Canal Boat - - Skin Tanks -

Ver­ti­cal tanks are prefer­able be­cause they main­tain the max­i­mum amount of con­tact with the outer sur­face. Hull base tanks are less ef­fi­cient due to the fact that the hot wa­ter re­mains at the top of the tank away from the cold base/ outer hull. They can, how­ever, be made more ef­fi­cient if they are kept to a min­i­mum depth of 30- 40mm util­is­ing the same baf­fle sys­tem as the ver­ti­cal tank. Weld­ing ‘fins’ to the base be­fore man­u­fac­ture of this type of tank can be even more ef­fi­cient. En­gine kW ÷ 32 = area square me­tres

for alu­minium boats you can use the fol­low­ing rule be­cause it has a higher ther­mal con­duc­tiv­ity, the cooler size may be smaller:

En­gine bhp ÷ 5 = area in square feet En­gine kW ÷ 40 = area square me­tres. This sur­face area is a min­i­mum for an en­gine de­vel­op­ing its max­i­mum con­tin­u­ous power at full en­gine rpm.

In prac­tice, much smaller ar­eas have been used with­out over­heat­ing due to a num­ber of fac­tors that af­fect the en­gine – the power used by most boaters when cruis­ing on the canal is con­sid­er­ably less than max­i­mum and many canal boat en­gines are over-propped and in­ca­pable of reach­ing their max­i­mum rpm/power, even on a river. ex­pan­sion. When wa­ter heats up its den­sity drops thus in­creas­ing its vol­ume, a typ­i­cal wa­ter an­tifreeze mix of 50 per­cent at 10C has a den­sity of 1043 kg/ m3, this falls to 1005 kg/m3 at 80C (a typ­i­cal en­gine run­ning tem­per­a­ture).

This is ap­prox­i­mately four per­cent dif­fer­ence in vol­ume, and so for a ten-gal­lon sys­tem, the ex­pan­sion is around three pints which means that there must be pro­vi­sion for ex­pan­sion of three pints. If there isn’t, the wa­ter will be lost through the over­flow and have to be re­placed each time the en­gine cools down.

So the larger the cool­ing sys­tem, the larger the ex­pan­sion; the ob­jec­tive must be to keep the vol­ume of the to­tal sys­tem as low as pos­si­ble us­ing a slim­line tank.

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