Rocker'n roll

Hi Blogosphere it's been a while since I've posted. Sorry about that, we all got knocked down with the flu and Real Life caught up. While laid up at home I had a good opportunity to peruse the Net about sailboard construction. It has certainly been an interesting exercise. Lot of negativity (or maybe practicality!) out there. However, what it did bring home was a couple of points.

1/ For a one-off amateur board builder, there is not much room for trial and error if you want to end up sailing something which is not a total dog. So it really is important to come up to speed with the state-of-the-art. Move away from this at your own peril.

2/ A lot of amateur-built boards turn out too heavy. My interpretation of this issue is that during the production board design process, a lot attention is paid to weight minimization through providing the strength only where it is needed. Another possibility is that production board manufacturers use advanced materials and building techniques that are not available to the amateur builder.

With regard to 1/ there seems to be enough information available on the web to reasonably tightly constrain the shape of a modern competitive longboard. There are tabulated intercomparisons of boards; nice plan views of the various manufacturers boards (i.e here, here, here, here and here); a more limited number of side on views (i.e. or here) for comparing rocker; and many interesting forum discussions on the merits of the alternative board designs. With respect to 2/ I think it should be possible to use a fairly simple sandwich technique to provide a stiff board. High density polystyrene foam- computer shaped in 2-d for the core and an s/e glass epoxy layup. Follow this up with a second thin foam layer on the board top (possibly using vacuum bagging to get a good even bond). Use a second layer of s/e glass on the board top to complete the sandwich and then add a layer of carbon fibre to the working areas of the board. Piece-of-cake ;-)

Now on to the consideration of rocker- which was the primary intent of this posting. I like the definition that John Carper provides in "Shaping 101". This is illustrated in the following figure which demonstrates that the rocker consists of three components. 1- the entry; 2- the centre or planing section; 3- the exit. Getting these three components of rocker working correctly together is critical for the design of any type of planing board, be it a surfboard, the slalom sailboard or a racing longboard. In the case of the latter, an additional complication is that the rocker has to work across all of the board configurations- upwind sailing on the rail with the centreboard fully extended and the mast track forward and the sailor positioned in the upwind straps; downwind planing with the centreboard retracted, the mast track fully back and the sailor positioned in the tail straps; non-planning conditions, sailor's weight over the centreboard.

There is an interesting discussion on the UK sailboarding website Boards regarding the rocker of the Equipe-III from "GraemeF" who seems to have some experience with this issue. To quote

".... It'll probably have a Euro rocker, they always do, it certainly wont have the benefit of the old Mistral rocker profile. Complicated things Long board rockers, it's a three stage rocker.

Half the reason for the long track is using it to transition rocker stages, if they have mad(e) it with the track way back it's because they're using a flat straight rocker, good up wind, O.K. on Euro lakes, but totally useless on the sea.

The reason the current Equipe or Pan Am is still so successful these years later is because of the rocker. "

So the Euro rocker is designed for flat lakes and the Mistral rocker is designed for choppy/open sea conditions. Given the comments of GraemeF, it's informative to consider a plan view of the Starboard Phantom 380, the Equipe-III and the Exocet Warp-X (see the figure). When comparing the Phantom 380 and Equipe-III you can see that there is quite a marked difference between the locations of board components. In particular the mast track front end terminates 21 cm further back on the Equipe, the centreboard is located 11 cm further back and the reaching straps are positioned 12 cm further back.

The differences are even more marked in the case of the Warp-X which has all components located closer to the bow, even when compared to the Phantom. I'd hazard a guess that the rocker of the Phantom and Warp-X may not be significantly different and that the placement of the components on the latter are also influenced by the removable tail fixture.

The comparisons shown in the figure seem entirely consistent with GraemeF's posting and if nothing else, demonstrates the importance of matching component location with rocker characteristics.

The majority of my sailboarding will be taking place on Port Phillip Bay at Elwood sailing club. For any sort of onshore wind conditions (which includes bay- and sea breezes), the area builds up a steep chop. Given this, my board will be constructed with a three part rocker which is consistent with these conditions. The following plot shows the normalised rocker (normalised by board length) which I am intending to use. I've derived this by looking at images of boards on the web and by measuring up a couple of older boards which I have access to. Also shown, for comparison is the normalised rocker of an older and slightly shorter board which was developed for flatter conditions.



You can see by comparing the two profiles that there is a significant amount of additional rocker required for ocean-going conditions.

All the best for now.

