Keel

[Voyager1]

I have ODay 302 that has crack around the keel that leaks slightly, boat is out of the water in a cratal with mast down. I Would like to rebed the keel. My plan is to Loosen the keel bolt until the last couple of threads, use some screw jack and lift the boat off the keel 3 inches, clean the old sealant with acetone and scrapping, reseal with 5200. Boat is 4800lb. Not crazing about doing it this way but the boat yard is being unreasonable on what they want to do the work. Has anyone ever do something similar that could lend some advise.

 

[Tally Ho]

Your plan sounds pretty reasonable. You won’t be able to inspect the fiberglass layup in the keel,stub very well (a potential issue with this design O’Day (272 and 322). Not sure if you will be able to get a good look at the bolts (particularly between the nuts and the keel).

But I think you will be able to get a good bed of 5200 between the keel and stub. Getting the bolts torqued after will be key.

Let us know how it works out (photos would be helpful too). I should do the same to my 322. I torqued the bolts before I splashed this spring, and sealed the joint seam with a little caulk where it was cracked. But I would feel better making sure it was bedded really well with something like 5200. Not sure what happens if you ever need to separate the keel in the future though.

But I think the plan is pretty solid.

Greg

 

[njlarry]

I would most definitely not use 5200. It is unecessary and will make future repairs most difficult. What if you have a hard grounding? You'll curse using 5200 instead of 4200 or something else. Luckily the builder did not use 5200 so you can do the repair. It is only a sealant not a glue to hold the keel, the bolts do that.
With the keel off, check the stub fiberglass layup as that is one critical issue.
Good luck.

 

[Voyager1]

Thanks Greg, best encouragement I got. I will post some photos if it goes good,

 

[Richard19068]

Thanks Greg, best encouragement I got. I will post some photos if it goes good,

We would learn as much or more from photos if it goes bad.

Thanks

 

[Will Gilmore]

I don't see why you're plan wouldn't work great. I'm with njlarry on the 5200 vs 4200. Maybe raise the boat to clear the bolts so you can see their entire length.

Good luck.

- Will (Dragonfly)

 

[Voyager1]

njlarry
What am I checking for with the fiberglass layup . Thickness, condition. What is considered good.

 

[GregL564]

I respectfully disagree with the earlier posts about 5200 not being an adhesive or recommended for the heel/stub joint. 5200 is in fact exactly that. Or more precisely, a combination adhesive and sealant, with a tensile holding strength of 885 PSI when properly applied.


http://multimedia.3m.com/mws/media/434382O/marine-adhesive-sealant-5200-tan-06501-and-21450.pdf


Putting this in perspective, properly adhered and prepared, a surface area of only about 3 square inches would be sufficient to hold a 302 keel (2400 lbs)in place with no keel bolts (although I would never recommend that). Since the stub area of a 302 is probably 3-4 times that, you have a good margin of safety. And the 5200 is there, and originally used by manufacturers, to hold the keel in place, with the addition of the keel bolts as an additional factor of safety.

In comparison, 4200 has a tensile strength of only 180 PSI. That is much weaker than 5200, and would require a minimum surface area of 13 inches, with no margin of safety, to support the weight of the keel.

Also, I absolutely and strongly recommend using 5200, or something similar like Sikaflex, to reseal/adhere the keel to the stub. For the following reasons:

First, the bond, with both keel bolts and 5200, will be much stronger. The 5200 will spread the tensile load over the entire bottom surface area of the keel stub. This is much stronger than relying only on the single line of keel bolts (or a much weaker sealant like 4200), which will concentrate most of the weight and stress of holding the keel on those little stainless backing plates behind the keel bolts. That is pretty much a recipe for disaster. The stub was designed to hold the keel using both an adhesive like 5200 and keel bolts. You will compromise the integrity of the keel stub structure if you rely only on the strength of the fiberglass stub underneath the keel bolts, which it was never designed to do, likely leading to failure and possible disaster.


I also don’t understand the concern about 5200 being “permanent”. Yes, it surely is, and if you ever want to remove it, or whatever you seal/adhere to it, it is going to be really difficult. But we’re talking about the keel of the boat here… not something anyone should be thinking about removing every season. You want it to be permanent.

