Keel Bolt Repair Trailer Sailor

[Tops]

Hello Boat Design Peoples!
My 40-something year old trailer sailor (Luger Southwind 21) was laid up with 5/8" fiberglass (roving visible) at the keel and then had a 'grid' of sorts (3/4" plywood over the keel, 2" deep floors, all glassed with .094" mat) glassed in and then was drilled for the (8) 1/2" SS through bolts for the external keel. Some the of the bolts had a sloppy coating of old orange RTV and a couple of those would leak as sailed and the plywood and timbers in the wood and chopped strand mat grid are discolored. Inspecting a couple spots I see rotten plywood. I am sure these holes were never over-drilled/filled with resin/and re-drilled to make them waterproof...

So, a couple/few questions:
1. How to seal these holes going forward?
2. Could a repair e made with oval patches of fiberglass board, removing mushy plywood and glassing all back into the 'grid' and down to the hull?

Sailing looks good this weekend, considering a temporary fix to the one hole back to better than status quo and doing a deeper dive later.

Thanks for your consideration and ideas!

 

[kapnD]

Looks to me like you’re on the right track to repairs, the encapsulated wood is the weak link here, it may need to be entirely removed, as I can see black spots clear up against the bulkhead end.
A nice thick chunk of G-10 channel bedded in epoxy would do nicely.
If the holes are enlarged and filled, I’d recommend to glass heavily over the entire top, overlapping onto solid hull laminate.

 

[Tops]

Aloha and mahalo KapnD!

With the channel, were you thinking the hollow side up between the floors? And yes, tie it all together with cloth and resin to the existing grid and hull.

I work in a facility that consumes FR4 (epoxy+fiberglass) boards and the scrap is available so I was thinking to use that to replace the rotten wood at the bolt locations. It comes in 1/4" (6.4mm) so I was going to do at least 2 layers or maybe 3 which would put me back to nominal with a little sanding. I am wondering if the oblong shape is really necessary to prevent a hard spot/fault line or if a simple hole saw (between 1.25 and 2" diameter) and dig out-fill in-glass over is adequate for this repair.

 

[fallguy]

Well, I'm not qualified to answer, but not unwilling to ask a question or discuss.

The floors here seem to be structural. They keep the plywood keelson from movement. Repairing a single area of rot of the keelson is not a structural repair because you cannot intertwine the wood fibers. Even using epoxy and a section of G10 as a plug does not offer significant strength against sheer on my instinct, although can be calculated.

In order to do a structural repair, the keelson needs to be as strong or stronger than before. So the G10 plate would go between the floors on top of the keelson after the keelson is fixed and then all of that would be tabbed back onto the floors and hullsides which means the G10 would need radiuses on the side edges. Then the floors would get fillets and the keelson/hull intersection fillets and then glasswork would go onto the hullsides and onto the floor sides. But then the keelbolts are short as is..sometimes it matters, here probably not?

Alternatively, you show four floors which could be removed after the keel is, and the entire keelson replaced instead.

I'd do the repair in epoxy because it is not very much material and the cost savings for esters will not be great.

Before you go too far, I recommend you do a bit of math on the repair. You ought to know the strength of a plug versus plywood. It is easy to get caught up on 'anything is better', but that is not really wise.

 

[Tops]

Well, I'm not qualified to answer, but not unwilling to ask a question or discuss...Before you go too far, I recommend you do a bit of math on the repair. You ought to know the strength of a plug versus plywood. It is easy to get caught up on 'anything is better', but that is not really wise.

Welcome aboard! I appreciate the comments. Here is a concept I am working on to get me through the short season. Bolts are 1/2-13 UNC SS x 3" long (8 places).

 

[fallguy]

The thing to worry about is the keel falling off. If, for example, you remove the keelson completely, or effectively by rot, then the hull is the only thing carrying the keel. A large heel would allow it to break off easily. You know this already, but don't forget it in the process.

So, if you forget the keelson for a moment, the addition of a washer or plug adds to the ability of the hull to carry the keel.

Adding back, the bond strength of the plug to the old keelson is critical and really easy to do wrong. End grains like the keelson would be after cutting suck resins and the bond failure is quite easy to do. Using a structural bonding putty here as well as managing resin suck is important. For these reasons, I am not a big fan of counting on the plug and would not. So then you think, well, I am going to glass over it. But that doesn't help keep the keel from falling off; it presents a measure of coupon holding only.

I'd rather chisel off some amount of the keelson and replace it with G10 and structural putty which is what I believe @kapnD meant, perhaps.

so, instead, plug the rot holes say 1/4" low using structural putty (and your plugs) then chisel off the plywood between the floors about 1/4", and add back a G10 plate with structural putty and bolt to the plate...

this method will require the hull to break off the entire keelson and the keel would never push up through in a slight grounding, plus you can repair any extra rot you find

honestly, not sure you need todo more than tab the G10 to the floors this way as the glasswork offers little more than insurance to the G10 bond to the keelson

This bond is also subject to drysuck, so use caution and make sure and precoat the old plywood so that you don't create a bondline failure here either..

I can almost guarantee, as a builder, that I can create a bondline failure here, mainly on the plug, intentionally, by making a small error and no precoating that many would do without thinking.

