Thread: looking at building a timber strip kayak, just a few questions

Something else that worries me a bit (assuming I have the right impression about where and how you intend to use this kayak) is that you seem to have gone all out for low drag and speed to the extent that the kayak will be very unstable.

Stability is more complex than just making it wide to get stability.

For example do you know why this version

http://www.fileden.com/files/2008/7/...5444/no003.yak

is much more stable than version no002, even though it is the same width?

Forgive me if you already knew all this and are sure you want something that is more suited to racing than comfortable cruising. I may be misreading the situation. I am trying to be helpful, but I realise what I have written may sound patronising. It is not my intention.

don't stress about posting up your opinions, critisism and whatnot, everything is helpful, if it sucks, please tell me, i have no idea on boat stability, or the effects of what it all does i'm just good with the actual construction side of things

no, i don't know how to roll the kayak, i do want to learn hopefully youtube and making a fool of myself can help with that though

the target is an all-rounder, mostly it will be used paddling around the lake in forest lake (after work), fishing on the weekends, extra weight and drag won't bother me too much, just means more muscle will be built up- but i do want it to not be compromised too much when i take it into the rougher stuff- like 2 foot choppy waves, and paddling against strong river mouth currents- as i won't be doing this too often, i won't need to accommodate too much for it

for the fishing rods, i was thinking of just attaching some cradles (like raised wings) on the side of the kayak (or some alloy plates to hold these attachments so i can put them in the storage bin when not in use)

Howdy,

One Idea ... when I move into a new area of design that I am not super familiar with I often spend a period looking at existing designs and do some sketches on paper or on the computer.

Just to get a feeling for different rockers and different cross sections. Nothing too precise.

If it is to design a paddle or an oar ... I will look at modern manufactured designs and also look at traditional approaches.

I can't look at the files you have created (and don't want to download another piece of software I don't need) but a general mistake that first time designers make is almost always to make the boats too "arrow like" ... their feeling is that pointier is faster and cooler looking.

This is perhaps the biggest flaw you see looking throught Yachting magazines and they are introducing some "new designer" who has a beautifully rendered image of a 60' supercool boat that has not been built yet.

Pardon the editorialising ... but I would much rather see 10 or 15ft boat that the person has actually designed and BUILT - like you are planning to do. For someone who is wanting to design boats for other people it is even better if the person then uses it in company with other boats and finds out what it can really do - rather than smile in splendid isolation.

Back to the point.

If I can find out some of the technical specifications of a range of well respected designs that do what I want then I will write down the properties of the different models. Length, beam etc and more technical specifications like prismatic co-efficient (overall and maybe for the bow and stern individually) , wetted surface and maybe the metacentric height (not commonly available - it is a stability measure - but if you have a bunch of existing boats provided with your software then it might be possible to extract these numbers.)

Then after collecting this information I then sit down in front of the computer and start drawing - trying first to hit the curves then as it looks more boatlike I start checking the numbers. After that I alternate between lines and numbers until it all starts falling into place trying to hit the numbers and hit the curves that you have in your head by now.

Look at your paper sketches and collected material if you have a specific question ... but don't focus on them too much.

One thing I would avoid is choosing one design that you like and trying to clone it... you will learn nothing at all and you won't bring anything new into the world - it is like being a proud Holden, Ford or Renault owner - they might be nice - but really, they are the same as everyone elses'. And cloning is a bit like stealing anyhow - you should pay the girl/guy for the plan if it is that important to you.

By the way ... I do talk about the design process of the Rowboat plan on my website

Best wishes
Michael Storer

The danger with trying to create an all-rounder is that I have seen attempts to do that where the kayak finished up not doing anything particularly well.

A kayak which is wide enough to be very stable will be very difficult to roll and of course will probably be significantly slower than one which is narrow enough that you have to concentrate all the time to stay upright. Your original design would probably be easy to roll, provided you were a snug fit in the cockpit, but it would be downright dangerous to try to fish from it.

However it is possible to create a design that is pretty good for a number of applications, so don't be put off trying to do it.

