Checking Condition of Keel Bolts for Boating Season

This is a very strange period in our lives. Marinas are just starting to launch, and social distancing will make sailing very difficult. When we can, there are some checks that we all need to do on the boat before launch. One of them is the condition of the keel bolts. Admittedly you can see only a small portion of them from the bilge, but it does give you an idea on the condition they are in. Add the inside condition to what you see or don’t see, from the outside and you get a rough idea of the overall condition of the bolts.

If the bolts look clean and dry, there’s no visible corrosion, and the hull-keel joint is not cracked open, showing water, or has rust trails running from it, there is a good probability that the bolts are in good condition. There is a very big but to this. The only way to know for sure what condition the bolts are in is to lower the keel and look at them. The bolts corrode mainly in the area where they go through the FRP hull. It is here that the water can get trapped and no oxygen can reach the bolts — this condition promotes corrosion. So, if there is any doubt in your mind at all or if something doesn’t look right, call in a qualified professional to inspect them for you. This is not something that you want to ignore. The loss of a keel can be a tragedy. Spend the time so you are not a statistic, please.

If there is reason to believe that the bolts are in bad condition and require inspection, MarsKeel Technology can help. This process will require the keel to be removed from the boat. We will then pick it up, repair it, and return it to the yard ready for reinstallation.

Replacing bolts in a cast lead keel brings the keel back to virtually as new condition. We replace the bolts in the current positions (as close as possible, likely within 1/16” or more) and re-fair the keel making it ready to go back on the boat. On most keels this process is straight forward, however, we have run into older foreign-made keels that have bolt-to-bolt connections inside the casting that make removal and replacement difficult and very occasionally not possible.

In almost 20 years I have only seen one keel that we couldn’t remove the bolts without destroying the keel in the process. However, we were able to get around that as well. We cast a new keel using the old one as the pattern. For all other keels, the removal and installation process is accomplished easily by our very experienced staff.

Cost of Keel Bolt Replacement

For a general breakdown, let’s define the keel as follows:

It is 5,000 lbs. with 8 bolts and within 1,000 miles of us. The taking apart, cleaning, and putting back together of the keel is up to your local yard and this additional cost is not covered by MarsKeel Technology.

The bolt replacement is $475.00 USD per bolt plus freight.

8 Bolts

8 x $475

= $3,800.00
Freight approx. 1,000 miles

2 x $1,200

= $2,400.00
Total estimated cost = $6,200.00

So as you see it is not a massive expense. A new No 1 jib could cost that, but it is a personal decision.

Examples of Keel Bolts We Have Replaced

Below are some pictures of keel bolts we have replaced. They illustrate what can happen to the keel bolts if water and time are allowed to work on them.

The above bolt was removed from a keel that showed heavy corrosion in the bilge and the FRP region. Compared to the new threaded rod, the reduction in diameter it has suffered is clearly visible and cannot hold the weight it was designed for.

This is a keel with what looks like surface rust on the bolts from inside the bilge, but it has serious corrosion where the bolts pass through the FRP. This is exactly the problem you want to find and fix. At this point, there would have likely been water and rust stains running down the keel, but that is not a guarantee. That is why you need to check every year, especially as boats age.

This is a photo of a keel with the bolts on the port side melted out. Once the old bolts are removed, the new bolt is positioned during the refusing process by the channel left in the remaining keel.  So, the bolts do get replaced very close to the original position. This is not a project to do yourself or let your yard do. The reason is, if you just fill the void with molten lead, you have soldered the bolt in place and it will fall out. Once we are done with the refusing there is no trace that the keel was ever touched, it is as strong as the day it was cast.

So, if you see a problem, or think there might be a problem, or want to avoid a problem, have your keel checked by a qualified member of our team. If there is a problem, we can help you.

Have a safe summer!


MarsKeel is North America’s largest keel manufacturer, supplying keels to the top production yacht builders and offering repair and modification services for over 40 years. Contact us today for you keel production, repair, and modification needs.