Well-said
With a heavier boat, the consequences of a mistake might happen more slowly. On that line of thought, while extra inertia can be an advantage when you screw up, it's still a disadvantage when you do everything right (or I'd add, a lot of times even when you try to and fail, since I'm betting that the slower reactions of a heavier boat will be as likely to cause you to fail some maneuvers as save you when your own actions are lagging).
of course
NEwton again. The heavier longer hull prob has more bow outward sweep rising to the gunwale for more upfloat on incoming waves.
Class 2+ in flood downhill eyeyahhaha…
Galt cruiser…Grumman…
Inertia
There is one time I have noticed that inertia definitely helps and is an advantage. Climbing ledges when poling upstream, some extra weight does help complete the attainment once you get it going. But I prefer that weight to be camping gear and food - not the canoe.
I use a couple of dumbbells
to help trim and stabilize, depending on conditions.
They are 15 lb. each and they make a big difference in tracking and handling, depending on where they are placed.
The combined weight of 30 pounds is almost insignificant when placed in the middle, but when each is moved towards or at the ends, the tracking and handling improves greatly.
This “working with weights” concept has been touched upon before, although its dynamics is somewhat mystical.
Handling improves?
Surely you are talking about certain specific aspects of handling and not all aspects of handling. Giving extra rotational inertia to the boat would be counterproductive in a lot of cases. I wouldn’t choose to move any on-board weight from the center to the ends when ease of pivoting is an advantage, or when I want the ends to be less prone to plunging in waves. Those situations involve “handling” too.
Absolutely right, the dynamics depend
upon the circumstances and the desired responses.
Some experimentation with the dumbbells would help to find out what the results would be.
Sometimes, dumbbells would not be an advantage.
I think there is some linear exponential effect when the dumbbells are moved to the extremities, but I have not been able to formulate it well enough to describe it.
right
use https://goo.gl/xZS1Q7 10 liters velcroed and strapped to keel floor either cross keel or with keel.
Drinking water plus moveable ballast.
In a kayak, MSR bags form functional deep keel as on a sailboat for easy rolling up.
…BUT when one is [fly]fishing from a
canoe you are not dynamically moving your COM like a paddler is. When just fishing you want to be on a non-moving barge…and a lighter material will ride higher in the water, subjecting itself to more chaotic wave/chop force…as well as being blown about by the wind.
Draft
Well the difference between the two boats in question is 22 pounds. Displacing an additional 22 pounds of water in a 12’ canoe might increase the draft by about 1/4". That’s not going to do much to the windage of a loaded canoe.
That’s a stretch.
Leverage has nothing to do with it, I suppose.
Easy and safe ballast…Cheap large drybag from Dick’s or the like. Fill with water but leave a little air space before sealing. Lay on floor where weight gives desired trim.
It won’t slide easily or roll around. And if you happen to swamp the boat, the bagged water ballast will not sink it - as any denser-than-water ballast will.
fixed
tight to hull.
Moving weights on hull bottoms paddle as well as us but in the opposite direction…Newton again.
But last we heard, dry bags leak. Best used inside out ?
Newton didn’t cancel the effects…
…of friction. Those cheap pvc coated drybags don’t slide that easy when filled with a little water. Never yet had a problem with leakage in that use either.
Vagabond
Buy the Vagabond! My friend used his kevlar one last weekend on Indian Lake in the ADK’s and the wind was really kicking. With a double blade he just cruised over the whitecaps and took a few pictures along the way. I tried to get that boat for my friend but he is still waiting.
this article explains it all!
http://www.surfski.info/getting-started/tips-other/story/1547/relax-a-few-extra-pounds-may-be-a-good-thing-in-your-surfski.html
this is the article I have been looking for. it goes over why lighter boats inherently feel more tippy. it reaffirms what everyone has felt with some simple math and physics.
I suggest everyone read it. it’s worth your time
Surf ski is not a tandem canoe
But the three forces are present. Tandems have their ends weighted by people. Not in the center. So all three forces can act not only at the same time but they are also magnified at the paddling stations Light boats are often lightly reinforced at the sidewalls and tend to twist with forces at each end pinning them down.
I am willing to lend a 43 lb 18.5 foot Wenonah tandem. Paddle it empty. Paddle it with the recommended 600 lb load.
Paddle in five foot waves for each test. The light bulb will go off.
Not really. Some math and experience.
The author admits racers will go for the lightest boat.
He then tries to make the case that a lighter hull of the same shape can feel less stable along the axes of pitch, roll and yaw. I agree with this conclusion, but not with his math calculations or the practical importance of the conclusion.
As to the math, the author states that rotational angular acceleration is proportional to 1/mass (1/m). I don’t know if that’s correct, but I will assume it to be true.
For a hull that is 1/3 heavier than another hull, the author concludes on the basis of this 1/m proportion:
“So now our 1/3rd heavier boat should theoretically cut the rotational acceleration of the boat by roughly 1/3! With the rotational acceleration of the boat reduced (pitch, roll, and yaw rates slowed down), it’s easier for our bodies to react to the (now slower) changes in boat angle, and thus the boat will feel more stable.”
