It didn't sound egotistical to me. Granted it sounded a little technical for my limited boat knowledge, but that's just because I'm not a boat guy. I think most of us aren't.
Tom
Tom
Don't move the upline!
- Thread starter TSandM
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jim T.
Guest
Thanks for the reassurance Tom.
I'll make this my last digression/highjack but it does relate to TS&M's original post and account in that some of the same considerations she and Peter had to take into account on the charter boat's anchor line will be the same for one's own boat.
The info. below relates to anchoring in the bottom, but it may pertain even more to anchoring on a wreck, especially before the anchor is additionally tied into the wreck or after it's been moved to another portion of a wreck...
IF one's own boat is using an anchor that's been moved the ratio of scope can easily be reduced not only endangering the divers but the vessel itself if the crew doesn't know the scope has been reduced when a diver moves the anchor.
Here's a brief "primer" for anchoring in the hopes that'll be a help to newer boat owner divers or to just "keep an eye" on whoever your present skipper is...
I guess what's going on is that divers have to take classes and pass tests to become certified and in most states that isn't he case (yet) for boaters. When the two activities/sports are combined it's easy to not know what ya don't know.
I see a lot of lake boaters who simply drop a mushroom anchor to the bottom and are used to counting on the weight of the anchor to keep the boat in place using such anchors in open salt water environments with currents present. (This is a ratio of 1:1 scope).
When a plow, bruce or danforth style anchor is used, a proper ratio of "scope" is called for. Basically the more horizontal the pull on the anchor chain/rode (rope) and anchor is, the better chances of it remaining set is.
5:1 is often recommended (even 7:1) This includes the height from the surface of the water to the bow roller for the anchor. Ex.: in 30' with a 4' height from surface to roller (think of it as 34' now...) multiply 34' X 5=170' of chain/rode to be played out.
In most instances (crowded anchorages, rock encircled small bights/coves, etc.) 3:1 scope is
often used. Commercial fishermen often use 2:1 but personally I think that's kind of nuts.
They also usually have a watch all night or an anchor drag alarm connected to a GPS, etc.
Also different anchor types are appropriate for different bottoms. Danforths are best in sand or mud but are vulnerable to having their holding power halved by spearing a beer can on the bottom with one fluke or even seaweed. They are lighter on deck and more easily stowed (folded) so they are very popular on light motorboats and RIBs. They don't do well on rocky bottoms. Mushroom style anchors do not dig in at all! They hold a vessel by their weight only.
Plow type anchors (CQR) and Bruce (brand) anchors are popular in the PNW.
A section of a minimum of 2 fathoms of chain should always be included in a rope rode to prevent chafe and also to help the anchor to set due to the additional weight near the anchor itself.
Two ways to be "sure" you're dug in are to: either drop the hook while you're still moving downwind and have the anchor swing the boat hard around when it grabs or to drop the hook with about 2:1 scope and back down hard until you're sure the boat has completely stopped
with the engine in reverse for a while-then let out the appropriate total scope and back down again.
Don't back down so quickly that the anchor doesn't get a chance to dig in.
Always do an anchor watch if there is current before leaving the boat (with a knowledgable crew member onboard.)
I like to sleep well at anchor (overnight) so I always use the next size up anchor on the manufacturer's charts for a larger (than my) boat. If using rope/rode on smaller boats, there is a weight that can be lowered down the rope to the anchor/chain with a separate line, called a "messenger line". It can add a lot more holding power while still using relatively light ground tackle. (Anchor, chain, rode.)
Anchoring procedure books I'd recommend are: Chapman's Guide to Seamanship
and in part: Hal Roth's "After 50,000 Miles".
Lynne and Peter, hope you didn't mind this additional info. which is a little off base from your original points, yet related and apparently not known by a lot of local boat divers I'm seeing
in the San Juans lately...even folks with 45' trawler yachts who simply kick the anchor and chain over the side, jump in or take their dinghies and go ashore for hours without any anchor watch.
