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greendane

Core Sound 17 keel maintenance

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greendane    8

@PaulSmith -    When you say "on a bed of filled epoxy"--can you elaborate? Include wood flour to thicken it? And if so, how thick of a layer? I also assume I'll want to put a fillet the length of the keel on both sides. Should I put the fillet on at the same time as fastening the keel? Or will some of it ooze out and need to be filleted later? 

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PAR    188

Let's get the terms right. Bedding is a sealant and some (most) have adhesive properties. If it's "bedded" it's mechanically fastened (over bedding compound). These compounds run the range, but polyurethane and polysulfide are the modern choices. Some of the polyurethanes can rival adhesives. Bonding on the other hand, is like gluing. Thickened epoxy is the usual choice, particularly if you need to fill gaps. Gaps can be handled with a relatively heavy pile of goo on the centerline, which gets wiped off or filleted along the skeg. Once dry, temporary fasteners can be removed, if you used them. 

   Ooze out is desirable with epoxy bonds, as it's a simple way to determine if you've got good contact, between the parts. Again, this ooze out can be wiped away or made into a fillet. When bonding stuff with epoxy, just bring the parts in contact, but this is all you need. Excessive pressure from temporary fasteners or other means to hold things in place, can "glue starve" the contact patch, so just enough to make things touch the goo, but not so much it's "squished out" (technical term) of the joint.

   On your fillet or bond, I'd use a milled fiber and silica mix, no wood flour. You're bonding to a previously epoxied surface so this is a good mix. Make it stiff enough to not sag, which is about the consistency of peanut butter.

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Hirilonde    171

Jamestown Distributors used to publish a chart with the tensile strengths of bedding/sealants.  I found it very useful and memorized the key products I used  They went in order of bonding strength:

1. 3M 5200 - 700 psi  polyurethane - extremely adhesive ( I use this only when I see no need to take it apart ever.  There is a serious danger of damage doing so.)

2. 3M 4200 - 300 psi  polyurethane

3. Sikaflex 291 - 220 psi  polyurethane  (I use this when I really want white that won't yellow and I can live with the nuisance taking things apart later)

4. 3M 101 and BoatLife LifeCaulk - 150 psi  polysulfides  (These are my beddings of choice for hardware.  The only problem is that the white will yellow over time.)

5. Dolfinite - nil -  oil based goo - not an adhesive at all  (AKA  boatyard bedding.  This is the product from the old days.)

 

OK, they still have one, but I had to look:

https://www.jamestowndistributors.com/userportal/document.do?docId=1170&title=Marine+Adhesives+Strength+and+Usage+Comparison+Chart

 

I find the most important technique for using any but Dolfinite is to smear both surfaces and make sure no bubbles or voids exist, then put them together with at least some ooze out all the way around.  Masking can make clean up easier and in some cases I leave the ooze  to cut off later with a utility knife.

 

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Thrillsbe    62

My understanding of epoxy fillers is that cabo-sil has great tensile properties, whereas wood flour weakens the joint a little.  Wood flour's main purpose is to color the epoxy as it thickens.  This is why most builders mix it two parts of cabo to one part wood flour.  I'm not sure where MAS' Cell-o-fill falls in the strength category, but it is much, much safer to use than milled silica dust.

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Walt S.    14

Dave,

 

What bedding compound do you use with keel strips?  What if the keel strip is HDPE and nothing sticks to it?

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greendane    8
On 3/5/2017 at 10:56 PM, PAR said:

You don't need to fill the cloth weave, before attaching the skeg, just fasten/bed or glue it down. The thickened goo or sealant will fill the voids and fabric weave.

   The CS-17 needs a 2" tall skeg at the aft end, which quickly tapers down to 1" for most of its length to the bow. It's not dead straight but follows the keel profile for most of its length. Only the last two or three feet does it straighten out, being 2" tall just forward of the transom. I simply used a length of 1x2 stock,the full length, then tacked on a little triangular piece at the aft end. To get this triangular shape, I tacked a string about 36" - 48" forward of the transom and stretched it aft over a 2" tall block, mounted on the transom edge. I traced this shape, partly "letting" it (about a 1/4") into the 1x stock I'd previously installed. It was glued in place atop the initial 1x batten. I could have made it from one piece, but found this easier. I let it into the batten to prevent a feather edge on this triangular piece, facing the flow and to lock it in position. 

 

@PAR I just bent the pre-ripped 2X2 down on the hull to see how well it will bend. I will rip it soon and anticipate some of the effects I'm about to describe to diminish as the stock is reduced to 1" thick, but not entirely. There are some "high spots" along the line of the hull and consequently, when I bend it down, the keel stock bends up away from the hull. The brings up several concerns in my mind:

 

1) The epoxy goo is likely to get squished out too much where the pressure points are on these high spots. with not much material between the keel and the hull. Is this ok?

 

2) Should I build up more filler ahead of time in the gap? Or should I remove some wood from the back of the keel? Or will the screws mostly take care of all of this? 

 

3) I was hoping to use minimal screws to temporarily clamp this down. What's the best approach for how many to put down? And what is the best way to fasten? Screw in and then back out a little so as not to squish the filler out too much? Pre-drill? If so, should the pre-drilled holes be larger than the screw shaft? I read a little here (http://forum.woodenboat.com/showthread.php?138013-Removing-screws-used-for-clamping-epoxy-glue-ups) about using screws temporarily, but my situation is a little different.

 

Thanks in advance. 

keel stock pre-fit.jpg

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Hirilonde    171
4 hours ago, Walt S. said:

Dave,

 

What bedding compound do you use with keel strips?  What if the keel strip is HDPE and nothing sticks to it?