 

[Will Gilmore]

Greg,
Your logic is excellent, and I am inclined to agree with you. however, if there is need to drop the keel and inspect or repair a compromised portion of the keel to stub joint, as there is in this case, using 5200 means cutting the keel off as a permanently integrated part of the hull, not a bad thing at all, but dangerous in terms of accidentally damaging the stub plate when you don't need to. The bolts themselves, should be strong enough to hold the keel on, the addition of a glue seal may be desirable also, but making that joint easier to pull apart for repairs or replacement of the bolts, makes the whole job easier by far. I'm mostly going with my "gut" on this and am very interested in reading further arguments on the subject. If this is a job that is expected to be done periodically, use the easier glue to remove. If you have reason to believe it can be made permanent so there will never be a time to do this again, use the more permanent glue. Certainly there are lots of successful sailboats out there whose keels are mono-constructed.

-Will (Dragonfly)

 

[GregL564]

Hi Will,

Thanks for your comments. Good discussion. I should probably clarify what I mean by “permanent.”

For a 30-year old boat, I would say that even “permanently” bonded elements like the keel should be inspected for integrity and overall condition.

In the case of the original poster, it seems like someone glassed or epoxied over the keel joint. In doing so, they changed a joint that, because of the 5200, may have had some allowable flex in it; to a rigid, inflexible joint. It’s hard to tell from the photo whether the crack is superficial, caused by some lateral movement of the keel as the boat heeled, and for which the brittle epoxy skin was too thin to resist, or there was some impact damage (for which other evidence, such as a gouge in the keel, should exist).

In any case, I would advise that the poster drop the keel, inspect the integrity of the keel sump, and reinforce or repair if needed (I would probably reinforce in any case, given the problems with other 302s we’ve seen). With the keel off, I would inspect the condition of the keel bolts, and repair those if necessary.

Once all repairs and reinforcements are complete, I would reattach the keel with 5200. Why? Because at this point, I would take the strength and integrity of 5200 over the accessibility of 4200. If done properly, I would expect a 5200 joint to last at least another 15 years (based on how long the original seals/joints have lasted). No inspection required unless water starts seeping in from the keel joint, or if water seeps from the outside after hauling. In either case, that is an indication the seal has failed and some repairs are necessary.

If you use something like 4200 to bed the keel in order to make repairs easier, that would be like a self-fulfilling prophecy… using 4200 would I believe make it much more likely that you would be looking at another keel stub repair or failure in the near future. And that is one prophecy I would definitely not want to come true.

I don’t think it’s a question of the bolts being strong enough. Unless there is significant corrosion, they will always be strong enough to hold the keel. Again, unless there is corrosion, I don’t think I’ve ever seen a case of keel bolt failure. It’s always the fiberglass sump that fails, pulling away from the rest of the hull by the bolts. So by transferring and spreading the stress to a broader surface area, using a powerful adhesive like 5200, the joint is much stronger and less likely to fail. I’ve seen keels bonded with 5200 survive a hard impact on a granite reef. The keel was damaged beyond repair—wing bent back like putty—but the keel sump was undamaged and no water in the boat. Relying on only the fiberglass under the keel bolts I believe make it more likely that will rip out from the bottom in the case of an impact, leaving you with a pretty big hole in the bottom of the boat.

 

[Will Gilmore]

Thanks Greg,
You are making a convert out of me. Nice explanation and yes, great discussion.

- Will (Dragonfly)

 

[Voyager1]

Any ideal how much sealant will be required for a ODay 302 keel. I ordered thee tubes which is 30oz, looking at it, this does not seem enough.

 

[Davidasailor26]

Putting this in perspective, properly adhered and prepared, a surface area of only about 3 square inches would be sufficient to hold a 302 keel (2400 lbs)in place with no keel bolts (although I would never recommend that). Since the stub area of a 302 is probably 3-4 times that, you have a good margin of safety. And the 5200 is there, and originally used by manufacturers, to hold the keel in place, with the addition of the keel bolts as an additional factor of safety.

