----- Original Message ----- From: "Mike Casswell" <[EMAIL PROTECTED]> To: "Canals-list List" <[email protected]> Sent: Sunday, March 11, 2007 6:41 PM Subject: [canals-list] Stability
> As I have mentioned before, Jemima D has had her old and > failing fibreglass cabin replaced with a new steel one. > > I am aware that this will have raised the centre of gravity > and the boat does seem less laterally stable than before. > Yesterday I had the opportunity to try a crude experiment. > Whilst the boat was tied to the bank, we added people to > the near gunwale one after another. Result: One person - > OK, two people - more tilt than I would have expected, > three people - significant tilt, four people - everybody > very quickly jumped off as the boat did a good impression > of starting a full roll. > > This seems worrying, although I have never previously > carried out the same procedure on this or any other boat. > It's very difficult to equate three or four people on a > gunwale to real life situations. > > JD never had any ballast throughout her 30ish years of > steel hull and fibreglass top. It looks as if we now need > to add some. But how much? > > The big question is how do I determine whether the boat is > safe in this respect. Is there an equivalent of the double > decker bus test, whereby it is deemed OK if it rights > itself from a specific angle of displacement? > > I have found nothing directly addressing the issue in a web > search. I have found references to the "Canal Boat Builders > Association Code of Practice for Steel Inland Waterways > Craft and Narrow Boat Construction". Can anyone tell me if > this publication refers to lateral stability? Any and all > advice will be gratefully received. Hi Mike First a few questions: Is JD flat bottomed or a V hull? What is the draft at the stern and (say) 5 feet back from the stem? Do you know the weight of the new steel plates? (if not that should be easy to calculate. Have you noticed whether or not she is floating any deeper with the new cabin (although I assume you might not have put back interior linings etc etc) ? For a boat the length of JD, ½ ton of ballast should bring her down an average of almost one inch overall. If JD is flat bottomed, I am wondering whether she has much shallower draft towards the bow. If the counter (horizontal swim plate) is already about an inch or so below water you will want to avoid adding ballast at the stern . If she needs any ballast at all it would appear that might/may be needed just forward of amidships. Phil
