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Next board, chop eating 6.0 to 8.0 machine
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jingebritsen



Joined: 21 Aug 2002
Posts: 3308

PostPosted: Fri Aug 30, 2019 4:41 pm    Post subject: Reply with quote

dlee, not always. lots of exocets plane early and ride smooth. lots of race boards across an array of brands do the same
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dllee



Joined: 03 Jul 2009
Posts: 4588
Location: East Bay

PostPosted: Fri Aug 30, 2019 4:47 pm    Post subject: Reply with quote

Physics.
Some say that about the Hypersonic too.
The right blend is key.
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cgoudie1



Joined: 10 Apr 2006
Posts: 2259
Location: Killer Sturgeon Cove

PostPosted: Fri Aug 30, 2019 8:15 pm    Post subject: Reply with quote

So I'm thinking about the "physics" of this, and a double concave through the planning surface would have more surface area than a flat (or even a V of the same depth). That leads my physical mind to believe that caves plane earlier, not later, and more cave, ergo more surface, like a hypersonic
would be even planier. Just looking at the phiysics ;*)

-Craig

dllee wrote:
Physics.
Some say that about the Hypersonic too.
The right blend is key.
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dllee



Joined: 03 Jul 2009
Posts: 4588
Location: East Bay

PostPosted: Fri Aug 30, 2019 8:56 pm    Post subject: Reply with quote

But when you actually ride a Hypersonic, that theory is just that.theory.
That set needed one meter bigger sails to plane, and gave good smooth ride.
Good smooth ride is absorbing power.
Good board for beginning shortboarders who want a smooth ride and don't mind using bigger sails.
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boardsurfr



Joined: 23 Aug 2001
Posts: 1210

PostPosted: Sat Aug 31, 2019 9:19 am    Post subject: Reply with quote

cgoudie1 wrote:
So I'm thinking about the "physics" of this, and a double concave through the planning surface would have more surface area than a flat (or even a V of the same depth). That leads my physical mind to believe that caves plane earlier, not later, and more cave, ergo more surface, like a hypersonic
would be even planier. Just looking at the phiysics ;*)


Take a closer look. A larger planing surface will only lead to earlier planing if you keep everything else constant. If you change the form, that's not the case anymore. Otherwise, we could windsurf on hull shaped like catamaran hulls.

The lift force generated by the hull basically comes from pushing water down. Action = reaction, so the hull gets pushed up. In first approximation, water will be pushed in a direction perpendicular to the hull. If you change from flat to V or double concave, some of the push will go sideways rather than up, thus reducing the lift. You can approximate the lift generated by looking at just a two-dimensional projection of the surface onto a plane perpendicular to the water. You'll end up with the same area regardless of whether you got a V, double concave, or flat bottom. Any kind of V or concave shape will increase the area in contact with water, though, and therefore increase drag. That's made up for by increased control.

This is just a simplified discussion. In reality, some of the water displacement is downward, some to the side. For wider hulls, a larger part of the displacement is downward, so a wider hull will plane earlier than a narrower hull, provided there is enough force (wind) to overcome the increased resistance drag. Jim Drake gave two different formulas for narrow and wide boards.
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dhmark



Joined: 04 Sep 2007
Posts: 301

PostPosted: Sat Aug 31, 2019 10:03 am    Post subject: Reply with quote

Early planing is not particularly high priority for me (OP). I use the Fanatic Cross currently with 6.0-8.0, but I can tell it is a bit small for optimum use of the 8.0. The 8.0 is very compact though, rigs on 460 mast and 208 boom. As I said, current board works wonderfully on 6.0, lively feel and smooth, and I wonder how much of that I would lose by going to a wider board. I am intrigued by the 120 Fox with its deep concave and reputation for smoothing chop, but it is really wide at 70 cm. Anybody with personal experience with this board? My only experience with a slightly wider 115 L board is Naish Starship, which was nice but not very exciting ride.
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cgoudie1



