Difference between revisions of "Anchoring"

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== Anchor Basics ==
 
  
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Here's a typical danforth type anchor like the one's we've been using:
+
NOTE: This page is in the process of being rewritten.
  
−
[[file:hooker.jpg]]
+
= Anchors =
 +
== Anchor Types ==
 +
[[file:hooker.jpg|thumb|left]]
  
−
They work by lying flat on the bottom, and having their flukes (blades) dig into the sand or mud.  "Scope" refers to the ratio between the line length and the depth.  The more scope, the flatter the anchor lies and the better it holds.   
+
* Danforth (shown) + Fortress - GREAT for Bay Area mud.  Great for the mud in the deep water (15'+) areas of the Delta.  Pretty directional and not ideal for heavily shifting winds.  Fortress is lightweight aluminum, a very similar shape to Danforths, and generally a really good anchor.
 +
 +
* Bruce / CQR - Okay at all types of bottom conditions, but not great at anything.   
  
−
[[file:anchor_on_bottom.jpg]]
+
* Rocna - New computer based designs, really good in almost all conditions, but $$.
  
−
== Scope Table ==
+
Note - Third party knockoffs resembling popular anchors might have slight differences in terms of build quality and geometry that make them not nearly as effective as the name brands.
 +
{{clr}}
  
−
According to Don Casey, this table shows anchor holding power as related to scope:
+
== Holding power ==
  
−
10:1 100%<br>
+
The type of anchor, and it's size (usually denoted by it's weight) determines how big of a boat it can hold in place.  For each anchor type you should be able to find charts indicating what size is appropriate, in how much wind, for a given boat weight or size.
−
7:1 91%<br>
 
−
6:1 85%<br>
 
−
5:1 77%<br>
 
−
4:1 67%<br>
 
−
3:1 53%<br>
 
−
2:1 35%<br>
 
  
−
[[http://www.boatus.com/boattech/casey/34.htm|link]]
+
As an example, for Danforth Standard anchors.  
  
−
Note this is approximate and it assumes a flat seabed. If the floor is sloped, then the calculations get more complex.
+
Weight : Max Holding Power : Boat size in 20knots of winds.
 +
14lb : 920 : 31'<br>
 +
16lb : 1300 : 36'<br>
 +
25lb : 1600 : 40'<br>
 +
43lb : 2000 : 45'<br>
 +
70lb : 3000 : 55'<br>
 +
100lb : 3500 : 60'<br>
  
−
Example 1:  If someone tries to use 50' of line in 25' of water, then the scope is 2:1 and the holding power of anchor will only be about 35% of it's max.   
+
These numbers assume a minimum of amount of of chain.   
  
−
Example 2: If the same line is used in 10' of water, the scope will be 5:1 and the holding power should be more than twice as strong as it was in the first example.
+
http://www.danforthanchors.com/standard.html
  
−
== Chain ==  
+
= Scope =  
  
−
On all boats except the very smallest, chain is attached to the anchor line. The chain adds weight to the end of the line and helps the anchor stay set on the bottom.  I don't have any numbers for how much chain helps, but it's important. 
+
[[file:anchor_on_bottom.jpg]]
  
−
Addendum: a crucial benefit of the chains is that they reduce the initial vertical force you exert on the anchor when you tauten the line, helping set the anchor into the riverbed rather than pulling it up or just along the bottom.
+
Anchors work by lying flat on the bottom, and digging down into the sand or mud.  "Scope" refers to the ratio between the line length and the depth.  The more scope (up to a point) the better the anchor holds.
  
−
[[File:anchor_with_chain.jpg]]
+
* For beginners, 6:1 is our recommended minimum
 +
* For beginners, 10:1 is recommended better holding
  
−
== Danforth Holding Power ==
+
If there's 10' between the anchor roller and the bottom, 6:1 scope would mean 60' of line/chain out.
  
−
Weight : Holding Power : Boat size (20knot winds)
+
Mark your line or chain in 10’ or 20’ increments. You should be able to know at a glance how much you have out.
  
