’d like to see a design that minimises the force required for transition from displacement mode to planning mode, following the lead of efficient skiff designs such as the 49er.
Reviewing some first principles of hull dynamics helps to understand the compromise that board designers face. The illustrative diagrams below (adapted from “Higher Performance sailing” by Frank Bethwaite – highly recommended reading) show the relationship between board speed and drag for several different hull designs.
Some observations:
• The drag of displacement hulls is initially low, but rapidly increases with speed – at high speed, they are relatively slow and difficult to control
• The is a significant “hump” to the speed-drag curve for most raceboards – this reflects the effort required to move from displacement to planning mode (”getting onto the plane”)
• The 49er hull does not have this “hump” – there is no discontinuity between displacement and planning modes
The dream would be to have a “humpless” raceboard hull design like an 18 foot skiff or 49er. The image below clearly shows the hull design of the 49er, incorporating a fine displacement-like bow and a broad flat planning stern. This is the hull design that allows the remarkable “humpless” performance.
Given the light weight, small size and universal joint of a raceboard, a skiff-like design with a “humpless” drag curve may not be possible. However, I believe that it is in this direction that future raceboard development should focus.
Prompting Progress
It appears difficult for manufacturers to justify investment into the raceboard class because the market is relatively small (albeit a fast growing segment). In many ways, the raceboard community has recently been relying on competition between Star-Board and Mistral to progress raceboard design, but with the Equipe 3’s future in doubt, there may not be any incentive for Star-Board to invest in new designs. However, the recent success of the Pan-Am at the world championships (beating the Phantom) may prompt further development.
Although the raceboard class is a development class, its rules are relatively restrictive and prohibit further development. In particular, I believe that the thickness limit (which I understand was introduced to prevent the use of displacement hulls) and the production board registration requirements limit further development of the class. The size restrictions on centreboards, fins and sails can also be considered to be deterrents to development.
As an ex-sailor of Moths and 18 Foot Skiffs, I appreciate the progressive environment created by few rules. We used to joke that in 18s that there were (basically) 3 rules: maximum hull length was 18′; the race starts at 2pm; and the first across the line wins. Moth rules were similarly simple. It is no wonder that these classes led the most stunning developments in sailing design: apparent wind sailing; and foiling.
Although such free-wheeling rules prompt development, they come with a penalty: potentially higher cost and fewer participants. The raceboard class can hardly afford to turn away participants. However, Moths and 49ers (an 18 derivative) are now two of the fastest growing sailboat classes in the world – catering for the high performance segment of recreational sailing.
For Discussion
I don’t have the answers, but I’m interested in creating a discussion around the following questions:
• In what direction should raceboard design evolve, particularly in regard to the compromise between displacement and planning sailing?
• What should be the future of the Olympic sailboard class?
• What design direction would be in the best interest of the class?
• Should the raceboard class rules be changed to prompt further progress the class?
Share your thoughts.
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 places in their respective world championships and he was the world junior champion in the Moth class. He is also a civil engineer specialising in fluid dynamics.
I don’t even see raceboards out in New England anymore.
I bought a beautifull Equipe II for $200 with mast , sail and boom.
Let me know if there is anyone out there interested in a upwind tacking dual.
If you went to the darkside and have no boards left, I still have my IMCO and superlight both here and in florida.
John Yanusas
jsyhorizon@aol.com
As one of those who drew up the original Raceboard rules, based on lengthy evaluations done by the Bretons , I know what the original intentions were.
Bad rules using half height beam measuremant ended in up round bottom hulls that were very difficult off wind in a blow.
As the class measurer in Pusan I witnessed,on the course, Lechners racing in 35 knots of wind and 2 metre wave height.
No other olympic class boats were allowed out in those conditions and only the best sailors got round.
The Raceboard Rules “ring fenced” a group of already existing planning boards that were deemed to be reasonably equal from 6 to 25 knots, we deliberately excluded boards that had better light wind performance,like the Mistral Superlight and the specialist Div 1 boards popular in the UK.
Planning hull characteristics were guaranteed by the ” rise of floor ” limit templates..
D 1 boards also had limits set by rules that had been drafted around the Mistral superlight but inadvertantly allowed semi displacement hull forms to develop.
These were only marginally slower in very light airs than Lechners ,easily railed to windward and as fast and stable as raceboards off wind.
Most were custom built from styrofoam ,hand shaped and over 300 litres volume so “production board” status was a non starter.
According to my current copy of the Class Rules the only limits on the hull dimensions are length and beam without thickness limits at all.
