RE: [Paddlewise] Wing paddle and hull speed was (Re: Who Took Shaun White Sea Kayaking?)

Paul Hayward wrote:

>
> Matt, I'm being lazy asking you - I should really go and read up lots of SK
> back issues ;-)



No need to get the back issues (but I have many hundreds of them I'd love to
unload) go to www.marinerkayaks.com and find the "Downloads" link. There you
can download a very similar spreadsheet to the one I use to calculate the
estimated drag of kayaks. These are all calculated at the weight of the kayak
plus 250 pounds for paddler and gear. We figured a 150 pound paddler with 100
pounds of gear and water would be a good average for kayak touring. All the
kayaks that were measured and run through the spreadsheet are listed below
with their dimensions and results. You could take that data and add a few
formulas to the spreadsheet and do an analysis of the factors. I thibk you
will find that for sea kayaks over about 13 feet long that hull speed isn't
much of an issue until around 4 knots (with 250 pounds aboard). If I recall
correctly the 13' 5" long by 23" wide Coaster had lower drag at 4 knots than
the majority of the kayaks on that long list.
>
> I believe the usual point where the hull's wake drag starts to overwhelm
the
> skin drag is around 3 to 5 knots - which is why one looks for a longer
kayak
> if one wants to spend time at higher speeds.
>
> Most tests are done with (essentially) an empty kayak - with say 20 Kg of
> kayak and 80 Kg of paddler and PFD. Let's say 100 KG as a nice round
number.
>
> What happens when Freya adds 50 Kg of gear and water into an Epic ?
> Obviously, both more skin (the kayak's, of course ;-) is dragging and the
> hull is lying deeper and creating a bigger (taking more energy) wake.


The paddling tests are usually with a lightly loaded kayak but the drag
calculations are with a significant load. I think Freya said that at times,
after resupply, she had something like 100 Kg of gear load. If this is so she
needs the added length to have a narrow kayak and enough volume to float that
load. The other choice to handle that much weight would have been a wider
kayak but that would have hurt her efficiency even more.



>
> Something tells me that if you add this 50% to the displacement, you will
> only add perhaps 20% to the wetted area - but increase the draft and so the
> wake (?) - by 50%. I think these figures are about right if the hall has no
> flare at all on the beam or the ends - which is a gross simplification, of
> course.



I don't have exact data but I think you will find that neither the wetted area
or the wave drag will increase nearly that much with added weight. Somewhere I
used to get raw data from Sea Kayaker that told how mauc extra weight it took
to increase the draft 1". Multiplying that 1" (1/12 of a foot) by around 2.1
times the length of the waterline should give a good approximation as to how
much wetted surface to add to the listed wetted surface. My recolection is
that ypically it took about 90 pounds to increase the draft of an average
kayak one inch.
>
> If that is even remotely true, then loading up a kayak should increase the
> importance of length. Let's say that you have enough in the tank to
overcome
> the extra 20% skin drag - but you are going to run out of puff a lot sooner
> with the wake drag kicking in sooner (and being worse) by 50%.



The reality is that most paddlers can not maintain a pace that a longer
waterline kayak will be of any benefit to them because they rarely ever go
fast enough where wave drag is much of an issue. By making the kayak longer
you are adding even more friction to overcome and that increased friction is
causing drag at all speeds. The higher hull speed gained is only enjoyed by
the most powerfull paddlers when they are racing. Adding weight increased the
wetted surface friction so it is even less likely the gear laden paddler will
ever benefit (in speed) from the longer kayak. They might well increase the
gear capacity with less of a penalty that making the kayak wider would entail
though.
>
> So you should be willing to trade more skin drag (lower down in the speed
> range) for less wake drag higher up in the range - the classic argument for
> a longer boat.
>
> Then, if (and only if) you have the horsepower of a Freya, you can really
> motor...




I'm sure Freya is a strong paddler but when you start fighting gravity (hull
speed) you can dump in twice the energy and only gain a small fraction of a
knot in speed. In a trip like Freya's efficiency is what counts and you gain
that by staying under the point where wave drag is a significant factor. When
we were younger and more energetic Cam and I could push our heavily loaded
(original) Mariners (16' 1" waterline by about a 20" waterline beam) at about
4.5 knots for several hours at a time essentially competing against each
other. Back then (early 1980's) I also won several races in that original
Mariner and when I got second or third it was usually because male former
Olympic team member(s) was in the race. I was paddling the empty Mariner at
around 5.5 knots for 5 or 6 miles. I'm sure Freya was in better condition than
I but I doubt she was pushing her (admitedly slightly faster) kayak that fast
for very long.




> Can one generalise on any increase in loading and its effect on the kayak's
> suitability for higher speed work ?
>
> Best Regards
> Paul Hayward, Auckland, New Zealand
***************************************************************************
PaddleWise Paddling Mailing List - Any opinions or suggestions expressed
here are solely those of the writer(s). You must assume the entire
responsibility for reliance upon them. All postings copyright the author.
Submissions:     PaddleWise_at_PaddleWise.net
Subscriptions:   PaddleWise-request_at_PaddleWise.net
Website:         http://www.paddlewise.net/
***************************************************************************