Dynel rubstrips - how to safely trim the edges during application

I'm getting ready to add Dynel rubstrips to the bow and stern keel line of a Sectional Shearwater Sport. The hull is glassed/filled/fared/sanded and paint ready. I have all the materials and am referencing some notes on the installation here: https://www.clcboats.com/shoptips/fitting_out/rubstrips.html.

The process seems pretty straightforward but I'm not totally clear on how to safely cut away the edges of the dynel after the initial epoxy application. It seems like the dynel should be laid down and epoxied so that the edges actually lay slightly over the tape used for masking around the application area, and then cut away after the epoxy has dried. I'm struggling to see how I could score a line only through the dynel cloth, especially after it's secured with dried epoxy, while not cutting into the fiberglass and epoxy layers beneath. This seems risky and I worry about scoring too deep and possibly even exposing a pathway to the wood itself.

Should I plan to cut away the edges before the epoxy is totally dry so that minimal knife pressure is needed to make the cut? I'm also wondering if it would be helpful to pull up the makeing tape while making this cut and then re-tape before later filling the dynel weave. If I'm not mistaken this is also how some folks mange epoxying overalapping layers of fiberglass cloth. Any tips on this are really appreciated!

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RE: Dynel rubstrips - how to safely trim the edges during application

Hi rjacobs, 

i have a lot of experience with the dynel strips. and yes, the key to a clean line is cutting it when it is plasticy with a very sharp razor (i always use a new blade on a dynel cut).  the cut will go through the dynel and not do much more then scratch the underlying cured epoxy.

my approach for the dynel strips is not to tape underneath the material (you can't really see through dynel anyway) but to tape on top of the dynel and use the tape to pull it down nice and tight over the keel/bow and keel/stern.  otherwise it tends to puff up and get difficult to lay out nicely.  

once i wet it out, now i only have to cut just inside the tape and pull the plasticy bit off the hull which is easy if you time it right.  obviously, this also creates a problem if you somehome fail to monitor the situation or fall asleep.....

for subsequent wet outs, i remask the hull on the cutline to avoid getting epoxy where i don't want it.

below is a picture of my shearwater 17 with rubstrip.  the only other advice is you don't need to make these vary large.  once you have covered the keel, how much you go up the sides is more of a decorative concern than anything else

if you are painting the hull, there is another approach that i have been using that looks really slick....so send a note if that's the case and i will describe it.



RE: Dynel rubstrips - how to safely trim the edges during application

Thanks Hspira, that's very informative!

I've never worked with Dynel, so I didn't even consider that it might stay opaque when wetted out. That certainly changes the strategy a bit. Does the Dynel tend to wick up the epoxy? I'm just wondering if much of the epoxy would get absorbed under the tape and possibly leave a mess after cutting away the partially-cured edges. I suppose that even if some is absorbed it should be easy enough to clean up with a bit of sanding before re-taping.

When researching the archives I think I encountered an older post where you outlined a trick to use faring material to make the strips flush with the rest of the hull (if painting). That sounds pretty slick. I'm not sure I'll have time to explore that with this build. It might be something to look into for the next one!


RE: Dynel rubstrips - how to safely trim the edges during application

it will wick a little bit but not that much.  and yes, a little clean up with sandpaper possibly.  i usually clean it up right after the cut with denatured alcohol carefully applied to a rag and then use a flat head screw driver into the rag to allow me to rub off any remaining uncured epoxy adjacent to the cut edge.


RE: Dynel rubstrips - how to safely trim the edges during application

So I worked on this over the weekend, mostly using the techniques outlined by Hspira. It seemed to work well, but here are a couple additional observations:

  • Cutting the edges before the initial epoxy dried really was the way to go here. Somewhere between hour 3 and hour 4 things had set enough to make the cut, though I probably could have waited longer.
  • The Dynel did turn pretty translucent when wetted out (see picture with wetting in progress). Because of this I think I would have been able to place the tape underneath and still follow it when cutting. This may have resulted in a slightly cleaner line, though the small amount that oozed under the tape was easy enough to clean up. That denatured alcohol plus screwdriver tip worked well here.
  • No matter what initial masking strategy used it seems like you still end up with the graphite mix brushed-out over a tape line. Given the way this mix seems to sag/run, a lot ended up oozing over this line, so it seemed important to pull the tape up before the graphite mix cured. This was also an exercise in timing. Had I waited too long I suppose another knife cut may have been needed (and that one would have been blind as you most certainly can't see though that graphite mix). However, pulling the tape before the graphite mix stopped sagging could lead to a permanent blob. Here too, somewhere between 3 to 4 hours seemed about right.

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