−
14lb : 920 : 31'<br>
+
== Scope Table ==
−
16lb : 1300 : 36'<br>
 
−
25lb : 1600 : 40'<br>
 
−
43lb : 2000 : 45'<br>
 
−
70lb : 3000 : 55'<br>
 
−
100lb : 3500 : 60'<br>
 
  
−
These numbers assume a minimum of 4-8' of chain. 
+
According to Don Casey, this table shows anchor holding power as related to scope:
  
−
[[http://www.danforthanchors.com/standard.html]]
+
10:1 100%<br>
 +
7:1 91%<br>
 +
6:1 85%<br>
 +
5:1 77%<br>
 +
4:1 67%<br>
 +
3:1 53%<br>
 +
2:1 35%<br>
  
−
== Removing stuck anchors ==
+
http://www.boatus.com/boattech/casey/34.htm
  
−
After 4 days of anchoring in last year, some of our anchors were stuck in the mud.  Pulling up failed to free them, so we tied off the anchor line to a cleat on the houseboat and motored forward at full speed to break them loose. 
+
== Scope Details ==
  
−
This year, with a longer event and bigger anchors we are likely to have anchors which are really stuck in the mud.  Trying to yank them out with a cleat and the force of a motor is likely to damage the boats.
+
Measure total depth from roller, or point where line crosses the deck, not just the water depth.
  
−
Instead, here's what one reference recommended and I'm paraphrasing:  Pull the line tight, and then let the motion of the waves to gradually work the anchor loose.
+
Remember tidal shift -- 6’ of depth at low tide, might be 11’ at high tide.
  
−
On the delta, we probably won't have the waves to help us work the anchors out.  But a group of people pulling, with patience, should be able to slowly work an anchor out of the mud.
+
Disadvantage to more scope is more swing, and more likely for someone to cross your anchor line w/ their own anchor pulling them both us, so don’t just by default put out 300’.
  
−
== 2011 Anchoring ==
+
Note this is approximate and it assumes a flat seabed. If the floor is sloped, then the calculations get more complex.
  
−
In 2011, almost all of the anchors used were 14 pound anchors (TODO - verify that!) that came with the houseboats. The came attached to 50' of line (TODO - verify that!).   
+
Example 1: If someone tries to use 50' of line in 25' of water, then the scope is 2:1 and the holding power of anchor will only be about 35% of it's max.   
  
−
As we can see from the info above a 14 pound anchor is only strong enough to hold a 31' boat in a stiff breeze while they were being used to hold 40' houseboats. 
+
Example 2: If the same line is used in 10' of water, the scope will be 5:1 and the holding power should be more than twice as strong as it was in the first example.
−
 
 
−
In addition with 50' of line, assuming 20' depth, the anchors only had about 40% of their holding power (2.5:1 scope).  As such, they didn't hold at all.  After we tied two ropes together, we had closer to 5:1 scope and the anchors mostly held.
 
−
 
 
−
The picture below shows the approx. strategy used for anchoring:
 
−
 
 
−
[[file:Anchoring.jpg]]
 
  
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Even with all of the anchors, the city broke free once and floated downstream. 
+
= Chain=
  
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It took a very long time to assemble the city and to take it apart.  Once boats were in place very few of them moved until the end of the event.
+
[[File:anchor_with_chain.jpg|thumb|left|150px]]
  
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== 2012 Anchoring (ideas) ==
+
Chain adds weight to the end of the line and helps the anchor stay set on the bottom. 
  
−
=== Baseline ===
+
It's recommend that all anchors have at least at minimum 10' of chain in addition to the line.  A rule of thumb is that the chain size should have 1/2 the size of the line.  e.g. If you have 1/2" rope for your anchor the attached chain should be 1/4".
  
