Close hauled - Lee bowing…
It has occurred to me whilst sailing single-handed dinglies such as Laser/Phantom, the skipper has the ability to pull the mainsail to windward slightly whilst sailing close hauled and using tiller inch the bow to windward without losing too much speed - in effect, sailing to windward quicker than others who do not.
Does anyone know the disadvantages of this manouvre?
In essense it’s similar to a gybing centreboard.
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In my experience, oversheeting the main can effectively produce a lot of bad air for any boat following and slightly to weather if my boat is sailing fast. Seems faster my boat, the larger the wind shadow. That said, I also found a distinct tendency to hook the leech to weather slowing the boat down. I would only use a main with traveler to weather in medium or light winds, but not sheet tight. I then eased traveler to about 4-6 inches to leeward and oversheeted the main only when winds were strong enough to blow open the leech.
On my boat, I sail with rotating mast and main only, so any sheeting or traveler to weather has no effect on the jib and it’s trim.
I am not sure there is that much of a gain in the little boats, and once again, without being on board, it is impossible to feel the slight differences of speed as you fool with traveler or mainsheet. One would almost have to “trial horse” against an identical boat to see if there is any gain. In the little multihulls, I know that raising the board slightly reduces tipping tendency in heavy air, and increases speed with a bit of crabbing from reduced lateral resistance, but - again - how much to lift is hard to tell from shore and is a need for yet another servo/winch, weight and one more thing to go wrong.
I have noticed that few classes use any form of traveler, but that may be due to the narrow beam on our models, and the more frequent use of boom vangs/kicking straps.
You have to heel the boat ontop of you in a dinghy to make it work for any distance, so its not going to be that effective for a model. Used to be able to do it on my Rs 600 while in marginal trapeezing conditions, does pay but with that boat it was very hard to keep the boat heeled to windward without tea-bagging. Works well on hiking singlehanders though.
Luff 'em & leave 'em.
Can you further explain ?tea-bagging? the term is foreign to me.
Sorry Dan! It’s when you sailing a trapeeze boat and the boat heels to windward far enough to drop you in the water whilst your still on the trap. Hence you become a human tea-bag! It’s normally pretty stable postion to be in but not fast, and you either have to wait for a gust to pull you out of the water again or un-hook and scramble back in the boat. Hope that clears that up…
Luff 'em & leave 'em.
Also known as “Chumming” or “trolling” - as in fishing! [:D]
A couple of unique things happen when you are in a lee bow position.
Aerodynamic: The close proximity of the two boats results in a change in the aparent wind direction for each boat. The lee bow boat will see a lift and the windward boat will see a knock. This effect alone is often times enough for the lee bow boat to climb up on the windward boat and gas him off. In fact this effect can start to be felt when you are dead abeam of the windward boat. Because the wind is being turned by his sails, is you are aft of dead abeam you will feel a knock. But if you ahead of dead abeam you will feel a lift.
Tactical: When you are in a leebow position, you often times want to squeeze off the boat to windward and force him to tack away. This frees you up to be able to tack when you want to and may even result in your competitor sailing the wrong way (away from the mark or away from the next shift, etc). So, in that situation you are willing to pinch up. you will ooose some boatspeed in the shot run, but you are trading that boatspeed for a better position relative to your competitor that will give him more dirty air and force him to tack. As you say, sometimes you want to make his air even dirtier. you can do this by stalling your own sail a little which will cause turbulent and even more bent air to head his way. You will slow down, but he will slow down more. So if all you are worried about is that one other boat, performing this maneuver will allow you to gain a couple of boatlengths on him.
I have done this maneuver in model boats. You need to be able to overtrim your main which I can do with my sheeting arangement(see the latest issue of Model Yachting for details). It works as well in model boats as it does in full size boats, but you have to be very close to your competitor (just like in full size boats) and that can be harder to judge in model boats. But I have been able to squeeze off competitors coming into windward mark roundings or windward finishes or even on the starting line.
You probably would have a hard time in a multihull getting close enough to pull this off, but in a monohull with a well executed lee bow tack, it is quite easy.
SHORTER PASSAGE TO THE WINDWARD MARK…
Well, I certainly got a response from all you ICE SKEETA’s regarding ‘Lee Bow’
However, I wonder how my next query will be received?
Take any yacht, being a land or ice yacht, ocean going racer or sailing dinghy. They all come under the same umbrella as far as this next issue is concerned.
