Saturday, August 1, 2020

BoardOff Twin Tip Design and Analysis Tool for MS Excel

  • Get the latest copy of Board-Off, the free Twin Tip design tool for MS Excel >> Here V1.3.16 adds ability to design mutants and surfboard outlines. Posted 6/3/2013
  • Kicking off your new project? Set up a thread on the forum and share the journey  >> Here

Tuesday, December 31, 2013

I beat Cabrihna to the punch!!!

I just had a look at the Cabrihna site and noticed that they have added a board made using Basalt Fibre!!!! I finished my Basalt board a few months before they released theirs.

Basalt, come on Cabrihna that is so last month :)

Monday, July 8, 2013

Naish Demo Day

With all the action happening on the Forum these days I thought I'd post on the blog to make sure it still feels loved.

On the weekend here in Cairns Naish held a demo day of the kites and boards. It was great to be able to ride everything back to back in solid conditions so that it was possible to closely compare everything without having to factor in changing conditions. 

I rode the Dub and the Monarch boards in wind chopped water in 15-20 knot range. Both boards have a lot of rocker but distributed a bit differently. Naish use these rocker descriptions ( love it) that helps put tags on it and makes comparing a bit easier. 

Dub R18/3/6     with flex F32
Monarch R10/6/8   with flex F28

I mentioned in a previous post that these relate to what they describe as 'tangential radius' which I still don't clearly understand but for comparing I think its reasonable to think of it as the radius of curvature of an arc that matches the curve through most of the 3 section ( mid 1/3, mezzenine 1/6 and tip 1/6 of the length). A larger number means flatter through that section.

The flex is anyone's guess but I am guessing its some measure of deflection under a standard load but no idea what the load is. Based on the flex modelling I've done on mother boards I would guess ( finger in the air) that in my standard 20 kg tip load test the flex would be about 50% of the difference between the current board and my chinese newspaper board which would make it about 65-70 mm under the 20kg load. 

In both cases most of the rocker is introduced in the mezzanine section between the mid and the tip. The dub has more rocker in the mid section compared to the marginally flatter Monarch.

Although the Naish marketing material says they've stiffened the boards up to me they appeared quite flexible and when there was any load on it it seemed pretty clear that the rocker between the feet, what there was of it, all but disappeared. Good for speed and softening landings but not much else that I could see. I think the idea of most of the rocker in the mezz section is for the sake of keeping the nose high and riding over chop when the board is loaded.

A big difference is the pattern of channels on the underside. the Dub has some channels in the tip but the mid section was smooth with the rails slightly relieved ( negative concave at the rails). The Monarch on the other hand has deep channels all the way along, about 6 of them, but still with slightly relieved rails. No prizes for guessing that the dub is slippery so needs to be edged hard. The channels on the Monarch changed the grip of the board very noticeably. Not just that it gripped more but the the board could ride flatter ( not so much heal pressure) and rather than the smooth flow of water off the bottom of the board like you get in a single concave board there is more of a sense of riding on a bed of white water rather than riding the rail like a keel. The only thing I could feel was materially different in the handling was that the monarch always feels loaded against the water even as you roll from heal to toe side or come off the lip of a wave without the self righting effect of large fins. This brings with it a sense of greater control and power without having to relentless bear down on the rails.

The marketing gumf says that the channels make for a smoother ride. However, I found the board so flexible that, having made mostly very flexible boards, that I wasn't really expecting the ride to be rough and that seemed to be the case because the roughness of the ride of the dub and monarch was imperceptible. I suspect the channels are just distributed fins and as the Naish designer in previous interview mentioned a way of saving weight without loosing too much strength of stiffness.

On the other hand the dub slips around and you really need to control the edge. I suspect this would be a good candidate for boots to help get the leverage from your legs to get the rails in. The slipperiness is great for quick carves on the waves and bad landings.

They are a very different ride and effect of the channels was apparent in how loose or tight the board was. However, I have to say I was very pleased with how favourably my own crafted boards compared and my latest effort I think strikes a very nice middle ground between the two. 
The stiffness of my board between the feet means that a lot more rocker is maintained in the mid section which I am finding great for all sorts of things ( carves are great, launching of the face of waves). 

