Posted: Sun Jun 26, 2011 10:13pm

Hi, I have a 70 foot canal boat shell that is out of the water and I want to be able to put the concrete blocks in while she is out of the water so that i can renovate her up fully while she is on dry land. I am not sure how much weight to put in. would i need to put her in water to put the concrete blocks in before i start on kitting her insides out? and if not how much weight would you recommend i put in before she goes back in? If i do put her into water once she has been fully kitted out would it be safe to just add more concrete blocks to the ones that have already been put in if she needs it? many thanks for your help

Posted: Mon Jun 27, 2011 8:52am

AS most narrowboats seem to have the floor fixed and the the bulkhead and fittings mounted on top of the floor then yes, the ballast will have to go in before the floor. If you fit-out in such a way that the floor can be put in place after the fit-out then the ballast can go in later although I suspect this would complicate the job. Now, I can not be much help over how much. I know that you will need the uxter/swim plate at least 1" below the water when the boat is at at rest. I know you will need to get the fore-aft trim such as the boat will pivot at a point you are happy with. But how much ballast I can not tell you because I have no idea about the weight of the shell. If you have a 25mm baseplate you may only need trimming ballast. If it is 6mm you will need a lot more. If it is a new shell then the supplier should be able to give you some idea. If it is an old shell and you can ascertain the waterline then 1000cc of water weights 1Kg. so you will need to add ballast to displace the amount of water needed to sink the boat to the level required. Measure the length and width of the "box section" part of the hull. Multiply these together with the amount you need to sink the boat to the correct level. For each swim measure the length and its maximum width (all in cm). Multiply the figures for each swim as detailed above and halve the answer. Add the three answers together and that will tell you how many CCs of water you need to displace. Divide by 1000 and you have the amount of ballast in Kg. make sure you leave a bit out and make provision for placing the final trimming ballast AFTER the boat is fully fitted, equipped and afloat. Tony Brooks

Posted: Mon Jun 27, 2011 10:28am

PS If this is a new hull then then I would expect the weight to be in the RCD documentation. If you had the hull lifted out be crane the crane driver may have told you the weight because mobile cranes have a weighing device on them. If you know the weight then use the above calculations to find out the weight of water that you need to displace. Then subtract the weight of the hull and what remains is the weight of the ballast. If you do not know the weight of the hull you will have to measure and calculate the amount of steel in it and the use 7850 kg per cu. metre to estimate its total weight. Tony Brooks

Posted: Tue Jun 28, 2011 10:13pm

Hi David I,ve recently fitted out a 50ft shell with 10mm baseplate. The builder had placed the ballast using a rule of thumb of one 2ft X 2ft X 2inch thick concrete slab per foot of boat. I found this was not enough and added the same amount again to get the boat to the correct level. Best of luck. Arthur Lewis