Thursday, October 24, 2013

Anchoring Vector

We are still anchored in a cozy spot, Bow Cove, on Mill Creek off the Patuxent River, in Solomons, Maryland.  I had so much ground to cover when I posted yesterday, that I omitted the difficulty we had finding a spot to anchor here.  We are still pinned down by weather today, so I thought it might be a good time to spend a few moments explaining what is involved in selecting a spot and getting settled.

The decision to anchor in a general area is made well in advance of arriving.  Generally speaking, it is made before we even depart the previous location, as part of our route planning process, which could be (and probably will be, at some point) the subject of an entire post unto itself.  Sometimes, though, it gets made while underway, due to circumstances such as weather or mechanical trouble.


In either case, lots of resources come into play in selecting a general location for anchoring.  Chief among these are the detailed nautical charts for the area in question.  We have paper charts for everywhere we go, but the most detailed and up-to-date charts we have aboard in electronic format.  Here in the US, they come directly from NOAA, and we can read them with any of three electronic charting programs we have aboard -- OpenCPN, Sea Clear II, and Polar View.  Right now we use our laptops, but I am also in the process of converting the primary helm navigation system from a dedicated chartplotter to a PC-based system so we can actually drive the ship with these programs.

The charts show us where protection from wind and waves might be provided by geographic features, how much water depth is available, and the type and condition of the bottom surface, to which the anchor must attach.  They also indicate areas where anchoring is prohibited for one reason or another, such as underwater cable crossing areas, fish sanctuaries, unexploded ordnance (really), or navigation fairways and traffic schemes (more on these in a bit).  It does take a bit of practice to be able to look at a chart and know, based on wind direction and other factors, which spots make for a good anchorage.  We get better at this every time, but it is a skill which we are still developing.

Other Resources

Fortunately, there are some other resources as well.  These include cruising guides (both printed and, more recently, on the web), anchorage handbooks, the Coast Pilot, and web databases such as Active Captain.  All of these resources list "suitable" anchorages in various places, based on the experience of the author or the collective experience of other cruisers.  But there is a reason I put the word "suitable" in quotes; permit me a brief digression to illustrate.

We began our cruising life on the Intracoastal Waterway (ICW), since we bought the boat in Savannah, which is along that waterway.  Moreover, we had previously started our training along a different stretch of the ICW, in Florida, way back in 2009 when we booked a one-week training charter there.  Back then, we had purchased a guide called Skipper Bob's Anchorages Along the ICW, and we made good use of several of the anchorages listed therein over the course of our training cruise.

Fondly remembering Skipper Bob's as a useful guide, we again purchased an updated copy for use aboard Vector, and we referred to it several times during our training cruise along the ICW in February.  What we learned from that is that Vector can use only perhaps 10% of the anchorages listed in that guide.  As our training captain said at the time, "Remember, Skipper Bob had a 36' boat with a 3.5' draft."  He also helpfully pointed out that Vector did not need nearly the same amount of protection that most Skipper Bob readers will need in their much lighter and/or smaller boats.  He pointed to an area on one of our charts and said "look -- you could anchor anywhere in here, even though many other boats would have trouble."  The area he pointed to did not show as a suitable anchorage in any of our guides.

Fast forward several months to our month-long cruise up the ICW from Hilton Head to Norfolk, wherein we confirmed without question that Skipper Bob and similar guides were not for us.  It quickly fell into disuse and now sits forlornly on the shelf -- I doubt we will even take it out again on our cruise south.  Information in the Waterway Guide, which we use primarily for marinas, is similarly suspect for us.  Beside the fact that we simply do not fit in many of the listed anchorages, among the biggest problems with these guides is that the conditions in the anchorages that might fit us can change considerably between the time they go to press and when we might arrive at the anchorage.

The Coast Pilot. by the way, has the opposite problem.  Whereas publications such as Skipper Bob and its ilk are generally targeted at vessels smaller than Vector (or, at least, with less draft), anchorages listed in the Coast Pilot are generally intended for large ships.  Sea conditions that can scarcely be felt on the deck of a 900' freighter with 30' or more of draft could have us bobbing around like a cork, and we'd have to put out all 400' of our chain to anchor in water that deep anyway.

Returning to our current practice, we find the information in the Active Captain database to be the most useful adjunct to our own experience.  To be sure, a majority of anchorages listed there are unusable for us due to depth, accessibility, or swing room, but there are more listed to begin with than in any printed guides, and we can page through the user-generated reviews of each anchorage.  These reviews often reveal critical details such as actual depth, where the best water is, which side of the entrance channel to hug, etc., and they are dated, so we can tell if the information is fresh. Still, we take everything with a grain of salt -- conditions can change in as little as a day, depth sounders can be off, and information can be entered incorrectly.

