How Heavy Is Too Heavy?

@CA139 said:
Second I am not talking about a loaded boat in terms of weight. I am talking unloaded or weight as built without paddler or gear.

No, I am - to prove a point, which apparently was lost:
If the weight of unloaded vs. loaded doesn’t change the handling much, why should the weight of the boat itself.

So I am pretty sure that the difference is in the stiffness rather than in the weight.

It’s true that the difference in straight-line acceleration of a 40# vs 80# kayak is not going to be huge. Assuming a paddler weight of 180#, then the total weight goes from 220# to 260#, an increase of 18%. Meanwhile, the skin friction and wave-making resistance of the hull will not change much assuming a minimal increase in draft. So the overall increase in paddling effort to accelerate the hull might change by 10% or so, and the effort to paddle at constant speed will be the same. The increase in inertia, meanwhile, will give the hull increased glide so in some respects the hull may feel faster once it’s up to speed. Much of this is mentioned above.

EDITED TO REFLECT CORRECTIONS (in italics) MENTIONED BY ALLAN IN POST BELOW:

With respect to maneuverability, the rotational inertia of a long thin body is dominated by weight at the ends (see mass moment of inertia, proportional to mass times distance from center of rotation squared). The weight of the paddler contributes almost nothing since it is located near the center of rotation. Doubling the weight of the boat, then, effectively doubles the mass moment of inertia making the boat more resistant to turning. This is why heavy boats are more difficult to handle on land. In water, the effect is mitigated somewhat because the hydrodynamic resistance to turning (due to the shape of the hull and skin friction) remains the same. But I have to guess that the difference may be large, not sure by how much.

A 180# paddler in a (ridiculous) 180# kayak, would have 1.6 times the linear inertia and 4 times the rotational inertia vs a 45# kayak. Again, the aggregate increase in paddling effort would be reduced by the unchanging magnitude of fluid resistance in each case, but still…

None of this says anything about stiffness, which is undoubtedly a factor, but is not really part of the weight question that was asked.

@carldelo said:
Doubling the weight of the boat, then, effectively quadruples the mass moment of inertia

Mass moment of inertia has a linear relationship with mass, and a quadratic relationship with distance from C.O.G. But we aren’t changing any distances here.

If the mass distribution of the boat along the length of the boat is equal, and the boats are equally long, the boat with the double mass will have double the mass moment of inertia.

Anyway, I will still claim that when turning a kayak, the effort used to overcome inertia means next to nothing compared to the effort used to overcome opposing forces from wind and water, which try to either prevent you from turning or even in a lot of cases try to turn you in the opposite direction of what you want. If overcoming inertia was such a huge part of turning, then we would have to use a lot of effort to stop the turn when we have reached the direction we want.

I will throw another aspect in: super-light skin on frame boats like those that I usually paddle (both the “rigid” type and foldable craft) tend to be faster and more stable in rough confused waters than similar sized stiffer boats of any weight because they flex somewhat to absorb and ride over the force of waves rather than being buffeted and knocked around by them.

Well, a hull that weighs more than the water it displaces is too heavy. All the rest gets the question, "Too heavy for what? "

@Allan Olesen said:

@carldelo said:
Doubling the weight of the boat, then, effectively quadruples the mass moment of inertia

Mass moment of inertia has a linear relationship with mass, and a quadratic relationship with distance from C.O.G. But we aren’t changing any distances here.

If the mass distribution of the boat along the length of the boat is equal, and the boats are equally long, the boat with the double mass will have double the mass moment of inertia.

Anyway, I will still claim that when turning a kayak, the effort used to overcome inertia means next to nothing compared to the effort used to overcome opposing forces from wind and water, which try to either prevent you from turning or even in a lot of cases try to turn you in the opposite direction of what you want. If overcoming inertia was such a huge part of turning, then we would have to use a lot of effort to stop the turn when we have reached the direction we want.

Allan - you’re right, you caught my careless mistake. My internet access has been down but I will edit the original post now if I can.

