It is currently October 20th, 2020, 4:33 am

All times are UTC - 5 hours




Post new topic Reply to topic  [ 241 posts ]  Go to page 1, 2, 3, 4, 5 ... 17  Next
Author Message
PostPosted: February 4th, 2009, 6:11 pm 
Offline
User avatar

Joined: September 3rd, 2007, 11:17 pm
Posts: 108
Location: Ajax, ON
This has probably been covered earlier, but I searched the forum and couldn't find any info on this question. So I'll just post the question and see what types of answers I'll get.

What I'd like to know is how much of a difference does an asymetrical hull make? I know that asymetrical hulls are more efficient, or faster if you will. But how much? If we take all other factors to be equal (LWL, beam, draft, wetted surface) and have two identical shapes (ie. both of them are Prospectors or Chesnut Pals) how much of a difference is there in moving the point of maximum beam aft (and the resulting necessary moving of the maximum draft forward)?

How much of an advantage is gained? I believe that the difference is related to the drag coefficient. By changing the design do you gain 1%, 10%, or 20%? Theoretically, that would then be gained distance or less effort, whichever you choose. If people can canoe an average of 20km per day, the above numbers would then relate to an increase of either 200m, 2km, or 4km. Just wondering.

If this threatens to destroy the marketing line that asymetrical is far better (say the advantage is actually only 1.7%) and no one wants their marketing blown to bits, then ignore this thread have apply to the admins to have it removed. Otherwise, I'd be interested in finding out.

Dave

_________________
David Laaneorg
_________________________________________________________
"Everyone must believe in something, I believe I'll go canoing." - HDT


Top
 Profile  
 
PostPosted: February 4th, 2009, 6:49 pm 
Offline

Joined: September 8th, 2006, 7:11 pm
Posts: 921
Location: winnipeg
I read Winters' book some time ago. Much of it was over my head. I am no expert, but have considered this one a bit.

Here are my recollections/beliefs (I may be wrong):

1. Asymmetrical, either fish form or Swede form, are both more efficient when moving through a consistent medium. I.e. a submarine or aircraft would benefit most from asymmetrical design.

2. The box-fish, a strange looking animal, was the inspiration for a car designer - Mercedes, if I recall correctly. While boxy, it moves through the water well.

3. The boundary layer between air and water, the fact that the boat is in neither, muddies up the simple physics and may make your question very difficult to answer - not impossible, mind you. Propably some designers have programs that can calculate it on flat-water at a given velocity.

4. Velocity - I bet that the differences would be more or less as one varied the speed. Not sure, but would bet a few dollars.

5. Wave action - I have heard many people say that a certain boat is as fast as another, but when in choppy waves, is not nearly able to keep the pace. To speculate, maybe a fish form would be more efficient at low speeds and calm water, while a swede form would excel at high speeds and choppy water.

6. I claim to prefer symmetrical hulls, but I suspect many of the differences are small. I also bet a competent paddler could do well in either, assuming the design was appropriate for the task.

7. A symmetrical hull, not perfectly level in either dimension, will not, be symmetrical anymore.

8. Sorry I don't have the answer. I am curious if anyone has the number you are asking for.

9. If I am totally wrong about something, I would like to know. Please be kind.


Top
 Profile  
 
PostPosted: February 4th, 2009, 7:37 pm 
Offline
User avatar

Joined: August 27th, 2002, 7:00 pm
Posts: 2562
Location: Geraldton, Ontario Can
I don't have any science behind this, just experience, playing with my GPS last summer. My son and I, paddling a Winisk (Asymmetrical) fully loaded on a lake with no wind advantage, average 7 to 7.5 k an hour, according to my GPS. In my Old Town Poly pig, with the same load, we average 6 to 6.5 k. Although the Old Town is symmetrical in design, I'm sure the excessive oil canning would give it a classification all to itself. On school trips, I will often give the asymmetrical designs to the weaker paddlers, as they are better able to keep up with the group then.

However, there are some quirks that I have noticed, particulalry when paddling into a strong head wind. The narrow entry tens to slice through the waves as opposed to riding over. One has to back off on the forward thrust to achieve lift, so to speak. When I want to make large miles on flatwater, I always go for the winisk, or the 20 foot Quetico I made.


Top
 Profile  
 
PostPosted: February 5th, 2009, 12:45 am 
Offline
User avatar

Joined: September 3rd, 2007, 11:17 pm
Posts: 108
Location: Ajax, ON
Thanks for the responses so far.

mr_canoehead18, your observations regarding weather, trim and speed are well taken. I had considered them and for that reason I wanted to express that all other things being equal, what would the difference be? Wind, weather, waves all will effect a change on performance. Trim and loading (eg. adding more weight thus getting more wetted surface in the water) also will change performance and symmetry. As well, even with aerodynamics, the lift and drag coefficients of a wing change with the speed it travels. This also applies to hydrodynamics. All boats have a hull speed, the maximum speed the boat can travel without planing which is directly related to it's length in the water. Planing hydrodynamics are another game altogether, and I have yet to see someone paddle a canoe up on plane (please correct me if I'm wrong on this one). I was just wondering what the difference would be in a best-case/perfect-world scenario.