The updated Active Captain data is always available on the Internet, but we don't always have Internet available as we are searching for a spot.  This is especially true if we are having to modify plans under way due to weather or other factors.  For this reason, we ended up buying the Polar View chart software, even though we already had the free OpenCPN and Sea Clear software aboard.  In addition to reading and displaying the same free NOAA charts, Polar View can also download the entire Active Captain database for offline use.  We update the database when we have Internet access, and then it is available whenever we need it.

Anchorage Requirements

So what makes a good anchorage for Vector?  With our six-foot draft, we like to have at least eight feet of depth available at mean lower low water (MLLW), which is how depths are reported on charts.  That eight foot (or more) depth must extend out in a circle from where we drop the anchor for a distance at least as great as the amount of anchor chain we deploy plus the 52' length of the boat.  This is known as "swing room," as the boat swings around the anchor position in response to changes in wind and current.

In something of a catch-22, the amount of chain deployed also depends on the depth of the water.  There is a great deal of debate in nautical circles (pardon the pun) about the amount of anchor rode required for a given depth, a concept known as "scope."  That, too, could be the subject of an entire post, and tomes have already been written.  Suffice it to say that we are engineers, and we understand the simple trigonometry involved in the scope calculation.  We would never consider leaving the boat or going below to sleep with anything less than 7:1, and we extend that to as much as 10:1 if we are expecting storm conditions (notwithstanding the reader who once berated us for a 7:1 scope, on the grounds that we were using up too much of the anchorage -- see "courtesy" below).

What that means is that if we anchor in eight feet of water, we need to deploy at least 56' of rode, including our eight-foot long nylon snubber which is attached at the waterline.  If we anchor in ten feet, we need 70', 20' of depth would require 140', and so on, up to the total available amount of chain.  Our 400' of chain means we can anchor in relatively calm conditions in water up to about 57' deep, or, in rough conditions, water only up to 40' deep.  Note that, while we use depth at MLLW to establish where we can and can not anchor in shallower water, we need to instead use the depth at high tide to establish the amount of chain deployed.

As an example, where we are anchored now, the depth (at the anchor) ranges from about 11' to over 13' depending on wind and tide.  That means we need at least 91' of rode.  If the rode becomes tight, due to wind or current, that 91' of rode translates to 90' on the surface, and adding in the 52' of boat length, our swing circle becomes 142' of swing radius or a circle diameter of 284'.  Allowing for some imprecision in exactly where the anchor dropped, and/or some movement of the anchor (not uncommon if the boat swings around it in a circle),  this is really more like a 300' circle.

It's important to note that within this circle there must be not only no depths less than eight feet, but also no other objects such as docks, pilings, buoys, or other anchored or moored boats, nor can it encompass any prohibited area.  This is where it gets tricky, and why we sometimes need to move on even though a spot may look good on the chart.

Anatomy of an anchoring

When we first arrived here in Solomons, we already had in mind two or three spots that looked good on the chart and had favorable information on Active Captain.  But as often happens, other boats were already here, taking up many of the "prime" spots.  One of the things we have to do when other boats are involved is to mentally map out their swing circles as we assess ours.  It's OK, and often unavoidable, for the circles to overlap -- wind and current tend to move all the boats in the same direction.  But boats don't all swing at the same rate or in the same manner, so it's best to keep the overlap to a minimum, and preferably no anchor itself is overlapped by another boat's circle.

This problem increases in complexity the more boats there are in an anchorage.  It's also impossible to know just by looking how much scope another boat has deployed or exactly where its anchor lies.  It becomes a game of adding safety margins on to best guesses.  And so it was that we took a stab at a good place to anchor just upstream of a pair of already-anchored boats, in a space bounded by the shoreline and its accompanying shoal, a dock, and the main channel of the creek.  The depth there was 16' when we arrived.

We made two passes to get the anchor to set, and then paid out some 110' of rode.  The track on the left of this photo shows how we moved around before and after dropping the anchor.  (There may be some image distortion on your screen from a photo artifact known as a Moiré pattern -- click to enlarge and then make it original size to minimize this effect.)  Once we were securely anchored, though, the wind had us positioned very close to the main part of the navigable water.  That felt too uncomfortable to us, so we weighed anchor and headed further up the creek (off screen to the top).  Finding nothing better there, we returned and tried again on the other side of the creek, where we are now.  We've been here a while -- the dark semicircle with the boat in it represents all the swinging we've done here, and the anchor is more or less at  the center of that semicircle.

