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#1
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long term mooring design - an engineering question
I have a mooring problem maybe someone has solved befo its a bit
long trying to explain the situation... Background: Weather conditions in winter are re-enforced tradewinds, 20 to 35, blowing down a bay 2 miles long. Wind generated waves reach 4 to 5 feet, max. Many days of calms in between stretches of wind. Summer conditions are mostly calm, with often occuring squalls from any direction, and an occasional hurricane. Early January saw cyclone Heta graze by, with winds of 90 to 100 for about 12 hours. Our boat is on a mooring, in 40 feet of water, at the head of a bay fed by a small stream. The mooring is a 1200lb ships anchor, with 150 feet of 5/8" chain. The chain is attached to an 8 inch diameter galvanized steel ring at appx 10 feet below the surface, to which is attached a 3/8" chain with a mooring ball which holds the chain "up". Attached to this same galvanized steel ring are my one-and-a-half inch diameteer, led thru the bulwark hawsepipe and secured to the sampson posts. The chain/float/mooring lines connection is at 10 feet below the surface due to the high corrosivity in the water here in the top 6 to 8 feet; the junction below that level greatly extends chain/shackle life. There is no swivel, as the weight of the chain (about 6 lbs per foot) binds the swivel upon deployment. I tried this for two years, and can confirm that the swivel is useless. Additionally, of the ten boats here on moorings, two in the last two years have gone aground due to a mooring failure, and each time it has been swivel failure. OK, now for the problem: The wind here is highly variable, with some periods of calms in-between. Boats are oriented by tides, multi-directional winds, and (in calms), by the stream. This results in the boats being rotated around their moorings continuously, with the result of mooring lines twisted around the mooring ball chain. And THIS requires an almost weekly "untwisting" of lines and mooring ball chain. Either in the water to do the untwisting with mask and snorkel, or spinning the boat around the mooring with the dinghy. Its really pretty humourous watching three dinks spinning three boats either clockwise or counter-clockwise at the same time on calm days. I sometimes wonder what people on shore must think... Unfortunately, when its blowing 25 to 30 for three weeks, this is impossible. And if the line is severly twisted when it starts blowing, the coral/barnacle growth on the line combined with the tension caused by windage on the boat literally saws the mooring lines in half. The only solution I can see is to eliminate the mooring ball, and shackle the mooring lines directly onto the 8 inch galvanized steel ring ten feet below the boat. This eliminates the tangling/knots that result, but then puts the mooring chain load directly onto the boat via the hawsepipes. Two boats here have now been doing this for a year, without any apparant problems. They niow wave merrily from deck when the rest of us are "rotating our boats". All boats survived Hetas 90 to 100 knots, but there was adequate time to prepare. Every reference source I can find indicates that using a mooring float is the "correct" procedure. But I cannot get around this snarling of mooring lines and pennant! Other than the danger to the boat, it is getting expensive replacing mooring lines...Anchoring bow and stern is not possible, as we can see winds from the entire quadrant in excess of 40 knots on any particular day. Any ideas welcome. Mitch sv KOMFY American Samoa |
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#2
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long term mooring design - an engineering question
Do any of those using the "direct connect" arrangement have twist/wear
problems at either any of the attachment to the ring or at the point the big chain is attached to the anchor? If not, a way to "unload" the boat/hawsepipes in light conditions would be to put a float very close to the boat, . The float would take the load until heavier water or wind conditions began to take the catenary out of the chain, at which time the load would begin transferring to the boat in any arrangement. "mitch" wrote in message om... I have a mooring problem maybe someone has solved befo its a bit long trying to explain the situation... Background: Weather conditions in winter are re-enforced tradewinds, 20 to 35, blowing down a bay 2 miles long. Wind generated waves reach 4 to 5 feet, max. Many days of calms in between stretches of wind. Summer conditions are mostly calm, with often occuring squalls from any direction, and an occasional hurricane. Early January saw cyclone Heta graze by, with winds of 90 to 100 for about 12 hours. Our boat is on a mooring, in 40 feet of water, at the head of a bay fed by a small stream. The mooring is a 1200lb ships anchor, with 150 feet of 5/8" chain. The chain is attached to an 8 inch diameter galvanized steel ring at appx 10 feet below the surface, to which is attached a 3/8" chain with a mooring ball which holds the chain "up". Attached to this same galvanized steel ring are my one-and-a-half