Is is normal for the new Tsunamis to have rough bottom? The rest of the boat is smooth, but the bottom and lower edges (most parts that are underwater) are rough like sandpaper? I would think this would slow me down? My older tsunami 125 is not like this.
That’s weird. I’d call WS to see what they say. I’ve had several of their boats and no rough hulls until I make them that way.
No, it won’t slow you down unless you are an Olympic grade paddler.
It’s to reduce scratches and gouges. Several boats by Confluence have textured hulls.
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@rnsparky said:
It’s to reduce scratches and gouges. Several boats by Confluence have textured hulls.
Interesting. Thanks for the info!
@rnsparky said:
It’s to reduce scratches and gouges. Several boats by Confluence have textured hulls.
Now that’s a good one! I heard they are developing a Yak that put’s out a stream of air bubbles under the hull for an air ride! Solar powered micro-compressor of course.
Here’s what the kayak shop had to say:
a lot of newer models have the textured hull… not just Wilderness Systems. As it was explained to me, the reason is that water has less tendency to stick to textured surfaces than smooth. Putting a texture on the bottom of the hull actually makes for less friction between the kayak and the water as it glides through, in turn making the kayak faster.
This sounds counter-intuitive to me, and I can’t really see this reducing friction, but that’s what they say.
Wow, just found this:
https://www.sciencedaily.com/releases/2014/01/140117153637.htm
I guess they know what they’re doing 
Cool. I’d heard about this. Shark skin and dimples on golf balls etc.
https://www.sciencedirect.com/science/article/pii/S2405451816300484
Smooth causes laminar flow; rough causes turbulent flow. Turbulent increases lift.
This all may be true, but I’d put money on it being primarily to reduce the cost of the mold. It’s much less expensive to produce and maintain rough surfaces than glossy smooth. Hand this factoid to the marketing people and watch them spin…
“It’s a feature, not a bug”.
@E.T. said:
Here’s what the kayak shop had to say:
a lot of newer models have the textured hull… not just Wilderness Systems. As it was explained to me, the reason is that water has less tendency to stick to textured surfaces than smooth. Putting a texture on the bottom of the hull actually makes for less friction between the kayak and the water as it glides through, in turn making the kayak faster.This sounds counter-intuitive to me, and I can’t really see this reducing friction, but that’s what they say.
Your intuition is correct, as I believe this is nonsense.
@Rex said:
Cool. I’d heard about this. Shark skin and dimples on golf balls et.https://www.sciencedirect.com/science/article/pii/S2405451816300484
Shark skin works by having grooves aligned with the flow, combined with a compliant skin. Rough skin kayaks have neither. The Reynolds number (non-dimensional velocity) of the flow is also an issue, and is unlikely to be similar between the two cases. Flow around a shark will also be highly unsteady, so other mechanisms are involved.
Dimples on golf balls work in a very narrow range of Reynolds number. By triggering turbulent flow, the low-pressure wake region behind the spherical ball becomes smaller, reducing drag. Note there are no dimples on other sports balls, since they operate in a different Reynolds number regime and the effect would not be produced. Also, kayaks are not spherical…
@string said:
Smooth causes laminar flow; rough causes turbulent flow. Turbulent increases lift.
Sometimes. Turbulence can increase lift in some situations by allowing flow to stay attached to the lifting surfaces when it would otherwise separate, creating a stall. The effect is produced by bringing high-speed flow in proximity to the surface which delays flow separation. Drag is also increased. Turbulence can reduce lift in many situations, but usually always increases drag (but not in the golf ball described above). In any case, lift is not being produced while paddling a kayak.
@E.T. said:
Wow, just found this:
https://www.sciencedaily.com/releases/2014/01/140117153637.htmI guess they know what they’re doing
This appears to report drag reduction in the specialized case of turbulent flow over a ridged surface made from hydrophobic material. The material traps tiny air bubbles between roughness elements since the material does not like to get wet. As they note: “In theory this means that the surfaces can trap air bubbles, creating a hydrodynamic cushion, but in practice they often lose their air cushions in chaotic flows”.
It might work in a some controlled situations, and the mention of modified turbulent structure is very interesting. I think it’s doubtful it could be extended to flow over a plastic kayak out in the world but, never say never I guess.
Think of duck feathers and the fur on seals and otters.
When I think of flow rates, they would seem far faster than those generated by a kayak.
@greyheron said:
Think of duck feathers and the fur on seals and otters.
Those creatures exhibit incredibly interesting flow phenomena which can have trapped air layers, fur/feathers with elasticity can bend in response to pressure waves, the bodies twist and deform causing unsteady flow, vortex generation, biological oil secretion, etc. The down on owl wings has been shown to reduce noise, tubercles on whale fins can increase maneuverability, and so on. Much to study from the natural world.
On the other hand, a rough kayak hull is not so interesting, it’s just rough. In fact, if the kayak is going slow enough, a roughened hull may even be considered hydro-dynamically smooth, meaning it will have the same drag as a smooth-skinned hull. I can’t remember the calculation off-hand, I’ll have to look it up and see how a rough kayak figures in.
@string said:
When I think of flow rates, they would seem far faster than those generated by a kayak.
Very true, and also significant.
Think ……. “Think” , Epic and Stellar…………when they put textured hull surfaces I’ll believe it makes it faster.
@Overstreet I somewhat recall that Greg Barton experimented with a texture or micro grooves in his racing days.
Found it in the FAQ on the Epic site: https://www.epickayaks.com/faq Go to the “Should I Wax my Kayak” section.