Anchor is next on the checklist...
- Thread starter garyf
- Start date
Micahbigsur@msn.com
New member
We went from a Rocna roll bar over to a 24# Rocna Vulcan as we really liked the spade we had on an earlier boat, the Vulcan shank is slightly shorter so it stows better on the bow roller and we like not having a roll bar. We have 50' of G4 5/16 chain and 160' of 9/16 nylon braid. We like the heavier chain with a bit less length so we can use the nylon as a spring instead of a snubber you need with all chain out.
We keep a danforth type aluminum fortress anchor as a stern/backup anchor.
We keep a danforth type aluminum fortress anchor as a stern/backup anchor.
Garyf, Make your life more easy and go with 75 feet of chain, if you like round numbers.
Bob said:
I'm not so good at math so, I have 3 feet vertical distance, water to bow tip and about 2 feet from there to the windlass. I might have 6 feet of chain that is not in the water out of the 73 feet. Like I said, I'm not so good at math so not sure how that adds up to 13 feet. For me it has worked out like a 7:1 scope, with maybe being off a few inches. (Bob, Where do you get the 10 feet from?)
Harvey
SleepyC :moon
Bob said:
I'm not so good at math so, I have 3 feet vertical distance, water to bow tip and about 2 feet from there to the windlass. I might have 6 feet of chain that is not in the water out of the 73 feet. Like I said, I'm not so good at math so not sure how that adds up to 13 feet. For me it has worked out like a 7:1 scope, with maybe being off a few inches. (Bob, Where do you get the 10 feet from?)
Harvey
SleepyC :moon
hardee":fyw4swvy said:
10 feet is the depth of water + 3 feet from the surface to the bow roller = 13
13 x 7 = 91
... but that can be a combination of chain and rope, right? So you can get 7:1 in 10 ft of water with 70 ft of chain (or 75) (or 60)...? It's just more convenient, measurement-wise, to know what you've got when all the chain is out and you're at the splice.
I guess if we really want to go nuts with this... should we be taking draft into consideration? If you're going by your depth finder, isn't that the distance from the transducer to the bottom - or do you calibrate that out in the depth finder setup or something? If the former, seems like you should add another foot for draft of a transom mounted transducer? I haven't set up my depth finder yet (hell, haven't received it yet) but the readings when I was in the Navy were always referred to as "depth under the hull".
14 x 7 = 98
What is a safe way to mark rope? Is paint OK, or would that deteriorate the rope material? Putting a mark on the rope at the 91' point (or elsewhere, depending on your needs) might be handy.
hardee":l4t81o0b said:
Harvey it seems to be a fairly common misconception that "scope" means only water depth. In your example you considered the 7:1 scope (70) and then apparently added 3' for the distance of the bow off the water. The scope is only measured at the water surface if the rode is attached at the water surface (I had a snatch block with a snubber line running thru at the forward water line--bob stay fitting--which attached to the chain. In that boat the roller was 8' off the water)
The scope is calculated by the depth of the water, plus the distance off the water the place of the line or chain comes off the roller--in the 22 and 25 about 3 feet off the water. (Also expressed as the height of the bow roller off the sea bed floor.) Therefore to have a scope of 7:1 (which is about 8* angle of pull at the anchor shank head). Thus you would use 13 feet (3' off the water, plus 10' water depth" and multiply x 7 (91 feet) to give 7:1 scope for your C Dory 22 anchored in 10' of water (as per your statement above.). You were actually anchored on a scope of 5.6: 1. In the case you outlined with 73 feet of chain. Does it make a difference in holding? Maybe in a storm, depending on type of anchor.
The amount of chain on deck or height of where it is secured is irrelevant.
To answer Gary F's question about the transducer. You can put the transducer offset (depth under the water (about 12" at rest-maybe an inch on full plane). I just add the 12" in when I figure water depth. We are also good at judging 8* after many thousands of anchoring experience, as we pull back on the rode with the boat in reverse setting the anchor, with the rode nearly bar tight.
smckean (Tosca)
New member
One thing that hasn't been mentioned is paying attention to the tide state. I do a lot of anchoring. Having a CD means I can spend the night in very shallow spots (a pleasure to me). If one anchors in 15 feet or less of water (my preference), and the tidal swing is 9 feet as it was during a 4 day crusie I just returned from, I can see anywhere from 3 feet of water to 12 feet depending on the tide state.
