fsiljelof

Keel joint cracks - epoxy?

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What is the best way to deal with cracks in the keel joint? Flexible epoxy? If so, can a flexible epoxy be coated with a normal epoxy primer? This is an old image, now the hull is painted white with epoxy and I’d preffer a white solution - is there a white flexible epoxy? Or can I paint it with durepox?

A4AA62AA-A320-4C37-9500-FC5C5615AE34.jpeg

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Keel joint cracks are typically between the stub and the keel.  I think you have something else going on.  If that was a faired in flange the crack would be parallel to the keel.

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And there's ferrous metal in there.

I'd sand it down to find out what's going on under there.

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7 minutes ago, SloopJonB said:

And there's ferrous metal in there.

I'd sand it down to find out what's going on under there.

I did sand it all down last year after this picture was taken - there is a steel plate behind ... refilled it with epoxy filler and coated it with primer last year - now they are back :-( 

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41 minutes ago, Blitz said:

Keel joint cracks are typically between the stub and the keel.  I think you have something else going on.  If that was a faired in flange the crack would be parallel to the keel.

I’m sure its steel behind, opened it up last year, I can’t think of anything else than that it’s bolted to the keel -any other idea?

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20 minutes ago, Blitz said:

Some sort off steel frame glassed in that the keel bolts to?  What boat?

Yes exactly, it’s a Prima 38 

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Not familiar with the boat but someone here should be.  My guess is the frame is corroding and swelling inside the laminate and that outside skin couldnt take it anymore.  Not sure its an easy fix.

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7 hours ago, fsiljelof said:

I did sand it all down last year after this picture was taken - there is a steel plate behind ... refilled it with epoxy filler and coated it with primer last year - now they are back :-( 

Welcome to the club of steel keels :) 

It is difficult to know exactly why it looks like it does, I guess these mis-colored lines are just the surface results of the epoxy filler you used. 

Sand it down again and this time use an epoxy paint made for painting on steel keels (at least earlier thera was VC Tar, should be painted in a minimum of 6 layers. An alternative is Interprotect - temp has to be above 10 centigrade when using this as it it is very thick - personally I prefer the epoxies with low viscosity, ie thin,  they at least give the impression of penetrating into all small holes ). 

Epoxy filler is not as good as a barrier as epoxy paint is. The filler is to be used as a ... filler (putty).

Myself I am using Sikaflex as the filler outside the epoxy paint, to even out things. Those epoxy fillers I have been using (mainly "Watertighte") is too hard and brittle wheras Sikaflex can take up rather much flex. 

Even so, this is a recurring procedure. Not every year, but rather often. 

From what I have seen the Prima 38 is a quality boat, very well built. Made for racing with possibility to cruising. A fast boat, can really challenge many of the hott new ones.

//J 

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I should add .... when you have sand it, paint it with VC Tar the very same day. If you plan your work you will be able to paint two layers the first day - no sanding between layers.

VC tar contains some amount of solvent, this makes it "thin" and easy to work with. Drawback is ... the solvent. If has to disappear. Temp should be at least 5 centigrade, preferably 10-15-20 - planning this work has to be a compromize between when you have to launch and the temps (just noted you are in Stockholm area, lousy spring this year but now things are picking up it seems).

It is also possible to use eg West system epoxy, or NH epoxy - but be aware these are difficult to handle for the antifouling paint. VC Tar is compatible with many antifouling paints.

//J

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56 minutes ago, Blitz said:

Sailboat data says lead ballast but they arent always accurate.

Most probably the case. I was sloppy earlier on. But there is something in steel attached to the hull, lead doesnt coorode- not in this way at least.  Ballast probably as a bulb - maybe there is a steel thing between the bulb and the hull?

//J

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1 hour ago, Blitz said:

Sailboat data says lead ballast but they arent always accurate.

Hi the bulb is lead - the blade is iron 

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2 minutes ago, Jaramaz said:

Most probably the case. I was sloppy earlier on. But there is something in steel attached to the hull, lead doesnt coorode- not in this way at least.  Ballast probably as a bulb - maybe there is a steel thing between the bulb and the hull?

