I have a small leak comming from the aft port side keel bolt. Can repair be done while in the water?
Water leak at keel bolt
- Thread starter Tom23400
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Hi Tom, probably not. One good first step is to...
make sure that all keel bolts are torqued at the right setting. If that does not stop the leak then you need to haul the boat and determine the leak source. One possible source is the keel stub joint seal has been compromised. I'm not aware of any method that will stop the leak while the boat is in the water other than the checking the keel bolt/nut torque. Terry
make sure that all keel bolts are torqued at the right setting. If that does not stop the leak then you need to haul the boat and determine the leak source. One possible source is the keel stub joint seal has been compromised. I'm not aware of any method that will stop the leak while the boat is in the water other than the checking the keel bolt/nut torque. Terry
Scary pictures Maine Sail! *yks
Do you know what year/model/manufacturer the keels were from? I guess there is no way to inspect the bolts without taking the keel off of the boat? Maybe some sort of cool portable x-ray machine????
Do you know what year/model/manufacturer the keels were from? I guess there is no way to inspect the bolts without taking the keel off of the boat? Maybe some sort of cool portable x-ray machine????
Disagree slightly ....
Critical strength structures on a boat are usually designed at 4 times (for offshore) or 3 times (for 'coastal') the expected working load. This is the normal safety factor of design that is inbuilt to take care of 'unexpected and unforseen' loadings. Id certainly torque those bolts to at least HALF their specified range ... and if this breaks the those bolts the bolts would have broken catastrophically during 'normal' loading. Why have the bolts break off when you are far from port when 'something' beyond normal stresses the bolts. Better to know 'up front'. IN all probability the bolts are 304 or even 302 stainless and should be 316 (or better) that is more suitable for service in seawater. 316 better withstands intergranular corrosion (crevice corrosion), especially in seawater.
Critical strength structures on a boat are usually designed at 4 times (for offshore) or 3 times (for 'coastal') the expected working load. This is the normal safety factor of design that is inbuilt to take care of 'unexpected and unforseen' loadings. Id certainly torque those bolts to at least HALF their specified range ... and if this breaks the those bolts the bolts would have broken catastrophically during 'normal' loading. Why have the bolts break off when you are far from port when 'something' beyond normal stresses the bolts. Better to know 'up front'. IN all probability the bolts are 304 or even 302 stainless and should be 316 (or better) that is more suitable for service in seawater. 316 better withstands intergranular corrosion (crevice corrosion), especially in seawater.
Stress risers ....
It's not only the loss of diameter that is the problem nor would be my chief concern. Intergranular corrosion also is 'planar' in that it penetrates the macroscopic structure like a knife and makes macro-microscopic 'cleavages' deep into the metal along the 'grain boundaries'. Lines of stress like to be equally spaced so that you actually get the performance rating from a material. Stress risers (artificailly bringing all the lines of stress close together) are formed at sharp edges, square holes, ridges, etc. and radically reduce the structural load capacity of a material. Since intergranual corrosion (crevice corrosion, etc.) penetrates deeply along the 'grain boundaries' of a metal it notoriously sets up micro-stress risers and can greatly weaken the metal and despite the "apparent remaining cross section". So anytime you notice any such intergrannular corrosion such as what you see in these keel bolt pics ... there is NO WAY to visually tell what has actually happened to the material. Once intergranular corrosion begins, the fatigue (additive micro-cracks) of the metal rapidly increases ... so now you have 3 simultaneous modes of failure occuring 'all at the same time' - grain boundary failure, fatigue failure, and ductile failure of the remaining intact metal. The only 'safe' but temporary means is to 'proof load' the item (torquing in this case) to *prove* that the working load can be carried (until ASAP replacement). Such crevice corrosion failure isnt predictable, usuallly terminates in a catastrophic 'brittle failure' .... and I wouldnt trust 'anything' where I find it. Proof loading to some torque etc. value below the design strength will allow you to get 'home' with some confidence. Before the 1980s stainless was designed with respect to its Ultimate tensile values (~90,000 psi) but with advanced dynamic testing, etc. methods nowadays stainless (300 series @~90ksi) used in 'important' or 'dynamic' situations/applications shouldnt exceed 30,000 psi .... called the 'endurance limit' of fatigue. Those keel bolts that were designed before the mid 1980s would be considered to be greatly 'underdesigned' by todays standards .... now that we better understand 'stainless steel', with respect to its fatigue propensity and its propensity for crevice/intergranular corrosion. For such keel repair - for me - using the same bolt materials, I'd at least double the 'number' of attachments of the original design. To repair such keels with the SAME size and number of fasteners would lead to the exact same result ..... its a FAILURE. The original design was inherently weak - by todays knowledge and standards.
