Keep­ing your en­gine’s cool

CB,

Canal Boat - - Skin Tanks - WORDS AND PIC­TURES BY NICK WALL

We of­ten get queries about skin tank and cool­ing here at usu­ally if there’s an over-heat­ing prob­lem, so here are some facts you might like to know

Most nar­row­boats on English canals have some form of keel cool­ing, as do some boats that use es­tu­ar­ies and ports where fine silt and mud can block more nor­mal seago­ing heat-ex­changer cool­ing sys­tems.

‘Keel cool­ers’ or ‘skin tanks’ are usu­ally just a dou­ble skin of steel boxed onto the side of the hull. That might sound sim­ple, but the ac­tual de­sign is very im­por­tant due to the amount of heat that needs to be dis­si­pated.

Gen­er­ally, a typ­i­cal mod­ern diesel en­gine is roughly 30 per­cent ef­fi­cient which means that fuel, when com­busted in the en­gine, only uses 30 per­cent of the heat for power and the rest is not utilised; a se­cond 30 per­cent goes through the ex­haust, 30 per­cent goes into the coolant and the fi­nal ten per­cent is ra­di­ated from the en­gine it­self.

When put into con­text, a typ­i­cal 50 or 60ft nar­row­boat fit­ted with, say, a Beta 43 en­gine pro­duces 43hp/32kW at full load and speed of 2,800rpm.

At the same time, this en­gine also pro­duces 32kW of heat into the cool­ing sys­tem. This heat flows to the keel cool­ing (skin) tank and is trans­ferred through the steel hull and the ‘in­su­lated’ thick painted sur­face, into the canal or river. To lose such a large amount of heat through what is a thick painted sur­face means it re­quires a large area. Gen­er­ally, though, most boats cruise the canals and rivers at around about 1,400rpm, cre­at­ing cor­re­spond­ingly less heat that needs to be lost.

The most im­por­tant fac­tors to con­sider when de­sign­ing a keel cool­ing tank for a canal boat are: The sur­face area of the tank in con­tact with the cold wa­ter out­side the boat. The abil­ity of the tank de­sign to en­sure that all the wa­ter pass­ing through it is forced to make con­tact with the cold sur­face and can­not take a ‘short cut’ – a baf­fle is nor­mally needed. The to­tal vol­ume of the sys­tem and the ef­fect on ex­pan­sion.

Based on cal­cu­la­tions and ex­pe­ri­ence, the best keel cool­ing tank for a canal boat should be ver­ti­cal and built into the swim. For en­gines up to 100hp, the tank should be slim prefer­ably 30- 40mm, with the in­let at the top one end, and the out­let at the same end but at the bot­tom, mak­ing sure that there is a bleed screw at the high­est point.

The tank should have a baf­fle di­vid­ing it into two, forc­ing the wa­ter to flow around in a U shape. This baf­fle should be con­tin­u­ously welded to the outer plat­ing of the hull to give good ther­mal con­duc­tiv­ity and as tight a fit as pos­si­ble to the in­ner side of the tank. A sim­ple baf­fle is prefer­able to keep the re­stric­tion placed upon the en­gine cir­cu­lat­ing pump

And that’s where the skin

tank gets its cool­ing

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