I would recommend that you do a lot of research to get an idea about the dimensions and shapes that seem to work best in various situations. There are an enormous number of sites with that sort of information written by people with a lot more experience than me. I can recommend some sites that I have found very useful if you have trouble finding the good ones.

I like the idea of having a kayak that is reasonable efficient. I paddle a lot with a group of people who are mostly retired. We normally paddle at quite a leisurely pace because some of them have very short sit-on-top plastic kayaks. I have noticed that even though they start by insisting that they are quite happy with their plastic tubs, it normally only takes one experience of having to paddle against the wind and tide at the end of a long day to realise that they would enjoy themselves more in something where they didn't have to paddle flat out just to keep up. In the last year at least two of them have immediately swapped their tupperware SOT for a Mirage sea kayak after one such experience.

I think you have the length about right. Anything between 4.5 and 5.5 metres would probably be OK.

If the bottom was a shallow V, it would be much more stable than your original rounded shape. The drag would increase very slightly.

The very fine bow and stern means that only a small part of the length of your kayak is close to the maximum width. If the bow and stern get wider closer to the ends, in other words are blunter, then much more of the length of the kayak is fairly wide. That can make an enormous difference to the stability. Once again there will be a slight increase in drag.

That is why my version 3 of your design is much more stable than version 2. The only thing changed was how fine the bow and stern were. It is quite easy to make a 500mm wide kayak more stable than a 550mm wide kayak.

Most of your other dimension look OK at present. A higher bow will probably give a drier ride in choppy water, but it will catch the wind more. Greater volume will give you more storage space, but will also mean that side winds affect the kayak more as well as making it heavier and more expensive to build.

I like a cockpit that is about 760mm long and I only need about 390 mm width to fit my hips, but I fit thigh braces to create a keyhole shape. That lets be get in and out the easy way, backside in first and then legs but still allows me to lock myself in firmly when necessary.

You might notice that when I modifies your design, I had the CLA just a bit behind the LCB and the greatest draft close to the same point. That seems to be regarded as desirable.

You make the point that you won't often need to paddle against the current and against the wind so you suggest that you don't need to build something that will be especially good at that. The problem is that such a situation is potentially a dangerous or desperate one where you need all the help you can get, so even though you might only do that once or twice a year, it's a bit like saying that in your car you only brake really hard once or twice a year, so it isn't very important to have good brakes.

However it is possible to come up with a design that sacrifices very little in that area, so it needn't be a problem. I just wanted to make the point that the number of times you might need the kayak to have a particular characteristic is not necessarily a good guide to how much attention you should pay to that feature in the design.

I've raved on for long enough for one post. I really enjoyed developing the design of my wife's and my kayaks and would like your experience to be equally rewarding. Keep at it.

Let me know if you need help finding some good articles and sources of ideas.

I would like to endorse much of what Boatmik has said.

It might not have been your intention to create a cool looking kayak, but it is certainly true that your original design, as I have already said, is much too sleek for its intended use.

You already knows this,Chicoroll, but for the benefit of others who might be contemplating designing their first kayak, the program Kayak Foundry is a very good tool.

It is free. A new design starts with a complete kayak design already on the page. It is easy to modify that design to achieve something close to the design you have in mind or scribbled on a scrap of paper. It also tend to limit how ridiculous a shape you can create.

I know there are much more powerful design programs available, but I have yet to see a free one or a demo of a commercial one that gets you off to a flying start the way Kayak Foundry does. The ones that started with a blank page just seemed too daunting and seemed a bit like using a sledge hammer to crack a nut.

It is available from here if anyone is interested.
http://www.blueheronkayaks.com/kayak/index.html

While Boatmik makes a very valid point about a simple boat actually completed being better than a flash design that never gets built, I think a program like this offers a good excuse to design a few kayaks that might never get built.

First, it is so quick and easy.
Second, I found it a very good way to learn a lot about kayak design. I discovered for example that all other things being equal (which of course they never are), a 5.4 metre kayak is likely have more drag than a 4.5 metre kayak below about 4.5 knots.
Third, it gave me the stimulus to do a lot of research to try to learn how some of my designs might work or conversely, having read about how certain features are supposed to affect a kayak's performance, to then try to create a design that combined those features in a way that would produce a kayak ideally suited for a particular purpose.