So the related "takeaway point" is: that if a diver moves the anchor the ratio of scope may have been changed as well, possibly putting the vessel at risk IF the skipper and crew aren't aware of the change and the engine isn't fired up.
Even if the vessel is tied in to a wreck, the pitch of the boat and upline can cause more strain with a vertical (1:1) pull than with a bit more scope out.
I'll make this my last digression/highjack but it does relate to TS&M's original post and account in that some of the same considerations she and Peter had to take into account on the charter boat's anchor line will be the same for one's own boat.
The info. below relates to anchoring in the bottom, but it may pertain even more to anchoring on a wreck, especially before the anchor is additionally tied into the wreck or after it's been moved to another portion of a wreck...
IF one's own boat is using an anchor that's been moved the ratio of scope can easily be reduced not only endangering the divers but the vessel itself if the crew doesn't know the scope has been reduced when a diver moves the anchor.
Here's a brief "primer" for anchoring in the hopes that'll be a help to newer boat owner divers or to just "keep an eye" on whoever your present skipper is...
I guess what's going on is that divers have to take classes and pass tests to become certified and in most states that isn't he case (yet) for boaters. When the two activities/sports are combined it's easy to not know what ya don't know.
I see a lot of lake boaters who simply drop a mushroom anchor to the bottom and are used to counting on the weight of the anchor to keep the boat in place using such anchors in open salt water environments with currents present. (This is a ratio of 1:1 scope).
When a plow, bruce or danforth style anchor is used, a proper ratio of "scope" is called for. Basically the more horizontal the pull on the anchor chain/rode (rope) and anchor is, the better chances of it remaining set is.
5:1 is often recommended (even 7:1) This includes the height from the surface of the water to the bow roller for the anchor. Ex.: in 30' with a 4' height from surface to roller (think of it as 34' now...) multiply 34' X 5=170' of chain/rode to be played out.
In most instances (crowded anchorages, rock encircled small bights/coves, etc.) 3:1 scope is
often used. Commercial fishermen often use 2:1 but personally I think that's kind of nuts.
They also usually have a watch all night or an anchor drag alarm connected to a GPS, etc.
Also different anchor types are appropriate for different bottoms. Danforths are best in sand or mud but are vulnerable to having their holding power halved by spearing a beer can on the bottom with one fluke or even seaweed. They are lighter on deck and more easily stowed (folded) so they are very popular on light motorboats and RIBs. They don't do well on rocky bottoms. Mushroom style anchors do not dig in at all! They hold a vessel by their weight only.
Plow type anchors (CQR) and Bruce (brand) anchors are popular in the PNW.
A section of a minimum of 2 fathoms of chain should always be included in a rope rode to prevent chafe and also to help the anchor to set due to the additional weight near the anchor itself.
Two ways to be "sure" you're dug in are to: either drop the hook while you're still moving downwind and have the anchor swing the boat hard around when it grabs or to drop the hook with about 2:1 scope and back down hard until you're sure the boat has completely stopped
with the engine in reverse for a while-then let out the appropriate total scope and back down again.
Don't back down so quickly that the anchor doesn't get a chance to dig in.
Always do an anchor watch if there is current before leaving the boat (with a knowledgable crew member onboard.)
I like to sleep well at anchor (overnight) so I always use the next size up anchor on the manufacturer's charts for a larger (than my) boat. If using rope/rode on smaller boats, there is a weight that can be lowered down the rope to the anchor/chain with a separate line, called a "messenger line". It can add a lot more holding power while still using relatively light ground tackle. (Anchor, chain, rode.)
Anchoring procedure books I'd recommend are: Chapman's Guide to Seamanship
and in part: Hal Roth's "After 50,000 Miles".
Lynne and Peter, hope you didn't mind this additional info. which is a little off base from your original points, yet related and apparently not known by a lot of local boat divers I'm seeing
in the San Juans lately...even folks with 45' trawler yachts who simply kick the anchor and chain over the side, jump in or take their dinghies and go ashore for hours without any anchor watch.
