When You Demand Strength and Sea-Keeping
World Speed Record holders with our own vessel and crew
SEA TRIALS IN STORMS AT THE ENTRANCE TO CORK HARBOUR,
The How, Why & Where, including Video production.
By Frank Kowalski
The entrance to Cork Harbour situated on the South coast of Ireland can produce some pretty 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.
Above, Thunder Child II undergoing sea trials at the entrance to Cork Harbour in preparation for her Trans-Atlantic voyage
On a spring ebb tide, a large body of water from the inner harbour and estuaries around Great Island 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 rough conditions in the centre of the channel, and can extend right across the entrance, although the worst area is in the centre. In a storm, the entrance can become nothing short of a maelstrom. Very steep, closely spaced breaking waves occur across the entrance. The worst period being approximately 2hrs after the turn of the tide and 2hrs 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 almost un-navigable during the middle of the ebb, as we have seen breaking waves 10m high stretching right across the entrance. 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 the Rock, you are 'committed' as turning around can be to 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 effect the race has on sea state.
At the mouth of the harbour, the tidal flow moves around a bit according to the state of the tide, but there is an area east of the Cardinal buoy extending to just north of the E2 buoy where an eddy forms, and in this area that the seas are calmer. When undertaking sea trials with two boats, it is in this eddy that the camera boat can hold station in relatively calmer waters out of the worst of the race, (safer in storms), close to, but out of the surf zone, which we will come to later. 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.
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 6-7m, the waves feel the bottom and break very heavily like surf on a beach, with near vertical faces and heavily plunging crests, as shown in the two photos below.
This 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 over the rock 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. But when they arrive, conditions can be quite spectacular to observe, and indeed challenging to navigate through.
Above, the entrance to Cork Harbour showing the Western and Eastern channels, the Harbour Rock between, the surf zone and the eddy. Waves are biggest when the wind blows S – SS/W.
The swell tends to break in quite a predictable 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. But in general the swell breaks first on the Western side, East of W1 buoy in a wide break, which then continues to break right up to west of the Cardinal buoy, creating a ‘surf zone’ of white water more than a ¼ of a mile long in a storm. The second main break is on the Eastern side, outside and to the west of E2 buoy. The first break here can be very high, but does not extend so far in as the Western break, however a second break of the same wave sets occurs north of there just before the eddy.
Above: the difference between being in the surf zone and out of it in the eddy. The pilot boat is out of the surf zone and the XSV20 is in it. The difference in impacts a boat experiences between a breaking and non breaking wave can be clearly seen here and the difference is dramatic.
It is when the wind blows from the South or SS/W during a big storm that the swell becomes the biggest, and it is the resulting big breakers that occur as the swells break that are the most dangerous. Taken slowly, or most often almost stopped, they can be transversed safely head on, the caveat being in a suitably well found boat designed for surf operations, if caught at the worst moment, that being as the wave plunges, a huge weight of green water traveling at over 20kts comes over the bow and hits the foredeck and cabin windows with tremendous force. Needless to say everything has to be strongly built to survive such impacts. 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. 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 we always avoid. Running back in and having one of these breakers rear up and hit you from behind is also something to be best avoided, but with skill, it’s a 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. When the waves are this 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, in practice it doesn’t always happen like that. If for whatever reason a big breaking surf wave is about to hit you astern, and I can only speak from experience on our type of boats, which are of pretty heavy displacment, with a low CG and a flush weather deck that cant hold water, the best solution is slow right down, keep the boat dead square to the wave and let it break over you and run right through you. If you try and run faster 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 its 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.
Often people are completely unrealistic of how fast you can go into big 5m+ 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 few thousand kg lands after flying through the air, are completely different compared to the forces involved when a boat weighing 20+ tons lands.
Above: Thunder Child II stationary as the wave hit her, imagine how airborne she would have been if she had been moving faster!
The G forces the hulls structure experiences are many times higher as a consequence of the boats size and weight. Personally I find, at least in our type of boats, that the best course of action when a big 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 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.
Its 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 ones going to be pointing the right way when you recover, ready for the next wave.
Below, example of a 'ramp' taken a bit to fast and the consequent airborne moment followed by a hard landing
Capturing the video footage.
When capturing photos and video of the boats during sea trials, like most things, good equipment is the key, although the attrition rate can be high and we lose at least one camera a year when it gets drenched in spray or rain. The best photos always come when we have a second boat to act as a camera boat, as you are then right in the action close to the subject, so much less affected by poor visibility or rain, as is often the case during a storm. Roches point lighthouse also provides a great vantage point to take photos from, as it is only 300m away from the Harbour Rock, and with a good telephoto lens, great photos can be captured in good visibility conditions. Capturing good video can be more challenging. Trying to get footage from the camera boat is not easy due to the extreme motions aboard. Unless you are very close to the subject it's almost impossible, as if you try and zoom in camera shake is amplified and the footage unusable. For video from a boat the best footage is captured with a stabilised gimbal type camera such as the DJI Osmo Mini, which gives amazingly stable footage, however you do need to be quite close to the other boat. Go Pro’s mounted to the front windows and mast are used to capture epic breaking wave moments as they break in front of the boat and over the bow, although water droplets can frustratingly ruin the footage when they appear on the lens right at the best moment.