Joined: 10 Apr 2006
Posts: 2259
Location: Killer Sturgeon Cove

PostPosted: Sat Aug 31, 2019 10:17 am    Post subject: Reply with quote

I agree that the drag is increased due to more area also, and that would
be the case with any hull shape that, as you say, had more surface
area, flat or caved, so you can factor that out (just have a look ;*) ).
I also agree that the entire planform needs to be analyzed because as you
suggest not all of the planing portion of the surface area is fully efficient
for planning. Some of it's planning force is undoubtedly lost (actually worse than lost) when not providing a vector to push the hull up. But if you're suggesting a flat bottom is the ultimate for planning, I'm not sure I agree.
And of course, the planform can't be tuned just to get over its bow wake, or
you would see boards that looked like a door (most early planning boards are a little like a door in outline)

-Craig

p.s. I've ridden Hypersonics, and I agree with Dlee, too much cave, so you can go too far.

p.p.s. caves are better chop eaters in my experience.

boardsurfr wrote:
cgoudie1 wrote:
So I'm thinking about the "physics" of this, and a double concave through the planning surface would have more surface area than a flat (or even a V of the same depth). That leads my physical mind to believe that caves plane earlier, not later, and more cave, ergo more surface, like a hypersonic
would be even planier. Just looking at the phiysics ;*)


Take a closer look. A larger planing surface will only lead to earlier planing if you keep everything else constant. If you change the form, that's not the case anymore. Otherwise, we could windsurf on hull shaped like catamaran hulls.

The lift force generated by the hull basically comes from pushing water down. Action = reaction, so the hull gets pushed up. In first approximation, water will be pushed in a direction perpendicular to the hull. If you change from flat to V or double concave, some of the push will go sideways rather than up, thus reducing the lift. You can approximate the lift generated by looking at just a two-dimensional projection of the surface onto a plane perpendicular to the water. You'll end up with the same area regardless of whether you got a V, double concave, or flat bottom. Any kind of V or concave shape will increase the area in contact with water, though, and therefore increase drag. That's made up for by increased control.

This is just a simplified discussion. In reality, some of the water displacement is downward, some to the side. For wider hulls, a larger part of the displacement is downward, so a wider hull will plane earlier than a narrower hull, provided there is enough force (wind) to overcome the increased resistance drag. Jim Drake gave two different formulas for narrow and wide boards.
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coachg



Joined: 10 Sep 2000
Posts: 2769

PostPosted: Sat Aug 31, 2019 10:24 am    Post subject: Reply with quote

I'll throw my $0.02 into the debate here because in addition to hull shape I find that construction materials also play a big factor in how a board rides. I find wood boards are much more forgiving in chop than carbon boards at the trade off of early planing. Ride a wood board & identical carbon equivalent & you will feel the difference as well.

Dlee is absolutely correct in that you will sacrifice some early planing for a smoother ride; there is no getting around that. The question is, how much early planing it sacrifices. That being said I have ridden the Cross & it is no dog. I think the Cross planes plenty early enough for a smooth riding board.

Coachg
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dllee



Joined: 03 Jul 2009
Posts: 4588
Location: East Bay

PostPosted: Sat Aug 31, 2019 10:52 am    Post subject: Reply with quote

Basically looking for a big FSW board, take a straighr edge and measure V across, length of flat, thickness of rail, width od WP vs width at 12" up from tail, thickness of tail vs thickness of middle and nose...and compare with other boards.
Unless you want to depend on opinions of others who probably haven't tried most of the boards you're considering.
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dhmark



Joined: 04 Sep 2007
Posts: 301

PostPosted: Wed Oct 23, 2019 8:41 am    Post subject: Reply with quote

To follow up, I found a used Severne Fox 120 and decided to go for it. The Fox is a somewhat wide (70 cm) board with an odd set of characteristics, extreme V from bow to aft and tail cut-outs. So far I have only used it in overpowered 6.0 conditions. It is indeed a chop-eating machine that really smoothes out severe chop. For my particular conditions, it was perhaps wishful thinking for a board to handle 6.0 to 8.0, because a board that can handle an 8.0 catches a lot of air in high wind simply due to the width, so it was flying more than I am used to. I wish I could use my 95L FSW in those conditions, but it is a 200 yd schlog to a wind line with shifty 0-15 kt winds when it is blowing 20-25 everywhere else. For slightly less wind to light wind I think it will be perfect.
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