So the related "takeaway point" is: that if a diver moves the anchor the ratio of scope may have been changed as well, possibly putting the vessel at risk IF the skipper and crew aren't aware of the change and the engine isn't fired up.
Even if the vessel is tied in to a wreck, the pitch of the boat and upline can cause more strain with a vertical (1:1) pull than with a bit more scope out.
Interesting. I never heard the term "scope" before. I always thought the amount of anchor line played out on a boat was in relation to the amount of current present. Normally the only boating we do in on a flat lake with no currents down in Arkansas. If the water is still, if there any benefit to playing out any more scope than 1:1? We usually use two anchors, one fore and one aft, to keep us in place.
Tom
Tom
Gilldiver
Contributor
In the northeast where we will normally tie into the wreck, the larger boats and many 6-packs will:
Hook the wreck with an anchor or grapnel.
The boats mate or the first diver/team in will tie in the anchor or grapnel and then signal the boat that the line is tied in. This signal many times is a Styrofoam coffee cup and the Shout "The Cup IS Up," becomes familiar.
The Boat may then motor up the line as the deck crew pulls in as much scope as possible so that the rest of the divers have a minimum amount of line to go down. This can be important in any appreciable current.
The last diver/team down or another mate will untie the line, foul the anchor/grapnel into the line so that it doesn't re-hook and ride and guide the drift out of the wreck
An alternative is to drop a shot line and send the team down that. Once it is tied in, and the signal is made, the boat will then go and pick up the line.
If we will not have someone on the boat, many times will drop a second line down the anchor line and tie it into another location so that both need to pull out or part to get the boat adrift. We will also do this on any morring where no one may be on the boat or where there is any question on the status of the morring.
Hook the wreck with an anchor or grapnel.
The boats mate or the first diver/team in will tie in the anchor or grapnel and then signal the boat that the line is tied in. This signal many times is a Styrofoam coffee cup and the Shout "The Cup IS Up," becomes familiar.
The Boat may then motor up the line as the deck crew pulls in as much scope as possible so that the rest of the divers have a minimum amount of line to go down. This can be important in any appreciable current.
The last diver/team down or another mate will untie the line, foul the anchor/grapnel into the line so that it doesn't re-hook and ride and guide the drift out of the wreck
An alternative is to drop a shot line and send the team down that. Once it is tied in, and the signal is made, the boat will then go and pick up the line.
If we will not have someone on the boat, many times will drop a second line down the anchor line and tie it into another location so that both need to pull out or part to get the boat adrift. We will also do this on any morring where no one may be on the boat or where there is any question on the status of the morring.
Ok, I guess I'll put my 2 psi in,
As I haven't seen anyone responding from NC, I'll explain what our procedure is. We use 2 divemasters, one goes in holding the anchor, which has a safety chain already connected. The boat keeps its engines going to stay over the wreck, as the line is paid out, and the bubbles traced to follow the diver's movements. Once on the wreck, a suitable place is found for the anchor, it is chained in, and a liftbag is attached to keep a solid tension on the line. When the other dm makes his dive, either with the knowledge everyone is onboard, or a ring is dropped down the line. Then we pull, and take a ride
If the anchorage is deemed unfit, we run a line from its old point to the new.
-J
As I haven't seen anyone responding from NC, I'll explain what our procedure is. We use 2 divemasters, one goes in holding the anchor, which has a safety chain already connected. The boat keeps its engines going to stay over the wreck, as the line is paid out, and the bubbles traced to follow the diver's movements. Once on the wreck, a suitable place is found for the anchor, it is chained in, and a liftbag is attached to keep a solid tension on the line. When the other dm makes his dive, either with the knowledge everyone is onboard, or a ring is dropped down the line. Then we pull, and take a ride
If the anchorage is deemed unfit, we run a line from its old point to the new. -J
jim T.
