Questions asked by magazine readers and answered in ‘expert advice’ pages:
Chain strength and loadings
Please could you advice me where I can find the average breaking strengths of 6, 7 & 8mm galvanised anchor chain and the tonnes pull exerted on a 25, 31 & 35′ LOA sailing vessel at anchor in a force 8 gale. It seems from just looking at how small many anchors are on vessels in any marina, that many of us may have got our sums wrong.
Many chandler websites include this information (Jimmy Green, Plastimo, etc) Quoting from the Plastimo catalogue, breaking strength and safe working load figures are as follows:
- Plastimo Grade 40 DIN 766
- 6 mm 1630 kg SWL 400
- 7 mm 2548 kg SWL 630 kg
- 8 mm 4030 kg SWL 1000 kg
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However, note that 6 and 7 mm figures are for ISO 4565 uncalibrated chain, although the figure for both ISO 4565 and calibrated DIN 766 for 8 mm is identical.
Most of the information you could ever require on chain dimensions, loadings, strengths etc can be found at the Bradney chain website, http://www.bradneychain.com/_pdf/short_link.pdf
So far as the loadings on anchor rodes are concerned, there is enormous variation of advice, dependent upon the safety and other factors included in the figures. I wrote a detailed response to a similar question for YM in 2008. In my view one of the better ones is that proposed by Professor John Knox, inventor of the Anchorwatch, whose theoretical equation is backed up by measured values. His equation is:
Force (in kg force) = (1/500) x (LOA in metres squared) x (wind speed in knots squared)..
So far as the load that an anchor can hold is concerned, many tests have been carried out over the past 10 years or more. Perhaps the most authoritative of these was by Yachting Monthly in conjunction with West Marine and Sail magazine. Results are dependent very much upon the bottom at the anchor sites, but in general the latest anchor designs can hold the highest forces. The West Marine site details the procedure of the testing and the full results were published by YM.
Anchor rode length
The standard method to calculate the amount of anchor chain to use is by multiplying the depth of water by 5 (or other fixed numbers, depending on who you read). Why is this, when the effectiveness of the chain will vary hugely according to the depth?
For example in 3m, 15m of a chain weighing 1.5kg/m would be able to take a load of about 520N (52Kg) horizontally before the chain started to lift the shank of the anchor off the seabed. If the same calculation (5x depth ) was used with 10m of water, 50m of chain would be used – and this could take a load of 1850N (185 Kg) before the shank lifted. In fact a chain of 28m would achieve the same result as 15m of chain in 3m. The results would be similar (although the maths slightly more tricky) if you looked at, say, 5 degrees or 10 degrees of lift of the anchor shank.
The ‘simplication’ of the normally taught calculation can lead to too little chain being put down in shallow anchorages (particularly since the anchor is attached to the boat at least 1m higher than the water surface). It can also lead to some decent anchorages needlessly being dismissed as ‘too difficult’ because of the difficulty of retrieving so much chain.
Your observation is quite correct and has been considered in considerable depth (!) by several investigators, shown on the following Internet sites. Peter Smith, designer of the Rocna anchor, shows a number of variables in graphical form at http://www.petersmith.net.nz/boat-anchors/catenary.php Alain Fraysse’s website includes downloadable spreadsheets that allow the user to input their own yacht details to calculate the optimum rode length under a variety of conditions. Professor John Knox, on his website at http://www.anchorwatch.co.uk/index-page04.htm has derived the formula:
Chain length = (1/16) x (Yacht length) x (wind speed) x Square root of (Depth /specific chain weight) The expression advises rode lengths along the lines that you suggest, although I find that for my boat it only gives sensible values for higher wind speeds.
In reality, the 5:1 guideline is good enough for the majority of anchorages, perhaps between 3 and 8 metres depth. In the Mediterranean I have on occasion been forced to anchor in greater depths, up to 18 metres, where I have been able to hold safely with 55 metres, a scope of only 3:1.
In bad conditions it’s worth remembering the old adage: chain does you no good in the locker! Last season I anchored in 2.5 metres and deployed nearly 40 metres of chain in a three-day gale. A Dutch boat not far astern of me, in slightly greater depth, had 70 metres out. We both held throughout, whereas many other boats dragged.
Given that any mechanical contrivance is only as strong as its weakest link, why do rigging designers continue to incorporate such an inherently weak component as a split pin in a structure bearing such enormous loads? Why not, for example, a threaded clevis pin with a self-locking nut? As a sometime climber I would certainly never use such an obviously unreliable component in any system of belays, or in an abseil anchor, or as part of a crampon, for example. Why build rigs with such clear potential for failure?
Can one of your experts explain, perhaps?
