: Anyway... The design will be by Rob Macks who actually suggested 1 of his
: boats to me in the first place when I posted a question looking for a good
: rough water boat. I think a North Star with a bit of length and width
: taken out of it. I'm 6 foot 2 inches and about 180 pounds , so tall and
: skinny. I know i'm at the lower weight limit for that boat but I think the
: next size down is a little shorter than I want. I will speak to Rob about
: volume to payload ratios before starting.

Good idea to stay in touch with the designer. Keep in mind that shortening the boat will slightly reduce its theoretical top speed, while thinning it will decrease its stability and increase the speed. It is more than just volume to payload., or potential displacement versus size and weight.

If you drew the outline of a kayak and made that into something a foot high (roughly 30 cm) you would have a boat that could float. (probably badly!) Press that down in the water so that 6 inches (15 cm) is submerged and you'll have the remainder above water. Make the same outline 2 feet high (60cm) (double the height) and it would displace about 3 times the original volume. You'd have 18 inches (45cm) under water and still have 6 above (15cm). It would still be afloat (still flaoting bably!) but the handling characteristics would be much different as the amount of boat underwater--being affected by drag and water pressure, just to name two items--would make this a much different boat. What would stay nearly the same is the "sail" area, or the amount of boat above water which can catch the wind.

As long as there are ballast materials available I don't think you will have paddlers who are "marginaly" too light for a given design. If the boat is designed for a 200 pound paddler and you weigh in at 180, then bring along 20 pounds of gear and grub and go forth happily. If you don't eat that much, then bring some empty 2-liter soft drink bottles and fill them with the readily available water. At roughly 2 pounds to a lite, each bottle adds 4 pounds. 5 of those in your cargo area will add on your 20 pounds of ballast.

Should you catch a good sized fish, or need to transport back a fellow kayaker who has had some misfortune, you can dump the water from those bottles to lighten your boat and make it more seaworthy with the added load.

: As I like playing in the surf I would use the S glass for strength more than
: weight reduction.

Check the price and stats on your glass. S-glass can be 30% to 100% stronger than E-glass of the same weave and weight. But E-glass is fairly common and may be far less expensive. If you are a bit light for a given design, putting some extra weight into the boat is a good thing. If the boat weighs 48 pounds instead of 42 (for example) then you just need 6 pounds less ballast. Two layers of E-glass may not only match the strength of a single layer of S-glass, but by being a bit thicker they will add abrasion resistance, puncture resistance and a bit of stiffness. Since the cloth is slod in large strips, cut to large rectangles, but the hull and deck shapes are large pointed ovals, you will have a lo of scrap fabric. Which you pay for. You can frequently combie the scrap from the deck and hull to give you enough cloth to give he hull an additional layer of fabric at no additional cost. From an engineering standpoint it is not a glamorous solution, but from a builder's standpoint it is a very practical one.

: Bulkheads will probably be Aircraft Birch ply , 3mm only epoxied no glass
: except the foot brace bulkhead which "may" be 2 layers with a
: layer of glass to stick them together or carbon kevlar. This bulkhead will
: be tilted forward for my feet a little and have a foot pump mounted on it
: , so it needs to be strong and stiff. I will also have 2 others as I do
: want a day hatch. Helmet , cag food etc will be kept there with a VCP
: hatch.

I'm not a big fan of using thin plywood as a footbrace. Definitely not a fan of mounting a foot-operated pump on something that will flex a lot. Making the bulkhead out of two or more layers of plywood just doubles or triples the weight. Eventually you'll get it thick enough to be stiff, but why bother. Screw, glue, or even nail a couple of thicker pieces of lumber behind the plywood. In the states I'd use a couple scraps of 1 x 2. That is a "nominal" size for a piece of wood which is about 3/4 inch thick (19mm) and 1 1/2 inches wide (38mm). Added behind a piece of 1/4 inch (6mm) plywood makes that support a full inch thick (25mm). Even without glass that will provide plemty of support. Do something like that and you'll have something substantial to mount the pump on, and your bulkhead won't flex so much when you are sliding down a wave and putting all your weight on it. From the cockpit you'll have a beautiful flat plywood face. Behind it you'll have some cheap strength.

Do this experiment. Cut a piece of plywood which you will use for your bulkhead, place it on supports about 15 inches apart (about 37 cm). Stand on it. Bounce on it. See how much it flexes. Now get a friend to climb on your shoulders (or pick up two 80-pound bags of concrete) and check for additional flexing. Listen for any cracking sounds.

I know from my time in the gym that I can exert well over 300 pounds pressure with my legs. Just standing up I have almost that amount of weight on my feet. When I row I am using some of those leg muscles, and adding in more muscles from the rest of my body to pull. I can probably apply 400 pounds of pressure to a foot rest. My 150-pound son regularly cracks his 1/2 inch thick plywood skateboards (and won't let me build him any that are reinforced with 'glass)
A thin piece of plywood alone is not going to take your weight forever.

