Hi all,
The other day I went shopping in the only store in our country that sells canoes above entry level, where I bumped into two brand new Mad River Explorer Heritage/Duckhunter canoes for sale. I immediately fell in love with the gorgeous woodwork on those boats. Combined with the production stop on Royalex I already pulled the trigger on buying on of those guys, only to find out that one was already sold and on the other one was a reservation. Bummer.
As I still couldn’t get my eyes off the canoes, I noticed one of them had a hull which was remarkably concave instead of - as one would presume with that particular boat - more or less convex. This was even more apparent as the other, similar canoe in the shop didn’t have that ‘problem.’
As I shared my observation with the staff of the shop their only reply was: “oh well, no Royalex hull is the same.”
This answer didn’t quite satisfy me and made me think even more about hull construction as related to (the amount of) rocker. As I went home, I immediately checked out my own Explorer (Rx 16), and found out that from both sides (bow and stern) going midship only the first meter (or so) was convex, and after that the middle of the canoe hull was (not even flat but) slightly concave. This was measured with the canoe upside down and out of the water, so even without taking into account the (I must say, very annoying) oil canning of the boat if in the water.
I admit: I always thought that ‘rocker’ meant a convex shape all the way, thus implying that the ‘lowest’ point always resides in the middle, canoe-hull wise. My recent observations however made me wonder if I may be wrong. And if so: how do canoe makers measure/define rocker on their boats?
For instance: Mad River claims that their Explorer 16 has a moderate rocker of 6 cm. at both bow an stern. From where to where do they measure that? If I would draw a vertical line at both tips of my Explorer, 6 cm. rocker would already be achieved when going no more than 2 cm. horizontally inwards from the tips of the canoe. And furthermore: the middle 2,5 meters of my canoe hull are even concave.
So where does the rocker start and end? Of course I know there is more to canoe manoevrability than rocker alone (especially with a V-hull like the one on the Explorer), but somehow MRC finds the mentioning the exact amount of rocker of their canoes very relevant. So why not reveal the way they measure it?
Have a good paddle,
Henk-Jan ten Brinke
The Netherlands
there is no single definition of rocker
Its the rise of the bottom from some arbitrary distance from the stem. No one has agreed on that distance. It can be ten inches… it can be to the center point of the canoe.
But your real issue is not the measurement of rocker. Some jackass is trying to dupe you into buying a hogged ( negative rocker) hull which should never happen
I would so not go back to that paddlesport store. The salesman assumed you were ignorant or he was. That is a hogged hull and never acceptable. Concavity in a canoe hull viewed from outside is not “royalex is all different”. I’d like to give the salesperson a piece of my thoughts.
It may have been deformed by improper storage , improper shipment or escaped the factory due to careless quality control
Rocker
Rocker is just how not flat a hull is. Little or no rocker will track straighter. More rocker will enable easier turning. I’ve heard that more rocker makes the boat more “playful”.
If you look at the bottom of the boat, the center should be lower than the front and back. The lower it is the more rocker the boat has.
when you’re talking about the center of
the hull being the lowest, you’re more likely to be talking about whitewater boats. Usually rocker in flatwater boats is limited to the last foot(+/-) of both ends.
When measuring…
rocker, it’s best just to say, slight, moderate, or a lot. Even those words don’t mean much.
JKaz
not always true
Prospectors have stepped rocker as well as some of the more nimble touring boats
There might be a tenth of an inch over the first foot, a quarter over the next, a half over the next etc…
I have a bunch of DY boats that do not sit quite flat on the floor. He has used stepped rocker on some like the Fire Series.
Wildfire 2.5"
The Wildfire spec’s say 2.5" of rocker at the bow and stern, which seems to be about where the boat starts to turn up at the stems.
http://www.flickr.com/photos/eckilson/29808800275/in/dateposted/
There may be some stepped rocker, but like most flatwater boats it is still basically flat in the middle.
http://www.flickr.com/photos/eckilson/28408202822/in/album-72157668553300693/
The banana shape is more apparent on old-school whitewater boats like my Encore that has 5" of rocker. Even on grass you can see the banana shape.
http://www.flickr.com/photos/eckilson/14842935940/in/album-72157646842117505/
Or maybe extreme…
Like this one (made by Kaz).
http://www.flickr.com/photos/eckilson/29727129061/in/album-72157672310265472/
Assume that is a Prowler - what’s the rocker on that?
Beautiful boat.
talk to David Yost
the designer. My Wild does have a gap from way toward the center to the ends. The Aria too. Stepped rocker can be subtle.
It is fun to talk ellipses with DY
Is your Wild Rx? Different mold.
Eyeballing a bottom sometimes misleads. What Charlie does with a helper is hold a rope taut and level and lower it until some part of the rope contacts the hull. Then you can see gapping more clearly
Anything stronger
N the hull becomes rhomboid.