//J

Hi the keel blade is iron - only the bulb is in lead ...

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10 minutes ago, Jaramaz said:

Most probably the case. I was sloppy earlier on. But there is something in steel attached to the hull, lead doesnt coorode- not in this way at least.  Ballast probably as a bulb - maybe there is a steel thing between the bulb and the hull?

//J

See post 7, there is some sort of steel frame in the laminate of the hull.

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9 minutes ago, Blitz said:

See post 7, there is some sort of steel frame in the laminate of the hull.

On that I am not so sure. Stell frames use to be either inside - maybe bonded with grp, but still on the inside, as frames. Or on the outside. Again guessing, this is something on the outside, bit wider than usual, to give a large attachment area. That would be a good way to handle to rather high loads from the sail area and bulb hanging ~ 2.5 m down. So I think this is a part of the keel blade. (there could even be a corresponding steel frame on the inside - that would be a very solid construction.

OK, this is a guess. I did see what the OP answered, but to have a steel fram in the laminate is unusual. And dumb. But of course, you never know.th

If it is as I guess, it is  simple to fix. If it is as you (Blitz) say, then .... more difficult.

//J

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1 hour ago, fsiljelof said:

Hi the bulb is lead - the blade is iron 

"stainless" is not always stainless.  I like Jaramaz' idea to block the moisture, then maybe even another layer of glass and fare it out.  Water is getting in so there is some degree of flexing going on.  

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That looks as though your boat is trying to emulate a hotdog. It is either the bun wanting to let go of the sausage which is serious or purely superficial where only some ketchup/mustard is leaking out. I suspect the latter and so you can only hide it as impossible to stop without remaking the entire hotdog from scratch.

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5 hours ago, Jaramaz said:

On that I am not so sure. Stell frames use to be either inside - maybe bonded with grp, but still on the inside, as frames. Or on the outside. Again guessing, this is something on the outside, bit wider than usual, to give a large attachment area. That would be a good way to handle to rather high loads from the sail area and bulb hanging ~ 2.5 m down. So I think this is a part of the keel blade. (there could even be a corresponding steel frame on the inside - that would be a very solid construction.

OK, this is a guess. I did see what the OP answered, but to have a steel fram in the laminate is unusual. And dumb. But of course, you never know.th

If it is as I guess, it is  simple to fix. If it is as you (Blitz) say, then .... more difficult.

//J

I’m 90% sure it’s part of the keel, never had any cracks in the actual joint hull/blade, I think the keel is sort of a T bolted to the hull - as the keel moves a litle movement is larger in the T edges - gelcoat cracks water comes in and rust comes out :-( nothing visibel on the inside - nothing looking like a steel plate on top or in the laminate from the inside.

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Looks like what a farr40 keel looks like when it’s bolted on wet. 

 

Theres a big steel flamge that recesses into a depression in the hull- there’s water in there for sure- you can bog it all you want but it’ll still weep until you remove the keel fin, remove the corrosion and properly rebed the keel-  

until then, you’re chasing your tail.  

 

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1 hour ago, USA190520 said:

Theres a big steel flamge that recesses into a depression in the hull- 

USA if so that must be the largest keel flange in human history and they then glassed over it?? They might as well continued it and had a steel hull.

If there is no steel plate the hull laminate has sheared and the stain is caused by water egress.

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5 hours ago, fsiljelof said:

I’m 90% sure it’s part of the keel, never had any cracks in the actual joint hull/blade, I think the keel is sort of a T bolted to the hull - as the keel moves a litle movement is larger in the T edges - gelcoat cracks water comes in and rust comes out :-( nothing visibel on the inside - nothing looking like a steel plate on top or in the laminate from the inside.

Yes, most likely. The usual theory goes along the difference in thermal expansion of steel and GRP and the difference in temps when on the hard in a climate as in Sweden: difference in thermall expansion coefficient is about a factor of 2 (depends very much on GRP, glass fibre orientation and so on) and temp swing is 50-60 centigrade.