You make a good point about the relative magnitude of inertial vs fluid effects while turning. I don’t have a good estimate of that. The estimate of a 50/50 split between inertial vs fluid effects in straight line acceleration seems about right.

@Overstreet said:
Well, a hull that weighs more than the water it displaces is too heavy.
Unless it has wheels…

@CA139 said:
I have found that lighter and stiffer boats tend to be nicer to paddle. I think they can be more or less bundled together because stiffer materials don’t have to be as thick, thus they don’t weight as much so it’s not a 1:1 or 100% correlation, but lighter tends to usually mean stiffer and vice versa.

A little confused by what you are saying here.

If two Sairy Gamp’s are made of the same material – say S glass – and one is made of two layers while the second is made of three layers, the second will be both heavier and stiffer.

On the other hand, if you are talking about two Sairy Gamps being made of completely different materials – say one made of polyplastic while the second is a lamination of S glass and Kevlar – then the second could be both lighter and stiffer. Most sophisticated paddlers would probably prefer the on-water performance of the SK Sairy Gamp. People who are less concerned about subtle on-water performance differences, but are more concerned about durability for bashing on rocks and dragging along parking lots, may prefer the poly Sairy Gamp.

As to Willow’s claim that skin-on-frame boats are faster in rough waters, I doubt that even though I have never paddled a SOF boat. No racer in any paddling discipline I’m aware of – marathon canoe racing, whitewater slalom and downriver canoe and kayak racing, outrigger and surf ski ocean racing, or Olympic sprint racing – uses a SOF craft.

@Allan Olesen said:

@Overstreet said:
Well, a hull that weighs more than the water it displaces is too heavy.
Unless it has wheels…

Yes. It’s going to need to roll along the bottom.

I’ve built 3 Greenland-style SOF kayaks and have never noticed any difference in speed compared to composite or molded boats. That said, I really don’t care that much about speed and don’t monitor it, either. I also own a Pintail, which really hits a wall when you push it, due to its short waterline and resulting low max hull speed. My SOFs have all been faster, but it’s a pretty low bar to beat. I’ve owned several longer, faster boats and the SOFs seemed to be comparable in performance. The frames are relatively rigid, but probably more flexible than any of the composite boats I’ve owned. What flexes most on an SOF is the skin,, which assumes a somewhat concave shape between the keelson and the stringers. I haven’t seen any studies of how this affects the speed of an SOF kayak, but it does affect the tracking.

Regarding flexibility, some Aleut Baidarkas are designed to flex in order to handle rough water better. These designs also tend to have long waterlines, which makes them faster. Whether the flex contributes to speed or not is questionable, but if it keeps more of the hull in the water, there’s at least the potential for higher speeds. Again, I haven’t seen any definitive studies on the subject.

I don’t think studies are necessary. Just look at the empirical results in all serious paddlesport races. They are won by lightweight composite boats in every category I can think of. If racers thought a SOF boat would win their race, they would definitely use them. They don’t.

Personally, I’m not a racer and never cared much about maximum hull speed with any canoes or kayaks even when I was young, strong and fit. During my 20 years as a serious whitewater open canoeist, I did value acceleratability. Very often and continuously in hard rapids you have to accelerate very quickly to make some move or to avoid something. You have maybe two or three or four strokes to do it. Hulls that could leap quickly forward were important. In other words, slalom hulls.

I’d like to offer a definitive answer to the title question – one that made sense to me and stood me in good stead from about age 40 to 70: Any solo canoe or kayak that is over 45 pounds is too heavy. Spend the extra money to get a lightweight composite boat, learn how to paddle it, take care of it, and it will treat you, your muscles and your ligaments well.

At age 70 I revised the upper weight limit to 35 pounds, but unfortunately by then my wallet had become too light.

First off, why would you (GMacG) disdain a statement on the performance of skin on frame boats in the same breath where you admit you’ve never paddled one?? Second, of course nobody would use a skin on frame or folding kayak preferentially in most of those racing events you list because the relative speed and handling advantage over rigid boats exists in confused very open rough water, not in other conditions that would be more common in a racing situation.

