him&her

How close can the sails be? (i.e. the "slot")

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Looking at fast boats that carry multiple sails downwind I've come to wonder...

How close can the sails be to each other, and still have enough of a "slot" for the wind to cause as little interference as possible?

Is there some kind of calculation for this?

 

For example... the Volvo Open Ocean 65's seems to have them, what, 5ft apart?

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depends on soooooooooo many variables.  VOR 65 or TP 52 is going to be very very very different than some 4 kt shitbox.  close and sheeted tight for them when at speed, not so much for regular schmoes 

YMMV

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1 hour ago, some dude said:

depends on soooooooooo many variables.  VOR 65 or TP 52 is going to be very very very different than some 4 kt shitbox.  close and sheeted tight for them when at speed, not so much for regular schmoes 

YMMV

Rough numbers from my experience/recollection of upwind sheeting angles:, the good old Cal 40 = 11°,  Typical 35'-40' PHRF racer = 9°, Farr 40 or similar = 7°, TP52 = 5° (or narrower if the driver/trimmer team are pros.)

 

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27 minutes ago, Left Shift said:

Rough numbers from my experience/recollection of upwind sheeting angles:, the good old Cal 40 = 11°,  Typical 35'-40' PHRF racer = 9°, Farr 40 or similar = 7°, TP52 = 5° (or narrower if the driver/trimmer team are pros.)

 

Good answer, but I believe the OP is concerned more about offwind than upwind - i.e. staysails and the like.

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29 minutes ago, 12 metre said:

Good answer, but I believe the OP is concerned more about offwind than upwind - i.e. staysails and the like.

The boats he's referencing never go "off wind" with the apparent wind aft of 90°.  However, the answer OP may be looking for comes from the distance between the sails, the wind angle and wind strength.  To go three headsail reaching, the VO 65's are at 80° to 90° AWA, in about 20 knots of pressure and they have probably 38' of distance between mast and end of sprit.   A TP52 has about 27' of distance.  So the gap between headsails is about 9' to 12'.  Almost what the J measurement is on a 35' PHRF boat.   They also use  use headsail selection to keep the power matched with conditions.  Interesting to note that they apparently have pretty much stopped using their A-3 kites as they rarely go that deep off wind.  The Masthead 0 (MH0) and the Fractional 0 (FRO) seem to get all the work.  Plus the jibs on furlers as staysails.

There is a famous photo of the 40' IMP back in the '80's three headsail reaching in SF Bay with lots of breeze.  But the quality of those sailors, sails and boat is rarely equaled.  Not to be successfully tried by 99% of sailors.  

 

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Can i add:

1. Dont worry about area; less is often more.

2. For each inner sail, the tack point  needs to > 33 % behind the next outer sail. 

The volvo 65s obey this  well.

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As close as they need to be to maximize speed, and no more. Seriously, that is the answer. Probably determined with careful testing. Also the whole "slot" mental exercise is pointless.

The aircraft wing analogy above is apt. The flaps give a huge increase in lift for a given airspeed at the expense of a huge increase in drag. Like a race boat on a reach, aircraft have a surplus of power, especially when landing, to overcome the drag. In the case of an airplane it allows lower speeds. For a race boat is ekes out a bit more speed for the given wind. Also looks super cool.

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On 1/18/2018 at 8:16 PM, Left Shift said:

<SNIP>

There is a famous photo of the 40' IMP back in the '80's three headsail reaching in SF Bay with lots of breeze.  But the quality of those sailors, sails and boat is rarely equaled.  Not to be successfully tried by 99% of sailors.  

 

Now I wish I kept all those large format calendars I used to have! That was a great photo, if it is the one I am thinking of.

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Here are a couple of images taken from a classic paper on High Lift Aerodynamics by A.M.O. Smith. The paper essentially points out that more slots give more lift, as the angle of attack increases. At low angles of attack, a single foil works better, but by the time the angle of attack gets into the 30s and 40s, then more slots work better. Basically, when you reach the angle of attack where a stall occurs, having another slot prevents the stall so lift continues to increase with increasing angle of attack (Figure 5).

But note in the data in Figure 4: its not always true that another slot helps. Sometimes extra foils (slots) hurts (more drag than lift). For example, the 8th one is usually worse. Note the area below 1 on each: for foil 1, 2, 3, and 4, at least half the time its worthwhile. But as the number of foils (and slots) increases, the angles of attack where lift is improved gets smaller and smaller, so it gets more and more likely that your sail trim won't be good enough to get an advantage. With lots of slots, getting it wrong hurts more than getting it right ever helps.

