Media Releases from Maxwell Marine
On the Rode again: Anchoring tips by Nick Cohen
Date: 14 May 2000
The anchor, probably the most internationally recognised boating symbol, has changed a lot over the later part of last century. Historically anchoring was typified by the weight of the anchor, the heavier the better, however more recently designers began to focus on strength and holding power. The results are a number of strong lightweight designs with proven ability to penetrate and hold in various ground types.
These later generations of anchors better suited smaller boats and it is now no longer necessary to haul bulky heavy anchors in small boats when strong easily handled types provide better grip and holding power.
No matter how you visualise the bottom of the sea it is simply ground covered by a massive amount, in depth and weight, of water. The ground at any anchorage can be simply described as either clay, sand, mud, rocks, or kelp; or it could in fact be a mixture of any of these. So many and varied are the combinations that every anchorage is different and these differences help in determining how best to set and use a particular anchor type to give maximum holding power.
If you look around the marinas you can quickly identify the three main types of anchor that are widely used on today’s boats. The first group are the stereotypical anchor types with two or more fixed grapnel like arms that rely on hooking to hold.
These typical types have a proven ability to hold in rocks, from which they may be hard to recover. However to be effective in softer surfaces they need to be heavy as it is their weight that helps dig them in or ‘set’ them. Therefore to be effective for their design they need to be relatively large but their fixed arms make them neither easy to handle nor stow. Good examples of these types are often found adorning the entrances to boating clubs and Naval bases.
The second anchor group comprises those with moving flukes. Probably the best known type and forefather of this modern style anchor is the Danforth. By comparison to other types these neat lighter weight anchors that are easy to handle and stow flat either on deck or in a locker. Their holding power- in hard mud, clay or tight packed sand- belies their weight and size, particularly when set correctly.
The Danforth has twin movable flukes, which burrow as load is applied to set them. If the set angle is correct they will burrow well, however the movable flukes mean that as your vessel swings with wind or tide, the change in angle can cause the anchor to lose grip and you will drag. If the anchor sets easily, initially it will usually reset itself to the new direction but only if it is unencumbered with vegetation or other bottom changes.
These types are less effective in light sand or heavy kelp where their lightweight works against them penetrating beneath the vegetation into the bottom below. In rocks they are nearly useless. But the Danforth is well regarded as a general-purpose anchor. Stowage is simple either above or below decks and the movable flukes mean it is possible for the flukes to sit fairly flush against the hull or deck.
So good has been the reputation of the Danforth that there are a wide number of copies and derivatives. Whilst some are obvious rip-offs, which may not perform as well, other manufacturers have further refined the design by the use of lighter grade hi-tensile steels and alloys.
Other innovations on these anchor types are self-release mechanisms which aid anchor recovery. Usually this means the anchor line (or rode) can slide up and down the anchor shaft so that when you are setting the anchor it pulls from one end, forcing the flukes down. But when recovering, the rode slides to the head of the anchor to effectively pull it out backwards.
Where the pivoting fluke types can best be described as double fluke anchors the other main group are the fixed fluke anchors which tend to be single fluke designs. These include names like CQR, Bruce, Manson, Taunton and Delta but all are design variations on the single fluke theme.
Single fluke anchors are less prone to dislodging as a boat swings because the fixed fluke angle better follows the load as a vessel swings. These types hold well in sand and their heavier weight and fixed penetration angle gives them some advantages in kelp and rocks as well. Their odd fixed shape means they are usually best stored on the fairlead where they tend to protrude forward of the vessel.
Which type of anchor best suits your vessel is therefore best determined by a number of factors. The areas and anchorage’s you frequent plus the size and type of boat you have. Looking at a chart of these areas will give a good indication of what bottom types you are likely to encounter and this should be used to predetermine your primary anchor type. However bear in mind those areas where you occasionally cruise to as this may also be a determining factor. Also talk to local boaties in the area and ask at local stores, a knowledgeable reseller will not only be able to give good advice but will also be able to offer a selection of anchor types and sizes suited to your vessel.
Size is important!!!
