When You Demand Strength and Sea-Keeping
World Speed Record holders with our own vessel and crew
PILOT BOATS, A DESIGNER AND BUILDERS PERSPECTIVE.
By Frank Kowalski, Managing Director at Safehaven Marine.
Background.
Safehaven Marine build a range of vessels for many different operational roles such as patrol, survey, crew transfer to name a few, but what makes Safehaven unique is that we specialize in pilot boats, with 80% of our production dedicated to just this area, and have supplied over 50 pilot craft all around the world over the last 17 years. This has allowed us to amass a good deal of experience in this very specialized area of boat design and engineering, as a pilot boat has to endure quite possibly the toughest and most challenging of operational roles. Coming alongside a ship at night in a gale with 5m+ waves, and transferring a pilot aboard has to be the most demanding sea borne operation a coxswain can undertake. And for the vessel to survive what is in effect a controlled collision many times daily, certainly is the most demanding of operational envelopes for a hulls structure, and the vessels engineering to be capable of withstanding day in, and day out reliably for many years.
As managing director at Safehaven Marine for some 25 years, I am also the designer of Safehaven’s craft and responsible for the naval architecture. When I was a young man I skippered my own Comercial boat offshore in Ireland, and I guess the years doing this gave me a fine understanding and respect for the sea, and an appreciation of what the term ‘good seakeeping’ meant having been caught out many times in bad weather. I’m also lucky that I have a couple of local pilot boats that Safehaven built at my home port of Cork Harbour, and am good friends with many of the pilots and crew there. As such I’ve been able to experience first-hand over the last 14 years what a pilot boat does and how the pilots and crew operate. Having
watched with bated breath pilots climb up ships ladders and seen the skill of the coxswain’s coming along side in rough conditions I’ve developed the utmost respect for the pilots and crew. But also these experiences have helped me understand better the requirements of a pilot boat, and has allowed me to continuously refine design elements of my pilot boats over the years.
Specialised design considerations for pilot boats
A pilot boat due to its specialised operational role has some unique requirements beyond that of normal Comercial craft and workboats:
Extra strong construction.
An ‘all weather’ pilot boat obviously has to be very strongly constructed to withstand the slamming loads that a hulls bottom can be subjected to, as will be the case with all boats that operate in heavy seas. However in addition a pilot boat is subjected to unique side impact loadings on the hull especially at the pilot boarding area, and this specific area along with the transom quarter needs to be heavily reinforced. We use transverse framing at close 500mm centres which creates a pretty strong structure overall, but we also add additional reinforcement at these areas. Having the hull primarily transversely framed rather than longditudaly in my opinion is probably preferable, at least on a pilot boat hull, as the transverse framing is better able to withstand side impact loadings. A pilot boat hull has to be able to withstand what is in effect a ‘controlled collision’ many times daily, and in heavy seas these collisions can be pretty severe at times. We do not use cored structures, at least not on our pilot boats, as whilst a cored structure is certainly very strong, the outer shell is by necessity much thinner than on a solid laminate, so just by the nature of a pilot boats work the more durable solid laminate is probably preferable, even though there is a weight penalty. Also a solid laminate is much easier to repair should the pilot boat suffer damage, especially in geographical regions where repair facilities may be limited. That said we do use cored structures for some areas and components in the superstructure, such as the roof which are not subject to impact stresses and for some internal fit out structures to reduce weight.
Wide side decks and slightly angled cabin sides are preferable to prevent the pilot or crew member from becoming trapped or injured when the pilot boat rolls towards the ship during boarding manoeuvres in heavy weather. Although a common MO is for the pilot to access the ships ladder from seaward there will be times when this is not possible, so it’s best to ensure by design that there is enough space to walk or shelter on the boarding side without there being a risk of getting crushed, no matter the pilot boats angle of heel in extremis. Some 600mm is a good width for the side decks and the actual area where the pilot boards should be quite spacious so he and the crew have plenty of space to manoeuvre themselves. The grab rail should allow the pilot to reach out and take hold of the ships robe ladder whilst still holding on to the safety rail to steady himself. Sometimes an extra safety rail can be incorporated forward of the boarding area if the push pit rail cannot be reached easily from here.
