In harbour your problems tend to be those of handling the boat in close proximity to other boats and harbour installations. Out at sea you will come up against a whole range of different conditions to those in harbour and there are many new techniques to learn. It is wonderful to leave the harbour for the freedom of the open sea, but the first thing you notice out there is that the surface of the water is usually far from calm.
You may be lucky and choose a calm day. If you do make the most of it because calm days are not always the norm and in most situations you will have to cope with wind and waves. The effects of these will be felt most if you have a planing boat because as speed increases the effects of the waves tend to become magnified. The secret of handling a big cruiser at sea is to match the speed of the boat to the conditions. The handling techniques for displacement and planing boats are quite different. Displacement boats have a top speed of about 8-10 knots, but a planing boat is likely to achieve speeds in excess of 20 – 25 knots quite easily. With both types of boat, however, it is essential to match the speed to the conditions.
With modern boats the weak link in the whole system tends to be the crew rather than the boat and its equipment. The boats are generally built to a very high standard and are capable of taking considerable punishment from the wind and the waves. It is likely that the crew will start to object to difficult conditions long before the boat. Do not ignore the protestations of your crew – rather, heed them as a warning signal and try to find some way of improving conditions. When life starts to become uncomfortable it generally means that you are pushing the boat too hard. After all, in most cases you go out to sea for pleasure, so having a comfortable ride should come somewhere near the top of your list of priorities.
Even in a displacement boat, speed can have a significant effect on comfort. It is all a question of the speed of encounter with the waves. Hence, when you are travelling into a head sea with the waves coming towards you, your period of encounter with the waves will be much quicker and therefore the speed at which you travel is likely to be a lot more critical. In a following sea you can maintain a higher speed because the waves are travelling in the same direction as the boat and the period of encounter is much slower. In a following sea, therefore, unless the seas are quite rough, full speed will probably be the order of the day. However, there are other factors to be considered with following seas, as we shall see when we look at this in more detail.
In a planing boat the higher speeds obviously increase the speed of encounter with the waves quite considerably, but to a certain extent the hull of the boat is designed to take this into account, and so you do not always have to ease back as soon as you might think. The warning signs come from the motion of the boat: if this starts to get too lively for comfort it is time to ease back. If the boat starts to fly off the top of the waves you are probably pushing things too hard, although this can be exhilarating in the short term and most good quality cruisers are built to take this sort of treatment.
The Effect of Waves
It is not only the speed of encounter with the waves that affects the performance of the boat, but also the shape of the waves. In some conditions (usually when the wind is against the tide) the waves are quite short and steep. Conversely, when the wind is with the tide there may be a flattening out of the waves and the change when the tide turns can be quite dramatic. In an area where strong tides run you should be aware of this change because a nice gentle sea can, with the space of an hour or two, change into very uncomfortable conditions with short steep seas.
When seas become short and steep, the wave length (i.e. the distance between the waves) also reduces and this means that the period of encounter is also speeded up. From all this you can imagine that life can become quite uncomfortable on board. In this situation it may not always be easy to match the speed of the boat to the conditions, because the boat may not recover from one wave before it meets the next. When handling a powerboat at sea you need to have a reasonable understanding of waves because they have a very significant effect on the boats. The wind acting on the surface of the water generates waves. In winds of up to about Force3, the waves generated under normal conditions are not likely to have very much effect on the boat. It is only when the wind starts to freshen that the waves increase to such a size that you will have to adjust your speed to suit the conditions. The main waves come from the direction of the wind, but there are usually residual waves and swell from previous blows which tend to make the waves irregular and to a certain extent, unpredictable.
The shape of a wave is not even. The windward face of a wave always has a gentler slope than the leeward face, which can be quite steep. This means that when you are going into a head sea you face the steep side of the wave but have a gentler slope when you get over the crest. In a following sea you have a comparatively gentle ride up the back of the wave, but there can be quite a sudden steep drop on the other side. This steepness can be exaggerated quite considerably if the wind is against the tide and it is the steep leeward face of the wave than can cause most of the trouble. If the wave is breaking then you have a moving body of water that has considerable power, and in these sea conditions you will need to handle your boat with considerable care.
Handling In Head Seas
Head seas produce the most uncomfortable ride for any powerboat because the period of encounter with the waves is more rapid. The period of encounter is a combination of the boat’s speed and the speed of the waves, so you could reach a situation where the bow of the boat has not fully recovered from one wave before it has to lift to the next, so it gets out of step with the waves and starts to give a rough ride. Simply easing back on the throttles can make the ride more comfortable. Once you have found a comfortable speed, set the throttles and relax a little, but bear in mind that the larger than average waves can come along unexpectedly so your hand should never be too far from the throttles.
