When You Demand Strength and Sea-Keeping
World Speed Record holders with our own vessel and crew
HEAVY WEATHER SAILING
Boat handling & design factors for operating powerboats in heavy weather
AS FEATURED IN ALLARD COLES HEAVY WEATHER SAILING BOOK
Chapter written by Frank Kowalski
Above: Undertaking rough weather sea trials at the entrance to Cork Harbour, Ireland
I think it will be useful to give some background as to where most of my experience in handling boats in heavy weather has taken place and the kind of seas and conditions that prevail there. The entrance to Cork Harbour situated on the South coast of Ireland can produce some extreme sea states during the winter storm months. There are two main factors that influence the sea state at the entrance, the first being the ebbing tide, the second being shoaling waters over the Harbour Rock, this is situated at the entrance to the Harbour off Roches Point lighthouse, right in the middle between the Western and Eastern channel entrances. Although every stretch of challenging water will have its own unique features, Cork Harbour is pretty representative of any area of water that has a strong tidal influence, such as a headland or where an estuary or river runs out into the sea, or where a bar exists with shoaling waters creating surf conditions.
On a spring ebb tide, a large body of water from the inner harbour and estuaries is forced between Roches Point and Weavers Point, a distance of approximately ¾ of a mile between the two headlands. On a spring tide the speed of the ebb can reach 2 ½ kts. This ebb causes a tidal race at the entrance, which even in moderate conditions can create very rough conditions. In a storm, the entrance can become nothing short of a maelstrom. Big, steep, closely spaced breaking waves occur across the entrance. The worst period being approximately between 1hrs after the turn of the tide and 3hrs before slack water. In a full blown storm of force 10 and above which has been blowing for more than 12hrs, the entrance can become un-navigable during the middle of the ebb, as we have seen breaking waves 10m high stretching right across the entrance.
Above, the type of big breaking seas at the entrance to Cork Harbour, and that will occur over any bar or shoaling area of water in a storm.
When out on sea trials in such conditions sometimes the only option is to wait for the tidal run to subside a bit. When it has, we are then able to run out through the centre of the harbour entrance over the Harbour Rock, taking the breaking seas head on slowly, then turn around in a lull between sets and run back in through the Eastern channel, where conditions are generally not so violent. However when you do commit to transversing over the Rock, you are 'committed' as turning around can be too risky until you clear the entrance and race, and move into open water. The difference in conditions that exist in a tidal race between the ebb and flood can be like night and day, I would estimate a Force 6 during a spring ebb in the race creates waves that are harder to navigate through than a Force 8 in open water, such is the dramatic effect the tidal race has on a sea state.
Over the years in the course of undertaking our trials we have developed an intimate understanding of the sea state and conditions that can exist at the entrance in a storm and having the local knowledge, understanding of the topography and experience of the conditions that can prevail at your home area of water is very important.
Apart from the tide, the second factor that influences conditions at the entrance is the shoaling water over the Harbour Rock. The Harbour Rock is approximately ¼ of a mile wide West to East, and has a water depth on average at datum low water of 22ft, with its shallowest area, a small pinnacle being 14ft. When the wave height exceeds 6m with a long period, the waves feel the bottom and break very heavily like surf on a beach, with near vertical faces and heavily plunging crests, and I imagine it is pretty representative of any stretch of shoaling water that might be perfectly safe to navigate through in calm weather, but very dangerous in a gale or storm.
This ‘surf’ wave is a different wave than caused by the ebb in the tidal race, which although steep and violent tends to be a more ‘spilling, & tumbling’ type of breaker. It is the ‘heavy’ surf breaking wave that forms in shoaling waters that is the most dangerous type of wave. It takes a quite prolonged storm that has been blowing hard for many hours with a long fetch to build up the high, long frequency swell for these waves to occur here. But when they arrive, conditions can be quite spectacular to observe, and indeed challenging to navigate through. The swell tends to break in quite a predictable area and manor, however that been said, nothing at sea is completely predictable, and suddenly out of nowhere, a breaking sea can rise and catch you out.
Navigating through big, breaking seas.
