C-Forum

I'm looking at replacing the seam tape on my BigBoy and was looking for a little advice.

From what I can gather the Bias tape is the way to go and I'm thinking about the 1.5" Twaron tape from Sweets composites.

What do most of you guys that have experience with this use and also can anyone offer any advice or tips on appliation of the tape?

Thanks,
Marshall

A real good thread regarding this discussion can be found at:

http://www.cboats.net/cforum/viewtopic.php?t=4456

In addition to John Sweet's site, a more comprehensive and greater variety of boat building material can be found at the US Composites website:

http://www.shopmaninc.com/

For seams, Kevlar is the norm with a top layer of S-Glass. I believe Twaron is close to Kevlar in performance; however, not quite as strong as Kevlar. Due to the war effort Kevlar is hard to come by; however, US Composites seems to be maintaining a decent inventory though in 3 and 6 inch widths. John Sweet may have some Kevlar tape as well.

Some additional hints/assumptions:

1. When working with Kevlar, get a good pair of Kevlar scissors and use them for nothing but Kevlar! No kidding, only Kevlar! Cut nothing else with them!

2. Inside seams can be handled differently.

3. As with the thread I referenced, sand/grind all areas until the fibers are exposed!

4. Please, Please, Please USE A RESPIRATOR not a dust mask!

5. Wear goggles! MEKP (hardener) can fry your eyes in about 30 seconds with no recovery!

6. Measure, cut, layout your material and rehearse how you will apply them several times before you start mixing up glue. With some people (like me, LOL!) an "Epoxy Panic" sets in and you start doing stupid things if all is not prepared ahead of time.

Also, Inquiring minds want to know, How come you are replacing/repairing your seams? Something fail or just normal wear and tear?

Good luck!

Tom
Laytonsville, MD

I assume that you're talking about replacing an outside seam. Check out the following thread for some advice: http://cboats.net/cforum/viewtopic.php?t=4456.

Bias tape will more easily conform to the changing contours, which is why fabric is always cut on the bias for laying up cockpit coamings. However, bias tape wasn't readily available the last time I did an outside seam, so I can't speak from personal experience.

I've never used aramid for an outside seam, only for inside seams. Aramid is stronger under tension than compression, which is why, if you are using other fiber layers (e.g. e-glass, s-glass, polyester, nylon, dynel, etc.) as well, aramid is typically used as the innermost layer. However, aramid is used more exclusively as a lay-up material now than it was when I was last building boats.

I like to add a layer or two of dynel on the on-side outside seam extending from the catchpoint back to where I execute the hook on the J-stroke. Dynel has the best abrasion resistance of any of the fibers and this application of it has insured that I've never worn through an outside seam due to paddle abrasion. However, if aesthetics are a concern, dynel stays milky white when saturated with resin. Unless you add pigment to your resin when you do your seams, the dynel section will come out a somewhat different color than the aramid only sections.

Hope this helps.

John

Tom, thanks for pointing that thread out, I'll be reading that this afternoon.

One question, that's probably answered in the thread, is can I use regular epoxy for the seam tape or do I have to use something that requires MEKP, I've used it once wuth vynilester <misspelled> and I'd rather stay far away from it?

As for why I'm replacing it, the outside seam tape is not fully adhered in may places, I belive the other owner of a BigBoy had this same problem, and while I have the time in the winter months I'd like to fix it before it becomes a problem. It only has one layer of tape now and I thought that was all I would need to replace it with but it sounds like multiple layers are the norm.

I also checked Sweets site and was going to order from him/Davey but it appears the only Kevlar tape he has is 2", which to me seems a little too wide for what I'm doing but I could be and probably am wrong.

Marshall:

Epoxy resin is fine and has better strength and adhesion than vinylester. MEKP is a catalyst only for vinylester and polyester resins, so you won't be needing it with epoxy. The referenced thread talks about fast cure vs. slow cure epoxy. Fast is fine as long as you get all the materials prepared in advance and are confident that you can get the whole seam finished before the resin "goes off" (i.e. begins to gel). As suggested in the thread, it is generally easier and safer to tackle the seam on one side at a time. If you're not confident of your technique and think you'll need more time, then you might consider slow cure.

