Round Profile

[Kayak Jack]

What I'm saying is that to compare two things, you have to remove as many variables as possible. Adding effects of current, wind, individual paddler, etc. muddies up the situation so much that you are no longer able to separate fly specks from the pepper, nor are the results reliable.

The examples of various shaped cross-sections of boat bottoms, all the same length is a fer instance. While there was an arbitrary waterline presented, what was omitted is the AREA described by each, individual cross-section under that waterline. Each cross section, though having the same length of line for a bottom, would hold a different volume.

What that means is that each one, if loaded with the same weight, would no longer have that same, arbitrary waterline. Only with varying loads would that imaginary waterline remain a constant. The cylindrical cross-section will provide more volume, therefore carry more weight. The more closely a hull shape approximates cylindrical, the more load bearing capacity it will have with minimum wetted surface.

A perfectly cylindrical cross-section is impractical for real world use, so designers alter and tweek it some. That's where individual designs and handling characteristics begin to vary quite widely. A semi-round bottomed with pointy ends will handle considerably different than a boxy, flat-bottomed boat. I guess, you could even use a square mortar box (like what is used to hand mix mortar and concrete in) as a boat, but I'd rather not.

I recommend that you have private email-type conversations with Matt, and listen carefully to what he says.

 

[beekeeper]

Kayak Jack said.....

I gotcha. Thanks Mr. Jack.

beekeeper

 

[Jimmy W]

The examples of various shaped cross-sections of boat bottoms, all the same length is a fer instance. While there was an arbitrary waterline presented, what was omitted is the AREA described by each, individual cross-section under that waterline. Each cross section, though having the same length of line for a bottom, would hold a different volume.

What that means is that each one, if loaded with the same weight, would no longer have that same, arbitrary waterline. Only with varying loads would that imaginary waterline remain a constant. The cylindrical cross-section will provide more volume, therefore carry more weight. The more closely a hull shape approximates cylindrical, the more load bearing capacity it will have with minimum wetted surface.

That diagram with the various cross-sections stated at the top that each had the same area and showed the differing beam and girth of bottom. Although as drawn example F sure looks like a larger area to me. The reason that it was brought up was to show that a 15 degree change in the slope of the sides of a pirogue isn't likely to be noticeable until the pirogue is leaned over to one side. When the pirogue is tilted, the 15 degrees will have an effect on the stability.
The original question here did ask about a pirogue, but I doubt if anyone here can point to an example of a pirogue or similar sharp chined boat winning any major paddling race in the last 10 years.

 

[tx river rat]

Depends on what you call major races. In LA they have perow races that turn in some pretty good times.
Ron

 

[beekeeper]

Here is a pic of a extremely fast perow

This is a 3 panel and can walk off from a lot of yaks.
The reason for a smooth rounded bottom being faster up stream ,the water cant catch on the rounded shape a sharp chined boat will be faster downstream.
Ron

Do you know the dimensions?

beekeeper

 

[Kayak Jack]

The hull on this boat looks an awful lot like a West Greenland kayak

 

[Jimmy W]

Depends on what you call major races. In LA they have perow races that turn in some pretty good times.
Ron

I meant like the AuSable race, the General Clinton, the MR 340, the Texas Water Safari, an Olympic type ICF race. The races where the top racers come to compete against each other.

 

[JEM]

What I'm saying is that to compare two things, you have to remove as many variables as possible. Adding effects of current, wind, individual paddler, etc. muddies up the situation so much that you are no longer able to separate fly specks from the pepper, nor are the results reliable.

But if you want real-world comparison, you have to factor in real-world issues. Otherwise it's just theory. Round bottom, in general, is more efficient. But in a race between a round bottom hull that is capsized because the paddler couldn't keep it upright and a flat bottom pirogue, pirogue wins every time.

You could then say take out all vairables and end result is flat bottom is faster than round bottom.

 

[jdupre']

Theory is fine most of the time, BUT..... I've read that, theorectically, a helicopter and a bumble bee shouldn't be able to fly. Perpetual motion is theoretically impossible , but the planets have been revolving around the sun for a LOOOOOONNG time. If that ain't perpetual , it's dang close.

Joey

 

[tx river rat]

I am really going to muddy the waters here.
Things that I feel like are set in stone about boats.
We are talking performance now
Long water line is more efficient 17 to 22 ft
The narrower the boat the faster
Round has less drag but also sits in the water deeper and is less stable
Now all these dont lend there selfs to a boat we would like to own and paddle
All this depends on the motor and if your good enough to supply the power
Now here is the big one,there is no perfect boat for every environment
second some folks can paddle a bath tub faster than we can paddle our fastest boats
Big races are normally won bye pros or simi pros in K 1 type boats ,most of us cant paddle one 30 ft without being upside down. In solo class ,now they want carry much gear ,dont turn worth a flip,and even the pros start falling out of them as they get tired. Useless for our kind of paddling. Even the pros in long distant races are starting to go to hybrid designs ,slower ,more forgiving, but they can stay upright when they are tired,
After 12 boats I am on a steady progression of getting longer and slimmer,eventually I will hit a point where the boat is to touchy for me to paddle
I dont like round bottom boats for the way and places I paddle period.
Dont get to deep in wetted area and all the theorys just like me and most folks on here if you had the ultimant speed paddle craft you couldnt stay in it,if you did your paddle efficency would be no where close to being able to get the performance the boat is capable off.
And the biggy you would hate the boat
Take baby steps build each boat a little more efficient and learn what suits you , are be really smart and build proven designs that are a combination that give good results.Like Matts designs
Ron







Ron

 

[gbinga]

Water line length hasn't been mentioned enough, I think. Generally speaking, if it is a displacement hull (that is, you aren't trying to plane) and it has a decent hull shape, then the longer the boat the faster it is capable of going. There is a phenomenon called "hull speed" that I am not bright enough to explain. Basically every displacement hull has a hull speed, and trying to exceed hull speed takes a tremendous amount of power.