The determining factor for size is LOAD not vessel length and trailer boats have very variable loads for their size. With underfloor tanks full and three or four adults and their dive gear aboard the total vessel weight is far greater than for a quick fish after work by yourself. The total weight determines the load put on the anchor and associated lines and this load increases dramatically as wind and sea state deteriorate.
Bear all this in mind when looking at manufacturers recommendations. Remembering the heavier the anchor the better it’s holding power. If you are unsure err on the too big side rather than too small. The best advice comes from people who make and sell anchors not necessarily those who use them irregularly.
Not so long ago it was easy to justify a lighter anchor, than should be carried, because it was easier to handle whether deploying or retrieving. The same logic also meant that a lot of anchors had rope rodes fitted directly to their shanks without any initial length of chain. A point I shall come back to. But in these days of well-priced electric capstans and winches these arguments simply don’t hold.
When we talk about anchoring we are talking about anchors, ie: more than one, because there are situations where it is advisable to use more than one anchor. And as many divers know it is not uncommon to come across a lost or discarded anchor wedged into a reef. Of course having the anchor is only part of the equation, what you use for your anchor line (rode) and how you set it will make it work best for your vessel.
In order to best set any anchor it ideally requires a horizontal pull to make it dig in. Of course unless you own and are anchoring a submarine this is pretty hard to achieve, however with the correct type and length of rode the anchor will feel a horizontal pull no matter what depth of water you are in.
As you increase the distance between the anchor (on the bottom) and the vessel (on the surface) the rode you have “paid out” will sag and the pull on the anchor will appear more horizontal than vertical. This distance as a ratio to the depth of water is called the “scope” and an ideal scope is 7:1. This means you will pay out 70 meters of line to anchor in 10 meters of water.
If your anchor fairlead is 1 meter above the water line then this amount should be added to the depth for the purpose of these calculations ie: 10m of water and 70m of scope becomes 11m of water and 77m of rode!!!
A 7:1 scope assumes a rode comprised almost entirely of rope however if an all chain rode is used the scope can be reduced significantly to the order of 3:1 depending upon chain weight and size. Most anchor manufacturers will have recommended chain sizes to suit their anchors for the rated loads.
Of course rope is cheaper than chain and nylon has an in built ability to stretch which absorbs load changes due to wave action. Rope is also easier to man handle and quieter, however if a good length of chain is paid out the greater weight means there is more sag to absorb some wave action and a rope spring can easily be used at the boat end to minimise noise.
If rope is your rode of choice then there are benefits in adding a short length of chain at the anchor end of the rode. This chain will help pull the rope down and can aid in reducing the required scope. It will also be more resistant to wear on rocks near the bottom. If this is your preferred option a minimum of at least one boat length of chain is a good recommendation.
A common question is ‘how much rode is enough’ and the answer is always as much as you can afford and then some. Anchor rode is a bit like money... it’s the last thing you want to run out of and you can never have too much!!! Always carry as much as you can, one day you’ll be glad for it.
Once you get the anchor rode to the boat there are two important things to be done. Firstly mark it off in measurable intervals. There are a number of ways of doing this either with numbered bands or painting links or braid at regular (say 5 metre) intervals or chain counter. This way you will know how much rode you have out with reasonable accuracy.
Secondly the first thing you do before you load the rode into the ‘chain locker’ is to secure the loose end to a strong point in the vessel. The last thing you want to see when you are laying your anchor is the last piece of chain disappearing through the fairlead. Perhaps this is why some refer to it as the ‘bitter end’ of the rope. (Also another good reason to carry two anchors!!)
Setting a single anchor is the most common form of anchoring. And before anchoring you must pick the right spot. Although you must take into consideration wind, tide, depth, bottom type and other boats the task is nowhere near as daunting as it appears.
First check the time and status of the tide, in some shallow bays tidal extremes can mean there are many metres between the high water line and the low water one. More than one of us would have at least seen someone that has found out that water has retreated during the day to leave only ground under the boat!
Look to see what other hazards, both above and below the water, you might encounter as your boat swings either with the tide or wind. Remembering all the time that you have to consider both where you want your anchor to be and where you expect your boat to be whilst taking account of the scope.