Let’s assume a 30 lb. hull and one that is 1/3 heavier, which is 40 pounds. Does the rotational acceleration between the two boats change by 1/3 because the comparative masses of the hulls changes by 1/3? No, for two reasons.
The author’s first mistake is that he completely ignores the mass of the paddler. If the paddler weighs 170 pounds, the two boats have comparative hull+paddler masses of 200 lbs. vs. 210 lbs. This means the heavier boat has only 1/20 more mass, not 1/3 more mass. That would result in a rotational acceleration difference of 1/20, not 1/3, according to the author’s calculations with the 1/m formula.
However, the author makes a second mistake: his math calculations with the 1/m formula are wrong. Let’s even forget the paddler’s mass and just deal with the 30 and 40 pound hulls, which I’ll simplify to 3 and 4 pounds for calculation purposes.
According the the author’s formula of 1/m, the hulls would have rotational accelerations of 1/3 vs. 1/4. Those fractions, however, don’t represent a DIFFERENCE of 1/3 in the rotational accelerations. The fractions represent a difference of 1/12 in the rotational accelerations. (1/3 = 4/12; 1/4 = 3/12; hence the difference between the fraction 1/3 and the fraction 1/4 is 1/12.)
When we add in the mass of the paddler (and gear) and calculate the 1/m differences correctly, the stability difference between a 30 and 40 pound hull, measured by rotational acceleration, is trivial.
Finally, at the practical level, a skilled paddler is not going to have any problems with a lighter hull’s slightly greater propensity to be knocked around by waves than an identical but heavier hull. That’s because the lighter hull is – by the same physics – easier to correct back on course. Skilled paddlers need only apply autonomically-learned pressure and directional changes on their submerged paddles to keep a light boat on course in waves.
(Someone should check my math.)
physics are physics…
the boat is irrelevant. the physics of acceleration are a universal law. ( whether or not they were applied properly though, that is a valid point)
people's experiences in this thread support what the article says
also, Glenn, as to 20 vs 30 lbs vs 200 vs 210 lbs, wouldn't the math be closer to the 20/30 since the force that makes people capsize most often is rolling force? as it relates to roll, the person isn't much if a factor other than your hip movement, so I feel as it relates to roll, a heavier boat accelerates more slowly, more than 1/20th I mean. As for pitch, yaw, forward or up and down movement, I bet it is in fact very small.
Math OK, but
The math in the cited article seems correct, if simplified, but whether rotational inertia is the correct proxy for stability is not clear, at least not to me.
It’s true that a boat’s rotational inertia depends on the distribution of mass. Each bit of the hull has a mass and a distance from each of the three rotational axes. The sum (integral) of the contribution of each bit (m*r^2) will give a Mass Moment of Inertia with respect to each axis (Ix, Iy, Iz). Simply doubling the mass of each bit of the hull will indeed double the I values.
The doubling doesn’t take into account the paddler. The paddler’s mass is significant (many bits of mass) but they are mostly close to the axes of rotation (low r values). The major contribution of the paddler will be in I values for pitch and roll, as the heavy chest and head are relatively high above the axes of rotation. The paddler probably won’t contribute much to the I for yaw.
The contribution is further complicated because paddlers move around, and we know experienced paddlers move themselves to compensate for imposed motion from waves and wakes. But ignoring that, it seems a heavier boat should increase rotational inertia somewhat, although not as much as the net increase in weight might suggest, and not by the same amount in the three rotational axes.
The change in total mass will influence the maximum straight-line acceleration of the hull, but as has already been pointed out, that matters mostly for racers or the impatient. Now that I have lightweight boats, I dislike paddling a heavy hull that takes more than a couple of strokes to get up to speed. This aspect is more important to me than the rotation effect, I think because I rarely go into dicey wave conditions.
Forget all the math…
and technical terms…bottom line to me is that hull weight is entirely insignificant compared to hull shape when it comes to any kind of handling parameters you wish to consider. You gotta go by hull shape, not weight, to enhance any particular handling characteristic. And if the hull shapes are reasonably similar, I’d go with the lighter canoe EVERY time.
I think the boat is relavent
Many people paddle canoes from a kneeling position. When seated, the boat has a pretty pronounced ability to pivot beneath the paddler’s butt, and act quite independently of the paddler’s mass in its rolling motion. In that case, I’d say there’s some truth in what you say, that boats are boats. But for a kneeling paddler, the paddler has an extreme ability to make his own mass control the rolling action of the boat, to the point that I think the boat’s contribution to overall rolling inertia is slight. I’d say that if a person were to stand in the water and try to roll a canoe out from under the paddler and the paddler were not allowed to brace with the paddle, the person doing the rolling might notice a small amount of difference between a heavy boat and a light one for a seated paddler, but for a kneeling paddler, he’d have a much harder time rolling the boat in the first place, regardless of whether it was light or heavy.
I’m not trying to shoot down your premise, only modify it very strongly.