Just in case someone is interested in following this conversation, this was Chikoroll's original design.




This is my suggestion about a few small steps in the right direction while keeping the original appearance.

I've been reading this with great interest. Very interesting.

I have a question if I may. I assume the area forward of the cockpit is higher to accomodate the legs. Why is the area rearwards so low ? Is it just to reduce skin area ?

I know something about sail boats and rowboats but really nothing about kayaks.

Sorry to intervene.

Thanks Anewhouse for posting those plans. Could someone tell me how to view the files that have been posted in Kayak Foundry? I downloaded KF some time ago but haven't played with it much.

I would recomend taking the changes anewhouse made and exagerate them a little more. This would give you a shape similar to the NDK Explorer which is one of the most forgiving rough water kayaks ever made. http://www.seakayakinguk.com/kayaks/range/explorer.html

With regard to the hull cross section a shallow V is better for a sea kayak than a U shape. Although it has a little more drag the V makes edgeing much easier which is the key to turning. More V towards the ends will give a softer ride in chop and some flare above the waterline gives a softer landing when dropping off the backs of swells as well as a dryer ride. Flare above the waterline also helps with rolling.

Chines that are only slightly rounded will give better stability and a more definite feeling of when you are up beyond the point of no return when coming up from a roll.

I agree with anewhouse about the cockpit, a keyhole is much easier to use. I'm the same height, weight etc as you except for smaller feet. The size cockpit that anewhouse suggested should allow you to sit down first and bring your legs in afterwards which makes launching and landing in tricky situations much easier. The suggested cockpit will also allow you to use an off the shelf spraydeck instead of having one custom made. You could even make the openning a little longer, the largest on the kayaks I own is 83cm internal, 92 cm external on a whitewater kayak. If you look at the explorer I linked to above you can see how thigh braces are incorporated into the cockpit, this allows you to lock yourself in which is essential for rolling.

Hope this helps
Kelvin

Damien, the low rear deck reduces windage in the back half of the kayak which reduces weathercocking and makes lay back rolls easier.

Kelvin

Originally Posted by damian

I've been reading this with great interest. Very interesting.

I have a question if I may. I assume the area forward of the cockpit is higher to accomodate the legs. Why is the area rearwards so low ? Is it just to reduce skin area ?

I know something about sail boats and rowboats but really nothing about kayaks.

Sorry to intervene.

Don't apologise. Feel free to join in. This isn't a private conversation.

The rear deck is almost always lower.

It tilts the cockpit to make entry and exit (or should that be egress) easier. Anyway the tilt makes it easier to get in and out.

It also makes it much easier to execute an Eskimo roll because it allows you to lie back to keep your centre of gravity much closer to the kayak than would be the case if you sat upright.

It also helps reduce weathercocking, (turning into the wind).
Almost all kayaks weathercock. Some do it a little, some do it a lot. A small number don't and a tiny number of very badly designed ones leecock.
Having less height behind the paddler helps reduce that a little bit. Although of course a high bit right at the stern will have more effect than a high bit just behind the cockpit.

Originally Posted by KJL38

Thanks Anewhouse for posting those plans. Could someone tell me how to view the files that have been posted in Kayak Foundry? I downloaded KF some time ago but haven't played with it much.
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Kelvin

The exact steps depend on the browser you are using, but in Firefox, you right click on the link and select Save Link As or Save Target As and save the file in a convenient place. If you save it in the Kayak Foundry directory, it means one less step when it is time to open the file.

Then you just open the file in Kayak Foundry in the usual way.

Let me know if you need more detail.

I like the look of the Explorer that you mentioned.

Thank you for the replies, that all makes sense.

