08-13-2007, 10:37 AM
08-13-2007, 04:51 PM
Personally I like loose footed mainsails, but there are things to consider. The boom must be stronger then the minimum necessary on an attached foot boom. With a Vacationer (Weekender too), most opt for a solid boom which is overly strong. The additional weight of the solid boom helps maintain sail shape as the sheet is freed up. This is normally controlled by a boom vang, but gaffers typically don't use this tackle, so the boom can rise as the sheets are eased. This rising boom bags the sail unnecessarily and spoils sail shape. The heavy boom helps with this to some degree and the reasoning behind electing to use a solid boom.
In any case the boom and it's attachment at the mast (gooseneck) have to tolerate much higher compression loads on a loose footed main. This is because the sail is only attached at two locations, so all the forces are transmitted through these points. This is why the boom must be strong on a loose foot mainsail.
In heavy air, the loose footed main will shake, which kicks off the wind that has attached itself to the leeward side. This isn't an issue except in a healthy blow, where the loose footed main will depower from the excessive shaking. In the wind strengths these boats generally see, you'll probably not have a problem with this, though around 20 knots, you see noticeable shaking and this is hard on the sail and gear.
Another point to consider about loose footed mains is the "end plate effect". The boom on an attached foot sail acts as an end plate, much like those used on rudders, fin keels and STAL strips on aircraft wings. The principles are the same, they slow down the bleed off of high pressure (windward side) to the low pressure side (leeward). A basic rule of physics is that high pressure always seeks low pressure. On a sail (or boat hull, fin, rudder, etc.) the high pressure air will try to escape around the edges of the sail and bleed off into the low pressure side. Ideally, if you can prevent this (you can't) or slow this down you'll get increased efficiency. If the boom is attached to the foot (and is kept close to it, if not touching) the air will slide down the belly and attempt to escape off the foot, but is hampered by the bulk of the boom. This cause the air to "pile up" along the foot, further increasing the pressure on the windward side. A loose footed main, doesn't have this luxury and the air just slides right off the foot. Most racers take advantage of this feature and design their booms to have a flat top, to best block the air flow.
It's easier to make a loose footed sail and it holds a better foil shape along it's length then an attached foot. In recent years, many racers have switched to loose foot mains for this reason. They figure the lose in foot bleed off is offset by the better sail shape. In heavier air the boomed sail is at an advantage, but in light air (which most of us sail in, including racers) the loose foot has things to offer.
I like the look of a loose foot better and you can gain a slight amount of additional mainsail area, by having the foot droop down, below the boom. In the end it's likely 6 of one and a half a dozen of another, with the way these boats are used.
An added note; a manufactured sail, intended to be attached to a boom, sets like crap if rigged as a loose foot. The other way around is also true (and looks even worse). This is because the sail is cut to taper into a flat plane, along the foot of an attached foot sail, which can't adopt a foil shape, no matter what you do, if it's set "flying" like a loose foot does. The loose foot sail cut, has the full foil shape carried down to the very bottom (foot) of the sail, so if you attach this to a boom, it will bag and wrinkle up like no one's business. You have to use the sail as it's cut.
In any case the boom and it's attachment at the mast (gooseneck) have to tolerate much higher compression loads on a loose footed main. This is because the sail is only attached at two locations, so all the forces are transmitted through these points. This is why the boom must be strong on a loose foot mainsail.
In heavy air, the loose footed main will shake, which kicks off the wind that has attached itself to the leeward side. This isn't an issue except in a healthy blow, where the loose footed main will depower from the excessive shaking. In the wind strengths these boats generally see, you'll probably not have a problem with this, though around 20 knots, you see noticeable shaking and this is hard on the sail and gear.
Another point to consider about loose footed mains is the "end plate effect". The boom on an attached foot sail acts as an end plate, much like those used on rudders, fin keels and STAL strips on aircraft wings. The principles are the same, they slow down the bleed off of high pressure (windward side) to the low pressure side (leeward). A basic rule of physics is that high pressure always seeks low pressure. On a sail (or boat hull, fin, rudder, etc.) the high pressure air will try to escape around the edges of the sail and bleed off into the low pressure side. Ideally, if you can prevent this (you can't) or slow this down you'll get increased efficiency. If the boom is attached to the foot (and is kept close to it, if not touching) the air will slide down the belly and attempt to escape off the foot, but is hampered by the bulk of the boom. This cause the air to "pile up" along the foot, further increasing the pressure on the windward side. A loose footed main, doesn't have this luxury and the air just slides right off the foot. Most racers take advantage of this feature and design their booms to have a flat top, to best block the air flow.
It's easier to make a loose footed sail and it holds a better foil shape along it's length then an attached foot. In recent years, many racers have switched to loose foot mains for this reason. They figure the lose in foot bleed off is offset by the better sail shape. In heavier air the boomed sail is at an advantage, but in light air (which most of us sail in, including racers) the loose foot has things to offer.
I like the look of a loose foot better and you can gain a slight amount of additional mainsail area, by having the foot droop down, below the boom. In the end it's likely 6 of one and a half a dozen of another, with the way these boats are used.
An added note; a manufactured sail, intended to be attached to a boom, sets like crap if rigged as a loose foot. The other way around is also true (and looks even worse). This is because the sail is cut to taper into a flat plane, along the foot of an attached foot sail, which can't adopt a foil shape, no matter what you do, if it's set "flying" like a loose foot does. The loose foot sail cut, has the full foil shape carried down to the very bottom (foot) of the sail, so if you attach this to a boom, it will bag and wrinkle up like no one's business. You have to use the sail as it's cut.
08-13-2007, 07:49 PM
Thanks, Paul,
I had thought that a loose foot and possibly even an outhaul rather than a fixed clew would be a better way to control the shape, but I have no experience with such a rig.
Brett
I had thought that a loose foot and possibly even an outhaul rather than a fixed clew would be a better way to control the shape, but I have no experience with such a rig.
Brett
08-14-2007, 05:21 AM
I fly what I call a semi loose foot main, I tie down the first three grommets on the sail so the sail does not load so much in one spot. I just use a block on the eye bolt at the back of the boom and a small cleat for the out haul. I like this set up because it allows much greater control of the shape of the sail than with the conventional lacing all along the boom. It will allow you to really harden the sail and spill wind before you have to reef or you can let it ballon out on a really light air day to keep it from spilling wind.
01-08-2008, 07:26 PM
Mine has flown loose on only the outhaul and a loop around the mast to hold it aligned with the stick since the first month in the water. Only way to go if your sail is cut for it. Else use like Angie says.