Once we are "set" we go about double-checking our circle and the distance to any hazards.  While the electronic chart with our position shown is a guide of sorts, charts are notorious for inaccuracies and mistakes.  We instead use the radar set to verify the actual distance to the shoreline, other fixed objects, and any other boats that might be anchored nearby.  The radar is extremely accurate, and can also validate the position of any charted surface objects (such as the shoreline) when we set it to superimpose the radar image on the chart data.  Here you can see my cursor (the X below and to the right of the blue dot representing the boat) is on the return from a nearby dock, and the top of the display tells me it is 0.03nm, or about 180 feet, away.  The three red blobs to our left are the radar returns from three anchored boats.


We've received a number of comments since we moved aboard about perceived inappropriate anchoring, including being anchored "in a channel."  Since we ended up moving in this case because we felt too close to "the channel" for comfort, now is a good time to address this issue.  There are really three main factors involved here: "rules of the road," safety, and courtesy. Let me take these one at a time.

1. "Rules of the Road."  I have to put that in quotes, because that's not really what they are called out here on the water.  There really are rules, though, and they are codified internationally in the IMO's International Regulations for Preventing Collisions at Sea, which are themselves incorporated into the US Coast Guard's Navigation Rules, International - Inland.  The regulations are nearly universally referred to as the "ColRegs," short for "collision regulations," because the full title is a mouthful, although the Coast Guard often calls them simply the Nav Rules.

Our copy of the Nav Rules.

All vessels in US waters are required to follow the colregs, which can be downloaded for free.  Due to Vector's size, we are required by law to keep a printed copy aboard at all times as well.  I have more than a passing familiarity with them, because I have completed the full course of study for my Master's License.  At the moment, I lack the sea time for the license, so I will not take the exam until I have the required sea time under my belt.

The ColRegs prohibit anchoring (circumstances permitting) in a "narrow channel" (Rule 9).  However, "narrow channel" is nowhere defined in the rules, and it is generally left to admiralty court to sort out any fault in a "narrow channel" collision.  This article on a forum for tugboat skippers illustrates the ongoing confusion in this regard.  It is generally recognized, though, that the narrow channel rules apply in places where vessels of certain beam or draft are constrained to navigate in a confined part of the waterway.

Under the Colregs, no part of this section of Mill Creek constitutes a "narrow channel." The water is nearly the same depth all the way across, and vessels of such a size as to be able to navigate in the creek at all can easily avoid other such vessels anywhere in the creek, whether under way or at anchor.  One quick test for whether an area is a "narrow channel" is to apply a different part of Rule 9: if you are in a "narrow channel" you are obliged to keep as far to the right as possible at all times.

Another test for narrow channels is to apply Rule 34, which obligates all vessels to sound whistle signals any time another vessel is passed (in either the same direction or opposite directions).  If there is enough room on the water for operators to run their boats without need of keeping far to the right and/or arranging passing via whistle signals, then that area of the water is not a "narrow channel" as defined in the rules.

2. Safety.  Having established that we were not in a narrow channel (nor were we in a "traffic separation scheme," another anchoring prohibition defined in Rule 10) , we could legally have remained anchored right where we were.  In fact, this morning when I came upstairs I noted a sailboat anchored more or less dead-center in the middle of the creek, not far from that spot -- he came in after dark last night and left sometime this morning.  But just because it is legal to do so does not mean that it is either safe or wise.

This sailboat is anchored mid-creek, even further from shore than our first attempt.

We'd like to think that all boaters are familiar with the ColRegs and take seriously their responsibility to keep a proper lookout and operate their vessels in a manner that avoids collisions.  Nevertheless, collisions do happen.  Anchoring in an area that has a lot of traffic can increase the chance of a collision.  For this reason, we generally choose to stay off to the side of any well-trafficked part of the waterway.  This is particularly important when visibility is reduced due to weather, or in very dark areas on moonless or cloudy nights.  We did not think visibility here would be a problem, but we didn't know how much traffic the creek saw or how fast some of it moved (even though there is a 6mph speed limit buoy right next to us).  We opted to move for safety reasons -- so we wouldn't get creamed by a speedboat in the middle of the night, perhaps after a few beers.

