Checking and Replacing: Keelbolts, Part 1

It is almost impossible to generalize about the longevity of keelbolts, since so many variables influence the life of a metal immersed in water.


Nevertheless, this safety margin does not guarantee eternal life for keelbolts. Corrosion takes its toll, sometimes more quickly than you might think. It is almost impossible to generalize about the longevity of keelbolts, since so many variables influence the life of a metal immersed in water. If there are signs of deterioration in underwater fittings such as sea-cocks, struts, or propellers, the same forces may be chewing away at the bolts which secure the ballast that keeps your boat rightside up.

Checking and Replacing Keelbolts
How can you be sure about the condition of your keelbolts? Simple. You look at them. This does not mean looking at the nuts in the bilge. This means pulling one out and examining it from top to bottom. In practice, this may be a monumental task, or a simple chore

Keelbolts are commonly installed in one of three ways. They can consist of long rods, threaded at either end, which extend from the bilge of the boat all the way through the ballast casting, with nuts set up in recesses in the bottom of the casting. This arrangement is usually seen in boats with fairly long, shallow ballast castings, rather than fin keels. It is used with both iron and lead keels.

Sometimes, rather than bore all the way through the casting, pockets are cast or cut near the top of the ballast casting. The holes for the bolts are drilled from the top of the casting into the pocket, and large nuts and washers installed. The pockets are then filled with lead or cement. The advantage of this arrangement is that shorter bolts can be used, and the labor of drilling entirely through a deep ballast casting is avoided. This method is seen on lead keels, and can be used on deep fins as well as shallow castings. It is rarely used with iron keels.

Tapping into the top of the casting, then screwing a threaded rod into place, is another common technique. This can be done with either iron or lead, although it is more commonly seen in iron keels.

It is not necessary to tap very far into the top of the keel. As a rule, if the bolt is threaded four times the nominal bolt diameter into the top of the keel, it will hold the full strength of the bolt. In practice, it is probably best to drill and tap to a depth of five or six diameters, since it may be difficult to get really good threads in the very bottom portion of the holes, and debris may keep the bolt from reaching the bottom of the hole.

Another technique used with fin keels is to cast the bolts in place when the keel is cast. This can only be done with lead keels. If you tried to do it with cast iron, you would melt the bolts.

Cast-in-place keelbolts should be fitted with nuts and washers inside the keel mold before the casting is made. It is folly to assume that the molten lead will neatly flow into the threads of each bolt, just as if the holes had been tapped in after the casting was completed. A cast thread has less holding power than a cut thread, and the shrinkage of the casting as it cools may yield a very poor fit between the threads of the bolt and the lead of the keel.

Sometimes, the keelbolts will be bent at an angle inside the mold before the keel is cast, the theory being that it would be necessary for the bolts to straighten out before the keel could pull loose from the boat. The disadvantage of this method is that it makes it almost impossible to remove the bolts from the lead for examination or replacement. Unfortunately, this is one of the most common ways of installing bolts in a modern fin keel.

It may not be clear from looking at your keel exactly how the bolts are installed, except when the bolts go all the way through the casting, or when pockets in the casting are used. Grinding the keel to bright metal almost always shows up pockets in either the bottom or side ofa keel attached using either of these methods.

The construction plan for your boat probably shows the way the designer intended for the bolts to be installed, but it is fairly common for builders or keelmakers to modify the designer’s plans to the way they normally do the installation. If the builder of your boat was not the molder of the keel, he may have no idea how the bolts are installed. The builder’s primary concern is that the bolts protrude from the ballast casting in the proper locations, so that the keel may be bolted to the hull with minimum difficulty.

Removing Keelbolts In some areas, portable x-ray facilities may be available, making it possible to examine bolts in place without going through the trouble of removing them. This method works for steel and stainless, but is almost useless for bronze, since the corrosion process is somewhat different.

More often that not, however, removing a keelbolt for examination is the most practical way to determine its condition. This can be a simple job, or it can be almost impossible. While it isdifficult to generalizeabout which type of keelbolt installation makes for the easiest extraction, theoretically at least, a stud threaded into the top of the casting should be the easiest to remove.

