Test on stability of asymetrical hull

[tx river rat]

One last example
take you a basket ball ,and a wooden box that is the same measurement accross that displace the same amount of water then get on the outside edge and see which one is easiest to roll over , then take the same box push it down by pushing in the center of a flat side the do the same thing on one of the corners.
You will get three different results just from hull shape
Ron

 

[seedtick]

stability of any boat is dependent on the location of the center of bouyancy, center of gravity and it's metacentric height

while the basketball and box may seem like apples and oranges,

if you're sitting at the bottom of the inside of the basketball such that the center of gravity is directly below the center of bouyancy, the ball is extremely stable and will tend to self right with minor shifts to the center of gravity. You can reach a point where it will tip

by the same token if you're above the sides of the box, it's easier to move the center of gravity away from the center of bouyancy and flip the box, the higher the center of gravity is away from the center of bouyancy the more unstable it is. that why most folks can't stand up in a pirogue and cut a tree down

there's a lot more to naval architecture than a couple of parameters and i know i don't understand it all

 

[jdupre']

Jimmy, you are right about the displacement. The hull always displaces it's weght in water. But, the force of bouancy acting 1 or 2 inches further out from the centerline definitely adds stability. That's the whole idea behind wide boats. And that is also the reason highly flaired boat sides contribute to stability. They displace water much further from the centerline, acting like a continuation of the bottom.

 

[tx river rat]

Seedtick
I agree with one exception, sit in the center of the box and sit in the center of the ball, start leaning out ward the ball will roll over a whole lot quicker, same weight same height same displace ment ,less stability with one hull shape than the other. Its like you said on another post when you ask about the round bottom hull and stated a log is round and it isnt stable at all.
Get in an 18 inch wide perow ,and then into a 18 inch wide surf ski or K 1 it will explain the whole thing to you in about 15 seconds. :lol:
Ron

 

[Jimmy W]

Ron, I haven't forgotten about center of gravity. I never said that one design couldn't be more stable than another design. I said that leaning a boat of any design would not cause it to displace more water. I stand by my statements that both attaching helium balloons to the gunnels or adding ballast to the boat will change the displacement and will change the center of gravity. To lower the center of gravity is why ballast is used in sailboats and ships. When I was talking about running whitewater, I mentioned that I often paddled with the boat heeled to one side, that was mainly because I was paddling a 35 inch wide boat and it was easier to reach over the side that way. It also made it easier to turn as in the Canadian paddling video. I also paddled kneeling and sitting on a foam saddle. My knees were about exactly in the center of the boat and with the weight on my knees, it lowered my center of gravity. I could also reach forward and pull the front of the boat over to one side.
Your test, as pictured, did not test a symmetrical and asymmetrical hull. You showed the same piece of Styrofoam and just changed the location of the weights. I remember back in the 1970's when I first bought my aluminum square stern canoe. I would sometimes paddle it while sitting backwards on the front breasthook or deck. That would raise up the back end out of the water and make it very unstable, but back then, I found it fun to do. By the way, that boat was asymmetrical because only one end was squared off. I don't think that made it more stable.
Did anybody take the time to read Roger Long's writing that Seedtick posted the link to?

 

[tx river rat]

Jimmy
You need to go back and read the original post again , I built 2 hulls not just one, I just showed the pics of one to make it simpler, changing the the hull design changes the CG ,even leaning or heeling you shorten the boat add more rocker and change the center of balance just like moving sq inches around in a hull configuration will make it handle the weight in a different way .I heel my boats ,my butt stays in the middle of my boat but my center of balance moves with my leaning
You just agreed with me and havent realized it, I bet if you put your rear on the squared of (,Asymmetrical end ) it was a heck of a lot more stable. :lol:
The adding weight in a sail boat or ship is factual , but add to much weight to a yak can make it unstable,depends on the design.
I read the article as well as every thing I can get my hands on. It interest me. It shared one thing with the rest of the articles ,it is very vague and there are no hard answers in it. Most are a lot of theory and quotes.
That is why I tried this, and It has got funny, There has been everything brought up and talked about ,from displace ment ,to taller loads to weight to the outside ,I can go on for a while
This was about ,the same hull width and length the only difference being the shape and how it affects initial stability. Simple deal .
Ron

 

[Jimmy W]

Jimmy, you are right about the displacement. The hull always displaces it's weght in water. But, the force of bouancy acting 1 or 2 inches further out from the centerline definitely adds stability. That's the whole idea behind wide boats. And that is also the reason highly flaired boat sides contribute to stability. They displace water much further from the centerline, acting like a continuation of the bottom.

