POINTS FROM THE BILGES - A FEW THOUGHTS
The idea of this page is a bit of a blog to record thoughts on various topics and list my top tips. Some items are on the design process and which drove me in a particular direction, others are on any topic, some may not be connected with barges.
Hulls, Superstructures and Seaworthiness
Hull strength is probaby the most important consideration for any vessel that is going to operate on anything rougher than a UK canal and can only really be checked by a qualified marine architect or a surveyor. The best way is to use Classification Society rules such as Lloyds or DNV rules for small craft. However, the American Bureau of Shipping (ABS) has a very simple rule of thumb:
"The thickness of the hull plating should not be less than 1/100th of the distance between the transverse frames or longitudinal stringers."
For example using typical 6mm plate for the hull side means that there should be frames or stringers with centres at every 600mm. On old dutch barges the standard frame spacing is 500mm, so in practice 5mm plating should be sufficient. In many barges the acceptable minimum thickness is 4mm, as determined by insurance companies. I personally would be wary of subjecting any hull that does not meet the ABS rule of thumb to waterways rougher than inland canals. Even on a calm day at sea, the swell can induce hogging and sagging stresses that the vessel will not have been designed for. On a new construction barge not being constructed to Classification Society rules, I would insist on meeting the ABS rule for the entire hull - bottom plates, chine plating, hull sides and weather deck up to the gunwhale.
Superstructures also have a marked effect on a vessel's seaworthiness and the wheelhouse construction of a dutch barge in particular has a considerable impact on seaworthiness. In many ways the superstructure and wheelhouse must be as strong as the hull. This is particularly important if considering building a vessel to cope with more severe weather and larger waves. Survivability requires water tight integrity of all openings such as windows and hatches, etc. Despite this fairly obvious requirement it is quite common for dutch barges to have a relatively large wheelhouse windows in a large lightly built wood or aluminium wheelhouse structure. Hulls may be reasonably strong, but see the comments above. True survivability can hardly be claimed for boats with big picture windows and lightly built superstructures...! or the sake of achieving a good view
On the other hand, a 180 degree range of positive stability for power vessels that do have strong and rugged superstructures and with small and robustly constructed window and door openings will not ordinarily be an excessive claim. If structure is approached conservatively, if the openings are designed with an adequate support structure, and if the glazing is of the right materials and adequate thickness, this degree of survivability amounts to only a slight penalty in terms of weight and cost.
I think it unreasonable to expect any form of folding wheelhouse with large windows to cope with waves that the hull may be able to cope with. Most hulls can be built to a MCA standard. A folding wheel house probably will not be. A reasonably sized chunk of water that might come off a 4m wave weighs the same as a small car. Would a folding/collapsing wheelhouse support a car on the roof?? or resist a car hitting the front or side at say 5 mph??. I think not.
Round Bilge/Hard Chine debate
A thought on the round vs hard chine debate. Round chines are useful if you want to maximize hull cargo capacity but they also mean greater hull volume so greater displacement which probably means more ballast for our vessels. The hull does do not "grip" the water as well as a hard chine hull, so less longitudinal stability and roll resistance which can be overcome with bilge keels or leeboards, but then more bits stiking out to snag on canal sides etc. Also more expensive to produce - the wretched curved sections plus additional keels. So unless you are a stickler for complete authenticity, I would suggest go with a hard chine if going for a new build.
Hydraulic Drive
Hydraulic propulsion is most often promoted in order to enable placement of the main propulsion engine in a location other than amidships, in other words to make use of an unfavorable location in terms of trim and pitching moment. Although ordinarily highly reliable, any hydraulic propulsion system must be engineered correctly or it will be very unsatisfactory. Even if engineered and installed correctly, the use of hydraulics for primary propulsion is expensive to install, highly complex, ordinarily very noisy, and incredibly inefficient when compared to a simple direct shaft drive. This can hardly be viewed as a "feature."
On the other hand, one might very rationally consider a modest hydraulic drive system for a get-home installation, primarily to save weight and to provide flexibility of machinery location. A PTO on the generator might for example be used as the motive force. In this case, the hydraulic propulsion equipment will still be somewhat expensive, noisy, and inefficient, but it will not be asked to operate continuously, nor at full vessel speed.
A UK designed and recently built barge of approx 24m was fitted with a very sophisticated, and I recall very expensive, hydraulic drive system. The vessel's hull form is very similar to the example of a UK replica shown on the Hull Statics page. The owner has punlished the following comment on his system:
"Hydraulic power has many advantages..like space and position of equipment, but anything less than twenty five percent power can cause difficulties. You can only run the engine on tick over in certain situations...and certainly not where there is any danger of risk involved. On the big rivers like the Rhone and Saone, you need full chat, and fuel consumption for the engine and genny leaps to 400 litres a day."
This certainly bears out the comment on inefficiencies at para one above. The vessel is fitted with a single engine of 245Hp, so using 2 smaller engines might have been better but possibly negating the space advantage, plus a 32kw genset. The hull form also needs considering and it is likely that the drag penalty of the UK design over the dutch vessels (1920s hull and ESS hull) is contributing to the fuel consumption. It probably puts the vessels energy efficiency towards the end of the alphabet.
Colin's Top Tips
In no particular order:
Tip 1. When filling with diesel, get the supplier to put a splash into an empty glass jar - jam jar is possibly too small, Tesco gherkin jar is ideal. Check that fuel is clear and bright with no obvious bits or water at the bottom. Check for moisture with water finding paste. Label jar with supplier and date. Keep in cool dark place and observe. If fuel was contaminated with microbes, then they will be seen multiplying in the jar.
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