hoop said...

Hey decrepit, not sure if you've built a stepped board or not before. >>> I've done a couple since and put a layer of 4oz over the stepped section to give it some strength when it goes in the bag. Hope that makes sense.

Thanks hoop, yep my first stepped board.
That makes good sense, I was thinking of d-celling the steps first.

Gestalt said...



hi decrepit,

i meant a single concave only in the front part of the board at the nose. maybe front fifth of the board.

Think that's about were Mr Love's doubles are, same reason, to trap air I guess.

The double concaves on mine are pretty shallow , they just look deep on the images as the light is shining across the board with a chrome shader .
They are about 1.5mm deep at 1500 from the tail and are gone completely at 600 from the tail . I just wanted to soften the ride a bit in the chop you get at the bottom of the speed run . I know they are technically not as fast as flat V but if I am more comfortable I will push harder. Thats the theory anyway.
Single concave to flat V just doesn't seem to be a natural shape to me , you get a really weird transition from the concave into the V. I have modelled a big slalom board with single concave running to flat and V side panels running parallel to the concave . It looks like it would work on a wider board but not sure about a narrow speed board .I,ll stick an image up tommorrow .

After 4 months of waiting. I got to sail my missile xs for the first time. Compared to my warp speed the control is amazing. We have found a half decent speed strip about an hour from where i live and it's bring some good results already.

It was blowing 25 to 35 maybe 40 in the gust. The weather station near the spot was giving 50 gusts but it wasnt that windy. I went out on the warp speed first and as with the DBW event i was having a mare with the slingshot into the very broad course. The wind was getting under the nose started to tail walk then spin out.

I went back in to get my xs and the 5.3 C4. On the slingshot there was only a slight hint of nose lift which settled down with no trouble at all. I only got one run in as the tide was getting too high. What impressed me was the way the board sustained its speed. I had a 40.89 v-max with a 40.119 10 second and a 39.961 250. The course goes broader the further you go down it so while trying to get a 500 i tried to go with a bigger gust and span out in the chop with a pretty brutal catapault. My impact vest makes a great hat. I wish i had the xs when i was sailing in 40 plus knots at the DBW. The controll is amazing.

Anyone have their settings for their xs that they would like to share? Especialy Tony Winhoven who has taken the xs to some world class speeds. Thanks!

Hardy was kind enough to bring the Thommen SR50 and his missile round today.

And guess what Gestalt, the SR50 has a concave nose, flat middle, and concaved V tail.

The Thommen has 130mm rocker and the missile 150mm, so I have about the right amount of rocker, but both the other boards have the rocker distributed more evenly, mine has more of it at the nose itself.
I guess this could increase aerodynamic drag, won't be much trouble to even it out a bit.

So thanks Andrew for spotting that!

mr love said...

>>>>>
It seems to me the only way you can run single into double or into V without a strange surface transition is to have it go dead flat at some point .
>>>>>

That's just what the Thommen SR50 does. Elmo says it has a very harsh ride in chop, I've only tried it on flat water, so can't comment on that.
All I now it was a pain to get planning in medium winds, but at 50litres it's a definite sinker, even for my 68kg

Hi Mr love,

i'm not suggesting your design is flawed at all. certainly v up front adds to smoothing out the chop. your bottom shape sounds similar to the missile and it's clearly a very fast board.

my point with the single concave in the nose was to improve early planing. i've got it on smaller boards and it works for me. it seems to help release the nose of the board which i think is handy on boards with less nose scoop. to much nose scoop can cause tail walking at speed as the whole board lifts off.

to go from single to double concave a flat section is needed. but flat in terms of where it occurs in the overall rocker. the easiest way is to use a spiral V.

when i was mucking around in cad i found it possible to set 2 rocker lines on a board. one for the centre and one for the rails. by altering the relationship of the apex of both rockers it was possible to adjust the V. doing this can allow flat or shallow v to deep v to mono concave at the nose. the relationship is then very smooth between the curves. double concaves would then be hand shaped into either side of the v to flatten the rocker in that area for planing. varying the depth of the douvble concaves and amount of centre rocker makes the v either bigger or smaller. the curves i was using were elipse curves with nose scoop

mr love said...

Hi Justin , I realise some waveboards have single concave to double then to flat V and I would be really interested to take a good look at one. Every time I have tried to model it I find when I put the evaluation tools on the surface it looks like crap . It seems to me the only way you can run single into double or into V without a strange surface transition is to have it go dead flat at some point . Thats fine if thats what you want , but if you want a reasonable amount of V at or in front of the mast track it means your single concave is going to be very short , right at the nose.
I am certainly not saying that single concave is wrong and there are obviously reasons why designers do it and I would be really interested if somebody could educate me. I just see double concave as a cleaner and simpler way to add some concave to a board that has V.
I have modeled a big slalom board with single concave running to flat in the tail with V side panels . It looks interesting and I will stick up an image tommorrow.

Gestalt said...

[>>>

hi decrepit, too much nose scoop will also make the board lift off as well as the drag.

i like the idea of your tail stepping out. i've noticed some of the recent speed boards seem to be talking up slightly chunkier tails.

Thanks Gestalt, looks like I just have to build it then.

Yoyo , Unfortunately not work , after hours fun. Work is designing this.

And the rails are a bit soft at the rear. For a given design length a wagon should have the back squared off for clean air release and to maximise interior space. Those big flares look a bit 90s.
You could tuck narrower wheels under for fuel economy gains with very little loss of stability.

I am a designer not an engineer , it's all about looks!!!!!!!!

OK, It does look good in a muscle car sort of way, who buys boxy railed Volvos anyway?

yoyo said...

Put an image for you to see.

Rear half is dead straight. Same width and thickness at mid section as at tail. It trucks back upwind with even the smallest fin.

It rode too flat. He has since added another 2.5cm? to the bottom before the step. Of course bringing the step further back would have the same effect.

Dan not sure of fin posie. (Whether it is any better than normal.)



Mind you, I think Dan did close to 44s on all his boards.

Sean Cox made his first full on step board in the mid to late eighties. When i saw it my eyes popped out of there sockets. After getting a bollocking for picking it up by the footstrap that was still curing. He let my have a go on it. it planned in a fart and once it got going it kept planning through the lulls with no problem at all. Also it made harly any noise. The step was at least 100mm high with a very thin tail. The step had to be glassed on after the initial lay up as the top of the step would be a weak point. No gps then so no speeds. Sean then modified it with a very deep single concaveso it was planning on 3 points. I think he put a patent on it.

I used one of his less radical step boards at Weymouth in 95 and was second fastest. This one had a single concave going into a 20 to 30mm step. It tried to kill you if it span out. A great concept though.

Don't really understand the step board,i always thought that clean and simple would be faster.
Wouldn't a flat section up the front to a pronouced concave from the front straps through to the tails have the same effect as the step board?

There is an optimum AOA for best L/D for a planing surface. The problem for a zero rocker planing boat or plane float, the faster you go the more lift = the flatter the trim = increase in surface area.
With the step , the angle is set by the step depth and it stays constant. ie at the optimum angle The faster you go the smaller the planing surface = less resistance as you lessen the suction behind the step then constant resistance as increasing surface drag with increasing speed is compensated by reducing surface area. I hope MI doesn't read these pages.

Of course the CA boards have a tail kick to stop them riding flat and engaging too much board.