centerboard leading edge

[sscoville]

I know there is much about this already on here, but I failed to read it before glassing my centerboard.  I have glassed the sides of my centerboard and the inside of the trunk.  I did not run the glass over the edges of the centerboard.  Thus, the leading edge is bare wood at this point.  I was going to add a bead of epoxy thickened with cabosil to the leading and bottom edge to serve the same purpose as the epoxy saturated polyester rope others have used.

Any thoughts on this? 

[kmrmike]

I constructed My CB from foam and glass and used glass fibers in the leading edge. although I have had no problems, if I were to make another I would do the rope trick...you will probably hear from others that it is very wear resistant...Mike

[JeffM]

I put a fumed silica & epoxy "shoe" maybe 1/2 inch thick max on the lower end and part of the leading edge.  It has taken a pretty fair beating without problems.  (I tend to use my board as a depth sounder, the more since I have the downhaul on a releasing clamcleat.)

[Howard]

Since you already have the board built and glassed, I'll toss out another idea and you can decide if you want to be the guinea pig.......

The benefit of the rope, along with being a rounded shape, is it's a very tough material that once saturated with epoxy offers a durable surface which resists abrasion and whacks from hitting stuff.

Something similar might be that flat nylon webbing. Same stuff used on a trailer winch or tie down straps (the good ones). Lay down a fully saturated strip on either side of the leading edge (like glass tape), and let the two edges meet along the leading edge of the CB with a small gap between them. Either fair that in with thickened epoxy or fill the gap with a much smaller piece of rope.....say 1/4 inch and fair that in. Same along the bottom edge. You can cut darts in it to keep it from puckering along curves.

I don't think the webbing is flexible enough to wrap over the edges, so meeting in the middle would likely be your only option. May offer similar abrasion protection and over a wider area.

Downside is that unless you were planning for this when you shaped your CB, you may get a "bump" from the extra material. Probably as much as 1/8" or more.....and that would have to be faired in behind the webbing too. May alter your foil shape too much.

[JeffM]

Would the board so equipped fit into the trunk?  And if not how would you shave it down?  My cabosil edge is simply slathered roughly into place (maybe in several layers), then ground to shape.  Done.  Of course, I'm in less danger of hitting big rocks than just scraping bottom in mud, sand and gravel or ocassionally cobbles.

[PAR]

Epoxy will not stick to Nylon.

The saturated rope trick will long out perform a silica reinforced edge. When the silica is cracked and large chipped out chunks have fallen off the leading edge, the rope will still be there protecting the blade. This is because the modulus of elasticity of the rope matches that of the epoxy, where as the silica is considerable more rigid then the epoxy so when push comes to shove, the silica rich filler cracks. The fibers of the saturated rope also provide a mechanical interlock that isn't available with the silica.

On the other hand, if you also mix milled fibers in with the silica, maybe 2:1 fibers you'll dramatically increase the mechanical linkage with the leading edge, making for a tougher strip of protection.

[Howard]

Paul:

Your comment about nylon and epoxy piqued my curiosity.....so I did what I often do....I whipped up a little test.

Turns out what I thought was nylon is probably not. It was a scrap of some kind of leftover from when I built myself a Sunbrella cockpit cover. Straps were used for the corner grommets, D rings, etc.  It's 1.5 inches wide and I think is this stuff (going from memory......can't find the receipt):

http://www.sailrite.com/Categories/Polyester-Webbing

So polyester vs. nylon. But most of the lines like Sta-Set are also polyester.

My test (not much thought given) was initially to see what the peel strength would be. First thought was to saturate it completely, so I put down a strip....poured some thickened epoxy over that, covered with plastic and set a board with some weight on it to mash it flat. That saturated and buried the piece.

Next, I gave thought to just wetting out the strip, along with a small piece of line to see what the peel strength would be. To wet out the line, I submerged it in some slightly thickened epoxy for a minute or so...and dabbed and worked it, trying for saturation. Once I felt the epoxy starting to warm, I got it out, stretched it out and nailed it down.

So the three samples looked like this:

I used fast cure, and let it setup overnight (not long enough). For peel strength, I hung a 20 pound vice from the edge:

The web strip held that until I pushed hard on it....about double the weight I'd guess, and then it peeled. More like the uncured epoxy let go.

