Would I be correct in saying:: 1.3 multiplied by the square root of waterline length will give the hull speed of the 260? So the answer!!
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Warren M.
Hull speed is theoretically 1.34 times the square root of your waterline. The key word is "theoretically." The formula needs to be adjusted according to the hull design and displacement of your boat. The formula is, IMHO, only a general guide to how fast your boat will sail.
Yes and no
There are a lot of conditions that also have a lot to do with hull speed. For instance your boat will go a lot faster if the tide is behind you and a lot slower if its in front of you. Heavy wave action will slow down a boat if your going into them but if your surfing down big swells you'll be surprised what the speed can reach. I have a boat not known for its speed with 22 feet in the water. I was sailing upright on a broad reach last summer in Penobscott Bay Maine doing 7.6 knots. Everything was working in my favor.
There are a lot of conditions that also have a lot to do with hull speed. For instance your boat will go a lot faster if the tide is behind you and a lot slower if its in front of you. Heavy wave action will slow down a boat if your going into them but if your surfing down big swells you'll be surprised what the speed can reach. I have a boat not known for its speed with 22 feet in the water. I was sailing upright on a broad reach last summer in Penobscott Bay Maine doing 7.6 knots. Everything was working in my favor.
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Mark
Yes wel Rich I understasnd all that
But there is in theory a "boat speed". So with the Hunter 260 being I think about 22' on the water line what is its hull speed??
But there is in theory a "boat speed". So with the Hunter 260 being I think about 22' on the water line what is its hull speed??
Mark, I think your formula is right
The square root of your 22 foot waterline is 4.7. Times that by the given 1.3 and your hull speed is 6.1 knots (7 mph or 11.3 kmh). I've seen boat manufactors indicate there constant (the 1.3) is higher due to hull shape or another. But 1.3 seems to be the standard for monohulls.
The square root of your 22 foot waterline is 4.7. Times that by the given 1.3 and your hull speed is 6.1 knots (7 mph or 11.3 kmh). I've seen boat manufactors indicate there constant (the 1.3) is higher due to hull shape or another. But 1.3 seems to be the standard for monohulls.
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Ed
Mark you are correct.
A displacement hull boat can only sail at it's theoretical hull speed or less. Usally less. That speed is 1.34 times the square root of the water line. This is due to physics and is not surmountable by any type of engine or other thrust applied. Remember that is the Theoretical speed. Read that to mean that any growth, turbulence inefficencies of the hull design will slow down this speed. Often on this site I have seen incredibally high speeds that boats have accomplished. They are probably not calculating the speed of the water that they are sailing in. Specifically your hull speed limits you to the speed you can move through the water, not the speed over ground. Soooooo - if the water is going with you, such as tidal flow, surfing down a wave front on a thirty foot wave etc. you will not exceed and will probably never reach your thepretical hull speed, but will travel the speed of the water movement plus the speed you are advancing through the water combined to make speed over ground, or the speed measured by your GPS. I am sure someone will dispute this. Do a search on your computer and look for theoretical hull speed and displacement hull and it will explaing the nitty gritty of bow and stern waves and the need for the boat to "displace it's own weight in water" or it would sink. (this applies only to a displacement hull) That is why a larger boat often has a larger crusing area - not simply because of seaworthyness, but because of the additional distance it can cover over a given time frame. I used to sail in Fishers Island Sound in a 240, ventured out in the ocean in my 320, but would make much longer passages in my 426 due in great part to the distance I could cover in a day. That being said remember it is a formula with a square route invoved so even though the water line doubles the hull speed doesn't. In you specific instance the 260 would have a speed of 6.46 due to it's 23'3" water line, the 44 DS would top out at 8.36 with a 39' water line. Dosen't sound like much of a difference, but it is almost 30% faster and in the course of a ten hour sail represents 19 nautical miles further you can travel. All this assumes straight line motion and the entire trip at hull speed, not too likely!! All this makes me want to by another boat! Have fun sailing!
A displacement hull boat can only sail at it's theoretical hull speed or less. Usally less. That speed is 1.34 times the square root of the water line. This is due to physics and is not surmountable by any type of engine or other thrust applied. Remember that is the Theoretical speed. Read that to mean that any growth, turbulence inefficencies of the hull design will slow down this speed. Often on this site I have seen incredibally high speeds that boats have accomplished. They are probably not calculating the speed of the water that they are sailing in. Specifically your hull speed limits you to the speed you can move through the water, not the speed over ground. Soooooo - if the water is going with you, such as tidal flow, surfing down a wave front on a thirty foot wave etc. you will not exceed and will probably never reach your thepretical hull speed, but will travel the speed of the water movement plus the speed you are advancing through the water combined to make speed over ground, or the speed measured by your GPS. I am sure someone will dispute this. Do a search on your computer and look for theoretical hull speed and displacement hull and it will explaing the nitty gritty of bow and stern waves and the need for the boat to "displace it's own weight in water" or it would sink. (this applies only to a displacement hull) That is why a larger boat often has a larger crusing area - not simply because of seaworthyness, but because of the additional distance it can cover over a given time frame. I used to sail in Fishers Island Sound in a 240, ventured out in the ocean in my 320, but would make much longer passages in my 426 due in great part to the distance I could cover in a day. That being said remember it is a formula with a square route invoved so even though the water line doubles the hull speed doesn't. In you specific instance the 260 would have a speed of 6.46 due to it's 23'3" water line, the 44 DS would top out at 8.36 with a 39' water line. Dosen't sound like much of a difference, but it is almost 30% faster and in the course of a ten hour sail represents 19 nautical miles further you can travel. All this assumes straight line motion and the entire trip at hull speed, not too likely!! All this makes me want to by another boat! Have fun sailing!