It's not only the loss of diameter that is the problem nor would be my chief concern. Intergranular corrosion also is 'planar' in that it penetrates the macroscopic structure like a knife and makes macro-microscopic 'cleavages' deep into the metal along the 'grain boundaries'. Lines of stress like to be equally spaced so that you actually get the performance rating from a material. Stress risers (artificailly bringing all the lines of stress close together) are formed at sharp edges, square holes, ridges, etc. and radically reduce the structural load capacity of a material. Since intergranual corrosion (crevice corrosion, etc.) penetrates deeply along the 'grain boundaries' of a metal it notoriously sets up micro-stress risers and can greatly weaken the metal and despite the "apparent remaining cross section". So anytime you notice any such intergrannular corrosion such as what you see in these keel bolt pics ... there is NO WAY to visually tell what has actually happened to the material. Once intergranular corrosion begins, the fatigue (additive micro-cracks) of the metal rapidly increases ... so now you have 3 simultaneous modes of failure occuring 'all at the same time' - grain boundary failure, fatigue failure, and ductile failure of the remaining intact metal. The only 'safe' but temporary means is to 'proof load' the item (torquing in this case) to *prove* that the working load can be carried (until ASAP replacement). Such crevice corrosion failure isnt predictable, usuallly terminates in a catastrophic 'brittle failure' .... and I wouldnt trust 'anything' where I find it. Proof loading to some torque etc. value below the design strength will allow you to get 'home' with some confidence. Before the 1980s stainless was designed with respect to its Ultimate tensile values (~90,000 psi) but with advanced dynamic testing, etc. methods nowadays stainless (300 series @~90ksi) used in 'important' or 'dynamic' situations/applications shouldnt exceed 30,000 psi .... called the 'endurance limit' of fatigue. Those keel bolts that were designed before the mid 1980s would be considered to be greatly 'underdesigned' by todays standards .... now that we better understand 'stainless steel', with respect to its fatigue propensity and its propensity for crevice/intergranular corrosion. For such keel repair - for me - using the same bolt materials, I'd at least double the 'number' of attachments of the original design. To repair such keels with the SAME size and number of fasteners would lead to the exact same result ..... its a FAILURE. The original design was inherently weak - by todays knowledge and standards.
Keel calcs..
That Green Keel Main Sail showed has 8 bolts at 11/16 each. Total area is 8 * Pi*5.5/16^2 = 2.96 sq. in. If that green keel weight is around 5,000 pounds, the load those bolts would see would be about 5,000 / 2.96 = 1,689 psi. Now I know that the bolts will not share load equally and there must be a de-rating for that and there are probably numberous other factors to de-rate but, using your numbers of 30,000 psi, I would say those bolts have a significant saftey margin already. Why then RichH do you think that the green keel is underdesigned? Or, are you talking in general terms about keel bolts?
That Green Keel Main Sail showed has 8 bolts at 11/16 each. Total area is 8 * Pi*5.5/16^2 = 2.96 sq. in. If that green keel weight is around 5,000 pounds, the load those bolts would see would be about 5,000 / 2.96 = 1,689 psi. Now I know that the bolts will not share load equally and there must be a de-rating for that and there are probably numberous other factors to de-rate but, using your numbers of 30,000 psi, I would say those bolts have a significant saftey margin already. Why then RichH do you think that the green keel is underdesigned? Or, are you talking in general terms about keel bolts?
Why then .....
There is a relationship between intergranular corrosion and fatigue failure. Stainless when designed for cyclical stress starts to form micro fatigue cracks at or above 30Kpsi. Starting from day 1, these microcracks are additive. Such cracks are the sites for crevice corrosion to begin. Yup, a Factor of Safety of 3 consistent with a 'coastal' design would be that the stainless max. load would be AT ~30kpsi. To keep well below the fatigue endurance limit would have to raise the FS to at least 4; therefore, the design is 'light'.
There is a relationship between intergranular corrosion and fatigue failure. Stainless when designed for cyclical stress starts to form micro fatigue cracks at or above 30Kpsi. Starting from day 1, these microcracks are additive. Such cracks are the sites for crevice corrosion to begin. Yup, a Factor of Safety of 3 consistent with a 'coastal' design would be that the stainless max. load would be AT ~30kpsi. To keep well below the fatigue endurance limit would have to raise the FS to at least 4; therefore, the design is 'light'.
One sturdy Keel
The keel bolts for that green keel have a max load of 1,689 PSI, by doubling them as you suggest, it would reduce it about 850 PSI. In terms of analogies, it would be like putting a max load on an 8-32 screw to 15 pounds. RichH, If I need an unsinkable ship I will have to hire you for the design team
The keel bolts for that green keel have a max load of 1,689 PSI, by doubling them as you suggest, it would reduce it about 850 PSI. In terms of analogies, it would be like putting a max load on an 8-32 screw to 15 pounds. RichH, If I need an unsinkable ship I will have to hire you for the design team
hmm
a few weeks ago, I noticed my boat's (on the hard)keel bolts were loose-ish when I removed the nuts to put a backing plate down. Upon re-torquing, a small amount of water squeezed out. I dug all the sealer out from the outside of the hull-keel joint, let it sit a few hours, sealed with 5200, but didn't drop the keel. Are you saying I will be causing ireversible damage if I leave it this way? Note: there was NO noticable leak from the keel - the water was bilge water that got down in the hole.
a few weeks ago, I noticed my boat's (on the hard)keel bolts were loose-ish when I removed the nuts to put a backing plate down. Upon re-torquing, a small amount of water squeezed out. I dug all the sealer out from the outside of the hull-keel joint, let it sit a few hours, sealed with 5200, but didn't drop the keel. Are you saying I will be causing ireversible damage if I leave it this way? Note: there was NO noticable leak from the keel - the water was bilge water that got down in the hole.
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