Speed sailing fin spin out any idear how to stop this from happening at speed.I'm useing 87lt isonic with 30cm black projects fin and 5.6 severne reflex in 25kts and above?

well that shouldn't be happening, with a fin that size. In those conditions I'd be using a much smaller fin, how much smaller depending how flat the water is.

So how flat is the water? Bouncing around in chop can expose the fin to the atmosphere and let it ventilate.

Have you got a good seal on the fin bolts? At speed the fin produces a lot of suction, and air coming down the bolt holes can also ventilate the fin.

The other possibility is the fin leading edge being too blunt, (although the black projects I've seen look to be OK) A blunt leading edge will help stop spin out going upwind, but will encourage spin out going downwind.
Then of course there's technique, but with a fin that size you should be able to use a lot of backfoot pressure.
In fact are you struggling to control the board's trim? If the windward rail lifts up too much that will also let air get onto the fin.

Then there's all the usual stuff, not enough downhaul, outhaul, harness lines too far forward, etc causing too much backhand pressure, which transfers to the back foot.

Yep, that should not be happening. I sail an Isonic 87 as well. Usually use a 34cm C3 Venom or 34 Select Lightening with 6.2m and 5.8m KA Koncepts and can really stand on the fin when moderately powered up. If it's a bit weedy I use 28cm, 30 degree Lessacher Duo but it also works well with 5m sail and 26cm Time Machine carbon (TM26) pointer or 25cm Lessacher Duo. I have not really had much joy with 30cm slalom pointers though, but that may just be me or the particular fins.

I have played with the new 23 (20cm) BP speed weed 50 degree and it works fine once I have some speed up, but it needs a higher back foot in chop being so small.

Sail is trim pretty good no back hand pressor water was little bumpy coming onto realy flat water it happens rite off the wind running for speed i moved mast base back 1cm max that stopped a lot of spin out but not all of it

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decrepit said..
The other possibility is the fin leading edge being too blunt, (although the black projects I've seen look to be OK) A blunt leading edge will help stop spin out going upwind, but will encourage spin out going downwind.

It could also be "too sharp" ? ie: too small a radius on the leading edge.

Do you sail with a high or low boom? Lowering the boom in 1cm increments on each run until the fin feels safe and secure helped me sort out a similar issue that I had.

Just my 2 cents worth ??

You could try moving your back foot strap forward one position.

Duane

I had big spin out problems Sunday on a Nitro 34cm which is probably my best fin.

Yesterday I said "Stuff it" and tried a 35 Select - Worked hell of a lot better and is only a reasonable fin plus the bonus of a PB 2 sec and 10 sec.

Make some time to experiment with your gear combo's.

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AusMoz said..
Duane

I had big spin out problems Sunday on a Nitro 34cm which is probably my best fin.

Yesterday I said "Stuff it" and tried a 35 Select - Worked hell of a lot better and is only a reasonable fin plus the bonus of a PB 2 sec and 10 sec.

Make some time to experiment with your gear combo's.

Just my opinion, but those Nitros are the worst fins I've ever used. Bad for spinout. Bad for going up wind. Bad for going fast. Just bad, bad, bad.

The more I think about it the more your right but I do put a lot of back foot pressure on it and I like being over powered so I guess they are not made for it. Will be going through my fin collection tonight and making comparisons with them all.

Looks like I will stick to the Select Lightning's. The bigger Nitro's seem good on the bigger boards and Formula Board

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mathew said..

decrepit said..
The other possibility is the fin leading edge being too blunt, (although the black projects I've seen look to be OK) A blunt leading edge will help stop spin out going upwind, but will encourage spin out going downwind.

It could also be "too sharp" ? ie: too small a radius on the leading edge.

Matt, I think too sharp is more likely to cause spin out at high angles of attack, a 30cm fin with a 5.6m sail going downwind should have a small angle of attack.

I also sometimes spin out during the sling shot. It's happened with different board and fin combos, so I don't think it is an equipment issue but rather down to poor technique. It usually occurs when there is a chop in the turning area and I load up my back foot too much during the turn. I successfully prevent it by unloading my back foot and slightly feathering the turn

John I had exactly the same thing yesterday, conditions a bit choppier than I'm used to, started to bear of, hit a bit of chop and had a micro launch, I don't think the fin came all the way out of the water, but it was exposed enough to suck a whole pile of air down.

Remember every one that fin size is really based on water speed and not sail size for the speed dwane is going he might be better off with the 32.5 cm but undoubtably technique could stop the spinouts also. The most common thing ive found cause spin out for me is not enough down haul of sheeting in with the back hand .

Hmmm. So on the weekend I had a similar experience. 54 wide board and Black Project Weed Speed 28cm. Never used the fin before so spent some time learning it with the board (only 2nd time on it too). I found when powered up heading off the wind it was no problem but if I took pressure off the fin at this point it would slide and for the first time ever couldn't reengage it. I'm not a heavy guy or sail with a heavy back foot and found this sensation most unusual. I need more time to work out what's going on with it as it had me puzzled. Only upside was it's not a complete spin out situation and stack. Just a crabbing but the usual shimmy under my bum with the board wouldn't reconnect it.

Duane - Is it something you can reproduce or totally random? Have you had any help from the speedsters you are sailing with?

Come on Simon i got PB's all round on Sunday sailing with Leo his first run was 40knts plus mine wasn't that fast but i'm getting faster every time i speed sail.

Martin I used to have that with my wave gear, drop down a wave, and release fin pressure in preparation for a bottom turn and I could just feel the fin let go. If I tried for a bottom turn I'd just slide out, to reattach the flow I'd have to go upwind a tad with back foot pressure. These fins would also spin out going dowwind with very little back foot pressure. I'd made these fins with a fairly blunt leading edge so I could get upwind in the lulls. Sharpening up the front of the fin stopped this happening.
Which begs the question, what's the front of the foil like on those BPs?

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decrepit said..
Martin I used to have that with my wave gear, drop down a wave, and release fin pressure in preparation for a bottom turn and I could just feel the fin let go. If I tried for a bottom turn I'd just slide out, to reattach the flow I'd have to go upwind a tad with back foot pressure. These fins would also spin out going dowwind with very little back foot pressure. I'd made these fins with a fairly blunt leading edge so I could get upwind in the lulls. Sharpening up the front of the fin stopped this happening.
Which begs the question, what's the front of the foil like on those BPs?

No idea sorry. I hadn't really paid much attention to it before slotting on the hole and taking out. It is however much thicker than all my slalom upright fins so you could be onto something. I've also been told to give it a lick with some wet and dry as the trailing edge where the paint is might have some high spots causing a point of cavitation. All food for thought.
Cheers
Marty

Some weedies are very wide, longer than the box is quite common these days. to maintain the same thickness to flow ratio they also need to be thick. That's OK, if the foil is a fairly gradual curve from leading edge to about 2/3 back, thickest part about 40% forward. It's when the thickest part is closer to 30% forward, and the curve at the front is much more pronounced, down wind problems start to occur.