The deck should incorporate a good high grip, non-slip surface. The boarding area and side decks should be well illuminated with LED lights on the cabin side low down to illuminate the walkway, we have found that only actual ‘under water’ type lights survive here due to the harsh environment.
Larger and durable fendering.
Over the years we have used many different fendering systems but whatever type and material is used for fendering it needs to be much bigger than on a typical workboat. As standard we nowadays use a polyurethane fender incorporating a 150x150mm ‘D’ section hollow fender at the deck edge, the size we use on our 12-15m size pilot craft. We also incorporate a slightly smaller lower run above the waterline and multiple diagonals along the side which provides good all round protection for the boat. In our experience there are two areas of the pilot boat that receive the most wear, these being the shoulders right at the boarding point where the pilot boat is continuously pressed against the ship whilst holding station for the pilot to transfer and the transom quarters, as these often impact as the pilot boat pulls away from the ship. At the shoulders we use a much larger section of fender of polyurethane material nowadays with a size of 300x300mm. The larger fender here significantly softens and absorbs the boarding impacts achieves two other purposes. The first is that by incorporating a large, and correspondingly, inevitably heavier fender only where it is most needed, it allows the boats weight to be kept lower. The second advantage of this being that the difference in size between the two fenders creates a gap for the pilots boarding ladder to sit as the pilot boat lays alongside. Avoiding getting the ships rope ladder getting caught is probably the greatest challenge during boarding, and represents one of the biggest risks for the pilot as he boards. Having this gap also almost eliminates the risk of the pilot getting his foot crushed between the pilot boat and ships side, as where he is standing and boarding from, there is always a gap that cannot be closed.
There are however many other excellent fender systems available on the market and sometimes the client will have a preference, and we sometimes incorporate these systems, the pre-requisites of any fender system being that it is very tough and durable, capable of absorbing boarding impacts and can relatively easily be replaced at venerable areas such as the shoulders and transom quarters if it gets damaged.
Above, Safehaven’s Sacrificial shoulder fender and the gap it creates for the ships pilot boarding ladder
The gap is created in front of the larger shoulder fender which is approx 1.5m long and behind. Pilots choose their own preference whether to board forward or aft depending on sea state but in heavy weather aft would be preferable. As this large fender suffers the most abuse and damage, we make this section easily replaceable and call it our ‘sacrificial shoulder fender’. We also often add an additional run of fender that wraps around the transom quarters below the main fender as this is the other area most prone to impacts and damage.
Recovering a pilot from the water
An efficient means of man over board recovery, we’ve incorporated many different systems over the years: swing out Davits on the superstructure side deploying a life ring or Jason’s cradle work well, but we developed our own MOB recovery system mounted on the transom many years ago and have continuously refined it over the years. Incorporating a platform that is folded back out of the way when not in use but can quickly be lowered to the waterline or underwater some 400mm, it can then also be accessed by a crewman by ladder to assist an injured or unconscious pilot on to it. We have also incorporated a prop guard at times, although the preferred MO is to approach the casualty from the bow and transfer by lifeline or Matesaver to the stern with the engines in neutral. Any recovery system should be quick and easy to deploy, we’ve tried to keep it simple and of manual operation not depending on hydraulics or electrics, as being pretty exposed to the elements such systems require maintenance and at the moment of crisis unless serviced and checked regularly could fail, but we do powered versions as well that incorporate a manual backup. Any manual system should not be too hard to raise by hand and be capable of being operated by a single crewman.
Above and below photos show the MOB recovery system in use with the casualty being drawn by life ring or boat hook to the platform, then being lifted to deck level.
Other important design considerations. Good visibility from the helm to both port and st/bd to be able clearly see the point of touch at the shoulders, so one can perfectly judge the manoeuvre as one comes alongside without having to guess distances. Good visibility overhead towards the ships deck allows the coxswain to observe the pilot on the ladder especially on high side ships. A central helm position is ideal as it allows the coxswain the same level of visibility to the boarding area from either port or starboard boardings, and have the same overhead view. This gives the coxswain equal confidence regardless of the side of approach.
Above, the central helm position on our pilot boats gives the coxswain coxswain control of the vessel whether boarding from the port or St/bd side.