Pieces in the puzzle

It's good news with StyraPak getting back to me and indicating that they can cut 2-d patterns in foam blocks. All I need to do is supply a .dxf file (preferably) or a suitable technical diagram. Looks like all that effort put into climbing up the learning curve with Sketchup may pay off, with dxf files being one of the outputs of the pro-version of this software. Hopefully the longitudal direction (which includes the rocker) of the longboard design can be included as one of the two dimensions that StyraPak can put on their cutting jig. Just need to finalise the shape now so that StyraPak can quote a price.

In the last posting Shapers Australia was mentioned as being a good one-stop shop with pretty much all of the materials required to build the longboard. One thing that caught my eye was a set of DVDs featuring tutorials from some of the top guys in the surfing scene in the areas of shaping and glassing boards. So I lashed out and ordered Shaping 101 (took me back to those hazy days doing Maths and Physics 101 at Uni) by John Carper, a guy who seems to be pretty well known in surfing circles (i.e. check out the following interview in TransWorld Surf). Haven't had time to check out the entire DVD as yet, but it does appear to be full of good practical advice with respect to board shaping, and I've already learned a lot.

I just love how the years of surfboard shaping has made John Carper so skillful yet so casual. Here he is introducing one of his high tech cutting tools know as the hand saw. He then proceeds to demonstrate how you cut out a board outline in 20 seconds flat- no hesitation and perfectly square. I'll be sticking to that old adage measure three times and cut once- slowly.

The goal now is to have a first design put together over the next couple of weeks. At this stage the materials are firming up as H-grade polystyrene foam; 6 oz glass on the top and bottom with a layer of carbon fibre over the working area of the board (i.e. from the tail to the tacking area in front of the mast track; carbon fibre tape over the remainder of the rails and nose; marine ply (thin) reinforced with glass for the centreboard case; foam+carbon fibre for the centreboard; tuttlebox for the fin (not sure whether to build the fin as yet or to purchase) ; and perhaps something innovative (and drawn from dinghy sailing equipment) for the mast track.
Bye for now.

Foam Blanks

The last time (way back when), that I built a board, the sourcing of materials was dead easy. Basically you went polyurethane for the blank and e-glass/polyester for the shell and that was it. The task was also simplified because it was a short-board hence no centreboard, the mast base was fixed and consisted of a finbox and the blank was small enough to fit within the standard repertoire of a surfboard maker- and so was easy to purchase.

The longboard racer is a different ball game.

Not only has the choice of materials increased, but now it is necessary to deal with a sliding mast track system, a fully retracting centreboard and a board length beyond that of even a surfer's stand-up paddle board. The latter makes the purchase of a blank+stringer directly from a surfboard manufacturer more difficult. Additionally, it now appears that expanded polystyrene or extruded polystyrene are the materials of choice for the blank. A good introduction with respect to these materials can be found at Fibreglass Supply

After some searching, I've been able to source some blanks of a suitable size. Shapers Australia is a good possibility for people who live in Queensland Australia, not only having blanks, but also appearing to be a one-stop shop for most of the other materials required to build a board. Unfortunately I have not found a surfboard manufacturer in Victoria who can supply a blank with stringer of the required size. However, Polyfoam Australia have high density (24 g/l) EPS blocks of dimension 500cm x 120 cm x 60 cm which can be cut down to a suitable (rectangular) size. And, wonder-of-wonders- a sister company StyraPak P/L can supply computer cut blocks of EPS or the higher density XPS. The computer-cutting capability presumably means that they could cut a rocker into the block and potentially save heaps of elbow grease and some of the agonising during the shaping stage. I've just emailed StyraPak and am waiting to hear back. Stay tuned!

Working on the fundamentals

Thank-you rob134 for the encouraging comments and the 'Crownie' challenge. Thank-you Pat for the offer of help in the board design and the chance to contribute to a blog on LBWS. It's great to see that some Starboard Phantom 380s have made it to Australia.

The last couple of weeks has been spent working on some of the basic requirements of the board building project. This has included board design, coming up to speed with software for drafting the board design, and researching and sourcing the best materials for board construction. Although this is all very much work in progress, it's probably worthwhile getting these ideas out into the blogosphere.

Board Design
It seems to me that board design may be predicated on the following.

1. If the wind speed is light enough for pumping to dominate board speed- particularly upwind, then basically the fastest sailboarder will be the one with the highest strength to weight ratio and small variations in board shape are probably not significant.
   
   
2. For wind speeds above the 'pumping regime' and barring big variations in average board speed downwind due to wipe-outs, upwind board speed is probably the dominant factor in determining who it going to make it around a course in the shortest time. Of course in making this statement I'm thinking sailboat courses and equilateral triangles- not sausage courses!
   