Steel alwyas rust, we can just slow down the process. Sooner or later you will get som rust spots on the blade as well - that is just natural. To some extent the rust is merely cosmetic, but it is always good to control it. In particular in the area wher the keel is bonded to the hull rust should be kept to a minimum, ironically that is also the area where rust appears most easily due to the reason mentioned above.

Walk around in the "boat yard" where you have your boat, look at the different keels. Most are made in steel, and most have some rust spots.

Good luck with the work.

//J

 

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9 minutes ago, jack_sparrow said:

USA if so that must be the largest keel flange in human history and they then glassed over it?? They might as well continued it and had a steel hull.

No so large, from the picture it looks like it is just some 10 cm wide at each side, measured from the keel blade. Just a good way to spread the loads over a wider area, in contrast to some other boats that have been discussed.

There is no information indicating it has been glassed over. Painted, yes of course.

//J

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47 minutes ago, Jaramaz said:

No so large, from the picture it looks like it is just some 10 cm wide at each side, measured from the keel blade.

Jara with some reference it is impossible to tell. My eye says more than double what you see.

50 minutes ago, Jaramaz said:

There is no information indicating it has been glassed over.

The OP says as built it is glassed in with gelcoat. He has attacked it before, filled and painted it.

On 08/04/2018 at 8:45 AM, fsiljelof said:

Yes exactly (glassed in), it’s a Prima 38 

 

6 hours ago, fsiljelof said:

gelcoat cracks water comes in and rust comes out

 

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2 hours ago, jack_sparrow said:

Jara with some reference it is impossible to tell. My eye says more than double what you see.

The OP says as built it is glassed in with gelcoat. He has attacked it before, filled and painted it.

 

 

10cm sounds on a little low, however it’s not much more - I’d really think it’s the Farr solution - many other ideas from that design in the Prima - I redid the hull last year, the keel is up this year,  the image here might show proportion. By glassed in - it was only glassed by 1 or 2 layers, the entire keel blade was also glassed in one or two layers - not constructional, probably for painting or fairing?595D1221-CD9A-435B-AAB9-74983C087A49.thumb.jpeg.e97807f66607a851dc963fd3050cd32a.jpeg

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22 minutes ago, fsiljelof said:

the entire keel blade was also glassed in one or two layers - not constructional, probably for painting or fairing?

That answers your question. It is a encapsulated keel utilising a flange. While this approach OK for old/long cruising keels, not exactly a very friendly approach for dropping a fin keel that is more prone to transfering excessive loads to structure (seems you have had a laminate failure and moisture has got in or under torqued or even failing keel bolts) and so requiring regular fixing and or inspection. Would have been far smarter to forget the encapsulatuon.

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^^^To add to my post above here is what you should do IMHO.

A. SEEK BUILD DETAILS

You have a production/semi production boat. Source the keel structure details and dimensions incl recommended keel bolt torques.

B. FIND THE CAUSE

1. Check and rectify if necessary the torque on the keel bolts. Uniform starting torques close to recommended is good. No uniformity/under torqued is not good.

2. You can then satisfy yourself that the keel bolts with adequate sized and thickness washers are not the cause of any movement between keel and hull structure.

C. RECTIFY

1. If the answer to A. above is  negative you have to drop the keel and replace keel bolts. See Items 4 & 6 below.

2. If the answer to A. above is positive then the source of moisture ingress is laminate failure either over the flange/at its surrounds and or around the flange in the hull structure. 

The former is maybe a cosmetic issue and a relatively quick fix.  Refer Item 3. 

For the latter the keel has to be dropped. See Items 4 and 6.

NB. Without knowing the flange dimensions the absence of uniformity and not thinking a flange would be so wide leads me to think there has been a surrounding laminate failure caused by groundings and or a skinny laminate design.

3. Mechanicaly prep steel and lead bulb back to bare metal. Coat with a 2 pack underwater rated paint system within 30 minutes before metals start to oxidise. Fill, fair and apply a epoxy barrier coat followed by your prefered paint system.

