By Brett Becker

Often it's the things you can't see that can hurt you. We know the adage about things that are out of sight are out of mind, which is usually true, but not always good. Think Titanic and iceberg. Think submarines. You get the idea.

Likewise, way down deep in your Bravo drive, the rubber parts that help keep your boat afloat are out of sight, but you need to be aware of them and either inspect or have them inspected at the proper intervals. If not, well let's just say your boat could fare about as well as the Titanic. Let's begin with the U-joint bellows.

The bellows is the beefy rubber boot that goes from the transom assembly to the upper drive housing. It's a bit difficult to see unless the drive is pinned to one side or another. It looks like an accordion. Oh, and it's black, just like the rest of the drive. Inside, it's reinforced with spring steel in the crests of the bellows and is clamped at both ends. The output shaft from the engine runs through it, from the gimbal bearing to where the pinion meshes with the upper gear set.

"Mercury recommends they be serviced every six years," said Angel Astacio, a service writer and certified technician with Parker Boats in Orlando, Fla. "We check them every year for cracks, wear and tear, depending on weather. Mostly you see them cracking, weathering and dry-rotting.

"If the boat just sits with the drives turned and the sun beating on the back of the boat," he continued, "you'll see them cracked on one side and good on the other side because of how and where they parked it."

When they crack, water can seep into the boat and soak your output shaft and gimbal bearing. If you're beached, it's no big deal because there is only so far your boat can sink. But let's say your boat is docked for the evening during an overnight poker run. Then it is a big deal. Think Titanic. Here's what happens.

Water seeps in the cracks in the boot, floods past the gimbal bearing and into the bilge. Sure, the bilge pump should keep up with the flow, but the real question is how long your batteries will be able to provide power to run the pump.

"Your boat could sink if it's sitting in the water, and if it's a twin-engine boat, it could be pretty quick," Astacio said. "There's a seal that keeps water from getting inside the U-joints if water comes from inside the boat, but it doesn't work the other way. Plus there's a little hole on the bottom of the transom assembly that lets water inside the boat if water gets inside the U-joint area."

As you can see, the boot is worth checking. They're easy enough to see if you pin the drives to one side, then the other. Look for cracks and other signs of dry-rotting. Use your fingers to pull apart the folds of the boot so you can see into its valleys. Also, whenever you have the drives off for servicing, be sure to look at them from the inside or have them looked at. Check for rust on the output shaft and U-joints, which is a sure sign water has intruded.

"If they begin to leak, what you'll notice first is you'll hear a roaring sound coming from the back of the boat," Astacio said. "You're going to think it's the drive making noise or the engine making noise, and it's actually water getting to the gimbal bearing. That's the first sign. It's basically water getting to the bearing and getting in the grease and rusting the bearing."

But wait. There's more. The shift cable that runs through the drive has a boot of its own. Although it is completely hidden and not susceptible to possible photo-aging, it can split, which allows water in, not into the gimbal bearing unless it spills in from the bilge. The factory-recommended service interval also is six years, and the leak is typically slower, but you already know the potential end result.

"That one, we've seen, will break more than all the others because it's smaller and a little bit thinner," Astacio said. "We've seen those rip at three years."

There is one last piece of rubber in your drive, but it won't sink your boat if left neglected. It might make it overheat, though. The raw-water feed hose also has a six-year service interval, but it's still a good idea to check it annually, Astacio said.

"Very rarely will I see one of those hoses break," he added. "Those are double-wall hoses. The only thing I've seen them do is collapse. The inside walls separate and collapse, but that's very rare."

Clearly, what is out of sight and out of mind can cause you some trouble. The good news is that if you keep an eye on them from time to time you don't have to worry. Of course, icebergs and submarines are another matter altogether.

Contact Information
Parker Boats, 455 S. Lake Destiny Road, Orlando, FL 32810, 888-256-4817
www.parkerboats.com