Once you feel you have considered all the variables it’s time to anchor. Slowly approach the spot you want the anchor to be in by heading to it upwind. When you reach the point stop motoring and lower the anchor. Throwing it over the side does nothing except increase the chances of back strain because even the lightest anchors go straight down!!, (And you still have to pull back on it to get it to set.)
When the anchor reaches the bottom, idle astern whilst paying out the rode. When you have paid out the length you determined, given the scope and depth, cleat the rode off. As the anchor bites the vessel will come to a halt even whilst in reverse. If the rode tightens up you know you have a good set, if it vibrates and does not tighten then the anchor is skipping along the bottom. You will have to haul the rode in and try again. This is not uncommon.
The greater the scope you use the better the chances of a good initial set, then you can pull line in to reduce the scope back to the preferred amount.
Once you are comfortable with your set and position, allowing for any swing, you can cut your engines and enjoy the day. However first take some bearings to fixed objects so that you can check to ensure you are not dragging. If these change appreciably let out more rode or reset the anchor. Remember marking off the distance to the anchor on the rode helps you determine just how much you do have out for any given depth.
Weighing anchor is simply the reverse procedure, Slowly motor up your line recovering the rode as you go. When you get above the anchor the rode will be vertical and the load should pull the flukes away unless they are well glued in or stuck in rocks. Some anchor types allow you to fit ‘trip lines’ which can be used to pull the anchor up by its head rather than shank. This is a good way of getting out of rocks because it reverses the action which set and locked the fluke(s) in.
Some designs even have automatic tripping mechanisms but these types are generally not recommended for use overnight where tide/ wind changes may swing the boat enough to automatically release the set.
There are times when it may be necessary to use two anchors. Either to hold the boat because of a tight anchorage or mooring, or because of weather extremes.
Where the confines of a narrow channel or anchorage limit the amount your boat can swing, or a long stay is planned it makes good sense to set a second anchor directly astern of your vessel. The bow anchor is set as normal then twice the rode is paid out to drop back to the point where the stern anchor is to be dropped. As the vessel moves ahead, to set the stern anchor, the bow rode is taken up until you are back in place. The stern anchor is then cleated to the same bow cleat as your forward anchor. In this way your vessel will ride better to wind and tide but it will not block a passage or swing widely with changes. It also gives you the security of knowing you have a secure anchor for each side of the tidal swing.
Of course if others around you have not set the same way then they could swing onto you or across your anchor lines which makes for further fun.
In extreme cases you may need two anchors just for holding power against the wind. In such instances set both anchors off the bow each at 30’-45’ either side of the prevailing wind. Also allow some extra scope to ensure the pull on each anchor is a horizontal and even as possible.
With the use of modern electric anchor winchs capable of handling both rope and chain plus the advantages of electronic rode counters it is now possible for anchoring to be completed by the helmsman with the aid of a few buttons.
However more typically on trailer boats the anchor locker and anchor are accessed through a forward hatch. Increasingly we see new boats fitted with electric winches which are also being retrofitted to second hand boats.
When using electric winches you may have to upgrade the vessel battery capacity or fit a separate battery for the purpose. Take care to ensure your engine is always running when you use these winches because they consume large amounts of energy, even on short retrievals, and if you have a lot of rode out then they will be working for longer periods quite capable of ‘flattening’ a standard battery.
Nowadays anchor winches are capable of handling a chain rope combination further improving anchor handling. Floor mounted foot switches or higher mounted buttons that can be operated by hand or knees also free both hands allowing one for the vessel and one for the task at hand.
All in all anchor handling is now simpler and safer with the advantages of modern anchors offering greater and more reliable holding power provided you select the best system for your vessel.
One of the most important things to consider aboard your boat is securing your investment. It is the reason why proper anchoring technique and the proper selection of the correct anchor winch for your particular vessel is so important. However, choosing the ideal anchor winch is not the whole equation.
Rode selection, particularly chain selection, is extremely important and if the rode and winch are not perfectly suited then the results could be disastrous. Choosing a winch too small for the job will only result in frustration and when the going gets tough and a lot more is asked of the winch than it is designed for, the inevitable result could compromise safety and result in costly repairs.