Below, footage from a Go Pro on the front window and mast of a big breaking sea about to engulf the boat.
Video from shore can also be challenging, as invariably in a storm one has to contend with poor visibility and often rain. Due to the distance from shore to the boat inevitably you have to zoom in, and then because of the strong winds, even though ones using a tripod, camera shake can be a big problem. Constant cleaning of rain and spray off the lens is also necessary to ensure good quality video. Locally conditions during a storm can provide a fleeting window of opportunity to capture the best footage, often there will come a moment when the rain stops and the sun comes out and it blows like hell just before the wind veers Westerly and the seas die down.
In recent years we have been using drones to capture some of our best footage ever. Although flying a drone is relatively simple and capturing video of stationary subjects and landscapes is easy. However flying dynamically following a boat at speed, keeping it in frame and not crashing is far from easy, and takes a lot of skill and practice to do this well, and Carl Randalls who fly's the drone nowdays certainly has this skill. The HD stabilised video from a drone is amazing. Of course, for the footage we try and capture during storms, flying the drone can be challenging in the extreme. We have flown the small DJI Mavic 2 zoom that we have found the best drone around, in 50kts of wind speed, far exceeding the drone’s operational envelope. Sometimes the drone has been at max power and going backwards trying to make headway into the wind. It can take 15 minutes to fly out 300m across the water to reach the boat in very high winds, leaving just a few minutes of time ‘on subject’ before one has to return to home before the battery runs out. Whilst from a safety point of view the consequences aren't high, as the drone just falls into the water if you run out of battery life, you do however lose the footage, and of course the drone! But when you’re successful, the footage can be world-class.
Photo above. Just occasionally we are lucky enough to have 3 boats launched together at the same time
The purpose of our rough weather sea trials
Safehaven Marine build ‘All weather’ S.A.R. craft, patrol boats and pilot boats. What does ‘all weather’ mean? Put simply it means the boat is capable of operating in all weather conditions, up to storm force 10 and 6-7m waves. Pilot boats, especially those operating out of open Atlantic coasts experience big seas regularly, often on a daily basis during winter months and need to be especially capable of dealing with heavy weather. Many times we have been offshore undertaking trials in a storm and our local pilot boat has passed by us to undertake a ship boarding in 5-6m seas. I have tremendous respect for the crew and pilots who have to head out to sea when almost all other craft are taking shelter. Imagine heading out at night offshore into a storm and coming along side a ship that is rolling heavily side to side, with the pilot boat rising up and down the side of the ship 5m, in the dark and driving rain and trying to board that ship from a rope ladder. Respect! Merchant ships under passage ensuring World trade continues, often have no choice but to proceed on their voyage to the port of destination and unload their cargo.
As such the capabilities of some of our vessels is far removed from the typical operational envelope of a pleasure boat, that whilst should be capable of weathering rough conditions if the occasion arise, it's not expected to operate regularly in extreme sea states, and have a completely different set of no less demanding priorities in their design.
If ones building a formula one race car, then clearly you’re going to want to test it on a race track, driving it on the public roads is simply not going to allow one to test its full capabilities. The same applies when one is designing boats that have to operate in extremely rough conditions, testing the boat in calm conditions in small waves is not going to allow you to test the design to its ultimate capabilities, to do this you simply have to test the boat in rough conditions, conditions that can only be generated by a storm. Therefore undertaking sea trials in rough, storm generated conditions has been, and continues to be a fundamental part of both our design process in both understanding what constitutes good sea keeping, and ensuring the boats engineering is fully capable of withstanding the tremendously violent and harsh conditions experienced by all elements of the boat whilst weathering a storm.
As such we always endeavor to test our pilot boats in rough conditions, often with the owners aboard, as its far preferable for any component to fail, or something to leak, (as sometimes happens on a newly launched boat), whilst the boat is with us during sea trials, before it is handed over to the owner and enters service. Things fail in rough conditions, generally nothing fails in calm seas, so we don't want the crew to have to contend with anything the first time the boat encounters hard conditions, hence our rough weather sea trials.
To safely operate boats in storms and especially in surf conditions safely there is no substitute for experience. Over the past 20 years since we have been undertaking our rough weather trials I've probably been out a 100 times in weather conditions of Force 9 and above and waves over 5m, so have a pretty good understanding of, and respect for, the sea state and conditions that can exist at the entrance to the Harbour, and of course the limits of my designs. As do the only other helmsman who drive the boats on these days, Ian Brownlee, who has worked at Safehaven for 15 years and Ciaran Monks. Ciaran is a coxwain on the Cork Harbour Pilot boats, (our own Interceptor 42 & 48 pilot boats) as is Carl Randalls, and as such they have many years of experience trans-versing these waters. We're also lucky in so much as we most often have two craft at sea during our heavy weather sea trials, the second 'all weather' vessel also acts as a safety boat should we experience any issues, so we can look after ourself's.
A selection of photos taken over the years during sea trials in up to Force 12, 120kt wind speeds
Videos of some of our storm sea trials showing the breaking waves that occur over the Harbour Rock and dynamic drone flying
SAFEHAVEN MARINE