Well, I have some luck learning from this place, thanks to everybody. There was a discussion on the subject of anchoring in a deep water not that long ago, but nobody mention what is actually the problem, necessity to have a long line? Is there something else? And what you'd consider deep water? Dan.
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Dennis Thomas
Scope
For an anchor to work, the pull must be as horizontal as possible. This is the reason for 5:1 or 7:1 scope (anchor rode out = 5 to 7 times water depth). Just how much rode will you be carrying? Two hundred feet of rode restricts you to a maximum depth of 40 feet in normal weather. As the wind picks up, rather than increase scope, you would need another anchor. Additional chain (or other weight on the rode) reduces the amount of scope needed to keep the pull horizontal at the anchor.
For an anchor to work, the pull must be as horizontal as possible. This is the reason for 5:1 or 7:1 scope (anchor rode out = 5 to 7 times water depth). Just how much rode will you be carrying? Two hundred feet of rode restricts you to a maximum depth of 40 feet in normal weather. As the wind picks up, rather than increase scope, you would need another anchor. Additional chain (or other weight on the rode) reduces the amount of scope needed to keep the pull horizontal at the anchor.
Several factors
Dan: Dennis pretty much spelled it out for you. 5:1 scope or better is the rule of thumb if you want to be safe. But there are other things to consider too. First is the bottom. Are you in sand, clay, rock, grass etc. Each anchor has it's strengths and weaknesses. So you should know the bottom and the anchor. Have at least two different types of anchors aboard so you can adapt to the environment. Second is the rode. You can cheat a little if you carry more chain. 6ft is sort of a minimum and 30 is usually very nice to have. If you can store more chain then all the better. The chain will tend to make you anchor lay on the bottom better than a line. Third is the conditions: This is going to probably be the largest single influence. Are you dealing with seas, current, high winds. These factors will incluence the state of affairs when anchoring. Last but not least. Drop you anchor off the boat, Do not throw it. If you throw the anchor it can get tangled in the rode and will probably not set. After it hits the bottom, you can back up or go forward depending on how you are anchoring until you have enough scope out. Then secure the rode to the cleat and put enough force on the anchor with the engine to set in on the bottom. Please be sure that you anchor is set before de-boarding your vessel. I really don't want your vessel on top of mine or see you trying to get off the rocks.
Dan: Dennis pretty much spelled it out for you. 5:1 scope or better is the rule of thumb if you want to be safe. But there are other things to consider too. First is the bottom. Are you in sand, clay, rock, grass etc. Each anchor has it's strengths and weaknesses. So you should know the bottom and the anchor. Have at least two different types of anchors aboard so you can adapt to the environment. Second is the rode. You can cheat a little if you carry more chain. 6ft is sort of a minimum and 30 is usually very nice to have. If you can store more chain then all the better. The chain will tend to make you anchor lay on the bottom better than a line. Third is the conditions: This is going to probably be the largest single influence. Are you dealing with seas, current, high winds. These factors will incluence the state of affairs when anchoring. Last but not least. Drop you anchor off the boat, Do not throw it. If you throw the anchor it can get tangled in the rode and will probably not set. After it hits the bottom, you can back up or go forward depending on how you are anchoring until you have enough scope out. Then secure the rode to the cleat and put enough force on the anchor with the engine to set in on the bottom. Please be sure that you anchor is set before de-boarding your vessel. I really don't want your vessel on top of mine or see you trying to get off the rocks.
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ted
alot of chain
if you dont want to carry 700 ft of rode, then run 100 ft of chain and 300 ft of rope, alot of chain will also keep your anchor on the bottom plus add weight. when your anchoring in 120 ft of water its unrealistic to go 7:1 or even 5:1. if the set up seems to heavy to pull by hand then get a windlass.
if you dont want to carry 700 ft of rode, then run 100 ft of chain and 300 ft of rope, alot of chain will also keep your anchor on the bottom plus add weight. when your anchoring in 120 ft of water its unrealistic to go 7:1 or even 5:1. if the set up seems to heavy to pull by hand then get a windlass.
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Dennis Thomas
Conditions & Scope
I just returned from a charter in the BVI's. The boat had an all chain rode and in one harbour we used !all! of it in 40 ft of water! Why? The wind was near 30 knots and the holding wasn't good. We reset twice and drug at 5:1 scope then moved out and just kept dropping chain till there was no more. At that point it held, but I didn't want to sleep there! The water was clear. We could see the chain being lifted from the bottom! It wasn't just dragging. On almost any reasonable bottom, if the shaft of the anchor stays horizontal it will dig in and hold. If the shaft lifts, the anchor drags. Imagine standing on an open dock holding your boat by the anchor rode. You can't cleat it down, you can't wrap the line around a post. Just hold it. That force, applied slowly by the wind, lifts the rode from the bottom until the weight of the rode equals the force of the wind. In a good blow it will lift all of your line, including the chain. If you have enough scope, the pull will still be nearly horizontal even when all of your rode is lifted from the bottom. Then it's just how well is the anchor dug in until it starts to drag. Sure, there are lots of days when 3:1 scope holds fine. On this same recent trip, while snorkeling at the Baths, I saw a boat with less that 1:1 staying in postion. But you could see the drag marks for 50 yards until the anchor hit a rock! Conditions change. Never assume you are anchored safely until you have out at least 5:1 OR GREATER. In some cases where deep water comes in near shore, you do your best, then run a second line to a tree or rock ashore or to a second anchor in shallow water near shore. At Lake Powell in Utah, for instance, the water is so deep right up to the beach and the bottom so hard, some boats don't even bother carrying an anchor cause it's never used. You must always run lines ashore!
I just returned from a charter in the BVI's. The boat had an all chain rode and in one harbour we used !all! of it in 40 ft of water! Why? The wind was near 30 knots and the holding wasn't good. We reset twice and drug at 5:1 scope then moved out and just kept dropping chain till there was no more. At that point it held, but I didn't want to sleep there! The water was clear. We could see the chain being lifted from the bottom! It wasn't just dragging. On almost any reasonable bottom, if the shaft of the anchor stays horizontal it will dig in and hold. If the shaft lifts, the anchor drags. Imagine standing on an open dock holding your boat by the anchor rode. You can't cleat it down, you can't wrap the line around a post. Just hold it. That force, applied slowly by the wind, lifts the rode from the bottom until the weight of the rode equals the force of the wind. In a good blow it will lift all of your line, including the chain. If you have enough scope, the pull will still be nearly horizontal even when all of your rode is lifted from the bottom. Then it's just how well is the anchor dug in until it starts to drag. Sure, there are lots of days when 3:1 scope holds fine. On this same recent trip, while snorkeling at the Baths, I saw a boat with less that 1:1 staying in postion. But you could see the drag marks for 50 yards until the anchor hit a rock! Conditions change. Never assume you are anchored safely until you have out at least 5:1 OR GREATER. In some cases where deep water comes in near shore, you do your best, then run a second line to a tree or rock ashore or to a second anchor in shallow water near shore. At Lake Powell in Utah, for instance, the water is so deep right up to the beach and the bottom so hard, some boats don't even bother carrying an anchor cause it's never used. You must always run lines ashore!
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