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23-11-2020, 08:03
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#46
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Registered User
Join Date: Jan 2011
Location: London
Boat: Oyster 49
Posts: 235
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Re: Anchor Scope - From Waterline or Bow Roller
The Rocna website has a lot of good advice about scope. There they emphasize that the distance that is key is the distance from the bow roller/fairlead to the sea bed, and not just the depth alone
Scope vs catenary (Rocna Knowledge Base)
You do not have to have a Rocna to learn from the site
TS
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23-11-2020, 08:04
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#47
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Registered User
Join Date: Jan 2016
Location: Near Chesapeake Bay
Boat: Presently between vessels
Posts: 79
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Re: Anchor Scope - From Waterline or Bow Roller
Scope = length of tackle/distance to seabed
The scope is determined after the snubber or bridle is in place. If you attach it and let out more tackle to load the bridle, you have increased the scope.
Distance to seabed is from the fair lead (where snubber engages the hull) to seabed. Same as water depth plus height above water to the fair lead. The bow roller isn't relevant since there is no tension on the chain/rode there. I understand some boats are different.
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23-11-2020, 08:33
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#48
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Registered User
Join Date: Dec 2019
Location: Puget Sound, WA
Boat: Nauticat 43 ketch
Posts: 794
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Re: Anchor Scope - From Waterline or Bow Roller
Quote:
Originally Posted by gcaws
Bow roller. If I have neighbours then I ask how much they have out and whether they’re using chain or rode then try to match (unless it’s sketchy of course). Plus it’s a good way to introduce yourself and show you care and that you’re thinking of everyone’s safety. Alone I always anchor conservatively so 7:1 or more with an over sized Rochna. I’ve got the chain and it’s not doing me any good sitting in the anchor locker. Plus I hate dragging. I really hate it. Yes, I know different scopes for different anchors but the more chain I have out , the better I feel. And over 25 years I’ve done a ton of anchoring. So I’ve lived through a lot of wind and bumpy anchorages. Did I say I hate dragging?
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Gcaws, you are my hero. When Canada restrictions finally lift I hope to share an anchorage with you some day.
I'm surprised that no-one in this discussion has mentioned figuring tidal depths into their scope. When anchoring I always check the tide level and figure my minimum scope for High tide AND the expected forecast.
My current location has a typical tidal range of 14 feet, so if I anchor at zero tide I will typically add 12 feet to the depth for calculating scope.
Like Gcaws I feel secure with 7:1 scope but 5:1 is my minimum, even though I've tested that my oversized primary bower can hold with much less scope (3:1) in 30 knot winds. Why push it? I like to sleep at night knowing my chances of dragging are slim to none.
I usually have more scope out than my neighbors expect. When I drop my hook I set a waypoint and use radar when a new boat comes into the anchorage to gauge their position relative to my anchor. A couple of times this year I had to let newcomers know in a crowded anchorage that they were about to drop right over my anchor.
Another fun fact that I haven't seen addressed in this discussion is that the boat's position and swing can change after anchoring. We usually anchor in mud and after a few days of calmer winds when the tidal current or wind direction has swung our boat, the chain gets embedded in the mud and becomes the new "anchor"position. It's amazing how strong the chain can hold the boat when it's stuck in the mud. Typically 25-30 knots or so is enough to break it out but in our last anchorage we had gusts to 44 knots and our position didn't change (we were 80 feet from the anchor with 200 feet of chain out).
This means we can't assume the location of the anchor of a boat in a tight anchorage, so Gcaws practice of asking before dropping is wise and courteous.
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23-11-2020, 09:57
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#49
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Registered User
Join Date: Mar 2014
Posts: 6
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Re: Anchor Scope - From Waterline or Bow Roller
The load and angle doesn't stop at the waterline.
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23-11-2020, 10:46
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#50
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Registered User
Join Date: Jul 2010
Location: Pompano Beach, FL
Boat: Manta 44 PC Pangaea
Posts: 50
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Re: Anchor Scope - From Waterline or Bow Roller
Quote:
Originally Posted by SV__Grace
Gcaws, you are my hero. When Canada restrictions finally lift I hope to share an anchorage with you some day.
I'm surprised that no-one in this discussion has mentioned figuring tidal depths into their scope. When anchoring I always check the tide level and figure my minimum scope for High tide AND the expected forecast.
My current location has a typical tidal range of 14 feet, so if I anchor at zero tide I will typically add 12 feet to the depth for calculating scope.
Like Gcaws I feel secure with 7:1 scope but 5:1 is my minimum, even though I've tested that my oversized primary bower can hold with much less scope (3:1) in 30 knot winds. Why push it? I like to sleep at night knowing my chances of dragging are slim to none.