3. Courtesy.  This one might be the hardest to define of all, and we've certainly noticed a plethora of discourteous boaters in our short time on the water.  But we do try to keep some distance away from marina entrances, fuel docks, private homes, and obvious thoroughfares whenever possible.  When sharing an anchorage, we also try to keep a minimum scope to be fair to other users, so long as it is safe to do so.

The waterway is a shared resource.  While we try to be courteous, it is unreasonable to expect that we can always anchor where no other boat will ever have to go around us.  I've already lost count of the number of times I've had to go around someone else, or had to abandon a plan altogether because we were simply too late, and this is a first-come, first-served environment.

Other Factors

So far we have not encountered a situation where our anchor would not set.  But we know that day is coming.  Every anchor has its strengths and weaknesses -- there is no one "magic" anchor that will work in every bottom.  Our 50-kilo Bruce is good in mud, sand, and loose rock, but we've heard it will have trouble in sea grass.

Unfortunately, the design of the boat permits us only a single main anchor (many boats have dual rollers on the pulpit to carry two anchors) and the size of the bow roller limits how large it can be.  Adding another roller or enlarging the one we have would involve a great deal of cutting, welding, fitting, and painting, over and above the cost of the components and the anchor(s), so it is not really in the cards.  We do have a Fortress 85 stowed in the lazarette with a 250' nylon rode that serves as our emergency anchor, stern anchor, and perhaps our sea grass anchor.  And we will be looking into what other types and sizes of anchor might fit in our existing bow roller.  But for now, we're certain we will have to turn away from some otherwise perfect anchorage because we simply can not set the hook.

However well-set the anchor may be, sometimes they do come out, and the boat can "drag" the anchor from its original location.  I wrote here about how we witnessed an unmanned sailboat drag all the way across an anchorage and end up banging into a dock.  To combat this, we set the anchor under power, and we set multiple "anchor alarms" which track the boat's position relative to the anchor and sound a loud alarm if we exit a predefined circle.  One of these alarms utilizes our ancient GPS-equipped iPad and a free application called, appropriately, Drag Queen.


Our anchor day shape.

One of the rules established in the colregs is that vessels at anchor are to identify themselves as such both day and night.  Among other things, this lets other skippers know that avoiding a collision is entirely on them, as your vessel is not under power or command and unlikely to be able to take evasive action.  While we seldom see it on other anchored boats, we do deploy the required single black ball "day shape" (Rule 30) during daylight, and always use the all-around white "anchor light" after dark or in reduced visibility.  Although our size does not require it, we also turn on some of our LED deck lights at night if we think it is warranted.


Anchoring can sometimes be stressful, but it becomes easier for us each time.  We've come a long way since we once had to abandon the anchor and chain after a failed attempt.  When we first passed Bow Cove here we thought it might be too tight a fit for us with proper scope, but in hindsight it is a perfect little anchorage and we are glad we moved here from across the creek.  We felt secure enough to drop the tender and go out to dinner last night at Stoney's Kingfisher restaurant, which has its own docks for cruise-in guests.  Of course, I had to fix the temperamental davit again first, but that's a story for another day.


  1. As a daytime pleasure boater, 26 feet, I never fail to learn something from reading one of your blogs....

  2. You'll have a lot of trouble with that 7:1 & 10:1 scope if/when you make it around to the PNW. We carry 550 feet of chain and still find ourselves on 5:1 at most and often less than that. And we're only 4.5 feet draft.

    1. Bob, thanks much for your comment. I am guessing we will encounter these issues well before the PNW as we expect to be in the fjords of South America on our way there.

      Perhaps in time we will develop a confidence to lie to a 6:1 or even a 5:1 scope, at least under some moderate conditions. More likely we will get a different anchor before then, which might have different breakout characteristics. And/or we might increase our total chain, now that our chain locker is deeper and can accommodate perhaps another 50%.

      The issue for us is that the design our anchor, a 50-kilo genuine Bruce, has a breakout angle of around 8°, according to the best information we can find (Bruce has exited the recreational anchor market, nearly a decade ago). That is to say, the anchor is designed to hold fast at an angle of pull (from the seabed) up to that amount, but will tend to break out at angles above that.

      A 7:1 scope works out to an angle of 8.2° when the catenary goes taut, whereas even a 6:1 scope is already an angle of 9.6° -- well over the Bruce's breakout angle.

      It can be argued that in moderate conditions our heavy 1/2" galvanized chain will offer sufficient catenary to ensure the angle will remain below the breakout point, and that's probably true for static loads such as a steady wind or current.

      A bigger problem arises when you account for surge loads and our 110,000-lbs of mass. A strong gust or a big wave can easily send us to the end of the chain briefly with the snubber taut and visible just below the surface.