Obviously, you calculate the scope based on the highest water level the boat will see (middle of the night maybe), but equally important is to be sure that at lowest tide state, anywhere in your swing while at anchor, you don't end up on the bottom! Like thataway, I explore the bottom with my depth finder before I anchor. I like to insure that I have 3 feet of water as a minimum (sometimes 2 feet in restricted areas) anywhere in the tide cycle. I'm always a bit surprised in a morning low tide to see how little water the boat is floating in.....kind of satisfying too when you realize how easy it would have been to "anchor over there" which is now bare rock or mud.
Obviously, you calculate the scope based on the highest water level the boat will see (middle of the night maybe), but equally important is to be sure that at lowest tide state, anywhere in your swing while at anchor, you don't end up on the bottom! Like thataway, I explore the bottom with my depth finder before I anchor. I like to insure that I have 3 feet of water as a minimum (sometimes 2 feet in restricted areas) anywhere in the tide cycle. I'm always a bit surprised in a morning low tide to see how little water the boat is floating in.....kind of satisfying too when you realize how easy it would have been to "anchor over there" which is now bare rock or mud.
Oh Yeah, the depth. (BIG WHOOPS on me.) 10 foot depth.
No matter where the tide level is currently, I calculate my scope for high tide, and ensure the minimum depth will be at least 5 feet at low tide. Remember, as the tide level goes down, the scope will increase, so the diameter of the "swing" will increase. I use my radar to measure my circle, but a rangefinder would work well too. The other way is to estimate your circle and keep a margin of safety.
Harvey
SleepyC :moon
No matter where the tide level is currently, I calculate my scope for high tide, and ensure the minimum depth will be at least 5 feet at low tide. Remember, as the tide level goes down, the scope will increase, so the diameter of the "swing" will increase. I use my radar to measure my circle, but a rangefinder would work well too. The other way is to estimate your circle and keep a margin of safety.
Harvey
SleepyC :moon
I've been looking at this anchor. Not sure if anyone has experience with it. www.mantusmarine.com
thataway":13cbamp6 said:
Looking at the M-2, it has 2 things that would make me skeptical. 1. The close distance between the anchor point and the attachment hole at the top of the shank. Too close for comfort in my book. 2. the angle of the fluke or blades plane is near parallel to the direction of pull so it appears it would just slice along under the surface. Not the case with the M-1.
Harvey
SleepyC :moon
Marco Flamingo
Active member
The Trawler Forum just had a recent post about exactly how to calculate "scope." Turns out there isn't a clear definition. Some definitions include the distance from water to deck only once. Some definitions triple the water to deck distance in calculating scope. Some definitions ignore it and define scope as only what is in the water.
INCLUDE THE DISTANCE:
Boat US: http://www.boatus.com/boattech/casey/34.htm
Scope is the ratio of the length of deployed anchor rode to the height of the bow chock above the seabed.
---
“Chapman Piloting Seamanship and Small Boat Handling 62ed” Hearst Marine Books, New York, page 254
Scope. The ratio of the length of the anchor rode to the vertical distance from the bow chocks to the bottom (depth plus height of bow chocks above the water).
---
“Knight’s Modern Seamanship Sixteenth Edition” Van Norstrand Reinhold New York, 1977 page 259
Scope: the length of chain measured from hawse to the anchor by which the ship rides is the scope.
---
Department of the Army Technical Manual TM 55-501 “Harbor Craft Crewman’s Handbook” 1958 page 68. A safe minimum anchor rode length in normal weather conditions is a 7 to 1 (rode length to depth) ratio, or 5 to 1 for an all chain rode. "Depth" in this case is the actual depth of the water at high tide, plus the height of the anchor hawser above the water's surface.
---
“Boating Skills and Seamanship Twelfth Ed.” US Coast Guard Auxiliary, page 4-21
To compute the “depth” add the distance from the water’s surface to the chock the line passes through on your boat to the actual depth of the water.
---
Rocna Anchors: http://www.rocna.com/kb/Scope_vs_catenary
Scope on the other hand is the ratio between the length of rode deployed and the distance the boat is from the seabed (the height from the seabed to the bow-roller or hawse-pipe, not just depth).
---
“The Practical Encyclopedia of Boating: An A-Z compendium of seamanship, boat maintenance, navigation, and nautical wisdom”, by John Vigor, published by The McGraw-Hill Companies, Inc.
The term scope refers to the length of line or chain between the anchor and the boat’s bow relative to the depth of water in which the boat is anchored. Thus, a scope of 3 to 1 indicates that a boat lying in 10 feet of water has an anchor line 30 feet long. In fact, the scope is measured to the bow roller, so the distance from the bow to water level must be added to the depth of the water.
