Small Kayak - Under 13 feet - Stability?

hi All,

I'm in the process of planning a Small Kayak for backwaters, and canals. I cannot afford to make a 17' Sea Kayak. I never would use this kayak on the sea, so my idea is only to make it as small as possible.

I plan to make it under 10 feet.
I do not have prior experience in making Kayaks or Boats.
I'm a first time builder, and I'm planning a SOF Touring Kayak.

Stability is important, do not need agile speed, maneuverability is important.
Please help me decide the LOA and the Cockpit size, and target displacement.

I weight just under 220 lbs.

thanks,
MS

 

For your weight, under ten feet will be a challenge if speed is an issue.
A kayak can be long and slim or short and fat. Your idea of a short kayak (under ten feet) means a rather beamy shape not only because of the length but also because of your weight carrying requirements.
A nine foot kayak for you might be 36" wide.
What happens to performance? The boat will be very efficient at low power input but when you treally want to move it will hit "the wall" early and waste your energy making waves.
If you enjoy paddling along at 2-3 miles per hour, you'll really like the short and wide kayak.
The shorter hull won't track nearly as well as the longer type. It will be more maneuverable, however, and you can load gear in it more easily due to the better (larger) access at the cockpit opening. The weight of gear will be closer to middle too, which is a plus.
Now, for stability, initial stability will be very good compared to a longer boat in potential, depending on the bottom shape. All things being equal, however, the wide boat will be initially very stable.
Final stability, meaning tndancy to be stable at greater angles of heel, will be poor with the wider boat. The reason has to do with the fact that such a shape becomes very narrow as presented to the water when heeled a lot, like a pancake on edge, while the narrowest of boats would be more like a banana on edge.
If rolling your kayak is how you intend to recover a capsize, get a narrow, long boat. If avoiding capsize in the first place is most importasnt, if you're happy with the slow speed limitation, go for the short wide boat.

Alan

 

NO rolling Thnaks Alan.

I intend to carry camera equipment, and never wanna roll with them all! :O

I'm looking to do some Bird watching, and photograph them.
So faster is not the 1st criteria or a criteria at all.

The shorter it is, the easier for me to transport, I have a small car.
The shorter, the easier for me to store (apartment).

So I will compromise on the speed for these priority.

Some one tell me how wide should the boat be? for a 9 foot LOA.

9' x 30" with a cockpit that is about 32" x 15" ?? would it work?

 

That would work I think, as a waterline beam, if you don't carry much extra weight. A good margin would be to figure you might occasionally carry another 10-20 lbs.
You can figure this yourself easily. Multiply your proposed (underwater) midship section with the waterline length and then multiply again with .54 (an average prismatic coefficient). This gives submerged cubic feet.
Then multiply by lbs per cubic ft (of sea water, 62 lbs fresh, 64 lbs salt) to get displacement.
The displacement should be figured at about the weight you anticipate would be your average, meaning you, the boat, and average cargo combined.
You can adjust the depth, beam, and curvature athwartship until you come up with your target displacement using the formula. Every little change you make will also affect stability and speed, since you'll be working with bilge and bottom shapes to achieve the ideal.
A dead flat bottom amidship will make for a wider beam and greater stability but will have more skin friction than a bottom that's rounded more, and so it will be a bit slower with the same paddling input.

A.

 

Alan = that was really helpful in demystifying the formula.
I read it else where, but you explained it easier to understand.

I'm seeing KFoundry the Kayak software from blueheron site, and it seems useful, though it is specially made for Strip Built Kayaks.

My only hinderance to start building was to get some figures on board to make me confident to start building.

I searched yesterday night for many Kayak Shops online, and gathered a lot of LOA X Width X Height combinations that take an average of 300 lbs paddler.

It worked out well, and I understood the shorter the Kayak, the wider it became. So with that ratio in mind, I started to work out some ratios.

I have a discussion going in kayakforum about the LOA. Many debate to build a longer boat and I will be a happy man. And tell me it is not that difficult to carry a 14 foot boat in my smart car.

Guess experience talks, wondering if I will learn by my mistakes after making a short boat, or is there a trick to make a short boat decently fast.

I have summarized my application above, and you know I dont wanna race with my Kayak. Just go about without wobbling, and going with the wind.

What come up to your mind? Throw some light!

 