Considering how often you keep mentioning carbon fiber and kevlar fabrics, I think you have not yet made the complete mental transition to thinking in terms of a true *composite* construction based on a wood core. In making "fiberglass" boats manufacturers will use essentially the same molds and techniques , but substitute fabrics with different characteristics in order to save weight or increase strength. They are trying to do rather direct substitutions of materials. With wood core constuction the same rules do not apply in the same way. By changing the thickness of the wood core and the amount of glass on each face we can make a material which is cheaper, stronger, and maybe even lighter, than a few layers of epoxy-impregnated carbon-fiber cloth.

When you are making your bulkheads, if you are laminating two layers of plywood, you don't want your glass in the center of this sandwich. For strength and protection, you want the glass to be the outside layers. Wood fibers will stretch and compress as a piece of wood flexes. Glass fibers trapped in a layer of plastic resin resist such tension and compression. Putting them on the outside of the composite "package" means that every time the wood core tries to flex it will have to pull or compress that layer of glass. The thicker the wood in the center, the harder that is to do. You can substitute other reinforcement fabrics here, kevlar, spectra, dacron, dynel, carbon fiber, or boron fiber. You can even go back a few centuries to see that animal horn, leather, sinew, cotton, and linen fabrics were used to stiffen and strengthen wood bows for archers. Right now the best material for the money is E-glass cloth. It is easily obtained in a variety of weights and thicknesses, and its working characteristics have good documentation and history. We pretty much know how it will work and what it will do for us.

Yhere are several ways to make haches. Look for "Leidy Lids" in the archives and you may rethink buying the vcp hatches.

: I want a stiff hull but don't want it to crack where the bulkheads are which
: is why i was thinking of atleast having them at an angle so it would still
: be stiff side to side but not as much up and down.

Putting it at an angle is kinda like intalling a diagonal crossbrace on a fence gate. It spreads the forces and keeps the gate from sagging. Look at your boat from three directions (do this in your head at least) and consider how a tilted or slanted bulkhead will affect the stiffness.

1. Looking from the front to the back this bulkhead appears the same as if it were straight up and dowm. It has no effect on stiffness in this plane.
2. Looking from the side the bulkhead is at a slant, serving like that gate's diagonal bracing. The slant covers an area perhaps 3 to 4 inches wide, so the bracing effect is the same as using a 3 to 4 inch wide brace.
3. Looking down from the top we see a solid plug which appears to be 3 to 4 inches thick.
Looking at it this way, I'd say the slanted bulkhead would have the same amount of stiffening on left-to right flexing as on up-and-down flexing. So you won't be getting what you are seeking. I'm not sure what you are looking for is a good thing to have anyhow. I think most kayak designs should have a good deal of flex in them. Consider mounting your bulkhead with an elastic material, but mounting your pump to one wall or the other. Make it part of an adjustable footrest system, or mount it to a block of wood secured along the keel line. If you do not try to tie the two sides of the boat rigidly together you will still have some flexibility.

: Coaming speed?? when I launch i usually wait for a wave to pas then dump my
: bum and quickly get the skirt on before getting the next wave in my lap. I
: cant have a fully recessed coaming that i would need to feed the skirt
: down onto. If it takes more than about 2 or 3 seconds to get the skirt
: seated then thats too long.

OK, What you have here is just a matter of making the recessed area around the coaming wide enough that you can get your hands on it as fast as with a taller coaming. This doesn't have to be a problem. Consider this: If your coaming is 20 inches long and the recessed area is 21 inches long then you'll have barely 1/2 inch in the front and again in the back to work your sprayskirt in. I'd say that is trouble. On the other hand, if the recessed area was 30 inches long you'd have a good 5 inches,(more than the width of your hand) to play with on all sides. That should give you the same speed as you'ld get with a non recessed coaming. You might even work as fast with something a few inches smaller. Actually, if the recessed area was much longer than that it would probably just flow right into the lines of the deck and look like it wasn't even recessed. So, the trick here is to make your coaming recess large enough to work around. You'll be building the boat and cutting the hole--so just make it big enough to suit yourself. It is not like you are buying something from the store. If it's too small, you don't have to take it back and exchange the whole boat. Just cut out the coaming, set it aside, cut a biggger hole for the recess, fill in with some left over strips, glue and glass the coaming back in, and go paddling.

Or, let all the water fall into your lap, and get some use out of that pump

At this point you should order your plans. You have amde enough decisions up to this point and it is time for some action. Have them modified if necessary, and by the time they arrive you should have sourced your wood materials, and priced the various fabrics and resins you are thinking of playing with. Clean out the garage so you have a place to work. You can make final decisions about glass or carbon-fiber later on. It will take a while to get enough strips ripped and installed. You'll have plenty of time to ponder while the glue hardens.

Send along some pictures.

PGJ