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Go Back   SailNet Community > Contributing Authors > Gear and Maintenance Articles
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Old 02-25-1999
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Check the Propeller

Before launching, a few minutes devoted to the drive-train machinery could well prevent an inopportune haul-out after the season is underway. Sailboats have a short propeller shaft, so complete survey can be completed in not much more time that it takes to read this article.

Start inside the boat and examine the following:
Check to see that all transmission output flange bolts and nuts are present and securely tightened. If the cap screws that secure the flange onto the propeller shaft have little holes in their heads, they are missing a safety wire used to prevent vibration from loosening them. If the seizing wire is broken or missing, replace it now.

Inspect the key to ensure that it hasn't moved or fallen out.

To make future repairs possible, clean and repaint the flange if it is badly rusted. If it needs replacement, consider upgrading to a flexible shaft coupling. Not much more expensive than a standard coupling, these reduce vibration on board. Additionally, they allow minor engine misalignments without excess wear on the transmission. They will also absorb shocks from hitting floating objects.

Inspect the packing gland and nut to guarantee that they are not loose.(We will cover re-packing the stuffing box in a future article.)

Now go outside to the business end of the shaft for further checking: Grab the propeller and try to wiggle it side-to-side and up-and-down. Do this with some force. Nothing should move or rattle at all.

If motion is detected, the most common culprit is the shaft moving in a worn cutlass bearing. The propeller will need to be removed to replace a tired cutlass bearing, and it is easiest if the shaft is also removed. Some professionals, however, have the tools to pull an old bearing without removing the shaft.

If the shaft is pulled, look for grooves or deterioration where it contacts the cutlass bearing. Replacing the shaft is the only possible repair. Check to see that set screws holding the cutlass bearing in its housing are tight and that any seizing wire is in good condition.

Motion caused by a damaged strut is a more serious matter because it requires removing the strut, cleaning all surfaces and re-bedding the metal back to the hull. A few fiberglass boats have struts literally molded into the hull. Repairing these is usually a major job that is best left to a professional.

The measurement between the aft end of the cutlass bearing and forward side of the prop should be one shaft diameter or less. Any more invites shaft vibration, bending and whipping. But do not cut an old shaft down until you have ensured that the new prop position will clear the hull.

With a putty knife or scraper, remove barnacles or other residue left on the propeller. Use a light abrasive, like 400-grit sandpaper, to polish it up. Deep pits or dings in the blades will require a trip to a prop shop for restoration.

A bronze prop that is soft with its edges eaten away or which has turned a magenta red color is a clear sign of electrolysis problems. You will need to check out both the electrical systems of the boat and the marina where she berthed.

Hold a ruler or straightedge against the hull so that one propeller blade just kisses it. All the other blades should swing by and kiss it in the same way. If they don't, the prop will need to be reshaped and balanced.

Look at the propeller nut, lock nut and cotter pin. Make sure they are tight and that the pin is in good shape.

Replace the shaft zinc. If the boat is not equipped with one, consider adding one.

For northern boats with a sail drive, the gear lube should have been drained and replaced in the fall. Water contamination in the oil can freeze and split the gear case, causing expensive repairs. If not, inspect the case and change the oil now. Check the prop, prop nut and zincs. In addition, look at the seal between the sail drive and the hull.

Check Those Transducers Now Too

Now is a great time to check any electronic transducers on the bottom of the boat. Unfortunately, they're no simple test for depth transducers. If the transducer gave trouble last season, now is the time to change it. They are relatively inexpensive and easy to replace.

Many speed transducers are removable from their housing in the hull. They depend on O-rings to prevent water coming in. On both the transducer and the dummy plug, these O-rings require periodic replacement due to cuts and wear. Do not grease O-rings. Many will swell or become misshapen when subject to petroleum products.

Clean the paddlewheel assembly carefully and check for missing blades. Most brands of speed/logs sell replacement paddlewheel kits.

Lastly, turn on the speed instrument and have someone turn the paddlewheel by blowing over it. A good puff can register up to 10 knots.

Photographs by Kathy Barron

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