M
Mark
My two cents on hull speed
Hull speed is the theoretical maximum speed of a displacement hull through water. It's not the speed over ground (SOG) that you get with a GPS and is not affected by current. However, the key word is "theoretical". Among other things, the formula doesn't consider hull shape. A modern, light-weight, beamy, fin-keeled hull is certainly faster than a narrow, traditional full-keeled hull. Also, if the hull is capable of planing (fine entry and flatter section aft) and the rig is powerful enough, the bow can rise clear of the water and its wave disappears. Since the trough is eliminated, resistance to the hull's movement is reduced and the boat accelerates. That's why small high-performance dinghies and windsurfers can sail at double-digit speeds, especially upwind and reaching, where the apparent wind works in their favor. Finally, boats surf when gravity aids their forward motion. It usually happens on the face of a wave. The effect is heightened by the forward motion of the wave. However, not all boats surf, some surf more easily than others and if left alone a surfing boat slows down on the back of the wave. Surfing is an effective downwind technique so racers will try to do it as long as possible. Peter H23 "Raven"
Hull speed is the theoretical maximum speed of a displacement hull through water. It's not the speed over ground (SOG) that you get with a GPS and is not affected by current. However, the key word is "theoretical". Among other things, the formula doesn't consider hull shape. A modern, light-weight, beamy, fin-keeled hull is certainly faster than a narrow, traditional full-keeled hull. Also, if the hull is capable of planing (fine entry and flatter section aft) and the rig is powerful enough, the bow can rise clear of the water and its wave disappears. Since the trough is eliminated, resistance to the hull's movement is reduced and the boat accelerates. That's why small high-performance dinghies and windsurfers can sail at double-digit speeds, especially upwind and reaching, where the apparent wind works in their favor. Finally, boats surf when gravity aids their forward motion. It usually happens on the face of a wave. The effect is heightened by the forward motion of the wave. However, not all boats surf, some surf more easily than others and if left alone a surfing boat slows down on the back of the wave. Surfing is an effective downwind technique so racers will try to do it as long as possible. Peter H23 "Raven"
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Ed
Last comment
Yes, new hulls are faster - that is why older types can't approach their hull speed, and the newer ones can APPROACH theoretical speed. The reason dighys and other types of boats can sail at faster speeds is that they are semi displacement or non displacement hulls. Cats are almost unlimited and have good stability. There are motor sailors that you can water sky behind - but alas they are not full displacemnt boats so sail rougher in heavy seas. In conclution newer designs do take advantage of better design and will sail faster than most older designs, but I am not too sure they can "lift out of the water" on a plane. At least none of the 40 foot keel boats I have seen. But who knows, quatum physics proffesors never thought there was such a thing as a quark, maybe someone at Hunter is working on a breakthrough to change the laws of physics as we know them.
Yes, new hulls are faster - that is why older types can't approach their hull speed, and the newer ones can APPROACH theoretical speed. The reason dighys and other types of boats can sail at faster speeds is that they are semi displacement or non displacement hulls. Cats are almost unlimited and have good stability. There are motor sailors that you can water sky behind - but alas they are not full displacemnt boats so sail rougher in heavy seas. In conclution newer designs do take advantage of better design and will sail faster than most older designs, but I am not too sure they can "lift out of the water" on a plane. At least none of the 40 foot keel boats I have seen. But who knows, quatum physics proffesors never thought there was such a thing as a quark, maybe someone at Hunter is working on a breakthrough to change the laws of physics as we know them.
D
David Foster
Exceeding hull speed
Hull speed is not a limit. I is the approximate speed where a significant increase in power is needed to lift a vessel out of the bow wave that has lengthened with increasing speed until it is the same length as the waterline. The added force can come from the wind, or gravity (moving down the face of a wind-driven wave. Once the boat has moved onto the bow wave, it is planing. Some hull designs as already described are better at achieving and holding a plane. The Cal 40 first applied such a design to winning ocean races. Of course, lower weight makes it easier to move up onto a plane. Some older hull designs lengthen the waterline as the boat heels, but this small, dymanic increase in waterline length only adds a few tneths of a knot to the hull speed. Our '77 h27 weighs about a ton more than her modern sisters, and does not have a hull designed for planing. But in great reaching conditions, we have averaged one knot over hull speed for an hour or more on more than one occasion. We need great reaching winds, and a good sea state, but a displacement hull can sustain speeds over hull speed. David Lady Lillie
Hull speed is not a limit. I is the approximate speed where a significant increase in power is needed to lift a vessel out of the bow wave that has lengthened with increasing speed until it is the same length as the waterline. The added force can come from the wind, or gravity (moving down the face of a wind-driven wave. Once the boat has moved onto the bow wave, it is planing. Some hull designs as already described are better at achieving and holding a plane. The Cal 40 first applied such a design to winning ocean races. Of course, lower weight makes it easier to move up onto a plane. Some older hull designs lengthen the waterline as the boat heels, but this small, dymanic increase in waterline length only adds a few tneths of a knot to the hull speed. Our '77 h27 weighs about a ton more than her modern sisters, and does not have a hull designed for planing. But in great reaching conditions, we have averaged one knot over hull speed for an hour or more on more than one occasion. We need great reaching winds, and a good sea state, but a displacement hull can sustain speeds over hull speed. David Lady Lillie
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