Barrens build

[Alan Gage]

I know we've talked some about losing efficiency by adding rocker. Is there a point where the efficiency really drops off ?
​ And if rockering one end or the other makes more, or less of a difference, at least on the computer model ?

​ My hulls are pretty straight keeled, and so this intrigues me.

Jim

I hesitate to keep talking about these design considerations too much. Not that I don't enjoy discussing it but I'm afraid people might start to think I know what I'm talking about, which I don't, or else start to think that I think I know what I'm talking about, which I don't. So with that in mind....

I think there are two different efficiency considerations. There's the efficiency that has to do with the hull's resistance as it moves through the water and the efficiency that has to do with how well a hull tracks; and for us mainly straight ahead paddlers a hull that tracks better would feel more efficient. From what I've read, mostly from J. Winters, these two things aren't necessarily related.

Adding rocker means less hull is exposed to the water, which equals less resistance. Less rocker usually means a longer waterline (less resistance at higher speeds) but more of the hull is in contact with the water so a little more drag to overcome at lower speeds.

One of the benefits Winters gives to a differentially rockered hull is that by adding rocker to the bow you're putting fewer square inches in contact with the water without having a large effect on tracking. Looking at the shape of racing kayaks and surf skis you'll see they have tremendous about of stern rocker to cut down on the amount of hull that's in contact with the water. As a result of this they're completely dependent on a rudder to keep them going straight.

When messing around with my designs in Delftship I can definitely see the resistance numbers change as I add and remove rocker and try to find the happy medium. Just where this sweet spot is, to me, varies from design to design depending on how I plan to paddle it.

I'd highly encourage anyone who finds this stuff interesting to spend the $25(?) and buy a copy of John Winters' Shape of the Canoe from Greenval. Then you can get the information from someone who really does know what he's talking about. If you poke around you'll find a few short sections of this work published online but it's nothing compared to the information in the actual book. Well worth the money. I've read it a few times and am due to sit down and read it again. It makes more sense each time.

There's no shopping cart on the site. Just contact Martin, the owner of Greenval, and he'll send you a copy. http://www.greenval.com/TheShapeOfTheCanoe.html

Alan

 

[martin2007]

Your modesty is refreshing to say the least! To acknowledge that we know next to nothing, but to dive in anyway and learn as much as we can in the short period of time we've got is probably a good map for travelling to wonderful places. Paddle on!

 

[Canotrouge]

I hesitate to keep talking about these design considerations too much. Not that I don't enjoy discussing it but I'm afraid people might start to think I know what I'm talking about, which I don't, or else start to think that I think I know what I'm talking about, which I don't. So with that in mind....

Alan, I'm sure you know less than some, but I'm certain of one thing is you know way more then others... Including me!!

 

[Alan Gage]

I'm having trouble reconciling some of those diagrams with each other and with your photos. When you have a chance could you list the complete hull specs: LOA, LWL and BWL at load, max beam, gunwale beam, depth at center, bow and stern, rocker at bow and stern, and height at bow and stern.

LOA - 16'
Max width - 32"
At gunwale - 27.5"
Height at bow/center/stern - 21/14/18
Waterline length - 15.3'
Beam at waterline - 29.9"

Since there's no hard and fast rule about where to measure rocker I'll just post a picture and let everyone determine on their own where to measure it:

berens rocker 330 by Alan, on Flickr

In case it's hard to see the first horizontal line is 0", the second is 1.6", and the third is 3.1". The waterline is shaded in white at 4.3" with 330 pounds of total load (includes weight of the boat). Bow and stern rocker are the same. I suppose I'd call it just over 2"

For reference a day tripping load (220 pounds total weight) puts the waterline at 3.2":

berens rocker 210 by Alan, on Flickr

There is some discrepancy when it comes to the displacement. The program I design the boats in (Delftship) and the one where I do the stability calculations (Polycad) do not agree by quite a bit. When Delftship gives a displacement of 330 pounds Polycad says 370 pounds. I'm not sure which is correct. Someday I either need a 3rd piece of software to break the tie or learn to do the calculations by hand.

Hope to finish stripping the hull tomorrow. Will post some pictures of the progress then.

I'd love to have stability graphs in hand for a bunch of actual canoes on the water, so I could get a real world proprioceptive feel for what the graphs mean to my stability preferences.

Yes, that's one of the most frustrating things. You get all this wonderful data and information but don't have a way to correlate it to the real world.

Alan

 

[Jim Dodd]

Is it possible to put an existing plan or design, say a Chestnut Prospector into Delftship, and use that for comparison ?

