Even though boating takes place in a potentially extremely hostile environment, it remains a statistically safe activity. However, there are a number of predictable situations that may take complacent crews by surprise. If your boat’s in good condition with the appropriate safety equipment. And assuming you have good knowledge of the local area, along with the latest detailed weather forecast, then there are five main hazards to avoid.
A number of potentially challenging effects tend to happen at headlands. Firstly, the wind can be accelerated by as much as 5-10 knots compared to the surrounding areas and may be more gusty as well. Secondly, tidal rates increase at headlands, with the two effects tending to accentuate the sea state in wind-against-tide situations.
On top of this, the seabed off headlands is frequently very uneven, possibly with deep trenches either side of a high ledge. The effect of this is to create turbulent seas as the tide sweeps the water across the different depths – it first tumbles into the trench, then is pushed up to the surface at the ledge, before tumbling down into another trench. If you can picture in depths the chart shows in three dimensions, then it’s easy to imagine the effect. These are therefore areas to be avoided at all costs in all but the most benign conditions.
2. Wind against tide
This creates short, steep waves that at best are uncomfortable and may be dangerous in some situations. Fast motorboats therefore tend to plan their activities for periods when the wind and tide are in the same direction. This produces a noticeably flatter and more comfortable sea state.
Many sailing yachts are denied this luxury as they cannot make good progress upwind when also fighting the tide. Nevertheless, it’s important to ensure you’re aware of problems that may occur with extra-large breaking waves off headlands, or at the entrances to rivers and harbours.
Wind-against-tide conditions also increase the wind speed you experience when afloat – in effect the speed of the tide is added to the wind speed. By contrast, when the wind and tide are in the same direction, the effective wind speed is diminished.
How to berth safely: wind against tide
3. Overfalls and tide races
Tide races can also occur anywhere the local geography restricts the movement of water, funnelling it into a narrow channel or strait. As well as at headlands, these typically include narrow harbour entrances and channels between islands. If the seabed is uneven then you’re also liable to find overfalls – areas of unregimented and often breaking steep waves.
A number of harbours or estuaries have shallow banks of sand or gravel to seaward of the entrance. These can create dangerous conditions in strong onshore winds, especially while the ebb (outgoing) tide is running. Chichester on the South Coast and Salcombe in Devon are two popular locations in which dangerous seas are created with on-shore winds and an ebb tide. Providing there is sufficient depth in the channel, bars tend to be at their best between HW-3 and HW+1 and at their most dangerous when the ebb tide is running, or near low water. With very strong onshore winds or gales it may not be possible to negotiate a bar safely in any kind of vessel.
UK boating destinations: 10 of the best.
5. Other traffic
Wherever you sail it’s inevitable that you will encounter other vessels. Even a picturesque estuary may have a commercial quay in its upper reaches. It may surprise you how large the shipping to and from these landings are, meaning they are very constrained in their ability to change course or speed.
The key defence against collision is a diligent and constant lookout, along with a good knowledge of the International Rules for the Prevention of Collisions at sea. However, on its own this may not be sufficient to avoid larger shipping. You also need to have an appreciation of the route that ships and other large, deep-draught vessels are likely to follow. This means studying the location of deep water channels on the navigation chart, along with the safe areas on each side that have sufficient depth for your vessel.
If you know where ships – from ferries to oil tankers – are likely to berth, it’s much easier to figure out the route they are likely to follow to get there. Then it’s just a question of maintaining an effective lookout to ensure the other vessel does as expected. There’s no cast-iron guarantee a ship will actually stay within marked deep water channels.
Additional dangers: being prepared
Potential hazards such as darkness, fog, strong winds, cold, rain and salt water spray are all predictable, providing you’re looking for the right signs and have a “what if” attitude. As with other dangers experienced afloat – from rocks to mud flats – that also means giving them an appropriate margin of safety. If your boat is not equipped for navigation at night, for instance, it’s prudent to plan to return to port at least a couple of hours before sunset. That allows for delays as a result of changes in the weather, or minor breakages on board.
False sense of security
The ability to forecast local conditions is a product of experience, but there are a few well-defined situations that frequently lull the unwary into a false sense of security and an encounter with unexpected conditions. Perhaps the most obvious of these is a calm and sunny morning somewhere like Chichester, especially if it coincides with spring tides, with high water around lunchtime.
The on-shore sea breeze that’s likely to build during the afternoon, will cause the apparently benign conditions mid-morning to turn nasty when the out-going tidal stream starts to run against the full sea breeze in mid-afternoon. Similarly, a glassy calm morning in the Needles Channel can turn into an effective Force 5-6 by mid-afternoon, combined with a wind-against-tide sea state that can be challenging for small boats or inexperienced crews.
High and low pressure in close proximity
High and low pressure systems with centres close together have the isobars between them squeezed tightly together. This can result in stronger winds than you might expect, even if you are on the high pressure side with warm temperatures, clear skies and bright sun.
There are often casualties in this kind of weather, mostly as the result of people being complacent due to presence of warm sun, whereas if they were sailing in the same wind strength, but with lashing rain they would take many more precautions.