@willowleaf said:
First off, why would you (GMacG) disdain a statement on the performance of skin on frame boats in the same breath where you admit you’ve never paddled one?? Second, of course nobody would use a skin on frame or folding kayak preferentially in most of those racing events you list because the relative speed and handling advantage over rigid boats exists in confused very open rough water, not in other conditions that would be more common in a racing situation.

I have no opinion on the comparative handling or stability of SOF’s, but I do on comparative speed. How? I’ve answered this question twice above. I look at the empirical past – namely, the boats that winning racers have used. Any water race.

But you want to focus on speed in “confused and very open rough water”, Okay (with some links). How about any slalom or downriver whitewater race ever held in class 3-4 whitewater? Think a SOF could win? I’ve never seen or heard of it, and I’ve been watching whitewater racing for 40 years on every level from local races to the Olympics.

How about the annual 41 mile ocean race across the Molokai channel in Hawaii? BIG water. (The video is only of the OC6 boats, but it shows the carnage conditions.) No SOF constructed boats ever seen there to my knowledge.

How about any of the many open class ocean races such as the 20+ mile annual Blackburn Challenge around Cape Ann, Massachusetts, in which “the water can be very rough, with strong winds and high waves.” Never heard of a SOF having the fastest times, which are all published.

You don’t have to be a meteorologist to know empirically what the weather was yesterday.

@Glenn MacGrady said:
…age 40 to 70: Any solo canoe or kayak that is over 45 pounds is too heavy…
…At age 70 I revised the upper weight limit to 35 pounds…
What a great ‘rule of thumb’ (just 'cause that’s what I think).
I might amend that with an exception - if you always paddle with friends that always will be there to assist in carrying. (I paddle 90% solo)
Also, if you think that a lighter weight boat will get you on the water more often, spend the extra bucks on the kayak (get a cheaper car next time, put off the kitchen remodel)

Every year me and my kayak gain 2 pounds!

My feeling is that our Wilderness Polaris at 85lbs is a little heavier than we’d want but we can do it (we’re in our 40’s) and we are right on the water. I do appreciate the weight just for momentum and handling rough seas as it’s right on a tidal bay that has very rough water, but we would never want to take that boat out anywhere else, ever. I wouldn’t have it if we weren’t staying where we are.

180lbs pure, unloaded boat weight is just too much and that was my suspicion. That kayak could be disassembled in 3 pieces but two of them were about 80lbs each, too much to handle! I saw it took over 2 hours to assemble, and 2 hours to disassemble too, not practical. And it felt heavy enough that not only was it a no-go on land, but it felt like a no-go on water. That’s my unqualified opinion.

Well Glenn you may be on to something. I just sold my heaviest solo canoe (45 pounds) because it was too heavy. Now I have 5 solos with 3 around the 35 pound limit…but my Shearwater is over 40 and I’m pondering selling it and replacing it with a lighter one. My Bell Merlin II is around 40 but I can never sell it because we’ve done too many things together. I recently test paddled a Northstar Trillium and I was impressed with the boat’s performance and also with the 26 pound weight.

CA139 - I’ve always thought that a boat is too heavy if you ever hesitate to use it because of what it weighs.

I’ve been carrying this kayak on my shoulder
to go paddling} for over 15 years. I turned 67 this year and determined it was now too heavy to solo carry. I weighted it when I took it apart a week ago 75 pounds. I bought a 50 pound Nordkapp LV to paddle instead. Feels light to carry {

My new {to me} kayak

Hi Roy. Would love to know how you do with the Nordlow. My eldercare issue is gradually resolving so my time is more predictable, looks like I can count on getting my roll dialed back in on both sides this winter so I can come out next spring in JIm’s Nordkapp LV. I have been playing extreme safety in my choices of boats because of paddling solo so it should be a lot of fun to try out the other.