Fig4_RAF19.thumb.png.3620d1a331a1603afb24fada427c5d53.png

Fig5_RAF19.png

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7 hours ago, Knut Grotzki said:

Sometimes the slot is bigger on IMP

Imp_photo 3.jpg

The "slot" in that setup is probably running around the leech of the main forward into the spinnaker.  One of the best looking blooper sets I've seen.   Flatter than most, I suspect.

What logo is on those sails?  

 

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10 hours ago, fastyacht said:

Oh my GOD!   T H A N K S for finding that!

Sleddog is in there somewhere. Probably driving.

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On 21.1.2018 at 4:38 AM, Left Shift said:

The "slot" in that setup is probably running around the leech of the main forward into the spinnaker.  One of the best looking blooper sets I've seen.   Flatter than most, I suspect.

What logo is on those sails?  

 

I could give you some pics of best looking bloopers which are not flatter than most ... well ok, back to business ... here is one:

tumblr_mqr1y3xYvV1r7fii7o1_500.jpg.db96a851acf5ad02d194e97f2084a5ad.jpg

Anyway, their thrust vector should point in the right direction, which I doubt at some pictures. Or they counteract the side force of the spinnaker, but in the end the induced drag needs to be overcome. This is what probably killed them - when boats sailed faster than the old lead mines permitted.

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On 1/20/2018 at 3:05 PM, fastyacht said:

Oh my GOD!   T H A N K S for finding that!

The cool photo of iMP was taken in the last race of the 1977 SORC, the 30 mile Nassau Cup. iMP won that race and with it, became SORC high-point boat over RUNNING TIDE. The photo appeared in  a Sports Illustrated article, helping to launch the legend of iMP

In answer to the question "what logo on those sails?"  they were all blue bags.

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3 hours ago, Knut Grotzki said:

I could give you some pics of best looking bloopers which are not flatter than most ... well ok, back to business ... here is one:

tumblr_mqr1y3xYvV1r7fii7o1_500.jpg.db96a851acf5ad02d194e97f2084a5ad.jpg

Anyway, their thrust vector should point in the right direction, which I doubt at some pictures. Or they counteract the side force of the spinnaker, but in the end the induced drag needs to be overcome. This is what probably killed them - when boats sailed faster than the old lead mines permitted.

Two kites, one blooper, and a reef on the mizzen sail.

What does the sail selection binder look like that has this as an option?

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21 minutes ago, Tax Man said:

Two kites, one blooper, and a reef on the mizzen sail.

What does the sail selection binder look like that has this as an option?

Transpac Notebook Page 2:  "4 days out of Long Beach:  Hoist all this shit."

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as many as you want, quite close together. I count 3 red and 3 white sails here.

as many wings as you want.jpg

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17 minutes ago, CrushDigital said:

I think the logic is that the mizzen is just getting in the way of the mizzen spin.

There's no fooling you, Captain Obvious!

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sail the cloth!!!!!!

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On 1/23/2018 at 5:09 AM, Knut Grotzki said:

I could give you some pics of best looking bloopers which are not flatter than most ... well ok, back to business ... here is one:

tumblr_mqr1y3xYvV1r7fii7o1_500.jpg.db96a851acf5ad02d194e97f2084a5ad.jpg

Anyway, their thrust vector should point in the right direction, which I doubt at some pictures. Or they counteract the side force of the spinnaker, but in the end the induced drag needs to be overcome. This is what probably killed them - when boats sailed faster than the old lead mines permitted.

I have always thought it was amazing that the photo was taken at the exact moment that they threw the jockey pole (reaching strut for 'mericans) over the leeward side.

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Mizzen Envy... a sad affliction of those who are less well endowed.:D 

We rolled over a Tartan 3400 & under a Ranger 33 Sunday with our Mizzen Staysail in < 5kts wind.

Couldn't hold the Ranger on the tighter reach in < 2kts. 

 

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5 hours ago, Somebody Else said:

There's no fooling you, Captain Obvious!

You see, that's what happens when someone deletes the post you're responding to.

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9 hours ago, Zonker said:

as many as you want, quite close together. I count 3 red and 3 white sails here.

as many wings as you want.jpg

Whci hyear is thois one? I can't keep up wiht them. Every time they wurte a rule, which seems every hear, there s another clever whay around it. Is this where all the old IOR master desigers went?

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I don't think its current year (look at the ugly nose). I just picked one with a good view of the front wings. For F1 I think it's the aero gurus who are driving the design more than chassis/engine.