inch diameteer, led thru the bulwark hawsepipe and secured to the sampson posts. The chain/float/mooring lines connection is at 10 feet below the surface due to the high corrosivity in the water here in the top 6 to 8 feet; the junction below that level greatly extends chain/shackle life. There is no swivel, as the weight of the chain (about 6 lbs per foot) binds the swivel upon deployment. I tried this for two years, and can confirm that the swivel is useless. Additionally, of the ten boats here on moorings, two in the last two years have gone aground due to a mooring failure, and each time it has been swivel failure. OK, now for the problem: The wind here is highly variable, with some periods of calms in-between. Boats are oriented by tides, multi-directional winds, and (in calms), by the stream. This results in the boats being rotated around their moorings continuously, with the result of mooring lines twisted around the mooring ball chain. And THIS requires an almost weekly "untwisting" of lines and mooring ball chain. Either in the water to do the untwisting with mask and snorkel, or spinning the boat around the mooring with the dinghy. Its really pretty humourous watching three dinks spinning three boats either clockwise or counter-clockwise at the same time on calm days. I sometimes wonder what people on shore must think... Unfortunately, when its blowing 25 to 30 for three weeks, this is impossible. And if the line is severly twisted when it starts blowing, the coral/barnacle growth on the line combined with the tension caused by windage on the boat literally saws the mooring lines in half. The only solution I can see is to eliminate the mooring ball, and shackle the mooring lines directly onto the 8 inch galvanized steel ring ten feet below the boat. This eliminates the tangling/knots that result, but then puts the mooring chain load directly onto the boat via the hawsepipes. Two boats here have now been doing this for a year, without any apparant problems. They niow wave merrily from deck when the rest of us are "rotating our boats". All boats survived Hetas 90 to 100 knots, but there was adequate time to prepare. Every reference source I can find indicates that using a mooring float is the "correct" procedure. But I cannot get around this snarling of mooring lines and pennant! Other than the danger to the boat, it is getting expensive replacing mooring lines...Anchoring bow and stern is not possible, as we can see winds from the entire quadrant in excess of 40 knots on any particular day. Any ideas welcome. Mitch sv KOMFY American Samoa |
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#3
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long term mooring design - an engineering question
Employ a large/huge swivel near the bow of the boat: easily inspected,
convenient to inspect, will prevent the chain from 'hockling' and breaking because the links are 'tangled'. It really doesnt matter WHERE the swivel is located on the chain just as long as there IS a swivel and the swivel is SOMEWHERE between the anchor and the boat! There is no 'magic reason' for a swivel to on or near the anchor. In article , mitch wrote: I have a mooring problem maybe someone has solved befo its a bit long trying to explain the situation... Background: Weather conditions in winter are re-enforced tradewinds, 20 to 35, blowing down a bay 2 miles long. Wind generated waves reach 4 to 5 feet, max. Many days of calms in between stretches of wind. Summer conditions are mostly calm, with often occuring squalls from any direction, and an occasional hurricane. Early January saw cyclone Heta graze by, with winds of 90 to 100 for about 12 hours. Our boat is on a mooring, in 40 feet of water, at the head of a bay fed by a small stream. The mooring is a 1200lb ships anchor, with 150 feet of 5/8" chain. The chain is attached to an 8 inch diameter galvanized steel ring at appx 10 feet below the surface, to which is attached a 3/8" chain with a mooring ball which holds the chain "up". Attached to this same galvanized steel ring are my one-and-a-half inch diameteer, led thru the bulwark hawsepipe and secured to the sampson posts. The chain/float/mooring lines connection is at 10 feet below the surface due to the high corrosivity in the water here in the top 6 to 8 feet; the junction below that level greatly extends chain/shackle life. There is no swivel, as the weight of the chain (about 6 lbs per foot) binds the swivel upon deployment. I tried this for two years, and can confirm that the swivel is useless. Additionally, of the ten boats here on moorings, two in the last two years have gone aground due to a mooring failure, and each time it has been swivel failure. OK, now for the problem: The wind here is highly variable, with some periods of calms in-between. Boats are oriented by tides, multi-directional winds, and (in calms), by the stream. This results in the boats being rotated around their moorings continuously, with the result of mooring lines twisted around the mooring ball chain. And THIS requires an almost weekly "untwisting" of lines and mooring ball chain. Either in the water to do the untwisting with mask and snorkel, or spinning the boat around the mooring with the dinghy. Its