The Official Magazine of the Bluewater Cruising Association

Checking Your Keel Bolts

Barb Peck & Bjarne Hansen

Hoku Pa'a
Niagara 35
May 11th, 2017

If the title of this article invokes the same reaction as when your partner mentions you ought to book a doctor’s appointment to get _______ checked out, then maybe:

a) you have never done it and suspect that you would rather not know, or

b) you did it and had a bad experience involving lots of time or money.

Fortunately for us, we fell into a third category: been there, did it, and it worked out well.

Here’s the tale of what we went through. Our Niagara 35 Classic was built in 1980 and as far as we know, the keel and stub have been like a happily married couple for the entire 37 years – never separated, and comfortable with each other. A lot can happen in that time, and we were curious as to the condition of the joint. Curiosity, however, doesn’t usually justify pulling something apart that seems to be working fine.

In our case, we had noticed some water seeping from the joint while hauled out. If water was entering the keel/stub seam – was it also reaching the keel bolts?

The final impetus was a comment by the surveyor attending Hoku Pa’a after hurricane Newton tipped her over while on the hard. He said the bolts could have become misaligned or bent from sideways forces during the knockdown. While we didn’t necessarily agree with his assessment, we knew that the insurance company would need to see proof either way.

So, whilst on the hard in Marina Seca Guaymas, Sonora, Mexico, we decided to drop the keel, clean and inspect the hardware, and then hopefully reassemble everything again. First step was to locate all the keel bolts. There are seven on a Niagara 35: four of ¾ inch diameter and three of 1 inch diameter. All but two are readily accessible, but these two are hiding underneath the holding tank. Ugh!

Holding tank being removed to access keel bolts.

We had to disassemble our galley cupboard to access the holding tank, then disconnect the plumbing and remove the tank. Fortunately we hadn’t used the tank in almost one year, so the few remaining contents weren’t particularly malodorous. We took this opportunity to clean the inside of the holding tank of years of calcium salts buildup.

Next step was to remove the keel bolt nuts. We ordered two sockets (1-1/4 inch and 1-5/8 inch) on Amazon and built a long wrench by welding some scraps of stainless pipe together.

Deep sockets for nuts.

A cross-arm of 1 meter gave the leverage to remove all the nuts relatively easily (though not so easily that we suspected them of having worked loose).

Homemade socket driver.

In the meantime, we built three supports from 2″x4″ lumber to keep all that lead from keeling over, once the hull was lifted off. Nothing like righting 5,500 lbs to give one an arm-muscle workout.

The Travelift showed up just after lunch on a Friday, and we hopped into high gear. Due to the operator not wanting our boat in the sling more than about 2 hours, we had to be efficient for the next steps.

One unfounded fear we had was that the keel would be bonded so well to the hull that even though the nuts had been removed the keel would lift up with the hull, requiring wedges be pounded in and sawing at the joint with piano wire. This turned out to not be necessary, as the keel separated with a startling crrrrack as the boat lifted.

Keel supported by wooden braces

This sound, which scared the lift operator as well as us, was actually the breaking and snapping of the remnants of the epoxy bond between the keel and stub.

Our initial impression of the bolts was that they appeared OK, but we needed to clean them and the joint thoroughly, for a closer look as well as to promote a good, new watertight bond. With the looming deadline of two hours, we scraped all the loose epoxy off and cleaned the threads of the bolts.

One bolt after cleaning.

We particularly ensured that there was bare metal exposed for several cm around each bolt, to allow for an adequate thickness of sealant to protect each bolt. While doing this, we noticed about 4 or 5 small aluminum rectangles a couple mm thick, embedded in the epoxy. We speculated that the builder included these to shim the keel to the proper angle, and also to ensure that the joint was not starved of epoxy, once the weight of the boat squeezed down on the keel. We didn’t reinstall these spacers, as there were enough patches of well-adhered epoxy on the keel to maintain the original angle and to keep an adequate thickness of sealant, especially around the bolts.

The bolts themselves looked very good; only one had any signs of corrosion, and it was missing a small patch of metal on the unthreaded shaft, to a depth of less than half a mm.

