Check my math ...

EDIT!!!! [snip, snip - gone] Please, spare the CPA Kayaker server (I removed the link that I had above). Apparently that site can't handle the typical PNet traffic generated by my question.... Anyway, my question was answered here by suiram and in the replies below the basic math is repeated again.

Basically, ignoring a lot of practical factors and purely relying on the [somewhat unreliable] kayak hydrostatic calculations for the 14 vs. 17 foot kayaks we get this:

Paddling a 17 footer vs. a 14 footer at 3 knots wastes about as much more energy as it is needed for lifting about 3 times a kayak that weighs 60lb from the ground to the roof of a vehicle 7 feet tall.

And, a 17 footer will be easier to paddle at 4 knots than a 14 footer by as much as it takes to lift a 60lb kayak 30 times from the ground to the roof of the vehicle 7 feet above.

Thanks!

decision

For a start, I’d try to paddle a 16 before you make the decision. If you contact CLC they’ll give you the contact information for builders/owners in your area. If you’re going to do the work of building a boat, make sure it’s one you’ll be happy with.

On the size question, the problem is that length is usually tied to other dimensions. “All else being equal” never is. For the same load capacity, a longer boat can be narrower than a shorter one. Decreasing width can reduce drag and improve paddling efficiency.

IMO, the most common beginner mistakes are buying a boat that’s too big(too much volume), and focussing on length while ignoring width and depth – two factors that make a huge difference in paddling comfort and efficiency.

The boat needs to match your size and abilities. My petite wife got faster when she traded her “normal”-sized sea kayak for a shorter, narrower, lower boat.

A foot of length doesn’t make a big difference in ease of transport unless you’ve got a hard limit somewhere.

relative vs absolute

Sonoma 0.85kg

Looksa 0.86kg

Work = Force * Distance

10 miles = 16000 m

Sonoma 0.85 * 9.8 *16000 = 133280 Joules
Looksa 0.86 * 9.8 *1.5)=4.25 times.

*16000 = 134848 Joules Difference = 1568 Joules How much is it? In kayak terms - 1 kayak = 50lb, say 25kg. Lift above car ~ 5 ft = 1.5m 1568/(25*9.8

That work is done over ~3 hours, it would be more realistic to consider something less heavy.

Werner Cyprus weighs 652 g. (210 straight)

Werner Tybee weighs 907 g ( 210 straight)

Thats 0.250 kg difference

Let’s consider 0.5 m lift (less than 2 ft)

Then total number of repetitions to work 1568 joules is 1280.

So, just switching from one paddle to another you could make up the work difference quite quickly without noticing too much.

1280 reps at “standard” strokes per minute of 60 is ~22 minutes.

Hey, don’t confuse me with …

the OP -;). I’m the nut who did the math -

i’d go 17 feet

If i am on the high end of the weight range, i’d definitly go for the 17. Even if you lose weight, if you’re paddling you’re going to gain muscle, and muscle weighs more than fat. At the very least though, if you ever want to go camping, or load anything in the hatches, you’ll have alot more available weight in the 17 than the 16

Thanks

I did the formula correct, but I guess I messed-up the conversion to “how many kayaks to lift on your car” part -

Let me fix that in the other post… Your math is correct on that part.

I am especially proud of calculation estimating the effect of paddle change!

Just shows how useful numbers are.

Yup

I immediately thought of that analogy too, but that was off-topic for that other thread. Just imagine the “savings” in energy one would realize from using a lighter (say ONNO brand) paddle compared to the typical 35+oz big-store “high-end” paddle…

Quick question

What do the values 0.85 and 0.86 kg represent?

Values of …

These are the "pull" needed to propel the two kayaks at 3 knots speed.

Sorry, I had to remove my original link that explained it. The values come from here: http://unold.dk/paddling/articles/kayakvelocity.html

There is an explanation about them there. I picked these particular boats somewhat arbitrarily. I own a Sonoma 13.5 and that link above lists the Looksha IV as having virtually the same volume and width so I thought that would make for an interesting comparison.

Thanks for the link

Thanks for the link, I’m going to find that info very useful. I find it weird to express drag in units of kilograms, as the correct unit should be Newtons (or pounds-force). Although incorrect, I think that’s the convention historically in naval architecture. I’ve noticed quite a few of these anachronisms in the field lately.

Calculations are bogus

I’m a mechanical engineer by training so I know a little about calculations. But the simple formulas you use here do not take evering thing into account.

I’ve never seen anyone paddle at 3 or 4 knots all day long. I have a 16 foot boat that is slower than my 17 foot boat for me by one knot at top speed. At my average speed of 4.2 mph or 3.6 knots the 17 footer still seems easier to paddle. But given multiple days of hard paddling I’d choose the slower 16 footer for comfort every time. I’ll be fresher and able to do more on days two and three in the most comfortable boat.