A knowledgeable boatbuilder will not cut the tops of the keelbolts off flush with the tops of the nuts. Instead, he will leave enough threaded rod projecting through the nut so that a second nut can be tightened down onto the regular keelbolt nut to lock it in place, preventing the nut from turning on the rod when you try to unscrew the rod from the keel.

Here’s the method. First, using a socket wrench, an extension, a breaker bar, and a liberal dose of penetrating oil, loosen the keelbolt nut slightly on its rod. If you are lucky, the whole rod will start to turn out, instead of the nut merely loosening on the rod, and you can extract the bolt in one simple operation. Of course, if the rod starts to turn freely, you may also have sheared the bolt, but if it broke that easily, it needed to be replaced anyway.

If the nut has loosened on the rod, back if off just enough to clear the washer or backing plate on the inside of the hull. This means that when you apply torque to the nut to try to back the stud out, you won’t have to overcome the friction of the nut against the washer before torque is applied to the bolt itself.

If nothing wants to turn, stop for a moment. Three things can happen if you apply enough torque: either the nut will turn, the stud will turn where it is threaded into the casting, or the rod will shear. What are you going to do in each case?

If the bolt shears, you will have to drill through the hull into the ballast casting, tap a new hole, and install a new bolt in a slightly different location from the original. Is there room to do this? Will you have to install some reinforcement in the hull to carry the load of the new bolt? If you can’t answer these questions in a reasonable way, you should not try to remove the bolts.

If the nut has loosened and there is enough thread sticking out, take another nut of the same size and thread it down firmly on the keelbolt nut. Hold the lower nut in place while tightening the upper nut. You will really have to crank these together to get them to hold in place.

Usually, the nuts used on keelbolts will be of the configuration called “full heavy” nuts. For the jamming nut used on top, a “full finished” or “finished jam” nut should be used, if possible. These nuts are slightly smaller than “full heavy” nuts. In practice, this means that you can slip a socket over the two nuts to loosen them, and if the nuts are properly aligned, all the torque of the socket will be transmitted to the lower nut, and there will be little tendency for the upper nut to loosen.

With the two nuts jammed on the bolt, it should be possible to turn the bolt out, once again using a socket, an extension, and a solid breaker bar. With very large bolts it may be necessary to use a pipe extender over the solid breaker bar to get adequate leverage.

Use a little common sense with breaker bars and extensions, because you can get tremendous leverage on the nuts and bolts using them. Mild steel bolts in a cast iron keel may seize solidly. Bronze or stainless bolts in lead should break free quite easily.

Bolts which consist of long rods passing entirely through the ballast casting can usually be driven out from above. The holes in the bottom of the keel are usually plugged with concrete, wood, or some type of hard putty.

The first step is to loosen the nut at the top of the bolt. Unlike the situation with a bolt tapped into the keel, you must be able to loosen the nut at the top of the bolt. It is best to apply penetrating oil, and even heat from a propane torch, to free these nuts before applying a lot of torque. Heat is extremely effective in loosening seized nuts, but it must be applied carefully to avoid damage to a fiberglass or wooden hull. Traditionally, asbestos cloth is used around something you are heating up to avoid damaging adjacent surfaces, but asbestos is a material that must be used with extreme caution, since it is a known health hazard.

Loosen the nut until it is flush with the top of the bolt in the bilge. Then strike the nut squarely with a heavy hammer. A light hammer will do little more than peen over the end of the bolt, causing you a lot of trouble. Needless to say, the confines of the bilge of your boat are pretty close for wielding a sledge hammer, but that is exactly what you will have to do.

If the bolts are deep in the bilge, you may have to rest a rod on top of the nut, and strike the rod rather than the nut. You will need a helper wearing heavy gloves to gripthe rod, which will have to be held rock steady. Obviously, the helper is going to have to have a lot of faith in your ability to strike the rod, rather than his or her hands.