After the extra 30 minutes we begged for, the lift operator returned and indicated that our time was up and the boat was coming down. With adept skill he aligned the boat with the projecting bolts and lowered the hull slightly until the two stern-most bolts (the longest ones) were just entering the stub. This alleviated another of our worries (that we wouldn’t be able to reinsert the bolts without great difficulty). We grabbed two caulking guns and quickly spread 3M 5200 and 3M 4200 liberally around the bolts, as well as covering the rest of the mating surface. The operator then slowly eased Hoku Pa’a the rest of the way down as we watched 3M ooze out of the joint. Success!

Bjarne checking the joint after replacing the keel.

We had to wait about a week before we could cut away the excess sealant. These polyurethanes take a long time to cure, particularly in low humidity environments (it’s less than 20% relative humidity in the Sonoran Desert during the daytime).

With the hull back on the keel, we reinstalled the nuts and tightened them to the approximate torque recommended by the manufacturer. In areas where sealant had not squeezed up all the way along the shaft of the bolt, we added some 3M 4200 to ensure that bilge water would not make its way down past the nuts and washers.

One of the bolts with nut reattached.

We’ll recheck the bolts after we get in the water, as well as ensuring there are no leaks. For now, the job looks done!

Working in a boatyard results in great discussions with other boaters, who often relate their own experiences. During this particular project, interesting topics included:

  • How can you tell your bolts might need checking? One or more of: water seeping out of the joint when hauled out; water entering the bilge via a bolt hole; an older boat, especially one used extensively in salt water; hard grounding or tipping over; significantly uneven torque on the nuts; large amounts of rust originating from a bolt or nut; or to satisfy an insurance company.
  • How do you ensure the keel-stub joint isn’t starved of whichever bedding compound you use? Spacers can be inserted (as ours was from the factory) or there may be remnants of an existing cured epoxy layer. If you want to verify how thick of a joint you’ve created, then before you drop your keel, scribe several parallel lines a known distance apart in several locations straddling the joint. In our case we used calipers to scribe lines 2 inches apart at the aft, middle, and forward part of the keel on both port and starboard. After rejoining our keel, we measured the lines as 2.007 inches to 2.020 inches apart, so we know our draft is now 20 thousandths of an inch deeper 🙂



  1. Carolyn Daley says:

    Great article you two…. thanks for sharing. Carolyn.. SV Shannon’s Spirit

  2. John Simkins says:

    Great article. I like the support structure you built for the keel. I have added a keel bolt tightness check to my biannual maintenace list and will make a socket with enough depth to fit. This suggestion also came out of a Catalina 42 Rendevous at Roche Harbor a few years ago.

  3. Al Kitchen says:

    Well Done guys! The article is well presented and the topic is so relevant. I know of another couple who had worked for a couple of years preparing their boat for offshore but neglected doing the keel bolts because the delay would have meant they missed another season’s opportunity to head for Hawaii. (they headed off in late September as it was) Shortly after departing from Neah Bay they were hit by a pounding storm that had water gushing up the keel bolts and flooding the boat! The U.S. coast guard managed to get a pump aboard and get them turned back to safety but it ended the adventure and the relationship. Lesson learned the hard way. Don’t listen to her (or him) when that important job should be done but she’s impatient to get going.

  4. Sam says:


    1981 Niagara 31 owner here. Where did you find the torque values for the keel bolts? Mine seems in pretty good shape but it does have a hairline crack at the joint. I thought I should double check the bolts have loosened at all but my manual does not list torque for the keel bolts. I haven’t been able to locate the torque numbers online anywhere.


    1. Bjarne Hansen says:

      Hi Sam!
      I checked our notes: we didn’t find definitive torque-values in the Niagara manual. So when we reassembled our keel we looked at two sources: what values other similar-displacement boats with lead keels were using; and what the general industry values were for SS316 bolts of the same diameter. There’s a good summary at which you may already have come across.