When heading out through the entrance, taken slowly the big breaking waves can be navigated through safely head on, the caveat being in a suitably well found boat designed for such conditions and big enough, as at sea size matters! As a wave begins to feel the sea bottom when it encounters shallow water it begins to increase in height and peak, to the point where the steepness of its face causes it to crest and break. Ideally the safest moment to go through these waves is either just before it breaks and plunges, or after it has broken and is spilling. If caught at the worst moment, that being as the wave plunges, a huge weight of green water curls over and plunges downwards, the very top of the waves face being almost vertical as it curls over at that moment and will be traveling at over 20kts.
Above, holding back till the wave plunges and then below, taking it as it is spilling. One can appreciate the near vertical wave face of waves over shoaling water just as they break. At sea the size of the boat maters!
If it comes over the bow right at that moment, it hits the foredeck and cabin windows with tremendous force. Needless to say everything has to be strongly built to survive such impacts. To be able to survive this moment the boat has to be sufficiently long enough so that enough of its weight passes over the crest before the near vertical top part of the wave and plunging crest hits the boats centre of buoyancy, so obviously the longer the boat, and the more forward its centre of gravity the bigger the breaking wave it can handle head on, but this mostly applies to a heavily breaking wave rather than a normal offshore wave where boat size is not so critical, as the face of an offshore wave never gets so steep as a surf wave. When the wave has broken and is spilling, which it can continue to do for a long distance depending on the topography of the sea bottom, the wave consist of mostly aerated water rather than solid green water. So whilst it still hits the boat with a lot of force, the force is not as great as if were solid green water. So if you are crossing over a bar you need to hold back and try to judge exactly where the waves are breaking. As you approach the break if you see a wave ahead begin to rear up and curl, stop to allow the wave to break and then when it’s spilling proceed through the wave. Conversely if a wave begins to rise in front of you and it looks like it may break on you, if you have time accelerate so you reach the wave before it begins to curl over to get through the wave before it breaks. Just be sure to slow down sufficiently before you go over it to avoid falling heavily into the trough as you go through it. The most dangerous course is getting hit side on to one of these breakers, as there is a risk of at least a hard knock down to 90 degrees or at worst capsize or roll over. Needless to say getting caught side on is situation you always want avoid at all costs.
Below: The difference in impacts a boat experiences between a breaking and non-breaking wave can be clearly seen here and it’s dramatic. The pilot boat in the foreground misses the breaking section of the wave and the XSV20 is hit by it and carried backwards a full boats length. Although it looks violent the landing was soft because the boat was carrying little or no forward speed at the moment of impact.
Often people are completely unrealistic of how fast you can go into big breaking head seas. I think this is because they see, or themselves jump waves in small RIB’s or jet skis. The difference is that the forces involved when a small RIB or boat weighing a few hundred kg, or even a couple of thousand kg lands after flying through the air, are completely different compared to the forces involved when a boat weighing 20-30 tons lands. The G forces the hulls structure experiences are many times higher as a consequence of the boats size and weight, and needless to say any boat operating in heavy seas needs to be extremely strongly built.
Personally I find, at least in our type of boats, (fairly heavy in displacement) that the best course of action when a big 5-6m breaker rears up in front of you about to break is to literally stop so you have very little way on, straighten up so your absolutely dead square to the wave, and just as the wave hits you give her a little burst of power to gain forward momentum, but very little speed. You can expect to be thrown backwards a boats length as the wave hits you, but this is preferable to flying off the crest landing heavily if you try and pass through the wave to fast. Best analogy I've heard is, "if it looks like a ramp, it is a ramp"! You’re going to fly if you go over that ramp to fast, and you risk damaging the boat, especially if you land on the side in this situation, and this is something to bear in mind. It would be great if every time you went over a wave the hull landed perfectly upright allowing the ‘v’ of the hull to soften the landing, but in reality what more often than not happens is that as you go over the crest some other external influence affects the boat, be it a cross sea wave the heels the hull over right at that moment, a steering input or just the wind, either way what happens is that rather than landing comfortably upright you land heeled over to an extent on your side, and here the hull impacts the water on its flat surfaces with a heavy slam. How much throttle, momentum and forward speed you need depends to a large extent on the boats displacement, if the boat is very lightweight in displacement despite its size, it maybe needs a bit more thrust to resists the waves force and prevent the wave bodily taking the boat along with it, but it’s a fine line as going into a wave to fast in a lightweight boat is going to result in a much more vertical attitude of the boat as it flies off the crest and a hard stern first landing. Ultimately there is of course a limit as to how big a breaking wave any boat can survive, and if the wave is big and powerful enough that it is capable of fully engulfing and carrying the boat with it, then there’s probably not a lot you can do to get through the wave unscathed, and it would have been an error of judgment on the skippers behalf to have attempted taking on such big waves relative to the size of his vessel. It’s also surprising how little one needs to be off 90 degrees to the wave before you are swung round. Just having the bow 20-30 degrees off as the breaker hits the boat can resulted in one ending up close to beam on after the wave has passed through you. This situation is confounded by the momentary loss of vision and orientation as the breaker engulfs the boat, whereas at least when the wave is taken head on, the likelihood is that one’s going to be pointing more or less the right way when you recover, ready for the next wave.