I usually have more scope out than my neighbors expect. When I drop my hook I set a waypoint and use radar when a new boat comes into the anchorage to gauge their position relative to my anchor. A couple of times this year I had to let newcomers know in a crowded anchorage that they were about to drop right over my anchor.
Another fun fact that I haven't seen addressed in this discussion is that the boat's position and swing can change after anchoring. We usually anchor in mud and after a few days of calmer winds when the tidal current or wind direction has swung our boat, the chain gets embedded in the mud and becomes the new "anchor"position. It's amazing how strong the chain can hold the boat when it's stuck in the mud. Typically 25-30 knots or so is enough to break it out but in our last anchorage we had gusts to 44 knots and our position didn't change (we were 80 feet from the anchor with 200 feet of chain out).
This means we can't assume the location of the anchor of a boat in a tight anchorage, so Gcaws practice of asking before dropping is wise and courteous.
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Cheers to Grace & Gcaws!! Knowing our neighbors status and our environment is a must.
While teaching sailing (and boating) in SFO Bay, I did many anchoring classes and the basic first estimate for an unknown anchorage... ( DECK TO DIRT + TIDE) times (SCOPE)
The Process: The student anchor committee reviews chart and based on current conditions chooses an anchor spot and depth. Then review today's tide table and calculates maximum tide rise and estimates deck height.
SCOPE First guess is 5x for lunch hook, full time deck watch , light conditions, OR 7x overnite. Now for negotiations... neighbors, local knowledge, boat and gear considerations.
Student / Newbie procedure: Lay out planned scope on deck so it can pay out smoothly. Snub on cleat at ~80% to set anchor.
When we reach planned spot, modify plan as needed and anchor.
Happy Cruising
Gene
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23-11-2020, 10:52
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#51
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Registered User
Join Date: Jun 2019
Location: Whangarei NZ
Boat: Buccaneer 16ft
Posts: 166
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Re: Anchor Scope - From Waterline or Bow Roller
Quote:
Originally Posted by thomm225
Whatever happened to simply eyeballing the angle of the rode and if in doubt let out a few more feet of "rope?"
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Yep exactly. But I’m starting to worry now, I must have been only lucky for the last 50 years.
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23-11-2020, 10:58
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#52
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Registered User
Join Date: Sep 2011
Location: Good question
Boat: Rafiki 37
Posts: 14,140
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Re: Anchor Scope - From Waterline or Bow Roller
Quote:
Originally Posted by Old fella
Yep exactly. But I’m starting to worry now, I must have been only lucky for the last 50 years.
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Nah, just skillful based on lots of experience .
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23-11-2020, 11:14
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#53
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Registered User
Join Date: Apr 2013
Location: British Columbia
Boat: Sceptre 41
Posts: 1,928
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Re: Anchor Scope - From Waterline or Bow Roller
"When I drop my hook I set a waypoint and use radar when a new boat comes into the anchorage to gauge their position relative to my anchor. A couple of times this year I had to let newcomers know in a crowded anchorage that they were about to drop right over my anchor."
We set our Watchmate anchor watch where we drop anchor.
I like radar because it gives your position relative to all nearby boats and land (my Furuno is great as it gives distance in yards/metres; friend's Raymarine radar only gives in nm...).
But this year we found a faster/easier method to check distance when a new boat arrives to anchor: an inexpensive golf/hunting rangefinder
e.g.,
https://wosports.com/collections/hun...l-measurements
Takes only seconds to get distance.
(We've also found the rangefinder's golf "flagpole" detector useful for getting distance to crab trap floats, etc... something radar can't do.)
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23-11-2020, 13:57
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#54
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Registered User
Join Date: Oct 2010
Location: michigan
Boat: CORBIN 39
Posts: 338
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Re: Anchor Scope - From Waterline or Bow Roller
we are talking about a anchor and the rode , you do not need to be a engineer to make this work . this sounds like a question on a test. if the anchor drags, let out more scope.
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23-11-2020, 19:23
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#55
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Registered User
Join Date: Mar 2011
Location: Australia
Boat: S&S 40
Posts: 930
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Re: Anchor Scope - From Waterline or Bow Roller
Quote:
Originally Posted by UFO
I was having a conversation with an old salt and he thought I was crazy for including the distance up to my bow roller for my scope equation.
His point was that my bow roller is 1.6m above the waterline, so if i am anchoring in shallow water - Say 1.5m I will be more than doubling my scope.
His method 1.5m x 5 = 7.5m whereas the way I do it would be 15.5m - which to him was a scope of over 10:1 - He went as far to say that I was being selfish in letting out all that chain!
