​Stranding: Just how dangerous is Legerwall for motorboats?

What is Legerwall and why are motorboats particularly affected?

A stranding occurs when a ship is pushed ever closer to a leeward coast or an obstacle by an onshore wind, swells or a strong current, without being able to gain any distance under its own power.

For motorboat operators, the risk of finding themselves in a ‘legerwall’ situation is particularly high. Sailboats, at least, still have the option of hoisting their sails and attempting – albeit with some difficulty – to manoeuvre clear of the situation, perhaps just in the nick of time. Motorboat skippers, however, are entirely reliant on their engine. If this fails – whether due to engine or gearbox damage, a lack of fuel, a propeller that has stopped working, or any other cause – the boat will drift uncontrollably. The only remaining option is then to drop an anchor quickly. However, if the anchor fails to hold, the journey will end at the next groyne, the next rocky outcrop, on the sandy beach or in the reeds.

You can read everything you need to know about anchoring in our special feature.

​The most common causes of Legerwall’s syndrome

1. Onshore wind, bottom currents or tidal currents drive the boat towards the leeward shore or an obstacle, without it being possible to gain any more distance.
2. Drive failure due to engine or gearbox failure, running out of fuel, or a damaged or jammed propeller.
3. Gradual offset (dogleg): Wind and currents push the boat off course or out of the fairway without the helmsman realising, because he is using only a fixed point ahead as a reference.
4. An unsuitable or overly confined mooring: If the wind shifts to an onshore direction or the anchor breaks loose, the anchorage becomes a death trap.
5. Groynes on rivers: A boat that drifts out of the navigation channel whilst the current is flowing can be pushed against a groyne in a matter of seconds.
6. Weirs: The backwater effect increases the flow velocity immediately above the weir. Anyone encountering problems there may have only seconds to react.
7. Access roads to locks: Cross-currents and eddies can quickly cause a boat that is unable to manoeuvre to become uncontrollable.
8. A weak outboard motor or an empty fuel tank during a flood: Increased current, wind and swell can overwhelm a propulsion system that is too weak or inadequately powered.

The ‘dog’s bend’: Gradual misalignment as the cause

Even without a loss of propulsion, motorboat operators can find themselves in a situation where the boat drifts off course, for example due to gradual drift. This occurs in flowing waters when the helmsman uses fixed landmarks, such as fairway buoys or landmarks on the shore, for navigation. Wind and current can then gradually push the boat off course or out of the fairway without the helmsman realising it. The helmsman feels as though they are still on course because the fixed point they are heading for is still directly ahead, but may not realise that the boat’s actual compass course is gradually changing. This is known as a ‘dog’s curve’: the vessel is sailing in an arc rather than a straight line, and the skipper may still believe they are on course – for example, in the fairway – based on the bearing ahead, when in fact they have already strayed from it.

Incidentally, the term ‘dog’s curve’ is to be taken literally. Imagine a wide river with a current: on one bank stands the owner’s wife with the dog, on the other the owner. Once let off the lead, the dog jumps into the water and wants to swim to the owner. Its snout is always pointing directly towards him. However, the current carries it along, so that its course will increasingly point against the current until, depending on the strength of the current, it ends up swimming directly against it and may never reach its destination. His path from his owner to his master was not a straight line, but a curve. Had he set his sights on a point just upstream of his master, he would have arrived by the most direct route. This is called ‘holding the course’.

‘Pre-aiming’ means not aiming directly at the desired target, but at a specific angle to counteract the offset. There are various ways of determining how large this angle needs to be.

Avoiding dog-leg bends using a plotter

To do this, it helps to check the plotter to verify your actual position. If this is outside the previously set course line, the boat has been carried off course. You should then return to the course line as quickly as possible, taking the shortest route. Then set a course for the destination again and constantly check your position against the course line. If the position drifts off the course line again, choose a course that is more towards the cause of the drift – in other words, more into the wind or the current. The required angle of leeway can only be determined by constantly monitoring your position. If the boat is still being carried off course despite maintaining this angle, you must increase the angle of leeway further.

Avoiding a ‘dog’s turn’ using a figure-of-eight bearing

However, a ‘dog’s curve’ – also known as a ‘banana course’ – can be avoided quite easily without the use of electronics. A regular glance astern will reveal whether the bearing taken from the stern is still pointing towards the previous reference point. This could be the last navigation buoy you passed, the harbour you have left behind, or another reference point you passed earlier. If this bearing is still valid, the boat is on the desired course.

However, if the bearing taken from the stern shows a greater deviation from this point, the boat has veered off course. To correct this, sail back against the wind or current towards the original course until the bearing is restored. To do this, repeatedly point the bow towards the target and take a bearing from the stern until the previous mark is back in the bearing. Once this position is reached, initially choose a slight head-of-wind angle towards the target. Check this repeatedly using the same method – that is, align the bow with the target and take a bearing over the stern, correcting the angle of head-up if necessary. The course will thus resemble a zigzag rather than a straight line.

Particularly in shipping lanes, taking a bearing astern to the previous buoy should be part of your standard routine.

Avoid anchoring at Legerwall

There is also a risk of grounding whilst at anchor. If the wind shifts to onshore overnight and, in the worst-case scenario, also picks up in strength, what appears to be a safe anchorage can quickly become a dangerous situation if the anchor breaks free or the boat’s swing range has not been adequately taken into account. In such a situation, the only solution is to start the engine quickly and move clear of the coast.

