Canal Boat - - This Month -

Brick­ing it; drive for knowl­edge; the value of so­lar; try­ing to get in trim; on the horn; tak­ing care of a cruiser’s bot­tom; gen­er­at­ing cor­ro­sion; a leak at the back; putting the bat­ter­ies to bed

QWe are restor­ing a 1981, 58ft boat. There was a fair amount of wa­ter in the cabin bilge which was caused by a leak in the side hatch, now fixed.

While re­plac­ing the dam­aged floor I found rot­ten joists and that gravel had been used as bal­last. A lo­cal boat­yard said gravel is not good for bal­last and I should use Class A engi­neer­ing bricks. So I re­moved it a sec­tion at a time (weigh­ing it first), cleaned the rust, painted the steel with bi­tu­men and re­placed the gravel with the equiv­a­lent weight in bricks.

The bricks are a fairly snug fit. There is room above to al­low some air­flow, but I am con­cerned I am over­fill­ing the bilge. Should I be con­cerned that I have over­filled the bilge?

The boat seems to sit a lit­tle deeper than be­fore and I am con­scious that the gravel was damp when weighed. I have been con­sid­er­ing re­mov­ing a line of bricks at the back to cre­ate more space where the bilge wa­ter could col­lect.

ROB WAIN­WRIGHT, via email

ATONY REPLIES... Engi­neer­ing bricks or steel off-cuts are per­haps the Rolls-Royce of bal­last. Most nar­row­boats use con­crete paving slabs. You did the cor­rect thing as far as the longevity of the hull is con­cerned, even though it must have been mas­sive amounts of work. You need ac­tual engi­neer­ing bricks be­cause or­di­nary house bricks will ab­sorb mois­ture like gravel, may flake over time and will weigh less.

Ideally the ux­ter plate (the flat plate above the swim and pro­pel­ler with the cut out in it for the swim) should be about one to two inches be­low the wa­ter­line and the bal­last placed so that the boat sits level or slightly stern down.

This at­ti­tude will al­ter as you empty and fill the wa­ter and fuel tanks, so make sure the ux­ter plate is still at least an inch be­low the wa­ter with an empty diesel tank and a full wa­ter tank. Al­ter­ing the fore-aft trim changes the boat’s pivot point when turn­ing. Nor­mally bal­last is placed be­fore the floor goes down with steel of­f­cuts of­ten added to the ux­ter plate in the en­gine bay for trim­ming.

Un­der-bal­last­ing al­lows the pro­pel­ler to draw air from the sur­face which pro­duces lots of foam but lit­tle thrust. Over-bal­last­ing is not an is­sue for a pri­vate boat as long as the ‘through hull’ holes are safely above the wa­ter­line. You would need a greater depth of wa­ter, but the re­duced head­room you need through bridges and tun­nels might be an ad­van­tage. It is very im­por­tant on nar­row­boats that the ‘straight-through’ ex­haust out­let is suf­fi­ciently high above the wa­ter­line.

It is vi­tal to leave an area at the back of the boat with­out bal­last to al­low wa­ter to col­lect; if the boat trims nose down, the wa­ter will flow the other way.

You also need to think about mois­ture drain­ing from un­der the bricks and this is usu­ally achieved by plac­ing the bal­last on some­thing. If you don’t have much room above the bal­last I would sug­gest plas­tic wall tile spac­ers or long scraps of house wiring in­su­la­tion.

You should have more than enough air space for ven­ti­la­tion, es­pe­cially if you leave the trap that is used to in­spect the back of the bilge off when you are away from the boat in the win­ter.

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