Fibergalssing a skiff's bottom- please help

[TomMcKinney]

I have given in to the wisdom of proven methods and I will be fierglassing (epoxy and cloth) the bottom of my flat bottom skiff over the holidays. Although the other ideas I have might save money, tghe tried and true will work, so someone else can fund an experiment.

The fiberglass is not required by the plans-- but I want to reduce checking of the fir plywood and reduce trailer abrasion.

Plans call for bottom to be but blocked with 2x6's-- I have substituted tape joints--but may still add the 2x6's as they can be used as part of an optional frame (Its a Lumber Yard Skiff--16 ft)

If I glass the whole bottom with 3 oz. cloth can I skip the 6 oz. tape on the bottom side of the joints--so long as the seams of the cloth are set between the floor seams (i.e. staggered)?

Since cloth is for checking/abrasion purposes can I use pieces most efficiently using odd sizes/ shapes or should I "waste" cloth to keep number of cloth seams down?

If I do use the 6 oz tape can I butt the cloth up to the tape or do I lay it over the tape?

Thanks

[Bob Cleek]

I wouldn't advise substituting tape for a 2"x6" butt block, if that's what the designer indicated, but it's your boat, I guess. Sixteen feet is a fair size for a plywood boat and at that point I'd expect the plywood needed those butt blocks, but... suit yerself.

It doesn't much matter whether you tape a seam or lay a whole yard of cloth over it. Same stuff, same outcome... given that the weight of the material is comparable and the amount of googe is about the same.

You can lay up as many seams as you want... hell, make a checkerboard patchwork quilt out of it if you want as long as you have a bit of overlap on the seams. Problem is, the more seams, the more fairing problems you will have when it sets up. It's going to look like rock hard frozen snot painted on with a swab once it's kicked off... then the sanding begins! Heh, heh, heh...

If you use tape, lay the cloth right over the tape. You'll save cutting and fitting and a bunch of fairing when it all hardens. I'd strongly urge you to use Dynel and epoxy rather than glass cloth and epoxy. The Dynel fabric is sort of like Lycra, it has some stretch to it in all directions, and is far more accommodating when you go to lay it over shaped surfaces. It also doesn't break up into little needle-like slivers which work their way into your skin and itch like the devil when you're working with it.

Hope that answers your questions? BTW, check out the search engine thingy in here... you'll find a lot of info from guys who've done what you are doing.

[JimD]

Tom, read Bob's post several times, especially the parts about omitting the butt joints (meaning DON'T DO IT!!. Unless maybe they're omitted over very short spans. 2x6 sounds excessive (understatement - really? As in 2 inch x 6 inch? Can't be unless I read your post wrong)), and the 'heh heh heh' about sanding frozen snot. Also, I've never used Dynel, heard many good things about it, but it is said to soak up about twice as much epoxy if that matters to you. Tape seams create quite a ridge to be sanded off but that could be the least of your problems if you cloth the bottom patchwork.

[Todd Bradshaw]

I think you may find 6 oz. cloth much easier to work with than 3 oz. Many of the really light weights of glasscloth are really tight weaves that don't do contours or sharp angles without a real battle. Combined with that, even 6 oz. cloth is so light that one can barely call it structural. It wouldn't surprise me if fir plywood could easily overpower the check-preventing power of 3 oz. cloth and if you intend on dragging the boat up on the beach it certainly wouldn't hurt to have a double layer of 6 oz. on the bottom and corners. That's about what it takes to start getting some serious abrasion protection.

[jwaldin]

I'd go with all of Bobs advice.
Dynel would be my choice by far.

[Buddy]

Echoing some comments above, consider Dynel ( get it from Defender). I gather this is your first glass job. What everybody bitches about, never again, is the itch fron sanding down bumps in rough fiberglass. So use glass tape at your joints. While the glass is semi cured, use a Stanley Surfoam file to remove only the bumps and ridges at the edge of tape. Then use epoxy/milled fibers miz to feather that edge done to to level of the unglassed plywood. Because you will use more epoxy filling its weave, going with Dynel costs more considering the additional resin and the finished boat will weigh slightly more, but you're not talking about a kayak you've got to lift onto a car rack here. The Dynel will have far more impact resistance than the fiberglass and costs about the same per yard. Easier to get to smooth over and work into corners, harder to keep the weave pattern straight if you're leaving it course for a non skid deck. For what it is worth, many "outside" restored museum boats use Dynel and epoxy instead of cotton duck and paint to achieve the look of tradition canvas decks with modern low maintenance materials. You could make a great cockpit sole for a fishing boat this way.
You can fill and fair and sand away on it to a show boat finish if you want, and you won't ever itch.
I think of Dynel as the fiberglassed plywood boatbuilder crowd's most undiscovered secret. I guess it's because you can't buy it at the retail boat stores or Home Depot that it's news to most people.

