plastic kayaks get slower in time due to hull scrapes.
but such a miniscule amount it’s not even worth worrying about.
The real truth
Plastic kayaks get slower as their owners get fatter and older.
Fat Elmo's canoo gets faster as he loses mo' haar fro' his noggin'...
Plastic kayaks get slower
as the account holding bucks for a glass 'yak increases.
Application of 303
will certainly make up for any scratches or additional , er, phat. This stuff works so well that one must be careful loading on rack lest it zoom off the opposite end. Swooosh!!
In any practical terms scratches are completely insignificant. In fact, it may work the other way. Irregular surfaces can produce cavitation, which would produce less friction.
The effect must be small. I did think
that shaving and resurfacing two fuzzy composite WW kayaks improved their speed, but it’s hard to get objective data for a small effect.
Some of the data on non-smooth surfaces and boundary layer effects comes from studies of nuclear submarines and other craft moving at much higher speeds than canoes and kayaks go.
more scratches…more wetted surface… more friction.
I agree with Celia (nmsg)
so that would apply to composites too
then by your reasoning Steve.
but i’ve never heard anyone mention this about composite boats, only plastic.
Composite boats too
Composite boats are also affected which is why sprint paddlers use boat covers and are very careful when placing their kayaks on the ground. The fact that the kayaks are less than half the weight of a seakayak does make this easier.
It’s the truth
After a plastic hull has been dragged a lot and develops lots of fuzzys,hairys and rough edges it has to effect the glide somewhat.
Any severe oilcanning that refuses to pop back to the original shape must make a difference too.
friction is friction
glass, kevlar, roto, wood…it don’t matter. rough creates friction.
glass is harder to scratch and when it does it is miniscule(sp?)
don’t worry…go paddlin’!
303 and the Zoom effect
First hand…303’d America on the J racks and what seemed like tight and snug all of a sudden found a boat two seconds from exiting stage left off the ranger. After that; I began using a strap to the front bumper and …laying off the 303.
Apparently affects aircraft as well
That is why aluminum-skinned planes have flush rivits instead of domed ones. All of the little irregularities do add up.
Fact … a 40 micron 'high spot’
will effect the laminar flow on a 40 foot yacht.
If memory is correct … 40 micrion = 400 grit.
True for 3 reasons.
First, flexing from paddling makes it lose
rigidity, loosing transfer of energy.
Second, the hull deforms making it less
Third, the scratches begin to multiply giving
the hull bottom the resistance of a
Scratches increase drag - significantly
If this was put to a vote my statement would lose, but I will state it anyways: Scratches, that are deep enough, significantly increase drag in any body that moves through a fuid.
Most scratches that occur from a rock meeting a plastic kayak are deep enough. Even worse are any plastic proturbances that stick up from the surface of the kayak. Those are instant turblators.
Its complicated but a scratch that is deep enough will cause laminar flow to transition to turbulent flow. Drag from turbulent flow is at least double that of laminar flow. This transition to turbulent flow starts as wide as the scratch and spreads wider as the fluid moves further along the body. Therefore a scratch that runs perpendicular to flow will create significantly more drag by causing the turbeulent flow to start wide and grow wider along the length of the body. Also a scratch in the forward third of a body will have a larger impact because most flow will transition from laminar to turbulent on its own usually somewhere in the forward half of a hull.
The worse thing you can do is drag the forward part of your kayak sideways across a rock. The scrath it creates will pretty much eliminate any chance of maintaining laminar flow for any distance along your kayak.
Now it may be that a new plastic kayak already has some roughness or texture that does not allow any laminar flow even when new. If I were ever to buy a plastic kayak, I would look for one with the smoothest possible surface. The closer to a composite boats smoothness the better.
Due to various differences between the viscosity, density and velocities associated with water and air, a sea kayak’s fluid dynamics are actually a very close to sub-sonic jets. It seems hard to believe, but its a fact. Now think about how much effort airliners go to maintain a smooth surface. Also think about how easy it is for a jet to fall out of the sky if there is a little build up of ice on the leading edge of wings. That ice causes the laminar flow to turn turbulent and airflow become unattached from the wing losing lift.
If you want to read more about fluid dynamics and how it applies to kayaks, I suggest the following book:
The Symmetry of Sailing - The Physics of sailing for Yachtsmen by Ross Garrett, ISBN 0-229-11759-7
While this is mostly about sailboats, the sections on downwind sailing are 100% relevant to sea kayaks. Much of the examples are of boats and keel moving through water at 4 knots. The beginning half of the book explains the hydrodynamics of boats in language any high school level reader should understand. Then the second half repeats the info with heavy formulas and more college grad school level of detail. There is also some great information on waves and how boats react in waves.
Well I’m glad
that I’m such a powerful highly skilled paddler that the scratches on my hull don’t slow me down at all.