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Posted: Thu Jan 22, 2009 9:38am

Post Subject: air vents

I have a harborough narow boat I have air vent close to the waterline I have to navigate the river humber and am cocerned I may take on waterif its choppy any ideas on sealing these and venting with a motor, the engine is a lister SR2,oh and what horse pwer would it be too.... thanks Mark


Posted: Thu Jan 22, 2009 10:35am

Post Subject: air vents

Dear Mark, the MCA list the engine as being between 6 hp & 1200 rpm & 12 hp & 2500 rpm. (see ps_fishing_engine-details?model_id=31&make=L ISTER%20MARINE%20DIESELS) [all on one line]. The maximum revs of your engine may well be limited by the propeller to the maximum torque speed, but I do not have that information but would estimate it at bit over half the range above, so think around 8 to 10 hp. All the Lister Sxx models are air cooled and so they demand vast amounts of cooling air. I expect you have two vents, one side to draw the cool air in and the other vent trunked from the engine so the hot cooling air is directed overboard. The Lister SR/SL manual on the Dutch manual site (link from bottom of the minimum unobstructed area of the air vents as 60 sq in for the hot outlet and 78 sq in for the inlet. The outlet being ducted from the engine, usually with heave canvas or some-such. I think you would need to make up a pair of upright trunks of those dimensions as a minimum and cut two large holes in the cockpit floor. Then mount & seal the trunks to the cockpit floor and rearrange the trunking so it connects to the outlet trunk. Some details of similar structures are in the manual on that Dutch website. Personally I would be just as concerned with the front well deck. If that took a big green-un I suspect you could loose the boat. I would not rely upon any cratch cover so the well deck & front doors need attention as well. It is vital that you make sure your fuel tank has no water in the bottom and start with clean fuel filters and ideally a fair sized water separator between the tank & engine. Carry spare filters and know how to change them and bleed the engine whilst bobbing about and rolling across the waves. Also make sure your bilge pump(s) are large enough to cope with significant water ingress. One pump per bilge area (so it could be 3 pumps - Well deck, Cabin Bilge, Engine room bilge, but that depends upon the design of your boat. Tony Brooks

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