[Keith Wilson]

I wouldn't skip the tape on the bottom of the butt joints. 3 oz is awfully light for a boat this stout. With the tape, I think the taped joints will be just fine. First, a 2 x 6 butt block sounds like wretched excess, unless it's used as a stiffening rib on the plywood panel. It’s thicker than anything I’ve ever heard of on plywood. The "lumberyard skiff" is designed to be pretty stout, and I suspect that the designer specified 2 x 6 because it's easy to get, has plenty of depth for screws, and is more than strong enough. If you have a plywood panel that's strong enough, and the taped joints are as at least as strong as the rest of the panel, what's the problem? I would bet a lot that the designer of this boat didn’t do stress calculations to optimize panel thickness. Here’s a picture of the Lumber Yard Skiff showing the 2 x 6 butt blocks on the bottom. If you find the bottom flexes in a chop, you can always put in some transverse pieces to stiffen it, but you REALLY don’t want that joint opening up unexpectedly.

http://www.oldwharf.com/images/owd_16_LYS_shop2.jpg

I have used both Dynel and glass. Dynel tends to soak up more resin, but if you do a proper job of it, the resin/fabric ratio isn't much different than glass. A "proper job", IMHO involves applying three coats, squeegeeing well and letting it cure at least partially between coats, not applying too much resin at once, and taking great care to keep things flat and smooth. Here's a link to an article by Ted Moores (http://www.westsystem.com/webpages/epoxyworks/16/fiberglassing.html) (a true fanatic) on how to do it almost perfectly. I don’t normally advocate such fussiness, but I do it ‘cause I’m basically lazy and HATE sanding. Care taken in applying resin to cloth will save a LOT of very unpleasant work later; in fact, if you're careful and don;t want a yachty finish, you may not have to sand at all except on the edge of the cloth. If it were mine, I'd use as few pieces of glass as reasonably possible, not for structural strength, but because the fabric edges are always trouble - the fabric frays and bunches and generally drives you crazy. Glass cloth isn’t that expensive.

Dynel and fiberglass each have pros and cons. Fiberglass lays down flat better on flat or moderately curved panels (like most plywood hulls), while the Dynel will go around sharper bends a lot better, and can handle more extreme compound curves. Todd’s right that 6 oz is easier to work with than 3 oz. Dynel has better abrasion resistance, while the glass has greater tensile strength. I would be wary of substituting Dynel fabric for glass tape where tensile strength was critical, as in a stitch-and-glue hull, but not your boat. Fiberglass is also better for impact resistance because of its greater tensile strength. Either will work fine in your case; like you said, the lumberyard skiff is built heavily enough that it doesn’t require the glass at all. Fabric in epoxy works like re-bar in concrete; it allows a thicker layer of resin without cracking and so prevents the epoxy layer from cracking as the fir plywood tries to check, and for this, it doesn’t much matter what kind of fabric it is.

[ 12-19-2003, 10:39 AM: Message edited by: Keith Wilson ]

[Bill Perkins]

Tom Dynel or xynole I think are the way to go because they're more abrasion resistant than glass .I just sheathed my boats bottom with the xynole ,a polyester fabric .It's very drapeable ,and could run over the chine and on to the topsides with no problem running over the fairly sharp bend at the chine .

You can get it in 69 in. wide rolls ,by the yard . Would that be wide enough to get the bottom and on up to the bootstripe in one piece ? Defender has it I believe . I bought mine from Raka .

A taped joint may be as strong as the plywood ,but I think the 2by6 is there because the ply alone isn't stiff enough .You'd need the reinforcing crosspieces even if the boats' bottom was one huge seamless piece .

[ 12-19-2003, 11:00 AM: Message edited by: Bill Perkins ]

[Paul H]

Can't add much to what has already been said. Two keys to saving labor are trimming the cloth over runs just after the resin firms up with a utility knife, and using a scraper to take of bumps and drips of resin. I highly recomend the carbide scraper that Jamestown carries, just got one, and it just peels off excess epoxy, and goes through glass like butter.

One other commend on sanding, most folks have the tendancy to try and bring the bulk of the resin down to the low spots, intstead of just getting the surface mostly fair, then building up the low spots.

I personally like 4oz cloth, but the key to using it is not to put the resin on the wood first. Roll out the cloth on the surface, and work out the wrinkles. Then mix up the epoxy and squegee it right through the cloth into the wood. The one care to be taken with thin cloth is putting another layer of resin on to fill the weave before sanding. You can go through thin cloth in a heartbeat.