Author Topic: Double concave vs flat  (Read 4521 times)

coldsup

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Double concave vs flat
« on: February 15, 2019, 02:46:30 AM »
What do you reckon the benefits are to having a longboard SUP with a double concave hull are compared to a flat hull or one with slight V.

Bean

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Re: Double concave vs flat
« Reply #1 on: February 15, 2019, 04:03:54 AM »
In the tail, a slight concave will give it a little lift and depending on the rails, a little better hold on the wave face.  Flat is generally faster but you sacrifice some hold, a slight v will make the board more maneuverable at the cost of speed and hold. 

Some might say a slight concave is faster, but only if it allows you to use a smaller fin.

Dwight (DW)

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Re: Double concave vs flat
« Reply #2 on: February 15, 2019, 04:58:11 AM »
Flat adds a bit of a skatey slippery non direction feel. It can a help a big pig like SUP feel a little more alive.

coldsup

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Re: Double concave vs flat
« Reply #3 on: February 15, 2019, 05:11:07 AM »
Take the Infinity New Deal for example....mono concave to a double concave and vee in the tail.   I get why you put mono in the nose and vee in the tail, but why choose double concave in the main section of the board? Better lift and speed?

Bean

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Re: Double concave vs flat
« Reply #4 on: February 15, 2019, 05:42:36 AM »
That's a great example coldsup, Dave B puts a lot of thought into his shapes.  And this is a complex shape to be sure.  I have not had the pleasure of riding the ND yet, but I think you are right.  As a performance longboard, the focus is on speed an maneuverability, so it's important for the water to release at the tail.  In this case there is a pretty significant kick at the tail, and I think the double concave might serve to direct the water flow.

As Dave has demonstrated in his videos, the ND also rides well off the nose.



anonsurfer

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Re: Double concave vs flat
« Reply #5 on: February 15, 2019, 07:13:48 AM »
What do you reckon the benefits are to having a longboard SUP with a double concave hull are compared to a flat hull or one with slight V.

The double increases lift and loosens up the board.    While flat bottom is theoretically faster I find that a single/double is actually faster and handles better on the types of waves I surf. 

I design most of my boards with a single (0.15" - 0.30" deep) to double with the double starting anywhere from 24"-42" from the tail and with maximum depth occurring between the fins.   The wider the board the more subtle you should make the concaves as you don't want too much lift.     

Vee helps with maneuverability but will slow you down.  It is useful if you surf waves with lots of power.  Not so good if you surf slow waves and need to generate speed.   When I do put vee in my boards it is typically only in the last 12" of the tail (usually 0.07" - .20" max vee) and/or in the first 12"-18" of the nose (usually 0.1" max vee).  Subtle rolled vee in the nose helps smooth out water surface bumps.
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coldsup

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Re: Double concave vs flat
« Reply #6 on: February 15, 2019, 07:55:53 AM »
Had double concaves on my Nalu 11,4 ..very subtle but whatever it did it felt good down the line.

supsurf-tw

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Re: Double concave vs flat
« Reply #7 on: February 23, 2019, 08:03:56 AM »
Concave is used to straighten out water flow and allows the board to go on the rail easier when used in the middle. Too much and the board sticks. Double concave helps this when used on wider boards.
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burchas

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Re: Double concave vs flat
« Reply #8 on: February 23, 2019, 07:53:01 PM »
By adding a concave to the bottom you're adding a form of drag (as I
understand it) which sits well with the notion of hold and control.

At what point and under which circumstances do you see that translates
to lift and when too much of a concave just sticks and nothing more?
in progress...

Dwight (DW)

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Re: Double concave vs flat
« Reply #9 on: February 24, 2019, 04:09:15 AM »
By adding a concave to the bottom you're adding a form of drag (as I
understand it) which sits well with the notion of hold and control.

At what point and under which circumstances do you see that translates
to lift and when too much of a concave just sticks and nothing more?

I see you guys are getting a bit confused.

Concave promotes early planing. Once planing, a board is faster, so concaves are faster in that they help you plane. Before planing speed is reached, they are not faster. Displacement bottoms are faster.

Deeper concaves tend to reduce ultimate top speed. More surface area. So in racing windsurf boards, the shallowest concaves possible are used, going to flat usually.

There are other factors, but this is the basics.

coldsup

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Re: Double concave vs flat
« Reply #10 on: February 24, 2019, 04:19:39 AM »
By adding a concave to the bottom you're adding a form of drag (as I
understand it) which sits well with the notion of hold and control.

At what point and under which circumstances do you see that translates
to lift and when too much of a concave just sticks and nothing more?

I see you guys are getting a bit confused.

Concave promotes early planing. Once planing, a board is faster, so concaves are faster in that they help you plane. Before planing speed is reached, they are not faster. Displacement bottoms are faster.

Deeper concaves tend to reduce ultimate top speed. More surface area. So in racing windsurf boards, the shallowest concaves possible are used, going to flat usually.

There are other factors, but this is the basics.


Aids acceleration in other words....

burchas

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Re: Double concave vs flat
« Reply #11 on: February 24, 2019, 06:06:43 AM »
Concave promotes early planing... Deeper concaves tend to reduce ultimate top speed. More surface area...

Thanks for the clarifying. That was the general picture I had in mind.
Slight single concave running front throughout the entry rocker.

As I understand it, The concave in that section is specifically
for using the speed of the wave to overcome the drag created
by the concave and break early hence early planing?

I'm referring only to that section and that kind of open
concave to keep it simple.
in progress...

 


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