I have a 1982 Hunter 33 and was asked if I had tighten the keel bolts, which I have not. Will stainless steel keel bolts loosen over time the where they need to be tighten? Thanks
Do keel bolts become loose?
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Keel bolts
Under ordinary use, no. When we purchased our 1991 model Hunter P42, the keel bolts had never been tightened and no indication that they needed to be. Hunter does a good job in sealing the keel stub joint. If your keel has struck a solid object, that can cause the bolts to stretch, which can result in the keel stub joint seal to be compromised. In that case other factors need to be considered.
Terry Cox
Under ordinary use, no. When we purchased our 1991 model Hunter P42, the keel bolts had never been tightened and no indication that they needed to be. Hunter does a good job in sealing the keel stub joint. If your keel has struck a solid object, that can cause the bolts to stretch, which can result in the keel stub joint seal to be compromised. In that case other factors need to be considered.
Terry Cox
Keel bolts
I believe it is certainly possible for keel bolts to loosen, even without the trauma of a hard grounding. Just think about the pressure on a keel and its bolts every time you sail. A friend of mine, with a 1986 Pearson 28-II, was repairing the "keel smile" on his boat every spring. He would scrape out the keel/stub joint and squeeze in 3M5200 or something similar. Then one year, he actually saw his boat in the lift straps. With no weight on the keel, he could see a clear space between keel and stub. He had the bolts tightenend and has had no "smile" since.
I believe it is certainly possible for keel bolts to loosen, even without the trauma of a hard grounding. Just think about the pressure on a keel and its bolts every time you sail. A friend of mine, with a 1986 Pearson 28-II, was repairing the "keel smile" on his boat every spring. He would scrape out the keel/stub joint and squeeze in 3M5200 or something similar. Then one year, he actually saw his boat in the lift straps. With no weight on the keel, he could see a clear space between keel and stub. He had the bolts tightenend and has had no "smile" since.
Maybe
Many boats have a plywood stub that the keel bolts go through. It is possible for this or some other part to compress a little. I retorqued my keel bolts on last haul out, and got 1/4 to 1/2 turn on a couple of them. I would not just start cinching down though. If your going to tighten them, find the specs and torque to specs. If you get a lot of movement from the bolts, look for a reason.
Many boats have a plywood stub that the keel bolts go through. It is possible for this or some other part to compress a little. I retorqued my keel bolts on last haul out, and got 1/4 to 1/2 turn on a couple of them. I would not just start cinching down though. If your going to tighten them, find the specs and torque to specs. If you get a lot of movement from the bolts, look for a reason.
Yes, but when it is sitting on keel blocks so that most of the weight of the hull is pushing down on the keel, there is no stress. The extent of the gap that may exist when the boat is floating can well be hidden.
If the bolts are loose, the keel can move enough to bend the bolts slightly because they flat of the casting is no longer held tightly against the keel stub. The fatigue and corrosion from water intrusion will lead to premature and possibly catastrophic failure.
Hanging the boat in the straps is a good way to assess what thing may look like in the water.
If the system is designed correctly the bolts will be collectively several times as strong as the weight of the keel. The nuts will be torqued to a tightness proper for that size bolt. The materials being bolted together will have suffient compressive strength to sustain the bolt loading. This is the manner with which machinery is assembled. The bolts should never stretch, the interior structure of the bilge that supports the keel should be as incompressable as the bolts are strong and nothing will move. If the keel bolts need annual tightening then there is a design flaw or there is deterioration in the keel support structure.
Stress on the keel bolts in water or hanging in a sling
In the water the keel is being supported by a bouyant force pushing upward that subtracts from the stress on the keelbolts as apposed to hanging ina sling. Since the keel is a fairly large displacement object this force is quite large. Granted the keel will not float by itself but the forces are still there.
In the water the keel is being supported by a bouyant force pushing upward that subtracts from the stress on the keelbolts as apposed to hanging ina sling. Since the keel is a fairly large displacement object this force is quite large. Granted the keel will not float by itself but the forces are still there.
How a system is designed and how it is actually constructed are often quite different. Ideally, the bolts should not corrode either... but they do... and in many cases quite drastically.
If the boat is old enough, removing and inspecting the keelbolts should be done. While the keel may appear to be held in position sufficiently, hidden crevice corrosion may leave the bolts with little safety margin in the case of an impact or grounding.
If the boat is old enough, removing and inspecting the keelbolts should be done. While the keel may appear to be held in position sufficiently, hidden crevice corrosion may leave the bolts with little safety margin in the case of an impact or grounding.
The lead in your keel will be closer to 700 because it will be scrap and have tin and other stuff in it to make the casting stiff enough to be practical. Seawater weights 64 pounds per cu.ft.
Keel Bolts
1- Many builders do not take keel or hull imprints to match the two surfaces 100%. This is labor intensive and requires dropping the boat onto the keel twice. Unfortunately this leaves small surface area high spots between lead and hull that do not tend to compress when the keel is first installed and torqued. To understand more about face matching the keel to the hull read this: S/V Stella Blue Keel Re-Set (LINK)
Fast forward 20+ years with boats sitting on keels all winter long, and sailing hard, and these high spots, despite strong compressive resistance over large surface areas, can deform and compress. This can happen in the lead or the laminate. Once these high spots compress it leaves the boat with a new found gap and slight movements in the keel hull joint where the sealant fails and begins to crack. While the nut has not loosened you can now take a turn because the high spots have compressed leaving the appearance of loosening bolts.