4. If dropping the keel there is no point preserving encapusation in part or in full. Mechanicaly remove the laminate sheath (that can't be grit blasted off). Grit blast the fin and bulb back to bare metal and coat with a 2 pack underwater rated paint system within 30 minutes of completion before oxidisation starts.

5. Rebuild structure under and around keel box area as required to suit a non-encapsulated outcome. 

6. Refit keel, fill, fair and apply a epoxy barrier coat followed by your prefered paint system.

D. EXPERT ADVISE

The above is for guidance to seeking professional advice and then assessing it. Their advise will be guided by yours being your boat being a keeper or you are trading up/getting out.

The internet is full of free advice like mine, you only get what you pay for.

 

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10 hours ago, jack_sparrow said:

The internet is full of free advice like mine, you only get what you pay for.

Very true, these words. Where Jack sees close to immediate disaster I just see the same rust we all (in Sweden with the temp diffs) have with steel keels. I have about the same on my boat, and had similar on the previous ... and so has all other with steel keels (in Sweden ...). 

This Prima is about 15 years old. Far too early for the keel bolts to be in danger - depends of course on where the boat has been, how it has been sailed and so on. If one feels unsure it is possible to check the keel bolts torque as Jack mentions; I did that on a previous boat - torque was beyond the designers values.  

To drop the keel is a huge operation, not something to embark on without substantial reason. 

Glassing in the keel blade is to invite problems with rust. Maybe a previous owner wanted to "improve" the blade profile - that was popular some years ago. The flanges are probably glassed in to give a smooth surface. Myself, I would remove all that and paint with epoxy. OTOH - not very critical. 

The rust seen in the picture should be stopped, however. You do not want this to develop. 

//J

 

 

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Thank you all for very wise advise, I’m pretty confident it’s the Farr type of keel and so far I think the keel bolts are safe, I’ll grind it down again, I’ll try and get all rust out of there, prime it all ASAP after with epoxy primer - I’ll check the nuts on top, but I don’t think I’ll be able to find factory torque, Seaqust are long gone and so seams all knowledge of the design - I’ll refill with a flexible epoxy filler - hopefully it will slow things down - next winter or in the future, I’ll check my options om dropping the keel, sounds a bit drastic and expensive, but a refit like the Fart above is tempting and I guess it could be combined with some profiling work on the blade and bulb.

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Torque is based on the bolt size, material and thread count - not on what it's bolting.

It doesn't care if it's a bridge gusset or a sailboat keel so "factory torque" is not a factor.

Look it up on any of the numerous tables available on the Interweb.

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1 hour ago, SloopJonB said:

Torque is based on the bolt size, material and thread count - not on what it's bolting.

It doesn't care if it's a bridge gusset or a sailboat keel so "factory torque" is not a factor.

Look it up on any of the numerous tables available on the Interweb.

Here's a table for up to 1 1/2" dia bolts: http://www.engineershandbook.com/Tables/torque3.htm

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12 minutes ago, 12 metre said:

Here's a table for up to 1 1/2" dia bolts: http://www.engineershandbook.com/Tables/torque3.htm

I think that in those kinds of tables torque is being used as a proxy for stress. The condition of the threads will change that relationship. Thus, the "dry" specification (ie. as new without lube). Also, any movement or sticktion, etc in the system (eg. bedding goo) could invalidate the torque to stress calcs. On the third hand, there's a technique to taking torque readings. In practice it tends to work but typically neither the spec nor the measurement are exact or foolproof. A manufacture may have considered these kinds of complications and could provide practical guidance. In theory. IME, not so much.

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I've done a couple of keels - one new mount of an IOR lead fin and one remount of an iron fin fairly similar to the one being discussed - flange top on an iron keel with a bulbed bottom and mounted in a rebate in the hull - not as radical as the one under discussion but kind of close.

Following engineering tables for torque worked just fine in both cases. Torque tables usually assume lubed threads and a little bit of 4200 that may get on the threads is not going to change the torque readings enough to matter (or even measure most likely). In my case I lubed the threads with anti-seize to help avoid galling of the stainless.

