Test on stability of asymetrical hull

[oldsparkey]

It is the person in the boat that makes it roll , the boat will not do it on its own , it need encouragement. Plus it is not hard to figure out the wider it is the more stability there will be in it , the great margin of error in the persons favor.

Something else , a guy will flip a boat faster then a female will due to the center of gravity in them.
It is a understood scientific fact ......A males center of gravity ( body mass) is higher then a females which is lower ( even discounting upper silicon treatments) . I am sure all you married guys know that from the old , "Honey do these slacks make my butt look big ". :wink:

Chuck........
Running and ducking the incoming from that last statement.

 

[WDfrmTN]

The little test was to prove a asymetrical swede form was stabler than an symetrical design
because of width where the most weight was.
Ron

I can see a few minor problems with the test.
1. The model and weights are not representative of truly comparative bouyancy and loading.
2. Weight is not at fore/aft centerline, contributing to rolling moment.
3. No sides removes the corrective tendencies of those sides.

What you'd need for a more accurate test are either two compaarable sized boats (or scaled models), loaded on fore/aft centerline with identical real-world loads (or or loads to fit the scaled models).

 

[tx river rat]

Wd
You need to go back and look at the pics, the weights were set the same distance from the centerline both directions.
The sides have no bearing on initial stability or very little, the half inch sides would represent about a 4 inch water line so that was enough.
I dont understand your statement about weights . With the weight in the same place from the center lines , adding or subtracting weight doesnt effect the out come.
I have boats that are asymmetrical and symmetrical and I guarantee the asymmetrical has more initial stability.

 

[jdupre']

Ron, I think the assymetrical shape displaces more water than the symetrical per degree of lean. That's where the extra bouancy and stability comes from. Your model did a good job of showing that.
Joey

 

[oldsparkey]

Personally , I am just happier then a possum in a persimmon tree if mine float.
Folks you can't get happier then that. :wink:

 

[Jimmy W]

Ron, I think the assymetrical shape displaces more water than the symetrical per degree of lean. That's where the extra bouancy and stability comes from. Your model did a good job of showing that.
Joey

Any displacement boat (not on plane) is going to displace an equal weight of water to the total weight of the boat and everything in it. Amount of lean, shape, amount of beer drunk by operator, etc isn't going to change that. Hot air or helium balloons attached to gunnels will reduce displacement and probably add to stability unless in a strong cross wind.

 

[tx river rat]

Joey
I understand what you are saying .
Ron

 

[Kayak Jack]

A model should have a complete hull, including bottoms and sides. Otherwise, results lack reliability.

 

[oldsparkey]

A model should have a complete hull, including bottoms and sides. Otherwise, results lack reliability.

A scale model would work quite well if the person has the capabilities of doing a test the way it should be done , under controlled conditions and with scale models.
I'm not sure but for the life of me I do not think any of us have a lab or an area where we can control the water flow , the wind , waves and all the rest that a paddler puts up with. Much less a miniature person to be paddling the model during the test.

A simplified model works good as an visual aid in the explanation of what is being expressed which I am sure it was meant to do in this case.

:lol: :lol: :lol: Had to come back and edit this post...since I overlooked a simple fact , along with all of you.... Not sure about all you guys but the boats I use only the bottom is the part in the water so why have a scale model with the sides and all the rest , it was not a wind test or capsizing but a visual flotation and displacement explanation for the bottom shape of the boat.

As far as the actual boats and how they handle. I for one tend to put faith in a person who has paddled both styles of the boats and go with there conclusions. Why would a model be needed , he has the real McCoy to use. :roll:

It appears that Joey summed it up using Ron's model as a visual aid.......... " Ron, I think the asymmetrical shape displaces more water than the symetrical per degree of lean. That's where the extra bouancy and stability comes from. Your model did a good job of showing that.
Joey "

 

[tx river rat]

This has got completely ridicules.
I did a test to see if what I felt in my butt was true .It worked out to my satisfaction.I could go into all kinds of stuf but I am finished with this conversation ,unless some one wants to spend the time and effort to build a model and prove me wrong. I spent the time and posted it
to give my findings to the forum. if you agree fine ,if you disagree fine. doesn't really matter
to me .
Ron

 

[Kayak Jack]

Pretty simple. When you lean the boat, the sides become active. If we're merely looking at a silhouette as a visual aid, that's one thing. Maybe that's what Ron intended in the first place?

 

[Jimmy W]

... I overlooked a simple fact , along with all of you.... Not sure about all you guys but the boats I use only the bottom is the part in the water so why have a scale model with the sides and all the rest , it was not a wind test or capsizing but a visual flotation and displacement explanation for the bottom shape of the boat.

It appears that Joey summed it up using Ron's model as a visual aid.......... " Ron, I think the asymmetrical shape displaces more water than the symetrical per degree of lean. That's where the extra bouancy and stability comes from. Your model did a good job of showing that.
Joey "

All of my boats have at least the lower part of the sides in the water when level. If I lean them to one side then one side will come out of the water and the other side will submerge more, but it will still displace the same amount of water. Adding ballast will make them displace more water and in sail boats and ships ballast is commonly used to increase stability.