2- Many production builders cut corners and laminated exterior grade or marine grade plywood into the keel stub. Plywood is more easily compressed than solid GRP and when subject to leaks from keel movement becomes wet, then saturated, and even more prone to compression. The bolts can actually begin to sink into the keel stub because the weight of the keel is pulling away from the hull by being allowed compress the softer core material. If the stub compresses by 1/16th of an inch you now have the potential for a 1/16th inch gap when the boat is in the slings under a static load and most definitely when under the dynamic loads of sailing.
This is not a keel bolt loosening it is the keel stub compressing: (photo cuortesy digital marine survey)
Plywood laminated keel stub from a Pearson 26:
Jibes comment about keels being lighter in water is true but basically irrelevant in a situation where the keel has a 1/16th inch gap or more in the slings. A 4000 pound keel will still weigh roughly 3600 pounds in the water. That 400 pound difference between the static position in the slings vs. the dynamic loads applied to the keel while sailing are not alleviated by the lighter weight of the keel in water and the 1/16th inch gap will still be a problem.
3) If your bolts are loose and you have a visible keel joint crack that leaks water for more than a few minutes after haul out you are running the risk of keel bolt crevice corrosion. This is the apparent melting of stainless from being submerged in oxygen deprived salt water. If your joint is wet and leaking the only proper fix is to drop the keel and re-set it..
Keel joint leak (photo taken in spring after months on teh hard and still leaking):
Crevice Corrosion:
You should check your keel bolts periodically. If they need to be re-torqued more than once you probably have some issues going on. I just checked mine last week and could get no more than a smidgen or about 1/8 of a nut turn at over 250 foot pounds of applied torque with a GIANT torque wrench.
While they should not loosen in the traditional sense of the word the appearance of loosening can lead one to believe this is what happened. I have listed some causes below.
1- Many builders do not take keel or hull imprints to match the two surfaces 100%. This is labor intensive and requires dropping the boat onto the keel twice. Unfortunately this leaves small surface area high spots between lead and hull that do not tend to compress when the keel is first installed and torqued. To understand more about face matching the keel to the hull read this: S/V Stella Blue Keel Re-Set (LINK)
Fast forward 20+ years with boats sitting on keels all winter long, and sailing hard, and these high spots, despite strong compressive resistance over large surface areas, can deform and compress. This can happen in the lead or the laminate. Once these high spots compress it leaves the boat with a new found gap and slight movements in the keel hull joint where the sealant fails and begins to crack. While the nut has not loosened you can now take a turn because the high spots have compressed leaving the appearance of loosening bolts.
2- Many production builders cut corners and laminated exterior grade or marine grade plywood into the keel stub. Plywood is more easily compressed than solid GRP and when subject to leaks from keel movement becomes wet, then saturated, and even more prone to compression. The bolts can actually begin to sink into the keel stub because the weight of the keel is pulling away from the hull by being allowed compress the softer core material. If the stub compresses by 1/16th of an inch you now have the potential for a 1/16th inch gap when the boat is in the slings under a static load and most definitely when under the dynamic loads of sailing.
This is not a keel bolt loosening it is the keel stub compressing: (photo cuortesy digital marine survey)
Plywood laminated keel stub from a Pearson 26:
Jibes comment about keels being lighter in water is true but basically irrelevant in a situation where the keel has a 1/16th inch gap or more in the slings. A 4000 pound keel will still weigh roughly 3600 pounds in the water. That 400 pound difference between the static position in the slings vs. the dynamic loads applied to the keel while sailing are not alleviated by the lighter weight of the keel in water and the 1/16th inch gap will still be a problem.
3) If your bolts are loose and you have a visible keel joint crack that leaks water for more than a few minutes after haul out you are running the risk of keel bolt crevice corrosion. This is the apparent melting of stainless from being submerged in oxygen deprived salt water. If your joint is wet and leaking the only proper fix is to drop the keel and re-set it..
Keel joint leak (photo taken in spring after months on teh hard and still leaking):
Crevice Corrosion:
You should check your keel bolts periodically. If they need to be re-torqued more than once you probably have some issues going on. I just checked mine last week and could get no more than a smidgen or about 1/8 of a nut turn at over 250 foot pounds of applied torque with a GIANT torque wrench.
Re: Keel Bolts
Those are not pretty pictures. They are very good pictures but they underline my contention that if the bolts need tightening there was a design flaw or something has deteriorated.
Mainesail , They always apply epoxy coatings to re-bar in highway construction but is epoxy coating ever applied to keel bolts?
Those are not pretty pictures. They are very good pictures but they underline my contention that if the bolts need tightening there was a design flaw or something has deteriorated.
Mainesail , They always apply epoxy coatings to re-bar in highway construction but is epoxy coating ever applied to keel bolts?
No because bilges are often filled with salt water. If the epoxy were to become perforated by a nick or scratch water could get under it and start eating away at the stainless. It also happens when a sealant fails and water gets trapped in between the keel and the bilge. Leaks are what cause the corrosion in those photos above..
Stainless should never be used for keel bolts but it has become almost universal on custom boats, probably because it adds .002% to the cost of the vessel.
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