I know with most boats, the smoother the surface the less friction as you pass through the water. With plastic specifically scratches along the hull can impact speed, but how much does the surface texture itself affect speed?
I ask because i was looking at a P&H scorpio this weekend, and when i touched the plastic it wasn’t the smooth surface most plastic boats seem to be. It seemed almost textured on purpose. Does anyone know the reason for this? and does it cause any extra friction? or is it soo little extra friction that i you would never know the difference?
rough skin
Yeah, I’ve noticed that too on certain plastic boats. It’s probably not enough to notice.
Shark skin supposedly feels like sandpaper and golf balls have those dimples that create mini vortices and affect the slipstream for more efficiency. I forget what that’s called. I also wonder if rough skinned kayaks are designed as such.
nothin to
Nothing to be concerned about. Part of the molding process. You won’t notice any effect on the speed of the craft.
Properties of Corelite?
Is it just a property of P&H’s corelite, or do other manufacturers have this happen to?
My observation…
– Last Updated: Apr-28-10 2:37 PM EST –
I have spent a bit of time in a P&H Scorpio LV and I own an Avocet RM.
Both P&H and Valley use a tri-laminate plastic in their current lines of roto-mold boats. From what I see on the market they are the only sea kayak manufacturers using said stiffer tri-laminated plastic, and as it happens both boat lines (in plastic) exhibit a 'pebbled' finish.
All I can definitely tell you is that this plastic is one tough son-of-a-gun.
Minimal effect
Depending on the dimension and spacing of the ‘pebbles’ in the finish, the effect on the boundary layer will vary. If they’re very small and randomly distributed, the effect is most likely very small. My feeling is that it would mainly result in a slightly earlier transition to turbulence in the boundary layer, along with an overall (tiny) increase in skin friction in the forward portion of the boundary layer.
The dimples on golf balls are finely tuned (in size and spacing) to the size of the ball and the typical launch velocity. Their benefit is reduced if the ball goes slower or faster than normal. In fact, there are alternate dimple patterns for golf balls that result in much longer flights, but as they are not approved for tournament play, they aren’t manufactured or sold.
As far as I know, riblets or grooves in shark skin have not been conclusively shown to reliably reduce drag. To work as theorized, the grooves must be aligned with the flow, which is not generally the case. The effect may be a result of the compliance of the skin as much as the riblets. The reduction in drag in ribbed competitive swimsuits has not been conclusively linked to the ribs either, and may be an effect of the compression of the swimmer’s body. I’m a little out of date with the literature, though, so I may be mistaken.
Texture
Hi All–
The texture does a couple of things. Most of all it makes helps us to keep the boats consistent as we pull them out of the molds. Part of it is cosmetic. And textured decks help to cut glare a bit. Texturing also tends to hide scratches.
On the performance side, it really doesn’t matter. At the highest level of racing performance a top athlete might have a few tenths of a second taken off their sprint times by a scratched up hull. But in the real world it just isn’t a factor. I have paddled the Scorpios a lot and they are fast, fast, fast.
Hope this helps,
Brian Day
P&H Guy
Rough Stuff
– Last Updated: Apr-28-10 3:46 PM EST –
Just to expand on what Brian is saying (I think)... a kayak is a relatively big and slow moving object. The overall shape of the kayak (width, length, rocker, etc.) will have FAR more impact on speed than will texture.
I've actually owned a plastic 'textured' boat and a friend had the same boat in Carbon/Kevlar. I paddled both boats extensively and there was really no noticable difference between the two on the water.
by design
– Last Updated: Apr-28-10 6:24 PM EST –
As others have noted, this occurs by design... and no, it's not just a corelite thing... I have seen other manufacturers use the same textured finish with more conventional plastic boats.
Molding something as big as a touring kayak out of plastic is a rather precarious undertaking... all kinds of things can and do go wrong. Often, the 'problems' are merely cosmetic and I think these textured finishes help hide cosmetic issues with RM boats that would be more apparent with a glossy smooth hull surface.