The range and type of anchor winches is extensive and whether it is a vertical or horizontal windlass, chain only or a combination of rope and chain winch, they all do the same job. Deciding on the correct anchor winch for your boat depends on the size, not only of the boat, but also the ground tackle (chain, rope or rope & chain).
The two basic types or style of winch; vertical and horizontal, are differentiated by how the drive shaft is orientated. Vertical winches, which make up the majority of winch sales, have the capstan and/or gypsy above deck and the motor and gearbox below deck. Horizontal winches are mounted completely above the deck with gypsy and capstan located to either side. Deck thickness and underdeck space are the two main considerations when deciding on which of the two types to fit.
There are a number of important criteria involved in selecting the correct anchor winch, such as the vessel size, displacement and windage; size of the anchor, the chain or the rope and chain required to do the job correctly. The only meaningful way to rate an anchor winch’s performance is by what it will lift and at what speed. The two things to consider are, (a) the maximum pull capability and (b) the working load of the winch. Maximum pull, sometimes referred to as stall load, is the maximum short term or instantaneous pull of the winch. Working load is generally rated at about one third of the maximum pull and is usually considered to be the load that the winch is pulling once the anchor is off the bottom.
The wattage of a DC electric motor is not the important factor. Rather, it is the efficiency of the whole winch including the gearbox and motor. With the increasing popularity of powerful and compact on-board generators, AC powered winches are becoming a practical consideration for bigger boats. Hydraulic systems provide another power source well worth consideration as they have the advantage of constant speed under all load conditions and can be run almost constantly while coupled with safe guards such as pressure relief valves. Modern hydraulic systems offer an integrated, low maintenance and efficient, centrally managed, power pack. Most brands of winches and capstans are designed to take chain only, rope only or a combination of rope and chain.
Although rope/chain systems are very popular on boats up to 15 metres (50 feet), chain only systems are still the most popular on larger sail and motor yachts. The advantage of the automatic rope/chain system is that there is a lot less weight in the bow. However, anchor locker size, the correct and optimal installation of the winch and the proper selection of rope and chain are important considerations if you are to get the maximum and most trouble-free performance from your winch.
There are two main types of anchor chain - short link, the most commonly used chain on small and medium sized boats & stud link, which is generally used on much larger vessels such as superyachts. The latter is characterised by a stud (bar) joining the two sides of the link preventing them from deforming when overloaded. High test or graded chain should always be used. Long link chain should not be used with anchor windlasses.
There are a wide variety of chain sizes available in both metric (mm) and imperial (inches) and this will have bearing on your final winch decision as it is important that the right size and right grade of chain is used to ensure a correct fit of the links to the gypsy. Ideally you should purchase chain that has been manufactured and tested to a recognised standard. If you don’t match the chain to the chainwheel you risk problems such as the chain jumping off the gypsy, clattering because the links don’t fit the pockets correctly and jamming as the chain will not feed smoothly through the chainpipe.
The chain wrap on a vertical windlass is a little over 180° which means that the load the chain links are carrying on the gypsy is distributed over more than 50% of the available, link carrying, chainwheel pockets. In a horizontal windlass the wrap is reduced to only 90° and therefore the load carrying pockets are reduced to less than 33%. The more chain on the gypsy, the more the load will be distributed. As chain to chainwheel compatibility is so important, you need to have a chainwheel to fit the chain as there is no such thing as a universal chainwheel!
Accessories such as chain stoppers, chain snubber or chain compressors are highly recommended for safe anchoring, the avoidance of accidental or unintentional self launching of the anchor and for preventing damage to your anchor winch. You should never anchor off your winch! It is designed to pull up a dead weight and should not be subjected to the strain of your boat riding at anchor.
Choosing the right anchor winch is important for trouble free boating. If you want to eliminate the possible pitfalls of poor chain wrap, the wrong sized windlass and chain link variations, then the best advice you can get is to contact the agents or distributors of the brand of winch you have decided on. If you think the combination you are considering may be too small, then go to the next size up. Better to have too much pulling power than not enough.