With this in mind I am currently building the tooling to produce a hollow sandwich 3800 long 640 wide D 1 style board with 805 centreboard. and a fully rolled unrockered deck line to maximise stiffness .
Registration should be complete by this years september deadline.
Great article Richard. Very thought provoking!
Peter, the board sounds interesting. LBWS would love to see some images and further thoughts on the board you are making and importantly registering.
Cheers
Pat
aus456@gmail.com
Great article, especially as I have an IMCO. I was surprised that you made such a distinction between the IMCO and the later Pan-Am, [ and I guess Equipe II, as I thought they were basically all the same board with the later models having an extra 20L or so volume plus a lighter constructuion.
Are the Pan-am and Equipe II so much different than the IMCO with the added volume? I ask mainly because I want to know if something comes along whether it’s worth the upgrade.
I often look at the new boards like the Phantom and wonder just how early planing they are considering their 70cm width, and whether they negate the need for a formula type board when paired with a grunty 9.5m sail…surely that combo must be very early to plane?
Richard, your description sounds like the Excoet Open 310 to me. But the kayak nose did apparently amke it uncontrollable in a swell downwind, so the moderated Pacer resulted.
Sorry for the late response – I’ve been on holidays. I’ll answer each comment separately.
PaulM – I like the Exocet Open 310 because it tries to improve the displacement performance of what is essentially a hybrid board. However, I think it’s limitation was its 310 length, which is not really long enough for high performance in displacement mode, particularly when retaining signifciant width. Its bow, although retaining some kayak-like characteristics, is not really very fine. This board does not come close to reducing the “hump”.
Can you share any more details about its performance in stronger winds?
rod – you’re right that the Pan-Am is an evolution from the IMCO. The link below provides some history of the Mistral line of longboards (be sure to read the comments afterwards):
http://www.lbwindsurfing.com/history/the-mistral-equipe-pan-am/
The Pan-Am and Equipe 2 have significantly wider tails than the IMCO and offered a significant performance improvement. The results from the worlds show that it is still the benchmark and offers elite performance, particularly for lighter riders. I ride a Pan-Am but would prefer a high volume board like the Phantom because I am a heavyweight.
I my view, high volume raceboards such as the Phantom will offer early planning (earlier than the Pan-Am) but not by a massive margin. A formula board will plane much earlier than even a high volume raceboard (assuming all other things equal), but of course offer radically superior performance in light winds and thus can be considered the better all-round board.
I raced Formula a few years ago, but would never go back. The tactical and strategic aspect of raceboards is far more interesting and enjoyable than in formula, and, of course, the all-round performance of raceboards is hard to beat.
Peter – I’m really excited that another production raceboard will be on the market soon. This is great news for the class and for the progression of raceboard design. Can you share any more information about the design (I am particularly interested in the design of the tail compared to D1/D2 and modern raceboards)? I intend on buying a new raceboard soon and may be a customer.
Thanks for clearing up the intentions of the original raceboard rules. My journal article was based on anecdotal evidence from discussions with seasoned raceboard sailors – “common wisdom” that required refinement. It is interesting to read about the “ring fencing” of the planing boards and the deliberate exclusion of displacement boards.
Further, it is great news that the raceboard rules now do not include a thickness (”rise of floor”?) limitation, opening a world of design opportunity, which you are clearly taking advantage of. This is great news for the class. Thanks for clarifying this.
Yagon, the ponity end looks pretty sharp to me
http://www.boardseekermag.com/special_features/olymic_board_2/pics/SF_exocetnose1000.jpg
more info on the open 310 here
http://www.boardseekermag.com/special_features/olymic_board_2/olympic_board2.htm
The RYA links are broken now but it was stated to be ‘at least as fast as an IMCO in displacement mode’. I think problems downwind in waves shouldn’t necessarily disqualify it for inland and estuary use. No one pans a wave board as ‘no good on lakes’. And it seems unlikely it was harder to control than a Div2.
I also recall reading a series on the creation of one the ‘Div2 nosed’ Div1 boards (there were several). I think that year the world championships had plenty of wind so they missed a chance for fame. The concept apparently did what is was supposed to, Personally I like the idea of having the option to go upwind on the fin when the breeze freshens. I was surprised to read the Excoet 380 manages this trick, because the tail looks far too narrow.
Hi again
The Raceboard rules contained both “rise of floor”(bottom roundness) and thickness limits at various points,especially near the bow . My design has a comparatively narrow beam in the forward sections with a bow like a rounded Lechner A380 ., maximum beam 640 just aft of centre. The tail is a Squash with a 30 cm off beam of 444 mm. Compared to 433 on the Phantom.