RHaslam, I would certainly agree that a 20ft canoe will invariably be faster than a 16 ft canoe, the hull speed of the 16ft'er will limit it's top speed to less than that of a 20ft'er. That's why I was wondering about the theoretical comparison of two identical boats in all other respects other than their symmetry.

Dave

_________________
David Laaneorg
_________________________________________________________
"Everyone must believe in something, I believe I'll go canoing." - HDT


Top
 Profile  
 
PostPosted: February 5th, 2009, 3:15 am 
doftya wrote:
[...] What I'd like to know is how much of a difference does an asymetrical hull make? I know that asymetrical hulls are more efficient, or faster if you will. But how much?
How much of an advantage is gained? I believe that the difference is related to the drag coefficient. By changing the design do you gain 1%, 10%, or 20%?

If designed well asymmetrical is supposed to be relatively easier to paddle and dryer in waves. But how much, I really don't know.
I suppose it will not be much more than 5 procent?
Nevertheless, its worth it for me!

for some interesting reading about this subject:
http://www.nswseakayaker.asn.au/mag/33/design.html
http://www.paddlewise.net/topics/boatde ... swede.html

Dirk Barends


Top
  
 
PostPosted: February 5th, 2009, 7:58 am 
Offline
User avatar

Joined: December 2nd, 2002, 7:00 pm
Posts: 3731
Location: Grand Haven, Michigan U.S.A.
Doftya,

Do a search here at CCR for JWinters as an author. You will find much along the lines of what mr. canoehead 18 posted. John, really has been the formost authority in canoe design for 30+ years now. He's really wiling to play email conversations with interested parties and his articles and books are oft quoted when conversations goe to efficiency.

John often likes to point out that effienciency can mean alot of things to different people, and that what people think they "feel" is often not found to be true when "emotions" are removed from a scientific study.

Personally, I don't feel that the hull shape has nearly as much to do with a percieved difference in "hull" speed, as many other factors when using a canoe. I own several canoes for different purposes. I travel slightly faster in my asymmetrical canoe than my symmetrical canoes. But only a small portion of any difference in speed can be attributed to the asymmetry. For example, Rob talked about his Winisk and the poly canoe he uses in his youth programs. There are alot more differences between these two boats than just asymmetry... like he pointed out hull flex, but even more basic, I doubt that the hulls have the same length, the same width, the same profile from bow to stern, the same cross sectional shapes at any place on the hull, they are made of different materials, have a totally different shape at bow entry and where the stern passes through the water, they likely have different amounts of rocker, the different materials have different amounts of surface tension and friction. Finally, they probably had different loads. But in the end his GPS measurments only detected a 1 mph difference with an reported error of atleast 1/2 mph.

I used to think it really mattered. I no longer do. I've yet to have the chance to paddle two boats that were identical except one was symmetrical, and one asymmetrical, and I've paddled alot of different boats through the years. That's because there aren't many boats that are asymmetrical that are really designed for the exact usage as a symmetrical boat. ie: John Winters didn't design his Winisk for the same purpose as the poly tub... (What are they Rob, Old Town Kineos?).

In my experience, I admit it feels faster to paddle an asymmetrical canoe.... so usually when I want to make time, I paddle the canoe I perceive is the fastest, but having participated in thousands of canoeing outings. It's never been the hull that determines which canoe is fastest... It's been a combination of the skills of the paddlers, their fitness, how hard they paddled, how much they carried, of something along that line.

So I think that if you had two truely identical hulls in all dimensions except the location of the widest part of the hull, it would amount to 1% or less. But if you feel better paddling one canoe because you think it makes you faster... and that's important to you.... then it matters to you that the canoe is asymmetrical or symmetrical regardless of whether it really makes a huge difference to the water.

But do talke to John, because it's amazing what he has found about this topic.

PK


Top
 Profile  
 
PostPosted: February 5th, 2009, 10:19 pm 
Offline
User avatar

Joined: September 3rd, 2007, 11:17 pm
Posts: 108
Location: Ajax, ON
Thanks pknoerr, you summerized in much better language what I was thinking. I realize that the question I have asked can only really be answered in the theoretical realm of hull analysis software. I was just wondering if someone had the numbers. Thanks for the suggestion to contact Mr. Winters, I think I'll do that.

