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Old 11-10-2003
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Keel Bolt Repairs


Replacing old or spent keel bolts should begin with a secure shoreside perch for the patient.
As a sailboat ages, the question of keel-bolt integrity takes on increasing importance for an owner whose vessel features a bolted-on ballast keel. Last month we took a look at both the signs of keel-bolt trouble and at how to assess the extent of the problem. If you missed that discourseor if you want to review it—click "Keel Bolt Concerns".

Replacement   Extracting the old bolts and replacing them with new ones can return a keel attachment to its original strength. This is nearly always how the weakened attachment of an iron keel is restored.  Of course, your first problem is likely to be access. Once you've gotten the boat out of the water, know that keel bolts are often hidden beneath tanks or under furniture, and considerable dismantling of a boat’s interior may be required.

Additionally, where galvanized keel bolts have gone uninspected for more than a decade, they are likely to be seized in the iron keel. Depending on the attachment configuration, getting them out may require the use of a heavy maul. A long pin (e.g., a length of round bar stock) is required to punch the bolt all the way out of the keel. The boat also must be supported in such a way that there is room beneath the keel to extract the bolt.  And, if you are not planning to separate the keel from the hull, extract and replace the bolts one at a time, applying full torque to the renewed nut before moving on to release and extract the next bolt.


If the joint between the hull and keel has deteriorated, removing the keel might be justified.
Should you separate the keel from the hull? In most cases the answer is no. Unless the hull shows structural damage that needs repair, the primary benefit of dropping the keel is that it allows renewal of the bedding between the two components. If the joint has clearly deteriorated, removing the keel might be justified, but if you are motivated simply by the sense that renewing this seal is a good idea, the effort expended will likely far exceed the benefit.

If the keel bolts in the bilge are under resin caps, they are most likely stainless steel. Builders have discovered that water is as likely to find its way to the bolts via the bilge as it is past the bedding between hull and keel, and the resin cap is there to prevent that. The first step in replacing a stainless steel keel bolt is to chip away the resin cap.


The resin cap has been removed here so that the nut and bolt can be properly inspected.
Stainless steel keel bolts in an iron keel are less likely to be seized in place by rust, but they can demonstrate an even more frustrating recalcitrance. Builders rarely use an anti-seize compound on the bolts when the nuts are installed. Combine this omission with the likelihood that the bolts were torqued with the help of a long pipe and you have the classic recipe for galling. When stainless steel bolts gall, the nut and bolt are essentially welded together. You will not be able to remove a galled nut without splitting it. You can use a nut splitter if there is room; otherwise you are reduced to cutting the nut with a rotary tool and finishing the split with a hammer and cold chisel.

Replacement bolts should not be 304/18-8 stainless steel. At the very least you want the corrosion resistance of 316 stainless. An even better choice is Aquamet 22 shafting material. Monel also makes excellent keel bolts, albeit at a high price. And, because iron is less noble than stainless steel, it is important to insulate the keel from the bolt. Occasionally this is accomplished by sheathing bolts with epoxy or nylon, but more often they are simply given a coating of silicone or polysulfide sealant. Because much of this is likely to scrape off when the bolt is inserted, it does not provide perfectprotection, but it does reduce the galvanic interaction between the keel and the bolts.

"An even better choice for keel bolts is Aquamet 22 shafting material."

Sistering    Keel bolts in lead keels may be installed from the bottom, or they may be threaded rods installed from the top, terminating in a backing plate and nut fitted via a "window" in the keel. In this latter case, the windows are typically a foot or so below the top of the casting. Although they will be filled, angled light should reveal their outlines. Bolts installed this way, if they are not galled, are relatively easy to replace.

However, both of these attachments methods are less common than J-shaped studs cast into the keel. Cast-in-place studs cannot be removed. Replacement usually requires the fabrication of a completely new keel. The installation of new bolts alongside the old ones—called sisterings—is possible and can be a more cost-effective response.

Whether sistering is applicable depends on how your hull is reinforced to take the strain of the bolts. A hull with a stub for the keel to attach to is likely to have ample strong locations for additional bolts, whereas a boat constructed with a reinforcing grid in the bilge may provide fewer strong positions. If your bilge exhibits space for more bolts—perhaps enhanced with some additional reinforcement—their installation is relatively straightforward.


Before cutting the window, drill in to find the new bolt hole, but use a cordless drill for safety.
The process—performed by lots of boatyards—is to cut a window in the side of the keel a foot or so below the joint, then drill down from the bilge into that window. In my experience, it isn’t easy to hit the window. You will probably have better success drilling down first, being careful to locate the new hole not too close to any existing stud. With the hole drilled to full depth, fill it with fresh water. Now load a 1/8-inch bit into a battery-powered drill (to safeguard againt electrical shock), and drill into the side of the keel where you expect the new hole to be. If you hit it, water will trickle out. If not, move less than the hole diameter to one side and drill again, and keep moving and drilling until you find water.

These small holes do not compromise the keel, and most will fall inside the window anyway, but with this method you know exactly where to center the window. A large spade bit can quickly cut a round window in lead. Then use a chisel to square the top of the window to accommodate the backing plate.

A rod threaded on both ends should be inserted from the top and captured in the window with a backing plate and a nut. A washer or backing plate and a nut at the top will complete the installation. Aquamet 22 shafting material is easily available and when threaded at both ends makes excellent studs for this use. Remember, it is essential to seal the stud at the bottom. The method I like involves saturating a "rope" of caulking cotton with polyurethane sealant and wrapping it tightly around the bolt above the backing plate. When the new stud is torqued, the saturated cotton forms a reinforced gasket at the bolt-keel-backing plate interstice.


With the keel firmly reattached, you'll get years of use out of your vessel, worry-free.
Do not caulk stainless steel keel bolts at the top. If they are leaking from below, you want to know about it. The new bolts should be encapsulated with resin to keep bilge water from draining down their sides, but future inspections will be more revealing if you have skipped the sealant.  And, one other thing, coat the threads with an anti-seizing compound before installing the nuts. You may not still own the boat when these new bolts are due for inspection, but someone will and what goes around comes around.

When all the bolts are tight, paint the interior surface of the window(s) with epoxy and then vigorously wire-brush the coated surfaces to expose fresh lead to the epoxy without exposing it to the air. Then fill the window(s) with a mixture of microballon (Microlight) and epoxy filler.  Don't forget your respirator.

Aquamet 22, by the way, has a yield strength of 135,000 psi, so three or four well-located supplementary bolts can go a long way toward restoring full strength to the keel attachment.

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