Tail width keeps the board planing longer in low wind at the cost of top end speed in strong winds. The imco is a classic exanple of the other extreme. When Rick Naish shaped this board it was designed for 12 knots and up winds as were the last long boards used by PWA. There is no escape from wetted surface drag without a pintail waterline shape and the old d2 shapes did this by the bottom roundness . Very good saIlors could cope ,I recall seeing Antoine Albeau and Michel Quentin overhead “donkey Kicking “Lechner A 380 boards in 30 knots of wind in Buenos Aires,to the total astonishment of the Locals out on sinkers .
I will be testing a pre production board with Max Woijic (Raceboard World Champ) at the end of august and will report progress after that.
Hi Richard,
Thanks for the interesting article. It fired me up to write up some thoughts about longboard rocker which I wanted to articulate as part of a project (which seems to be taking forever) to build a longboard from basic principals. These ideas are on the link above however it would be no problem to paste them into the discussion here if you see fit. I’m a strong supporter of LBWS.
Cheers
Martin
Yagon & Richard,
I’ve been using a standard Pacer (smaller bow) in strong conditions, and a real issue with is that bulk up front creates a lot more swing weight in heavy chop. I never really noticed that in my Div2 experience but to be honest that perhas down to not using’em in rough conditions. Still I guess you can’t expect everything in one board. After all the 49′ers have a few issues downwind in a blow too, as anyone who saw the Olympic ‘demolition derby’ will know
Sorry for the very late response to the above comments. I’ve recently started a new job and have not had much time.
Thanks to everyone for their thoughful repsonses – it’s a topic I’m very passionate about and I’m glad to hear others equally passionate or more so. I’ll make individual responses below.
PaulM:
The 310 does have a nice nose, but it is much more rounded than a skiff-like nose or a div2 board. In addition, it is not a true displacement nose because it has the broad planning nose directly above the displacement section. I’d be surprised if it really is as good as an IMCO, but I’d believe that it was the best of the Olympic protoptypes listed on your link (great link by the way).
I agree with your comment about designing / selecting a board to suit the conditions that you sail in. Raceboard manufacturers will tend to build an allround board in this regard for versatility.
The exocet 380 has a tail section that can be removed for higher winds. This is their attempt at bridging the displacement – planing compromise, but my view is that in the real world, it is clunky as an overall design. This board is an awesome performer in certain conditions, eg upwind in ~10 knots.
Peter England.
Again, this is really exciting news. Lots of questions:
What price? What price delivered to Australia?
When do you expect to start shipping boards?
What type of cross section does your board have in the: nose (vertical or near vertical bow?), mid & tail? Any vee or is it a flat bottom?
Does it have big chunky rails like the Phantom?
Re the compromise of surface area and planning – my view is that, measured on the basis of tactical racing advantage, the disadvantage of slower light wind speeds due to additional tail area is more than compensated for any earlier planning.
Peter – another question – what’s the feedback from the testing with Max?
Martin:
This is a fantastic website! Thanks for posting the link. I highly recommend that anyone interested in Raceboard design should have a look at this work.
Maybe you should write an article for LBWS?
PaulM
Interesting comments about the use of the board in stronger winds. With a skiff-like design, there can be real issues going downwind in a blow, but the saving grace is that the kite (spinnanker) lifts the bow and helps prevent nosediving. We would ALWAYs put up the kite in strong winds because it is unsailable without it.
If I do one day build a skiff-like raceboard, I believe that it would perform well in light and moderate winds, but would be a handful in chop and stronger winds. In addition, tacking may be slow because of the swing weight / drag (in a skiff this is not a problem because the bow lifts through a tack, reducing rotational drag, but this may not be possible with a raceboard because one needs to step around the mast).
Such a board may require new handling methods. I won’t know until I build one!
Yagon
Slight delays due to being at the Kona worlds in sweden on Jury Duty.and a short holiday
Last weeks proposed resting with Max a Weymouth was blown off, just look at the results of the Techno and Raceboard masters
where RSX boards dominated.
The bow is a slightly more rounded V than a Lechner 380 running to a very light rounded mid section,the centre runs into a light concave 600 mm in front of the c.b case to a max of 20 mm depth and out to zero (flat) at the transom. Max hull thickness is 225 .
This makes the bottom in the full planning area behind the C/B a light “W”
This shape adds stiffness and reduces central tail rocker when on a full plane.
The rails are more rounded than the Phantom and roll into the lightly rounded deck. They are designed to be as vertical as practical when sailing to windward when lightly railed, to maximise lateral resistance.
I will be building boards this winter and they are due to be available for dispatch next feb/march at a bit under £1000 ex works.
