On Thu, Dec 31, 2009 at 10:35 AM, John, <[email protected]> wrote:
> >SNIP< > > On no thanks - it was only a sort of generalised 'I wonder' with respect to > the topic under discussion, I don't have a boat so have nothing but a > moderate interest in the topic. We do from time to time on Sky TV repeats > see an ice breaker at work on the St Lawrence which has the capability of > blowing vast jets of air up it's sides to further assist the break up of ice > but I doubt that that is relevant to narrowboats! Many thanks for your > interest and all the best for the New Year to you. > John > > When the ship is under way, the plumes of spray you see flying up the sides of the ship are mostly from pieces of ice fracturing under great pressure. Pneumatic 'bubbler' systems are used mainly to keep ice from forming around the hulls of moored vessels--these are the Great Lakes carriers, which are nothing more than narrow boats writ LARGE. The ones seen on Lake Ontario and the St. Lawrence Seaway are 730 ft long--those on the upper lakes (above Lake Ontario) are up to 1000 ft. long and their passage is restricted by the size of the Welland Canal locks. Sound familiar? Bubbler systems are used on icebreakers too, to assist in breaking the friction between the hull and the pieces of ice alongside. If you recall in Laurence's video, narrowboat crews were seen rocking their boats from side to side; this also breaks the friction, and is accomplished on large icebreakers by pumping fairly large quantities of water ballast from one side of the ship to the other. On smaller icebreakers, which also service floating aids to navigation during the summer, the inclining of the vessel is accomplished by swinging one or two buoy anchors on the vessel's derrick. The anchors used are usually in the 3 to five ton range. cheers, Phil & Anne Irons nb pedantic Sydney, Nova Scotia [Non-text portions of this message have been removed]