In my experience the majority of keel bolts are tightened with a piece of pipe over a breaker bar and tightened "until the suckers screamed". Any sort of measured torque is a huge improvement over that.

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45 minutes ago, SloopJonB said:

Torque tables usually assume lubed threads

IME, they usually specify. The torque tables linked by 12 metre are for dry.

 

 

 

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26 minutes ago, weightless said:

IME, they usually specify. The torque tables linked by 12 metre are for dry.

 

 

 

My mistake.  I just pasted a link to the first table I stumbled across that had large dia SS bolts.  i didn't notice it only had dry values.

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main.php?g2_view=core.DownloadItem&g2_itFor reference, this is a Farr40 keel, note the size of the flange in comparison to the cracks shown above- 

 

 

 

 

 

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Thanks an exact match :-) at this time I’ve grinded it all down once again and it is very clear I’m dealing with the Farr type of flange ... the flange has been fitted in sort of a ”void” which has been filled with epoxy? not with glass anyway - the ”box” is about 10-20mm larger than the keel and the cracks are formed in the outer part of the box, that is why it looks a bit ”larger” in the picture

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1 hour ago, fsiljelof said:

the flange has been fitted in sort of a ”void” which has been filled with epoxy? 

Not epoxy. The recess is gelcoat off the  mould. They would have either bedded the keel flange in filler or sealant. My guess if orginal the former and then filled and faired. The barrier coat over the filler is either non existent or compromised and that is what is holding moisture and the flange rusting accordingly. Should be a relatively cheap fix subject to investigation.

PS. To call a flanged keel a Farr style is a bit of a misnomer. It is a far superior style of keel attachment as it maximises the lateral keel bolt spacing and carries the keel loads to the hull structure far more effectively even though the keel fin thickness is optimised. Farr I think persevered using this approach longer than most designers even though it added more cost compared to a simple hull/bolt up configuration now favoured by many but very an much inferior approach. I'm pretty confident your keel will not be falling off in a hurry.

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Usually the keel bolts are bedded in sealant with a bead around the flange then filler is faired around the void then sealed with epoxy and bottom flavor du jour.. 

The only remaining issue is weather salt water has gotten under the flange, if so the salt will retain moisture. Most likely it’s just the edges of the flange that are rusting but check carefully for voids or cracks in the filler, usually if there’s water in there it will migrate up under the flange between the filler and flange. Hence the suggestion to pop the keel off, clean and rebed it. But you’ll know next year if that’s the case- 

do yourself a favor and make a template of the recess so in the future you can put the template up, trace it and know exactly where the recess is and you can save a lot of grinding- 

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This is the recess of the 40- note the cut out- it’s been templated so once the location is found you can run a circular saw thru the filler opening up the recess

1C12E6C1-79B2-402A-B45F-15D46353AE95.png

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The flange and hull about to be mated-  note the flange has been coated with a barrier coat (yellow) to avoid rust. 

 

C47F1BAD-CFDE-46ED-A86E-2692362D05A8.png

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8 hours ago, jack_sparrow said:

PS. To call a flanged keel a Farr style is a bit of a misnomer. It is a far superior style of keel attachment as it maximises the lateral keel bolt spacing and carries the keel loads to the hull structure far more effectively even though the keel fin thickness is optimised. Farr I think persevered using this approach longer than most designers even though it added more cost compared to a simple hull/bolt up configuration now favoured by many but very an much inferior approach. I'm pretty confident your keel will not be falling off in a hurry.

Here are some photos and details of the build of a Davidson 29 which pre dates the Farr 40 by almost 10 years.  The  original lead bulb keel was recently replaced with a deeper T-keel.

Even the Cal 20 circa 1961 used a similar attachment. http://sailboatdata.com/viewrecord.asp?class_id=76

A couple of things about the Davidson: epoxy filler  is referenced in the drawing, and a bronze keel top/flange was used rather than steel

10858397_861583700539080_5250755233767419358_n.jpg

1610827_861582757205841_3355222624268380580_n.jpg

11330030_955662794464503_6074540196655427115_n.png

10453370_966821033348679_316134894633413159_n.jpg

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