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Engine and Performance
What is the standard height to mount the engine? For a propeller to best satisfy particular boating needs, the engine must be attached to the transom at the correct height. A correct conventional installation would generally place the antiventilation plate about even with the boat bottom when the engine propeller shaft is parallel to the boat bottom. Setting the engine lower (deeper in the water) tends to cause excessive spray, increase gearcase drag, reduce underwater clearance, and can adversely affect handling of faster boats. Raising the engine can provide several advantages including reduced lower unit drag thus increased speed, improved handling on faster boats, reduction of steering torque and greater clearance to underwater obstacles. In the past, the negative effects from mounting a stern drive higher than standard was an increase in propeller ventilation, which could cause difficulty in planing, (particularly with heavier loads) and overheating due to more aerated water with less pressure. Most raised installations today are found on high performance boats and these drawbacks are justified by increases in performance. In some cases special high performance drives with low water pickups are used with these installations. However, with Stingray's patented ZP-hull, it's now possible to have all the benefits of higher mounted engines without any of the negative effects or cost for special drives.  Why do most boats drive from the right
side? If trimmed "out" too far, the propeller may lose its hold on the water. Fast vee-bottom boats
may start to "walk" from right to left to right, etc. ("chine walking"), steering torque will
increase in the opposite direction to that when trimmed in, and getting on plane may be
difficult or labored. Porpoising of the boat may also occur. An engine is designed to run at wide-open-throttle (WOT), within certain rpm limits. Without
a tachometer, the operator has little opportunity to know if the engine is at a dangerously
high or low rpm level. Once the correct propeller is selected, the engine will run at
wide-open-throttle within the recommended maximum rpm range. Any deviation from this established
WOT rpm other than that associated with climatic conditions, elevation, or gross load changes,
is an indication of a possible performance problem. Special hull treatments, such as anti-fouling paint, will reduce the rate of bottom fouling.
However, because lower units (outboard and stern drive) are made primarily of aluminum, be sure
to select an anti-fouling paint having a copper-free, organo-tin base. The BIS Tri Butyl Tin
Adipate (TBTA) base paint will not set up a galvanic corrosion "cell" as it is completely
compatible with aluminum and avoids any electrolysis problems connected with many other paints.
Applied according to instruction, it is very effective in controlling marine fouling. The corrosion reaction occurs when electrons flow between dissimilar metals connected or grounded through water. In the process, one of the two metals is eaten away. This damaging corrosion can be eliminated by providing a sacrificial metal-zinc or aluminum, which will preferentially corrode to protect the lower unit, or by installing a Quicksilver MerCathode® system to your boat. Sacrificial anodes are available in several forms. MerCruiser stern drives and most Mercury, Mariner, and Force outboards utilize a trim tab on the antiventilation plate. Stern drives have additional anodes mounted at the outer transom plate. A transom-mounted anode kit is available to provide additional protection, if deemed necessary. The anodes' main purpose is for corrosion protection. By their very nature, they deteriorate rapidly and must, therefore, be constantly inspected and regularly replaced. The engine should not be partially tilted out of the water. If the anode is out of the water, protection for the parts still in the water is lost. Anodes are never to be painted, nor should the area under the anode be painted, as the ground must be maintained. Newer outboards and stern drives will be discontinuing using the trim tab as a sacrificial anode. Anodic protection will be found in other locations. When a docked boat is plugged in to shore power, destructive galvanic corrosion currents can
flow through the important, shock protection, neutral ground wire. A Quicksilver Galvanic
Isolator, which is wired in series with the ground wire, blocks the destructive corrosion
currents while maintaining the safety function of the neutral ground. Outside the USA and Canada, use gasoline that has a posted pump octane rating of 90 RON minimum. Premium gasoline (98 RON) is also acceptable. If unleaded gasoline is not available, use a major brand of leaded gasoline. Reformulated (oxygenated) gasolines are required in certain areas of the USA. The two types of "oxygenates" used in these fuels are alcohol (Ethanol) or ether (MTBE or ETBE). These reformulated gasolines are acceptable for use in your engine. If the gasoline in your area contains either Methanol (methyl alcohol) or Ethanol, you should be aware of certain adverse affects that can occur. See your operation and maintenance manual for details. In older engines that were designed to run on leaded fuel, use Quicksilver valve lubricant to
avoid the possibility of valve seat recession. Accompanying this weather-induced loss of power is a second, but more subtle, loss. At rigging time in early spring, the engine was equipped with a propeller that allowed the engine to turn within its recommended rpm range at full throttle. With the coming of the summer weather and the consequent drop in available horsepower, this propeller's lower rpm will result in further loss of horsepower and an additional decrease in boat speed. This secondary loss, however, can be somewhat regained by switching to a lower-pitch propeller that allows the engine to again run at the recommended rpm. For boaters to realize optimum engine performance under changing weather conditions, it is
essential that the engine be propped to allow it to operate at or near the top end of the
recommended maximum rpm range at wide-open-throttle with a normal boat load.
I have a boat with a MerCruiser engine. Is it normal for one exhaust manifold to run very warm while the other runs cool to the touch? MerCruiser says that this is normal. Their response is: Water coming out of the thermostat housing is not divided equally between the starboard and port side. Water takes the path of least resistance, and most will go out one side. The other side does get water, but not the same amount. Hence, one manifold (or exhaust elbow) will be cooler because of more water flow than the other side with less water flow. This should be more noticeable at lower speeds. At higher speeds, more water is flowing and both manifolds get closer in temp to the touch. My speedometer or speedometer hose is leaking water. What can I do? Over time, the rubber hose can start leaking from vibration or soften from the pressure of the hose. We have not found a screw clamp that will work because the hose is small and the screw clamp tends to pinch the hose on the side, causing it to leak. The best solution is to remove an inch of the hose to get a fresh end, install two small tie wraps, and pull them tight without the hose connected. Pulling the tie wraps down BEFORE installing the hose allows for a tighter connection once the hose is installed. Then push the hose back onto the Speedo barb, the hose connector or the barb on the transom plate bringing water from the pick up in the lower unit. This will usually cure any high speed-leaking problem. My trim gauge is not on the first mark when the drive unit is in the full down position. How can I adjust it? If your trim gauge is moving when you trim your motor, but the needle does not stop on the bottom mark of the trim gauge (at full down), the sending unit may need to be adjusted. A sending unit, which controls the trim gauge, is located on the gimbal housing between the lower unit and the transom. The trim sender is on the starboard side of the gimbal housing where the lower unit pivots in the gimbal housing. To adjust your trim gauge, loosen the two screws on the sender just enough to rotate it by hand. The sender requires very little movement to affect the trim gauge position. To adjust the gauge properly, the boat needs to be on a trailer or lift so the drive will clear any obstructions when you cycle from full up to full down position. The motor should be OFF, the drive in the full down position, and the ignition switch in the on position. Slowly rotate the sending unit until the trim gauge is on the bottom line of the trim gauge (not below it), and retighten the switch. Recycle the trim full up to full down and recheck the gauge for the correct needle position. If it is not correct, reset the sender and retest it. These instructions are for MerCruiser Alpha and Bravo drive units. DO NOT try to adjust the trim limit switch. See your Stingray dealer should any trim limit adjustments be needed. This switch controls how far the trim will move without using the tilt button and protects the drive from side load damage from excessive trim under power. Can I use ethanol fuel in my boat?
Information added Sep 12 2006 |
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