HULL HYDRODYNAMICS 101, DISCUSSION

Casey Patelski · Post by **Casey Patelski** » Sat Apr 05, 2008 5:10 pm

Look at all the photos we have in our albums. Study how the water is flowing around and out from under the board (hull). I noticed a lot of pushing water out the front of the boards on some photos. That suggests to me that the the water flow is slowing down the board speed as the water should be moving under and out the back of the board. Or it could be simply the board just hit a chop. But if the wave is clean faced, and the board is pushing water out the front, this board hull is slow or the surfer is in the wrong weighted position. Logic.

So Hydordynamics says, channel or direct that water with the least drag is the fastest design. My opinion the fastest design may be, 1. Nose Vee (to break the surface tension), to Single Concave (to move thru the chop and direct the water to the tail), out to Spiral Vee tail (to allow turning rail to rail) would be the least drag on the hull, resulting in the fastest planeing hull design. 2. Followed by a double concave (either side of the stringer), 3. followed by rocker only/flat bottom as the water pusher king. Granted if your rocker is whacked out (too much or wrong line for weight center), your going to push water no matter what hull design you try. What are your thoughts? Challenge your Kneelo brains and board experience and reply. Always looking for speed- Casey.

Mike Fernandez · Post by **Mike Fernandez** » Sat Apr 05, 2008 5:41 pm

There are so many variables while your surfing a wave, so many things change quickly that a picture might not capture what really happened on most of the wave, slowing down moment, stalls... I think the steeper the wave your in, the less water pushing your going to do just because your going so fast.
Even powerboats with vee hulls push water, unless they are going really fast. Ever notice how a flat bass boat plows water until you gas it, then it pops a wheelie, then the nose comes down slowly and gently, and it planes.
I would say a full concave like Badens boards would reduce it , vee helps, and the more rocker you have, the more water your pushing at slow speeds. You trade plowing water on slow waves for the ability to surf steep fast waves with some rocker.
Just my thoughts, I am no shaper.

Headwax. · Post by **Headwax.** » Sat Apr 05, 2008 9:36 pm

I once got pissed and sent Parksey a boring three page email on my thoughts on getting a board to go fast.

He wrote back and stated simply that though I might be right (note italics) , the fastest surfer in the water was the surfer with the most control.

My boards are 14 mill through concave (shallower for the feed in and feed out.)

They go good. Mainly cause they are flat through the stringer.

I've seen faster boards though. They had minimal tail lift. Tail lift gives negative pressure which slows you down as much (or more) as the positive pressure on the hull. Last I heard that chap was making big concave boards.

Of course when you put them on the rail you have a different story.

Nice to see you starting a design thread.

see here for another similar thread.

viewtopic.php?t=2731&highlight=

Good luck

http://users.tpg.com.au/users/mpaine/th ... l#nosedive

Search for mtbarrels. he has roteth a thesis on it somewhere on the WEB

Pity Rob isn't here he could tell you.

frankfqr · Post by **frankfqr** » Sat Apr 05, 2008 10:24 pm

True hull utilization and reference are items that are not touched on at all in these forums.

How the water is channelled an directed thru the tail is not a discussion regarding hull in my minds eye. I see it as a leading bottom curve or contour directing water flow over a soft round rail creating lift and hold. Something totally different from the majority of shapers and riders mindset. Skip Frye and Steve Lis still embrace this basic concept, nearly all others incorporate a chine to some extent. As I ride a soft rail I can weight and unweight the forward rail to allow it to engage or not. Just part of my kneeriding arsenal. With chines and harder rails I feel a need to pump it or work to maintain the high line

As GG declared,"Neutral Handling", the board naturally seeks the sweet line, maximum speed line. Parksey has it right, "surfer with most control."

Headwax. · Post by **Headwax.** » Sat Apr 05, 2008 10:56 pm

Hi Franq

Nice to see you coming from the other direction. How are those flex board's cruising?

I like this quote :"There are two main types of boats: displacement and planing vessels. The hull of a displacement vessel reaches well below the water’s surface, and slices through the water as the vessel travels. The hull of a planing vessel, however, generally reaches a relatively short distance below the surface. As a planing vessel travels, it dynamically lifts, and essentially skims the surface of the water as it moves. This skimming effect is a result of lift, which is generated as the vessel’s speed increases. Planing craft, in other words, rely more on dynamic lift than buoyancy to achieve the required sinkage and trim when in motion.

A surfboard is essentially a planing object. When surfing, it has a shallow reach below the water’s surface and relies only minimally on buoyancy—just enough to float when at rest. Likewise, a surfboard calls on the force of lift to shuttle a surfer along a wave’s surface.