A couple of heavy blows should free the bolt, and the nut will be driven down to the backing plate again. If you did not back the nut up flush with the top of the bolt, there is a good chance you have succeeded inpeening the top of the bolt, so that the nut cannot be backed off. A few minutes with a grinder or file should relieve the upset head of the bolt.

Check the bottom of the keel. Have the plugs fallen out, and is the nut moving out of the keel? If the nut has not budged at the bottom of the keel, but has moved an inch lower at the top, there is a good chance that the bolt is crumbling under the blows of the hammer, an indication that replacement is long overdue.

It should be pretty obvious that the boat can not be resting on its keel on the ground to this job. The keel must be blocked up, and the supports must be clear of the part of the keel through which the bolts pass. With a deep keel, it may also be necessary to dig a hole under the keel to get enough depth to drive the bolt free.

It is possible that the keelbolts could be several feet long, necessitating extremely deep holes under the keel in order to remove them in one piece. An alternative, when you know you are going to replace the bolts anyway, is to drive the bolt out as far as you can, cut it off, then drive and cut again.

Once the bolt has started moving, it should require relatively little force to finish driving it out. When the bolt is driven down flush to the inside of the hull, a driving rod will have to be used to finish the job. This should be a long piece of round bar stock that is both smaller in diameter and softer than the keelbolt; smaller in diameter so it won’t jam in the hole, and softer so it won’t damage the top of the bolt as it is being driven. Old bronze prop shaft-every boatyard has tons of this lying around-is ideal for the job.

Keelbolts which do not extend through the keel, but instead have nuts installed in pockets in the casting near its top, are likely to be the hardest to remove, since they can not be driven out. Instead, you will have to locate the pockets by grinding off the paint on the outside of the keel. If they are plugged with wood or putty, cut it out with a chisel. If they are plugged withlead, you will have to melt the lead out with an acetylene torch, which can be rented for the occasion. Once the plugs are removed, take the nuts off the bottom of the bolts in the pockets.

Now comes the tricky part. If you are lucky, you might be able to turn the bolts out, just like studs threaded into the top of the casting, using a combination of turning and pulling at the same time. It helps if someone else pries up on the bottom of the bolt from the outside at the same time. Usually, if you can get the bolt to turn, you will be able to pry it out.

The alternative is to jack the bolt out from inside the boat. Remove the keelbolt nut on the inside of the boat, and replace the existing backing plate or washer with a heavy steel plate, through which you have drilled a hole the diameter of the bolt. A pair of hydraulic or mechanical jacks is then used to pry the bolt upwards. Some ingenuity in fabricating the jacking plate may be required to make it possible to get the jacks under the plate.

Don’t try to pull the bolt out using a come-along attached to a deck beam or the cabin overhead unless you are willing to take the risk of looking very foolish when the deck collapses into the bilge.

If your keelbolts were installed by casting the bolts in place with nuts and washers, you may be able to back them out, just like studs tapped into the keel. If bent rods were used in place of nuts and washers, you may be out of luck. Instead of replacing keelbolts, you will have to add more bolts when the time comes.

In Part II, in the next issue, we’ll look at procedures for testing keelbolts, the options in metals for keelbolts, plus a few thoughts on replacing bolts found to have outlived their useful life.

Checking and Replacing: Keelbolts, Part 1

Darrell Nicholson
Practical Sailor has been independently testing and reporting on sailboats and sailing gear for more than 50 years. Its independent tests are carried out by experienced sailors and marine industry professionals dedicated to providing objective evaluation and reporting about boats, gear, and the skills required to cross oceans. Practical Sailor is edited by Darrell Nicholson, a long-time liveaboard sailor and trans-Pacific cruiser who has been director of Belvoir Media Group's marine division since 2005. He holds a U.S. Coast Guard 100-ton Master license, has logged tens of thousands of miles in three oceans, and has skippered everything from pilot boats to day charter cats. His weekly blog Inside Practical Sailor offers an inside look at current research and gear tests at Practical Sailor, while his award-winning column,"Rhumb Lines," tracks boating trends and reflects upon the sailing life. He sails a Sparkman & Stephens-designed Yankee 30 out of St. Petersburg, Florida. You can reach him at