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PostPosted: August 11th, 2018, 8:12 pm 
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OK I think I know what the first one is - some boats feel tippy until they are loaded with gear. Is that primary?

My Alchemist is like this. My buddy's Alchemist as well (different model).

I'm not quite clear on what secondary stability means.


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PostPosted: August 12th, 2018, 12:52 am 
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A flat bottom boat will resist leaning - this is primary stability.
When the conditions are fine and flat, this boat shines.
When the conditions are rough and rolling, this boat will pitch and roll to find the flat water below it (there is none).
As the boat rides up the wave it will pitch one way and then pitch the opposite way on the way down the other side.
This becomes very hard on the paddlers and is very inefficient.

A rounded bottom will lean with less resistance - this is secondary stability.
When conditions are fine and flat, this boat feels a little tippy all of the time.
When the conditions are rough and rolling, this boat will ride level because the rounded bottom will feel the same no matter what the water is doing below you.
As the boat rides up the wave the canoe rides level up the wave and level on the way down the other side.
This is very comfortable for the paddlers and is very efficient.

A boat that seems to do a good job of acquiring both of these characteristics is the shallow V-hull.
A little roley poley while level but stiffens right up when leaned over.

All boats will get more stable as more weight pushes the hull further into the water... to a point.
Once past that point it gets incredibly unstable.
Some hull shapes will provide different stabilities. Flared hulls are super stable and can take lots of weight whereas heavily tumblehomed boats are a little more stable and can have a maximum weight increase.


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PostPosted: August 12th, 2018, 3:36 am 
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Prospector16 wrote:
OK I think I know what the first one is - some boats feel tippy until they are loaded with gear. Is that primary?

My Alchemist is like this. My buddy's Alchemist as well (different model).

I'm not quite clear on what secondary stability means.

Not clear to me too,
but I have been told by canoe designer John Winters
that this is because "The term is really just one of convenience"...
as it is just a "laymans way to describe something that is quite complicated".

Personally I now judge boats on having good or bad stability:
good is if it is easy for me to balance a canoe even in difficult situations.
Which means sufficient initial but also good secondary stability that will be there in time when I need it ;)

For a better 101 explanation I would recommend reading this:
https://sites.google.com/site/barendsnoot/cchoosing.pdf

Dirk Barends

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PostPosted: August 13th, 2018, 8:46 am 
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I always thought that primary stability was a measure of how "tippy" the boat feels when you step into it, whereas secondary stability is a measure of how hard it is to actually tip the boat over after you have tilted it over to one side.

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PostPosted: August 13th, 2018, 8:58 am 
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My two pesos... primary stability is felt most when the hull is level with the water surface... when the hull is submerged by an equal amount port and starboard, more or less. The hull will resist tipping to the left or right as long as it's in that level position.

Secondary stability shows up when the hull is tipped significantly left or right so that the water surface begins to approach the gunwales. In a canoe with good secondary stability, the hull will resist leaning further to the left or right, so that there's more stability there than in the level position.

Flat-bottomed hulls should have good initial stability paddled level but once the canoe begins to tip over to one side, stability disappears and the canoe may tip over and swamp easily once it's past some critical angle. Arched or round-bottomed hulls with flared sides should resist tipping more and more the further they are tipped over from that level position.

All in theory, there's probably some combination of initial and secondary stability in most hulls... try 'em all, some hulls should show better stability when leaned over close to the water and others will feel very secure and stable when level.

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PostPosted: August 13th, 2018, 9:09 am 
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Initial stability is what you feel when you get in the canoe. Secondary stability is what happens as the canoe is subjected to change in conditions. That could be shifting loads like a fidgety paddler or a dog that won't sit still or it could be waves. Neither of those terms are a technical definition of stability, they relate to a paddler's perception.

The secondary stability is affected more by the sides of the canoe than the bottom. The most dramatic example is to consider fishing dories that have very pronounced flare sides. That kind of vessel is used in rough waves often while heavy loads are being hauled out of the water. The dory may bob a weave on the water but as the sides are tipped closer to the water the boat becomes more buoyant and rights itself.

A canoe that's described as being "stable" will have a flat bottom that gives the impression of stability when you get in it but as noted in this discussion, the down side is that when the canoe is leaned past a point the stability goes out the window and the canoe quickly tips.


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PostPosted: August 13th, 2018, 8:43 pm 
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A dory,though, has a fairly small flat bottom with a strong flare. I guess the bottom is too small to provide much primary stability. Re secondary stability: They were traditionally used by fishermen who hauled quite heavy nets in over the side. Their gunnels can reach a few inches of the water surface and be very difficult to tip any further.

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