the case of the flat board, a simplification of the rectangular kayak

[john5346]

I would like to thank everyone in the other thread for talking and giving ideas.

I may have to disapoint some of you because I wont be making a rectangular kayak anymore because I found a better thing and I want your ideas too. If it will work or not.

Anyway, you know the sport of surfing, like I do but recently I found something called SUP. It is stand up paddling. But I dont want to stand up. I want to paddle it sitting down. It is the simplest kayak in my opnion.

Here is a picture of what I want to achieve...





I dont know what dimensions I would need to achieve floatation.
I plan to build in those dimensions..
length = 10 feet
width = 36 inches
thickness = 3 inches

the design would be all flat with the tip round. Like a half circle. It is all flat. Would I be able to paddle it or would it be too slow? The construction I plan to do before fiberglass is to sandwich a piece of foam between two pieces of plywood.
What do you think about it? I think it will be easy to do.

Thank you

[daiquiri]

It all depends on your needs. If it is just for fun and ease of use, go for it. If you're looking for speed and ease of paddling, go for a traditional kayak.

I have paddled both a surboard and a kayak, there is no competition between the two. A kayak gives you a right feeling of speed, like sliding over a smooth oiled surface.
A surfboard slows down sensibly as soon as you stop paddling but is more easy to handle - and you don't give a damn if you hit the bottom.

The minimum volume necessary, in liters, is your weight plus the weights of the board, the oar and whatever you want to carry with you. That's because 1 liter of water weighs 1 kg. I would multiply the resulting volume by at least a factor of 2, in order to give you a sufficient buoyancy and stability for climbing on it from the water.

If you don't know how much will a finished board weigh, you can ask someone who builds surfboards, or can find tech-specs of a similar-sized board in a surboard catalogue.

[lewisboats]

I think 36" would be a bit too wide for comfortable paddling...more like 30-32"

do a google for paddle board...there are some older plans (svensons?) out there for exactly what you are looking for.

[cameron.d.mm]

Where's that picture of the woman paddling the single cane of bamboo again? I think it might be right up your alley john5346.

But seriously, there really isn't all that much difference between these paddle boards and some sit on top kayaks.

[Petros]

That is a great idea, and it should work just fine, but it is too short and too wide.

I have built 8 kayaks, and 11 boats total, so I have a few suggestions. Ten feet long would be hard to keep in a straight line. And depending how heavy you are, the back would likely be awash, just below the surface unless you weight in the 100 lb area.

That would be easy to make, and it would paddle okay, but i would make it about 14 to 15 feet long (no less that 12 feet), and about 24 inches wide (3 ft wide is to difficult to paddle). Rather than round ends just bring the front and back to a blunt point, curving in from each side (like the plan form of a fat canoe). I would just use 1/4" or 3/8" inch exterior grade plywood. Seal the plywood with oil based paint and glue it to the foam with Tightbond 2.

Put a comfortable seat and foot rests on it and go have fun.

I would also consider putting a small skag in the back, a 10" long 1x2 with a rounded front end, screwed into the bottom with 2" long screws. It will make behave much better but will not harm your ablity to turn it. Short fat kayaks can be squirly, so putting a simple skag would make it a much better boat.

I would not bother with the fiberglass, adds too much cost. cover it in polyester or nylon fabric (any color close-out stuff you can get cheap in a fabric store). Stretch it on good and tight, put the seam on the top. You can either stitch it closed with a "base ball" type stitch (uses two needles) or staple or tack in over the wood, much faster. Use either polyurethane floor finish, or any oil based paint, even acrylic paint would work (cheap too), to seal it up. Sometimes you get this for little or no money from a garage sale, or collecting left over paint from a construction site, or recycling center. Cost less and non-toxic.

It it were me, I would consider leaving out the foam, and just using some 1x4 lumber about 12 ft long, bend them into a "bow" about the shape of the kayak, and than glue and screw the plywood on the top and bottom, leaving it hollow. Seal up the ends with construction caulk and cover with fabric and paint as out lined above.