The clevis pin retained by a split pin is a strong, reliable articulated joint that is widely used in all branches of engineering, particularly in automotive and aircraft duties. When assembled correctly there is no load on the split pin, it is simply there to prevent the clevis pin from falling out of its drillings in the fork and tang. Correct assembly requires as follows:
The clevis pin should be round and undamaged.
The holes in the fork and tang should be round and at 90 degrees to the applied load.
The split pin should be new with each fitting. It should be a good fit in the drilling of the clevis pin.
The ends of the split pin should not be excessively long but they can be bent back on themselves to prevent snagging.
I would be interested to know why you state that the split pin had failed. Provided that the points above have been addressed I can think of no way in which the pin will fail. Wear of the clevis pin or its drillings may allow the load to be applied unevenly, in which case a lateral force could drive the split pin against the fork and, in extreme cases, through a very sloppy fit. My view is that the root cause is not a failure of the split pin.
The suggestion of using a threaded clevis pin and lock nut is interesting as it could well cause more problems than it cures. Nyloc nuts are reliable when used once only but how many would replace them every time the bottle screw comes off? Where nut reliability is essential, a split pin is used in conjunction with a castellated nut. Threading the clevis pin introduces stress-raisers that do not exist in the original version, introducing the probability of fatigue failure.
If you are concerned about possible future loss of your rig, I suggest you pay attention to the points above, plus pack the length of clevis pin between the fork and split pin drilling with suitably sized washers to take up any movement. Any large amount of movement between the fork and tang could be addressed in a similar way.
Anchor chain weight
I have a 1989 Moody 376 and I wish to up grade the anchoring equipment. I have already replaced the 35lb CQR look-a-like with a 45lb genuine CQR. The chain on the boat is 30mtrs of 8mm chain with a rusty link at 20 metres. All chain is kept in the forward chain locker. I would like to upgrade to 60 metres of 10mm chain.
Question: – as I estimate the weight of the new chain will be 400lb heavier than at present, would this extra weight at the front end be acceptable?
Some good news for you! Your estimate seems to be rather pessimistic, so the situation is not quite so bad as you fear. 60 metres of 10 mm chain, according to two sources, will weigh between 131 and 135 kg, or 288 to 297 lbs. Your current chain weighs 43 kg, or 94.6 lbs.
An increase of about 90 kg, or 200 lbs, is significant but not unacceptable, being about the same as a well-built man standing on the foredeck. I would expect a Moody 376 to cope with this weight without noticing a major reduction in sailing performance.
If this weight seems excessive, you could consider a part-chain, part rope anchor rode. There is a great deal of theoretical information showing that this arrangement is actually better in ultimate holding power than an all-chain rode. The downside is that in a crowded mooring a boat with a rope warp can be something of a nuisance, due to its increased mobility. However, for many shallow UK anchorages it is unlikely that very much of the rope will ever be deployed.
Some long-distance cruisers stow all of their chain and anchor below, close to the centre of the boat, before embarking on blue-water passages. The intention of this action is to reduce the boat’s moment of inertia, enabling the bows to rise over waves more readily. This is unlikely to be convenient for coastal cruising but may be borne in mind in case of future voyages.
Anchor rode loads
During our summer cruise in a Legend 33, we anchored in Dale Bay, Milford Haven on 5 July. The wind was west Force 8/9 during the night, with negligible tide. The sea bed, Delta anchor, 8mm chain, warp splice, 14mm nylon warp, additional warp, and cleats all held. We were happy to go to a marina the next day!
Does anyone know what the anchor loads are during these conditions? What is the safety factor in the warp? In a tide way does the anchor turn round with the tide? Thank you.
This is a very difficult question to answer!
Perhaps the most widely used figures are those of the American Boat and Yacht Council (ABYC), given for combined wind and wave dynamic forces, for various lengths of craft. For a Legend 33 the figure in 42 knots of wind is 818 kg (1800 lb).
However, many independent authorities have reservations over the values given, considering them to have excessive factors of safety. A calculation method given in Skene’s Elements of Yacht Designderives rode forces from the square of the wind speed acting on the cross-sectional area of the vessel. The figure predicted for a Legend 33, for the same conditions, is 481 kg (1058 lb). Professor John Knox, inventor of the Anchorwatch, has proposed the equation Force (in kg force) = (1/500) x (LOA in metres squared) x (wind speed in knots squared) that agrees well with data measured by his equipment. For a 35 foot boat the figure given by this equation is 402 kg (884 lb).
In the two examples of measured values known to me, the values quoted are considerably lower. Again, using the same wind speed of 42 knots, a 30 foot boat recorded loads of 170 kg (375 lb) and a 33 ft vessel using the Anchorwatch measured 150 kg (330 lb).