The potential flaw in the logic here is thinking that the 5200 will bond the keel to the whole hull. The problem is that it's a surface adhesive, so it actually only bonds to the bottom layer of the laminate. After that you'd be relying on the bonding between laminate layers to hold the keel on. The bolts and backing plate on the other hand rely on the full thickness of the laminate to support the weight.

 

[Davidasailor26]

njlarry
What am I checking for with the fiberglass layup . Thickness, condition. What is considered good.

Thickness of the laminate would be the priority to check. Search the archives here on some of the troubles others had with the layup thickness on the 3x2 series, particularly later hulls. I don't remember the recommended thickness but some of those posts discussed it.

 

[GregL564]

It is true that my assumption is that the 5200 will bond directly to the laminate (as opposed to gel coat, which is very weak). But fiberglass laminate is much stronger than 5400, so it should be able to hold whatever 5400 holds to it.

I haven’t yet found tensile strength values for fiberglass where the fibers are perpendicular to the load (which is the situation in the keel sump), but the tensile strength of chopped matt fiberglass—with only a few strands presumably parallel, is 22,000 PSI. Assuming that we would only want to count on 20 percent of that strength on a regular basis (a very conservative estimate), that leaves us with a tensile strength of 4,400 psi—well in excess of the strength of the 5200. So, properly applied, the 5200 will fail before the fiberglass. So if you have enough surface area for the 5200 to cover the load, the fiberglass will definitely carry the load, without (technically) needing the keel bolts. Again… I would never say not to use keel bolts, but the fiberglass laminate is well up to holding whatever the 5200 will bond to it.

 

[GregL564]

njlarry
What am I checking for with the fiberglass layup . Thickness, condition. What is considered good.

I would say add as much you can, limited by the length of the keel rods above the bolt (you probably still want a half inch of rod showing out of the top of the bolt). If you can get 1/2 inch or 3/4 inch of additional thickness, I would say that would be great, just based on the pictures of thicknesses of the keel sumps I've seen on other boats. I would also suggest using something like g10 plates to build up thickness and strength--easy to get and cut to fit. Embed them in epoxy, and that will make them part of the overall structure.

 

[Will Gilmore]

I haven’t yet found tensile strength values for fiberglass where the fibers are perpendicular to the load (which is the situation in the keel sump),

The fiberglass wouldn't be the structure holding the load in that case. It would be all on the resin and its adhesive properties. In that case, what you want to know is, how hard is it to pull layers of laminated glass apart. The glass is just a material in between the two points of force. On the other hand, in an underwater collision with the keel, the forces would be in sheer to the joint, not tension. Still, just the resin strength. That is the weaker section. 5200 would certainly stand up better under those conditions. If, the forces are strong enough to overcome the strength of the bolts, maybe there is no superior solution.

- Will (Dragonfly)

 

[GregL564]

It would be all on the resin and its adhesive properties. In that case, what you want to know is, how hard is it to pull layers of laminated glass apart.

- Will (Dragonfly)

That’s probably a good way of putting a lower bound on the strength of the laminate in that situation. Tensile strength values for resin is about 7,200 PSI, which is still well above the strength of the 5200, so I think we’re still in good shape—5200 will make for a strong bond, but it won’t be stronger than the fiberglass it is attached to.

Regarding the actual resolution of forces on the keel in the case of an impact, I agree that it is shear, and maybe some tension from the moment force as well. But it’s been years since I did any free-body force diagrams so I’ll have to tap out at this point.

 

[njlarry]

Thanks for all the tech specs on 5200 but I would still only use it for a hull to deck joint. There must be a reason the builder did not use it and there must be a reason the builder used all those keel bolts. Nothing is permanent on a boat but continuing repairs.
Your boat, your choice.

 

[Voyager1]

I finished raising the boat off the keel and adding 5200 to seal the keel today. Things went good. Photos attached. Raised the keel by cribbing it and using bottle jacks to lift the boat. Used the boat cradle for support. Cleaned the keel with chisele and acetone. Yard wanted 5K, Cost me 10oz if 5200. Thanks for everyone’s responsives.