Joey, I agree with that and never said differently. That isn't what you said that I disagreed with although it might be what you meant to say. I'm not so convinced that moving the wide part toward or to the ends helps. Especially when you put the center of gravity away from the center of buoyancy as shown in the second part of Ron's test. It seems the designer of Ron's under construction boat doesn't agree with the flare part.

 

[tx river rat]

Jimmy
Back up just a second, initial stability,tippy is what he is talking about, not secondary stability.
And I cant tell you yes or no on it yet.Right now it is a theory
Ron

 

[Jimmy W]

You just agreed with me and havent realized it, I bet if you put your rear on the squared of (,Asymmetrical end ) it was a heck of a lot more stable. :lol:
Ron

Both ends were asymmetrical with the other end, but yes sitting in the wide end was more stable than balancing on the skinny end because wider is more stable than skinny in boats. It has to do with that moving the buoyancy out thing.

 

[tx river rat]

Jimmy
How can both ends be asymmetrical ,or swede form.
My definition of asymmetrical swede form is wider in the rear than the front.
Symmetrical is even on both sides of the center line.
Ron

 

[Jimmy W]

I keep getting credit for things that I haven't said. I didn't mention swede form or fish form. I just said asymmetrical meaning that the two ends don't match each other. If the ends don't match, they don't exhibit symmetry with each other. My first post in this thread was when I disagreed with Joey about the displacement thing and even he now says that I was right about that.

 

[tx river rat]

I said swede form ,not accusing you of that.
Ron

 

[tx river rat]

here is the quote

Summary
Testing done by the Smith redneck institute
An asymetrical Swede form boat is more stable than a symetrical boat with the same length and width measurements.
Ron

 

[Jimmy W]

When you tested the un-pictured second hull did try you placing the weights in the center of the boat where a symmetrical hull is widest and where the center of buoyancy of the hull would be?

 

[tx river rat]

nope I put it in the same location as all my boats asymmetrical and symmetrical go . This is the point both trim out just a little nose high, why would I want to put it in the center nose down paddles like a pig.
My Laker is symmetrical , my T-V is asymmetrical so is my cuda the seat position is the same in all of them if there not carrying any extra load
The model was trimmed the same way , was in a paddling trim.
This was so pose to simulate a boat in paddling trim
Here is a picture of my symmetrical laker you can see the center line and seat placement

here is a link to Micks Laker build you will see he has about the same seating distance
viewtopic.php?f=10&t=4217
Ron

 

[Jimmy W]

Putting the weight in the center will not make it trim nose down, it would have to be ahead of the center to do that. Trimming nose up isn't going to make it faster. Actually as the hull approaches hull speed and starts climbing its bow wave some extra weight in front might even help. From what I have read that is when the swede form starts to really make a difference as the pointy bow helps to cut though the bow wave and the width in the back helps to support the rear. But you might be right, a properly trimmed swede form is probably more stable than a tail heavy symmetrical boat.

 

[seedtick]

old builders around here that built assymetrical pirogues put the wide part in front and paddled from the skinny end

of course their layout of assymetrical could be very diffeent from Ron's layout, their widest part was 4 to 6 inches forward of mathematical center.

 

[tx river rat]

Seedtick
They call it fish form and I really haven't paddled any of them so I cant express an opion about that shape. I know they do build them.
Jimmy
From paddling a lot of different boats,I am lucky there is a big boat building community in this area. I have to disagree with you on the trimming, Every boat I own paddles or performs better trimed level are just a little nose high, now there might be one exception ,I think you can sit closer to center in a boat with several inches of rocker on both ends. The handling is terrible on a nose down configuration ,tracking suffers badly, speed drops . Now these views come from running power boats ,conoes,yaks ,airboats and even a hover craft I built,so it isnt just off the top of my head.
Ron

 

[Jimmy W]

Putting the weight in the center will not make it trim nose down, it would have to be ahead of the center to do that.

Cliff Jacobson recommends paddling slightly nose heavy when paddling into a head wind or when racing.
http://tiny.cc/fb96r

 

[oldsparkey]

Putting the weight in the center will not make it trim nose down, it would have to be ahead of the center to do that.

Cliff Jacobson recommends paddling slightly nose heavy when paddling into a head wind or when racing.
http://tiny.cc/fb96r

BOY.... Things are really getting DESPERATE when you have to quote that FOOL. You are really scraping the bottom of the septic tank now.
I'm surprised a southerner ( Georgia ) would be quoting him , I would expect that from someone like Kayak Jack who thinks cliffy walks on water.