The same thing goes for paddles. I can get top speed from a heavy ancient whitewater paddle, and my lightest paddle is the slowest on a 15 mile trip. However for multi day paddling I’ll use the single blade sometimes and swap back and forth between it and the Werner carbon Little Dipper.

So it all come down to the fact that you have to try it or find paddlers who are like you who have tried it.

oh my

If you were to follow his reasoning in the original off-site thread you would understand that the point you just made is exactly what kocho was saying.

Very concisely:

Shorter boat will be slower at the top end, but easier to paddle at usual speeds.

The rest of numbers was just numerical masturbation, again sort of obvious if you tried to follow.

If your joules are big enough

none of the kayaks seem all that difficult. Get bigger joules.

And …

Thanks for stepping in -;)

If one was to re-read my original post above, I think the "scope" is pretty clear and narrow - given hidrostatic #s for two kayaks to find the effort needed to paddle them in practical terms.

The math is actually correct, by the way, even if it may be bogus [Grin!].

But ofcourse, not only does the math *not* take into account factors like comfort and choice of paddle, it also ignores other things such as the acceleration-deceleration cycle with the associated change in velocity and thus change in the very #s that we use in the calculation. And that happens at each paddle stroke...

This particular math is a simplification but I think a pretty darn good one if one is comparing two boats of similar design. I've watched my speed and heart rate numbers over multiple outings and they are consistent with the idea outlined in the post. But I was curious about quantifying these findings more in terms of comparable effort (e.g. lifting a kayak over your head, for instance) to give it a more practical view. That thread to which I responded (and to which I removed the link) presented the opportunity to refresh my physics memories in doing just that.

14 vs 17 foot

After 4 months I just finished building my 17 foot Pygmy Arctic Tern, but I looked at all the hydrostatic graphs before choosing it over the similar 14 foot version.

14 foot

23" beam

39 lbs

@ 3 knots - 1.86 lbs paddling force (KAPER graph)

@ 4 knots - 3.02 lbs paddling force (KAPER graph)

@ 5 knots - 9.07 lbs paddling force (KAPER graph)

17 foot

22.5" beam

43 lbs

@ 3 knots - 1.98 lbs paddling force (KAPER graph)

@ 4 knots - 3.66 lbs paddling force (KAPER graph)

@ 5 knots - 7.98 lbs paddling force (KAPER graph)

They have identical materials, construction, and hull design - just different weights and aspect ratios. The lower wetted surface of the 14 footer allows it to cruise at relaxed speeds more efficiently, but suffers at higher speeds and actually hits a wall when you really want to sprint. That said, I choose the longer one because of it’s space for camping gear. The 14 footer would still make a great day boat and over-nighter though.

Joules?

We don’t need no stinking joules!

Don’t understand your reasoning . . .

You said. “The 14 footer would still make a great day boat and over-nighter though.” Where do you get that impression of limitation?!!

The 14 has a volume that will carry the equivalent of two or three expedition backpacks. People disappear into the outback for weeks with backpacks that size.

Just because one boat is longer doesn’t mean that it is the only one appropriate for long trips, while the smaller one therefore is only a day/weekend boat. People who think that don’t know how to camp or pack . . . or they’re trying to justify their boat size decision.

I would not discourage people (especially smaller people) from building an AT14 out of fears of inadequate capacity - unless they plan a month-long expedition in the Arctic.

As far as The Wall is concerned, that some have talked about . . . I have met that (soft) wall, but it’s pretty far along, and not a problem for me. I’ve been in pods of long sea kayaks with my AT14 and can keep up, though I have to work harder to keep up, if they are in a hurry. But then, maneuverability is more important to me than speed.

incrimental

the math here is laughably flawed.

the numbers (may) be right but the effort it takes to move a 17 vs a 14 foot boat with comparable displacement (weight) may be the same at very slow speeds but speed retention over say 3 knots will change drastically.

you are moving water say 13 inches to the side and 4 inches down + -. Then having it return over 14 feet.

Versus 11 inches and 4 returning over 17 feet

the time you are doing that in makes a great deal of difference.

the speed may remain at 3 knots but is would suspect the number of strokes would change just a little.

the best way to check out this theory is to try to keep up with a friend in a Greenlander pro with a pamlico 14.

A 17 foot boat will leave a 14 foot boat in any distance involving speed over 3 knots.

Did you ever read the full post???

"… a 17 footer will be easier to paddle at 4 knots than a 14 footer by as much as it takes to lift a 60lb kayak 30 times from the ground to the roof of the vehicle 7 feet above."

I think you restated what I said in effect. For some reason though, preambling it with a statement that my reasoning is incorrect and replacing that with some clowdy logic instead of a clear numerical calculation…