The line let go under the weight of the vice alone. Again, not a valid test, as a properly installed rope is not just glued along one edge. It is on the edge of the CB, with epoxy formed on the bottom and up both sides, such that only the leading edge is exposed. In short, it's buried in epoxy like the middle strip is, and in the process, you get a nice rounded shape like you want on the front of a foil.

The middle piece was going to break the board. It never did let go.....but had cured a full day longer.

The point is, I still think you could use the right type of webbing, but I'd agree that the original rope trick is still the best way to go.

Jeff: as for your question about fitting in the trunk......as I envisioned this, it would be along the sides of the leading edge of the board, which is the leading part of the foil shape. Should not alter the overall width of the board at all, which at it's maximum point, is about 30% of the chord length back from the leading edge.

The middle piece added 1/16th, so doubled would add 1/8th inch at the front of the board. But put a rope on the front edge of that (added after the fact) would alter your foil shape.....maybe enough to matter a lot.

But I also think the best course of action is to plan for the rope trick when you build the board, and leave it at that.

[John Turpin]

So, what would be the best kind of rope to use?  I'm going to start on Lapwing #3's centerboard this weekend.  I've found posts referring to both nylon and polyester rope.  I remember doing this on my TwoPaw's board, but I think I just used some 1/4" sisal that was within reach.  What rope material takes up the epoxy the best?

[Tom Lathrop]

So, what would be the best kind of rope to use?  I'm going to start on Lapwing #3's centerboard this weekend.  I've found posts referring to both nylon and polyester rope.  I remember doing this on my TwoPaw's board, but I think I just used some 1/4" sisal that was within reach.  That rope material takes up the epoxy the best?

John,

It doesn't matter much what kind of line you use as long as it is synthetic and will soak up the epoxy.  It should be double braided to form the best surface though and smooth line is easier to finish than the soft fuzzy kind.  I have used this method on things from paddle blades to the keel of a 26 footer.  All have worked well.  I also use it on the stem of racing sailboats where the occasional ramming may take place.  While peel strength is important in some instances, this is not one of them.  What is needed here is impact strength and abrasion resistance.  The epoxy soaked braided line has those features in spades.

[PAR]

Most running rigging line is polyester. Docking, fender and anchor rodes are usually nylon or other more stretchy line.

Polyester works well, but nylon doesn't. Some are familiar with peel ply material to ease finishing efforts. It peels right off epoxy, leaving a texture. This is nylon fabric.

As Tom pointed out, you don't need peel strength so much as abrasion and impact protection, which saturated polyester lines offers quite well.

Your peel strength tests offered the rope very little surface contact compared to the other material samples, which really isn't a fair test.

[Howard]

Your peel strength tests offered the rope very little surface contact compared to the other material samples, which really isn't a fair test.

I'd agree with that 100%. Not only was it edge glued, I don't think it was ever fully saturated. More like a surface coating....despite being completely dunked.

I really do like the rope idea. I've built a few rudders and CB's, and did a repair on a mahogany rudder that had grounded a few times....getting chewed up in the process. For lack of better ideas, I installed an epoxy/fiberglass "cap" on the bottom edge, consisting of at least 3 or 4 layers of fabric, including one each of olefin and xynole polyester. It was probably built up at least 3/16th's of an inch. A custom fitted synthetic skid plate. I was pretty happy with how it looked.

Within a month, the ruddder grounded at low speed on an oyster bed and my little "cap" was scored clear through to bare wood. I don't think you would get that with a rope and in the event it does get chewed up, you can always replace it.

[PAR]

If you're a "board boat sailor" like I've been most of my life, you learn little tricks about board design, construction, care, etc.

One that I haven't seen mentioned so far, is very effective at long term life of the board and that is to cut the tip of the board off and reattach it with a fairly wide (1/8") thickened epoxy glue line. You know over the life of the board it's going to get beat up, especially along the leading edge and at the tip.

What the glue line does is isolate the tip from the rest of the board so, if you do damage the crap out of it, moisture can't get past the glue line and affect the rest of the board.

In the event you really bash the crap out of the end of the board, you can just cut off the tip, make a new one and glue it on.

Of course the rope leading edge trick helps considerably mitigate this need, but it's also a technique I've used for some time. 30 years from now, when the centerboard or rudder blade that just left the shop, need some serious repairs, someone will grind off the fabric and see the glue line and say, "cool deal, that'll save some work".

Also, I noted you wetted out the material samples with thickened epoxy in your post above. Don't discount the ability of neat epoxy to soak in and saturate. It's a step I've learned never to skip for best results.