---
“Sportfish, Cruisers, Yachts Owner’s Manual” NMMA Inc page 46
The scope is technically defined as the ratio of the rode length to vertical distance from the bow to the sea floor
---
Fortress Anchors: : http://www.fortressanchors.com/safe_anchoring.html
Scope is the length of anchor line relative to the distance from your boat’s deck to the sea bottom.
IGNORE THE DISTANCE:
From professional mariners site https://standard-club.com/media/1751..._oct_09_v1.pdf The ‘scope’ of the cable is the ratio of the length of cable paid out to the depth of water.
---
The Small Boat Handbook, D. Richey, T. Y. Crowell, New York, 1979.
"The minimum scope is approximately seven or eight times the distance from the surface to the bottom of the water."
---
Boating Skills and Seamanship, US Coast Guard Auxiliary Tenth Edition, page 2-17. "Scope is the length of the anchor rode measured in units of water depth."
---
Or from the RYA.ORG.uk where depth is water depth only.
And on and on and on. Pick one or the other and go with it. Both are better than losing count of the chain markers or miscalculating the tide.
As to depth sounders, I knew that both of my prior owners had used the CHITON for diving (the lazzerete had a rack for 10 SCUBA tanks). What I didn't realize is that both depth sounders on board were set to read the depth from the surface, not under the keel. Ask me how I know.
Mark
INCLUDE THE DISTANCE:
Boat US: http://www.boatus.com/boattech/casey/34.htm
Scope is the ratio of the length of deployed anchor rode to the height of the bow chock above the seabed.
---
“Chapman Piloting Seamanship and Small Boat Handling 62ed” Hearst Marine Books, New York, page 254
Scope. The ratio of the length of the anchor rode to the vertical distance from the bow chocks to the bottom (depth plus height of bow chocks above the water).
---
“Knight’s Modern Seamanship Sixteenth Edition” Van Norstrand Reinhold New York, 1977 page 259
Scope: the length of chain measured from hawse to the anchor by which the ship rides is the scope.
---
Department of the Army Technical Manual TM 55-501 “Harbor Craft Crewman’s Handbook” 1958 page 68. A safe minimum anchor rode length in normal weather conditions is a 7 to 1 (rode length to depth) ratio, or 5 to 1 for an all chain rode. "Depth" in this case is the actual depth of the water at high tide, plus the height of the anchor hawser above the water's surface.
---
“Boating Skills and Seamanship Twelfth Ed.” US Coast Guard Auxiliary, page 4-21
To compute the “depth” add the distance from the water’s surface to the chock the line passes through on your boat to the actual depth of the water.
---
Rocna Anchors: http://www.rocna.com/kb/Scope_vs_catenary
Scope on the other hand is the ratio between the length of rode deployed and the distance the boat is from the seabed (the height from the seabed to the bow-roller or hawse-pipe, not just depth).
---
“The Practical Encyclopedia of Boating: An A-Z compendium of seamanship, boat maintenance, navigation, and nautical wisdom”, by John Vigor, published by The McGraw-Hill Companies, Inc.
The term scope refers to the length of line or chain between the anchor and the boat’s bow relative to the depth of water in which the boat is anchored. Thus, a scope of 3 to 1 indicates that a boat lying in 10 feet of water has an anchor line 30 feet long. In fact, the scope is measured to the bow roller, so the distance from the bow to water level must be added to the depth of the water.
---
“Sportfish, Cruisers, Yachts Owner’s Manual” NMMA Inc page 46
The scope is technically defined as the ratio of the rode length to vertical distance from the bow to the sea floor
---
Fortress Anchors: : http://www.fortressanchors.com/safe_anchoring.html
Scope is the length of anchor line relative to the distance from your boat’s deck to the sea bottom.
IGNORE THE DISTANCE:
From professional mariners site https://standard-club.com/media/1751..._oct_09_v1.pdf The ‘scope’ of the cable is the ratio of the length of cable paid out to the depth of water.
---
The Small Boat Handbook, D. Richey, T. Y. Crowell, New York, 1979.
"The minimum scope is approximately seven or eight times the distance from the surface to the bottom of the water."
---
Boating Skills and Seamanship, US Coast Guard Auxiliary Tenth Edition, page 2-17. "Scope is the length of the anchor rode measured in units of water depth."
---
Or from the RYA.ORG.uk where depth is water depth only.
And on and on and on. Pick one or the other and go with it. Both are better than losing count of the chain markers or miscalculating the tide.
As to depth sounders, I knew that both of my prior owners had used the CHITON for diving (the lazzerete had a rack for 10 SCUBA tanks). What I didn't realize is that both depth sounders on board were set to read the depth from the surface, not under the keel. Ask me how I know.
Mark