 

[Kayak Jack]

<SNIP> If I lean them to one side then one side will come out of the water and the other side will submerge more, but it will still displace the same amount of water. Adding ballast will make them displace more water and in sail boats and ships ballast is commonly used to increase stability.

Right. Weight of water displaced is dependent on weight of boat and cargo including people. Geometry has nothing to do with that part of the situation.

 

[JEM]

Ron - I like your test. Just scientific enough to confirm a generality that you suspected was true. The results may be satisfying enough for you to do no more experiments or they may make you curious enough to try again with a diffent approach.

 

[Bellybuster]

ha, I love these threads. Permit me to add my take.
I think the test was accurate for what was being proved or disproved.
What I see as proved:
1. An asymetrical hull will indeed show more stability than a symetrical....if....the center of weight is placed at the widest point or close to it, keeping in mind that the models do not exibit the same displacement or width
2. An asymetrical hull will show no more stability than a symetrical ...if....the center of weight is moved away from the widest point

What i see as yet to be proved:
an asymetrical hull is more stable than a symetrical hull of equal displacement and width at the center of weight.

I understand exactly what I just typed....I think

 

[shikeswithcanoe]

"What i see as yet to be proved:
an asymetrical hull is more stable than a symetrical hull of equal displacement and width at the center of weight."

Also consider that MORE stable might not be the only thing of interest here. Even if the stabilities are pretty much the same, the hull being asymetric may offer other advantages (more hydrodynamic, more ergonomic, better suited for storing/carrying certain things, basic sex appeal....), in which case you've gained something with no downside...though that often isnt the case in the real word....but one can dream

 

[oldsparkey]

It appears that Ron did just what he wanted and that was to show something that all of understand , or should understand.

The wider portion on a boat will tip less then a narrow portion. So if you have a narrow boat that has a wider portion for where the paddler is there will more stability for the paddler in that area. If both boats have the same width then there is no difference in the actions of them. :roll:

If I lean them to one side then one side will come out of the water and the other side will submerge more, but it will still displace the same amount of water. Adding ballast will make them displace more water and in sail boats and ships ballast is commonly used to increase stability.

The test had nothing to do with ballast , just the stability of the different boat shapes. Plus everyone knows that when you lean a boat the one side goes down and the other goes up , to much and it is called swimming and all stability is lost. That's when it stops displacing as much water and lets the paddler displace water while cursing his loss of stability.

I believe Ron's test showed exactly what he wanted to show , page one of this thread in case you missed it.
If there is a question , build one of each and test them by paddling them , then you will know without any guessing.

 

[Jimmy W]

Chuck, you quoted Joey and agreed with his statement about a asymmetrical shape displacing more water per degree of lean.

It appears that Joey summed it up using Ron's model as a visual aid.......... " Ron, I think the asymmetrical shape displaces more water than the symetrical per degree of lean. That's where the extra bouancy and stability comes from. Your model did a good job of showing that.
Joey "

That is not true and I was trying to explain that it isn't true when I brought up the ballast. Gravity will pull a boat down and it will go down until it displaces an amount of water that weights the same as the boat. Shape of the boat or the amount of lean has nothing to do with it. If you want to displace more water then you have to add weight, ballast.

 

[tx river rat]

Jimmy
It is true ,your using tunnel vision and not looking at a couple more things,now this is without helium filled balloons circus performers or any of that junk. There are two more things involve here that you are forgetting ,one is center of gravity which moves as the weight changes positions. the second is 14 inches behind center is the seating position of your paddle (the weight) this is on both boats, I am just using approximate figures but an asymetrical boat is 26 inches wide at that point, the symmetrical is 22 inches wide at the same point. Now when you lean is where your displacement comes in , it is harder to push down an object that is 2 inches wider than it is the narrower hull. The center of balance changes and the boat goes into a slow roll, on the asymmetrical it tries to pick up the back of the hull and the nose drops down , on a symmetrical the opposite happens ,the stern drops down and the bow tries to pick up. That puts a narrower hull with the center of balance located still 14 inches behind center, same displacement but a diferent hull design will react differently.
Jimmy you paddled white water so I am sure you know how to heel a boat,all your doing is changing the CG and by leaning the boat your hull design changes,same displacement but the hull handles completely different
So Joeys statement is true . Displacement and weight do go hand in hand but I can stand a boat on end and displace the same amount of water . are you trying to tell me that it would be as stable as a boat sitting normally, your saying shape of the hull does matter,that want fly

Ron

 

[oldsparkey]

Sorry about that ... I should of been more specific.
I was agreeing with the stability and that the wider boat covers more of the water surface then a narrow boat thus leading to more stability , not necessarily more displacement unless you are referring to the displacement of the surface area and not depth....

Taking two boats of the same weight but different widths in there construction , the wider boat will float higher and offer more stability.

It sure would be nice if we had a ..... NAUTICAL ENGINEER ..... on here to settle this since no one can understand that even folks that design boats agreed on the matter of stability Ron's test proved. I guess that Ballast , speed , paddling comfort and all the rest is nothing more then a smoke screen to deviate from the topic of stability between two different boat shapes sitting in the water and seeing which one tips 1st as weight is applied to it. How can something so simple become so involved :?: :?: :?:
Till then I guess it is going to be a cracker barrel discussion till the cows come home so we can cover all the parts of the pasture and sometime close the gates.