For many reasons, I personally would prefer a fifteen foot long kayak for general use, but I use a nine foot one to ferry myself and cargo out to my sailboat because it is wide and stable in calm water. I say calm water because a beamy kayak isn't necessarily the most stable in rough water. It's more affected by the angle of the water surface it sits upon than a narrower round-bottom or arc-bottom type.
You mentioned that you'd be going out in relatively calm conditions, so beaminess is an asset for you.
You also said you don't mind a slow boat, but only if necessary. You have to strike a comprimise, of course. For instance, a slight arc in the bottom will reduce wetted surface, helping efficiency, though the final top speed will be about the same. Wetted surface doesn't change top speed so much as length does. A nine foot waterline length will limit you to 4.02 knots. A sixteen foot waterline, 5.36 knots. These figures are derived from taking the square root of the waterline length and multiplying that by 1.34.
The closer you get to the top speed, the harder you work to make the next quarter knot. Moreso with the beamy boat, which will be very tiring at four knots---- while the sixteen foot boat will be less tiring at say 5.2 knots.
The reason is in the shape itself, which favors the needle shape at the upper speed potential.
However, it's the short and squat shape (more 'bowl-like" as seen by the water) that takes less paddling input at the lower speeds, like at 1 or two knots. At very low speeds, length to beam ratios of 1:1 actually reduce power requirements because only skin friction matters, and a half-sphere hull underbody, for example, has the least surface area (wetted area) of all.
A small child with his tiny amount of power might do better with a bath tub shape, in other words.
You might choose a somewhat longer boat for one reason---- they track a lot better, which is itself an energy-saver. A zig-zag course wastes a bit of energy in addition to being less elegant to watch or experience.
My guess is, after reading this, you might think about a twelve foot kayak and its moderate speed potential of 4.64.
Everything in life is a comprimise.

 

Everything in life is a compromise - I liked that best of all! Alan - I more than agree!!

I have decided to go with a 13 foot, as a lot of you suggested.
A 13 footer that is!

Okay now coming to Offset Tables.
I have this offset table for a Kayak called Sea Bee by Tom Yost.
I thought I will use it to make my FORMS, and build over it.

I have just understood what these tables are, and how to interpret them.
I tried to Loft them on some poster board, and knew these are multi chine offsets.

http://lh3.ggpht.com/_v8LXlvxOgoY/SUk8XZOkDwI/AAAAAAAACGE/99Gx9JCOfFI/s128/IMG_5890.JPG
http://lh3.ggpht.com/_v8LXlvxOgoY/SUk8XXyEalI/AAAAAAAACGM/rTQU--3Rr8c/s640/IMG_5893.JPG
Would I need a multi chine (more work?) or will I do better with a Single Chine boat?

If so, how will I change this multi chine to a single-chine table?


Today I bought some bamboo and Poly twine.
The twine holds up a 20 KG UPS easily. I tried swinging my UPS, Ooh that was scary, but it took all the weight. It is easy to wax it and easy to use.

Bamboo looks healthy, green bamboo 20 feet, 1 incher, under $1
10 feet of it can be used for major frame construction, because of its nice even diameter.

Attached are the pictures of the Bamboo and Poly Twine.
http://lh3.ggpht.com/_v8LXlvxOgoY/SUiq0_oP2eI/AAAAAAAACFw/Czvh-kU3zvU/s512/IMG_5888.JPG
http://lh5.ggpht.com/_v8LXlvxOgoY/SUiq0-G1elI/AAAAAAAACFo/0bUrW0748Cw/s640/IMG_5885.jpg

Any suggestions welcome, I'm trying now to bind the bamboo in different styles. Will come up with some pictures later.

 

You won't easily change from multi-chine to single! It's a lot of work even if you're a qualified designer. Best to start with a single-chine kayak in the first place.
I don't understand the rest of your comment. If you're using that bamboo for lofting, don't. They are too crude. In fact, why would you need to loft? A multi or single chine boat has the advantage of stitch and glue construction, so all you need are mold patterns and station spacing, which is what you pay for in any multi-chine plan.
The boat you mention, Sea Bee, must be a strip construction, without chines.
The offsets provided require a surface (usu. a floor you na nail into, or better, two sheets of clean plywood or particle board to tack into if done over a nice floor.
There are many sources for how to loft, but basically, each view of end, top, and side are divided into spaced slices. Sometimes, diagonal lines are also included. Each view shows the crossing points (intersections) of all views. The completed lofted drawing is full size. Every measurement used to create the lofted drawing is shown in the table of offsets as a height from a baseline below the boat or a distance from the centerline, or from one end of the boat, depending on which view. Think of that as the zero line. That's what the figures in the table mean. The measurement system used will be shown. Usually, in the USA, the system is in feet, inches, and for example eighths or sixteenths, such as might be shown, 1-2-5, which would mean one foot two and 5/8 inches if the last figure is denoted as eightths.
That would be the distance from the zero line in one of the several drawings.
Lofting allows correction first, to "Marry" all the lines of all views by adjusting bending battens to fall on crossing points rather than trusting your measuring or the offsets exactness (they aren't exact, but are almost so).
Then, the lofted drawing allows "picking up" the shape of many parts and pieces as well as providing measurements for your building jig.
Look online for a "How to Loft" article or book you can order. There's a lot to know, but it's not rocket science if you're only building a kayak.

 

Alan
You have done a great job in explaining the design issues.

If I was looking for a camera boat to go on a car then I would certainly consider buying a sit-on fishing kayak in the mix as opposed to setting out to build one. Here is an example of what is available in Australia:
http://www.fishingkayak.com.au/fishing_kayak_espri.htm

I have no idea what could be sourced in Bombay but I expect there would be something similar.

I wonder how the cost of building would compare with buying once you take in all the incidentals like paint, fasteners and even paddle. If the materials can be sought at a good price then you might come out in front but it would pay to make the comparison.

