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Re: Thickening epoxy + Attach deck to hull
By:Paul Jacobson
Date: 9/14/1998, 3:59 am
In Response To: Thickening epoxy + Attach deck to hull (Wayne Bergman)

> some Questions regarding a procedure I will be facing
> where you attach the deck to the hull. My kayak will have no deck hatches
> to access the typical seam taping of the inside of the sheer line.

While having hatches is a plus, In David Hazen's book on stripbuilt boats he shows two kayaks that have no hatches, yet the decks are attached with interior and exterior applications of fiberglass tape and resin. His longest boat is 20 feet long. Working from the cockpit opening alone you'll have to go about 8 feet to the bow and 7 to the stern, which is a stretch, but not impossible. If he can do it, you should be able to also.

There have been a few techniques discussed on this board for doing this. For example: brushes tied to poles for applying resin at the very tip of the boat.

One of the more interesting ideas (at least in my opinion) shared with us on this board suggested using mere dots of resin spaced several inches apart to `tack` the first layer of interior tape in place on the hull. When you lower the deck into place, the tape is already in the proper place. A quick coat of resin is all you need. The tape won't bunch up, or flop all over the place. When the resin hardens NOTHING will flop while you tape the exterior.

> What I am hoping to do is Epoxying a long strip of something like
> ensolite foam to the inside of the hull the full length of the sheer
> lines before I clamp on the deck. This strip of ensolite (about 3/8"
> square and 18.5' long)will just act as a retainer to hold a 1/4" bead of
> thicken epoxy that will be used to glue the deck to the hull on the
> inside.

The foam has no strength to speak of, and since you won't be covering it with fiberglass fabric and resin, it is not getting any additional assistance. if it is 3/8 inch square, you'll have at most a bonding area 3/16ths wide on the top. and 3/16th on the bottom. With the wood beveled as you say, you won't even have this much contact area. Think: `weak joint'

Why not trash the foam idea and go with a strip of wood? You should have plenty of extra 1/4 thick strips left over. You don't even need full length ones. (Who is going to stick their head in to look at the joints?) If you are using 3/4 inch wide strips, you could glue them to the hull with regular resin, slather them with the thickened goop, and they would serve to align the deck when it is added. Each strip would give you a gluing area 3/8 inch wide and 18 feet long on each of the hull and deck joints. If you are short on clamps for attaching these strips, just put them on in short sections ( maybe 2 to 5 foot pieces. Use up your scrap.)

This illustration is pretty poor, but try to follow me: the regular strips have two parallel faces and look like this: | |

I'd try to reshape them into a `D' shape cross section, something like this: |)

I suppose a router, disc sander, belt sander, plane or spokeshave could be used for this. The idea here is that by shaping the edges of the strip in this fashion it would not appear to be as big a bulge, but still have most of its strength. Also, with the edges of this joining strip coming smoothly to meet the hull and deck, if you later wanted to cover the whole thing with a layer of fiberglass ( tape, strips, whatever) there would not be a stairstep to cover. Either way, the strength of this joint is about the same as the strength of the wood used in the hull. Except for it being covered on only one side with glass and resin (and I hope you'll re-think this) this joint is as strong or stronger than any other spot on the hull or deck.

> The outside will have the
> sheer line glassed with 6oz 3" seam tape.

Check the literature on this. I`ve seen several references to using two layers of tape, with the outside layer being wider. That would put the first layer at about 2 inches, and the second layer at 3 (or even 4) inches wide. The idea here is to stagger the edges of the tape so they don't leave a noticeable bump.

> My strips at the sheer line
> have been back beveled to 40 degrees to accommodate this thickened
> resin I hope to squish in here.

I can see WHAT you are doing with the beveling, but I can't understand WHY you are doing it. If your strips are bead and cove then they have a curved, mated surface for the thin, strong glue joint. If your strips have square edges, then they have as much as 1/4 inch of edge-glued surface to join one strip to the next. If you bevel these things by an angle of 40 degrees, you basically get the joint ( in cross section) to look like the two pieces coming together with a thin edge touching, and a wedge of filled plastic ( the resin) sitting between them. If I was welding something I might grind the pieces to those shapes, and fill the `valley' with molten metal from the welding rods, but this is not welding. A fillet joint like this, which works fine in stitch and glue construction, when it is later covered with glass cloth, could benefit from any additional reinforcement you can add. It seems to me you are going out of your way to make a weak joint when a stronger one is actually simpler.