−
Here's the baseline standard for anchoring a boat which you don't want to move.  You simply use a bow and stern anchor.  It's a very common practice among boaters.
+
If you're boat only has chain (no line) then there's very little stretch and there could be strong forces on whatever it's attached it.  It's often a good idea to add some line running from cleats to the chain.
 +
{{clr}}
  
−
The houseboats come with 14lb anchor (check).  With 100+' feet of line they may hold.  It would help dramatically if chain was brought and added to the line.
+
= Howto: Drop an anchor =
  
−
But ideally, according to Danforth's tables each boat should have a 25lb bow anchor with a smaller stern anchor.  Bringing a 25lb danforth anchor with 100 feet of line and 20 feet of chain, plus another 10 feet of chain to add to the 14lb danforth as a stern anchor would bring these boats up to typical nautical standards.
+
= Howto: Pull up an anchor =
  
−
[[file:One_boat_anchored.jpg]]
+
Release by pulling straight up and down.
  
−
1) To anchor:
+
After 4 days of anchoring in last year, some of our anchors were stuck
 +
in the mud. Pulling up failed to free them, so we tied off the anchor
 +
line to a cleat on the houseboat and motored forward at full speed to
 +
break them loose.
  
−
a) Drop the bow anchor.
+
This year, with a longer event and bigger anchors we are likely to have
−
b) Float backward until a sufficient amount of line has been release. 
+
anchors which are really stuck in the mud. Trying to yank them out with
−
c) Ideally with the help of a dinghy, the stern anchor is dropped well behind the boat.
+
a cleat and the force of a motor is likely to damage the boats.
  
−
2) To leave anchor:
+
Instead, here's what one reference recommended and I'm paraphrasing:
 +
Pull the line tight, and then let the motion of the waves to gradually
 +
work the anchor loose.
  
−
a) Tie the bow anchor  to a float, or give it the line to someone in a dinghy and release the line.
+
On the delta, we probably won't have the waves to help us work the
−
b) Float backward, hauling in the stern line until you're directly above the anchor.
+
anchors out. But a group of people pulling, with patience, should be
−
c) Pull it in.
+
able to slowly work an anchor out of the mud.
−
d) Now _carefully_ to avoid any floating lines, motor up to fetch the bow line and pull in the bow anchor.
 
  
−
3) To add or remove boats
 
  
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a) There is no issue because each boat has it's own anchors.
+
=Anchoring one boat=
  
−
=== Mini-flotilla ===
+
Captains, make sure to acquire the proper chain,
 +
anchor line, and connectors before you leave the house! Before you take
 +
your boat from the pier, look at connections between chain and anchor,
 +
chain and line, and make sure the line is in good shape. 2) MEASURE
 +
WATER DEPTH AND LENGTH OF ANCHOR LINE. For Ephemerisle use a minimum 5:1
 +
ratio of anchor line to depth. You can assume this means a minimum
 +
length of 125 feet of anchor line. 3) TIE THE LINE TO YOUR BOAT. Cleat
 +
it at 125 feet (or longer), and tie it again to an even stronger part of
 +
your houseboat
  
−
By lashing 5x 40'x15' houseboats together we effectively create (for the purposes of anchoring) a 75'x40' boat.
+
Check the tie off. Make sure the line is attached to the boat, and
 +
isn’t tangled on anything. 2) Check your position. Look in a direction
 +
perpendicular to the line made by your anchor line and boat. If you are
 +
drifting, your anchor hasn’t set properly. Start over! 3) Check your
 +
position AGAIN. And AGAIN. And AGAIN. Lots of things can cause you to
 +
come un-stuck from the bottom.
  
−
According to Danforth's table, we would need something larger than a 100lb anchor to moor these boats together in a windstorm.  We're not going to have any hundred pound anchors because anchors get _much_ more expensive as they get bigger, and also because the cleats on the houseboats are almost surely not capable of handling such force.
+
Backing up on an anchor
  
−
Instead, one idea is to use larger anchors (40+lbs) with chain as the bow and 25lb anchors with chain as stern anchors.  This would not get us up to nautical standards, but would almost surely be much better than what we had last year.
+
2) FEED OUT THE ANCHOR LINE. As you
 +
drive SLOWLY away from the cast anchor, feed the line out by hand,
 +
giving the occasional tug. 3) TUG AND HOLD. Tugging on the line, you
 +
should feel the anchor “set” into the mud.  
  