That should not cost more than about $40 or 50 if you have to buy everything. If you can salvage the paint and lumber, even the fabric, it would cost much less of course.

have fun.

Go have fun with it.

[ancient kayaker]

Originally Posted by cameron.d.mm

... But seriously, there really isn't all that much difference between these paddle boards and some sit on top kayaks.

Probably true, but there's a huge difference between a SOT kayak and the regular variety. I discovered this one day when I was trying to join a friend who had taken one of the rented cottage's SOT kayaks off for a paddle. I took the other SOT, about 5 minutes later, and set off in pursuit.

After about 15 seconds when I realized how slow it was and how much hard work it was going to be to push it along at any kind of speed, I returned to the beach and exchanged it for my regular undecked kayak, or double-paddle canoe, whichever name you prefer. I caught up with the other paddler in about 10 minutes, hardly even trying.

SOTs are designed for stability above all else; this is for safety - to facilitate re-entry in deep water. That's because they are often used as improvised swimming platforms. The higher CoG places even greater demands on its stability because the seating position is above the surface.

The design of a regular kayak does not have to contend with these challenges and most are more performance-oriented, significantly narrower than a SOT and without the center tunnel that many SOTs have which increases wetted surface and hence drag.

[john5346]

Thank you everyone, reading all your ideas, here is the upgrade :

Length 16 feet

width 24 inches

buildind methods:
lumber and plywood, like petros wrote it. No fiberglass or foam.

Since it will be big I will try to male it modular. 3 pieces.
Each piece about 5 feet. How to joint it?





thank you

any ideas? I think it will be easy to do.

[magwas]

About joining: http://oneoceankayaks.com/stitchglue.../scarfjig2.htm
It is also suggested to lay glass on the joint and use epoxy.
The latter seems to be easier.

[john5346]

Originally Posted by magwas

About joining: http://oneoceankayaks.com/stitchglue.../scarfjig2.htm
It is also suggested to lay glass on the joint and use epoxy.
The latter seems to be easier.

That looks permanent magwas.


I mean temporary joints that I could unlock it later for ease of transport and storage. Any ideas?

[magwas]

Originally Posted by john5346

I mean temporary joints that I could unlock it later for ease of transport and storage. Any ideas?

Screws?

[cameron.d.mm]

Good point Ancient.

[daiquiri]

Ok folks, don't ask me too much about legal issues, author's rights etc... This pdf file is in internet for everyone to see, so I'm just giving a link to it:

http://jfmillbiz.home.comcast.net/~j...ction_1977.pdf

It contains some good info about surfboard construction techniques, together with some plans and examples. It could be helpful in this case.

Anyways, I did perform a quick check before publishing the link. This 1977 book is out of print today, and I've also read that the publisher is out of business. So it's probably all ok from the legal point of view. If not, Jeff is free to cancel it.

Cheers

[Petros]

Originally Posted by john5346

I mean temporary joints that I could unlock it later for ease of transport and storage. Any ideas?

If you are going to have flat sides, than just a couple of 1"x4" cleats or gussets screwed to the sides across your joint should work. IF you want to simplify it further it might be possible to screw it on one side, and than use lashing or bungee cords to attach the the other side. A couple of cleats on the top side and wrapping a few yards of cord around it would be a simple way to join your sections. experiment with different ways to lash it to find a way that will be secure, and than mount your cleats.

This adds weight and complexity, I would keep is simple, make it one piece. It should be light, even at 16 ft (about 30 lbs or so), so it should not be hard to handle or transport on the roof of a car or even carry on a bicycle with some sort of rack.

[Petros]

Below is a link to free sailboat plans for an almost surfboard like small boat. I would consider using these plans, but narrowed to about 2 feet wide, and about 4 inches thick (just scale the dimensions), put a full flat deck on it. Build it with 1/4" or 5 mm plywood. It is more complicated than what you had in mind, but it would make a great plywood sit-on-top kayak. It would cost about the same to build too.

http://svensons.com/boat/?p=SailBoats/Tern

post pictures of what you end up building.

[bearflag]