Aft Keel Bolt on 411-what am I looking at? Hi all,
My 411 was leaking when I bought it. I have about an 1/8" gap at the rear of the keel when my boat is in slings, which should explain most/all of the leaking So I decided to tighten up the rear keel bolts. The good news is that they are exactly where they're supposed to be. Further good news is that I didn't have to remove the engine to access the aft bolt.
After drilling through the tunnel and the resin seal over the bolt, I came upon old packing. As I dug down through the packing, I came to this (see photo). I expected a nut. Is this just a spacer over the nut? I don't know why Nautor would have bothered. They only packed around the bolt threads to protect them.
Dear Don
The laminate is quite thick at the last bolt. You can make an estimate by comparing to the level at the bottom of the bilge sump aft of the lifting eye, and consider that the top of lead slope seen forward of the eye continues aft.
It appears there is a sleeve around the bolt, the purpose may be to extend it. Suggest you extract the sleeve and see what is found.
In order to tension the bolt properly there has to be a BIG washer under the nut.
Kind regards
Lars
Once I fully cleaned out the packing, I was looking at the nut after all. The top few mm just looked like a washer. Oops! I was able to tighten the nut between a quarter and half turn. that should dramatically reduce leakage. Now I'm digging the other nut/bolt just forward of the aft bolt. You're right--it is really buried.
Dear Don
It is suggested that you check the size of the washer under the nut. If too small, the laminate is slowly compressed under load, and you will have the same problem again.
Kind regards
Lars
Thanks for the advice. I'll check the size of the washer. Do I understand correctly that we're talking thickness? If necessary, I would add a second or third washer? What's the best way to lock the nut in place--a second nut on top?
I'm tempted to pack the bolts with cotton thread and a soft sealer over the top so I can tighten again in a year or two.
Don
The washer should have enough diameter in relation to the bolt, here about 3" would be suitable, with the thickness 5/16". Assume the bolt has M20 thread.
It might be advisable to recess the nut into the washer to avoid cutting a recess for it.
If there is much packing around the bolt the washer may bear only partly on laminate, and then the recommendation is to replace the packing with a harder material. Chockfast epoxy or similar can be cast in place.
For locking of the nut either a half height lock nut, or Loctite thread lock can be used
Kind regards
Lars
I'll start looking for a suitable washer. I finally got the second keel bolt cleaned out today. Its the second one forward from the backend of the keel. And the nut is nearly 3" down. I know how archeologists who chip bones out of rock feel. Like the aft most bolt, it tightened a good half turn.
Here are two photos. The first show both of the aft most keel bolts. The second is a close up of the deeply buried bolt.
Having been intrigued by the thread about the keel bolts and nuts, I wish to check few aspects with you. let me first describe what I can see under the mast step. I have also included some pics. Questions:
1/ is the mast shoe/step attached to the steel web through which the bolts and nuts appear? It is very difficult to assess this. If such is the case, replacing the mast step will necessitate the unscrewing of the keel nuts. I hope that i am wrong.
2/Looking at the attached pics, one can see that the keel bolts and nuts are on top of the bottom plate. This plate seems to be attached to the rest of the steel web constituting the mast step construction. Is it so?
3/If such is the case, and since the bottom plate is partly corroded, I am asking if there is another plate embedded in the joint section hull/keel? I hope so.
4/ I have tried to tighten the nuts without any success. There seem to be no way of moving them at all.
Summarising: is there an embedded plate under the nuts or is the steel web of the mast step the only thing there is?
Thanks a lot for any comments and help in understanding this issue.
Don, thanks for exposing the second nut from the back. I had the keel taken off a few years ago but did not get to see all the bolts positions during the works. So this one is a revelation!
Have you got any documents showing the positions of the keel bolts?
Dear Philippe
Your post dated Sept. 2014 passed unnoticed at least to me. Here the answers, regret the delay.
1/ The lower steel flange supporting the keel bolt nuts is an integral part of the mast step assembly, and the nuts have to be unscrewed in order to release the mast step.
2/ Pls see point 1/
3/ There are no other plates.
4/ The M24 nuts have originally been torqued to 260 Nm, and the M30 to 510 Nm, and you need equipment developing such torques to make the nuts move.
Kind regards
Lars
I don't remember the exact dimensions, but they're in an earlier post. It takes some faith because you can't find the bolt until you've drilled through both a fiberglass "tunnel" and through a layer of the hull. Then you have to go through at least an inch of packing. Fortunately, I didn't have to pull the engine. I have a newer Volvo Penta that apparently is a little shorter than the original engine. I did have to remove an accessory tray, however.
As a final note, once I put the boat in the water, I had several leaks and had to pull it back out. I noticed that there was still some cracking at the aft end of the keel. I pulled my new backing around the aft bolt and found that I got another full turn out of the nut. Interesting, because I "really" tightened it the first time. I fixed the other leaks as well. The boat is nice and dry now, so I must have finally closed the gap.
Don
If there were leaks this means that water entered along bolts, and then it is not sufficient to stop the leak just by tensioning the nuts. The bolts MUST be sealed with mastic all around right down to the lead so water is not able to stand in any void around them.
Stainless is sensitive to crevice corrosion, and water in a narrow slot develops a lack of oxygen which is the basic reason for this type of corrosion.
The appended photo shows what can happen if this goes on for a long time.
Kind regards
Lars
My apologies, Lars
I wasn't clear about the origins of the leaks. The stuffing box was not reinstalled correctly so we had to pull the boat back out of the water. At that time I noticed there was still an open crack at the keel interface. That's when I re-tightened the bolts. Even though I had used a long handle the first time to get sufficient torque, I apparently didn't seat the rear keel bolts sufficiently. I don't believe that water ever entered the hull around the keel bolts.
Don, I cannot remember the advice given by Lars about when and where to give the keel bolts the final turns. Either when standing on shore or when in the yacht is in water and the hull takes its proper shape.
Dear John
The recommendation is to tighten the bolts with the yacht ashore standing on the keel.
Torque recommendations available on request.
Kind regards
Lars
The boat was standing on its keel both times. Not sure why I wasn't able to take up all of the slack the first time. Fortunately, I got the opportunity to do it a second time.
