1995 Mariner Mercury Outboards Service Manual 50HP 4-Stroke, Page 19Get this manual
Conditions Affecting Operation 1Proper positioning of the weight inside the boat (persons and gear) has significant effect on the boat's performance, for example: aShifting weight to the rear (stern) (1 Generally increases top speed(2 If in excess, can cause the boat to porpoise(3 Can make the bow bounce excessively in choppy water(4 Will increase the danger of the following wave splashing into the boat when coming off planebShifting weight to the front (bow) (1 Improves ease of planing off(2 Generally improves rough water ride(3 If excessive, can make the boat veer left and right (bow steer)2Boat Bottom: For maximum speed, boat bottom should be nearly flat plane where it contacts the water and particularly straight and smooth in fore-and-aft directionaHook: Exists when bottom is concave in foreand-aft direction when viewed from the sideWhen boat is planing, "hook" causes more lift on bottom near transom and allows bow to drop, thus greatly increasing wetted surface and reducing boat speed"Hook" frequently is caused by supporting boat too far ahead of transom while hauling on trailer or during storagebRocker: The reverse of hook and much less common"Rocker" exists if bottom is convex in fore-and-aft direction when viewed from the side, and boat has strong tendency to porpoisecSurface Roughness: Moss, barnacles, etc on boat or corrosion of outboard's gear housing increase skin friction and cause speed lossClean surfaces when necessary3Gear Housing: If unit is left in the water, marine vegetation may accumulate over period of time in certain types of waterThis growth must be removed from unit before operation, as it may clog the water inlet holes in the gear housing and cause the engine to overheat