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Sep. 15th, 2022 10:20 am![[personal profile]](https://www.dreamwidth.org/img/silk/identity/user.png){kind=small}
scrottieBraindumping on lightly ballasted vs heavily and/or deep ballasted sailboats.
Lightly ballasted sailboats need to be able to turn very quickly and sharply to tack through the wind without the wind and waves stopping them cold before making it through. Ballast besides righting the boat is essential for her making way.
Righting is more complicated. Older boats tend to have hulls that taper back on the transom, optimized for less water resistance at lower speeds. Newer boats stay wide from the widest point all of the way back for more hull stability. Wide, flat hull (both relative) is hull that resists heeling. This is "hull form stability" and it's the main or only stability against heeling and capsize that sailing dinghies have. If the hull is flat enough on the bottom that it both acts as a long lever against heeling and allows the boat to go up on a plane and break out of the water mostly completely, so much the better. But flat hulls pound and slap and crash on waves and drag in lower wind when there isn't enough power to break them out on to a plane, which is hard to do unless there's good wind and the boat and everything aboard is really, really light.
Ballast is part of this lever too. Pythagoras applies at least for the simplification (naval architecture and hull design looks at every angle of heel and tries to optimize for expected or intended conditions). In one extreme, catamarans are typically unballasted, but have a very wide stance. The lever is from the center of heeling forces on the sail (which may be partially heeled to one side) all of the way out to the center of floatation on the leeward hull of the double hulls. In the other extreme, you have a monohull sailboat with a "fine hull", like a Cape Dory 30 or a Nordic Folkboat, that's narrow and a sharped "V" shape. There's not much hanging out side and buoyant to keep the boat from heeling, so the lever is from the ballast from the to the center of the heeling on the sail. If the ballast were to fall off, the buoyancy in the deep "V" shape would immediately knock her on her side. In the case of the extremely fine hull, the hull without ballast is anti-stable.
Typically, the hull extends out over the unheeled waterline so provide righting force when the hull does heel (overhangs, which were also historically used to cheat on length-at-waterline rules in racing regulation, which is another topic, but hull length limits speed until the boat goes up on a plane).
Most monohulls are a mix of both, so, pythagoras. If you have a wide hull (beamy) with a lot of floatation off to the side to keep her up (remember, sailboats basically have a radio tower mounted on them, then pin up the largest piece of cloth they can find to it), and that hull also has some ballast attached below it, then there are two righting forces to keep her up. Sounds great, but if you have a wide boat with a lot of weight on here, then you run in to another problem that slows you down, in that the weight is pulling a lot of hull surface area in to the water, and water going over a lot of surface area creates drag and slows you down. So, you typically see wide with a little ballast, or a lot of ballast and a little width, for cruising boats. Deep ballast (long lever) with most of the weight in a bulb at the bottom is common on newer boats but that righting lever is also a lever for ripping the ballast off and leaving you with a huge hole in your hull if you screw up, and we already talked about ballast and a narrow hull, so she'll sink in the most cartoonish fashion possible, but flopping over and going down like a brick, which helps explain why there's a rift between cruising boats and racing boats.
The "V" of the hull that isn't ballast poking down in to the water, if it is "V" shaped instead of "U" shaped (wineglass turn of the bilge, or "slack bilges") adds instability. If you have a wide hull and a slack bilge, she'll want to start heeling, then after a point, will resist heeling. This can be concerning as you'll think, holy cow, this boat is just going to tip right over!, when she easily starts to heel. And this is typical of 60s and 70s sailboats. Two other things happen to stop the boat from actually falling over, tho. The sail being at an angle dumps wind, which self-regulates up to a point. Also, the ballast as a lever isn't only the length of the lever and weight, it also becomes strong the more of an angle it is at, being strongest when (and if) it's sticking out 90 degrees to the side (which is a "knockdown") and out of the water.
Some boats with wide, flat hulls and very light ballast don't have enough ballast to right themselves even in this extreme case where they should be able to, unless you pull in the (now wet and full of scooped up water) sails.
Other boats that can right themselves break their masts only then, when the sails have scooped up thousands of gallons of water, thousands of pounds of lead lifted out of the water are trying to lift that water, and a wide, rounded hull floating all of that is acting as a fulcrum.
Brief review:
Catamaran: Likely have to gybe instead of tack if it's windy. Tends not to get knocked over, but when one does, you're screwed. Newer/most models are designed to drop the rig before they capsize but this is not reliable.
Fine hulled heavy ballasted sailboat: Enough mass to make it through tacks, less hull surface area than anything except a flat hulled planing boat so relatively fast, cannot plane, hope to heck that lead keel doesn't fall off or same situation as a capsized catamaran.
Round bottomed boat: Probably has enough keel lead to right herself without going capsized catamaran. Probably. Maximum hull surface area, but the hull at least stays more boat shaped if she does heel so sailing a bit sideways still manages to mostly work. May not be able to tack.