Jim

 

[Glenn MacGrady]

LOA - 16'
Max width - 32"
At gunwale - 27.5"
Height at bow/center/stern - 21/14/18
Waterline length - 15.3'
Beam at waterline - 29.9"

Since there's no hard and fast rule about where to measure rocker I'll just post a picture and let everyone determine on their own where to measure it:

In case it's hard to see the first horizontal line is 0", the second is 1.6", and the third is 3.1". The waterline is shaded in white at 4.3" with 330 pounds of total load (includes weight of the boat). Bow and stern rocker are the same. I suppose I'd call it just over 2"

For reference a day tripping load (220 pounds total weight) puts the waterline at 3.2":

Alan, I hope you realize that none of my questioning is meant to be critical. I greatly admire your design, building and paddling achievements. It's just that I like to understand other people's design and paddling preferences even if they differ from my own.

When looking around manufacturer sites re E glass, I noticed that you were generally right about modern solo canoes: Just about all the ones that have asymmetrical rocker have asymmetrical sheer lines. The older, symmetrically rockered canoes, such as the Chestnut Prospectors and their modern variants, tend to have symmetrical sheer. Perhaps you're treading on virgin ground with symmetrical rocker and asymmetrical sheer.

The dimensions confirm the large shoulder you have on the tumblehome that's pictured. This is one of the choices I don't understand. I can see tucking in the top two inches so the outwale is flush with the hull, as Galt did and Deal does, but I never understood the advantage of the big sloped shoulder that Yost does, even though I own one such hull.

Do you really think it would affect your switch paddling style if you eliminated most of that shoulder? If, on the one hand, you are trying to paddle vertically (of which I am not a proponent), you still have to clear that shoulder, which is at the maximum beam, the same as you would have to do if the outwale were at maximum beam. If, on the other hand, you paddle with your shaft at an angle (as everyone in the real world does, including Serge Corbin), you could still do that if there were much less shoulder. It's just that your angle might have to be a little flatter, which may not matter much if you are tall. Meanwhile, eliminating all or most of the shoulder increases secondary stability, volume for buoyancy and load, and may make it easier to fit packs. So it seems to me, paddling the Barrens with my failing mind.

I'm not much interested in the rocker graphs except to note that I don't see the bottom of the canoe coming anywhere near the 0 line. Maybe it does so further toward the middle. Is that black shadow under the white area part of the hull? Also, the shape of the hull stems seem quite different between the 330 and 220 pictures.

 

[Alan Gage]

I'm not much interested in the rocker graphs except to note that I don't see the bottom of the canoe coming anywhere near the 0 line. Maybe it does so further toward the middle.

Correct. The center of the canoe is touching the 0 line (the floor).

Is that black shadow under the white area part of the hull?

The software gives artificial lighting so creates shadows.

Also, the shape of the hull stems seem quite different between the 330 and 220 pictures.

The hull shape is unchanged. The only difference is where the waterline is drawn; although I see one of the pictures is zoomed in farther than the others.

I never understood the advantage of the big sloped shoulder that Yost does, even though I own one such hull......If, on the one hand, you are trying to paddle vertically (of which I am not a proponent), you still have to clear that shoulder, which is at the maximum beam, the same as you would have to do if the outwale were at maximum beam. If, on the other hand, you paddle with your shaft at an angle (as everyone in the real world does, including Serge Corbin), you could still do that if there were much less shoulder. It's just that your angle might have to be a little flatter

I suppose the simplest answer would be that every solo boat I've ever owned, except the Wenonah Vagabond that I had before I knew anything, has had a lot of tumblehome so it's what I'm used to. There are three places I see an advantage to it.

One is when I'm switching sides. When I'm paddling hard, especially into a wind, those switches are as low and fast as possible. At 60 strokes/minute I don't miss a stroke when switching sides. The padde is snapped over in an arc. So even though the blade still has to clear the widest portion of the hull that widest portion is farther down on the arc. It's easier to clear the gunwales without clunking the blade off them when they're tucked in.

The second is that when I'm paddling my bottom hand falls comfortably just to the outside of the gunwale, which keeps me from having to reach farther than I normally do.

I'm especially concerned about those two reasons with this new hull being 2" wider than any solo I've paddled before.

The third reason is that the sharp knuckle, as my Berens and Bloodvein have, adds a lot of rigidity to the hull. I don't know how much difference in makes after gunwales and thwarts are installed but when it's just a bare hull the difference is significant when compared to a straight sided wood strip canoe, of which I've built a couple (tandems).

I like this sharp edged tumblehome better than the more rounded shape, like my Bell Magic had. Aesthetically I find the rounded shape more pleasing but it has to start lower and doesn't seem to add as much strength to the hull. The sharp knuckle allows the widest part of the hull to be higher up.

Maybe if I built a hull without tumblehome I'd adjust and get along just fine, I don't know. But it's a hard leap of faith to take. I'd first want to find a cheap boat with similar dimensions that I could paddle on a regular basis to see how I adapted.

The biggest advantage I could see to a boat with no tumblehome and constant flare to the gunwales would be wave shedding ability, especially beam waves. You can imagine a wave breaking into the side of a hull with tumblehome sees a lot less resistance in that inward sloping hull shape than it would a hull that kept flaring outward. For that reason I tried to start the tumblehome as high as up the hull as I thought I could get away with and also tried to keep it confined as much as I could to just the paddling station. It extends farther to the bow than the stern to help clear the paddle blade and make packing behind the seat easier.

