Foil suggested angles of attack and identifying 0

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EdS
Posts: 188
Joined: Mon Aug 06, 2012 12:06 pm
Boat Number: GBR 1524
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Foil suggested angles of attack and identifying 0

Post by EdS » Tue Aug 07, 2012 8:26 am

1524 has the foil control brought to the middle of the rack with markings on the cockpit floor relating to the position of one of the blocks.

There are three marks, one of which we have estimated at around 0 - slightly lifting, depending on your reference. The other is lifting with the foil angled at the bow and the aft most is hugely negative.

How would you go about measuring the angle and also what might a suggested range be.
Basically so i can have a rough mark on the floor for a good lifting angle and a negative angle for when required.

I realise this is foil dependant, the boat is a B5 with foils from 2006, no idea of the section. The is purely to identify a reasonable range to start with.

Thanks,

Ed
Roaring Forties GBR1524

Dan H
Posts: 71
Joined: Wed May 18, 2011 11:02 am
Boat Number: 1515
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Re: Foil suggested angles of attack and identifying 0

Post by Dan H » Wed Aug 08, 2012 10:05 am

Ed,
Wouldn't get too hung up on identifying absolute angles - depends on how the foil was glued to rudder, assymetry of section etc etc.
For what its worth there is a def max on position beyond which the foil just gets more prone to stalling in any wave / bad moment of sheeting / steering.
This amount of foil should have both at back of rack at app 8kts boatspeed. You'll need to back off this a little in any waves, or in more breeze upwind as the boatspeed hits 9 or 10 kts +

For what its worth, the range from the max on to max off on my system is about 17deg. The max off is a sensible amount of bow up foil for all manner of silly windy 2 sail action and bearaways, but is too much bow up really for any 3 sail vmg action.
You may be able to identify this max on position whilst sailing, and measure the 17 deg wrt the max on and the pivot.

At a vague guess I would put neutral at 7 deg from max -ve, 10 deg from max +ve.
I wouldn't get too hung up on any position save the max on - generally you pull on as much as you can without sticking too much bow in - so more on upwind than down, less on in waves.

Re the WW hoists, the elastic is a good plan, also get deeper than you think - i.e helm into boat unless its windy - don't be afraid of letting the jib goosewing. Similar thing for WW drops.
Grab your handle with front hand to keep yourself hooked in whilst in the boat or standing on wing.
Also, not sure how good your elastic takeup is - i.e if the halyard is acceptably taut before the hoist, it may be lkess inclined to get caught in that trap.
Trawling can only mean too slow a hoist - esp in the early stages. Not helped by an old kite if thats the case

We are club racing at Netley tonight in 1515, and sunday. You should get stuck in!

EdS
Posts: 188
Joined: Mon Aug 06, 2012 12:06 pm
Boat Number: GBR 1524
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Re: Foil suggested angles of attack and identifying 0

Post by EdS » Thu Aug 09, 2012 7:55 am

Hi Dan,

Thanks for the response. I realise there are alot of factors but your explanation of where the max might be is useful, sailing with a foil is still novel.
I found over the weekend that it was difficult to come in to adjust the foil when going downwind and in one case we had too much, so just trying to establish sensible starting points. Do you run a twist grip??

Being at the back of the racks upwind is an odd concept and at the moment it doesn't appear to easy to stay there. practice required.

I will definitely be putting the elastic between the shrouds going around the forestay. The B14 had that arrangement and we did windward hoists alot and never encountered the problem.
Goose winging would eliminate the issue as well, good idea!

Speed is probably something, the spinnaker came out of the shoot as it went it. Normally with other shoots I have used the head comes out first and the clew stays in position until later. The older kite comment would explain this and poor technique.

Didnt see the message about last night, although definitely keen in future. What time is the start and how how often do they do mid week racing.
Is the sunday sailing at Netley or Weston? I need to find a crew for this weekend so will get on that.

Thanks for the input!
Roaring Forties GBR1524

Dan H
Posts: 71
Joined: Wed May 18, 2011 11:02 am
Boat Number: 1515
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Re: Foil suggested angles of attack and identifying 0

Post by Dan H » Thu Aug 09, 2012 12:16 pm

Ed,
Yep tfoil is a little odd at times, the old adductors can get weary after a while! get in a footstrap early even if it means spreading legs a little to keep weight fwd a little, f4 or more and you should be in back strap and crossed over most of the time.
I would recommend a foil cleat on aft rack tube - may need crossing over hands but having flirted with every possibility this was best when all is said and done.
Also speaking from bitter experience I would avoid trying twist grip unless you have a balanced lifting rudder where the foil is right under the pivot point.
I found that using 4:1 purchase - i.e coarse enough that you werent furiouysly twisting for 10 mins at each windward, that any positive foil overcame the drag on the twistgrip so was pretty much a waste of time. Just think 8:1 would be too fine and twisting on and off too lengthy.

Check Netley website for racing times - not every weds due to tide at that time of night.
There is often racing both days at Weston I believe

Dan

EdS
Posts: 188
Joined: Mon Aug 06, 2012 12:06 pm
Boat Number: GBR 1524
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Re: Foil suggested angles of attack and identifying 0

Post by EdS » Thu Aug 09, 2012 1:27 pm

Need to practice being crossed over. Who goes above who?
Getting in the straps is not an issue, much less uncomfortable than windsurfing.
Not falling forwards in a lull is more difficult.

Moving the foil control back is a good plan. I will look at that, shouldn't be hard to move.

Have some boats got both, coarse on a line then fine on a twist grip??
Seems like it might be a good compromise between repetitive strain and not being able to reach.

Ok thanks, i am not around for a while midweek. I intend to be out this Saturday and potentially this Sunday.
Roaring Forties GBR1524

Dan H
Posts: 71
Joined: Wed May 18, 2011 11:02 am
Boat Number: 1515
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Re: Foil suggested angles of attack and identifying 0

Post by Dan H » Thu Aug 09, 2012 4:09 pm

Crew back leg (bent) goes over helm front leg (straight) - bit of fwd twist in the hips will help.
Crew needs to be cogniscant of the fact that the helm will not be able to get back in whilst in this state - i.e. not one for marginal / patchy breeze
Yeah a few boats have both.
Youll need a hefty bungee return on a fine tune or a complex system that both winds on and off. Prob as good to get used to your marks and the boat.
May be out sat albeit with an off the beach crew if I am.
Forecast looks outstanding for Soton water.

EdS
Posts: 188
Joined: Mon Aug 06, 2012 12:06 pm
Boat Number: GBR 1524
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Re: Foil suggested angles of attack and identifying 0

Post by EdS » Mon Aug 13, 2012 11:49 am

Elastic over the top of the forestay from each shroud has solved the spinnaker issue!
Roaring Forties GBR1524

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