   
3. My experience (from a few years back now so it may be a little out of date) is that you basically go for the biggest centreboard possible for maximum railing and pointing under marginal conditions. In stronger winds, you take advantage of the fact that the railing 'moment' is pretty sensitive to the centreboard angle of rake, and so it is possible to de-power the board as the wind speed increases by raking the centreboard back. This also has the advantage of enabling you to stand further back on the board.
   
   
4. Sharp straight rails in the forward half of the board would seem to be the way to go for optimal upwind performance. The compromise to avoid digging in and wiping out downwind is to have some rocker and softening of the rails towards the nose of the board.
   
   
5. Maximum board width sounds like a good idea for early planing, and perhaps for increased power going upwind. Here I'm thinking back to some limited experience in 14ft skiff sailing and the need to move away from the centreline to increase righting moment.
   
   
6. It seems a good idea to have a concave shape on the underside of the board, extending from the bow and terminating somewhere near the centreboard case (are single or double concaves better?). It is envisaged that a concave shape will minimise wetted area when railing upwind, and will provide additional lift when planing downwind. The downside is that there will be more wetted area in displacement conditions- but here it is expected that power-to-weight ratio will dominate anyway as discussed in (1).
   
   
7. Flat bottom with some rocker in the back half of the board and a nice big fin which doesn't cavitate for good downwind performance in planing conditions. The latter is to avoid those catastrophic wipe-outs downwind as mentioned in (2).
   
   
8. It would be nice to have a narrow tail for demonstrating that carve jibes are possible on a longboard- however a wider tail (i.e. Phantom 380) may be preferable for earlier planning in marginal conditions, and for planning at deeper angles downwind (Starboard promotes this design feature with the 380).
   

That's it on board design for now. Be interesting to get some feedback.

Google SketchUp
This is an example of a nice little package for constructing 3-D models. I think it's mainly promoted by Google as a package for constructing buildings and other objects for embedding into Google Earth (i.e. check out New York with the building layer enabled and you'll get the idea).

The package appears to easily have the capability to draft up a longboard design. This is demonstrated (at a very basic level) below where I've taken a plan view of the Exocet Warp-X and constructed a simple scale model using the line and arc drawing tools. Note that the intention is not to copy the design of the Warp-X, nor any other contemporary longboard design. At this stage I'm just using the Warp-X as a model to help build up the requisite skills with Sketchup.




















Construction Materials
I've been trawling through some of the surfboard manufacturers websites trying to come up to speed with surfboard construction techniques where they appear applicable to the construction of a sailboard. More on this in the next Post.

A beginning

I've been looking to get back into sailboarding following a break of more than 10 years. When I left the sport, my sailing club (Elwood Sailing Club near Melbourne Australia) had regular Saturday afternoon longboard racing on sailing courses which we shared with the dinghy's. It was a popular activity, usually with 10-20 sailboaders turning up each week. There were a couple of really good sailors and the result of us were in it for the fun and the challenge of actually finishing.

However, over the intervening years this form of the sport appears to have largely died out, perhaps due to cost, perhaps due to the introduction of the Formula class; perhaps due to the invention of kite-sailing; or maybe because of the popularity of computers and home theatre systems?

However, it would appear that a resurgence in the sport may be underway with some of major sailboard manufacturers now producing racing longboards. Notable amongst these is the Exocet Warp-X by Kona Windsurfing and the Phantom 380 by Starboard Products. The Phantom Race 380 looks like a particularly good board, having won the 2007 RaceBoard World championships fairly convincingly.

I've looked into purchasing either of the Warp-X and Phantom Race, but both, unfortunately lie outside of my current budget, particularly when you factor in the cost of the rig (I'm starting from scratch, having sold all of my old gear off a decade ago to make a house repayment!). Additionally, both boards are difficult to get in Australia at the current time although delivery of the Warp-X does appear less problematic. Apparently only two Phantom Race boards are being made available for the Australian market this year (maybe). In this regard, I'm led to understand that some positive souls put a deposit down on a 380 last year and no deliveries were made.

Because of my limited budget, and because of the apparent delivery difficulties, I have decided to build a raceboard from scratch. This is done with the knowledge that such a board will not be ISAF registered and thus cannot formally race against other modern longboards. To be honest I don't think this is an issue for the next sailing season, because it is basically going to be me against the sailing dingies and perhaps one or two sailboarders who might be convinced to dust off their old raceboards and have a sail. In any event, half of the fun will be designing and building the board.

So that is an introduction to what I'm intending to do. The next stage is to research the best board design and the best (and most practical) construction techniques.

Wish me luck!