It is possible to drive the boat through head seas to make better progress by matching the speed much more closely to the conditions. To do this you adjust the throttle speed to each wave, watching out for the big ones that might approach from ahead. This type of driving requires considerable concentration, however, because you have to read every wave as it comes towards you and adjust the speed accordingly. In a diesel powered boat you may not always get the rapid response from the engines that you need in order to vary the speed quickly.
In a head sea the bow does tend to fly up into the air as it meets an oncoming wave, and if you drive too exuberantly the whole boat can fly out of the water. It is in these conditions that some of the other controls on the boat, such as trim tabs can be used to good effect. By putting the tabs down you will notice a significant drop in the bow. As with most aspects of power boating, a comfortable balance is what you are striving for when adjusting the trim tabs or power trim in the case of a sterndrive or outboard powered boat.
When you are running in a head sea and a large wave approaches, the tendency is to pull the throttles and reduce speed. Certainly there is a need to ease the throttles so that you don’t charge into a big wave at full speed, but the emphasis should be on the word ‘ease’ so that you drop the speed just a little and don’t pull the throttles right back so that the boat comes off the plane. By doing this there will be little change of attitude, but you will be at a more comfortable and resilient speed to meet the bigger wave and ride over it without any problems. Many of these comments apply equally to displacement boats running in a head sea and finding a comfortable speed is the secret of success. With a displacement boat or planing boat off the plane there is always a greater chance of the bow burying in the wave because the bow is more deeply immersed in these circumstances anyway and doesn’t have the same buoyancy as a boat up on the plane.
Handling In Beam Seas
In abeam sea the techniques for handling planing and displacement boats are very similar. In beam seas rolling is the problem, rather than pitching. Depending on the boat, the rolling may not be too uncomfortable and running in a beam sea can often be quite a comfortable way of making progress. Displacement boats tend to be more affected by beam seas than planing boats because the latter have much greater stability when travelling at higher speeds due to the dynamic effect of the hull on the water surface.
A displacement boat can roll quite uncomfortably in a beam sea and if the natural rolling period of the boat happens to synchronise with the waves, quite a dangerous situation can develop. There is a very simple remedy: alter course even just 5 or 10 degrees and you will probably find the motion of the boat changes dramatically. Therefore, in a beam sea, it is not usually a good idea to operate with the sea fully on the beam. Instead, alter course a few degrees, just to introduce a slight crossing element into the waves.
Apart from rolling, a beam sea can result in a fairly unpredictable motion, because at one moment you are running along the very uneven crest of a wave, and at the next making progress along its very uneven trough. The sheer unpredictability of the motion can be exhausting because it is so very difficult to anticipate. The part of the wave that usually causes the most trouble is the steeper leeward side because, with very little warning, you can often find yourself running on the crest of a wave and suddenly dropping down the steep face into the trough.
Operating in a beam sea is rarely dangerous unless the waves are breaking fairly heavily in something in Force 6 or better. If you can’t avoid it then you just have to drive for the conditions and only experience can help you decided what is a reasonable level of comfort for both you and the crew.
There are no particular techniques for operating in a beam sea. You can watch the seas ahead and you may be able to drive the boat around the bigger waves. You have the option of turning away from the sea and running from it or heading up into the wind and driving round the windward side of the wave. In beam seas as in other conditions, it is really just a question of matching your speed to the conditions. Certainly you have more freedom to adjust the speed in a beam sea because the stresses on the hull and crew will generally be much less than in a head sea.
Handling In A Following Sea
Following seas have a terrible reputation amongst boating people for producing conditions in which problems occur. There certainly are risks when driving a powerboat in following seas – but there are always risks when the seas get rough. It is only when there is a particularly heavy following sea that you are likely to find yourself at any real risk. In reasonably conditions handling in a following sea is quite straightforward and as with all other conditions, if you understand the techniques involved the boat will operate more comfortably and efficiently.
Displacement Boats in a Following Sea
In a following sea the waves will be overtaking you and there is not a great deal you can do to influence where the boat is in relation to them. The bigger the waves the faster they travel, but under normal conditions the waves will probably be travelling at between 15 and 20 knots – almost twice your speed. Small waves will have little impact: it is only when they are big enough to start lifting the stern, that you will have to drive the boat more carefully. The steering tends to become more erratic because the bow is buried in the water and the stern is in the air. The boat then tries to pivot about the bow, so that you have a sensation of over-steering.
