Newbie who would love your opinions

[Woody]

While building boats/kayaks will be a new thing to me, woodworking in general is not. I have been working wood for the last 4 years as my primary profession. I design and build furniture and cabinetry on a daily basis, so I do know that there is a lot of thought that goes into the design process. That said, I also know that there is a huge difference between building furniture and building a kayak. I also know that I have read an awful lot of books and articles and such before I jumped into designing furniture. And, while I have read a lot about building a kayak, I regret that I don't completely understand all the language and figures that are an inherent part of it.

I am aware that the design that I have come up with has some complicated curves to it with regards to building. I am wondering what you guys think of it as far as its stability, drag, etc. I read a post with regards to someone else's build which stated that you should build it according to it's normal load, not it's heaviest load. I'm 6' 3" tall and since I weigh in at 235, I figure that I would have about 15 pounds extra for a day trip, so 295 lbs for the design displacement. Will I be able to fit into it? Having never been in one before, I don't have a clue what size the cockpit should be. I think I am on track with the stability and such, but just really don't know for sure. Should the stability curves ascend quickly and descend in reverse, or will less ascent over a wider range be better? I can't seem to find anything that will explain the stability curves. Will this design be stable in a fairly wide range, or does that even make sense?

Thanks so much for you input! Forums like these are what makes the internet so valuable.

[RiverRight]

With respect, and before reviewing your design, dont you think it would be wise to get some experience paddling a variety of boats before you design your own? How else will you know what suits you.
Where do you plan to paddle?

[Woody]

I am planning on some of the area lakes, as well as some of the slow moving rivers that are around here. I am planning on going with a friend of mine who has built several of the Great Auk kayak's. He seems to like them a great deal, but they have don't have a shape that I like. While I can appreciate the fact that looks should take a back seat to function, I want both. Otherwise, for me anyway, it's not worth doing. He has offered to take me out when the weather gets cooler, and with all I have to do right now, I don't really have time to build one until then anyway. I figured that I might at least be able to figure out the design process a little bit in the mean time.

As far as paddling a variety of boats, I don't think that will be feasible unless I purchase them as we don't have that many people around this part of the country that have them. (At least as far as I can tell.) I don't recall the last time that I even saw one on any of the lakes/rivers that I have been to.

I also don't think that I will mind if I build one and then don't really like it that much (for me at least). I have always wanted to build a boat of some sort, and this seems to fit the bill so to speak. I am mainly concerned about whether or not I will fit into it, it will float with a beginner level of stability, will track reasonably well (I don't want it to make a 90 degree turn every time I put an oar to the water), and won't take a motor to move it in the water.

Thanks for your responses. I know that I don't know much of anything about kayaks, but I am trying to learn a bit before I give it a go.

[defer]

Ok then. Great to hear your interested in building your own. Even better to hear that you've got lots of time to learn the program. Your posted design has got a lot of problems. You should spend a lot of time reading previous posts and looking at the designs to which they refer.

A very good starting point would be to use the search function in the upper right and find "Buddy's tutorial"
It is about a half page on design basics.

To answer a couple of your initial questions, it sounds like you are abig guy, Kayak foundry lets you choose 1 of 3 different size cockpits. I would probably suggest the largest. It will make it easier to get your legs in and out.

In regards to reading stability curves, here is a brief idea of how to read them that I had written up a while back. More info can be found online by googling it.

....

Parts Of The Graph

The stability curves graph represents the force required to lean the kayak back to "even keel" from the various degrees of lean (heel) as noted on the graph.

The first point on the graph is with the boat sitting upright at even keel, and the last point, where the curve dips into the negative is the point where the the boat would capsize unless the paddler takes action to prevent it.

At any point between the two points, the boat would return to even keel on it's own.

Along the upslope to the peak, it takes greater force to capsize the boat than to settle back to even keel. The peak of the curve, is the point where it now takes less continued force to capsize than to settle back to even keel. It would still return on it's own, but from here on, it would take a smaller bump to capsize the boat than before the peak. (the natural "righting moment" becomes weaker - it feels tippier.) The higher the peak, the the more force is required to capsize the boat.

What It All Means.....

Boats with high Initial Stability (those that feel very stable while sitting upright on flat water) will have a steep upslope in the first half of the graph.

A boat with good Secondary Stability (those that still feel stable as the boat begins to lean) will show a large cross sectional area beneath the upslope to the peak on the first half of the graph. Such a boat usually has a "flared hull".