−
[[file:Mini_flotilla.jpg]]
+
Swings in the wind
 +
=Anchoring a raftup/island=
 +
Point into prevailing wind. 
 +
Anchor every 2-3 boats. 
 +
IMPORTANT: Make subjective judgments based on boat size and anchor sizes/types.  A small anchor from a 27’ boat will do effectively nothing next to some 50’ boats.
 +
Put out a stern anchor every 3-4 boats.  Especially in low wind, this will prevent the raftup from spinning and all of the anchors getting twisted.
  
−
1) To anchor:
+
= Anchoring Near Others =
  
−
a) First boat drops the bow anchor.
+
Generally boats put down one anchor and drift with the wind and the current.  If boats anchor closely near to other boats with each with one anchor and similar scope, they all shift together with the wind and current and avoid collision.
−
b) First boat backward until a sufficient amount of line has been release.
 
−
c) Each successive boat slides up to the previous boat and lashes off to it. 
 
−
d) Ideally with the help of a dinghy, the stern anchor is dropped well behind the final boat.
 
  
−
2) To leave anchor:
+
At Ephemerisle, it's been common for islands to put down multiple (3-4) anchors in opposite directions to fix themselves in place.  This can lead to collisions even without anchors dragging, if one boat or island is fixed in place and another is shifting freely with the tides. 
  
−
a) All of the middle boats depart.
+
According to the law, anchoring is first come, first serve.  If a boat is already anchored, boats who anchor after them have a legal responsibility not to crash into the boat already in place.
−
b) The leeward (downwind) boat floats down hauling in the stern anchor line, then pulls up the anchor.   
 
−
c) The windward boat, motors up, hauling in the bow anchor line, then pulling up the anchor.
 
  
−
3) To add boats
+
But there's also good manners and maintaining good relationships with your neighbors.  If a large boat or a large group of boats (island) has a specific need to be in a particular place, and a smaller boat or island can reasonably relocate somewhere else, it's very nice to do so. 
  
−
a) To add them to either end, they should approach slowly.  The boat should be partially lashed off.  Then the anchor line should be transferred to the new end boat.  Then the boat should be fully lashed off.
+
= Local Conditions =
−
b) To add them to the middle.  Unlash the boats where you want to add a new boat.  Using a 25 foot line allow half of the mini-flotilla to drift downwind away, then stop it.  Use the cleats!  When there is enough space the new boat drives _slowly_ in and then lashed off on both sides.
 
  
−
4) To remove boats.
+
There is a fairly strong current which runs NS and reverses on a regular basis in the Mandeville Channel. It's a serious hazard for swimmers.  And boat with a single anchor down should be expected to swing all of the way north then south with the tides. 
  
−
a) To remove an end boat.  Just transfer the anchor line and let them depart.
+
Strong winds, up to 20 knots, are common.  And they usually come from the West.  Your anchor or your largest anchor if you're putting out multiple should probably be put towards the West.   
−
b) To remove a center boat.  Use a 25' line to connect boats on either side of what will be the gap.  Unlash the boat and then let it depart.  Use the 25' line to bring the boats back together, but let the currents work for you, rather than working against them.
 
  
−
=== Tying off to a tree ===
+
There have been extreme winds (40 knots). All boats should be prepared for the worst of conditions to prevent serious damage to boats or injuries to people.
  
−
It is apparently relatively common practice in the Delta to create a secure anchorage by tying off to a tree.  A stern anchor would of course also be needed to keep the boat from being pushed into that tree.
 