So far as the strength of your anchoring gear is concerned, chain to DIN 677 has a safe working load of 825 kg and an ultimate tensile strength of four times this figure. 14 mm nylon multiplait warp has a breaking strength of about 4600 kg, for which a safety factor of 4 would give a safe working load of 1150 kg.
The answer to the final part of your query is that in my experience, provided that adequate scope has been laid, the anchor rarely turns even in the strongest of tides. The friction of the chain against the bottom seems to be adequate to prevent the full anchoring load from reaching the anchor. Of course, this does not occur should the chain lift from the bottom if the scope is inadequate or the wind strength is high.
|Table 1. Loads for Ground Tackle Systems (adapted from ABYC)|
|Boat Length (LOA) – feet||Beam (Bmax) – feet
|Load on Ground Tackle – pounds|
|Sail||Power||15 knots||30 knots||42 knots||60 knots|
I have a water maker on board with the seawater intake fitting in the engine compartment. I understand that the intake and seacock are made of ‘Naval Brass’ – CZ112. Is this secure or should it be DZR – CZ132? Were it to fail, it is an extremely awkward position to get at – a complete nightmare and the feeling of – ‘if only I had just…..’ doesn’t bear thinking about!
According to the Copper Development Association, Naval Brass CZ112 (1-1.4% tin) is no longer available, the nearest alloy to Naval Brass being a leaded brass CW712R, available in rod, bar and wire. The Classic Boat website describes Naval Brass as being used for ‘pre-war (WW2?) boat fittings’. This suggests that the composition of your fittings may not be as you understand.
Naval Brass is a 60/40 brass containing a small amount of tin, about 1% being typical. Small additions of lead are usually made, to improve its machinability. The corrosion resistance of the alloy could be expected to be rather better than that of brass but a long way from ideal for sub-surface use. The failed fitting analysed by YM a few months ago, although a 70/30 brass rather than a 60/40, had a similar tin content, suggesting that the protection offered by this amount of tin is insufficient for the duty.
In view of the consequences of failure that you mention it would be wise to replace the fitting, or at least vigorously heave on the hose and give the fitting a thorough visual inspection.
Moody 346 hatch
The Perspex on my Moody 346’s aft cabin hatch is sorely damaged. Most of it is crazing, but I think there are some deeper scratches. It’s unclear to me how deep the scratches are but the cover looks so crazed or scratched that you can’t see through it – and therefore looks unsafe to tread on. I have no idea how they’re fixed in. What cheap ways are there to replace them?
I have seen many crazed and scratched hatches, and some that were cracked right through, but I have yet to hear of anybody who succeeded in falling through, so I believe the risk to be minimal. Perspex is a trade name for acrylic sheet.
Photos of the aft hatch on a Moody 346 look like Lewmar ones to me although I cannot be certain about yours. The support section of the Lewmar website (www.Lewmar.com) lists spares for all their hatches, although spares for older models are no longer available. The acrylic and sealant are sold as a single item.
If yours is an obsolete model, or you want to replace it more cheaply, it is not difficult to do. The acrylic will either be retained by the sealant alone or will additionally be retained by small self-tapping screws into holes in the plastic. These need to be removed first. The acrylic can then be removed by cutting around the sealant with a sharp knife, then carefully levering it out. I use a piece of wood for this to avoid damaging the frame.
The old window can then be used as a pattern for a new one. Take it to a signmaker or a supplier of plastics, usually Yellow Pages will include several. They will cut a perfect copy, including holes for handles, self tapping screws if needed, etc. The frame should be cleaned off using a scraper, then apply a generous amount of sealant. There are specialist sealants for this, Sikaflex 295 UV or 3M 5400 FC are two. Fit the new plastic, screw in the self-tappers if appropriate, close the hatch and put a light weight on top so as not to squeeze all sealant out. Fill any gap between the plastic and frame and wipe off with a rag and white spirit. It will take about 24 hours to fully cure.
To do a theoretically perfect job you should use primers – one on the plastic and another on the frame. The cost of these would be prohibitive for one hatch and my experience is that they are not needed. Light abrading will ensure a good bond.
A completely different approach would be to have the whole job done by a specialist company such as Eagle Boat Windows, strongly recommended on the ybw.com forums.
I bought my Hallberg-Rassy 37 in June 2009 new from Ellös, Sweden. In March 2011 the boat didn’t move in the marina in Scheveningen after starting the engine. After bringing the boat ashore in April I found out that the propeller vanished and that the saildrive was heavily corroded, the anode was only normally corroded. There was no damage of the propeller shaft.
The dealer in the Netherlands rejects any claim by stating that I didn’t maintain the boat properly. My reaction is that any maintainance could not have prevented the serious corrosion of the saildrive nor the loss of the propeller. In my view Hallberg-Rassy made serious installation mistakes i.e. the isolation between the engine and the saildrive and the proper fixation of the propeller.
