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PostPosted: March 24th, 2010, 8:25 pm 
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Hello all,
I am in the process of building my first strip canoe , 15' ranger.
I have all the stations mounted on the strongback , and have got
a good feel for its lines. My question is if I wanted to add about 3/8"
more rocker , can I just shim up the three center stations 3/8 and
then taper off the shim towards bow and stern ending 2 stations be-
fore the stems . I hope that makes sense?
thanks mark


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PostPosted: March 25th, 2010, 7:43 am 
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My advise would be on your first build would be to, build the canoe as designed. This will give a better "feel" for the complete project. Do you think you would actually feel a 3/8" difference on the water?

I've sold many stripper kits and nearlly everyone wanted to make changes as they went along.................also had many calls asking "how do I fix this"

Good luck with your build.

Cheers,
Ken


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PostPosted: March 25th, 2010, 12:57 pm 
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Hmm, In general I would agree with rhumline. Most people just look at boat spec numbers and compare one model to another making assumptions... a wider boat will be slower and be more stable, a thinner longer boat will be faster and more lively, a shorter boat will turn faster, and the worst assumption, more rocker will make it more maneuverable. Those generalizations all tell us too little to really give us a good handle on how a boat performs when completed.

Not all rocker is equal. First off there is no one way to measure rocker... second, the measurement doesn't tell you anything about how that rocker is distributed along the keeline of the hull. So adding 3/8 inch from the very middle of the canoe will have a significantly different effect than just adding the 3/8 inch in he last foot as the keelline transitions to the bow rake. I personally would expect that you will notice the added rocker more the more you distribute that rocker towards the center of the hull, you will never feel it if it's just in the the last few stations. But the counterpoint to this is, that putting that rocker more in the middle of the hull will also effect how well the boat tracks more than if it's just in the ends.

So since there is no one way to measure rocker, and rocker measurements don't actually tell you how the rocker is distributed, then there really is no right way to distribute the rocker along the keeline either. So it comes down to what do you want this boat to do, how you plan to use it.

If you have paddled hundreds of different canoes, and you have built a few, then I think that modifying designs may actually allow you to develop a hull you want. Fine, modify your hull from the plans. But, if you are building your first boat, and just looking at the 6+ numbers a designer gives you for specs, and thinking you can design a better boat for you, then I think rhumline is probably right... build it according to plan.

PK


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PostPosted: March 25th, 2010, 3:14 pm 
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Thank you rhumline and pknoerr. Probably wise to follow your advice. I guess I was over thinking my canoe build,or not thinking enough. I was hoping that someone had tweaked the rocker before or that it wasn't a big deal. I know many have changed the length of their canoes by altering the space between station forms so I thought
why not. Would 3/8" be enough to butcher the design, its not alot when its spread out over 9 stations ( center and 4stations both ways). Is 3/8" even enough to free up the canoe a little bit or could I
tell the difference? I don't know. anyway thanks again
mark


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PostPosted: March 25th, 2010, 3:15 pm 
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Interesting and correct discussion of "rocker," PK. Rocker isn't just a certain amount of rise near the ends. It's a whole bunch of inter-related design decisions, usually best left to naval architects.

I have two tandems, an old Moore and a bastard Bluewater, that have a conservative approach to rocker. They have straight keel lines for much of their length, and then the keel rises in the last 3 feet or so to make turning easier. I used to think this was called "dead rise," but googling proves me wrong. Dead rise is a cross-sectional feature, not one affecting the long dimension of the keel. Then I found John Winters calling this end-of-the-boat rise "Dead Wood". No kidding. :roll: His reasoning is that what is removed from the keel to produce rocker is dead wood because it has little influence on parting the water.

If I were trying to increase maneuverability of a stripper without screwing up its overall behavior, removing some "dead wood" might be a good way to do it. But not in a 15 footer.


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PostPosted: March 25th, 2010, 5:53 pm 
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Mark, I don't know if I would say that adding 3/8 to the rocker along the keel line (regardless of where along the keeline you do it) as you are suggesting (ie: shifting a few stations vertically) will butcher a design, and even if it did butcher a design for one person, maybe you'd really like it. What determines a good boat is pretty subjective... you should read some of John Winter's discussions here on CCR about that.