Flat bottomed lightly ballasted boat: Likely have to gybe instead of tack if it's windy. Basically a catamaran with more hull surface area water resistance. Depending on the ballast and crew efforts, may be able to recover from a capsize.
Lightly ballasted sailboats need to be able to turn very quickly and sharply to tack through the wind without the wind and waves stopping them cold before making it through. Ballast besides righting the boat is essential for her making way.
Righting is more complicated. Older boats tend to have hulls that taper back on the transom, optimized for less water resistance at lower speeds. Newer boats stay wide from the widest point all of the way back for more hull stability. Wide, flat hull (both relative) is hull that resists heeling. This is "hull form stability" and it's the main or only stability against heeling and capsize that sailing dinghies have. If the hull is flat enough on the bottom that it both acts as a long lever against heeling and allows the boat to go up on a plane and break out of the water mostly completely, so much the better. But flat hulls pound and slap and crash on waves and drag in lower wind when there isn't enough power to break them out on to a plane, which is hard to do unless there's good wind and the boat and everything aboard is really, really light.
Ballast is part of this lever too. Pythagoras applies at least for the simplification (naval architecture and hull design looks at every angle of heel and tries to optimize for expected or intended conditions). In one extreme, catamarans are typically unballasted, but have a very wide stance. The lever is from the center of heeling forces on the sail (which may be partially heeled to one side) all of the way out to the center of floatation on the leeward hull of the double hulls. In the other extreme, you have a monohull sailboat with a "fine hull", like a Cape Dory 30 or a Nordic Folkboat, that's narrow and a sharped "V" shape. There's not much hanging out side and buoyant to keep the boat from heeling, so the lever is from the ballast from the to the center of the heeling on the sail. If the ballast were to fall off, the buoyancy in the deep "V" shape would immediately knock her on her side. In the case of the extremely fine hull, the hull without ballast is anti-stable.
Typically, the hull extends out over the unheeled waterline so provide righting force when the hull does heel (overhangs, which were also historically used to cheat on length-at-waterline rules in racing regulation, which is another topic, but hull length limits speed until the boat goes up on a plane).
Most monohulls are a mix of both, so, pythagoras. If you have a wide hull (beamy) with a lot of floatation off to the side to keep her up (remember, sailboats basically have a radio tower mounted on them, then pin up the largest piece of cloth they can find to it), and that hull also has some ballast attached below it, then there are two righting forces to keep her up. Sounds great, but if you have a wide boat with a lot of weight on here, then you run in to another problem that slows you down, in that the weight is pulling a lot of hull surface area in to the water, and water going over a lot of surface area creates drag and slows you down. So, you typically see wide with a little ballast, or a lot of ballast and a little width, for cruising boats. Deep ballast (long lever) with most of the weight in a bulb at the bottom is common on newer boats but that righting lever is also a lever for ripping the ballast off and leaving you with a huge hole in your hull if you screw up, and we already talked about ballast and a narrow hull, so she'll sink in the most cartoonish fashion possible, but flopping over and going down like a brick, which helps explain why there's a rift between cruising boats and racing boats.
The "V" of the hull that isn't ballast poking down in to the water, if it is "V" shaped instead of "U" shaped (wineglass turn of the bilge, or "slack bilges") adds instability. If you have a wide hull and a slack bilge, she'll want to start heeling, then after a point, will resist heeling. This can be concerning as you'll think, holy cow, this boat is just going to tip right over!, when she easily starts to heel. And this is typical of 60s and 70s sailboats. Two other things happen to stop the boat from actually falling over, tho. The sail being at an angle dumps wind, which self-regulates up to a point. Also, the ballast as a lever isn't only the length of the lever and weight, it also becomes strong the more of an angle it is at, being strongest when (and if) it's sticking out 90 degrees to the side (which is a "knockdown") and out of the water.
Some boats with wide, flat hulls and very light ballast don't have enough ballast to right themselves even in this extreme case where they should be able to, unless you pull in the (now wet and full of scooped up water) sails.
Other boats that can right themselves break their masts only then, when the sails have scooped up thousands of gallons of water, thousands of pounds of lead lifted out of the water are trying to lift that water, and a wide, rounded hull floating all of that is acting as a fulcrum.
Brief review:
Catamaran: Likely have to gybe instead of tack if it's windy. Tends not to get knocked over, but when one does, you're screwed. Newer/most models are designed to drop the rig before they capsize but this is not reliable.
Fine hulled heavy ballasted sailboat: Enough mass to make it through tacks, less hull surface area than anything except a flat hulled planing boat so relatively fast, cannot plane, hope to heck that lead keel doesn't fall off or same situation as a capsized catamaran.
Round bottomed boat: Probably has enough keel lead to right herself without going capsized catamaran. Probably. Maximum hull surface area, but the hull at least stays more boat shaped if she does heel so sailing a bit sideways still manages to mostly work. May not be able to tack.
Flat bottomed lightly ballasted boat: Likely have to gybe instead of tack if it's windy. Basically a catamaran with more hull surface area water resistance. Depending on the ballast and crew efforts, may be able to recover from a capsize.