My question is: Is it fair to say that the damage could have been prevented by me?
There appear to be two separate issues here, the corrosion of the saildrive leg and the loss of the propeller. Corrosion of saildrives is carefully controlled by their isolation from the engine and other parts of the boat by a special plastic gasket. It is most important that the isolated saildrive is not connected to anything else by a conductor. The saildrive and its bolts must not be used for an earthing duty or an SSB ground plane and the hoses supplying the engine should not be wire wound. Your photographs show corrosion of the anode to what I estimate is more than 50%, which is only just acceptable. It could be argued that this a contributor to the corrosion of the leg but the brightness of the anode suggests that it continues to function. Leg corrosion can be caused by any of the above but also by antifouling with a copper-based paint. It would be worth checking that electrical conductivity between the anode and saildrive is good, using a meter. Also check that there is infinite resistance between the engine and saildrive to identify any failure of the isolating gasket. Corrosion can occasionally occur in marinas due to external stray currents but a skilled technician would be needed to detect this.
It is inconceivable that your propeller has corroded away to nothing, complete with the fixing nut and split pin. It looks extremely likely that the propeller has simply fallen off due to the absence of the split pin, and possibly even the nut. Volvo folding propellers are electrically isolated from the drive shaft and have their own anode but other makes do not. The increased anode corrosion rates that can result from fitting others can be reduced to some extent by painting them.
From your facts as presented, and assuming that none of the saildrive defects described above have occurred, then it would appear that the damage was beyond your control.
Some time back, YM published an article about the value of anchoring with two anchors in tandem. I am, currently, in the Caribbean; and, am aware of the enhanced risk, this year, of tropical storms bubbling up, within the Caribbean, with little or no warning. My insurer allows me to stay within the Caribbean, during the hurricane season.
Should such a storm take me unawares, and I do not have the physical time to sail south of the storm, I would like to deploy two anchors in tandem. The first is a Fortress; the second, a Delta, linked together with 15ft of chain.
I have two questions:
(1) Recent correspondence in the MantaTech forum recommends the chain, linking the two anchors should be attached to the shanks of both anchors. My own preference would be to attach the chain to the shank of the Fortress and the crown of the Delta; but, which would be more effective in holding against hurricane force winds?
(2) Do I choose a sandy floor at, less than, or more than 15ft depth of water. I own a Manta catamaran with a 3ft draft. I am aiming for a chain scope of 10-20:1. Clearly, the less the water depth, the greater effective scope of chain; but, which depth is best for anchors in tandem?
To deal with the purely technical points first, there are two main ones.
- The effect on the holding of the secondary anchor (the Delta) of having an opposing force applied to its crown
- The strength of the Delta at the attachment point.
It is clear from reading the many anchor tests and experiences of users reported on forums that the setting and holding of anchors is influenced by quite small changes to their shape. For example, it is widely reported that the various copies of CQR and Bruce designs are considerably inferior to their source originals, minor shape changes having disturbed their effectiveness. It is reasonable to suppose that changing the angle of pull on the Delta by applying a force at some angle will not improve its holding.
I assume your intention is to attach the chain from the Fortress to the hole at the elbow in the shank. This point is not designed for this purpose, and although it may be strong enough to resist the enormous loads imposed by a tropical storm, it may not. There have been several reported cases in which some anchors have failed due to this treatment, although not a Delta to my knowledge.
Attachment by both shanks avoids both of these potential problems and also introduces a certain amount of flexibility into the overall system, which I believe would be beneficial. However, my preferred option would be to deploy a single large anchor, preferably one of the ‘new generation’ types, that will still be holding when the cleats are ripped out of your decks!
Many of the reported draggings and wrecks in hurricanes occur when the wind direction reverses as the storm passed overhead. The first priority must therefore be to hole up in a closed bay with minimal fetch all around. US and Australian catamaran owners often manage to insert themselves into mangrove swamps, where they can tie warps to trees and roots all around the boat. If this is not possible then the risk of anchoring in open shallow water is that waves from the direction of greater fetch could be feeling the bottom and steepening after such a wind change.
You need to be aware that any shock absorption due to catenary disappears at around wind force 6 when the chain is pulled straight. A good snubber of at least several metres of nylon rope will assist in reducing shock loads on the boat.
Delta drag in mud
The ground tackle on my Jeanneau Sun Odyssey 35 is a 16kg Delta anchor plus 60m of 10mm chain. Over the last few years I have anchored in more than 100 different anchorages along the south and west coasts of Britain and around Brittany, Ireland and Scotland and experienced no dragging problems until this year.