I don't ahve anything constructive to add so just for a change I'm keeping my typing fingers away

But I am reading with interest. I was never interested in paddlers, but have been thinking for a while that a canoe might be a nice thing, especially with a rig and a couple of outriggers

Originally Posted by Chikoroll

don't stress about posting up your opinions, critisism and whatnot, everything is helpful, if it sucks, please tell me, i have no idea on boat stability, or the effects of what it all does i'm just good with the actual construction side of things

G'day Chiko
I take it you particularly want to do strip boat ? It occurs to me that CLC's Mill Creek
15 ticks most of your boxes, but is a plywood boat. Has a large open cockpit
so getting in & out is easy, as is stowage of rods & etc. The couple of people I know
have or have had them found them a forgiving stable fishing platform, easy to paddle, &
reasonably dry in a chop. I wouldn't regard them as an open water boat, although a
chap named Fenger toured the Carribean Islands in something vaguely similar back in
1911. Down-side is that it won't come up dry even if you do learn to roll up.

As far as rod holders go, there are commercial rotatable/angle-able ones available
costing an arm & just a couple of toes. In previous boats, I have just let a piece of
40mm PVC water pipe in through the deck, & sealed the base to the floor. Needs to
go in up close to a bulkhead so that it isn't carrying any compression loads between
deck & floor. Note that sticking even a light weight up in the air affects the stability &
roll-rate of the boat. Enough to feel uncomforable until used to it.

Agree with MIK about pointy ends & stability. My current boat has fine ends & is a bit
twitchy, My son hates it. My previous boat, same overall length & beam has a wider
waterline beam & fuller ends. Everone who paddles it loves it. As you can see from the
pic below, there's not a huge difference in cross-section for this big difference in behaviour.
But carry that extra fore & aft for most of the length & those lots of little bits add up.

cheers
AJ

Is there a Mill Creek 15? I had seen the 13, but that is really too small for a grown man.

The Mill Creek is a proven, popular design and would make a good fishing platform. I'm sure it would be exactly what some people need.

However some people would consider that it is far wider than is necessary even for fishing. It is possible to have something stable enough for fishing that is closer to 24" than 29".

I have already said that 13 feet is too short for a full size adult, but a small adult whose fishing ground was only a few hundred metres from his launching point would probably disagree with me especially when he had to lift it up onto the roof racks of his 4WD.

To illustrate why some people would prefer a longer, slightly narrower kayak, have a look at these drag figures.

They are produced by Kayak Foundry and it has taken me longer to copy them and type them than it did to produce three almost designs, but with one at 13' x29", one at 15'x29" and one at 15'x24".

Of course these figures are not 100% accurate, but they give a bit of an idea of the difference.

Sorry about all the imperial measurements and the primitive layout.
Knots _____ 2.5_____ 3_____ 3.5_____ 4_______4.5
13' x29" ____1.4_____ 2_____ 2.9_____ 4.25___ _ 6
15'x29" _____1.5_____ 2_____ 2.8_____ 3.9____ _5.4
15'x24" _____1.3_____1.8____ 2.5______3.5_____ 4.9

They suggest that at slow cruising speed 2.5 knots or 4.6kmh the extra length doesn't help, but reduced width does.
At 4 knots or 7.4kmh, the longer kayak is significantly better and even more so at 4.5 knots or 8.3kmh. Trust me you are unlikely to get above that speed for more than a few metres, but if you did the benefit of the extra length would increase.
Another way of looking at the difference is that it takes about the same effort to paddle the slowest kayak at 4 knots as the fastest one at 4.5 knots. That is a big difference.

However getting obsessed about top speed isn't a particularly good idea. If you are going to paddle all day at 3 knots, there isn't much to pick between them and it is almost irrelevant that you could paddle the narrower 15' kayak about half a knot faster flat out. I say almost irrelevant because the time you really appreciate that extra bit of speed is when you find yourself having to paddle against a current that is a bit stronger than you thought.

As far as I am concerned, a more efficient kayak is not really about top speed. It is about getting wherever I am going with a bit less effort.

Just to make sure I haven't given the wrong idea, I am not criticising the Mill Creek. It is a great design for certain applications. I as just trying to make the point that for some applications, a different design would be better. For some applications I am sure that some people would find my kayak pretty useless, in spite of the fact that it does just what I want it to do.