Initially you will find that the steering has no effect but the boat could suddenly take off with a rush and may turn almost beam on before you have a chance to correct it. This is know as broaching and a serious broach can leave you dangerously exposed beam onto the waves. This means that in a following sea with moderate waves running you can find yourself working fairly hard at controlling the boat. Quick, responsive steering is a great help to keep the boat running straight.
When you find yourself working overtime on the steering, winding the wheel from side to side it is about time to look for an alternative course. Varying the speed may also help to improve control over the steering but do not slow down too much or you may lose steerage way. At what stage the steering on a big cruiser becomes difficult depends a great deal on the type of boat you have. If you have a displacement boat with a fairly fine bow, or even a semi-displacement boat operating at slower speed, you may well find that the steering becomes difficult to control in comparatively moderate seas. This is because the bow buries itself and acts as a fulcrum, which the boat tries to spin around.
A boat with a big full bow and cutaway forefoot will lift readily on the waves even though it is angled downhill and is far less likely to bury and thus as a pivot. The side of the rudder also has a bearing on the way the boat handles: a good sized rudder which has a powerful steering effect is better in this situation than a smaller, less effective one. In a following sea with a displacement boat, the solution is not to ease back the throttles, but rather to open them further because you get better steering control the faster you go.
However the motion of the boat can become quite uncomfortable in these situations because of the sudden change in angle as the wave passes under the boat. You may find that the boat, when angled with the bow down, tends to rush forward because of the downhill slope and then virtually stops as the wave passes under the hull and the boat adopts a bow up position. If the motion becomes too uncomfortable you may have to resort to driving the boat on the throttles, opening them wide to drive up the slope and then easing off as the boat comes over the top.
Planing Boats in a Following Sea
A planing boat is much easier to handle in following seas than a displacement boat. On a planing boat you have the option of overtaking the waves rather than having then overtake you. This enables you to dictate where you are in relation to the waves. One of the most comfortable positions is to be gently overtaking the waves, so that if the waves are travelling at 20 knots you want to be travelling at around 25 knots. This will mean that you have enough power to climb up the back of the wave. There will be a sudden change in attitude as you go over the crest, when the boat runs downhill before it lifts once more to the wave in front. Because the boat is only overtaking the waves at a gentle speed, you should be in full control of the situation and the ride will be fairly comfortable except when the boat changes attitude as it overtakes the wave crest.
You have a certain latitude to vary the speed, perhaps to try to find a more comfortable ride. But in general you won’t want to drop below the speed of the waves because the small rudder fitted to planing boats means that you may find yourself having difficulty maintaining steering control. The worst situation is to find you just matching the speed of the waves as the rudder can become virtually ineffective, leading to the possibility of a broach. With stern drive or outboard boats this would not apply and you have more flexibility both in control and speed because of the positive steering at all speeds.
In a planing boat you can run before a following sea even when the seas are quite big and it can be a very exhilarating ride. Although you feel fully in control of the situation you may not always appreciate that conditions are deteriorating. If you find yourself in a freshening wind running before the sea, it is a good idea not only to keep a lookout astern but also occasionally to stop, turn around and head into the sea to get a better indication of how the conditions are developing. It is very easy when running downhill to be lulled into a false sense of security so turning around and checking the developing conditions early, can allow you the time to make necessary alterations, such as running for shelter or looking for an adjacent harbour.
A Comfortable Ride
In general terms the skipper of the boat is out to give the crew a comfortable ride. On a long coastal passage, this can be quite important, since tiredness can have a detrimental effect on your reactions and can affect your decision making. Keep a careful watch on the stamina of your crew, particularly on a planing boat where the motion is often more violent than on a displacement craft and where you need to have your wits about you because things happen much faster.
Darkness adds a whole new dimension to reading the waves and boat handling. Firstly you can’t see any of the approaching waves very well, so to a certain extent you are driving blind. However you should use the same techniques as in daylight. Of course you will not be able to see the waves ahead, and the biggest danger will be from that larger than average wave which catches you when you least expect it or are going too fast. At night you will get little warning of the approach of these waves, so you should cut your speed back even more than during the day. This gives you a great safety margin should you have to deal with unexpected conditions.
