Here is a thought
I guy told me this one time when I was deciding on my boat construction. He said, put a one pound weight on the end of a 15 foot pole. Stand in the middle of the pole and twist the pole in a circle. Stop the motion and move it the other way. Then, take off the weight and move the pole. You will feel the difference two pounds can make.
Because of his explaination I went with carbon/kevlar. It is much more responsive latterally than my plastic boat. A touch of the rudder snaps it to a new heading. I am not sure the weight difference makes a big difference in straight line speed but any time the bow and stern are moving in opposite directions it seems to make a difference.
OnlyâŚ
â Last Updated: Nov-28-08 8:45 PM EST â
Only college football players are getting stronger. The rest of us are headed in the obverse direction, so lighter is always better. 'Less resistant to loading the boat, driving somewhere and plopping it in the water.
Another thought. Kids and smaller folk, who may be women, need the ultralights. If you weigh 120 lbs, a 60 lb roto-kayak is half your weight. If you weigh 240, it's a quarter; a lot easier to tote.
If you want your kids and a petite partner to enjoy paddling with you, THEY need the carbon/kevlar hull. Any decent male can suffer with a FG hull, until he's sure his family has hulls they can tote. Then it's time to treat yourself!.
Now the effect of ten or even twenty lbs of evenly spread hull weight on rotational force is pretty insignificant compared to the 200 lb wing-nut perched on a seat a couple feet aft of the rotational center.
Bill Mauldin in his ww2 Army cartoonsâŚ
âŚhas willie telling Joe, âYa gotta get rid of the extra weight. Throw the jokers outta yer deck a cards.â
Excellent Point
â Last Updated: Nov-27-08 10:11 PM EST â
I'd forgotten about that, but putting a load in your boat definetly slows its response to any effort on your part to make the boat pivot or otherwise change its orientation in space (riding over waves is another example of this). For any given load, this effect can be minimized by placing the weight near the center of the boat, well away from the ends. In any case, extra weight definitely shows the greatest negative effect on handling when you want to quickly turn or pivot, or ride over waves without digging in. Of course, just how much extra weight it takes to create a noticeable effect will depend on the situation, in the same way that extra weight can sometimes be your friend if it is windy.
couple more thoughts
I think all the feedback is spot onâŚcouple pounds makes a very small difference in on water performance but lighter is better for ease of use and you can hit a point where itâs the absolute (not relative) weight that is hard to manage. Personally, I do not like boats over 50 pounds and anything under 40 feels easy to manage.
I think that when youâre cruising along itâs just f=maâŚso if your total weight of boat + you is 300 pounds then 3 more pounds has only a 1% effect on acceleration/cruising.
There could be a more noticeable effect on boat turning response since a heavier lay-up of same design hull has more weight distributed towards the ends which one can feel in boat response (moment of inertia is proportional to the square of the distance of the mass from the center of gravity). As was mentioned if you take a 30 pound pack and put it in the end of the boat (or 15 pounds in both ends to keep trim constant) vs the middle it has a fairly big effect. A heavier and slower (and smoother) responding boat might even be preferable to some folks on the water, especially if youâre starting with a super responsive design like a Fire boat.
For momentum (mass times velocity) a little extra weight can actually help you. Thatâs why I like my Merlin II better with the dog since she adds 30% to the total weight and gives the boat 30% more momentum (feels like better glide) even though the boat is 30% harder to accelerateâŚbut the boat has such effortless acceleration by design that I like the trade-off.
GREATLY exagerated example however
Put one pound on the end of a 15â foot pole and swing it from center. This is going to feel much different than comparing a 15â pole, and another 15â pole that is 1lb heavier over its entire length. It will be much less noticeable.
Especially as that pole increases to canoe range weights⌠the difference in inertia is going to be less and less significant.
In other words, youâre going to feel the swinging difference in comparing a 1 and 2 lb pole to a much greater extent than in swinging a 35 and 36 lb pole. At 1 and 2 lbs, the extra weight represents twice the difference in weight. At 35 and 36lbs, the one pound represents only about a 3% difference in weight, and is aforementioned distributed more or less the length of the hull. But even that doesnât tell the story.