A tapered beam at the deck, where the transom has less beam than the forward shoulder’s can be preferable, although not always as it can depend on other design aspects, (our sacrificial fender naturally creates this taper as well). Incorporating a taper allows the keel to become offset from parallel to the ship as the helm is turned to break away, the offset forces a wedge or water to push the pilot boat away as it becomes parallel at the deck edge to the ship and helps reduce the chance of the pilot boat becoming ‘stuck’ alongside.
Quick responsive steering. On our pilot boat designs we use extra-large rudders that were commissioned as our own special rudder design, cast in NIAB. Probably 30-40% larger than the norm which does result in a slight drag penalty, but the advantage of these large rudders enables the boat to have its course altered very strongly with just half a turn of lock on the wheel, so really at speeds above 9kts you never have to ‘spin’ the wheel, and as one comes alongside only one hand is needed on the wheel with the other controlling the throttles, this gives the coxswain great control of the boat at this critical moment. It's difficult to quantify steering empirically but as example our pilot 48 can alter its course 180 degrees at max speed of 25kts in 8.4 seconds, which is a pretty tight turning circle.
Suspension seating for all crew and pilots is a must, and the seats should have armrests at least and preferably a lap seat belt as in heavy weather one can be accidently thrown from the seat by an unexpected wave encounter. There needs to be multiple grab rails so that one can pass through the cabin with each no more than an arm’s reach from the next, and you really can’t have too many.
A Hadrian rail is also essential for traversing around the cabin safely, especially so in heavy weather.
Every different boats hull design will tend to want to lie at a different ideal angle when holding station pressed alongside a ship as the pilot prepares to embark or depart, this area as well as being well illuminated can benefit from having yellow or some other easily distinguishable mark at the ideal boarding point, so the pilot can see where he needs to ideally step to as he disembarks the ladder to the pilot boat.
A lot of discussion has been made to having forward or aft angled front windows over the years, both have their pros and cons. Forward angled windows have the advantage of clearing water more easily and tend to suffer from reflected helm instrumentation lighting to a lesser extent, although this much depends on the helm design and its proximity to the windows so this is not always the case, and dimming of all helm lights can mitigate against this to a large extent. Lastly the actual glass area in m2 per window tends to be less compared to aft angled windows which have a more extreme aft rake, less glass area inevitably makes for a stronger window which directly leads to the main advantage of aft angled windows, that being the much reduced loadings on the window glass from a boarding sea. If a big breaking sea comes over the bow green solid water can impact the windows with tremendous force, if the windows are angled aft the pressure of water is deflected and greatly reduces the loadings on the glass and superstructure. However this needs to be put into context, it is only a ‘surf’ type of breaking wave of 4-5m+ that is of concern here, as typical breaking seas offshore tend to result in only spray and aerated water impacting the windows, whereas a plunging breaker can dump several tons of solid water onto the foredeck if it breaks right over the bow. So unless the pilot boat has to operate in waters where there is a bar or strong tidal influence and big waves are prevalent, it's not such a relevant factor.
Above, a big breaking sea coming over the bow makes one appreciate the need for very strong windows.
Below, a large lump of solid water running along the deck, a cubic meter of water weighing 1 ton travelling at 25kts…..
Pilot boarding ladders.
This seems to be quite a controversial subject, with some pilots preferring them and some preferring to board from the deck. Off the 50 odd pilot boats we have built, some 25% have had pilot boarding ladders incorporated, with the majority not incorporating them. Geographical regions appear to have a bearing with some regions using them and others not. From my understanding, and bearing in mind I’m not a pilot, the main advantage of the high level ladder is firstly that the climb up the ships rope ladder can be reduced, and obviously the less time spent on this ladder exposed to the elements is preferable. Secondly, the ships rope ladder can be kept above the plot boats deck thereby lessening the likelihood of the ladder becoming trapped between the pilot boats deck fender and the ships side, as the pilot boat moves vertically up and down as the waves or swell passes along the ship. As the platforms tend to be at a height of between 1- 2m above the deck, this means, in theory, that swells of up to 2m will not cause a correctly deployed ladder to become trapped. Another advantage is that as the pilot boat surges forward and aft when boarding in a following sea, the ladder can be pulled into position by the crewman.