Guest
Try a search on mushroom anchor techniques. Offshoreengineering.org/moorings/history/ had a good site with lots of pics. of various anchors and how they work. I tried to include the link here but it won't work for some reason. Google will get you there.
I've used mushroom anchors for lake fishing as a kid, a lot.
They're held in the bottom by the weight of the anchor and the amount of fill material in the bowl. Silt/Mud.
The problem is they have to penetrate the bottom, usually, by being heavy enough in the lst place to impact the bottom so that they actually fill. There is almost no way (except in gin clear water) to see/know that the thing has buried at all. It'll then be essentially a shot line rather than a dependable anchor.
Their best use is a a permanent mooring buoy where
divers literally bury the bowl in the bottom, sometimes even filling them with concrete. "Empty" they're usually considered to have a holding power of 2X their weight. Filled up to 10 times. They are principally held in place by suction. So...in sand or rock strewn bottoms they're not very useful.
Even though there are no currents on the lake, winds, squalls, curious swimming children
can easily dislodge a mushroom anchor. That's why bass fishermen, etc. can easily lift the anchor up by hauling in the line by hand. If a plow, danforth, Bruce is buried it isn't coming up
until you have 1:1 scope and you'd have to pull quite a bit harder than with a 'shroom. You may have to motor over it and pull it out form the opposite direction. More hassle but safer anchoring...
Adding scope to the mushroom anchor will likely pull/tip one side of the bowl up out of the mud
(unless you've got really really suction-y mud) pretty easily.
See what the 20'-25' (or larger) pleasure boats are using in your area if they're anchoring overnight places. Nothing wrong with a mushroom anchor if an operator is on board but I would be uncomfortable doing an hour's dive on a potentially windy mountain lake with no operator. On a pond-maybe no problem. I've seen bass fishermen's anchors bounce along the bottom when lifted and dropped by chop for quite a distance.
You'd of course have to size down for a larger boat's anchor but I'd still go one size up form whatever tha manufacturer's chart calls for.
Glad this info. is helping someone. If it gets to be too much of a Hi-Jack and deemed too unrelated to the OP guess it can be moved?
What JayJudge was saying about maintaining constant tension is part of this scope thang.
B1country, the amount of scope used does sometimes influence the placement of the "mother" boat over the wreck. How far of a surface swim will it be for the divers, can I anchor on the wreck and still stay clear of my competitor's dive boat, etc. I'm thinking that's what you meant?
I've used mushroom anchors for lake fishing as a kid, a lot.
They're held in the bottom by the weight of the anchor and the amount of fill material in the bowl. Silt/Mud.
The problem is they have to penetrate the bottom, usually, by being heavy enough in the lst place to impact the bottom so that they actually fill. There is almost no way (except in gin clear water) to see/know that the thing has buried at all. It'll then be essentially a shot line rather than a dependable anchor.
Their best use is a a permanent mooring buoy where
divers literally bury the bowl in the bottom, sometimes even filling them with concrete. "Empty" they're usually considered to have a holding power of 2X their weight. Filled up to 10 times. They are principally held in place by suction. So...in sand or rock strewn bottoms they're not very useful.
Even though there are no currents on the lake, winds, squalls, curious swimming children
can easily dislodge a mushroom anchor. That's why bass fishermen, etc. can easily lift the anchor up by hauling in the line by hand. If a plow, danforth, Bruce is buried it isn't coming up
until you have 1:1 scope and you'd have to pull quite a bit harder than with a 'shroom. You may have to motor over it and pull it out form the opposite direction. More hassle but safer anchoring...
Adding scope to the mushroom anchor will likely pull/tip one side of the bowl up out of the mud
(unless you've got really really suction-y mud) pretty easily.
