Pinching / Pointing

[RichH]

There are two kinds of stalls:
1. the stagnation stall where the luff of the sail visibly shakes
2. the separation stall where the important airflow boundary layer 'explodes' and the air becomes completely detached from the wing/sail but isnt visible to the naked eye, only to the tell tales.

Even without telltales the 'best' angle for pointing is (usually) the one that approximates the greatest heeling angle that you can attain .... so you can both use the tell tales AND the seat of your pants to get the best beating angle.

Alan's 'maximum horizontal point' on a polar diagram .... simply elegant, graphically IS the optimum trigonometric target sailing angle ---- and couldnt be simpler.


Of course their is an advanced technique that is better than simply beating off at the maximum angle: called power pinching. Anyone interested?

 

[Gudenuph]

Of course their is an advanced technique that is better than simply beating off at the maximum angle: called power pinching. Anyone interested?

[/quote]

RichH
Ya, sure, you betcha. 'Power pinching' at first glance seems to me an oxymoron. I'd like to hear what you have to say about it. Also in triming to maximum heel, how are the effects of lift separated from those of drag?
Geohan

 

[Todd Smith]

Of course their is an advanced technique that is better than simply beating off at the maximum angle: called power pinching. Anyone interested?

Of course we are interested, but first to continue the mystery. Does "power pinching" work in constant, non shifting wind ? Or does it require variations ?

 

[Don Guillette]

Gudenuph: Thanks mate, this gives me a chance to be scientific. One evening many years ago I was at the bar at Shoreline YC in Long Beach, Ca. One of the more scientifically minder sailors was explaining lift and drag to me and I remember he mentioned the lift/drag curve. I tried to get away from him as he was way over my head but what I did learn was I may not understand it but I sure know how to make it work for me even though I don't know what it is. I even added this little story to my book THE SAIL TRIM USERS GUIDE.

After a mate has been sailing for a while they get to "feel" the boat through their feet. They know when the boat is dragging and when it is lifted. I don't know how they and I do it but we do.

 

[Gudenuph]

Gudenuph: Thanks mate, this gives me a chance to be scientific. One evening many years ago I was at the bar at Shoreline YC in Long Beach, Ca. One of the more scientifically minder sailors was explaining lift and drag to me and I remember he mentioned the lift/drag curve. I tried to get away from him as he was way over my head but what I did learn was I may not understand it but I sure know how to make it work for me even though I don't know what it is. I even added this little story to my book THE SAIL TRIM USERS GUIDE.

After a mate has been sailing for a while they get to "feel" the boat through their feet. They know when the boat is dragging and when it is lifted. I don't know how they and I do it but we do.

Don

I have felt that also on those, rare for me, occasions when you are really groovin'. It's like being on a horse that--really-- likes to run! We didn't start sailing until 1952 and are nearing the end of our rope--er, line. Thanks for helping us get there once more.

Thanks much, Geohan

 

[Witzend]

There are many variables to consider when making the decision to pinch, sea state, currents, wind velocity delta, wind direction delta, a mark you may need to honor.

If you're into a nasty chop in a fading wind you will want to foot off and power up.
If you have very gusty conditions you may want to pinch up in a gust to keep from getting wiped out.
If you have 50yards to the mark and don't want to take another tack, you will want to pinch up if you think you can get away with it.
It's just not a cut and dry thing.

 

[sandpiper10471]

Frequently, a boat footing off slightly will end up upwind of a boat "pointing" higher. This is because as the speed doubles, the lift on the rudder and keel cubes. You have two sets of foils - one in gas and the other in liquid. Both work the same way regarding lift. Sea state helps determine just how far one must foot off in order to maintain good lift from the foils. Obviously, short choppy seas tell you to foot off more. Heavy boats seem to suffer less from pinching in the gusts as their momentum keeps lift on the foils working whereas lighter displacement boats decelerate faster. Also, boats with flat sails are less affected negatively by pinching that boats with fuller sails.

 

[RichH]

FYI -
I put a reply in Don's "Footing Off" thread ... that should be very applicable to optimizing 'pinching/pointing'. See - 'turbo-sailing' if you want just the 'meat and potatoes'.

