Please select your home edition
Edition
Protector 728x90

Use this simple secret for anchor holding power!

by John Jamieson on 3 May 2012
.. .
The other day, a reader sent in a query as to why I recommend a 7: 1 scope on anchor rode as opposed to 3:1. After all, less rode means less hassle with having all that line messed up by gooey mud, slimy bottom crud, and other unknowns beneath the sea.

Use enough scope to match the conditions you anchor in. You scope calculation should include present depth, expected rise to high tide, distance of your depth sounder transducer below the waterline, and freeboard (height of the bow above the water). Add all of these factors up. Multiply by seven for an average scope. Why so much?

Here's a simple, eye-opening demonstration of the power of anchor scope, which is easy for you to do in your home waters:

Grab a small anchor (Five pounds or less--easy to handle). The anchor type isn't important--even a tiny grapnel will do. Attach 20 feet of small diameter line to the anchor shank (long arm of the anchor).

Locate a sandy or soft ground area. Dig the anchor flukes into the ground just a bit. No need to bury them all the way. Walk to the end of your 20 foot anchor line. Turn around and face the anchor. Pull hard on the rope rode. What do you notice?

Your anchor will dig into the simulated 'seabed' and hold well. That's because most of the pull on the anchor rode will be horizontal. And that's the secret to keep your anchor dug deep. You want to do everything possible to keep the rode as parallel as possible to the seabed.

That's another reason to use a length of chain at the seabed end of a rope anchor rode if you are using rope. The chain protects the line from chafe (wear) and it provides weight to keep the rode more parallel to the bottom.

Now, let's simulate what happens with just 3:1. In our experiment, we will assume what the 20 foot piece of rope at the end represents a scope of 7:1. So, about half of that length would represent a scope of close to 3: 1.

Walk slowly toward your anchor. Keep tension on the rope rode as you go. Watch the angle that the rode makes with the anchor and sea bed. Stop when you get to a point about ½ of the distance to the end of the rode.

Look at the shank of your anchor. Note that the rode now has an upward (vertical) pull on the end of the anchor shank. Any vertical pull on an anchor shank has the potential to break out an anchor and cause it to drag. The shorter the rode relative to the water depth, the less chance that your anchor will hold. Avoid short scope for long term or overnight anchoring. Longer scope gives your anchor greater holding power over a broader range of wind or sea condition.

Remember, you will not always anchor on a flat plane of water. Wave action, ground swell, and boat wakes cause your boat to lift and fall in position. As we saw in our experiment, any vertical pull on the anchor will decrease holding power and increase the possibility of break out and dragging. Use longer rode to lessen vertical pull when your boat bow lifts and falls in choppy anchorages.

But what about vessels with all-chain rode? Sure, those with heavy chain might use shorter scope of about 5:1 in light to moderate conditions. But 7:1 will always be better. And, in storm conditions or in unprotected areas with heavy ground swell, you need 10:1. Use the maximum scope possible or set more than one anchor in crowded anchorages with limited swing room.

You will sleep better at night when you choose to use enough scope to keep your boat anchor dug deep into the sea bottom--wherever in the world you choose to cruise!

John Jamieson (Captain John) with 25+ years of experience shows you the no-nonsense cruising skills you need beyond sailing school. Visit his website at www.skippertips.com for a free sailing tips newsletter. Become a member for instant access to 550+ sailing skills articles, 100+ sailing video tutorials, 145+ sailing tips newsletters, 12+ sailing topic e-Books, and more!
Zhik Isotak Ocean 660x82Mackay BoatsWildwind 2016 660x82