Above two Interceptor 42 Pilot boats for different ports and countries, one operating without a plot boarding ladder and one with. Below, one of our designs of pilot boarding ladder with the platform 1.1m above deck.
Below, another design with a platform 1.8m above deck with a hinged outer platform and handrail.
The main disadvantage at least as I see it is that pilot boats motions are very greatly amplified by being 1-2m above the deck, and the small platform is inevitably a much more precarious a platform to be standing on than the larger and more spacious pilot boats deck. Another disadvantage is that the ladders platform has to be a certain distance away from the ships side to allow the pilot to step easily across the gap between the platform and ladder. Too far away and it's difficult to reach easily or safely, but if the platform is to close, then there is the risk that in heavy weather as the pilot boat or ship rolls the ladder can impact the ships side damaging the ladder, or possibly injuring the pilot. Finding the right compromise can be challenging, especially as one has to factor belting or other such protrusions that some ships can have along their side. Adjustable platforms which can have their platform’s set at a distance to suit the prevailing conditions can be a good albeit more expensive solution. It goes without saying that any platform as well as all other aspects of a pilot boats engineering needs to be extremely well designed and built, as well as being easy and straight forward to maintain over the years.
Good seakeeping and stability.
Good seakeeping and stability is clearly a very important factor for a pilot boat. The term good seakeeping can be best interpreted as ‘The vessel should inspire a sense of confidence and safety in her crew and should always behave in a predictable controllable manor, no matter the course or sea state’
Above. A Pilot 38 & 48 coxwains having confidence in their boats seakeeping as they encounter large breaking seas during sea trials at the entrance to Cork Harbour, on the South coast of Ireland where Safehaven Marine are based.
Within the almost infinite number or interpretations for hull design that exist, some of which will excel on some headings to a sea state and be less good on other courses, the best designs will be those that achieve a compromise or balance, so that they run well on all courses. The overriding factor is that the boat meets the above interpretation of inspiring a sense of confidence and safety.
Without taking into account variations on a boats beam in relation to its size (length to beam ratio), which obviously plays a big part in the hulls stability probably the single most important factor that influences how a fast monohull design, of typical proportions behaves in heavy weather is its centre of gravity. In heavy weather a low VCG is what you want or the boat or the boat will be ‘tender’ and prone to yawning or broaching, and everything that can be done in the boat's design to keep its CG as low as possible will result in a safer boat when big seas are encountered.
Self-Righting
All our pilot boat designs are inherently ‘self-righting’ achieved by a combination of a low VCG and the buoyancy of the superstructure. This means that once the point of vanishing stability of the hull has been passed, the superstructure comes into play to add an extra righting force when it impacts the water beyond 100 degrees of heel. How far the self-righting capabilities are taken depends on the area of operation of the pilot boat to an extent. For absolute full self-righting as in a SAR craft the boat pretty much has to be like a submarine so that no significant amount of water can enter the hull when inverted, and that everything inside the boat, including its crew stays in its position when upside down, however this does result in some design compromises (windows need to be fixed etc).
Above, an Interceptor 48 pilot undergoing a self-righting recovery test by being pulled over gradually to an inverted position by a crane to ensure she recovers to an upright condition simulating a capsize scenario.
However as a minimum the windows, doors and hatches should be strong and watertight enough, and cabin strength sufficient, so that as the superstructure is slammed into the water, nothing breaks. It is a pretty rare occurrence for waves capable of rolling over completely a well-designed pilot craft of over 12m to be encountered, mostly one could expect a hard knockdown to 90 degrees at which point the cabin buoyancy stops a full roll over, and it is really only the type of ‘surf’ wave that might be encountered crossing a bar or in shoaling waters, or waters subject to fast tidal flows that represent such a danger, so the requirement for self-righting very much depends on the sea states that might prevail at a port. That said ‘inherently’ self-righting is a desirable feature for a pilot boat as the sea can be an unpredictable environment, and interactions that can occur to a pilot boat whilst alongside a ship can be unpredictable as well, as there can be many different factors in play and in influence at any one moment.
Above and below, the kind of heavily breaking ‘surf’ waves that if encountered beam on at the worst moment as they are plunging could potentially cause the vessel to be capsized.