You might be able to get away with one layer; I've always used two. However, you should also ask yourself how solid the inside seam is. If it looks weak or damaged, then more layers on the outisde are warranted. Also, I typically use two because if I have to go to the trouble of all that grinding and other prep work, then I dam sure want that seam to hold up!!! If you choose multiple seams, then use different size tapes to avoid stress risers.

P.S. If you decide to add a dynel wear patch on your onside as suggested in my original response, note that it isn't available in seam tape. Go to the "Polyester..." section of the Sweet Composites web site and you'll find dynel cloth listed. You would need to buy a small quantity and cut your own pieces to width. The old method for getting a straight and clean cut resulting in as "tape-like" a product as possible, was to literally pull a thread out of the weave at the desired width. This marks the path that you need to cut carefully with scissors to avoid leaving dangling threads along the edges.

John

If you can find out how the boat was originally layed up that may help with the selection of a bonding system. The West System uses nice metered pumps and no MEKP. If you go down to Home Depot and buy a jug of "epoxy" you will use MEKP as a hardener. Check the dates on it as you want a fresh batch. Genarally speaking, if you are using drops of a hardener it is probably MEKP. If it is in a pump it is not. Check and read all terms and usage instuctions carefully as it is easy to get terms mixed up and interchanged, like I probably just did..... I read the instructions every time.

I doubt a BigBoy was layed up with a foam sandwich as race versions of slalom boats are. With a foam sandwich you need to pay attention to the temparature the catalyst brings the resin to as it could be high enough to melt the foam. This could have some bearing on your selection as well; however, I think this is just FYI for someones future search. Anyway epoxy would be better here as well.

When you get your seam tape ready try rolling it up onto a fabric roller or something else like that for application. This is particulary critical with inside seams as you cannot reach all the way down the inside of the boat. The roller can be attached to the end of roller pole as can brushs. Like I said earlier spend some time rehearsing your moves. Even a trial run on somthing non-critical is very usefull if you have never done these repairs before.

Work as dry you can with the resin. The temptation is to "goober" it up real good. This make things very brittle. From what I have seen about the time you think you have just the right amount of resin applied you probably have to much, LOL.

Have Fun, working with composite boats is a whole lot of fun and will make the winter go fast!

Tom

Marshall,

Just wanted to let you know that the thread referenced above about outside seam repair was me seeking advice to replace the seam on my bigboy. I hope you can learn from my experiences. So far mine is holding up very well and I really like the look of the black seam. Let me know if I can answer any other questions.

Also, make sure you allow enough time for sanding. I took me quite a while to sand through the gel coat or paint even using a random orbit sander.

Matt

Matt and Marshall,

Not sure how old your boats are; however, if you are both experiencing the same delamination problem on the same boat you may want to drop the manufacturer a note. It may be something they would want to look into to make sure they do not have a Quality Issue in their processes.

Tom

Marshall:

In reference to Tom's advice above about resin to fabric ratio, I generally agree that you want to use the minimum amount of resin necessary to fully saturate the fabric; that's what makes vacumm bagging such an effective lay-up method (i.e. the suction helps enable use of the minimum resin necessary for saturation). A lay-up with excess resin will be heavy and brittle.

However, an outside seam is the one place that I tend to break that rule - just a little. That's because, as noted in the previously referenced thread, I apply a little bit more resin than normal in order to make working out the air bubbles easier. However, in the process of doing so, I move any excess resin off the seam and onto the glass strapping tape used to mask the area, hence reducing the resin/fabric ratio back to more standard proportions. This description won't make any sense if you haven't read the referenced thread.

Good luck!

John

Thanks for all the information guys.

I've played with composite stuff a little bit but not much, I'm currnetly trying to make some glass hip pad anchors for the BigBoy after that i'm going to tackle the seamtape.

I'll post how it turns out.