> I have a couple of questions regarding
> the thickening of the resin and also others opinions of this method and
> or diferent methods that have worked you.

> -I have purchased a product called "mini fibers" that I will add to the
> resin for thickening and I was wondering about its strength compared to
> silica or the wood dust from my orbital sander as a filler.

I'll leave this one for the structural experts here, but as I see it, for greater strength you add `reinforcement', and to take up space you add 'filler'

Sincw we are talking about `filler', added primarily to keep the mixture thicker so it won't run out of the joint, I don't think any strength differences (stronger or weaker) are very significant.

> -If I go with the mini fibers I see it cures white in color and
> wondering when the stuff squishes out of the sheer line area onto the
> hull and deck should I clean up the excess while its still wet and with
> what?

Use a few pieces of index cards, or, if you have some decks of playing cards where you have lost a few, use those as disposable scrapers, squeegee style, to scrape and scoop off the excess while it is wet. After it dries, a light sanding should get the rest. The resin may soak into the wood fibers, but the filler is going to sit on the surface. Sanding things smooth should remove it all. If yo are going with that beveled wood edge for the joint, be VERY light in your sanding here. If you sand deeper your glue line will get wider and wider.

> -My boat is an eighteen and a half foot "Panache" from Bob Macks and
> will be used in calm waters. I realize my proposed method is not as good
> the seam tape
> inside and out but hoping as I am not going with hatches nor planing to
> be in open seas it will be an ok option?

Explain to me again, please, just exactly how hatches have anything to do with the strength of an unglued deck? There are certainly lots of issues with hatches, but I don't see how avoiding hatches affects the hull/deck joint. You either have a strong hull/deck joint or you don't. You either have hatches, or you don't. But you can't take one from column A and one from column B and come up with the idea that joint strength is in any way related to hatches, unless you are still working on the assumption that you MUST have hatches in order to tape the joint. Well, you don't.

There is a word for a kayak with a deck that comes off when the boat gets into rough water. It is called a canoe. If you want a canoe, don't attach the deck at all. This is a better option than attaching it weakly, as you'll save time and money.

Now, before I am criticized for my views on the strength of the joint you are proposing, let me mention that I have read of kayaks that did not have any interior fiberglass cloth. the entire bonding was in the edgegluing of the strips, and the exterior fiberglass cloth. Your boat would not be any weaker than these types of craft -- and they seem to hold up. The questions are, therefore, are you putting fiberglass cloth over the interior? If so, you are building a stronger boat, so why build in a weak area? A layer of glass cloth over the interior, coupled with the layer of glass on the exterior of the joint makes the boat as strong there as any other point on the hull.

YOU NEVER HAVE CONTROL OF THE WEATHER. I learned this from `Gilligan's Island' the water may be calm and glass smooth when you start out, but in minutes it can change and leave you facing heavy waves that you thought you would never take your boat into. At that point it is a little late to think about taping the interior of the seams.

> Also a variation to this would
> be to go with the ensolite and thickened epoxy just in the compatments
> between the bulk heads and the ends of the boat and then giving the
> cockpit area the proper seam tape method. What do you think?

See, see. In your very own words you know that using tape on the interior seams is the proper method. Go with your heart on this. Figure out away to tape things, and you will never again worry about them.

as for bulkheads. Take a frame you used for building your kayak and lay it on the material you want to use for your bulkheads (Plywood?) Trace around the frame, cut out the bulkhead and you will be 90 percent done with getting it to fit properly. You can install them after the deck is on.

Assume water or water vapor will somehow, eventually, get into those ``sealed'' areas. make preparations so you can get fresh air in there to dry them. Bulkheads with hatches in them give you access to those areas. You can use them for storage of gear, or they'll serve as flotation areas.

Hope some of these ideas help. Paul Jacobson

Messages In This Thread

Thickening epoxy + Attach deck to hull
Wayne Bergman -- 9/14/1998, 12:03 pm
Re: Thickening epoxy + Attach deck to hull
Jay Babina -- 9/14/1998, 9:30 am
Re: Thickening epoxy + Attach deck to hull
Paul Jacobson -- 9/14/1998, 3:59 am