  
−
=== More advanced ideas? ===
+
= Mooring =
  
−
I hope we can try to build upon these ideas...
+
It is apparently relatively common practice in the Delta to create a secure anchorage by tying off to a tree. A stern anchor would of course also be needed to keep the boat from being pushed into that tree. There are few suitable trees close to Mandeville Point. There are a number of pylons in the channel that cuts through Mandeville Point, and they are frequently used for at least a night or two, especially for boaters who arrive after sunset and are not able to raft up to boats that are already anchored. If you do this, bring citronella candles and bug spray and close your screens, because the closer you are to shore, the more you will be overwhelmed by insects.

Latest revision as of 23:27, 1 October 2021

NOTE: This page is in the process of being rewritten.

Anchors

Anchor Types

Hooker.jpg
  • Danforth (shown) + Fortress - GREAT for Bay Area mud. Great for the mud in the deep water (15'+) areas of the Delta. Pretty directional and not ideal for heavily shifting winds. Fortress is lightweight aluminum, a very similar shape to Danforths, and generally a really good anchor.
  • Bruce / CQR - Okay at all types of bottom conditions, but not great at anything.
  • Rocna - New computer based designs, really good in almost all conditions, but $$.

Note - Third party knockoffs resembling popular anchors might have slight differences in terms of build quality and geometry that make them not nearly as effective as the name brands.

Holding power

The type of anchor, and it's size (usually denoted by it's weight) determines how big of a boat it can hold in place. For each anchor type you should be able to find charts indicating what size is appropriate, in how much wind, for a given boat weight or size.

As an example, for Danforth Standard anchors.

Weight : Max Holding Power : Boat size in 20knots of winds. 14lb : 920 : 31'
16lb : 1300 : 36'
25lb : 1600 : 40'
43lb : 2000 : 45'
70lb : 3000 : 55'
100lb : 3500 : 60'

These numbers assume a minimum of amount of of chain.

http://www.danforthanchors.com/standard.html

Scope

Anchor on bottom.jpg

Anchors work by lying flat on the bottom, and digging down into the sand or mud. "Scope" refers to the ratio between the line length and the depth. The more scope (up to a point) the better the anchor holds.

  • For beginners, 6:1 is our recommended minimum
  • For beginners, 10:1 is recommended better holding

If there's 10' between the anchor roller and the bottom, 6:1 scope would mean 60' of line/chain out.

Mark your line or chain in 10’ or 20’ increments. You should be able to know at a glance how much you have out.

Scope Table

According to Don Casey, this table shows anchor holding power as related to scope:

10:1 100%
7:1 91%
6:1 85%
5:1 77%
4:1 67%
3:1 53%
2:1 35%

http://www.boatus.com/boattech/casey/34.htm

Scope Details

Measure total depth from roller, or point where line crosses the deck, not just the water depth.

Remember tidal shift -- 6’ of depth at low tide, might be 11’ at high tide.

Disadvantage to more scope is more swing, and more likely for someone to cross your anchor line w/ their own anchor pulling them both us, so don’t just by default put out 300’.

Note this is approximate and it assumes a flat seabed. If the floor is sloped, then the calculations get more complex.

Example 1: If someone tries to use 50' of line in 25' of water, then the scope is 2:1 and the holding power of anchor will only be about 35% of it's max.

Example 2: If the same line is used in 10' of water, the scope will be 5:1 and the holding power should be more than twice as strong as it was in the first example.

Chain

Anchor with chain.jpg

Chain adds weight to the end of the line and helps the anchor stay set on the bottom.

It's recommend that all anchors have at least at minimum 10' of chain in addition to the line. A rule of thumb is that the chain size should have 1/2 the size of the line. e.g. If you have 1/2" rope for your anchor the attached chain should be 1/4".

If you're boat only has chain (no line) then there's very little stretch and there could be strong forces on whatever it's attached it. It's often a good idea to add some line running from cleats to the chain.

Howto: Drop an anchor

Howto: Pull up an anchor

Release by pulling straight up and down.

