Trent hink wrote: ↑Sun Feb 07, 2021 11:35 pm
Hi Matteo.
I still vigorously disagree with your idea that volume makes no difference in a kite board for surfing waves.
It's in the physics of it. When kitesurfing, volume does nothing to increase the performance of the board because:
1. Volume produces no buoyant force unless the board is submerged.
2. In order to submerge the board, it needs to be moving at less than 3 knots waterspeed.
3. And then to utilize the last 5liters of volume, you need the board submerged to where there is water on top of the board.
4. When water is on top of the board, more buoyancy makes the platform less stable (part of the "corky feeling" thing).
5. Once you start moving from 1 to 3 knots, planing forces take over and the water "falls off" the top of the board showing that planning forces beginning to take over.
At number 5, think about how the board would work if you cut the deck off, and scraped all the foam out, leaving just about a half to a quarter of the rail height. At 3 knots of speed while kiting, the water in the space where the foam was would fall out the back. Could you prone surf it? NO! but you could surf it if you were towed up onto the wave. Thus the volume in a prone surfboard is ONLY there for its necessity when prone paddling onto a wave.
At the end of all of this is the reality that 51% of a shapers job is to find someplace to put that "volume" somewhere in the board where it does not hinder performance too much. For a good feel of the fins, the tail must be thin. Rails need to be thin also. And while the area under the front foot is not the best location for that extra volume, a prone surfer needs it there when paddling to keep thier body higher out of the water for higher paddling speed. But some volume needs to be spread out toward the rails so the front foot is not too far away from the planing surface. It is seriously the majority of a shapers job to deal with, and is the part that all "DIY" board builders mess up on with thier first ten boards (prone surfing).
But you dont even need the above example, since this is exactly how a TT can work with no volume.
So about every 6 months or so on this forum, some kiters think they are arguing with me, when they are actually arguing with physics. Honestly this would be much more fun if I could make a few quid per 100 words here.
Trent hink wrote: ↑Sun Feb 07, 2021 11:35 pm
Probably we just are disagreeing on what it means for a board to have volume.
Ummmm??? Volume is the ammount of 3 dimensional space contained inside of a shape. This results in water being excluded from that space when submerged. It is impossible to confuse this basic reality of physics.
Trent hink wrote: ↑Sun Feb 07, 2021 11:35 pm
Liquid force's example (kitefish) is cheaply made and ridiculously heavy, perhaps you just see it as low-volume because it is such a tank? For sure I agree there is no chance of that one feeling too "corky!"
The LF "Kitefish" is 1" thick. It is heavy, no question, due to the impervious (to water) and extremely dense which results in an unbreakable platform. I've built similar shapes in much lighter weight construction, and those boards had no "corky" feeling. "Cork" comes mostly from volume, though it can be mitigated somewhat with weight.
Trent hink wrote: ↑Sun Feb 07, 2021 11:35 pm
The lis fish is a fine design, but I do not care for the twin fin set-up, which seems to be more common and fits in with the original design. Quad fin versions of that design work better for kiting.
The "stock" fin setup was a thruster. I did extensive back to back personal testing with 2 to 3 Kitefish boards on the beach with different fin configurations and unmodified and modified fins.
To my surprise, stock thruster gave the best upwind performance. But its performance in head high waves was unimpressive. A larger center fin only provides marginal increases in upwind performance, at the expense of feeling like there is more drag on the board.
Twin fin in various sizes winds up too loose for my liking.
Quad fins, in the locations I have settled on, allow a good compromise of upwind, feedback from loading, and handle up to double overhead with only a bit of stance modification.
5 fins was a joke all the way down to where I made it work with a 1" TT fin in the center position.
Trent hink wrote: ↑Sun Feb 07, 2021 11:35 pm
More volume will be much more forgiving of sketchy foot switches, and will work much better for milking small or blown-out waves.
If you ever switch your feet while stopped, you use the kite to lift you anyway. Remember, the ammount of water you need to displace with the volume of the board to float you without sinking is equal to your mass in kilograms, in liters. Anything less, and you will slowly sink while stopped. If the ammount of volume in the board is around a third of your mass, then you sink really fast. And a no volume TT board will provide nearly the same resistance to sinking as a 25l surfboard over a typical short interval. Thus volume is not the primary factor.
Trent hink wrote: ↑Sun Feb 07, 2021 11:35 pm
Depending on local conditions, there's usually nothing wrong with using a higher volume board, particularly if you endeavor to actually ride waves, rather than simply riding through waves.
Yes, that is what the debate is about - how much un-needed volume and hence distance from your front foot to the planning surface, hinders the ultimate performance. Some say it is negligible to increase from 2.5cm to 5cm. Some actually like the feeling that "corky feeling" handicap provides. But there is demonstrably no increase in perfomance when increasing the front foots distance from the planinning surface. Doing so always results in less control over that surface.
Trent hink wrote: ↑Sun Feb 07, 2021 11:35 pm
Depending on local conditions, there's usually nothing wrong with using a higher volume board,
particularly if you endeavor to actually ride waves, rather than simply riding through waves.
This is true if you are looking to simulate the moves and feeling in prone surfing while surfing with a kite. But if you want to have a wider performance envelope, having less volume, and hence your front foot closer to the planning surface, you can do more than you ever could do prone surfing.
Trent hink wrote: ↑Sun Feb 07, 2021 11:35 pm
And for a beginner, especially strapless, a board with some width and volume will help you progress much faster.
The short and simple argument against this is "would you start off a beginner in a high volume TT?" NO! And this is not only due to volume not being beneficial, its actually detrimental.
However I do agree that width does help within some proportional limits relating to weight and conditions.
Trent hink wrote: ↑Sun Feb 07, 2021 11:35 pm
If it starts feeling too big, its easy to compensate by rigging a kite that is a couple meters smaller than whatever the other guys your weight are using.
This is a good idea to reduce the potential of the kite to overpower a "corky" high volume board. But if you have the same shape with lower volume, you can get more control over the planning surface by having your front foot closer to that planning surface. This allows you to use either the smaller or regular sized kite.
Trent hink wrote: ↑Sun Feb 07, 2021 11:35 pm
Keep in mind I am talking about waves that are less than shoulder high. You'd have to be a damn fool to take one of these low-rocker designs out in anything more and expect to have any fun.
I agree if you are talking about a board like this with over 5cm (2inches) of thickness. But at 2.5cm or 1 inch thick, you have a performance envelope that includes overhead and a half waves, or more with more rider weight, skill, and straps.