Imagine if you will an imaginary line from the stem (lengthways along the craft) to the centre point across the transom. When the yacht is close hauled, the aft section of mainsail boom, depending on the craft, is usually over the leeward corner of transom / side gunwale. Now keeping the exact shape of the mainsail and foresail, turn the whole rig (in-line) so that the tack of the foresail is allowed to move to leeward and the mainsail at exactly the same degree, to windward. The lift gained from the sails is exactly the same before, but it is now pointing, say 5 degrees off centre to leeward.
Would the craft benefit if the stem of the craft was then pointed 5 degrees to windward ?
How far could you take this without losing drive?
I can visualise the possibility that ICE YACHTs may well benefit in a seesawing fashion because the ice skates do not give way to side slip, but I’m a little dubious about water borne craft.
What do you think??
Actually few ice yachts use anything “but” a mainsail, since they generate too much apparent wind at speed, that the little “handkerchief” seems only to get in the way.
While it is a two hull comparison, most catamarans can actually point higher with just a main, than those that add on a jib. Interesting that many AMYA monohull classes “mandate” a jib and do not allow a main-only configuration.
Nice of you to make comment - appreciated!
Whilst I can know about apparent wind - how do you set the main up to start with? Do you make if full and as you gain speed, pull the main in to a close hauled position, even tho on a broard reach? and then flatten the sail to increase the speed yet again - or what?
I has just occurred to me as I was typing the previous message in reply, that if an ice yachts go that fast & they obviously do, would it be feasible to attach horizontal wings (like an areoplane) but with the leading edges points down at 20 degrees and the wing tips lower than the fuselarge (cockpit area) so when the craft is beginning to heel the windward wing has inverted thrust (ie opposite to lift) and the leeward wing will be in such a position that the leading edge although has the tendancy to create down thrust, it is almost cewrtainly pointing more into the wind than the windward wing…if you see what I mean.
Take 2 rulers, place them together end-on-end and then tilt the outer ends down for 20 degrees. Then twist the leading edges 20 or so degrees down. Holding them in that position, now rotate them so that 1 end lowers and the other end rises and trying to image the wind blowing towards the lower leading edges, you will begin to see what I mean - I hope…
You wouldnt be able to take it too far before the lift vector of the rig is at to 90 the centerline of the boat, and the drag is pulling the boat backwards.
Luff 'em & leave 'em.
take a look here: http://water.resist.free.fr/Anglais/Innovation.htm
Jean Margail, designer of the WATER RESIST series of Mini40 and 2 Meter multihulls (France) and an egineer at AIRBUS, is also into experimentation of WIG theory using wings aand ground effects. Kind of interesting, but I lost interest when he introduced the motor to the sailing platform to get more horizontal speed. Perhaps that is the only way to develop enough speed to generate wing lift?
this might be of use as well, it uses an asymmetric rear beam.
Have you ever studied the aerodynamic theories about sails?
Marchaj has a treatment of sail forces in his tome “The Aero-Hydrodynamics of Sailing”. What you will find in reading through that is that the sail drive vector is a function of the aparent wind angle. The sail drive can then be turned into forward motion for the boat. The heading and speed of the boat (combined with the true wind)sets the aparent wind angle. Combining all of these effects will give you a polar diagram of the boatspeed versus heading. You will find that the maximum VMG does not occur at the point where the boatspeed is maximized. It also does not occur at the highest heading that the boat can point. That is why when you pinch, you can still sail forward, but you will loose to a guy who is not pinching. When you foot, you will be going faster, but you again will loose because you are not making good speed to windward.
By turning the rig by say 5 degrees into the wind (while keeping the boatspeed and direction constant), you have reduced the angle of attack of the sails. This will result in lower lift from both sails and in general your speed will be reduced.
I should say that there are some poeple who have played around with the idea of operating the sails at lower angles of attack. The Dyna Wing concept that was floating around 5 or 10 years ago used a solid wing sail that would operate at much lower angles of attack. This produced a net benefit for driving force while at the same time reducing the heeling moment. But you need a hard sail to do this. A soft sail will simply luff if you reduce the angle of attack since the angle of incedence at the leading edge (luff) will go negative and a soft sail cannot support a negative angle of incidence.
I should also say that because of how we normally tack our jibs with a pivot that is a certain distance back from the bow. the rig does effectively end up angled a few degrees to windward (the forward edge of the jib boom is off to the windward side of the centerline). So we do have this effect to a small degree in typical model boats. But generally this is seen as a negative to boatspeed but is a tradeoff that has a net benefit to the boat performance because the boom ends up better balanced (allowing it to wing out easier off the wind) and you can achieve better jib boom toppinglift tension which allows you to control the jib shape better.