After 4 days of anchoring in last year, some of our anchors were stuck in the mud. Pulling up failed to free them, so we tied off the anchor line to a cleat on the houseboat and motored forward at full speed to break them loose.

This year, with a longer event and bigger anchors we are likely to have anchors which are really stuck in the mud. Trying to yank them out with a cleat and the force of a motor is likely to damage the boats.

Instead, here's what one reference recommended and I'm paraphrasing: Pull the line tight, and then let the motion of the waves to gradually work the anchor loose.

On the delta, we probably won't have the waves to help us work the anchors out. But a group of people pulling, with patience, should be able to slowly work an anchor out of the mud.


Anchoring one boat

Captains, make sure to acquire the proper chain, anchor line, and connectors before you leave the house! Before you take your boat from the pier, look at connections between chain and anchor, chain and line, and make sure the line is in good shape. 2) MEASURE WATER DEPTH AND LENGTH OF ANCHOR LINE. For Ephemerisle use a minimum 5:1 ratio of anchor line to depth. You can assume this means a minimum length of 125 feet of anchor line. 3) TIE THE LINE TO YOUR BOAT. Cleat it at 125 feet (or longer), and tie it again to an even stronger part of your houseboat

Check the tie off. Make sure the line is attached to the boat, and isn’t tangled on anything. 2) Check your position. Look in a direction perpendicular to the line made by your anchor line and boat. If you are drifting, your anchor hasn’t set properly. Start over! 3) Check your position AGAIN. And AGAIN. And AGAIN. Lots of things can cause you to come un-stuck from the bottom.

Backing up on an anchor

2) FEED OUT THE ANCHOR LINE. As you drive SLOWLY away from the cast anchor, feed the line out by hand, giving the occasional tug. 3) TUG AND HOLD. Tugging on the line, you should feel the anchor “set” into the mud.

Swings in the wind

Anchoring a raftup/island

Point into prevailing wind. Anchor every 2-3 boats. IMPORTANT: Make subjective judgments based on boat size and anchor sizes/types. A small anchor from a 27’ boat will do effectively nothing next to some 50’ boats. Put out a stern anchor every 3-4 boats. Especially in low wind, this will prevent the raftup from spinning and all of the anchors getting twisted.

Anchoring Near Others

Generally boats put down one anchor and drift with the wind and the current. If boats anchor closely near to other boats with each with one anchor and similar scope, they all shift together with the wind and current and avoid collision.

At Ephemerisle, it's been common for islands to put down multiple (3-4) anchors in opposite directions to fix themselves in place. This can lead to collisions even without anchors dragging, if one boat or island is fixed in place and another is shifting freely with the tides.

According to the law, anchoring is first come, first serve. If a boat is already anchored, boats who anchor after them have a legal responsibility not to crash into the boat already in place.

But there's also good manners and maintaining good relationships with your neighbors. If a large boat or a large group of boats (island) has a specific need to be in a particular place, and a smaller boat or island can reasonably relocate somewhere else, it's very nice to do so.

Local Conditions

There is a fairly strong current which runs NS and reverses on a regular basis in the Mandeville Channel. It's a serious hazard for swimmers. And boat with a single anchor down should be expected to swing all of the way north then south with the tides.

Strong winds, up to 20 knots, are common. And they usually come from the West. Your anchor or your largest anchor if you're putting out multiple should probably be put towards the West.

There have been extreme winds (40 knots). All boats should be prepared for the worst of conditions to prevent serious damage to boats or injuries to people.


Mooring

It is apparently relatively common practice in the Delta to create a secure anchorage by tying off to a tree. A stern anchor would of course also be needed to keep the boat from being pushed into that tree. There are few suitable trees close to Mandeville Point. There are a number of pylons in the channel that cuts through Mandeville Point, and they are frequently used for at least a night or two, especially for boaters who arrive after sunset and are not able to raft up to boats that are already anchored. If you do this, bring citronella candles and bug spray and close your screens, because the closer you are to shore, the more you will be overwhelmed by insects.

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