Inland waterways and rivers: groynes, weirs and hidden currents

When people think of a ‘Legerwall’, they usually think of the coast and the Seegatt. However, the basic principle applies to any body of water, including rivers. There, structures such as groynes – also known as ‘Stacks’ on the North Sea coast – can lead to ‘Legerwall’ situations. Motorboat enthusiasts will be familiar with these from the Rhine, Elbe and Moselle, for example. These stone or wooden structures across the riverbank narrow the navigation channel and protect the bank from erosion. A boat that strays from the channel – whether due to engine failure or a lack of attention – can be pushed against a groyne in a matter of seconds in a flowing current, leaving significantly less time to react than on the open sea.

Weirs are even more dangerous. Upstream of weirs, the flow velocity increases due to the backwater effect. Anyone encountering problems near a weir may have only seconds to react. The rule of thumb on flowing waters is: if you experience any technical problems near a weir, anchor immediately.

The approach areas to locks also generate significant cross-currents and eddies at certain water levels. Engine failure in this area can quickly become uncontrollable. During high water, the increased current combines with wind and swell: an underpowered outboard motor, an empty fuel tank or a technical fault can then be enough to cause you to lose control.

On lakes with no current – be it Lake Constance, Lake Müritz or Lake Chiemsee – an onshore wind can just as easily drive a boat that is unable to manoeuvre onto the shore or a jetty.

Act early: How skippers secure their room for manoeuvre

If you want to avoid running aground, you must plan ahead. Where possible, choose the leeward bank; on wide rivers or lakes, choose the windward side, provided the navigation rules allow this. In narrow passages with an obstacle downwind, establish a clear cut-off point. This refers to a predetermined point in time at which there is still sufficient propulsion and manoeuvring space available to abort the passage and turn back. An alternative to the original plan must then be devised. Generally speaking, planning is better than being caught off guard. Currents – whether tidal currents at sea or river currents – must be taken into account, as they cause the boat to drift constantly.

Part of your planning should also include ensuring that the fuel tank is sufficiently full and, in the case of electric propulsion, that there are sufficient energy reserves. On flowing waterways with weirs or locks, always use sufficient engine power to keep the boat manoeuvrable and to be able to navigate against the current. Always keep lines well clear of the deck or secure them properly: if one gets caught in the propeller, a minor mishap can turn into a grounding situation within seconds.

Having the anchor to hand should go without saying, and not just for extreme situations. A chain that is long enough reduces the angle of pull and significantly improves holding power. A line connecting the chain to the boat can act as a shock absorber and can be cut if necessary.

A radio call for help should be made sooner than you feel is necessary. It is better to call out on Channel 16 at sea a little too early than to wait too long. On inland waterways, Channel 10 is the working channel used by the water police. Other vessels in the vicinity may be listening in and can offer assistance.

You can read all about sparking here in our special feature.

​How to avoid Legerwall

1. Select page: Where possible, head for the leeward side of the coast or, on rivers and lakes, the windward side, so that a mistake does not immediately lead to disaster.
2. Set the breakpoint: In tight passages with an obstacle downwind, define a clear point in time up to which there is still sufficient propulsion and manoeuvring space for an orderly retreat.
3. Taking currents into account: Tidal currents at sea and river currents in inland waters constantly carry the boat along. If you don’t take this into account, you’ll drift towards the obstacle without realising it.
4. Position control via plotter: Regularly compare the actual position with the planned course line. Identify any deviation early on and adjust the lead angle.
5. Aft bearing: Without any electronic aids, a regular glance over the stern at the most recent landmark you have passed will show whether the boat is on course or is gradually drifting off course.
6. Ensuring fuel and energy supplies: Make sure the fuel tank or battery is sufficiently full before every journey. Without a reserve, the engine will stall even if there are only minor problems.
7. Sufficient engine power on flowing waters: On rivers with weirs and locks, allow for sufficient reserve so that the boat can travel against the current at any time.
8. Keep ropes away from the deck: Securely fasten or stow them away so that they do not get caught in the propeller.
9. Keep your anchor to hand: Always have a sufficiently heavy anchor with a long chain ready to be dropped as a last resort to prevent grounding. Secure the chain or line in such a way that it can be cut if necessary.
10. If you are near a weir, drop anchor immediately: Any technical problem near a weir requires immediate anchoring; do not wait.
11. Carry out regular maintenance on the machine and drive system: Many drive failures can be prevented. By adhering to maintenance intervals, you can rule out one of the most common causes.
12. Make an emergency call as soon as possible: It’s better to make a call a bit early on Channel 16 (lake) or Channel 10 (inland waterway) than to wait too long. Other vessels nearby may be listening and can help.

Insurance and gross negligence

Anyone who fails to react adequately to forecast strong onshore winds and loses the boat risks not only losing the vessel but also running into trouble with the insurance company. Charter skippers may lose their deposit and, in addition, face recourse claims from the charter company’s hull insurance. Skipper’s liability insurance that also covers gross negligence offers protection in such cases.

Find out what insurance skippers need in our special feature.

Even good seamanship offers only limited protection against force majeure, such as an unannounced extreme storm. But where possible, precautions should be taken: service the engine and propulsion system regularly, check the weather conditions, find a safe anchorage, check the anchoring gear, and organise anchor watches. Those who do so have the best chance of ensuring that ‘Legerwall’ remains nothing more than a term from the textbook.

On inland waterways and lakes, having an anchor to hand is often considered unnecessary. Wrongly so. Do you always keep your anchor to hand, no matter where you’re sailing? Let us know in the comments!