Pinching works when leebowing agains the boat wich you are leebowing. Also Pinching works in stable conditions because some keel profiles do not stall as easy as others, meaning that when the keels angle of attack chnages, it can provide more lift and makes you bale to point higher temporarily than the other boat. The nai effect is however thta the wind leaving your mainsail actually disturbss the upper boat more when you are pinching, because the end of your sail will turn the wind against the other boats sail. However on a big fleet these 2 boats will loose ground to others who are not in lee- bow battle as will explained.
“Expertice is gained trough mistakes. However repeating
same mistake is not learning but stupidity.”
Hi Will & Beechbum,
I’m not sure, but I think you may have missed my point. Okay, I’ll try a different tack (sorry about the pun).
Keeping the vessel and swinging rig in line, so-to-speak, (as you would do with a conventional fixed rig sailing craft) will generate the usual amount of lift from the sail(s).
Keeping the rig and sailing on the same heading to the wind (say at 45 degrees to the wind), now turn the bows of the craft/boat/yacht - without moving the angle of sail attach to the wind - 5 degrees towards the wind (in effect swinging the swing rig [the sails only] 5 degrees to leeward.
The craft does not have to be kept at 5 degrees. The helmsman can deviate from the normal close hauled position, by keepiing the sails in the same position and moving the bows into wind a little. Therefore, (particularly with an ice yacht because the ice ‘skates’ being sharp and digging into the ice, will not allow sidewards drift to leeward - certainly not as much as conventional water borne craft) because the craft is being pushed into the wind (albeit only 5 degrees or so), there will be more wind on the sails which will have a tendency to generate more wind pressure and therefore more lift from the sails and the craft should go faster.
I have to admit, I do not know anything about ice yachts, except from pictures I have seen and the very limited ‘number of reads’ from this site.
However, I have been intertested in sailing/yachting in a big way since 1958 (some 46 years).
I would suspect that a helmsman that has the ability to use this suggestion will have a swing rig - will be sitting on the windward sidse of the craft - will push the tiller arm down to leeward, so the bows deviate from the normal heading by about 5 degrees AND AT THE SAME TIME pull the mainsail boom to windward by the same amount.
THIS IS NOT PINCHING !!
Have a good day.
I would need to draw this, but i dont have the time now. This can work a short period of time, but the mainsail leach will be against the wind and therefore slow you down. Also the boat will drift more sideways. I admit the bow will be pointing higher, but the boat is not moving to the same direction as it usually does. And there wont be any more wind on the sails, just the angle of attack to the wing profile sail forms changes and therefore there will be more pressure, but the pressures force vector will point lower. When you add the increased drag of your keel or skates trying to go more sideways, you wont be on the gaining side on this.
“Expertice is gained trough mistakes. However repeating
same mistake is not learning but stupidity.”
I got your point, but perhaps my explaination was for the opposite case.
You really need to read Marchaj. The total drive force vector is calculated besed on the total force of the sail but also on the total force of the boat (drag and alteral resistance). The total sail force is pointed forward by the a very small angle (normally about 5 or 10 degrees). The total force of the hull is pointed aft by the same amount when the boat is in equilibrium.
Picture in your mind that the total force of the boat is made up of drag and lateral resistance (which is the lift of the appendages). The lateral resistance force vector points to windward. If you change the heading of the hull and appendages relative to the water, then you are effectively rotating the lateral resistance force vector aft slightly. This will result in a larger component of the lateral resistance vector acting as drag. Since the boat at equilibrium will have equal drive and drag and you have not changed the drive vector but added to the drag vector, the boat will slow down.
Since drag is made up of the viscous and wave drag of the boat slicing through the water plus the component of lateral resistance mentioned earlier. The boat will slow down until the viscous and wave making drag reduce by enough to bring the drive and drag back into equilibrium.
All the force vecotrs will be changing as the boat slows down since the aparent wind angle will shft aft resulting in the drive force rotating forward. Because the keel is moving through the water slower, you are going to need a slightly higher angle of attack of the keel to maintain enough lift to offset the sideways component of the sail force. This will result in a slightly higher leeway angle and a slightly higher component of keel drag.
But the bottom line is that by the time you re-equalize all the forces, you are going to be going slower.