 

[fallguy]

Bolting to your plug is not good, or insufficient in fewer words.

The keelson will be relatively easy to chisel down. Just run a small circle saw across it and chisel it off. On the edges by the floors, use an oscillating tool, but try not to go too deep and weaken the keelson that is staying..

If you have an access issue at the ends, you may end up short with the flat panel; I would glass over that and any other areas where the wood is exposed with epoxy as well. This would be a permanent repair.

You do need to make sure the plywood is overbored all the way because access later will be impossible from above. So, don't leave a good hole unrepaired..because if it leaks in 10 years, you won't know until the rot makes it to the edges

There is no 'short season' shortcut here, imo.

 

[Tops]

If I am understanding what you are saying...something like this with the red lines representing epoxy or structural putty and the doak rectangle replaced wood within the shaved-down keelson?

 

[fallguy]

I will not specify the repair for you. But I will tell you that this method avoids a bond line failure of the plugs resulting in a keel falling off because the keel is still supported by the keelson this way. The old keelson wood is thinner between the floors, but going to be pretty strong with structural putty. It would be good to get some other opinions.

I'm assuming you mean for the top of your drawing to be fiberglass. As long as you are glassing it, it would be wise to fillet the edges of the floors and make the glass tabbing a bit wider so it goes up onto the floor. The tabbing won't do much other than seal the remaining plywood keelson, but that is important

Also, to note, avoid cutting the entire keelson as you show in the drawing. Only remove rot. If the entire keelson is removed across it's width dimension, that changes the repair. In that situation, you would need to add layers of keelson and remove a floor timber.

 

[fallguy]

I see an awful lot of black here between the lower two red lines. If you take that whole section of keelson out, I'd probably modify the repair here so as to return some integrity to the section. Again, I am just a builder, not able to spec this, but wise enough to see trouble.

Also, are the floors cracked? They appear to have some stress cracks. That is a serious issue that must not be overlooked. If they cracked because of rotten keelbolts; they need replacement and the keelson needs to be inspected for deficiencies (cracks as well).

 

[fallguy]

Are there cracks on these blue arrows?

 

[fallguy]

If the floors are cracked as they appear; you need to rethink this whole thing....forget anything I said because this ain't fixing a rotten hole or two.

If not already, the boat must be grounded. And the hull needs to be checked for cracks by a surveyor.

I am sorry I missed it, but cracked floors you should have mentioned..

 

[Tops]

If the floors are cracked as they appear; you need to rethink this whole thing....forget anything I said because this ain't fixing a rotten hole or two.

If not already, the boat must be grounded. And the hull needs to be checked for cracks by a surveyor.

I am sorry I missed it, but cracked floors you should have mentioned..

Ain't fixing a rotten hole or two is a pretty good summary. Thanks for the input, will need to make decisions offline.

 

[fallguy]

If you need a surveyor near Duluth, I have a contact.

Please don't sail her on Superior or sell her, the boat has no flotation that I know of and would go down fast...the likelihood of loss of life here is high. As you said, season is short and water cold. Current sea surface temps are 6C, low 40s F. I love the lake and boats and fishing, so I keep an eye on it and fish the north shore, despite Wisconsin being better fishing.

The only way I see to do the repair on further knowledge here is a complete repair by removing the parts and getting the hull sounded. Work with a surveyor to avoid making quality decisions that could result in loss of life. A surveyor may tell you to scrap the boat and charge you an hour only.

I did not see those cracks until after I wrote the last post before I mentioned and zoomed it to look at the odd looking floor timber with the extra plugs, so please don't do a partial fix using my advice!

 

[Tops]

Hi Fallguy, I am not located near Duluth, thanks for being willing to 'hook me up' with a surveyor contact if needed.

Some more observations and thoughts:

1. Where the CSM (chopped strand mat and resin) is cracked on top of the floors, the plywood seems dry without cracking underneath. The mat is cracked in a very constrained location on the boat, between some of the middle bolts of the cast iron keel to hull and keelson assembly. I would have suspected the end ones to crack first if it were due to flexing of the hull or movement of the keel.
2. There are multiple locations where the original tabbing of the floors' CSM to the hull is de-laminated, allowing water ingress to framing members and underneath to adjacent locations.
3. There is no sign that the keel ever pivoted/levered on the hull or keelson to induce damage to the wood in the keelson or its CSM cover through the keel bolts.
4. There is moisture in the keelson at some of the keel bolt locations (I took one back to a 2" diameter hole so approx 3/4" in, still damp, known 'leaker'). This was the original problem cited in the post.

It looks like I am dealing more with a poor choice of materials (mat versus axial) and/or poor installation procedures (laminations and hole treatments that allowed water ingress) rather than a wholesale failure of the scantlings or 'ribcage' to support the hull and keel.

That said, replacing like for better with epoxy and axial cloths with proper surface prep and dry cores and proper hole filling would put me back at 'zero' plus better, but it is unknown if 'zero' was 100% adequate or if improvements should be made to the scantlings 'while I am in there' so to speak.

It would be great to hear from some others as well, especially those familiar with this size/vintage of sailboat.