Rick W

 

Thanks, Rick. My guess is the gentleman above is interested in the building process as an end in itself, but you're right, the comparison would make sense if dollars alone matter, especially if tools need to be puirchased as well.
Here in Maine, I see a lot of 10 ft kayaks all the time. New, as little as $300.00 USD on sale, which would be hard to beat!
A cheap kayak with good stability might be a box section (simple single chine Greenland type with a one-piece bottom). Two 4-6 mm plywood sheets would probably be enough--- three at most. Tape the seams and seal the rest. Maybe $250? Plus paint, paddle, hmmmm.
Yes, it has to be a labor of love.

 

Rick and Alan; you are completely right in that is is more practical to buy a little rotomolded yak than to build one. If Millionswords is set on building while keeping it simple and hopefully economical, then Mike O'Briens Six Hour Canoe could be given consideration. It is a hard chined model with only two sides and a bottom. It even looks pretty good. Two sheets of ply, one 2x4, and four pieces of 1x2 spec lumber is all it takes. And yes an ordinary craftsman could build one in six hours. (not including paint and finish)The only tools required; a saw, screwdriver, a jack plane, and the will to do it. The two sheets of ply even provide enough material to get out the double paddle. No lofting, no sweat. The only parts that are the least bit challenging are the stems. In the case of the stems, your brother in laws, or someone elses brother in laws, table saw will make short work of it. Otherwise one has to plane a lot.

To Millionswords; Lose the bamboo idea. You'll be glad you did if you intend to build other than a skin on frame boat. OK if you are determined, I think that you could build a decent skin on frame boat with a bamboo frame and plenty of lashing. It could be light in weight and retain some of the twisty behavior of a Baidarka. Walrus skins are not a requisite covering material such as used by the Aleutes. The Brits and Irish have built Coracles that way for a couple of centuries. Not with bamboo, but with willow. The Irish do not have bamboo or they might have used it. Multiple chines are not a problem with a SOF design.

 

Thanks Rick, Alan and messabout!

Quite interesting to see more views and replies in the thread.
Bamboo - ONLY driving force is it is cheap and abundant around here.
2. Loosing the idea is not the question. Learning without punching a hole in my pocket is the idea.

I certainly know the complications in making a frame with bamboo. I'm seeing it getting difficult in every step I take closer to building, I'm evaluating the work load vs cost in Bamboo vs Wood frame.

I shall keep the forums updated when I keep moving towards the goal. Nansen some how made it look so simple, there must be a certain trick, that has to be revealed while I ponder for the answers. I shall post it here when I realize the mystery!!

So far I have been planning not to use a strongback, but now I have been visualizing the use of a strongback to hold my frame's first pieces - the Gunwales.

Need to see how well Bamboo reacts to mortise joints, and lashing over it.
Thinking how big (diameter) a bamboo would I require to hold the deck stems and ribs together.

Will keep this thread updated too.

To Alan:

This is the plan that I'm using - Sea bee 13'

http://yostwerks.com/SeaBee13Offsets.html
http://yostwerks.com/SeaBeeMultiChine.html

 

In terms of boat performance the thing that counts is length first and slenderness second. Fairness and finish are a long way behind and I believe often overstated. These certainly make the boat look nice but do not add significantly to functionality.

I think a bamboo frame has considerable merit. You could even use large section bamboo on the gunwale to improve torsional rigidity.

So if bamboo is abundant and cheap I believe it is a good material to start with. I have already spent a lot of time with different materials and do not consider anything but carbon fibre for my applications these days but that is because of easy of handling and is on the opposite end of the scale to economy. So for an economic build I believe bamboo would be high on my list if readily available.

At one point I purchased a heap of small diameter aluminium tube for a skin on frame hull but did not proceed with it but it was an economic one-off for me. The bamboo would be a good substitute for timber or aluminiun tube.

Bamboo at the right price may enable you to build your boat for less than it would cost for a sit-on kayak. There are other threads here covering skin on frame construction and ideas for low cost fabric covering.

Rick W.

 

I'm unfamiliar with using bamboo for boat construction, so I'll leave it to others to comment. My concern would only be straightness. I would also be careful, no matter what species of wood used, to avoid grooving or otherwise interrupting (by cuts, etc.) the longitudinals, at least to any significant depth.
Thanks for the link to the Sea Bee design. Looks like a good first project.


Alan

 

Alan and Rick - thanks for the comments.
reason for choosing bamboo

1. Cheap
2. Abundantly available,
3. Needs less special tools such as motorized saw, draw knife, etching tool etc.
4 and Cheap again.

+ its light weight, sturdy, bends wonderfully, and stays afloat on water.

About the concerns on the Ridges that are found on the bamboo, If I'm able to make the frame successfully, I think I can some how manage to reduce the ridges by sanding and peeling etc. It may be a compromise to test drive my first kayak.

Later when I'm confident about making them, I shall opt to do a Aluminum folding Kayak, which I think I can pull out easily. But the cost of Aluminum and HDPE Plastic would be great for a trial run. All the required material for the folding Kayak is available and I'm constantly making notes for it too.

But my first float would be just under $50 to $60 including the canvas cloth and paint! if all goes well.