Boats with high Overall Stability will have a greater cross section on the graph than others using the same graph plot. Overall stability is a less specific generalization that among other things, averages the intial and secondary stabilities.

Novices may like high initial stability, but those with just a little more experience will likely prefer good secondary stability, which is easier to "recover" when a wave bumps you off balance as you head into more more adventurous waters.

[Woody]

I am a rather large fellow. I had wondered about that particular setting, and opted for the mid sized cockpit as I really didn't know.

I had read your article (which I found while reading numerous post on this awesome site) about stability curves. I also found it extremely helpful in deciphering what I might expect out of the finished boat. It really answered a whole lot of questions that I was having. I just didn't know what the appropriate amount of force should be required to keep a boat upright. In other words, should I be aiming for 6 lbs of force with a heel angle of 20 degrees or should it be 25 lbs. I looked a several that were posted, and decided that I must be somewhat close to normal, but does that fit the boat or is that just irrelevant all-together?

As of right now, I honestly don't know what is wrong with the design. I will keep reading though. There is so much to learn! Thanks for the replies.

[estrabanos]

I honestly don't know what is wrong with the design

I'm not expert

But there is few obvious think
Draw is not under cokpit
Red line in body plan show that boat is wider some where else than in sheer
Bow and stern have lot of concave section which will be hard to follow with ceder strips.

There is lot of think to learn(for me too) Have a look at another post and review

Good Luck

[Jimyak]

Hi Woody:

Welcome aboard.

I made some changes to get your design back into the realm of reality.

This is pretty close, see if you can refine it somewhat.

All the best,

Jim

[Woody]

I am not sure what you are speaking of regarding the realm of reality. Are you referring to whether or not the design will float or not, or are you referring to being able to build it? Maybe both. I can visually see what you have changed, but comparing most of the numbers, they are a lot alike. The stability has changed quite a bit with your design though.

[anewhouse]

One of the problems with your first design was that as the kayak leaned over, it was not long before the widest point went under the water. So by the time it was leaned 20 degrees, the force pushing you back upright was already decreasing.

On Jim's design, the force pushing the kayak back upright continues to increase right up to 40 degrees. In very simple terms, that is because there is a lot of the hull available to keep making the kayak wider as it leans over.

That means your design would quickly tip towards the point of no return while Jim's would keep feeling stable as it leaned over.

As has already been mentioned, that very pinched bow and stern would be very hard to build and it does nothing at all to help the performance or handling of the kayak.

Have a look at some of the other posts that discuss stability, hull shape, full bow and stern, hull flare, hard v soft chines, concave curves, CLA and LCB, weathercocking, tilted cockpit, banging knuckles and hull controls. There is something that you need to adjust in most of those areas.

[Woody]

Ok, I've spent way more time on this now than I care to admit. I'm so stuck on building a yak that I can't think of much else. I have read an awful lot of this forum as well as others. I hope that I have improved my design at least somewhat, but would really like to know what you guys think. I still don't know what the recommended drag should be in order to comfortably paddle for a few hours. I do wish that I had more experience on the water, but that is just not practical at present. I also don't know whether or not the stability of this design is acceptable or if it needs to be increased.

I can't seem to find where anyone has pointed out where the rocker is to be measured at either bow or stern. Is it measured at the last pre-indexed form in the software, or somewhere else.

[anewhouse]

Rocker is not easy to measure. What you have now looks about right.

Your design is very wide. 20" is not unusual, but almost certainly too narrow for what you need. 22" to 24" is beginning to get too wide for a lot of people. Even allowing for the fact that you are 6' 3", you will probably find 26.5" wide enough to be awkward to paddle.

You appear to have tried to make the kayak quite stable. In fact you have probably made it much more stable than it needs to be.

However you could have the same stability in a narrower kayak, or better still a little less stability in a much narrower kayak.

The problem is that only a very small part of the length of the kayak is close to the maximum width because of the very fine ends. Notice how the volume distribution graph rises to a very sharp peak. You need to flatten that peak. Make the ends fuller and you can add a lot to the stability.

Very fine ends on a kayak look sexy and they help a tiny bit to keep drag low, but they are very detrimental to stability. Don't worry too much about drag at this stage.

You can make the cockpit any size you want. After you select shape A, B or C, you can use the green control points to make it longer, wider and/or more egg shaped.