Assuming reasonably comparable shapes, the longer boat will have a higher hull speed and will go faster.

Now of course if the boat is thirty feet long you won't have enough muscle to reach it's hull speed, but if you compare a 17' boat to a 14' boat, the 17' should be faster.

Another factor that deserves more attention is that the differences are gonna be marginal and most of us would do better to concentrate on becoming better paddlers instead of worrying about our hull shape. But those of you who are really skillful with a paddle probably enjoy the difference a better boat makes.

George

 

[Jimmy W]

...a sharp chined boat will be faster downstream.

Big races are normally won bye pros or simi pros in K 1 type boats ,...

I dont like round bottom boats for the way and places I paddle period.
Ron

Ron, This is the point that I wanted to make. Those pros and semi-pros know what boats it takes to win races and they don't paddle sharp chined boats. Those are the boats that you like to build and paddle.

George, you are correct that longer is faster up to a point. You seldom see solo boats over around 18 1/2 feet because the increase in wetted area and drag offsets the advantage of the increased length.
This thread has gone way beyond Beekeeper's two questions about 15 and 30 degree sides.

 

[tx river rat]

Jimmy
The races I run the flatter bottoms work better for going over logs under logs through brush piles . I raced with some guys in K-1 and I would catch and pass them at every obstacle we came to but they had me on the straights.
and I didnt fall out of the boat :lol: :lol:
Ron

 

[beekeeper]

This thread has gone way beyond Beekeeper's two questions about 15 and 30 degree sides.

Thanks for bringing us back to my questions. I appreciate everyone's input. all the thoughts have been enlightening.
I will try to clarify my questions and thoughts one more time.
The subject matter should have been "Soft Chine" (Not Round) Profile. I was asking these questions in "theory". I thought the "round bottom boats are faster" idea was because they had a smooth transition between the bottom and side (less friction/resistance). That is a factor but the fact that they approach a cylinder profile is a greater factor.
When I asked question #1 I was thinking in the smooth transition of bottom to side idea. To my eye the 30 deg. sided boat was a softer chine. It may offer less friction at the juntion of bottom and sides, but this would not (if I follow all the above post) overcome the more streamline (cylinder) shape of the 15 deg. flared sided boat. It also has a narrower water line beam. This would make for a better width to length ratio. I'll put my eggs in that theory basket as to why it is more efficient. So the answer to Question #1 is, the 15 deg. boat is faster (more efficient), but/maybe/etc...... :roll:

The comparison is not accurate in the real world (as many pointed out), because this one difference created many changes in other aspects of the boat, mainly stability and draft. Question #2 was my effort to address this. Increase the bottom width of the 15 deg. boat or decrease the bottom of the 30 deg. flared one and they could be built to draft the same ( apples to apples now). Then which one is faster? How much? How about stability? Probably not a dimes worth of difference between the two, but / maybe / etc..... :roll:

I know our boats are made up of many compromises. If I can grasp the contribution of each feature, I can decide how to build a better boat for my needs or intentions. I apologize for my inability to clarify my questions better. Hope I have not misled anyone.

beekeeper

 

[Kayak Jack]

<SNIP> I know our boats are made up of many compromises. If I can grasp the contribution of each feature, I can decide how to build a better boat for my needs or intentions. I apologize for my inability to clarify my questions better. Hope I have not misled anyone.

That's why I said for us to consider only one variable at a time. Then, we can move on to other variables, one at a time. And, your fuzzy question has me grief stricken, appalled, and besmitten. :wink: Terrible, just terrible.

Part of your consideration may be obstacles. A boat designed to flow well in a fluid, performs differently when going over and through obstacles. If I remember rightly, Keith and Seedtick have a concave bottom on their pirogues so it can be broken loose from suction of a mudflat. Specific areas of use dictate heavily what features become assets rather than liabilities.

 

[beekeeper]

Jack you changed pages on me again. :x :wink: Stop that! :lol: If both boats were built to draft the same, any encounters with obstacles each would react the same for practical purposes. I would not think any differences in bottom width or side flare would matter.

beekeeper

 

[Kayak Jack]

I didn't change pages, just clarified my position. Well, maybe hull cross-section and draft doesn't matter . And so, you should build a coracle.

 

[beekeeper]

I.m getting off this horse (merry go round). I can't express my ideas well enough to keep the horse going in one direction. My thoughts were, in the example, that the bottom width, and side flair were insignificate in the real world when encountering obstacles. I was NOT saying it didn't matter at all.
Jack you did clarify your point. That was what I was trying for, one variable at a time. Unless I did not pick up on it, I don't believe question #2 was ever answered.
Build a what? :roll: :?

AS Forrest (Gump) woud say, "That's all I got to say about that."
beekeeper

 

[Kayak Jack]

<SNIP> Build a what? :roll: :? Go to your dictionary. (That big, dusty old book in the corner up there.) It'll edjumakate ya.

 

[oldsparkey]

I.m getting off this horse (merry go round).
beekeeper

Thank You......

It was making me dizzy watching everything that was going on. Thank goodness that a merry go round horse is wood.