Another 'trick' to enhance 'beating/pointing' when on the race course is to POWER-PINCH during the end of each tack/leg. POWER-PINCHING is accomplished by slight bearing off or footing off until max. speed is obtained, then by hard trimming in on the mainsail to increase overall draft (increases lift) ... and you 'ride' this powered up shape as 'high' as possible until the boat speed begins to decrease, etc.
When using VMG as your guide, powerpinching at the 'end' of a tack will not affect VMG .... and will allow the boat to 'climb to weather' ...... thus SAVING total distance on the 'next leg'.

When racing, I usually 'power pinch' for at least ~10 boatlengths from the 'lay line' .... the decrease of total distance sail ON THE NEXT LEG (several boatlength) can be substantial. Sailing to VMG is only valid at the 'beginning' of a tack, as at the 'end' of a tack you are essentially 90 degrees from the next 'imaginary mark' ... and VMG calculations 'go to zero' when your boat is 90° from the next 'mark'.
Power pinching at the end of a tack or when 'turbo sailing' (alternating between power-pinching and footing off), and especially when nearing the lay-line can 'save' a lot of distance sailed on the 'next' leg.

Sailboat racing is mostly a 'game of inches', every time you power-pinch you 'can' save a 'lot of inches' and if you continually over a race course 'save a lot of inches' you will place continually higher and higher in the fleet. Takes 'practice' to get it 'right'.

 

[Roger Long]

One of the more scientifically minder sailors was explaining lift and drag to me and I remember he mentioned the lift/drag curve. I tried to get away from him as he was way over my head ...

Those of us who fly (or used to in my case) airplanes do get a little nudgy at pinching being described as "stalling". It's a good word to use in these discussions but it's not the same animal.

Most pilots actually don't understand aircraft stalling. It isn't the wing losing lift but losing its stability in the airstream and rapidly seeking a new equilibrium. The wings can be deep into stall according to the lift curve and yet developing exactly the same amount of lift as in level flight. Sails can't stall in the same way because the hull isn't free to suddenly move upwind.

I won't muck up your thread further

 

[Maine Sail]

FYI -
I put a reply in Don's "Footing Off" thread ... that should be very applicable to optimizing 'pinching/pointing'. See - 'turbo-sailing' if you want just the 'meat and potatoes'.

Another 'trick' to enhance 'beating/pointing' when on the race course is to POWER-PINCH during the end of each tack/leg. POWER-PINCHING is accomplished by slight bearing off or footing off until max. speed is obtained, then by hard trimming in on the mainsail to increase overall draft (increases lift) ... and you 'ride' this powered up shape as 'high' as possible until the boat speed begins to decrease, etc.
When using VMG as your guide, powerpinching at the 'end' of a tack will not affect VMG .... and will allow the boat to 'climb to weather' ...... thus SAVING total distance on the 'next leg'.

When racing, I usually 'power pinch' for at least ~10 boatlengths from the 'lay line' .... the decrease of total distance sail ON THE NEXT LEG (several boatlength) can be substantial. Sailing to VMG is only valid at the 'beginning' of a tack, as at the 'end' of a tack you are essentially 90 degrees from the next 'imaginary mark' ... and VMG calculations 'go to zero' when your boat is 90° from the next 'mark'.
Power pinching at the end of a tack or when 'turbo sailing' (alternating between power-pinching and footing off), and especially when nearing the lay-line can 'save' a lot of distance sailed on the 'next' leg.

Sailboat racing is mostly a 'game of inches', every time you power-pinch you 'can' save a 'lot of inches' and if you continually over a race course 'save a lot of inches' you will place continually higher and higher in the fleet. Takes 'practice' to get it 'right'.

Cool, I never knew that technique even had a name. Of course with a crowded mark and boats stealing wind it does not always work the way you want..

 

[red_dolphin]

Sailing to VMG on a beat works great
IF
You have instruments that show your VMG against the wind, rather than against a mark.

All this assumes that your instruments can
-- measure apparent wind speed and direction [the weather vane and anemometer at the top of the mast].
-- know the COG and SOG of the boat [hopefully from GPS input]
-- do the math to determine true wind direction and speed, and VMG against the wind.

OK, none of this helps the dinghy sailor.
Moreover, experience in dinghy sailing will get you close, and keep you from relying on instruments that are clearly out of tune.
But when the instruments are in tune, VMG against the wind is a great figure-of-merit.