MY only point is that canoes are designed by a designer for a specific purpose, with a particular user in mind (afteall they want to sell a few canoes) and this user will need certain performance characteristics in that hull. So through numerous designs, often alot of experience with many canoes by many manufacturers, maybe even a little canoe history, a few hydraulics classes, maybe even a little naval architecture, they come up with a design. That design may or may not be what you want. Unfortunately, as EZ says, there is more to canoe lines than picking a few dimensions and fairing the hull between those points. Even highly regarded canoe designers have duds, and they also learn and evolve their designs based on experience.

But that doesn't mean that a little tinkering might not enhance some features that you want. For example, the little white solo in my avatar has been widened almost 3 inches to better allow me to move my long legs in the canoe. Widening the canoe increased the rocker slightly, slowed the canoe a little, changed how the boat feels heeled over, and likely a few other things too. All said, I really like the boat how it is. But everyonce in a while I get to paddle the same boat that we own that hasn't been modified. It's surely liveier, and I'm convinced it responds better to uninitiated freespins on a heel.

The good thing about my mod, is that I can pull the current kneeling thwart out, reinstall the original seat and thwarts and be back to stock in less than an hour. The problem with your adding rocker is that you never even got to paddle the boat un modified, and after you spend 100+ hours sanding ever imperfection, or installing your hand woven rawhide seats, you don't get a chance to modify it back to stock.

PK


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PostPosted: March 25th, 2010, 6:59 pm 
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wow ! pknoerr all good points
I am really liking this site, the info here reaches into all aspects of
canoeing, I think I'm addicted. As for my build I will probably go stock for the first one and see, then maybe some mods for the second one. ( nothing like planning 2 years ahead )
thanks mark


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PostPosted: March 26th, 2010, 8:29 am 
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Location: Lower Saranac Lake, NY
Rocker

I don't have a feel for your paddling desires, but Rocker is a secondary contributor to tracking ability. The most important tracking consideration is Block Co-Efficient, but let's use length/ Width ratio because it is usually similar and so much easier to compute.

River or general purpose canoes usually have a L/W around 6. Touring hulls which we usually expect to track well tend to run closer to 7. ICF hulls, designed for a 1000 m, straight line, affair of honor are closer to 12, but also have roughly, 3" rocker into the bow, 2" into the stern, both pretty well carried towards amidships.
Obviously rocker improves speed or it wouldn't be designed into these single purpose hulls.

Most introductory through intermediate solo paddlers prefer hulls with differential rocker - always more into the bow than stern. The dropped or skegged stern compensating for paddlers tendency to carry the paddle aft behind the torso into a sweep that turns the hull offside. The deeper stern resists turning force.

Pushed hard in both print and resin by John Winters from the late 80's, differential rocker has found it's way into almost all modern intro and tripping oriented hulls, both solo and tandem.

Rocker is a drafting convention, so Steve Scarborough, John Winters and David Yost differ on what 1" of rocker is. Differing stem lay-outs and radii further confuse any attempt at standardization, so comparing rocker specs in a magazine chart is useless. [Did anyone ever wonder why so many great designers are clustered at the end of the alphabet?]

References include Gilmer, VanZorn and Saunders, but the best work for paddlers remains John Winters "The Shape of the Canoe".


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PostPosted: March 26th, 2010, 10:27 am 
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Charlie, do others besides John Winters use "Dead Wood" to refer to creating some functional rocker by just lifting/ removing the final few feet of a hull, while leaving most of the keel straight? (Don't know if you saw my earlier post.) I've been trying to find an official term for this approach, having learned that "dead rise" refers to something quite different.


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PostPosted: March 26th, 2010, 1:31 pm 
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Deadwood is a pretty common term. I cannot give specific references because I'm in process of moving; my hydrodynamic texts are boxed somewhere in one of the two places.

cew


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PostPosted: March 26th, 2010, 1:41 pm 
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Although I probably won't change anything for my first build I do see myself tinkering a bit with the design in the future. After building the strong back, forms, leveling and buying all the misc, I can't see it being for just one canoe ! What I didn't make clear in my original post was that I am trying to understand if their is a proper way to increase the rocker. Now that my forms are cut would adding the shim to increase their elevations be a good way to do this?
My decision to go with the Ranger design is two/fold. One for my kids to learn and use together, and also for river travel. In my experience being in a canoe with moderate rocker magnifies any flaw with your forward stroke and so makes one a better paddler, given you practice proper technique.
thanks again everyone mark


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PostPosted: March 26th, 2010, 4:05 pm 
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Mark, I paddle high rocker whitewater canoes most of the time. In my observation, unless properly instructed, whitewater paddlers may NEVER learn to paddle properly. Most are still J-stroking and ruddering until the day they die.