I agree, But in order to understand a bit more of windsurfing, you need to know that is like a surfboard but it is powered by the wind. The rig is connected to the board by a free rotating flexible joint or U joint, unlike a sailboat, a windsurfer is steered by the tilting and rotating of the mast and sail as well as tilting and carving the board. Take note that while trying windsurfing the ideal planning conditions for most recreational sailors is 15-25 knots, good luck ! But why isn’t hard to go surfing?
Brin @ howtowindsurf.net
The idea of narrowing the gap between maximum displacement speed and minimum planning speed would make raceboards easier to sail and quicker in marginal planning conditions.
The maximum displacement speed is proportional to the square root of the waterline length so increasing the length from 380 to say 490 centimetres would increase the maximum displacement speed from about 4.9 to 5.6 knots. However increasing maximum length would at a stroke make all the old sailboards uncompetitive so is unlikely to happen. However it’s worth pointing out that some boats do exceed their calculated maximum displacement speed without planning. Any very narrow hull with an ultra very fine bow has this capability e.g. racing catamarans, rowing skulls and the Starboard Serenity. So in summary for maximum displace speed you need a long thin curvaceous hull like the Serenity.
To reduce the minimum planning speed you need to increase the lift generating area and keep it flat or nearly so. Lift is roughly proportional to area but its also proportional to the square of the speed, so a 10% increase in area will only decreases minimum planning speed by about 3 percent.
If you are still following you have probably spotted the problem, maximum displacement speeds needs a narrow hull, minimum planning speed needs a wide hull to get a large planning area.
However do not give up hope you can rail a hull to reduce its beam and then sail it flat when you transition to planning. I would predict that a wider and deeper raceboards, which can be railed to give a very narrow hull shape in the water, would out perform the current boards in marginal planning conditions. However it could be difficult to control in strong winds.
This was impossible with the old racing rules as depth and width were capped, however with no such limitations in the current rules so there is scope for development.
One rule, which really stops development is the need for all boards to be production boards rather than prototypes which measure to the rule. The great improvement in the design of Div 1 and 11 came through individual creativeness and not from corporations.
To answer the original question, 49er and 18 skiffs have less of a drag hump than a board because of their greater water line length which allows displacement speeds of nearly 6 knots at which speed it is possible to generate enough lift to plane. Making for the smoother transition between displacement and planning modes. So try building a 5 metre long board, it should be a real flier in marginal planning conditions.
If you try sailing a tubby formula board as opposed to a race board, the drag hump is massive and well timed pumps are critical to get it planning.
Richard Baker GBR148
Has anybody out there ever sailed the ISB (International Sail Board)?
It was designed by Guy Leroux (journalist, sailer, musician) back in the late 80’s for use in low summer winds. It’s specs are:
Length: 411.5 cm
Max Width: approximately 60 cm
Max Thickness: 15.2 cm
Volume: 275 liters
Square-tailed
Hollow with wood framework plus glass shell
It had very little scoop in the bow. This plus its long, narrow profile account for it’s speediness in sub-planing conditions (it was no slouch planing in 17 knots either).
Because of the length and square tail it was more stable than the IMCO on the reach and while tacking and gybing.
All in all, a fine board except that the company that built my board
(West Wind, no longer in existence) could not bring the weight below 18 to 20 kg. i.e. the design was good but for the price at the time ($1100 U.S.), it was difficult to get the weight lower than the said 18kg.
Only the Superlight and Div 2 boards barely beat it in less than 5 knots, which was anticipated since it was designed for the 5 to 10 knot range.
I had one for 16 years, but it’s pretty well beat up now.
Guy tells me that recently John Parton in Florida has come back to
building custom designs and because he built Guy’s original ISB (non-hollow) in 1988, he would be a likely candidate for constructing another at a lower weight than the West Wind version, but probably more costly.
Guy, if you’re reading this, I trust that I described the board precisely enough for your liking. Otherwise, I`m sure we’ll hear from you…..
Clark,
Montreal
In my previous posting, I, from experience, touted the advantages of the ISB in 5 to 10 knots.
Another approach that tempts me is the one mentioned by
John Reatti in his posting above.
Last summer, whilst sailing on my Mistral Prodigy, a fellow in a PS2000 Byte sailboat (with adjustable downhaul and outhaul),
sped past me in 8 knots like I was standing still. Huh, What the?
He had a wicked grin on his face. The Byte, as best I can see, is shaped somewhat like the capsized boat in John’s photo above.
A third approach is, of course, the catamaran/trimaran one. Anybody ever seen/tried such a board ?
Clark