heeling or under way.A water-box can be made from any material that can beeasily worked and lamented or attached to the hull, i.e.,fiberglass, "PVC" or acrylic tubing or wood. Someboatsmen recommend a short piece of 5 or 6 inchdiameter tubing. Naturally, the hull forms the bottom ofthe box. The bottom edges of the box or tube must beshaped to fit snugly against the hull, with epoxy or othersuitable cement used to hold it securely in place. Youalso will need to make a tightly fitting lid with a hole forthe transducer stem or connecting wire. The transommount type transducer can be used if mounted to theside of the box. Fluid in the "box" needs to have adensity similar to water. Care should be taken to use afluid that will not attack the hull material, and also a fluidthat will not create a dangerous hazard if by chance itleaks into the bilge. Stay away from anti-freeze becauseit will attack the epoxy transducer "window." Mineral oilor glycerine are frequently used, or water may be usedproviding it is drained prior to lay-up to prevent freezingand checked occasionally for evaporation. Check theliquid in the box if any difficulty occurs, since the fluidmay have leaked out. Wash the transducer withdetergent before installing to make sure the surface isproperly wetted.Position your transducer as close to the hull as possibleat first. Then adjust the vertical position by 1/8-inchincrements over a 1/2-inch total. This will enable you todetermine experimentally the best position for maximumdepth readings and strongest return signal. This isImportant, since the pulses will tend to cancel orreinforce within the water box as a function of thedistance between the hull and the transducer window.THRU-HULL INSTALLATION (WITH OPTIONALTRANSDUCER)As we said, turbulence and air bubbles at the transducermust be avoided as much as possible. This problem ismost common in planning hull powerboats. Generally,the best transducer location on a planning hull is a pointwell aft of where the hull enters the water when on aplane."Thru-hull" is certainly the most common and mostpermanent method of transducer installation. Generally,the mounting is done by a professional, or by a boatowner who has enough confidence and ability to drill ahole thru the bottom of his hull. Never mount thetransducer on the bottom of the keel where it will bevulnerable should you touch bottom. Also keep it atleast 72 inches outboard from the keel. On a flat-bottomboat, the transducer is bolted thru a drilled hole andbedded in marine caulking compound to prevent leaks.Vessels with shaped hulls require custom carved "fairingblocks" to keep the bottom surface of the transducerparallel with the water surface. The silhouette of thefairing block should be kept as small as practical tominimize drag and chance of being damaged.Remember, the more smoothly the water flows over thetransducer and fairing block, the less turbulence and airbubbles will be generated.Sailboats have a different set of problems. The thru-hulltransducer must be sufficiently outboard of the centerline to avoid sonic reflections from the keel. As a rule ofthumb, the average transducer has a cone angle ofapproximately 10' off of a vertical line. If this puts thetransducer too far outboard, as might happen on somenarrow, deep-keeled hulls, the transducer might bemounted ahead of the keel. If it is suspected that thelocation selected for transducer mounting is a little tooclose to the keel, try cheating a little on the clearanceangle by tilting the transducer by no more than fivedegrees away from the keel. -The effect on sensitivityand depth accuracy will be negligible. Remember thetransducer must always be underwater, regardless ofheel angle, for your depthfinder to function.20
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