[Woody]

Thanks for the response. My original design was a bit narrower if I recall. After Jim posted, I even left it narrower, but never could get my stability up until I widened it. Not knowing what kind of stability I should have, I opted to try and get my stability graph around what Jim's post had. I have dropped it back to 24" wide now, but can't seem to get anywhere near the stability out of it that Jim had or even my last one. Guess I'll keep working on it.

Should I be looking for a stability rating of about 100 like the program says, or should I be shooting for something along the lines of what Jim or I posted? I can't seem to even get close to those numbers when narrowing the hull.

[anewhouse]

You will struggle to get good stability without a lot of width while ever you retain those thin ends. Notice that the top stability graph in this image tops out at under 40 while the second one gets well over 60. The designs that created those stability graphs are below. They are just your current design and a modified version of your design. They are both the same width.
Click on the image to enlarge.

Compare the two hull shapes in this picture. The top one is your design as it is now. The bottom one is your design with fuller ends. It is the same width, but has over 50% more stability.

You could have the same stability you have now with a kayak that is 3" narrower. I have shown that in the image below.

You probably wouldn't want to change the hull shape as much as I did. I overdid the change a bit to make the point more clearly about the effect. I have also made a couple of other changes. The front of your cockpit is about 4" higher than most people need. I dropped it a couple of inches.

Don't try to add stability by making a little bit of the middle of the kayak very wide. Do it by making a lot of the length of the kayak a reasonable width.

As far as stability goes, a SF of 130 is the sort of stability that I would feel confident about sending my 90 year old mother out in.

Read what pdx1 had to say about how much stability is a lot in this post.
viewtopic.php?f=2&t=1630#p15179
You already have more than a first time Granny needs.

[Woody]

One of the reasons (aside from the sleek look) for having designed it so narrow (in the bow at least) was because I had read numerous posts that said the half angle of entry should be anywhere from 5-8 degrees. I was merely trying to keep that number within that range. I settled on about 7 degrees thinking that would be safe, however, it appears as though that number isn't as important as others. I had been able to get a design with the same overall shape as my last one that had a stability rating of 100 but it seemed to not have but about 10 lbs righting moment and was on the downhill about 35 degrees.

I have been working on this one, seems to be a bit of a compromise. It seems to have a wider range of stability but with less righting moment. I just don't know where that happy medium should be. I would really love to see a stability graph of what I should be shooting for given my intended purpose and skill level = 0. I had originally thought that Jims model was what I should be aiming for, however, from what others have said, that doesn't appear to be the case. I have been canoeing several times before, and found that very enjoyable, but I wouldn't be so bold as to place a canoe in the same realm as a kayak aside from maybe steering one. Thank you very much for your help!


I just finished reading the link in your last post. Thank You!!! That is soooo what I have been searching for! Given those numbers, wouldn't this one be a reasonably stable design for me or am I still missing something?

While adjusting different things, I have adjusted the height and size of the cockpit. It doesn't appear to change the other statistics any, so I figured that I would work on that last thing. I was planning on building some sort of "mock up" of the cockpit so that I could get a really good idea of what size I will need to comfortably get in and out of.

[pdx1]

Don't get too hung-up on numbers like half angle of entry.
Instead, try to make the boat look aesthetic, as in "pretty", with nice symmetry, good proportions (to the eye) and smooth flowing hull controls. It's easier said than done, and since beauty is in the eye of the beholder, we have seen on this forum quite a few very eccentric shapes that "only their creator would love"
As a general rule, boats with smooth and mostly straight lines, and few dramatic curves, are the most efficient.
Remember the meaning of the word "fluid".
The only exception to the above would be the upswept bow and stern typical in Greenland kayaks. Upswept bow helps to ride on top of the ice, and that's why the Inuit put in on their boats, but for anyone paddling in less severe conditions, it is mostly for decoration.
While you make your boat symmetrical and "fluid", keep your eye on stability graph, drag prediction graph (for your typical speed), and the LCB and CLA numbers. As long as they stay in the right ranges, don't worry too much about other numbers.
As far as your specific design:
1. It is much too tall: 20'' at the front of the cockpit. Even for a big guy like you, 13 to 14 inches would be the absolute max anyone would ever need.
2. As far as stability, shoot for 15+ lbs of righting moment, with the peak at 20 to 25 degrees of heel angle. This is good for anything you would want to do in this boat.
As an experiment, I reduced the height of your design to 13.2'' at the front of the cockpit. I brought up the design displacement to 295 lbs. With these figures, the stability was 23 lbs*ft with peak @23 degrees of heal, which are excellent figures.