My 2017 isonic 90 has around 1mm of negative tail rocker.

i Reckon I might be able to sand the negative tail rocker out if i sand in front of the fin box, and around edges of the tail cuts, as highlighted on the photo.

But, I think I would need to sand around 1mm deep. This seems like a lot of material to sand off, I'm a little concerned it's to much.

Any one know how thick the carbon is on isonics, and is it safe to sand 1mm off without damaging board strength?

I thought the consensus was that negative tail rocker doesn't matter?

No consensus that I know of, we have instances of eliminating -ve rocker that results in increased performance.

I work on 3 layers of carbon to the mm. there's probably only 1 or 2 layers there.
Sand 1mm off and you're thru to the foam.

You need to fill the low area instead.

I've used automotive spray putty as a filler with some success.

www.theboatwarehouse.com.au/boat-building-maintenance/epoxy-resins-hardeners-glues-fillers/norfill-epoxy-filler/?sku=NOR-1153&gad_source=1&gclid=CjwKCAjwtqmwBhBVEiwAL-WAYWmZ6q0ZLHmOpIBKxXxlrIarHl8rrNx1QIpvwaflOROXivICcfq-hxoCTVsQAvD_BwE

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decrepit said..
No consensus that I know of, we have instances of eliminating -ve rocker that results in increased performance.

I work on 3 layers of carbon to the mm. there's probably only 1 or 2 layers there.
Sand 1mm off and you're thru to the foam.

You need to fill the low area instead.

That's what I was worried about, I'll go down the filler route instead.

Many thanks all.

It could be done........to a point ,depending on how much bog they have used. On newer boards they can use a lot of bog , especially on the rail edge area you have marked. As long as you don't hit the carbon ,which is very thin . You might get half of it out and be happy with that.
Also , be careful how your measuring the negative rocker. Those marked side areas ,( If your measuring across the V ) , could be slight concaves on purpose . Make sure your holding your straight edge perfectly parallel to the board. ( you probably are , but I thought I might mention it ). That board should have about 1 mm tail kick. It's hard to be super accurate because it has continuous rocker and your straight edge will rock.
Now everyone will run and measure their boards and be horrified that most well used boards will have negative rocker Some newish ones will also

I can tell you straight up (from having to do a repair or two in that area on isonics around that era) theres not much carbon there at all.

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Subsonic said..
I can tell you straight up (from having to do a repair or two in that area on isonics around that era) theres not much carbon there at all.

Thanks everyone for the feedback.

Now I know that there isn't enough carbon to sand into, I'll probably use filler. It's a nice board, still fast and worth repairing.

Plus, my windsurfing OCD won't allow me to own a board with negative tail rocker!!!

Is 1mm negative really worth the effort? That's the main planing surface, and it goes through sorts of angle of attack variations and turbulence. How would 1mm make any material or detectable difference. Wouldn't the worst that could happen is a slight variation in nose height while planing?

Genuine questions and I am glad to hear the counter-arguments.

Yes you are right about nose angle. it lowers it, increasing wetted area and drag.
It puts lift behind the rider. Ok for early planning but not for speed.

OK , so for under 35 kts , general fast riding ,would 1mm of negative rocker be noticeable in small everyday chop ? What conditions and speed would notice 1mm negative rocker?

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Imax1 said..
OK , so for under 35 kts , general fast riding ,would 1mm of negative rocker be noticeable in small everyday chop ? What conditions and speed would notice 1mm negative rocker?

Good question, and I have to admit I don't understand the science in board shape.

Three of my Starboard speed boards had around 1mm negative tail rocker (W44, W49 and W58, cm width), all owned from new in 2010 and well used. All felt sticky and rode to low (similar to Decrepits description). After fixing them all, on the first outing on each board, I could immediately feel the boards felt loser and much less sticky. And on the W44, I actually got a PB on the first outing in less than perfect conditions.

I guess at 35knot speeds in chop, the speed difference may not be huge, but I'm pretty sure the ride would be much better leading to slightly higher speeds/control if the tail rocker is correct.

Here I'm no expert, but it seems good riders, "ride the fin" in chop. I suspect this would be easier if the board doesn't want to sit nose down.
It's all about where the lift is, Ideally it wants to under the riders feet, negative rocker can put it behind the rider, forcing the nose down.

Ok. I'm convinced now.

On boards designed to go over 35kts, what is the ideal tail kick ? Would moving the mast back a couple cm raise the nose to compensate 1mm negative tail rocker ? I'm finding I'm moving the mast base forward in flatter water to get top speeds , which is kinda opposite to what I would think. Im moving the mast back to lift the front in chop going across wind , forward to keep it pinned for when going deep downwind when its flatter . My boards are not normal and neither is my weight. I have a lot to learn when it comes to going fast. I would love a super flat playground to tune my gear , but then it won't work for the chop I ride in. Thinking of another board build but I don't know which way to go.Trying to absorb more rocker knowledge for the less that perfect conditions I ride in. I feel I got it sorted, but how would I know ? I think what's holding me back , is me. I just got to be braver going deeper over chop

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Imax1 said..
On boards designed to go over 35kts, what is the ideal tail kick ? Would moving the mast back a couple cm raise the nose to compensate 1mm negative tail rocker ? I'm finding I'm moving the mast base forward in flatter water to get top speeds , which is kinda opposite to what I would think. Im moving the mast back to lift the front in chop going across wind , forward to keep it pinned for when going deep downwind when its flatter . My boards are not normal and neither is my weight. I have a lot to learn when it comes to going fast. I would love a super flat playground to tune my gear , but then it won't work for the chop I ride in. Thinking of another board build but I don't know which way to go.Trying to absorb more rocker knowledge for the less that perfect conditions I ride in. I feel I got it sorted, but how would I know ? I think what's holding me back , is me. I just got to be braver going deeper over chop

Come down to Queens beach for a few sessions. You'll go back up to Sandstone fully dialed in!

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Shifu said..

Imax1 said..
On boards designed to go over 35kts, what is the ideal tail kick ? Would moving the mast back a couple cm raise the nose to compensate 1mm negative tail rocker ? I'm finding I'm moving the mast base forward in flatter water to get top speeds , which is kinda opposite to what I would think. Im moving the mast back to lift the front in chop going across wind , forward to keep it pinned for when going deep downwind when its flatter . My boards are not normal and neither is my weight. I have a lot to learn when it comes to going fast. I would love a super flat playground to tune my gear , but then it won't work for the chop I ride in. Thinking of another board build but I don't know which way to go.Trying to absorb more rocker knowledge for the less that perfect conditions I ride in. I feel I got it sorted, but how would I know ? I think what's holding me back , is me. I just got to be braver going deeper over chop

Come down to Queens beach for a few sessions. You'll go back up to Sandstone fully dialed in!

It is definitely on my to do list.