Also my bridle is 7M long, so I would have to put it 1/2m from the anchor, rather than 8.5M of my method.
What does everyone else do?
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Pretty obvious if you anchor in 1.5m depth you don't only let out 7.5 meters of chain.
My rule is minimum 4:1 so in 1.5m plus the 1.5m to the bow=3mx4=12m or so
If its windy say 15kn I usually go about 5:1, depending on swinging room, type of anchor and sand or mud .
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24-11-2020, 05:09
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#56
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Registered User
Join Date: Sep 2010
Posts: 2,909
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Re: Anchor Scope - From Waterline or Bow Roller
The biggest point for me, is that I try to never in a place where I can't put out as much scope as I want. At least not for an overnight.
I anchor like I'm going to get hit with a 60 knot gust every night. That probably seems like overkill to many, but it sure felt good that morning in Big Majors spot when we got hit with a 70 mph wind as a front arrived, that lasted for ten minutes, and I stood in my cockpit watching boats pass by me like there were in reverse, heading for an iron shore beach.
So, I usually put out 6 or 7 to one scope, all chain, and I figure depths from the bow pulpit, and I don't care when people tell me I could get by with less. If that's too much due to crowded conditions, I go anchor somewhere else.
And, I try real hard to not get in a position where I have to anchor overnight on short scope for any reason.
I don't ever want to be one of those boats, where people wake up, walk out into their cockpit, look over at, and say, "Oh, no. Look what happened."
__________________
Founding member of the controversial Calypso rock band, Guns & Anchors!
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24-11-2020, 08:58
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#57
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Registered User
Join Date: Sep 2011
Location: Good question
Boat: Rafiki 37
Posts: 14,140
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Re: Anchor Scope - From Waterline or Bow Roller
Quote:
Originally Posted by Group9
...I anchor like I'm going to get hit with a 60 knot gust every night...I don't ever want to be one of those boats, where people wake up, walk out into their cockpit, look over at, and say, "Oh, no. Look what happened."
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This is our approach as well. When I anchor I always put in the time, and effort, to know my hook is as secure as I can make it. This usually means lots of scope.
It is the very rare night where I'll settle for less than 5:1 (yes, as measured from the bow), and usually have more like 7:1, or more. Most of the time I anchor by myself, so there are rarely issues with neighbours. Often my limitation is just the topography of the anchorage.
That said, I'm not anal about measuring to the exact foot. I have my chain marked, but I sometimes lose count. I err on the side of caution, but I can also use the setting and digging-in process to refine how much scope is needed. I can usually feel how things are going.
As others have said, anchoring is both science, art and skill. The more you do it, the better the sense you'll have of how to do it right.
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24-11-2020, 09:06
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#58
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Registered User
Join Date: Jun 2019
Location: Rochester, NY
Boat: Chris Craft 381 Catalina
Posts: 6,207
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Re: Anchor Scope - From Waterline or Bow Roller
Quote:
Originally Posted by Mike OReilly
That said, I'm not anal about measuring to the exact foot. I have my chain marked, but I sometimes lose count. I err on the side of caution, but I can also use the setting and digging-in process to refine how much scope is needed. I can usually feel how things are going.
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That's why I came up with my own color scheme for rode markings instead of using any of the ones I've seen online. Most rely on counting every mark, or knowing which mark was before the current one. I find that too unreliable, so I figured out markings where each mark (every 25 feet) is independently readable. If I see a mark that's 2 green stripes followed by an orange stripe, I know that's 225 feet.
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24-11-2020, 09:14
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#59
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Registered User
Join Date: Sep 2011
Location: Good question
Boat: Rafiki 37
Posts: 14,140
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Re: Anchor Scope - From Waterline or Bow Roller
Quote:
Originally Posted by rslifkin
That's why I came up with my own color scheme for rode markings instead of using any of the ones I've seen online. Most rely on counting every mark, or knowing which mark was before the current one. I find that too unreliable, so I figured out markings where each mark (every 25 feet) is independently readable. If I see a mark that's 2 green stripes followed by an orange stripe, I know that's 225 feet.
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Yeah, I've gone to this as well using zip ties. My problem is, I sometimes forget what three whites and a green mean .
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24-11-2020, 10:43
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#60
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Registered User
Join Date: May 2015
Location: edmonton alberta
Boat: 1992 lagoon 42 tpi
Posts: 1,729
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Re: Anchor Scope - From Waterline or Bow Roller
Quote:
Originally Posted by Mike OReilly
Yeah, I've gone to this as well using zip ties. My problem is, I sometimes forget what three whites and a green mean .
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I've done the same, with paint, and written the pattern on the bottom of the hatch lid to the anchor locker.
That makes it much easier to remember[emoji846]
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