really pretty humourous watching three dinks spinning three boats either clockwise or counter-clockwise at the same time on calm days. I sometimes wonder what people on shore must think... Unfortunately, when its blowing 25 to 30 for three weeks, this is impossible. And if the line is severly twisted when it starts blowing, the coral/barnacle growth on the line combined with the tension caused by windage on the boat literally saws the mooring lines in half. The only solution I can see is to eliminate the mooring ball, and shackle the mooring lines directly onto the 8 inch galvanized steel ring ten feet below the boat. This eliminates the tangling/knots that result, but then puts the mooring chain load directly onto the boat via the hawsepipes. Two boats here have now been doing this for a year, without any apparant problems. They niow wave merrily from deck when the rest of us are "rotating our boats". All boats survived Hetas 90 to 100 knots, but there was adequate time to prepare. Every reference source I can find indicates that using a mooring float is the "correct" procedure. But I cannot get around this snarling of mooring lines and pennant! Other than the danger to the boat, it is getting expensive replacing mooring lines...Anchoring bow and stern is not possible, as we can see winds from the entire quadrant in excess of 40 knots on any particular day. Any ideas welcome. Mitch sv KOMFY American Samoa |
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#4
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long term mooring design - an engineering question
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#5
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long term mooring design - an engineering question
You have had several good suggestions. My 40' steel yacht is moored in a bay
where we get Typhoons (hurricanes) a couple of times a year, although the maximum fetch is less than 1 mile. Every moored boat here, and there are at least 500, uses a similar can buoy which supports the mooring chain. This can buoy has a hole through the middle through which the chain goes, ending in a metal ring protruding upwards. To this is shackled a very large swivel, always of stainless. We then use a nylon bridle (two lengths of heavy nylon which, in my case, are about 10' long). Each has a soft spliced eye in one the end whilst the other end has a hard eye shackled to the swivel. When we are off sailing, this bridle is left floating, with the end supported by a very small float (often a soft drink bottle) to ease the pick up. The eyes are taken across the deck through a fairlead to the opposite side and put over a pair of bits either side of the stem. If a storm is imminent, I use lashings to ensure that the eyes cannot come off the bits. These bridles are replaced every two years, as they suffer from the UV. Nothing ever tangles, even in the worst conditions. I know of no case of swivels failing, except on moorings which have had no maintenance. Incidentally, the edge of the buoy has tyre or an old piece of carpet fixed to it to protect the stem in calm conditions. Arni "mitch" wrote in message om... I have a mooring problem maybe someone has solved befo its a bit long trying to explain the situation... Background: Weather conditions in winter are re-enforced tradewinds, 20 to 35, blowing down a bay 2 miles long. Wind generated waves reach 4 to 5 feet, max. Many days of calms in between stretches of wind. Summer conditions are mostly calm, with often occuring squalls from any direction, and an occasional hurricane. Early January saw cyclone Heta graze by, with winds of 90 to 100 for about 12 hours. Our boat is on a mooring, in 40 feet of water, at the head of a bay fed by a small stream. The mooring is a 1200lb ships anchor, with 150 feet of 5/8" chain. The chain is attached to an 8 inch diameter galvanized steel ring at appx 10 feet below the surface, to which is attached a 3/8" chain with a mooring ball which holds the chain "up". Attached to this same galvanized steel ring are my one-and-a-half inch diameteer, led thru the bulwark hawsepipe and secured to the sampson posts. The chain/float/mooring lines connection is at 10 feet below the surface due to the high corrosivity in the water here in the top 6 to 8 feet; the junction below that level greatly extends chain/shackle life. There is no swivel, as the weight of the chain (about 6 lbs per foot) binds the swivel upon deployment. I tried this for two years, and can confirm that the swivel is useless. Additionally, of the ten boats here on moorings, two in the last two years have gone aground due to a mooring failure, and each time it has been swivel failure. OK, now for the problem: The wind here is highly variable, with some periods of calms in-between. Boats are oriented by tides, multi-directional winds, and (in calms), by the stream. This results in the boats being rotated around their moorings continuously, with the result of mooring lines twisted around the mooring ball chain. And THIS requires an almost weekly "untwisting" of lines and mooring ball chain. Either in the water to do the untwisting with mask and snorkel, or spinning the boat around the mooring with the dinghy. Its really pretty humourous