On one occasion when I was out during sea trials during a storm in two boats, I was driving Thunder Child II capturing video as the other boat took the breaking waves and decided to move my position to the other side. This involved turning and running across the surf zone. I thought I had timed it well in a lull, but just as I was beam on a big wave rose up out of seemingly nowhere and started to crest. I turned towards the wave giving full power to get her around but couldn’t get her head up in time due to the strength of the wind, and the wave broke right over the boat whilst I was still only at about 45 degrees to head on. Luckily Thunder Child II is incredibly stable with her catamaran hull form aft so we weren’t rolled to far over, but as we were engulfed in the wave we were bodily moved sideways about 40ft and completely swung round so we ended up side on. Not something I would want to repeat!
Below: Thunder Child II lying completely stationary as the wave hit her, imagine if she had been moving faster.
When running back in through the entrance to Cork Harbour in a storm with a following sea, (and the same will apply to any such stretch of very turbulent water), having one of these breakers rear up and hit you from behind is something to be best avoided, but over the years it’s been a pretty rare occurrence, as generally when you turn, your turning in a lull between big waves, and as such when your running back in you try and avoid being caught in a big set. In general there will always be a pattern to the waves, if you observe a sea state during a storm you will see that there will be a period when the waves are fairly uniform in size and severity, but every so often there will come a set of two to three waves that are much bigger, and when those bigger waves pass is going to be the time to turn and run with the following sea. When the waves are really big there is generally a fair distance between them, so the best course of action is to stay close to the wave in front, and run at speed ahead of a breaker that comes up behind you. That’s the theory, and it’s what ideally you want to do but in practice it doesn’t always happen like that. More often than not a sea state is confused and rarely consists of a regular wave pattern coming from just one direction. This means that when you’re trying to match the speed of a wave there can be an underlying swell that is travelling at a different speed that moves through the wave your following, or there can be a cross sea that interrupts its pattern and alters it’s shape, what results is a somewhat un-predictable wave train that is altering continuously making it very difficult to judge especially from inside a cabin, that even with good all-round visibility, it can be difficult to maintain enough spatial awareness, especially as in all likelihood the boats continuously engulfed in air borne spray. Certainly it’s easier to do this from an outside steering position such as from a flybridge, or open cockpit as here you have much better awareness of the sea state and waves surrounding you, especially from astern, but you are totally exposed to the elements and whilst this is an option in more moderate conditions, in a bad storm with 50-60kts of wind and driving spray it’s going to be difficult to undertake this for any great length of time. I have built vessels with fly bridges and sea trailed them in heavy weather, but to be honest when I’ve been out in a storm with big 5m+ seas I’ve always chosen the inside helm position when under passage (as opposed to close quarter manoeuvres) If for no other reason than it’s just a safer place to be, as simply being elevated one metre above the deck results in a massive amplification of the vessels motions let alone the 2-3m you could be on a flybridge.
Above, surfing on the crest of a wave, you have to judge it carefully so that you don’t fall over the crest.