Related Articles

Bavaria Yachts to introduce Cruiser 34 and Nautitech 46
The Cruiser 34 will be on show at the Bavaria Yachts display at the Strictly Sail boat show at Bayside’s Miamarina The Cruiser 34 will be on show at the Bavaria Yachts display at the Strictly Sail boat show at Bayside’s Miamarina, from February 16th to 20th.
Posted on 13 Feb
Unique Transatlantic Sailing Event - Building friendship across oceans
Rendez-Vous 2017 Tall Ships Regatta, organised to celebrate Canada 150, 150th anniversary of the Canadian Confederation. Sailing in the wake of the great explorers, international friendship and understanding is at the core of this once in a lifetime adventure - The Rendez-Vous 2017 Tall Ships Regatta, organised to celebrate Canada 150, the 150th anniversary of the Canadian Confederation.
Posted on 10 Feb
Frigid flying – Coast Guard aircrews take on New England Winter
Freezing rain? Teeth-chattering temperatures? Limited visibility? Coast Guard aircrews are still ready to fly. Freezing rain? Teeth-chattering temperatures? Limited visibility? Coast Guard aircrews are still ready to fly. At Air Station Cape Cod, aviation maintenance and electronic technicians work around the clock to ensure the MH-60 Jayhawk helicopters are prepared and ready to launch. There is one thing the maintenance crews and pilots cannot control: winter weather.
Posted on 9 Feb
On board interview with Lisa Blair - solo Antartica circumnavigation
So far, Lisa is tracking very well in her attempt to become the first woman to sail solo around Antartica. So far, Lisa is tracking very well in her attempt to become the first woman to sail solo around Antartica. After the setbacks of a delayed departure due to gremlins in the electronics, we are delighted to have these answers from her on board. She is well and enjoying her time. Climate Action Now, her Hick 50, left Albany in Western Australia on January 22, 2017.
Posted on 8 Feb
Yachting cartoonist Mike Peyton dies at 96
“The World’s Greatest Yachting Cartoonist” died on January 25, 2017 just five days after his 96th birthday. Mike Peyton, dubbed “The World’s Greatest Yachting Cartoonist”, died on January 25, 2017 just five days after his 96th birthday. A modest, shy man, he eschewed the spotlight and seemed unaware of the esteem which in sailors all around the world held him.
Posted on 27 Jan
Zhik Xeflex® - your shield against cold environments
This radiant barrier mid-layer nearly defies description. This radiant barrier mid-layer nearly defies description. How do you make a water resistant garment that really breathes, yet reflects your own body heat back to you? Where do you find a compression resistant and extremely insulating filling that is nowhere near as bulky as the Michelin Man, yet gives you that kind of warmth and comfort?
Posted on 17 Jan
Sounds like a boat - Lisa Blair's departure delayed due to electronics
Final preparations of her yacht, Climate Action Now by Sydney-based sailor Lisa Blair have uncovered an electrical issue Final preparations and safety checks of her yacht, Climate Action Now by Sydney-based sailor Lisa Blair have uncovered an electrical issue.
Posted on 15 Jan
Lisa Blair starts Solo Circumnavigation of Antarctica
Over 3,500 people have climbed Mount Everest, only two men have sailed solo, non-stop and unassisted around Antarctica. Over 3,500 people have climbed Mount Everest, over 500 have rowed across the various oceans and 12 people have landed on the moon. Only two men have sailed solo, non-stop and unassisted around Antarctica. Sydney-based Lisa Blair, 32, intends to become the first woman, the fastest and the third person in history to conquer such a challenge.
Posted on 14 Jan
When whales meet sails
CAMPER helmsman Roberto ‘Chuny’ Bermudez found himself nearly face to face with whale in middle of North Atlantic Ocean. Currently the database for marine mammal strikes is very sparse. We are requesting sailors and boaters help to submit information on current and past incidents, however long ago that may be. By giving a location, date, identification if possible, and any other relevant information you can help scientists better understand where marine mammals are at risk for strikes
Posted on 8 Jan
Potential instability in Atlantic Ocean water circulation system
One of the world’s largest ocean circulation systems may not be as stable as today’s weather models predict One of the world’s largest ocean circulation systems may not be as stable as today’s weather models predict, according to a new study. In fact, changes in the Atlantic Meridional Overturning Circulation (AMOC) — the same deep-water ocean current featured in the movie “The Day After Tomorrow” — could occur quite abruptly, in geologic terms, the study says.
Posted on 6 Jan