Scoping ‘rocker’ requires considerable visual immersion into visual comprehension off all known…and unknown rockers designs.
Without that effort, ‘looking’ at hull shape…naval architecture…is same as looking at a bicycle or sewing machine.
I think of 2 more extremes: the expanded bow giving a visual impression of concavity and dos, a complex touring design where rocker in the the designs attempt too ‘glide’ subtly moves into a visual incoherence
Erik…
It’s impossible to measure rocker accurately. In my opinion, anyone that says otherwise is just blowing smoke. No offense.
Jk
Actually have both…
Royalex and Whitegold. The picture is Whitegold.
Rocker?
Rocker is upturn along the keel line near the paddlecraft's stems. It can be carried out to center, as in original Prospectors or quite localized. It can also be differential, usually less at the stern to ameliorate the effects of dysfunction forward strokes such as when the paddle blade is carried aft of the body or the shaft is angled across the rails.
Stepped rocker is a change in rate; usually subtle rocker from near amidships suddenly becoming steeper near the stem[s]. Good examples of stepped rocker are apparent in several John Winter's hulls and Yost's recent Kewaydin series, both from Swift Canoe & Kayak.
It turns out bow rocker does not have much effect on tracking or yaw but does increase speed a little.
Winter's tried to get the industry to standardize rocker measurement, but, as DY stated at the time, rocker is a drafting convention unique to each designer, making standardization similar to herding butterflies.
So it goes.
It seems the OP was describing HOG, an upward, amidships, deflection of the keel line. That could be caused by heat distortion and or by putting rails on the hull. Rails are straight and need be bent to match the shear line. Wooden rails cane be bent somewhat when installed, aluminum rails need pre-shaping through a three roller set to not distort the hull. Hogged boats paddle horribly, but stems drag; the hull "trips" over it own bow, etc, etc.
We can change the rocker in hulls, particularly wood/fabric and RX ones by narrowing or expanding thwarts and seats. Cut a long axis edge from a business envelope. Spreading the center increases rocker, narrowing center spread decreases it. Naturally, this does not work on foam cored hulls like Savage, Swift and Wenonah where the bottom sandwich forms a quite stiff unit.
well yes & no…
....since I noticed the - indeed - quite 'hogged' Explorer hull in the shop and after that checked my own Explorer (and found that there was a slight concavety in the middle 3 meters of the keel line), I started thinking about this rocker thing and how this was measured. Especially by Mad River, as they specifically state that their Explorer hull has '6 cm. rocker at both bow and stern.'
And indeed at first I thought that a more or less 'rockered canoe' meant that the lowest point of the keel line always would be in the middle of the boat, but the replies in this thread show I was wrong by that.
However, this still makes me wonder if a hull that's more or less concave during a significant lenght of the hull in the middle, thus has its lowest points on boths sides and then rises near the stems to 'meet the rocker specs' is (and behaves) the way the designer intended it to be.
Sure, my own Explorer isn't nearly as concave as the one in the shop, but it is very slightly out of the water and in the water (especially tandem empty) much more due to the wobbly hull. I’m quite sure this translates to a different en less efficiënt behaviour on the water, as both the vertical and horizontal flex absorps energy transfer and thus affects responsiveness?
I didn’t have a chance to paddle another Explorer yet, so I really can’t compare apples to apples, but the other Royalex tandem boats I’ve paddled sure felt much, much more sesponsive (and were also lot stiffer) than my Explorer. This may (and will) also be due to difference in hull design, I know. But my new (15 year old) shallow arch Gatz Orca 16 Rx totally retains its (arched) hull form in the water, whereas my Explorer somtimes transforms into a flat-bottom (almost without any V’ left) on the water.
Below are links to 3 video’s, one showing the difference in horizontal flex between my Explorer and the Gatz, the other one ‘oil canning’ with me sitting in the bow seat (just slightly rocking) and the last one showing the water in the hull while I sit on the yoke to keep the boat level. If there would be someone in both the bow seat and the stern seat the bottom would come up much more.
After paddling all those other, stiffer Rx tandems and watching the deformed Explorer hull in the shop I guess I’m just starting to wonder if this hull behaviour is characteristic for a 16 Rx Explorer or if my hull simply is too ‘floppy’. I might add that I bought it brand new last year, and it was – since Royalex ‘is no more’ - the last one they had.
If it’s supposed to behave this way, I guess I’ll just have to deal with it (and maybe add some thwarts) or find a good buyer for it……
https://youtu.be/P7mbVz1LoUM
https://youtu.be/80E_13_U0oE
https://youtu.be/Zrjlslx5ZxI
I like this video!
http://www.youtube.com/watch?v=Azx9mDn09KI
Makes me want to get out in my tandem boat. Nice to see all the canoes. What river?
That’s
and old one! It’s the Ourthe in Belgium. In our neck of the woods white water is rare, so we’ll have to paddle this river mid winter…