On Tue, Dec 1, 2009 at 6:26 PM, Steve Haywood <[email protected]> wrote: > So how much coal could a traditional narrowboat carry? > > Steve
As someone new to cargo carrying narrowboats, I'm playing catch up, but this is how I see it (barring my terrible memory...): Every boat has a loading table, each one even of the same construction were slightly different, however it seems that no matter the type of boat there are some factors that remain similar. I'll explain the process of cargo measurement as an explaintion of what I've observed: To work out how much cargo a boat held, the "dry side" inches were measured. This is the height from the water to the gunnels, and is measured in four locations (either side at the "front end" at the end of the hold near the bow, and either side near the "back end" - which is the bulkhead between the engine room and the hold). I understand there are marked spots on some gunnels? These measurements would then be averaged. An unloaded and unbalasted narrowboat is the lightest a boat can be. Normally when a boat is guaged there would be various things on board, often including a good ton of coal for the fire, cloths and other boat related items, plus other "stuff", normally called "dunnage" on the guaging tables (one of my favourite words). The weight of all this other stuff will generally remain constant over time, and therefore not included in the loading calculations. As they loaded the boat with cast iron 1/2 ton weights (I have a 1/2 ton GU weight in the back of Victoria's hold) they would do the measurements at 4 ton intervals (or so) and averaged it to get a displacement per ton. Stolen from Pete Harrisons email on canalworld: (http://www.canalworld.net/forums/index.php?showtopic=12038) ---- begin ----- The B.C.N. gauge table for FIR (B.C.N. 1853 - 15 May 1935) (a severner motor boat) ---- snip ---- 0 - 4 tons = average drop 1.01'' per ton (34.58'' average freeboard @ 4 tons) 5 - 8 tons = average drop 1.01'' per ton (30.54'' average freeboard @ 8 tons) 9 - 12 tons = average drop 1.01'' per ton (26.50'' average freeboard @ 12 tons) 13 - 16 tons = average drop 1.02'' per ton (22.46'' average freeboard @ 16 tons) 17 - 20 tons = average drop 1.01'' per ton (18.38'' average freeboard @ 20 tons) 21 - 24 tons = average drop 1.01'' per ton (14.34'' average freeboard @ 24 tons) So I think that this is the point at which they put no more calibrated weights into the boat and continued by calculation. The tabular section of gauge table B.C.N. 1853 continues as: 25 - 28 tons = average drop 1.01'' per ton (10.30'' average freeboard @ 28 tons) 29 - 32 tons = average drop 1.01'' per ton (6.26'' average freeboard @ 32 tons) 33 - 36 tons = average drop 1.01'' per ton (2.22'' average freeboard @ 36 tons) 37 tons = average drop 1.01'' per ton (1.21'' average freeboard @ 37 tons) 38 tons = average drop 1.01'' per ton (0.20'' average freeboard @ 38 tons) --- end ----------- As you can see it is about 1" per ton from empty to full load, even for a butty is it a similar loading figure. However it doesn't tell the full story. Motor boats especially are uneven when unloaded, their propeller needing to be in the water. Some boats (all?) had the ability to take on water to ballast the back end down (Royalty, Star, and Towns I know at least do). However even without balast they have a large heavy engine at the back, as well as a steel (engineroom) cabin, a stove, and maybe even some fixed weight. With this weight at the back loading a weight towards the front of the boat will actually lift the backend up (I do this on Victoria to reduce her draft). What this means is that upto a cirtain load I can if loaded correctly not draw any more depth (about 20 I recon). So, on towards answering the question. There are two limits to how much cargo can be carried, height of the gunnels, and depth of the canal. First lets take the hold size. I don't have figures for Joshers, but the hold depths for GU boats are as follows, Royalty 4' 11", Star 4' 2" to 4' 6", and Towns 4' 9.5". At an average of 1" per ton you can clearly see that a royalty class boat can carry more (Victoria was gauged to 42 ton with 0.44" dry side - unlikely to be actually measured to this, though I understand boats have sunk when gauging!). However at this loading the boat draws 5 ft (the skeg is lower than the hold), so on to the next and usually more important limit. Canal depth varies from canal to canal. As built depths varried, the lower GU being built to 5' 6", and the regents to 6' something, however after over 100 years (200 or more in some cases) depths have generally reduced due to various factors. The more important ones these days are silting and rubbish. Different motor boats are built to a particular nominal depth, this is the distance from the uxter plate to the bottom of the skeg. Royalty boats, and most FMC boats this is 3' 6", Stars were usually 3' (I understand some are 3' 3"), and towns at 2'10". Why does this matter? Well, I'm not really sure. They reduced the figure because the canals were getting shallower over time, and I can only assume that because they were carrying lighter loads they wanted to ensure the uxter plate remained in the water to aid the grip of the prop in the water (reduce ventilation). It does mean there is more boat in the water once the loading takes the counter into the water, but I'm not sure this makes much odds. Cabin length is also important. Obviously an iron built steam narrowboat with their large cabins, heavy boilers, engines, and a good few ton of coal just for the engine could not carry as much as a wooden butty. But it's not just a weight issue, there is only so much space in the hold, and even with a "bulky" substance like coal it could fill before the boat reached it's loading limit. This was often the problem when the deeper hold butties had cabin extensions, and even with normal length cabins. How the boatmen got around this problem was, that with the extra bouyancy at the back end more coal could be piled up at the back of the hold. This was normally above the gunnels and so "gready boards" were used to hold the coal in. So now we are getting the crux of the problem, how much (coal) can a narrowboat carry? Any amount from 0 to about 50 tonnes (at a guess the full load of a 6 plank wooden butty). How much has any one pair of town class boats carried, Ray answered that one, 66 tons. How much was more often carried on a pair in the "good ole" days, usually about 55 tons, on about 4 foot draft spread more heavily on the butty (on the GU and other main waterways). On a motor, 22 tonnes is about as much as you could get away with on the GU these days - it doesn't matter what type of boat (to some degree) as a fully loaded Star class motor could carry this much without sinking, and all boats would draw about the same depth - though thanks to the extra weight of the higher sides, the town and royalty boats would be a little deeper by an inch or two. I know Tom Hill on Archimedes and Ara often finds the bottom at 3' 6" (with something like 20 tons on the butty), but Victoria is usually that underway and while bumps over at a couple of points, I suspect a few hours spot dredging could increase the depth to 4' without problem. This, of course, all assumes the pounds are up to level, and not down 1 foot as they were when I came over the top in Autumn! Why do you ask? Cheers. Mike nb. Betyoudidn'tnow -- Michael Askin http://shoestring_DOT_zapto_DOT_org/
