: This doesn't really fit into this category, boat builing, but when
: I tried to place it into trips I get a server error.

I guess that is fortunate. You are planning to build on to a boat, so you're in the right place

: I've been reading some of your posts and looking at the pics some
: of the members have that pertain to fiberglass work and was
: thinking of finally taking on my own project.

: I have a kayak that I really like paddling, but it has more of a
: race layout (which seems to amount to just fewer layers of
: fiberglass; I got the cheap layup) so it is kind of flexy and
: I'm not sure I'd be comfortable taking it on the trips I'd like
: to use it for.

: I was thinking of cutting out the partitions that
: separate the sections and adding a few layers of fiberglass to
: toughen and stiffen up the boat.

Cutting out the 'partitions'--we call them 'bulkheads'-- would be a really bad idea. They provide a lot of the bracing and strength that your boat has. They also create watertight compartments or air chambers which are vital safety features on your boat. Removing them defeats your purposes, and poses a safety hazard. . Think of them acting on the hull and deck like spokes on a bicycle wheel. Removing the spokes to lighten a wheel only works for people who can replace them with some high--tech invention.
For everyone else the wheel falls apart.

: I don't remember the exact
: dimensions, but I think they are in the 18+' x 20ish"
: range. This boat is entirely fiberglass no kevlar/carbon mix.

Trying to lay several layers of new glass and resin inside a closed, narrow boat is going to be a sticky, smelly mess. You'll have small openings to work in and no fresh air to breathe. It will be difficult to get the new glass smooth and nearly impossible to sand it between layers. Let's find another way to do this.

: If I was going to add a layer of fiberglass (more than likely I
: would have to add a few to get it to the point I would feel
: comfortable with) how much weight do you think that would add to
: the overall boat? It is currently close to 40lbs (44?) so adding
: weight it will lose the quickness of catching a wave, but 40lbs
: isn't super low and 10-20 lbs of boat is going to be trumped by
: the weight of gear/food/water (or so I think).

Frankly, I doubt a plain 18' fiberglass kayak weighs just 40 pounds, but I digress.

Simply adding layers of glass cloth and resin to the inside of the boat is a lousy way to reinforce it or stiffen it. Ever carry a 4x8 sheet of 1/4" plywood? If you hold it flat it will sag considerably under its own weight. Flip it on edge, though, and it doesn't sag at all. Same idea applies here, but more so. Apply a flat layer of new glass cloth and it is under 1/10" thick. That doesn't do anything to add stiffness. It adds weight. Use the same amount of glass, but orient it so it forms ribs or a honeycomb, or is corrugated (like the folded middle layer of paper in a piece of cardboard) and now you have some stiffness.

Those partitions you wanted to remove are oriented at 90 degrees to the hull and run across the width of the boat. They add stiffness and strength in that direction. You want something that runs the length of the boat. It doesn't need to run from deck to keel, though.

: Would it be okay just reinforcing the hull, or would it also be
: recommended to add fg to the under-deck too?

Reinforcing the deck may be MORE important than the hull! But again, flat fiberglass is not the way to go. When the bottom flexes the top has to flex, too. Stiffen the top--something you can do from outside of the boat if you wish-- and it is harder for the hull to flex.

: Is doing something like this a bad idea? I'd also like to add a
: keel strip and was wondering if that adds a noticeable amount of
: weight.

What kind of keel strip? Are you thinking of a couple layers of flat glass running along the keel line? That adds some scratch and dent protection in the most likely area to get scratched but does little to increase stiffness. It doesn't weigh much.

Or, are you talking about a genuine canoe-style keel? Look at an old aluminum canoe and you'll probably be able to figure out how it was made. They stamped a left side and a right side from sheets of aluminum and joined them by riveting the two halves to a 'T' shaped keel. The keel was about an inch tall and ran the length of the canoe. It may have helped with tracking, but that is not why it was there. Without that stiffening the hull wouldn't have any strength. That 1" 'T' beam was as good as a 1" 'I' beam.

Coleman's molded plastic canoes use an internal aluminum tube for the same reason--and I suggest you try to follow that lead. Adding an internal keel (also called a Keelson) should give you the most effective results for your time.

Simplest and cheapest idea is to use wood instead of fiberglass. Use some epoxy to glue a common 1x2 board on edge along the keel line inside the boat. Glue another one along the ridgeline (center line) of the deck. You can put this on the inside or on the outside of the deck. If it is on the inside no one sees it. If you are thinking of carrying some of your gear on deck during you travel consider putting a pair of wood strips on the deck. Put them about 5" to either side of the ridge. You can drill holes in the wood, or cut slots for lashing straps or drainage. If the strips are an inch to 1-1/2" high they'll do a good job of stiffening.
Spend your time picking pretty hardwood instead of sticky resin and glass. Cost is about the same.

If you want to use fiberglass instead of wood for your reinforcing, that is OK too. Ut your glass work needs to be shaped so it has some height. You can create a fiberglass tube or channel by wrapping glass around a lightweight core. You can leave the core in, or remove it.

Here is one idea: find the foam insulation which fits over water pipes. Usually this is sold in pieces which are 3' long and it is slit so it can snap over the pipes. The outer diameter of this is about 1.5". Cut lengths that fit snug between the bulkheads along the keel on the inside of your boat. If they don't stay in place by friction use a few pieces of tape to secure them. Cut strips of glass cloth 7" to 8" wide and saturate that in your resin. Roll up the strip, place the roll in a plastic bag, pour in some resin and knead it unttil all the glass is saturated. Unroll the strip of glass cloth over the foam. The saturated glass will drape over it and lay flat against the bottom of the boat. Three or 4 layers of glass can be applied at one time. Once that is hard you have a rigid hull. You can repeat the process on the deck or reinforce the gunwales this way.
If you don't use a foam core for your stiffening tube you can make a tube of paper. Or, wrap plastic kitchenwrap (Saran Wrap) around a water pipe, cover that with one layer of fiberglass. After the resin has started to set, but before it has completely hardened, slit it and remove it from the pipe. That gives you a fiberglass tube.

Just some ideas here for you. Hope this helps.

PGJ