Hey guyz and Galz
Been looking around at buying second hand boards for a couple of months and I bring my Spirit Level with me and have noticed the hull integrity is compromised on a number of boards I've looked at. The spirit level is identifying Rocker lines that have deformed, boards that are supposed have a flat rocker from back to 90cm, have a 1 to 2mm and even 3mm concave hollow for about 40/50cm. Boards that are supposed to have 1 to 2mm tail kick are straight.

I've heard the industry talk about the rocker line and its integrity being "everything" when it comes to performance. That 1 or 2mm makes a big difference. Banana rocker for turning and waves, straight flat rocker for speed. Slight 1/2mm tail kick being critical?

The big question is how much does this affect performance? Is it Industry Hype? If not hype then why are boards that are 1 or 2 seasons old have hulls/rockers that are deforming, now that either matters or it doesnt?

It has a big effect on performance as we see when the hollow is corrected.
Very easy to use a T stringer as Fanatic do/did?.
At the blank stage and under the PVC, a 35mm deep cut with the jig saw down the centre line from 250 to 1400.
Lay a piece of wet out carbon 150mm wide along the cut and poke it in the slot with a steel rule edge, carry on with the PVC layer and vac bag.
I've never had a hollow appear and my big slalom board has done 13 years now, still straight.
Production boards are all about keeping costs down so everything considered non essential goes in the bin.
Besides they don't want your board lasting 13 years.

It mostly ends up at about 2-3 mm. Possibly differential shrinkage between the thicker, curvier top deck and the flat bottom. If they don't use a stringer maybe they should mould it with 2-3 mm rocker anticipating that it will fade away as it fully cures? (Or use a stringer)

link.springer.com/article/10.1007%2FBF00859452

Try replacing fin boxes in quads. I measure and measure and measure then ascertain there is no centreline nor symmetry

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Ian K said..
It mostly ends up at about 2-3 mm. Possibly differential shrinkage between the thicker, curvier top deck and the flat bottom. If they don't use a stringer maybe they should mould it with 2-3 mm rocker anticipating that it will fade away as it fully cures? (Or use a stringer)

link.springer.com/article/10.1007%2FBF00859452

They are flat when new, the hollow appears with lots of use.

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hardie said..
Hey guyz and Galz
Been looking around at buying second hand boards for a couple of months and I bring my Spirit Level with me and have noticed the hull integrity is compromised on a number of boards I've looked at. The spirit level is identifying Rocker lines that have deformed, boards that are supposed have a flat rocker from back to 90cm, have a 1 to 2mm and even 3mm concave hollow for about 40/50cm. Boards that are supposed to have 1 to 2mm tail kick are straight.

I've heard the industry talk about the rocker line and its integrity being "everything" when it comes to performance. That 1 or 2mm makes a big difference. Banana rocker for turning and waves, straight flat rocker for speed. Slight 1/2mm tail kick being critical?

The big question is how much does this affect performance? Is it Industry Hype? If not hype then why are boards that are 1 or 2 seasons old have hulls/rockers that are deforming, now that either matters or it doesnt?

Any idea where I could find such rocker info for 2015 JPs? I bought a slalom-pro, wouldnt mind checking how straight it is - or isn't just for interests sake

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Te Hau said..

Ian K said..
It mostly ends up at about 2-3 mm. Possibly differential shrinkage between the thicker, curvier top deck and the flat bottom. If they don't use a stringer maybe they should mould it with 2-3 mm rocker anticipating that it will fade away as it fully cures? (Or use a stringer)

link.springer.com/article/10.1007%2FBF00859452

They are flat when new, the hollow appears with lots of use.

That's the usual reason given. But why do they stop at 2-3 mm? Because they become unrideable at that point? Has anybody seen that 2-3 mm in an unused but fully cured board? Do they continue to bend once you've bogged and flattened the bottom?

There was a thread a while ago on fixing this.

www.seabreeze.com.au/forums/Windsurfing/Gps/Negative-tail-rocker

I checked my main board I've had for 6 years/200 sessions and it was ok.
I think the water is choppier where I sail and sailing over chop would cause an issue, but I think its because I dont sail as fast as Mark62
I dont use slalom boards either. I think buying slalom/freerace boards secondhand its something you need to check for, which you have and found issues. Which boards have you found issues with?

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cald said..

Any idea where I could find such rocker info for 2015 JPs? I bought a slalom-pro, wouldnt mind checking how straight it is - or isn't just for interests sake

The German Surfmag did a test last year on 2020 slalom vs freerace boards (around the 70-71cm width sizes, Fanatic was 75cm size) and compared the rocker flat of the boards. They said (roughly translated)

The straight sliding surfaces fall very differently
off (rather short with 50 centimeters
at Fanatic, 53 at JP, 65 at Tabou, or
longer with 90 centimeters for RRD and 80
Centimeters with the Starboard iSonic) and explain
so individually only a little
Driving characteristics.

I would imagine they have changed between 2015 and 2020, but think its only where you get a concave on the rocker you would need to worry.

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PhilUK said..

cald said..

Any idea where I could find such rocker info for 2015 JPs? I bought a slalom-pro, wouldnt mind checking how straight it is - or isn't just for interests sake

The German Surfmag did a test last year on 2020 slalom vs freerace boards (around the 70-71cm width sizes, Fanatic was 75cm size) and compared the rocker flat of the boards. They said (roughly translated)

The straight sliding surfaces fall very differently
off (rather short with 50 centimeters
at Fanatic, 53 at JP, 65 at Tabou, or
longer with 90 centimeters for RRD and 80
Centimeters with the Starboard iSonic) and explain
so individually only a little
Driving characteristics.

I would imagine they have changed between 2015 and 2020, but think its only where you get a concave on the rocker you would need to worry.

Cheers, its a 66 wide ill give it a once over see if its anything but flat in the back 40-50cm

I forgot to mention that those measurements were for the slalom boards.