If a big breaking surf wave is about to hit you astern and you don’t have time to accelerate enough to outrun it, the best solution is slow right down, keep the boat absolutely dead square to the wave and let it break over you and run through you. There has been occasion when I’ve been unable to get dead square to the breaker coming and had to use one engine in hard reverse to quickly pull the stern round and try to stop the boat dead in its tracks, which wold be a better option than be caught off square going slowly ahead which would result in the boat being taken with the wave. Of course in doing this you need to be sure your boat is capable of taking a breaker over the stern, as most boats will be far more venerable aft. If you try and run to fast on the face of the wave at close to the speed the wave is moving at (around 20kts), you are just picked up by the wave and surfed ahead, uncontrollably sometimes. You can be lucky if the boat is exceptionally stable with great steerage that you surf straight, but the risk is of a yaw developing, which can be followed by a broach and a hard knock down. It is possible to sit right on top of the crest of the wave and surf, but it’s tricky as you have to carefully match the boats speed to the wave and avoid at all costs overtaking the wave and falling over the crest into the waves face. All the above can be done for a short period of time such as when entering a harbour or crossing a particularly bad stretch of water, but it takes intense concentration, and one simply cannot keep this up for long periods.
Head Seas
Running offshore in heavy weather into head seas of 3-4m the trick is to try and avoid becoming airborne, that means set your speed so that as you go over the crest of the wave as much of the boat as possible stays in contact with the water. Flying off the crest and landing heavily is sometimes unavoidable when you get caught out by a bigger wave, but you want to minimise these occurrences as it puts a tremendous strain on the boat as well as the crew. You also risk causing damage to the boat or injury to the crew.
Above, punching into head seas is the most punishing course for both the boat and crew.
The very last thing you want to have to deal with in heavy weather is some form of mechanical failure, so be as gentle as you can with the boat whilst still making headway. Most rescue situations in heavy weather are as a result of something breaking or failing on the boat rather than the seas themselves, and in my experience’s it’s the heavy landings and slams in a head sea that result in something failing. Over the years I’ve had some really heavy landings after which I’ve looked into the engine room to check things half expecting to see an engine lying on its side, such was the impact! During the course of our sea trials pretty much every failure be it mechanical, electrical or structural (which is the whole point of sea trials, to expose potential issues) has occurred running into head seas after a heavy landing, never whilst running downwind or beam on, so undoubtable head seas are the hardest for the boat and crew to endure. All the above applies to operating in heavy weather, in more moderate head sea conditions when it’s possible to go fast, or indeed very fast such as when racing, different tactics are possible, but I have not gone into that, as here were talking about heavy weather, with winds of force 7 and above and high seas.
If your boat is fitted with trim flaps or Interceptors these can be used with great effect to keep the boat glued to the water in head seas and make for a much softer ride by depressing the bow. Both only really become effective once you’re fully on the plane at speeds over12-13kts so if you can’t make that much speed their not so beneficial. Trimming the boats head down by the drives will also have a big effect on softening the ride as it keeps the bow in contact with the water allowing the hulls sharper sections to cut through the waves, at least in smaller head seas. In really big waves you’re depending on the boats natural trim and stability and there’s not a whole lot you can do other than adjust your speed. In following seas the reverse applies, and you definitely want to lift the bow up rather than depress it.
Running directly into head seas is always the hardest and most uncomfortable course, however taking waves just off the bow makes life significantly easier, as the length between crests increases giving the boat more time to recover, and the steepness of the waves face the boat encounters is less severe, correspondingly the ride is much more comfortable. When taking head seas on the quarter especially big seas that are breaking you have to be prepared to but her head up and slow down momentarily to take a particularly big or dangerous breaker head on, once through that wave you can turn back onto your course. In extreme conditions you must be prepared to do this quite regularly.
Above & below, the power and majesty of the sea clearly portrayed here, great care is needed navigating through such seas.