Finally figured out why they use the swan necks for uprights on the big wings on the GT cars. (These uprights attach to the top of the wings instead of the more obvious underside). Look like an inverted J.

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It's actually pretty simple as a thought experiment.

You can close the slot until you start back-winding the inside sail or you start stalling out the leech telltales of your outside sail.  In either case you've pushed too far and are losing efficiency because of turbulence.

The forces involved are simple to understand, but murderously complex to calculate.  Put simply, the more wind you can redirect toward the stern of the boat, the faster you will go.  A simple rule of thumb is that if you hold a windex in the center of the slot exit between two sails and slowly increase the size of the slot, you'll notice a point where it stops pointing parallel to the center line of the boat and starts pointing in toward the center of the boat some.  This is that point at which you know you're not directing all the air you can straight backwards, and that you may add some speed by putting up a stay-sail.

Nowadays you're doing yourself a dis-service on any new race boat if you don't use computational fluid dynamics programs on the sailplan to understand all the things that go on - like the fact that the slots near the top of the mast become increasingly worthless and actually hurt you because the sails are just too close together (which is why most stay-sails are partial hoists.....).  That's why the best answer is listen to the manufacturer.  They usually have the horsepower behind them to have studied the right way to sail the boat.

On your four knot shitbox, play around with a windex and telltales and try to understand what's happening with air flow as you adjust the trim of your sails.  Look how similar boats that do well are setting up their sail plans.  No one's going to pay $50k to do an analysis on your Cal 25.

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One thing everyone has failed to mention is that Volvo 65's use reaching struts to leeward and well aft. By moving the sheeting position so far outboard they have extra room in the slot for the staysail as well as the J1. If the Code Zero or A3 sheeted to the deck it would be a lot harder for this set up to work properly. They would probably loose the J1 and go with the staysail.

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Ok then how about this one, not a jib top but a top jib!

A common practice in the classic yacht fleet, I think the only benefit would be it gives more people something to do. 

IMG_0643.jpg

IMG_0644a.jpg

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On 1/24/2018 at 8:08 AM, Soley said:

One thing everyone has failed to mention is that Volvo 65's use reaching struts to leeward and well aft. By moving the sheeting position so far outboard they have extra room in the slot for the staysail as well as the J1. If the Code Zero or A3 sheeted to the deck it would be a lot harder for this set up to work properly. They would probably loose the J1 and go with the staysail.

Oh yeah... the manual for my 5ksb says that I'm supposed to be using a 6-foot reaching strut.  Didn't come with one, though the mast fittings are there.  When I first read that, the added complexity just sort of whited-out the action lobe of my brain.  Now... I might pick one up if I saw it at a garage sale or something.  

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On 25/01/2018 at 3:08 AM, Soley said:

One thing everyone has failed to mention is that Volvo 65's use reaching struts to leeward and well aft. By moving the sheeting position so far outboard they have extra room in the slot for the staysail as well as the J1. If the Code Zero or A3 sheeted to the deck it would be a lot harder for this set up to work properly. They would probably loose the J1 and go with the staysail.

RRS  Part 4 Rule 50.3 Use of Outriggers, specifically excludes them from racing, so VOR must have an amendment in place. But you could still try them cruising?

A reaching strut/jockey pole is not classified as an outrigger. Unless you use it to leeward.

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58 minutes ago, overbend said:

Ok then how about this one, not a jib top but a top jib!

A common practice in the classic yacht fleet, I think the only benefit would be it gives more people something to do. 

I can see potential benefit... not hard to verify which set up is best. The bigger the yacht the more likely the benefit....

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On 1/29/2018 at 5:27 PM, Sidecar said:

RRS  Part 4 Rule 50.3 Use of Outriggers, specifically excludes them from racing, so VOR must have an amendment in place. But you could still try them cruising?

A reaching strut/jockey pole is not classified as an outrigger. Unless you use it to leeward.

RRS  Part 4 Rule 50.3 c. Does allow a headsail to be trimmed to a whisker pole. A reaching strut attached to the mast is a whisker pole. So although it is not as effective as a VOR65 with a massive strut at the back of the boat, it will help a boat with non overlapping jibs as you can push the lead outboard at the mast area.

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Depends upon the rig too. I have a fractional setup, which obviously doesn’t give you the separation in the top of the sails as compared to a masthead. I can run a gennaker and staysail sweetly, I very much doubt I could squeeze in the headsail without disrupting the airflow and killing it . 

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