watching three dinks spinning three boats either clockwise or counter-clockwise at the same time on calm days. I sometimes wonder what people on shore must think... Unfortunately, when its blowing 25 to 30 for three weeks, this is impossible. And if the line is severly twisted when it starts blowing, the coral/barnacle growth on the line combined with the tension caused by windage on the boat literally saws the mooring lines in half. The only solution I can see is to eliminate the mooring ball, and shackle the mooring lines directly onto the 8 inch galvanized steel ring ten feet below the boat. This eliminates the tangling/knots that result, but then puts the mooring chain load directly onto the boat via the hawsepipes. Two boats here have now been doing this for a year, without any apparant problems. They niow wave merrily from deck when the rest of us are "rotating our boats". All boats survived Hetas 90 to 100 knots, but there was adequate time to prepare. Every reference source I can find indicates that using a mooring float is the "correct" procedure. But I cannot get around this snarling of mooring lines and pennant! Other than the danger to the boat, it is getting expensive replacing mooring lines...Anchoring bow and stern is not possible, as we can see winds from the entire quadrant in excess of 40 knots on any particular day. Any ideas welcome. Mitch sv KOMFY American Samoa |
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#6
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long term mooring design - an engineering question
The solution is to get the hell outta Amer Samoa and go cruising. You
been there too long already. "mitch" wrote in message . com... I have a mooring problem maybe someone has solved befo its a bit long trying to explain the situation... Background: Weather conditions in winter are re-enforced tradewinds, 20 to 35, blowing down a bay 2 miles long. Wind generated waves reach 4 to 5 feet, max. Many days of calms in between stretches of wind. Summer conditions are mostly calm, with often occuring squalls from any direction, and an occasional hurricane. Early January saw cyclone Heta graze by, with winds of 90 to 100 for about 12 hours. Our boat is on a mooring, in 40 feet of water, at the head of a bay fed by a small stream. The mooring is a 1200lb ships anchor, with 150 feet of 5/8" chain. The chain is attached to an 8 inch diameter galvanized steel ring at appx 10 feet below the surface, to which is attached a 3/8" chain with a mooring ball which holds the chain "up". Attached to this same galvanized steel ring are my one-and-a-half inch diameteer, led thru the bulwark hawsepipe and secured to the sampson posts. The chain/float/mooring lines connection is at 10 feet below the surface due to the high corrosivity in the water here in the top 6 to 8 feet; the junction below that level greatly extends chain/shackle life. There is no swivel, as the weight of the chain (about 6 lbs per foot) binds the swivel upon deployment. I tried this for two years, and can confirm that the swivel is useless. Additionally, of the ten boats here on moorings, two in the last two years have gone aground due to a mooring failure, and each time it has been swivel failure. OK, now for the problem: The wind here is highly variable, with some periods of calms in-between. Boats are oriented by tides, multi-directional winds, and (in calms), by the stream. This results in the boats being rotated around their moorings continuously, with the result of mooring lines twisted around the mooring ball chain. And THIS requires an almost weekly "untwisting" of lines and mooring ball chain. Either in the water to do the untwisting with mask and snorkel, or spinning the boat around the mooring with the dinghy. Its really pretty humourous watching three dinks spinning three boats either clockwise or counter-clockwise at the same time on calm days. I sometimes wonder what people on shore must think... Unfortunately, when its blowing 25 to 30 for three weeks, this is impossible. And if the line is severly twisted when it starts blowing, the coral/barnacle growth on the line combined with the tension caused by windage on the boat literally saws the mooring lines in half. The only solution I can see is to eliminate the mooring ball, and shackle the mooring lines directly onto the 8 inch galvanized steel ring ten feet below the boat. This eliminates the tangling/knots that result, but then puts the mooring chain load directly onto the boat via the hawsepipes. Two boats here have now been doing this for a year, without any apparant problems. They niow wave merrily from deck when the rest of us are "rotating our boats". All boats survived Hetas 90 to 100 knots, but there was adequate time to prepare. Every reference source I can find indicates that using a mooring float is the "correct" procedure. But I cannot get around this snarling of mooring lines and pennant! Other than the danger to the boat, it is getting expensive replacing mooring lines...Anchoring bow and stern is not possible, as we can see winds from the entire quadrant in excess of 40 knots on any particular day. Any ideas welcome. Mitch sv KOMFY American Samoa |
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