However, we spent this summer in the Western Isles and the north-west of Scotland and for the first time we experienced anchoring in soft, gloopy, black mud. It seemed that the anchor set easily but then ploughed silently at low loads. The lack of vibration meant that feeling the anchor chain (or hearing it) offered no warning of drag. This was alarming.
As we are gradually moving the boat around Britain, I need an anchor which performs well on all types of ground. Almost all anchor tests are carried out on sand or clay and so it is difficult to judge whether there would be a better anchor than the Delta for Scottish Lochs. Please advise whether there is a better type of all-round anchor or whether the real solution is to buy a heavier Delta.
Your experience very much resembles mine. I happily used Delta anchors on two boats for almost 20 years, never experienced dragging, and only once failed to set it, on a surf beach of hard sand. It was only when anchoring in very soft mud in Greece, admittedly in some horrendous wind conditions, that I suffered dragging. On three occasions within about ten minutes I was extremely embarrassed to find myself completely unable to remain in the same position on the seabed. In the end I reversed into the wind until I reached the shore in the shelter of some trees and took lines to them.
The Delta is a plough anchor and eventually, as you have found, if you pull it hard enough that’s exactly what it will do – plough the bottom. Its fluke surface area, which is the parameter that gives any anchor its holding capability, is not particularly high relative to its weight. The softer the bottom becomes, the lower the wind speed at which dragging will occur.
There are two types of anchor that offer higher fluke areas than the Delta – the Danforth/Fortress and the ‘new generation’ anchors, Spade, Rocna and Manson Supreme. The former of these offers very large surface area with quite low weight but, as you have no doubt read in these pages many times, they suffer from an inability to re-set when the direction of pull reverses, or even changes by 90 degrees. They cannot be recommended for bower anchor duties. In contrast the ‘new generation’ anchors hold well and re-set reliably in a wide range of bottoms. The various anchor tests agree in placing the Delta at around 60% maximum holding by comparison with the new types. My choice was a Rocna to replace my Delta. It has entirely lived up to my expectations for the past three seasons.
Since sending the original question, I’ve done a lot of research on anchor performance and find that it is fairly obvious that the Rocna, Spade and Kobra 2 anchors are all better than the Delta. On firm ground (sand or clay), you chose your test to decide which is the best. However, I can find very little comparative data on their relative performance in soft mud. Therefore, may I change my question slightly to ask whether there are any data or experience to show which of the anchors performs best in soft mud.
I know of only one anchor test carried out in mud, done by Powerboat Reports in 2001. This organisation ranked set and holding power in both sand and mud for 18 anchors, some of which are unknown in UK. Despite being the lightest steel anchor in the test the Spade Model 80 ranked first overall, never falling below seventh in any of the measured categories. The Delta scored almost as well, coming fifth overall. At that date the other ‘new generation’ anchors (Rocna and Manson Supreme) had not been introduced but I would expect them to perform similarly. Fortress and Danforth, which unsurprisingly showed high holding power, suffered from relatively poor set in both bottoms.
I own an X 482 which I have had for 12 years and enjoyed trouble free sailing. In the last 2 years I have started to suffer from blocked fuel lines and very dirty filters which I need to change every 20 engine hours or so. The contaminant is a black sticky oily sludge which has even blocked the fuel pipe at the tank take off point. I always filter the diesel whilst filling the tanks. I have cleaned the tanks but the problem persists. There is no evidence of any water in any of the fuel. It seems, from the internet, that this is a widespread problem with an equally wide range of possible solutions. I would be very grateful for the advice of any of your experts or indeed any of the readers.
Diesel bug is actually the dead bodies of the bacteria that have been breeding at the interface of fuel and water in the tank. The bacteria themselves are present even in fuel from the refinery but remain inactive without the ideal conditions which they meet when the fuel becomes contaminated. Your question suggests that the fuel you buy may already be contaminated with water, not unusual with marina and harbour bunkers that are replenished from barges. So firstly, I would sample your normal fuel source and change it if you find that fuel in a glass bottle shows signs of significant water.
Next, cleaning the tank. It is extremely difficult to clean a tank in situ using conventional means. The absolutely best way to eradicate the bug is to remove the tank and have it steam cleaned at an automotive garage. This is, of course, impossible to achieve in some cases, but at the very least you need to access the tank via an inspection plate, remove physically any sludge using mechanical means, then flush thoroughly using a low viscosity hydrocarbon, such as paraffin. Stir and if possible circulate the paraffin with a pump through a filter. Dry the tank as well as possible and fill with known good-quality fuel.
So far as additives are concerned, I and many contributors to the Motor Boat forum on ybw.com have had very good results with Startron (ex Soltron). My case was very mild but any darkening of the filter was completely eradicated with one dose. I have read of cases where contamination was extremely severe but this product seems to have cured it.