I discovered, quite by accident, that a good reach forward, a firm catch, and a short stroke ending before my lower hand reaches my hip, will cause my whitewater boats to paddle forward with no correction. The short, firm stroke shoves the bow, on the opposite side, into the water, creating a transient wave. During recovery, that wave of shoved-up water pushes the bow back toward the paddle side. This phenomenon is discussed somewhat differently as the "sweet spot" on the Ford-Foote-Dickert video, Drill Time.

I actually don't know if this technique works with fast, low-rocker solo canoes like the Bell Magic. It does work with my moderate rocker Mad River Guide Solo.

Help stamp out the J stroke and the rudder stroke.


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PostPosted: March 26th, 2010, 8:53 pm 
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ezwater wrote:
Charlie, do others besides John Winters use "Dead Wood" to refer to creating some functional rocker by just lifting/ removing the final few feet of a hull, while leaving most of the keel straight? (Don't know if you saw my earlier post.) I've been trying to find an official term for this approach, having learned that "dead rise" refers to something quite different.


Removing deadwood would increase the "functional rocker", not adding it.

Deadwood refers to the portion of the hull at the ends that is submerged but provides basically no buoyancy. In a wooden boat, it is mostly there to fill out the keel at the transom to provide extra strength and to skeg the stern for improved tracking and reduction of turbulence at the stern. Think of the ends of a traditional pulling boat like an Adirondack guide boat, or especially, a Whitehall boat below the wine-glass transom. In canoes, the term has been used to mean, in effect, vertical stems that distend well below the waterline. It is supposed to improve tracking and add to the waterline length without increasing the entry angle. Think of a classic Jensen designed boat.

Deadrise refers to the angle from the center of the keel to the widest part of the waterline. A boat with lots of deadrise is primarily vee-shaped underwater. Again, an Adirondack guideboat has a lot of deadrise compared to a canoe. Boats with a lot of deadrise are somewhat unstable when at rest, but increase in stability when underway. Most recreational canoes have very little deadrise except for some of the vee-bottomed racers, which can have a lot.

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PostPosted: March 26th, 2010, 10:48 pm 
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Thanks to Charlie and BK. So we remove some deadwood to increase the ability of the boat to turn. But what would we call such a hull? Deadwooded? De-deadwooded? I guess we know what we're removing and what we hope to achieve, but we still lack a term for the result. :doh:


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PostPosted: March 27th, 2010, 10:13 am 
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ezwater wrote:
De-deadwooded? I guess we know what we're removing and what we hope to achieve, but we still lack a term for the result. :doh:


Lol.

Actually, we're not removing anything. Deadwood is the result of the way the design was conceived and drafted. How about we don't call it anything and just don't draw it in the first place? :wink:


Mark, there is a guy who used to post here a lot who built a really fine Ranger. His CCR screen name is "dan." and he would likely be able to answer all kinds of questions. I've seen his boat, and it is a first class job he did on it. He's a fine WW paddler as well, so he would be able to give some insight into how much, little or not at all you should modify the rocker. Send him a PM and I'm sure he'd be glad to give his two cents.

I'm on board with most folks here in thinking you should build exactly as the plan calls for. Everybody thinks that, since they're building the thing, might as well customize it. Problem is that none of us are real designers, as in guys who have drawn up and built scores of different boats, often making only subtle mods here and there.

Build the first one straight and then, if you must, change one parameter at a time on subsequent builds. That is the best approach. For example, PK widened his Flash and it probably added a touch of rocker to an already well-rockered design. But by doing this, he also had to have widened the waterline a bit in the process. Which change is responsible for his observation that the altered boat is now slower? Hard to say since both changes resulted from one action.


Get John Winters book. It's like $25 on CD, and it includes great boat design software (FreeShip) and John's "Kaper" program that allows you analyze the hydrodynamics of your designs. FreeShip is a very robust design application that many folks are using to get started in canoe design. It's a bit confusing if you originally learned conventional lofting techniques, but there is lots of help from users available on the net.

The book is a bit heady, and there are some things that are stated but not fully explained. Yeah, I saw that JW puts the block coefficient way up at the top of the list of things that contribute to tracking, but I don't get why. After all, a gigantic bowl that displaces 400 lbs at the 4" waterline has a lower block coefficient than a 16' performance tandem canoe with the same displacement. Which one do you think tracks better when propelled with a single blade? :lol: Must be more to it than just that.

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