Following seas
A following sea directly down wind can be the most comfortable course in heavy weather. In large open water waves it’s a case of adjusting your speed relative to the wave’s size and steepness. In a fast boat you can comfortably overtake the waves assuming you have the speed to do so up to a point. That point will be when the waves exceed a certain height and you’re unable to go fast enough to jump from crest to crest, or the boat is not long enough to bridge the distance between crest. What happens if either of these limitations is exceeded is that you will stuff the bow into the back of the wave in front. The consequence and seriousness of that stuffing will depend on a few factors. If the boat is an open cockpit type you will in an instant completely fill the boat with water which will potentially seriously affect the boat’s stability and in a worst case scenario cause the boat to capsize. Any crew that will be hit by the flood of water could be injured or washed overboard. If you’re travelling at say 40kts and you drive the bow into the back of the wave just half a meter below its crest it’s going to be like half a ton of water travelling at 40kts running across the deck hitting either a person, or a part of the boat that was never designed to withstand this impact. When you look at a boat and wonder whether a part of the boat will withstand this the simplest thing is to ask yourself would you fit that to the hull bottom and expect it to survive as you pound through the water. So you can begin to appreciate the consequence of a bad stuffing. Therefore when you reach that point when the waves are getting to big and too far apart to be able to jump them the best solution is to slow down. You can still overtake the waves but you need to adjust the speed so that as you go over the crest the hull falls gently and slowly giving it time to pick up buoyancy, and fall more into the trough rather than the back of the wave in front. Once the hull stabilises after the fall the bow will have time to recover and lift, allowing you to ride up the back of the wave in front. You can continue this way as conditions worsen by adjusting the throttle to give you more power to push up over the wave in front, but pulling back on the throttle to reduce the speed that you go over the crest, preventing the bow falling to hard and burying deeply. There will however come a point when the fall over the crest will just be too hard and dangerous, as at that moment when your balanced on the crest there is very little of the boat in the water, and you’re in a precarious position it taking very little to upset the boats equilibrium. At this moment the safest solution is to slow down so that your traveling slower than the waves and let them overtake you, the speed you chose will be one that is comfortable for the conditions, I find around 16kts is a pretty comfortable speed for a wave train that is traveling around 20kts. At this speed you will tend to surf at up to 19kts as the wave lifts your stern, and then slow down to around 14kts as you run uphill on the back of the wave as it passes. The trick is not to let the surfs get too wild and if this starts to happen pull back the throttles a bit. All the above applies to under passage in open water, when it comes to running through extreme seas a different approach is sometimes needed as described earlier, but all the above still applies. Ironically it can be smaller waves that cause the most trouble if their length equals the boats and you get caught with the bow stuffing into the wave ahead and the transom lifted by the wave astern.
Above & below, running slowly in a following sea and letting the waves run through you and overtake the boat, the safest tactic when the waves are too big and steep to run fast overtaking them.
Below, stuffing.
Over the years I’ve had a few stuffing experiences. I remember once we were running in one of our faster 16m designs at around 45kts in I guess what was a 2m sea comfortably jumping from crest to crest when suddenly a big hole opened up as we encountered I guess a 3m wave, and we put the bow straight into the back of the wave burying the bow deeply into the wave. Before I could react a lump of solid water ran across the foredeck, stripped the wipers clean off the front windows then went over the cabin roof and took off the radar scanner and broke all the aerials. (This led to us developing a special wave deflector to protect the wipers and a redesign of the radar scanner position). Now I’ve never been too worried about the boat itself as all our boats are strongly built to survive such encounters with thick 15-20mm glass for the windows, but you can imagine that on a recreational boat not specifically designed for heavy weather with large front windows, the consequence could be severe and the windows be blown in, and even then for us it was a pretty intense and costly moment and not something I wanted to repeat. On another occasion we were pushing one of our wave piercing designs hard and to the limit, running through a tidal race with very steep seas and drove straight into the back of a 4m wave. I remember thinking just before it happened that this was going to be an interesting moment and deliberately kept the throttles down to discover the limit of its operational envelope. The ensuing event was pretty extreme, now the boat was specifically designed for such encounters so we didn’t suffer any damage, but the whole boat went dark inside the cabin as we were submerged in the wave, ultimately my nerve ran out and I pulled back on the throttles. At the time we were recording the sea trial with a drone overhead and it was fascinating to watch the footage later. You could see the boat completely disappear into the wave only to rise up seconds later like a submarine surfacing with water streaming off the cabin and decks.