      I suspect your much lighter boat (and also lower windage) does not suffer the same issues, and even if your anchor and chain is a good bit smaller than ours, expressed as a percentage of the mass of the boat its probably a larger share.

      I have no problem, BTW, lying 5:1 for a lunch hook, and I confess we've had to shorten to nearly that in a crowded anchorage, but in anything other than completely protected water it would make me too nervous to sleep.

    2. Its all good in theory but when there's 100 feet of water 100 feet from shore the theory falls apart. Shore tying helps and time will give you more confidence. And at the risk of starting an anchor war, that Bruce isn't big enough for serious anchoring with your boat nor do you carry enough chain IMNTBHO.

    3. Well, the good news is that the deeper the water, the greater the catenary effect, and the lower the required scope ratio. Rocna has a great write-up on this in their knowledge base.

      As far as anchor size, you're not going to start a war with me -- I'm with Steve Dashew on this: it's not big enough unless people on the dock are laughing at you. At least you admit to NTBH :-)

      The Bruce came with the boat, and it's so well integrated you'd think they built the boat around it. Crazy Canadians ;-). BTW, the original builders only included 200' of chain -- and this is in Nova Scotia, mind you. The last owner swapped it for the 400' chain we have now, which was really all that would fit in the locker without jamming.

      As it happens, I have been researching next-generation anchors for the last few days. We're looking to see if any of them would fit the existing "pulpit" (such as it is). I'd like a Manson Supreme, but I think the shank is too wide. It is possible either a Rocna or a Mantus would fit, in say 125 or 150 lb sizes. The problem is that, to know for sure, we'll have to make a mockup and try it. Which means first paying out all 400' of chain so that the roller is empty.

      That's a long-term project, so for now we will be making do with the Bruce. Which, BTW, has been absolutely fantastic here on the east coast -- sets instantly and then never moves.

  3. Great post with much useful information. Thanks.

  4. If you are serious about a new-gen anchor then check out the Sarca Excel. I expect it will fit right into your existing pulpit. Unfortunately you won't find them for sale in North America but Rex will work with you to get you one. Phone him and look at his videos. You won't regret it.

  5. My boat is nearly the same size as yours and about the same weight although I covet your bow eye. My 10 foot bow ends up adding a tremendous amount to my chain requirement. I'm anchored in 20 feet right now but that means it's really 30 for me. So yep, I put out 225 feet to set the anchor (my chain is marked in 25' segments).

    Here's a trick that I learned for tighter anchorage - and I use it all the time especially when you're not expecting a lot of very bad weather and swing - the trick is at the end. Let out the required chain amount for 7:1 or greater. Always, and I mean always power set the anchor. This takes some finesse and time. You can't just plow backwards because the anchor will often skip out. Instead, think about easing the anchor slowly into the mud. It takes practice. We'll go in reverse and go out of gear when we're 25' from the amount of chain let out (DragQueen on the bow is an excellent tool for that along with some type of wireless headsets). Let the boat ease back those 25' and grab slowly. It'll often spring back when it grabs a little and it often drags a little (20 feet is my limit). Do that a few times.

    The ultimate point is when the anchor is set and you're in reverse and everything is holding. If the weather might be bad, we'll up the RPM's in reverse to 800 or 1000 for our normal 600 RPM idle in-gear throttle. Leave it in reverse for 15-60 seconds watching that you're not moving back - DQ again is a good tool there. You'll often see it bounce forward and back as the chain has a little spring through catenary forces even though you're in gear.

    Here's the trick. Your anchor is set well now. Pull in chain so that you're at as little as 4:1 scope. I aim for 5:1 when needed. So where I am now (Tenn-Tom River in Mississippi), I power set the anchor at 225 feet and then pulled back chain until I was at 175 feet. That's about 6:1 but gave me a more comfortable swing room and more time to react if there was dragging. I've been here for 9 days now and I've swung completely around. Because I was set so deep initially, the anchor is likely still in its original orientation but is a few feet under the mud.

    In situations like this, it'll take a little more time to retrieve the anchor and you can't use the windlass to pull it from the mud (ever). That extra time is the best wasted time I get and I'm smiling the whole time.

    Safe anchoring,



Share your comments on this post! We currently allow anyone to comment without registering. If you choose to use the "anonymous" option, please add your name or nickname to the bottom of your comment, within the main comment box. Getting feedback signed simply "anonymous" is kind of like having strangers shout things at us on the street: a bit disconcerting. Thanks!