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Thread: Ericson 30+ aft keel bolt nut replacement

  1. #1
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    Ericson 30+ aft keel bolt nut replacement

    I was moping up some water in my bilge with my wet/dry vac and decided to clean under an inspection plate for the aft keel bolt. The water was from rebuilding my head pump (yuck). I can see the bolt clearly but the nut looks like a rusty mess. It does not look like the nut could have been tightened all the way down by the way the hull is designed there. I am thinking about grinding off what is left of the nut, cleaning/treating the threads, and installing a new nut. I was also thinking about building up the contact point where the nut and washer will rest with epoxy. Does anyone know what size the nut is for the aft bolt and the torque that should be applied to it as well as the torque for the other bolts forward of it. My boat is a 1984. Comments and advice please. Thanks

  2. #2
    1984 Ericson 30+, Nanaimo, BC
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    I've always heard that one can only reasonably tighten keel bolts when the boat is on the hard, not in the water due to the weight of the keel. I think I recall the nuts being tightened to 150 lbs. but I'm not sure of that.
    If the washer and nut don't sit flat and even, I wouldn't hesitate to build it up with epoxy to ensure good support. I would not use Bondo or similar junk sold in some stores.
    Frank

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    It seems intuitive that you'd want to torque the bolts on the hard so the weight of the keel is supported and the weight of the hull "helps", but really, I think that if the keel bolts can't easily pull up the weight of the keel then they're not really up to the job of keeping it attached are they? The torque specs for the bolt/nut pairs are typically near to (with safely margin) the elastic limits of the bolts, otherwise a smaller/cheaper bolt could be used. The tension on keel bolts properly torqued are vastly larger than the weights of the hull and portion of keel being supported. A single 1 inch stainless bolt has a minimum tensile strength of nearly 70,000 lbs. (304 or 316 alloy) meaning you could easily lift 2 or 3 *times* your whole boat and keel off the ground with a single keel bolt and only load it up about half way. If your bolts aren't torqued properly they are subject to flexing/sheer loads and oxygen depleted salt water which are bigger concerns (in my opinion) than where you do your torquing.

  4. #4
    1984 Ericson 30+, Nanaimo, BC
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    It's not that the bolts can't take it, it's that you will find it challenging to snug up the nuts on the bolts if you also have to lift the 4,000 lb. keel. It's much easier if the keel is supported on the hard, as then you're just dealing with the torque requirements of the nuts on the bolts. But that's just my thoughts, and I could be mistaken. ☺️
    Frank

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    Moderator Christian Williams's Avatar
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    Flycav,

    You may possibly be overthinking this. Clean the rust off the nut with a wire wheel and see what you've got. It's stainless, and there's probably plenty of metal left. If there's pitting of the bolt itself, same deal. If the keel bolts aren't leaking there is likely no issue. All keels flex, few keels exactly conform to the hull shape, most keel/hull seals need recaulking.

    Take a picture, others can compare to how their boat looks.
    Thelonious II, E381 hull 513 (1984) Universal 5432
    Table of Contents for Thelonious Blog here
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    Quote Originally Posted by Frank Langer View Post
    It's not that the bolts can't take it, it's that you will find it challenging to snug up the nuts on the bolts if you also have to lift the 4,000 lb. keel. It's much easier if the keel is supported on the hard, as then you're just dealing with the torque requirements of the nuts on the bolts. But that's just my thoughts, and I could be mistaken. ☺️
    Frank
    That was the point I was trying to make: A single keel bolt torqued properly is pulling close to 50,000 lbs or so. Lifting just 4000 lbs is trivially easy for even a single bolt and you'll have a number of them, say 4 bolts needing to only lift about 1000 lbs each. A short ratchet on the nuts would suffice for that.

    Or think of it this way: torquing the nuts on the bolts will result in tension (pulling) in the bolts proportional to the torque, but much larger. That tension is simply that: tension, and is independent of what weight, if any, is hanging on the bolt. If there were more weight in the keel, there would just be less compression between the keel and hull for that given bolt tension. The tension force of the bolts (say 4 bolts pully 40,000 lbs = 160,000 lbs) is much larger than the weight of a 4000 lb keel so the keel is insignificant in the static forces involved, supported or not.

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    Moderator Christian Williams's Avatar
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    Good physics lesson. Recalls the inclined plane by which a jackscrew can lift a house.
    Thelonious II, E381 hull 513 (1984) Universal 5432
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    Principal Partner Kenneth K's Avatar
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    A note I made in an old file says "keel bolts 250-270 ft-lbs." I know I got that from an earlier post on this site. I'm assuming that is for the larger (mid) keel bolts and not the smaller fore- and aft- bolts.
    Ken
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    torque is based on the bolt size, more for bigger. The actual value to use depends more on the material/washers/location than it does for the bolt. If you torqued a 1" bolt to it's actual breaking limit (probably close to 100,000 lbs on the bolt!) it might push your nut right through the keel stub.

    For most boats

    1/2 (small) bolts get about 80 ft-lbs

    3/4 (mid) bolts 150-250

    1 (big) bolts 250-350

    J-boats recommend 165 for 1" bolts in J/109, for example, so there are variances and boat specific values.

    Since 300 ft-lbs is a lot of torque, most people don't have a way to practically apply or measure it. Think of wrenching a nut as hard as you can with as big an extension as you could fit perpendicular in your boat. Use the length of extension as the "torque" value, using "as hard as you can" as the constant. Say 1' or 2' extension for 3/4 or 1" bolts if you can lift 150lbs with both hands without a lot of pain.
    Last edited by debonAir; 07-12-2019 at 02:37 PM.

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