Probably the best advice when running for a prolonged period in a really big following sea during a storm offshore, (as opposed to the short duration inlet or tidal race passage described earlier) is to simply slow down. Try to find a speed that the boat is comfortable at and let the waves overtake you, as the resulting consequence of being hit badly and the corresponding broach or hard knock down is greatly amplified by the speed you’re going. Something to bear in mind when running through the steep confused seas of a tidal race is that there is a probability, increased by the more time you’re at sea in such conditions, that as a consequence of your boat speed, wave length, wave steepness and angle, you’re going to be broached, it doesn’t matter how good your boats seakeeping is, there’s a scenario where the above factors all come together and work against you causing the boat to momentarily lose its composure.
Photo below, staying behind a big breaker as you cross a bar.
I recall one occasion when I was out on sea trials in a 17m 25 ton pilot boat during a pretty bad storm during which winds reached 96kts and waves were 5-6m in height. The tide was ebbing and there was a wind against tide creating a very violent sea state with heavily breaking seas. We stopped just back from the entrance of Cork Harbour for a while and observed the conditions, pretty much the whole horizon was white water as the waves broke and we considered it was touch and go as to whether the conditions were just too bad to attempt running out through the entrance. But there was a slight lessening of the severity of the breaking waves on the Eastern side, so we decided we would head out through there. Once we had cleared the entrance by running slowly and taking the breaking seas head on, and were in open water clear of the tidal race we turned around in a lull to head back in on the same course, which whilst keeping us out of the worst of the seas did put us closer to the rocks than you would want to be. I was only running slowly at around 15kts when out of nowhere a big breaking sea rose up behind me and picked the boat up on its face and accelerated us up to over 25kts, which is around the speed you can expect 5-6m waves to be travelling at. At first we surfed ahead on our desired course but slowly, degree by degree the boat began to turn and head towards the rocks below the lighthouse, no amount of corrective helm could alter her course. To try and get out of the situation I put the engines in full reverse but this had no effect, we were literally in the grip of the wave, out of control at 26kts completely at the mercy of the elements and there was absolutely nothing I could do about it. Thankfully, the wave’s violence eventually dissipated and the wave passed through us and we fell onto the back of the wave and slowed down before we hit the rocks. It was a pretty stressful few minutes as I tried to get her head up into the waves and clear the precarious position we were in and head out into safe water. This meant heading out through the entrance again before we could turn. This time we decided that it was just too risky to run close to the rocks and came in through the centre of the channel where the conditions were the worst, but at least we were away from the shore. It was quite daunting to have to head back in a second time wondering whether the same would happen again. This time I ran in very slowly at around 9-10kts and we never had a problem, at this speed the waves passed through us and we never got into a big surf. This showed that getting the speed right for the particular conditions is very important. Could I have picked a wave and sat on the back of it to run in at 26kts in textbook style? Quite simply no chance. In these conditions the surface of the sea was being stripped off and there was airborne spray 2m high, the wipers could barely cope and all around you all you saw were walls of water, there was no way you could read the wave pattern for long enough to run all the way through the entrance at that speed without coming a cropper.
Above, running through big beam seas and trying to avoid getting hit by a breaking wave.
Beam Seas.
Beam seas can be a tough course in heavy weather, and in extreme sea states of heavy breaking seas can be an impossible course to continuously maintain safely. But in a fast boat, they can, in moderately heavy seas be quite a comfortable course and relatively high speeds can be maintained. So long as the waves aren’t breaking heavily you can hold a beam on course, but there comes a point as on all courses when you have to adapt. A breaking sea poses a risk if caught beam on, ultimately if big enough and it hits the boat at the worst moment as it plunges you run the risk of getting knocked down. But one thing to realise is that when a hull is moving at speed through the water it generates a lot of hydrodynamic lift, so the stability of the hull at speed is much higher than if it were stopped. In other words if a boat were sitting stationary and were hit by a breaking wave the amount the boat was rolled would be much more than it would be if traveling at speed.