To be more realistic, letâs look at a common ~10lb difference between layups. Take a 45lb, 15â canoe turning circles at a rate of 3 complete revolutions per minute. Subtracting 10lbs (to a 35lb, 15â boat) is only going to equate to about 3 ounces difference in inertial force (1N). Add water resistance, and the ability to discern any difference has been virtually erased.
So it may be a slick way to sell a boat, but itâs not realistic. If a salesmen wants to sell a light boat, he should have the customer loading boats on top of cars, or carrying them 500â, not swinging sticks around.
funny math
I agree thatthe pole example is extreme but please write down your math and let the young folks check it, the pages in my textbooks are crumbling.
I thought the moment of inertia is directly proportional to mass so 35 pound boat (without paddler!) has a bit over 20% less inertia than 45 pound boat. I also thought that a Newton is a linear force unit so I donât understand your conclusion.
Sorry for being argumentative sir!
Hereâs my take:
Iâd have to go back to the old text books to check the math too, and I donât plan on doing that. BUT, when comparing angular momentum of two boats engaged in a pivoting motion, the difference in mass is not at some constant distance from the pivot point. It is spread all along that distance. Perhaps it would be accurate to assum that the difference in mass occurs halfway between the pivot point and each end of the boat, but I sort of doubt itâs that simple. In any case, the actual weight difference as compared at the ends of the two boats will be more significant that the difference that occurrs closer to the mid-point. Overall, the difference in angular momentum will be much less than the overall weight difference would imply using the over-simplified approach where the full length of swing is involved.
About 1% for every six pounds
In an average touring kayak, for every extra 6 pounds in the kayak, there is a 1% decrease in efficiency.
To me itâs a matter of physics âŚ
⌠I like the heavier boat (canoe) because it has a much greater ability to fight back .
That makes it easier on me in every condition .
Weight has more power so I use less of mine ⌠howâs that for twisted thinking .
Other boats may go faster , but thatâs a major trade off Iâm not interested in .
Weight has itâs own advantages , carry though is not one of them .
An extra pound or two
I doubt you could tell any difference that small on the water. I canât tell the difference between paddling a kayak with only my car keys vs. paddling it with a dry bag filled with lunch, splash jacket, camera, gloves, and neoprene hood, which amount to more than 2 lbs difference.
All the sea kayaks Iâve owned have been between 52 and 62 lbs. Was there a difference between the lightest and the heaviest on the water, yesâbut that I attribute to the lightest one being the stiffest (S&G wood), as well as big design differences.
But since I donât obsess about small weight differences, I am the wrong person to answer your question anyway. If the weight is acceptable (if I can carry it myself a short distance), Iâm OK with it. The other traits are far more important. I bought a glass boat that weighs the same as my favorite plastic boat, so Iâll pay more for stiffness and repairability but not necessarily for lighter weight.
Weighing in with an alternative
suggestion. My concern with weight was primarily about lifting and carrying. A few years ago I bought a dingy sailboat which requires trailering. After becoming proficient with backing up and maneuvering, I thought, Aha!, why not carry my canoe on a trailer?
I acquired a light (and foldable for storage) trailer for my canoe and now I rarely need to lift and carry. I can drag the canoe on and off and because the 16â canoe extends well beyond the 8â bed of the trailer, the weight is fairly balanced over the trailer wheels so that it can be freed from the tow vehicle and used as a cart to carry the canoe nearer to the put-in or take-out.