Alan

 

[Alan Gage]

Is it possible to put an existing plan or design, say a Chestnut Prospector into Delftship, and use that for comparison ?

Jim

You can import pictures, put them in the background, and then adjust the dimensions to match. If you have a lines plan it's not too tough.

Alan

 

[Jim Dodd]

You can import pictures, put them in the background, and then adjust the dimensions to match. If you have a lines plan it's not too tough.

Alan

Good ! I'll bring up some plans up next time.

 

[Alan Gage]

Finished stripping this afternoon and pulled staples tonight. Will start sanding tomorrow.

20161030_001 by Alan, on Flickr

20161030_003 by Alan, on Flickr

A straight edge to show the bottom shape:

20161030_002 by Alan, on Flickr

Alan

 

[Canotrouge]

Good on you Alan, you sure don't waste any time!!

 

[Jim Dodd]

Are there TWO of you ? Wow !

When are you going to glass ? I may be able to slip up.

​ Jim

 

[Alan Gage]

When are you going to glass ? I may be able to slip up.

I don't know. I'll probably be ready on Wednesday but if the Cubs can push it to game 7 I'll have to wait until Thursday. Be happy to have some company and an extra hand if it works out.

Alan

 

[Alan Gage]

Got it mostly sanded tonight with 40 grit. Then mixed up some thickened epoxy and spread it on to fill most of the staple holes as well as any gaps in the strips. Also added a thickened epoxy fillet to the sharp corner where the tumblehome meets the sheer strip so the fiberglass can make the corner. All that's left is to shape the stems, round over the edge of the tumblehome, and make one more pass with 40 grit and it will be reading to fiberglass....or carbon fiber....I haven't decided yet.

20161031_001 by Alan, on Flickr

20161031_002 by Alan, on Flickr

20161031_003 by Alan, on Flickr

Alan

 

[daveo4]

Perhaps you're treading on virgin ground with symmetrical rocker and asymmetrical sheer.

Pretty much all Wenonah canoes offered today have symmetrical rocker (those that actually have rocker!) and with few exceptions have asymmetrical sheer lines.

 

[Glenn MacGrady]

Pretty much all Wenonah canoes offered today have symmetrical rocker (those that actually have rocker!) and with few exceptions have asymmetrical sheer lines.

After I wrote that I realized that my Bell Wildfire, and all the Bell-Colden Fire boats, have symmetrical rocker and asymmetrical sheer. But it would be nice if there were more virgins in the world.

 

[Muskrat]

I don't think you should waste the carbon on this. I know you'll find some other use for it, and a cedar core is stiff enough to not need it. Save the carbon until you do an ultra thin lightweight stripper raceboat. Speaking of, when are you going to come down and do the MR340?

 

[Alan Gage]

I don't think you should waste the carbon on this. I know you'll find some other use for it, and a cedar core is stiff enough to not need it.

Probably true but it's the same problem a tinkerer always has without enough first hand experience or testing knowledge to back him up. A more flexible laminate that will give with the impacts (as long as it doesn't give too much) or a stiffer but stronger laminate that will resist flexing in the first place (as long as it's not too stiff)? Or maybe it doesn't really matter either way.

Save the carbon until you do an ultra thin lightweight stripper raceboat. Speaking of, when are you going to come down and do the MR340?

I already did that boat, it was the first one I ever designed. Quite happy with it. I paddle it a few times/year but still need to get it back in the shop to finish it up. 18.5' and sub-30 pounds. Very fast but relatively friendly to paddle (compared to a USCA C1) and the dog fits well. I think that was before you joined the board.

http://www.canoetripping.net/forums/forum/general-paddling-discussions/diy/19929-x-canoe-build

Part of the reason I built that boat was to use it in the South Dakota Kayak Challenge if I ever decided to try it again (I swore never again after the first two times I did it) and possibly the MR340. But I think my racing days are over.

Alan

 

[Muskrat]

Well in that case, I wouldn't want to be somehow responsible for stiffling your tinkering. Haha.

 

[Alan Gage]

Sorry, I've been holding out on you guys. I fiberglassed the hull a couple days ago and added S-glass and dynel skid plates last night along with the first fill coat. Second fill coat tonight. Full layer of 6oz. E-glass and 6oz. S-glass below the waterline.

Instead of rolling on the fill coats with regular epoxy I'm first thickening it with cabosil and then putting it on with a squeegee. Wasn't too thrilled with it after the first coat but now that the second fill coat is done it might have promise after all. It takes longer than just rolling on a coat but this second coat might have filled the weave already and it seems to be taking less resin. About 10 ounces for the fill coat tonight.

20161104_001 by Alan, on Flickr

20161104_002 by Alan, on Flickr

Alan