Part of the reason I'm asking is that I'm in the market for a canoe and there seems to be an increasing number of asymetrical canoes available. Not that I'm out to knock the advantages, but I have traditionally tended to favour the more traditional symetrical shapes. But I realize that this is more habit than reason. As well, I am not very interested in going faster, but I would be interested in expending less energy for the same return.

_________________
David Laaneorg
_________________________________________________________
"Everyone must believe in something, I believe I'll go canoing." - HDT


Top
 Profile  
 
PostPosted: February 6th, 2009, 8:35 am 
Offline
User avatar

Joined: December 2nd, 2002, 7:00 pm
Posts: 3731
Location: Grand Haven, Michigan U.S.A.
Even Symmetrical canoes are very rarely 100% symmetrical. Obviously, even static the canoe would have to be perfectly trimmed. But then lets consider the canoe in motion... the hull shape in water that is being deflected around the hull is not likely symmetrical either. But obviously an asymmetrical hull would be even more asymmetrical as well in motion.

For most paddlers it really probably doesn't matter. As I've said before it's the skills and the fitness of the paddler that will make the biggest difference. Personally, I think that most paddlers worry about not having an asymmetrical canoe, and that affecting whether they can keep up with other paddlers, or whether they can make the miles. But personally, I think that paddlers would be better served worrying about whether the type of paddling they do will require a more symmetrical hull. If you're just going to paddle the canoe forward then it probably doesn't much matter. But I love paddling backwards, I'd rather have a symmetrical boat. I'm not talking about backing out from the dock... but really paddling backwards. This is common obviously doing freestyle or Canadian "Style", but through twisty swamps, even on fast rivers complete with eddies, and surf waves. Why do I do it.... because 1) I can!! 2) because it's cool looking and 3) because, have you ever gotten stuck in an eddy backwards? Do you have to some how figure out how to turn around, of do you just power out backwards and peel out? It's a skill that makes my paddling better. So, I'd worry more about whether you might need the symmetrical boat, and worry about developing enough skills and fitness that it really doesn't matter if your friend has an asymmetrical hull, you can still out paddle him in whatever you're paddling.

PK


Top
 Profile  
 
PostPosted: February 6th, 2009, 9:25 am 
well I am not going to say that I love paddling backwards,
but on rivers I often do it -- when backferrying.
With enough bow heavy trim I have discovered that backferrying is absolutely no problem
in a well designed asymmetrical canoe (like my Kipawa),
but even my radical asymmetrical Dagger Interlude was not a problem then.

The only real disadvantage I have discovered, is that asymmetrical canoes
seem to be more difficult to handle when portaged in hard winds:
the more the extreme the asymmetry the worse it gets, so it seems.

Dirk Barends


Top
  
 
PostPosted: February 6th, 2009, 9:48 am 
Offline
User avatar

Joined: December 19th, 2006, 8:47 pm
Posts: 9053
Location: Rattlesnake Pond ME
Thats muddying the picture..by pitching the bow down and interacting with moving water..sure it loosens the stern. Its quite an appropriate technique especially for an asymmetrically rockered canoe that is usually skegged in the stern.

I really think the term "asymmetrical " is vague. Does it refer to hull shape when viewed from above or the shape of the bottom or what? We know its not from the side as very few boats have a symmetrical sheer line.

Now my Dumoine was not easy to paddle bow seat backwards.

Its stern had less rocker than the bow. And by reversing the boat I changed it from swede form to fish form..Theoretically that would make it turnier perhaps counteracted the skegged stern.. but the killer was the dropped stern sheer...what a wet ride.

A swede form boat will theoretically give you a faster ride. But how many paddlers can paddle their boats at hull speed? IMO its 90 percent paddler and ten percent boat. When you can't keep up look at your biomechanics;don't blame the boat.

I too prefer boats that paddle the same way backward and forward but most of my boats are asymmetrical at least in rocker. Its awfully common. That feature is intended to aid in "tracking" and I think has a couple of effects..People do not get as frustrated quite as quickly but on the other hand may not completely develop really good paddling skills.


Top
 Profile  
 
PostPosted: February 6th, 2009, 10:08 am 
Offline
User avatar

Joined: December 2nd, 2002, 7:00 pm
Posts: 3731
Location: Grand Haven, Michigan U.S.A.
littleredcanoe wrote:
I too prefer boats that paddle the same way backward and forward but most of my boats are asymmetrical at least in rocker. Its awfully common. That feature is intended to aid in "tracking" and I think has a couple of effects..People do not get as frustrated quite as quickly but on the other hand may not completely develop really good paddling skills.


