Double concave question

[iggy]

For Mr Neville or anybody who can drop a cent here.
Threads have been posted about adding a 5th fin of a potato hence flattening the spine towards the back fins. What would be the actual outcome of flattening the spine from the end of the front fins to the end of the board?

[Slowman]

Do you mean the flattening as a result of sticking the fin box in there?

[prjwebb]

It'd make it harder to roll rail to rail off the tail I'd have thought. might become a bit slidey if it was flat without a centre fin too. That's a wide tail.

[iggy]

Do you mean the flattening as a result of sticking the fin box in there?
pretty much!

[iggy]

What about on a non that wide tail?

[prjwebb]

bottom contours certainly aren't my strong point and it definitely depends on the rocker and outline of the board, but I'd of thought a flat bottom would possibly increase speed and release

[prjwebb]

this might be helpful
http://www.naturalcurvesboards.com/html/designhtml/bottoms.html

but doesn't really explain anything about a flat bottom off the tail. seems to be something not many do. i think greg griffen is a big believer in flat bottom boards.

[iggy]

Pretty instructive nonetheless.Tanks prj

[Slowman]

As I understand it concaves work like this; a single will channel water down the board into a narrowing funnel thus creating a faster water flow using the Venturi effect. A single to double and a full double do the same thing but also create a faster flow of water over the ridge between the double concaves as well when you are turning helping accelerate out of turns. By flattening it a little it might reduce this effect somewhat but then you still have the double concaves and if they are deep enough it would be minimal I would have thought. Though as already suggested without that defined ridge it might be harder to get it over on the rail if you didn't have a fin in there but then again in little waves maybe it isn't that critical.

[Chris]

yeah one other note is that concaves, both single and double can actually increase the rail rocker when compared to the centerline rocker. Essentially, if you have a dramatic bottom contour, more than likely, you will also get a a bit more rail rocker. when applied to hybrids, this is a great way to elevate performance while keeping the board user friendly.