Abstract: The invention relates to a method and apparatus for enhancing the heat transfer efficiency of a keel cooler by increasing the flow rate of coolant through the side tubes. Because the side tubes are exposed to a greater amount of fresh unhindered seawater, increasing the flow rate through the side tubes can have the effect of enhancing the overall heat transfer capability of the keel cooler. The invention relates to using apertures leading to the side tubes from the header and vice versa that are substantially arrow-shaped in design, wherein various benefits that lead to an increased flow rate are provided. The aperture is preferably symmetrically shaped so that a single die can be used to cut the aperture onto both side walls of the header.

Abstract: A first water header is connected to a second water header by laterally-spaced multiple parallel composite tubes, each consisting of two or more component tubes of vertically-elongated rectangular cross-section welded to one another along their horizontal narrower adjoining faces, the height of each component tube being a multiplicity of times the width thereof. The thus welded faces form intermediate partitions or webs of doubled thickness running the entire length of the composite tube. This greatly strengthens the composite tube thus obtained and also divides the cooling water flow into vertically-spaced thin streams or bands of cooling liquid. Rising from the first and second headers are first and second fittings which serve not only to transmit the cooling water into and out of their respective headers but also serve to connect and attach the header to the keel or other underwater location of the heat exchanger to the hull of the boat or vessel.