See what the 20'-25' (or larger) pleasure boats are using in your area if they're anchoring overnight places. Nothing wrong with a mushroom anchor if an operator is on board but I would be uncomfortable doing an hour's dive on a potentially windy mountain lake with no operator. On a pond-maybe no problem.
I've seen bass fishermen's anchors bounce along the bottom when lifted and dropped by chop for quite a distance.You'd of course have to size down for a larger boat's anchor but I'd still go one size up form whatever tha manufacturer's chart calls for.
Glad this info. is helping someone. If it gets to be too much of a Hi-Jack and deemed too unrelated to the OP guess it can be moved?
What JayJudge was saying about maintaining constant tension is part of this scope thang.
B1country, the amount of scope used does sometimes influence the placement of the "mother" boat over the wreck. How far of a surface swim will it be for the divers, can I anchor on the wreck and still stay clear of my competitor's dive boat, etc. I'm thinking that's what you meant?
piikki
Contributor
Have to thank you guys for reviving this thread. I had totally missed it being out of country at the time. Good things to remember.
Anyhow, I have a question. Was this a commercial operation? Did you pay to make the dive/s? Were you warned beforehand you were expected these duties underwater?
If you had said you do not know and do not want to do this unhooking/hooking would you have just simply been out of the dive? Effectively maybe robbed dive from all 5 divers?
Heebiejeebies, I certainly would not want to end up on a charter that expects me as a paying customer to do this without prior training. And I sure hate it when I lose dives too. Especially if I am not told beforehand the operator expects these kinds of dangerous tricks from me... (Dangerous since I do not know how to perform them safely).
Anyhow, I have a question. Was this a commercial operation? Did you pay to make the dive/s? Were you warned beforehand you were expected these duties underwater?
If you had said you do not know and do not want to do this unhooking/hooking would you have just simply been out of the dive? Effectively maybe robbed dive from all 5 divers?
Heebiejeebies, I certainly would not want to end up on a charter that expects me as a paying customer to do this without prior training. And I sure hate it when I lose dives too. Especially if I am not told beforehand the operator expects these kinds of dangerous tricks from me... (Dangerous since I do not know how to perform them safely).
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To answer your question, this is a commercial charter ... a basic six-pack boat. The standard agreement with the captain is that divers will unhook the anchor when they leave the wreck. In the event that the anchor is not unhooked ... and subsequently is lost ... divers will pay the captain to replace it.
Everyone who dives on this boat knows it. He typically caters to tech divers or those with sufficient experience to know how to do deal with moving an anchor ... sometimes you're doing this on wrecks that are very deep ...
... Bob (Grateful Diver)
Interesting post Lynne. Just as an aside for those not from this area since every geographical area has their own challenges and different types of diving...most of our boat diving isn't even on wrecks.
Most of our boat drops are live but we aren't having to hit a specific spot such as a wreck. Many if not most of our boat dives are live but are on walls where the point of the dive is to swim along/drift on walls covered with marine life (much like a reef in the tropics).
Therefore, the techniques needed for this particular dive aren't ones that are typically needed for our "typical" dives.
Again, it was an nteresting and informative post Lynne.
Most of our boat drops are live but we aren't having to hit a specific spot such as a wreck. Many if not most of our boat dives are live but are on walls where the point of the dive is to swim along/drift on walls covered with marine life (much like a reef in the tropics).
Therefore, the techniques needed for this particular dive aren't ones that are typically needed for our "typical" dives.
Again, it was an nteresting and informative post Lynne.
Charlie99
Contributor
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Scope is simply the ratio of depth to the length of anchor chain/rope used. Higher scopes like 5 or 7, particularly when you use a length of chain on the anchor end, will make it so that the pull on the anchor is horizontal. This helps the anchor dig in. When you want to bring the anchor back up, you bring back aboard most of the anchor rode and then the pull on the anchor will be near vertical which tends to pull the anchor out of the sand/mud/whatever on the bottom.
Even with no current or swells, winds will still try to move a boat and can cause you to drag anchor with a short scope.
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