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Beyond the Engine


Believe it or not, spring is right around the corner and with it comes the start of the 2006 sailing season. It won’t be long until you can feel the wind in the sails and the water rushing past as you trim in for your first outing of the year. In an ideal world we would spend all of our time sailing from one destination to the next, but unfortunately that is not always the case. More times than we would like, we end up using our auxiliary means of propulsion, more commonly known as our engine.

Moving while under power can be quite noisy and causes a fair bit of vibration. This vibration, while normal, is sometimes exaggerated by components of your drive train becoming worn out or misaligned. Before your boat goes into the water is the best time to inspect all of the elements of this system to ensure smooth operation of your sailboat while under power.

The first item we come to on our inspection underneath the boat is the propeller. The prop should be smooth and look completely symmetrical from one blade to the next. The slightest damage or imperfection to the prop can cause serious vibrations to occur while under power. Inspect the point where your shaft enters the prop, there should be absolutely no visible gap here whatsoever. If you can see any daylight, the prop is improperly mounted. Check to see that both nuts are tight and that there is a cotter pin in the end of the shaft. If you have a folding propeller, the blades should be tight in the hub and there should be very little play in the blades when they are open or closed.

The next step up the shaft is the propeller strut. The strut is able to hold the shaft in place but still allows it to rotate by means of a cutless bearing. This cutless bearing is a brass sleeve with a rubber liner inside of it. The brass sleeve is pressed in place in the strut and is usually held in place with setscrews. The rubber liner is what acts as the bearing for the shaft and it stays lubricated simply by the water it is submerged in. Although these bearings usually last quite some time, they will eventually wear out. Inspect the bearing from both ends and look for signs of wear. It is especially important to look for signs of uneven wear. Uneven wear can signify the need for bearing replacement as well as give you a clue about potential engine alignment problems, which we will discuss later in this article. Wiggle the shaft back and forth and see if there is any slop between the shaft and the bearing. This should be quite snug and any motion should be a cause for concern. If a cutless bearing fails, the rubber can become detached from the brass and fold over inside the bearing and cause serious problems. Inspect this area carefully and replace if needed. Do NOT oil this bearing.

The last inspection to be done outside of the boat is to the shaft itself. Grab the propeller and rotate it while closely watching the shaft where it exits the hull. There should be no sideways motion whatsoever. Any motion up and down can mean a bent shaft or potentially a shaft-coupling problem. Also look and see if the shaft exits the boat in the middle of the tube. If not, this could also be a clue to a potential alignment problem.

The first point of contact for the propeller shaft inside the boat is the stuffing box. The job of the stuffing box is to keep the water out of the boat while still letting the shaft rotate freely. The conventional stuffing box consists of a brass nut containing flax packing. By tightening this nut, the flax packing is compressed against the shaft and water is sealed out. When the packing is new, very little pressure is required to make this water seal. As the packing ages and dries out, more force is required on the packing to create this seal. This increased pressure over time can eventually get to the point were it will begin wearing grooves into the shaft. These grooves will in turn allow more water in, which requires the nut to be tightened more. This cycle can cause premature shaft wear as well as allowing unwanted seawater into your boat. If you have never replaced your packing, assume that it needs it. It is quite a simple procedure and can be done without too much difficulty.

The next step for your shaft is the coupling. This is the round T shaped piece that connects the shaft to the output shaft of your engine. It is very important that the shaft fits perfectly into the coupling. There should be absolutely no movement at all between these two components. If you can wiggle the two independently from each other at all, you need to have it corrected. This usually means replacement of either the shaft or coupling which is major, but crucial. This problem is one of the most common causes of excessive vibration and if this fit wears excessively it can cause the key and/or the setscrews to shear which can cause you to lose all drive to the shaft. If this failure were to occur while in reverse, it is possible that the shaft could even back itself out of the boat leaving you with a large hole in the boat as well as no forward or reverse. This fit is best checked with the coupling separated from the output flange of the engine and is most commonly done while alignment is being checked.

The shaft coupling is bolted to the output flange on the engine. It is important that these two mating surfaces are perfectly aligned with one another. Alignment is checked by first separating the shaft coupling from the output flange on the engine. The shaft is then positioned in the center of the tube where it exits the hull. These two surfaces are then inspected for alignment. If the two surfaces do not align perfectly with one another, the engine then must be repositioned until it is aligned with the coupler. This repositioning is done by adjustments that are performed with the motor mounts. These adjustments can move each corner of the engine up or down as well as side to side.

Motor mount breakdown is one of the biggest causes of engine misalignment and can dramatically increase vibration while under way. Inspect the mounts and look for any signs of them breaking down. The rubber on the mounts should appear firm with no cracks or tears. Keep them clean and free of diesel fuel or engine oil, as these products can break down the rubber. Motor mounts break down over time and will eventually need replacement. If you’ve never checked your mounts, now’s the time.

If you have any questions concerning any of the above information, please feel free to contact our service department at 231-759-8597 or send an e-mail to Brian Torresen. Torresen Marine also has expert mechanics on staff that are trained in the maintenance and repair of your boat’s entire drive train. Our mechanics are also available to assist you with inspections and repairs before your boat gets launched.

Whether you have a vibration problem or not, these are all items that should be checked in order to keep your drive train in proper operating condition. A little routine maintenance now can help keep your boat powering smoothly and help prevent expensive yard bills down the road.

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This entry was posted on Friday, March 31st, 2006 at 10:54 am and is filed under News From Torresen Marine. You can follow any responses to this entry through the RSS 2.0 feed. You can skip to the end and leave a response. Pinging is currently not allowed.

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