 

That's a tough one, because nothing sticks to it.  About all you can hope for is sealing the fastener penetrations.  I would probably try Sikaflex as it is a bit more tenacious than polysulfides and hopefully you can waterproof the fastener penetrations.  

 

Are you already invested in the HDPE?

 

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Walt S.    14
36 minutes ago, Hirilonde said:

 

That's a tough one, because nothing sticks to it.  About all you can hope for is sealing the fastener penetrations.  I would probably try Sikaflex as it is a bit more tenacious than polysulfides and hopefully you can waterproof the fastener penetrations.  

 

Are you already invested in the HDPE?

 

 

No, nor am I committed to buying some.  It seemed cheap and it would slide well if dragged.  

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Thrillsbe    62

If I were doing this job, I would use epoxy thickened with colloidal silica (taking extreme care not to breathe the silica dust).  I would use enough screws* to hold it in place until the glue cures.  No later than a day later, I'd remove the screws, and fill it with the same goop. I would not worry about gaps between the keel and the hull-- that's the beauty of epoxy!  This would set up the next owner nicely, when it came time to do this job again-- they'd just plane off the old keel and go again.  

 

* Torx-head deck screws are the least likely to strip out, followed by Robertson (square) drive.  The last thing you need is a stripped-out temporary screw!  (Been there, done that.)

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PAR    188

There are a number of ways to skin this cat. I was having a similar issue when I did the skeg, so I elected to scribe the profile and fit a filler piece, which I found faster and easier. I wouldn't worry about gaps, though I would grind down bumps to eliminate as many as practical.

   You do need to make a decision about bedding or bonding the skeg. The two are different and one doesn't need the other, if it's glued. I like to think about repairs and replaceability, so I went my way, but you may have different ideas or needs. Both a bedded or glued skeg can work just fine. Once the decision is made, you methods are the same. If you do glue it down, yep, watching for too much ooze out, from excessive pressure is a good idea. You can very slightly hollow out the underside of the skeg (where it lands on the hull) so there's a place for the goo to live, when bent into position. You also don't need fasteners, if you're gluing it down. Some weights will hold it in place until the goo cures. Rachet straps, Spanish windlass, even duct tape will do. 

   Don't use drywall/sheetrock screws as temporary fasteners. These will just piss you off, when you break them in the work. Use "deck screws" which are often coated gray. Also "tech" screws are handy to have a round too, with their button heads and point options. Both of these are much stronger and though slightly more costly, you can trust them to not break and they can be reused, repeatedly. I've found the drive type makes little difference if you're not asking too much from the fastener. A stripped out fastener is a pain in the butt, though you knew long before you were going to strip it, maybe because it was too small, you had a lousy drive angle, a rounded over tip, were applying way too much pressure for the size of the fastener, etc., etc., etc. Try to avoid making these mistakes, as soon as you notice you're about to try it anyway. I've caught myself countless times saying to myself, "I'm going to strip this thing". Age has finally taught me to pay attention to this inner voice and stop, rethink and grab a bigger screw.

   As to which filler, well you're going to need some silica to control viscosity, but I like to add milled fibers to improve elongation and cross link. Cotton flock (404) or a straight silica joint will do too. I dislike pure silica joints, because you can get dramatically weak areas in it, unless carefully mixed and it's more brittle in compression, which is precisely what a skeg will see in an impact. Both 404 and milled fibers are better in this regard, though you'll still need some silica to thicken it up.

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Dnjost    13

I am having flashbacks now as to when I put my keel on.  I put the boat on its side, and then my daughter drove the screws  from the inside, while I held the keel in position on the outside.  I do remember spending a good deal of time making sure all would line up prior to applying the epoxy.  Do a dry fit, then bed it in whatever floats your boat.  If using epoxy, you can use temporary screws, if using something not so permanent, use stainless or bronze screws.  

 

It came out great, however the trailer does damage the keel in transit.  But, a little epoxy putty and sanding takes care of it in short order. 

 

This link should take you to my blog that describes the process I used to put the keel on. http://jostboats.blogspot.com/2014_08_01_archive.html

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greendane    8

Thanks David for the link to your build blog. Great insight there. 

 

Last week I cleaned the hull to prep for glass and then the keel. Noticed a few things here and there that I may want to address but I am thinking on it. I could easily skip it this season, but eventually I may want to fix it. It does not appear that the original builder did much in the way of fairing compound. A couple of the seams are just plain bad. But I'd need to remove paint only (and not epoxy or glass) in order to get some on there and fill in the low spots (or more accurately, build up around the high spots to smooth over). Any thoughts on just doing this over the paint if I sand down to where it's more primer than color and not quite wood/epoxy/glass? 

 

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PAR    188

Without pictures it's a tough call, but generally you don't want to fair things over paint. Sand down until just through the primer and level the seam tape areas.

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greendane    8

First, is this a big enough deal to fix it? Or should I just finish my keel project, put another couple of coats of paint down and call it good? I'm not a good enough sailor to tell the difference if this ripple slows the boat. But perhaps one day I would be? Or maybe it's slowing things more than I know? I've only sailed this boat and only had it since May. Not concerned about it cosmetically. 

hull seam 1.jpg

hull seam 2.jpg

hull seam 3.jpg

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PAR    188

It's up to you and I've seen worse, though that is pretty bad. It's an easy fairing job, but you'll need to grind down to unmolested material, apply some fairing compound, sand until your elbows complain, then prep for paint again. 

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Walt S.    14

Greendane,

 

I made a fairing board out of 1/8" plywood about 22" long and 3" wide.  I epoxied on drawer handles, though dowel sections would work just fine as handles and be cheaper.  You can cut 3" sander belts and tack them to your fairing board using 3M 77 spray adhesive.  Get a wide plastic putty knife for fairing that section once you've sanded it down. You make putty out of epoxy thickened significantly with microballoons.  

 

 

 

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