Every year I remove my anchor & anchor chain from its locker and lay it meticulously on a pallet or something similar. I was asked by a thinking friend why I did it. I must say I found the answer rather difficult. The best I could come up with was every one else did!
Zinc is applied to the surface of chain to reduce the effects of corrosion, both by the atmosphere and by seawater. The application process may be by galvanising, a process that basically comprises dipping the steel chain into molten zinc, or by electro-plating. The former is preferred for marine use as it lays down a thicker coating of zinc, although some chandlers sell electro-plated chain. It pays to find out exactly what is being bought.
Zinc corrodes at a rate of about 1/25 that of steel in coastal atmospheres. Its corrosion resistance is provided by the formation of passive carbonate films on its surface. In humid conditions without the benefit of freely circulating air, condensed water evaporates very slowly. Slow evaporation of thin films of water from relatively large surface areas tends to increase the oxygen levels of the remainder, particularly affecting the water in the crevices between chain links. The oxygen-enriched water corrodes the zinc, producing white deposits of zinc hydroxide instead of the protective carbonate. The zinc corrosion rate is greatly increased by this process.
The conditions described above are typical of those to be found in an anchor locker over winter. Temperature fluctuations lead to deposition of condensed water, followed by slow evaporation, concentrating oxygen at crevices. Most yachtsmen will be familiar with the white deposits that indicate rapid corrosion of the zinc film. Flaking the chain out beneath the boat will not prevent it from becoming wet in the British climate but drying will take place rapidly when the rain stops. These conditions are far better than the permanent stagnant, moist conditions in the chain locker.
Removing chain also benefits the boat itself. Permanent damp in the chain locker can permeate to other parts of the boat and, in those where the locker is in the forepeak, is a known cause of dampness in the bulkhead and forecabin upholstery.
Chain around keel
I recently experienced a situation whilst anchoring in the river Guardiana, the border with Spain and Portugal. This is a delightful spot, which I am sure is known to many. I have visited this anchorage on many occasions in the four years that I have kept our boat in this area, but on this occasion, I decided to anchor 200yards south of St Lucar on the Spanish side. Our new boat is a Jeanneau 36i fin keel with a bulb on the keel. I was anchored in about 4 metres at high water and one and half metres at low water, these depths being under the keel. The current was running quite strongly and the wind was blowing 25knots against the current.this meant that the wind was having a greater effect on the boat than the current, and as a result the boat rode over the anchor chain and eventually wrapped itself round the bulb on the keel. This obviously shortened the scope of the anchor chain with the result that the anchor lifted and dragged in quite a busy anchorage. I had a scope of about 20metres of chain out.
Fortunately, a friend saw the incident, as I dragged past his boat and assisted me in setting a kedge anchor that I always keep handy, when this set, we were able to free the main anchor from the keel and no damage, other than a lot of epoxy being scratched off my keel, was caused. I have over 40 years of sailing experience and have never before has this situation arose. I have lived on anchor for two years in the caribbean without a problem.
Firstly, I believe that the design of the keel on the Jeanneau is partly to blame and maybe I should consider deploying a chum on the anchor chain, but your views on preventing this happening again would be appreciated.
The solution may be dependent upon how much space is available, and whether other anchored yachts around you are suffering the same problem. Deploying your kedge anchor will undoubtedly prevent your chain tangle but you may run the risk that another yacht not anchored in this way could collide with you.
One possibility is a Bahamian moor, used where the current reverses. The bower and kedge warps are laid in opposing directions, usually with the bower towards the stronger flow. Both warps are taken to the bow of the yacht. A chain gripper shackle or a long halyard shackle is connected to the chain and the kedge warp is passed through the eye of the shackle, upon which the chain is veered a couple of metres, taking the shackle to a depth lower than the keel, and preventing contact with it. However, my experience of this technique in wind against tide situations is that the yacht can finish up across the waves, rolling uncontrollably and preventing sleep for any but the most hardy, or very young babies!
Instead, a simple stern kedge will hold the yacht’s stern into the wind while the bower holds the bow into the current. In your situation the optimum way to use the kedge would be to run the engine in astern while letting out a further 20 – 25 metres of chain. Then drop the kedge over the stern, haul in the bower chain and check that the kedge has held. Provided that the wind does not change direction appreciably your yacht should remain perfectly safe anchored in this way. This technique is rather less tolerant of side winds than the Bahamian moor.
A chum can be useful in holding the yacht’s position in light winds or current, but a very heavy weight would be needed to be effective in conditions such as you describe. Carrying such a weight for use on extremely rare occasions like these could not be justified.
