Cutlass Bearing Replacement in the Water

By Tomas Iglesias, Yacht service diver, South Florida. Reviewed by Amanda McCallister, editor.

Propeller Removal & Repair | Hull & Bottom Cleaning Last Tuesday I was under a 58-foot Hatteras in Port Everglades. Water temp 78, visibility about 15 feet. The cutlass bearing had so much play that when I grabbed the shaft and wiggled, I could see a crack of light between the rubber and the shaft. The owner wanted to know if we had to haul her. I said, 'Not yet.' For a lot of boats, you can swap a cutlass bearing without pulling the boat. Hustle through the steps in a slack tide, and you can save a haul-out fee that would make your diving mask fog up. And if you're going to do this under a boat, you need to be straight about what you're getting into. It's not the same as doing it in a yard, but it's been done on pretty much every production motoryacht I've worked on in South Florida. Here's how I go about it.

When You Can Stay in the Water

The first thing I check is whether the shaft can actually be pulled forward enough to clear the strut. That means unbolting the coupling at the back of the transmission, inside the boat. The shaft has to slide forward at least six inches past the aft end of the cutless bearing. On a 50-foot boat with a straight shaft, that's usually no problem if the engine room has a little room to reach the coupling. With a V-drive or pod drive, forget it. You're pulling the boat. Then I look at the bearing itself. If the rubber has been skidding on the shaft for a while, it may have scored the shaft. That's a different job. And if the boat is sitting in a current with a riffle over the strut, you'll be fighting the water the whole time. I like slack tide, and I'll tell the captain we wait for a flat window. There's no way to press a bearing straight if you're getting rolled. Finally, check the space between the blade tip and the strut. If you've got less than a foot room to work with an all-thread rod, you're going to be pulling your arm apart. I've had to do it on a tight-shafted sailboat with the prop about a foot behind the strut. It's doable, but bring a helper.

What Goes in the Bag

Here's my kit for an underwater cutlass bearing job. I use a standard cutless bearing puller—the kind with a collet that expands inside the bearing and a slide hammer. If I don't have that, I'll use a long hacksaw blade, a cold chisel, and a piece of 1/2-inch all-thread rod with a big washer and a nut. That all-thread doubles as my press for the new bearing. And I carry a set of brass drifts, a mallet, and a tube of Trident #77 grease for the coupling bolts. For lube on installation, I just grab a squirt of dish soap from the galley. The bearing itself I'll order from the marina office or from Duramax Marine. You need the OD of the strut bore and the shaft diameter. On that Hatteras, it was a 1-3/4-inch shaft and a 2-1/2-inch OD bearing. Sizes vary. Get the rubber composition right, too—some boats run in fresh water, some brackish, but for saltwater, nitrile is the standard. If the strut is bronze, be careful. If it's anything else—like a cheap aluminum fabrication—you've got different problems. Bronze struts take the press well, but they can squeeze if you use too much heat. Don't heat a strut underwater. That's a recipe for cracking it.

Getting the Old One Out

Once I'm under the boat, I have the crew inside unbolt the shaft coupling and push the shaft forward. On most inboards, you can leave the prop on. The shaft will slide forward until the aft end clears the bearing. Then I work from the aft side. If the old bearing is loose, I just grab it with a screwdriver and it falls out. But if it's seized, I have to cut it. The rubber liner comes out first. I'll take a hacksaw blade and work it between the shaft and the bore, but only after the shaft is out of the way. I cut two slots 180 degrees apart in the rubber, then pry it out in chunks. That leaves a brass shell that's now too small to stay in place. I flatten one edge with a cold chisel, then drive the slide hammer into it. Sometimes it comes out in one piece, but often it splits. The key is to not mangle the strut bore itself. So I keep the chisel against the brass, not the bore. One thing I learned the hard way is to put a magnet on the ground before you start cutting. Bits of brass and rubber sink, and they're hell to find in murky water. A magnetic tray or a bucket under the job saves you a lot of cursing. And it keeps debris out of the bearing when you're installing the new one.

Pressing the Fresh Bearing In

After the old shell is out, I clean the bore with a stainless wire brush and a rag, then inspect for pitting or rust. If it's clean, I dry the bore and give it a light coating of dish soap. That's enough to let the bearing slide. Now, the press. I put a large washer and a nut on the all-thread, and I use a piece of pipe that's just bigger than the bearing OD to push from the aft side. You can also use a bearing driver with a socket on a long extension. The goal is even pressure. I thread the nut onto the all-thread, and as I tighten, the bearing gets drawn into the strut. I tap the outer edge with a mallet to keep it square, and I stop when the bearing is flush with the leading edge of the strut. On some struts it seats deeper—you want the flange fully against the bore, and the front of the bearing aligned with the front of the strut or slightly recessed. Don't bang it in with a sledge. You'll mushroom the edge and then you'll be chasing your tail. And if water gets inside the new bearing before the shaft is back, it's fine—they're designed to run wet. Just wipe the shaft and slide it through with the crew pulling from the other end. You want the shaft to spin freely in the bearing once it's home.

Sea Trial Before You Call It Done

The crew reconnects the coupling and checks the alignment. Then I do a visual circum-something: I look at the gap between the shaft and the bearing as it rotates. If there's a wobble, we've got a problem. Start the engine, let it idle for a minute, and I watch the shaft from the water. Then run up to 1000, 1500, and hold it. You're listening for vibration—the kind that rattles your regulator. I've seen more than one job where we had to go back in because the coupling wasn't torqued to spec. Use a torque wrench on those bolts, and don't guess. Check the bearing after ten minutes. If the water is just teeming with weed or whatever, the bearing could be warm. But if it's hot enough to feel through the shaft, you've got a misalignment. Better found now than five miles from port. And that's it. You can save yourself a haul-out and a haul-out bill. But you need to be honest with the owner: if the bearing was that worn, the shaft may need measuring for wear, and you might be back again. It's part of the job.

Frequently Asked Questions

Can you replace a cutlass bearing while the boat is in the water? Yes, if the shaft can be pulled far enough forward to clear the strut and you have an inboard engine. It's done regularly on boats in the 40-60 foot range. V-drives and pods usually need a haul-out. How long does an underwater cutlass bearing replacement take? Plan on two to three hours in the water, plus a sea trial. Some jobs go faster if the old bearing comes out easily, but if it's seized, add an hour for cutting and cleaning. What tools do you need to replace a cutlass bearing underwater? A bearing puller or slide hammer, a hacksaw blade, a cold chisel, a piece of all-thread rod, washers, nuts, a mallet, and a tube of dishwashing soap for installation. And a dive knife, obviously. Should I replace both cutlass bearings at the same time? If the boat has two shafts, yes, replace both. They wear evenly, and you're already wet. Just make sure the shaft alignment is checked afterward.