I think a good refinement to it would be to have channels in the mid section to make it a bit less slippery so that its easier to gain control after I land and maybe channels in the tip to help keep the board in control as you come off the water. 

Thursday, April 4, 2013

Board Off Downloads

I finally got around to tracking download statistics on Board Off design tool and I was very pleasantly surprised to see that it is being downloaded about 30 times a month for the last 2 months! I wasn't sure it was being downloaded at all was very happy to know that its it out there. What's also very cool is that it shows how global our community is. Here's the downloads from March by country. is tracking the number of time the download link (downloads from public dropbox folder) is clicked so the stats are accurate.

If you're a user of BoardOff would be great to hear from you about what can be done to make it better and more user friendly.

Wednesday, March 13, 2013

Naish Designer on Twin Tip Design

I've also posted this on the Forum but thought it was well worth reposting here for those who are regular visitors to the forum.

This is a good discussion by someone with a engineering background on some of the features of boards including multiple concave.

He also mentioned the new description of the rocker line which I had mistakenly thought was the amount of rocker in each of 3 sections in the board. It seems that its the radius of curvature for each section and not the amount of rocker. However it suggests that each section is an arc which seems too limiting me and of course when you intersect arcs of different radius the are tangential at the intersections so there is more to the rocker line than the piecewise arc design.

Is there some magic about arcs in the design? From my reading the circle has a slightly lift drag ratio of less than one meaning that it generally sucks in fluid flow situations. I'm sure there is an interesting things to find out.


I re-read the article and found the error of my ways. Larse used the term

' tangent radii creating a continuous curvature'. The tangent radii I interpreted as the slope of the tangent at pre-set points but now I think that tangent might be a red herring and what is meant is the curvature (defined as the second derivative of the rocker line) at the pre-set points. This also makes sense in the context of using splines to design the rocker because matching second derivatives is a common, strong, continuity condition applied to splines. However, the curvature of a spline at a discrete number of points does not fully characterise the spline unless x squared is it highest power but this is unlikely to be being used as this would restrict the possible curves available to much. So there are some unspoken constraints that are being applied. 

I made the changes in BoardOff to display the curvature ( which was already calculated to find 'kinks' in the rocker profile and it does give a good description that is not restricted to the continuously increasing issue.

Smoothing the outlines in Board Off

I've just made a minor change to Board Off to smooth the outlines. If you used BoardOff you may have seen that where the different sections (mid, mezz, corner, tip) join there is occasionally a small kink in the outline. This is the reason that the 'gradient ants' where introduced into the Draft window as they show the slope of the outline either side of where the sections join. The goal was then to adjust your parameters until the 3 Ants merged into one or close enough.

This was a short coming of the cubic splines used to draw the outline in that the way I'd implemented it it did not enforce and smoothness conditions at these kinks. I've made an adjustment to it so that for the corner-mezz, mezz-mid joins a continuity condition is in force and so there are no longer any kinks there. It wasn't possible to do it for the tip-corner join because the tips are so steep that the spline needed to approximate it has trouble turning the often small radius corners without causing the line to start going wild (oscillating). Also, for inverted tips its desirable to be able to have a sharp corner.

I've also applied this to the rocker and concave lines so that the kinks ( detected in the rocker and concave by the 'curvature' chart being discontinuous. They are now all smooth and much easier to work with.

The update did require some of the outlines to be modified as the continuity conditions to force a change in the shape of the outline in some cases. So you may need to check your own designs to make sure they haven't been affected.

Any questions, just post here and I'll endeavour to get back as soon as possible.


P.S I saved the new version over the old version 16. When you download it will say v17 even though the link says v16.

PSS Added the Naish rocker description I posted about earlier. I used equal length section ( 1/3 of the half length each). As I looked at the numbers it returned it became pretty clear that Naish is not using equal length sections. If they were then all numbers would need to be increasing otherwise the board would have and flat spot in the rocker. They must has different lengths. For my purposes the equal space ones are still useful as a shorthand way to describe it and compare others designed in board off.