Yachting Monthly’s anchor test comes up with a high rating for the Fortress, which we are consequently thinking of installing on our boat to replace the relatively heavy CQR main anchor. However, we note that the Fortress gets a ’poor’ rating as regards its holding ability when a boat swings, as it would in wind or tide. Could you clarify this seeming paradox in the Fortress’s performance?
Anchors have two principal properties: ultimate holding power and the ability to set and re-set under all conditions. The majority of anchor tests concentrate on the first of these because it is relatively easy to measure. As a general rule anchors with higher surface areas tend to do well on the ultimate holding power tests, these include many of the ‘flat’ anchors such as Fortress, Britany, Danforth, etc.
Reliable and repeatable tests of setting ability are extremely difficult to arrange because they depend upon the type of bottom, the speed of laying out the rode and the force applied, plus no doubt many others. Thus anchor test results are notoriously variable, being very subjective. However, the flat anchors, as a group, tend to suffer from specific re-setting problems both with low drag forces and with high.
When wind or tide reverse in light conditions the Fortress and others tend to skid across the bottom, lacking the weight that could force the fluke tips downwards. This clearly depends upon the consistency of the bottom, soft mud not being problematic but hard sand, shingle and weed giving major drag problems. This has happened to me twice, each on inland waters in very light conditions at low wind speeds. Fortunately both were during daytime and we detected our movement immediately.
In stronger conditions a change in wind or tide may cause the chain to drag beneath the anchor, where it can become jammed between the flukes and stock, preventing any possible hold on the bottom. This is a well-reported problem with all of the ‘flat’ anchors.
Thus the Fortress makes an excellent kedge anchor, holding large forces provided that the direction of pull does not vary. I carry one myself and use it frequently for anchoring in restricted areas, fork mooring in strong winds and any circumstance that requires an anchor to be rowed out in the dinghy. Since my adverse experience I would never use it alone as my bower anchor. If replacing your CQR I would choose either a Delta or one of the ‘new generation’ anchors.
Frequent rotation when anchored
I would appreciate your best advice on my predicament as follows;
I have been anchoring in a “lagoon” in Elounda Crete. Its about 3-5 meters in depth, sand/mud good holding barring various discarded articles strewn across anchorage. The biggest problem is that there is a constant swing of wind which turns the boat (a Granada 31) around in circles at least 4 times a day, often more. Sometimes this has a habit of pulling out the hook as if the wind is light the chain gets a big loop in it and can then pull from the other direction. I have been using my kedge anchor at about 40 deg from bow anchor and untangling the warps during the day as she spins. I am sure there must be a better way that I have missed?
You don’t say what type of anchor you are using for your bower. I would expect a good, modern anchor to re-bed regardless of the number of turns imposed upon it. I carry a Delta and a Rocna and both have frequently seen the conditions that you describe but without ever breaking out. Very recently we saw three complete turns in two hours and almost certainly several more before the anchor was next hauled, without suffering any problems. Some anchor types, particularly the ‘flat ‘ ones such as Danforth, Britany, Fortress, etc, are prone to dragging in the conditions you describe, when the dragging chain becomes wedged between the stock and the flukes. A swivel may also help to prevent any chain twisting that can contribute to tripping your anchor.
Otherwise, in light wind conditions a stern anchor would seem to be an excellent solution. I use a Fortress for exactly this purpose, when its deficiencies so far as varying pull direction do not occur. The big problem with lying to bow and stern anchors in my experience is that boats anchored at the bow only will swing to the wind, whereas you will not, and collisions can result.
I am a big fan of taking long lines ashore, which overcomes all the problems and provides great security. My pilot is not explicit about the possibility of this technique at Spinalonga, Elounda, but I would try it if possible.
So far as laying the kedge at an angle to the bower, I use this technique in winds over about force 7, when it cuts down yawing from close to 160 degrees to more like 45 degrees. All aboard appreciate the benefits in comfort that this brings. The Mediterranean Sea being what it is, by morning the wind has often reversed in direction and it is quite common for us to spend some time untangling the kedge warp, only to re-lay it a couple of hours later when the strong wind returns.
I read Vyv Cox’s article and agree with many of his points, but why have a swivel between your chain and your anchor, and not just a well-calibrated shackle? A Danforth-type flat anchor needs a swivel because they don¹t want to be ‘flicked’ over by a twist in the chain but others, if initially dropped on their sides want the ‘twitch¹ to turn them over to get the point to dig in. Surely a swivel prevents this?