      A couple of points seem important. First, keel bolts cycle between a least-loaded state (when boat is hauled and resting on keel) and a most-loaded state (when in the water, perhaps slamming down from atop a wave). One wants the bolts to remain in tension at all times between these two states (i.e. not cycling between compression and tension). Further one doesn’t want the most-loaded state to approach the elastic load limit, where the bolts would permanently stretch and possibly even break. A straightforward way of achieving this goal is to put a moderate amount of tension in the bolts when they are least-loaded (boat on-the-hard). Too much tension when resting on the keel could lead to exceeding the bolts’ tensile strength when the boat is working hard in the water. So, whatever ranges of torque one arrives at, it is probably better to err on the side of less rather than more – provided that there is indeed tension when the boat is resting on the keel.

      A second point I feel is pertinent is that the keel bolts act in concert with the sealant/adhesive placed between the joint; one wouldn’t expect the bolts to normally carry the full load of the keel’s weight. This was underscored by our experience in which the original epoxy-based adhesive actually briefly held the keel suspended in the air (with all the nuts removed), and by other stories heard of people trying to separate their hulls/keels with difficulty. The adhesive/sealant also serves to keep out water. Both these functions imply that one should avoid over-squeezing the joint when remounting the keel. Using thin spacers like some manufacturers, and avoiding over-tightening the nuts, should help avoid starving the joint of sealant.

      It’s likely a good idea to check the nuts shortly after remounting the keel and perhaps annually during haul-outs to ensure they aren’t loosening off.

      One final point is that the tensile strength of large bolts is high enough that one is not likely to be able to over-torque them by manually tightening with a wrench having a reasonable lever arm (e.g. type A4-70 Stainless 24 mm bolt has max recommended torque of 55 kg*m, so one would need to exert ~160 lbs of force on a .75m wrench).

      Sorry I couldn’t give you an exact number, but hopefully these thoughts help! Cheers, Bjarne

      1. Sam says:


        Thanks so much for taking the time to reply to this older post. My boat has had a pretty easy life as a family daysailer in freshwater its whole life. Currently on the Lake Michigan so luckily I don’t have to worry as much about corrosion. Thanks so much for the torque link I had not come across that before. After reading about your experience I think I will just check the bolts are still close to values listed in that link and keep monitoring. The keel has a small crack at the front of the joint but im thinking now thats just where the adhesive has aged and cracked. When pulled for the winter it does not weep water.

        You said you had noticed water weeping out, did you notice any seeping into the bilge from around the bolts? Do you think the water was just trapped inside the joint where the adhesive wearing away had created voids?

        One thing we have going for us is IMO hinterhoellers were well constructed boats, does not seem like they cut many corners which makes even my 41 year old boat worth putting time and money into keeping in top form. Seeing the pics of your keel bolts and the joints was pretty reassuring. Everything looked in great shape!

        Thanks again!

        1. Bjarne Hansen says:

          When we saw weeping water, it was definitely just trapped water in gaps between the lead and the hull as you surmised, because we never noticed any ingress of water into the bilge from the keel. Enjoy your Niagara 31!

        2. Jay D says:

          Hello Sam.
          Two weeks ago my wife and I purchased an 1981 Niagara 31 in Toronto, Ontario.
          She has been well taken cared of, but after transporting her 3 hrs north of Toronto I noticed a significant crack at the front of the keel.
          Im wondering if you are aware of any Niagara 31 forums where we can all share tips and tricks, especially your original question of torque specs for the keel boats.

          I might start up a facebook Niagara 31 owners page to share stories and tips.

          1. Sam says:

            Hey Jay!

            Congrats on the boat! I am not aware of any forums, I don’t think there were enough built and surviving today to support a traditional forum. Happy to share advice and tips though! I have done a lot of updates from new engine/saildrive to new main/sailpack, lighting, restoring the gelcoat and more. If you want you can email me at I would be happy to send you pics of my keel or any other systems you might have questions about.

            For me after bottom painting the boat looks like it has a crack between the hull and the keel. But this is just the paint cracking from the flexing of the keel joint. The bow end of the keel did have a slightly larger gap, but I sealed it with 5200 and painted over it and have had no issues since. If your keel is not weeping on the hard and there is not water getting in from under at the dock you are probably in good shape.

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