Wave piercing pilot boats
Mon, 10 October 2016
In recent years, various boatbuilders have begun to offer pilot boat designs with wave piercing bows, under a variety of names and often different marketing back-stories, but are they actually much different in their seakeeping abilities to their more traditionally hulled alternatives? We travelled to Baltic Workboats in Estonia to find out how one of these new designs actually feels on the water.
This magazine deals with and is aimed at a great range of maritime professionals, but one group that have always inspired my greatest respect are the crews of pilot boats. They endure long shifts at sea in all weathers in relatively small craft, followed by intricately calculated risk-taking during boarding and ultimately massive levels of responsibility during the piloting operation itself.
So there is a strong argument, that of all craft types, pilot boats have to look after their crews best. To have a pilot arrive at the start of the job beaten up and worn out, risks not only his safety, but also that of other vessels, the environment and countless others.
Baltic Workboats do Marketing in a big way. My attention was first drawn to their wave piercing bow design by a 3-D exhibit at SMM 2016 showing the (claimed to be appreciably lower) vertical accelerations of their bow versus a conventional one in a heavy sea. There is no denying that this was an extremely captivating exhibit for a trade show booth (it helped BWB win SMM’s award this year for the best technical showcase stand), but I think even management at BWB would argue that floating a video, in a black glass pyramid, apparently suspended magically in mid-air, is something of an attention grabbing gimmick.
However, thinking back to our hard-working pilot boat crew, long after the tradeshow buzz has died down and the 3-D video pyramid that looked so futuristic in 2016 has been consigned to the back of the stationery cupboard, the boat needs to do what it is supposed to, and continue doing so for several decades: marketing glitz counts for nothing with the end user of this product.
ON THE WATER
Looking from dead ahead at water level, BWB’s wave piercing bow (Which the literature refers to as 'the wave impact reducing bow geometry with diamond shaped cross section') is a diamond shaped bulb, with the water level at rest slightly below the point of the diamond. The principle is that the buoyancy of the bulb combined with the gussets formed between the top parts of the diamond shaped cutwater and the rest of the hull, mean that the bow will find a roughly median position in the centre of oncoming waves or chop, rather than rising up, or trying to rise up all or most of the way over each wave, then crashing down, like a conventional hull.
For our test drive of this 15m wave piercing pilot boat we had a fairly flat water day, due to an exceptional Baltic autumn heatwave. However, with shallow water, careful (or perhaps careless) treatment of hull tabs and throttles, and some sharp turns, we soon got just what we wanted: 1-1.5m of nasty, sometimes breaking waves, from multiple directions.
When hitting the first lot of lumps, close to the boat’s maximum speed of 27 knots, the first impact felt broadly similar to the first wave encountered in a conventional hull. The bow appeared to rise in a similar fashion to that of a conventional boat hitting a wave. However, the really surprising effect occurred when the boat hit the second, third, fourth, fifth etc. wave. I guess from experience of driving more conventional hulls, my body had come to expect that the first wave lifts the bow, it drops into the trough then the second wave ‘catches the boat by surprise’, creating a larger impact. This is then exacerbated by the third and fourth wave, and so on, with the bow feeling like it is constantly delayed from where you want it to be, until the occasional big slam where an oncoming wave slope meets the airbourne bow on its way down, and regardless of what shock mitigation seating the boat has, the skipper decides it’s time to back off the throttles before anyone gets hurt.
The experience with the wave piercing bow once the whole of the boat was in the same chop was that it found a position somewhere in the middle of the waves, and seemingly locked onto it with the existence of the chop only betrayed by a slight wavering up and down from dead flat.
With my background in the leisure marine industry, I’ve had plenty of experience of ‘developments’ that sound great on paper, and don’t pan out quite so well at sea (Dreams that tarnish quickly in the salt air!). But I was very struck by the different feel of this boat and hugely impressed by its kinder feel. If after a few minutes at the helm it makes the crew feel cosseted and well looked after, imagine extending that feeling out to a 12 hour shift in 40 knots of breeze.
However, this was not, by any means an exhaustive test. I have not, after all, ever worked as a maritime pilot and there are many more sides to a pilot boat than vertical accelerations in a given sea state. The wave piercing bow will probably have more lateral grip than a conventional one, so will high speed turning circles suffer? It will probably have slightly more underwater surface area and therefore skin drag than a conventional hull, but will the fuel reduction thanks to its ability to maintain a more even speed in rough water make up for this additional fuel cost? These are all questions that only more exhaustive comparative testing would answer, but if I was looking at replacing a pilot boat, I would most certainly ensure that at least one wave piercing design from a well-known manufacturer such as Baltic Workboats was in the mix.
Source: Jake Frith