Once we were undertaking sea trials at a place called the Daunt Rock, an area of shoaling water that creates breaking waves in a predictable pattern in a confined area. We were in two all-weather 13m SAR craft. One boat would run up to the breakers and hold station, eventually the tide would carry you out of the breakers and you would have to turn around and run across the surf zone and back down wind to come up again. Obviously one would time the turn it in a lull, but on this occasion as the boat crossed the surf zone a wave rose out of nowhere and began to break heavily bearing down on the boat. At that moment we decided the best option was to keep going at speed and try and get out of the way before it hit the boat, but we couldn’t make it and the 4m breaker hit the boat directly beam on. What was surprising is that we survived the impact. Later we looked at footage from a GoPro camera mounted on the bow and measured the angle to the horizon that the boat heeled to as 45 degrees, but I’m pretty sure if stationary it would have been knocked over to 90 degrees. That said it doesn't take a very big wave to roll a boat if caught at the worst moment, but all things being equal the faster the boat is travelling at when beam on to the wave within reason, the less the likelihood.
Below, interesting photos showing a 13m SAR craft getting hit at speed beam on to a pretty big breaking wave, the boat was heeled over to 45 degrees as the wave hit, but was not rolled over, which it more than likely would have been if stationary.
When beam on waves reach a size that they become a hazard to the boat the best solution is to alter your course to either take the waves off your bow, running at about 45-60 degrees to the waves or off your transom quarter and zig zag if necessary to reach your destination. This way you can still maintain good speed and although it will take longer to make your passage, you will get there in one piece. The other solution is to try and stay on your destination course even though it has you running beam on to the waves, but when a bigger wave approaches slow down and turn up into the wave taking it at 45 degrees, or even head on if necessary. It's quite possible to read the sea and judge when a wave is likely to hit you unless you take action. This way you can hold your destination course, but it will take pretty intense concentration to maintain this for a long period of time. Of course the caveat here is that you can see the waves coming, at night you can't, so this course of action would not be advisable if you were caught in a storm during the night time.
The effect of tide in coastal waters cannot be underestimated. Once on our voyages in Thunder Child II we visited the Gulf of Corryvreken, a wild stretch of water I had always wanted to see. The Gulf is famous for producing the second largest whirlpools in the World after the Saltstraumen and Moskstraumen Maelstroms in Norway and is renowned as being one of the most dangerous stretches of water in the world. Here a tidal race is formed between the islands of Jura and Scarba as the tide is forced between the two islands and can reach a speed of 8.5kts. Whirlpools are formed as water column’s sheer and these can be up to 50m wide and the hole at the centre of the whirlpool can be a metre deep and a couple of metres wide, they didn’t prove any danger to our 20m boat, but certainly would do for a small boat and were awe-inspiring to run through.
On the western entrance a basalt pinnacle rises up from depths of 70m to 29m, and lying to East, directly in front of the pinnacle is a deep hole in the seabed, with a depth of 219m. As the water flows through the gulf it falls into this hole, and then encounters the steep face of the pinnacle, causing a massive upwelling surge of water to rise to the surface. On a flood tide this surge meets swells entering the Gulf from the West, and creates standing waves that can reach heights of 9m. These standing waves are not like normal waves as they are stationary and tumble and break continuously on the spot and line up like ranks of solders across the gulf. In a normal tidal race the waves are slowed down from their normal speed and bunched up as well, but not to such an extreme level. The day were visited there was a force 6 blowing and the standing waves were only around 2-3m high, but still it was a challenge when we decided to run through them as the bow went straight through every single wave, and we lost all visibility as they continuously came over the bow and over the roof, which lasted probably 30 seconds until we cleared the area of turbulence. The word Corryvreckan translates to ‘Cauldron’ and that perfectly describes the seething sea state around the whirlpools, and it was quite an experience to have the throttles set for 6kts, holding station just ahead of the standing waves that were breaking behind the boat, and not be moving at all!
There is an Old Irish text known as Cormac’s Glossary written by the King and Bishop of Cashel, Cormac mac Cuilennáin who died in the year 908: “There is a great whirlpool which is between Ireland and Scotland to the north, in the meeting of various seas, its thunderous eructation and its bursting and its roaring are heard among the clouds, like the steam boiling of a cauldron of fire.” I felt that was a pretty cool description of the place as how the place might have appeared of old during a storm. But in a full gale without question the gulf during a westerly blow and a flooding tide would be completely un-navigable. So areas of tidal race should be avoided and if navigated through treated with the utmost respect.