Re: Obsession with weight:
It seems to come up wherever kayakers gather. It makes for interesting discussion, and in this case, reading, but it all comes down to the same answer. What one person feels comfortable with, another does not. I spend very little time loading or carrying my boats, but a lot of time paddling them. It seems to me, that a slightly heavier kayak just paddles better, and several of my friends deliberately add a bit of weight. Some boats I have paddled can be brought up into the wind a bit easier, with a bit of weight in them. As to loading, I think the system one uses is as important as weight. My boats weigh between 49 and 62 pounds, and I really donât feel that much difference in loading over the back of my Grand Caravan, and Iâm pretty old, (71) and at 5â10" and 165#, not a big guy. I think that a trailer is in my future, and that presents a whole new set of problems. Iâll need some advice there, too. All of that said, my light 16 footer is my favorite boat, but I donât think itâs because of itâs lighter weight. It just maneuvers, rolls and paddles the best. A very interesting thread, though, and I enjoyed the more technical observations. KenâŚ
An additional benefit
of a trailer is that the boat can be stored and ready-to-go on the trailer without the need to unload after the dayâs trip and reload before the next trip. I bought my trailer from HarborFreight for under $300 (some assembly required).
jimyaker,
âLighter, faster, cheaper. You can only have two.â
I disagree. Build a wooden kayak. It will lighter, faster, cheaper AND more beautiful (unless you screw up horribly).
For whitewater, most folks prefer to
deal with extra weight in order to have great durability. Sometimes I do that too. But I have found that, for any type and size of boat, a light composite layup pays HUGE dividends in whitewater handling. Shouldnât be surprising, when comparing a Royalex 65 lb OC-1 and a 45 lb composite OC-1. Or, a 45 pound poly whitewater kayak versus a 30 lb composite kayak. Or a 48 lb decked c-1 versus two composite boats I have that weigh 22 and 28 pounds.
If you can learn to quit smacking rocks, and to do an occasional repair, you can have light boats that thoroughly outperform their heavyweight poly and roylalex competitors.
makes sense based on physics
A guy I paddle with has a Bell Starfire in white/gold lay-up and itâs a heavy example at about 56 pounds and I woman I paddle with has an early black/gold example that is well under 50 pounds, and I THOUGHT it was easy to tell a difference, so I played with the math to see just how crazy I may be.
The moment of inertia for a uniform slender rod is 1/12 * mass * length2 so if you assume a boat has uniform mass distribution front to rear (seems like a reasonable first approximation) then if you double the weight it becomes twice as hard to turn.
If you assume the paddler is a uniform cylinder sitting vertically in the boat then the inertia is the mass times the radius of the cylinder. The inertia of a lump (like a pack) is also m * r2.
So for a 36 pound, 15 foot boat the inertia is 1/12 * 36 * 15*15 = 675 (inertia units) and for a 48 pound boat it would be 900. For a 185 pound paddler if you assume the weight acts against an effective radius of 1 foot (should be a bit conservative even for a chubby paddler) you get 185 (inertia units).
Total inertia is paddler plus boat so 1085 versus 860âŚa difference of about 20% which seems like it should be easy to feel. A 20-something pound versus 50+ pound kayak SHOULD be easier to turn!
The math shows that the weight of the boat dominates over the effect of the paddler and also shows why say a 30 pound pack in the end of the boat (say 6 feet in front of youâŚ30 * 6 * 6 = 1080) starts to have a big effect.
Torque to turn anything is I (moment of inertia) times alpha (angular acceleration) so for any given angular acceleration (turning the bow of the boat) the Torque (effort) required is directly proportional to the total inertia of boat plus paddler.
The math also helps explain why freestyle paddlers get up on their knees to get the weight as close as possible to center of rotationâŚplus it helps explain why fancy ice skaters spin so quickly when they pull their arms in tight!
My spelling is getting pathetic but my math is still sometimes better than a 5th-graderâs.
um
You have to convert units, at the very least.
Try a centripetal or centrifugal force calculator online somewhere.
lighter is quicker
I can get my carbon C1 up to speed easier than my old wooden Jensen 200. The light weight gives me a faster start off the line and a better ability to sprint, either to catch a wave or beat someone to a mark.
The C1 weighs about 22 pounds, the J200, about 37 pounds.
At speed, however, I canât really tell the difference.
Itâs just the start of a race and sprints.
Oh, and carrying it to and from.
You donât feel a difference when you
have to re-accelerate the boat with each stroke?
I guess itâs possible that once you get each boat up to its top speed, you canât feel a difference. Whitewater boats lose more speed between strokes, even the lightest, and a light boat feels easier to re-accelerate.