Yeah, I'm not a huge fan of any of the skegged sterns with less rocker than the bow, because, I absolutely hate how they hang in an eddy on peel-outs! Bell's Yellowstone will do this and the old Wildfire won't. Especially on rocky rivers.. These are often the places where you don't want to scoot off the seat to create a bunch of bow pitch so that the stern doesn't drag. But I agree that the intention of the asymmetrical boats with skegged sterns is to aid with tracking... it's sort of a dumbing down of the boat in my mind. I remember talking to Bob Foote several years ago over lunch about this. His contention was that most paddlers can't paddle straight, that's why alot of boats are build to track hard (especially solos). I sort of took the other side at the time that paddling straight wasn't really a problem, because my concern wasn't with going straight at the time but learning how to turn the canoe as sharply as I can. Sadly, the more I paddle with people, the more I realize that alot of folks really do need the skegged stern to track anything like a straight line.

PK


Top
 Profile  
 
PostPosted: February 6th, 2009, 10:10 am 
littleredcanoe wrote:
[...] And by reversing the boat I changed it from swede form to fish form..Theoretically that would make it turnier

Fish form is supposed to track more
I often paddled my MRC Pearl the other way around therefore.

Quote:
A swede form boat will theoretically give you a faster ride. But how many paddlers can paddle their boats at hull speed? IMO its 90 percent paddler and ten percent boat. When you can't keep up look at your biomechanics;don't blame the boat.

I can keep up with most, even many kayak paddlers...
But I still prefer an easier paddling canoe, even below hull speed -- whatever that may be, because I have paddled faster than that...

Dirk Barends


Top
  
 
PostPosted: February 6th, 2009, 10:45 am 
Offline
User avatar

Joined: December 29th, 2002, 7:00 pm
Posts: 6238
Location: Bancroft, Ontario Canada
Quote:
I realize that the question I have asked can only really be answered in the theoretical realm of hull analysis software.


Hm, maybe not, although this suggestion might not be much help... one way that's been used to measure the drag created by canoes moving through the water is to attach a spring scale to a canoe held in place in a river with a current. The greater the drag the canoe design creates, the greater the numbers shown on the scale.

The numbers the scale generates could be significantly different with a symmetrical canoe trimmed level in the water, vs the same canoe trimmed stern-heavy, so that the submerged part of the hull forms an asymmetrical shape.

This is probably more work than most would want to do, and will not be an exact replica of the dynamics when someone is actually paddling and moving the canoe through the water that way. Still, the difference in drag when symmetry is changed with trim could be interesting to see.

My wild-eyed geeky prediction is that drag will be lower with the stern-heavy trim although I can't say by how much. Symmetrical canoes seem faster paddled with slightly stern-heavy trim, possibly because there's less of a bow wave created that way. They also "feel" faster which might be the most important thing, along with the color of the canoe.

:wink:

Finding an engineer to plug the numbers into a computer would probably be a lot more precise and elegant, although again, the nagging question is always there, in just how relevant the theoretical computer-generated numbers would be to real-world experience.

_________________
><((((º>


Top
 Profile  
 
PostPosted: February 6th, 2009, 11:06 am 
Offline
User avatar

Joined: January 29th, 2007, 10:19 am
Posts: 2461
Location: Just outside the Blue Line
Oh God, here's another day gonna be wasted for me if I don't watch out. :lol:

pknoerr wrote:
Do a search here at CCR for JWinters as an author.

John, really has been the formost authority in canoe design for 30+ years now.


Well, with 150+ of some of the world's finest canoes designed to date (and still going), Dave Yost might have something to say about that. :doh:

For those who like their canoe designs "by-the-numbers" (I am not one of them), JW is without peer. His book "The Shape of the Canoe" is available on CD from Greenval for a measly $20. Worth its weight in gold, and it will provide all that you ask and a bunch more.

Here's a link to John's page at Greenval that has several short articles relating to canoe design. There is a link at the bottom of the page that takes you to the Greenval home page if you choose to order the CD.

John Winters Page

_________________
“We can have great disparities of wealth or we can have democracy. But we cannot have both.” - Former Supreme Court Justice Louis Brandeis


Top
 Profile  
 
PostPosted: February 6th, 2009, 11:12 am 
Offline
User avatar

Joined: December 19th, 2006, 8:47 pm
Posts: 9053
Location: Rattlesnake Pond ME
Yep I am a fan of David Yost boats too and have been for a while. I have seen him cited as the most prolific designer.

His approach is different from John Winters as DY starts with a particular person in mind and then designs the boat around them..

Nothing right or wrong about either approach but I somehow wound up with about a dozen DY boats.

And they both are friends too...thats the nice thing about paddlesport. I believe both are designing still for Swift..I know DY has been busy.

Boat boats in my avatar are DY boats.


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 241 posts ]  Go to page 1, 2, 3, 4, 5 ... 17  Next

All times are UTC - 5 hours


Who is online

Users browsing this forum: No registered users and 2 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  
cron
Powered by phpBB® Forum Software © phpBB Group