I believe that fitting a swivel close to the anchor is important, for a variety of reasons. As the boat swings at anchor the chain may very well acquire several twists. I was recently in an anchorage in the Eastern Peloponnese where we counted three complete revolutions in less than two hours! The consequence of passing the chain in its twisted condition through the windlass will depend upon exactly how much chain is laid and how many turns are in it. If the twist is able to reach the windlass without turning the non-swivelled anchor, a twist can pass through the windlass. This will jam it and can cause serious damage to its gypsy or gearbox. It is for this reason that most windlass manufacturers advise the use of a swivel. If the anchor lifts from the seabed before the twists have reached the windlass then the anchor will rotate. Most of the rotation is damped until the anchor breaks the surface, when it will rotate violently. Last year I watched this happen to a charter boat, the anchor striking the bow with some impact, fracturing a significant flake of gel coat.
Many anchors rotate as they are being hoisted using a windlass due to their unbalanced shape. My Delta does this quite markedly but the chain is not twisted due to the action of the swivel. I suspect that if I did not have a swivel I would run the risk of passing a twist through the windlass, with all the possible consequences.
So far as the ‘flick’ is concerned, this concept is completely new to me. All patent anchors are designed to bed themselves when hauled aft, regardless of whether they are on their sides, backs or upright. It is not possible to use any ‘flick’ method when anchoring using a windlass and I have never found any need to do so. In the past five seasons I have anchored for something like 700 nights, on Delta and, this season, on Rocna anchors and can say that I have never needed to ‘flick’ either of them to obtain almost 100% first time anchoring (Mediterranean weed excepted!).
Reversing after anchoring
Once an anchor is set, how much reverse throttle should you use to test it? If properly set, should it hold full throttle (if applied slowly) or is that too much to expect, particularly if you do not expect unreasonable winds (say >30knots)? I suspect quite a few skippers wonder this!
It’s not possible to give any exact figures, as every boat will be different. Reverse thrust of propellers, for example, varies greatly dependent upon their design, feathering ones in theory giving virtually the same as in forward, whereas some folding ones are notoriously very poor in astern.
To fully test that the astern engine force on the anchor rode exceeds anything that will be generated by the wind and waves it is necessary to measure both. There are high-tech and low-tech ways of doing this. The first was addressed in a YM article by Paul McNeill in January 2007, in which he described the use of an Anchorwatch linked to a laptop, with simultaneous input from wind instruments, to determine forces generated in the anchor rode. His boat was a Sigma 33C, for which he found that the force generated at maximum revs astern exceeded that of the wind up to about half way between force 8 and 9.
I have used the low-tech method briefly, when it seemed to give meaningful results. I attached a simple spring balance to my snubber and shackled its other end to the bow roller. It would take a great deal of time to match the results of an automated system such as that described by Paul McNeill but I hope to make a few critical measurements in the future.
Meanwhile, bear in mind that the holding power and characteristics of anchors varies enormously. The latest designs tend to continue driving downwards into the bottom as the force on them increases, whereas many older ones will rotate and cease to hold when the load on them reaches a certain, often quite low, value.
Anchorwatch details can be seen at: www.anchorwatch.co.uk
I am about to move my Moody 36 to a marina in Majorca. Sailing in the Balearic Islands is all about anchoring in remote calas and I’m not sure what combination of anchor and chain I need to have. What would you recommend?
There are two particular problems when anchoring in the many calas of the Balearic Islands. Firstly, the best of them tend to become very crowded, particularly during the hours of daylight. Some of the less popular ones are quite narrow and rock-strewn, unfortunately in some cases rather exposed to the weather.
The bower anchor needs to be completely reliable, both so far as set and re-set is concerned and for ultimate holding. The best available today almost certainly means a ‘new generation’ anchor, although Delta and Kobra anchors do well in the predominantly sand plus mud bottoms. All-chain rodes are favoured for chafe and wear resistance and for stability in shifty winds. 50 metre was always sufficient for me in the Balearics, but if your intention is to move further east later it may pay you to buy 60 metres.
Kedge anchors need to be easily portable for rowing out. The ‘flat’ anchors (Fortress, Danforth, FOB, etc) are the choice of most experienced yachtsmen, in combination with 5 – 7 metres of 8 mm chain plus rope. Multiplait nylon is excellent for this purpose, given its resistance to tangling, although braid-on-braid can be almost as good. The strength of 12 mm warp would be sufficient for you but a larger size improves handleability. 50 metres is a suitable length.
The technique of taking lines ashore to hold the yacht stern-to the cliffs is alien to tidal Britain but wonderfully apt in the Mediterranean. It enables large numbers of boats to anchor in a small cala without risk of collision. (Mostly!!!!) Braided polypropylene rope on a reel is ideal for the purpose as it floats, thereby avoiding snagging on underwater rocks when being rowed or swum ashore. I have two 40 metre lengths but some yachts carry as much as 100 metres on each of two reels. If the pushpit allows these can be permanently mounted.