By looking at surfboards as planing craft, the two students were able to focus their study on the effects of lift and drag, just as planing hull designers do."

Nice and simple stuff. Like me.

I like how vee in one position drags and in the other position planes.

frankfqr · Post by **frankfqr** » Sat Apr 05, 2008 11:43 pm

Good to see you back in form as well Mr. Wax. Flexy project on hold for now, life got in the way. My creation took venturi to the extreme, VERY FAST!!!! To a fault, it feels as if floating on a 2ft. platform of air. Fins need major tweaking, so does my life

When fully engaged the flex creates smooth strong hold. I picked up another quad fish and am tapping it's intricate details for further development of my own------On Topic---If taking Casey's inquiry at face value then hull is viewed as all encompasing, as you post and Mike points to,"so many variables" V's and concaves lifting rails and straightening rockers. Where to start? I still look at hull's from a Velo point of view, and as skasand recently posted a pic of. Then we'll be talking hull.

KneeBumps · Post by **KneeBumps** » Sun Apr 06, 2008 8:33 am

At the risk of taking this too far off thread....

If you have been following racing yacht design the past few years, they have made some incredible leaps in downwind planing speed on open ocean maxis and supermaxis. Round the world supermaxi hull racing designers made a quantum leap a few cycles back and realized that the fastest boats would be designed not just to sail, but to surf the huge waves generated in the Southern Ocean, while maintaining control at high speeds downwind (they often exceed the wind speed of 40+ knots when surfing down a big wave). They basically designed huge surfboards (derogatorily called sleds by sailboat designers, especially the multihull gurus) with retractable canard keels on each side (fins) to hold while they are out on a rail. Very cool stuff. As I heard one of the helmsmen explain in a show on the race, they use the sail to get the boat to the top of a wave, then surf it at max speed, then sail to the top of the next wave, etc. The crews that first tested these designs in the Volvo Round the World were essentially scared sh**tless at the speed they reached surfing these big boats on 40' open ocean waves.

I suspect there is a lot to learn from their designs, just have to tease out the relevant points to increase planing speed in monohulls (what we ride). While the "drive" comes from the sail, they still have to behave like surfboards for significant periods of time. I suspect that they learned a good bit from surfboard shapers as they progressed toward the design.

If you are interested, there are many threads to read on the subject in the Boatdesign and other hull design forums online.
A good place to jump in would be

http://boatdesign.net/forums/showthread.php?t=20038

KenM · Post by **KenM** » Sun Apr 06, 2008 3:25 pm

Casey, could you define "spiral vee"? Thanks.
-------------------
stupidme

red · Post by **red** » Sun Apr 06, 2008 4:34 pm

Casey,
A well known sheper sold me an over-rockered, over veed hull that I'm embarrassed to even try to sell 2nd hand - it's that slow and difficult to paddle! Every takeoff is a free fall.

Working within the parameters of the question you phrased, I'm finding that the flatter I make my bottom contrours (not rocker) the faster with control my boards go. This is giving me boards tha surf equally well in 2' and 8' - something a little challenging in the concave bottom paradigm (but I could be wrong).

By the way, my experience is that spiral vee slows a board down. Better to eliminate the vee (kneeboarders don't need it, anyway) and put dual concaves in a single and taking them all the way out the tail (allows you to lower the tail kick). Of course you pay a price in other ways.

KenM
Spiral vee is an old term referring to concaves cut into vee. The stringer remains higher than the rails, but a straight edge placed stringer to rail reveals a concave. The concave and be at the stringer, centred or towards the rail.

KenM · Post by **KenM** » Sun Apr 06, 2008 4:41 pm

Thanks Red!!

Hmm, lead to another question, what would be the differance between spiral vee and double concave?

Eric Carson · Post by **Eric Carson** » Sun Apr 06, 2008 5:32 pm

To add to Red's post, spiral V is a double concave, read (Concave) on both sides of the stringer, while the stringer remains higher than the rails.
This is my interpretation-feel free to correct me

Casey Patelski · Post by **Casey Patelski** » Sun Apr 06, 2008 7:46 pm

Yeah you are right about the Spiral Vee, as a concave on either side of the stringer. This was explained to me by Bruce Hart.

Jon Manss · Post by **Jon Manss** » Mon Apr 07, 2008 6:31 am

The two post above miss the point that the spiral vee started with a single concave up front above mid point that splits into the two concaves. At least that's the way I've seen them.

KenM · Post by **KenM** » Mon Apr 07, 2008 7:57 am

So, would the main differance between double concave and spiral vee be that with double concave the stringer and rail are the same height and with spiral vee the stringer is higher than the rail, both having concave on either side of the stringer the first through a flat plane the second through a veed plane? Thanks.
-----------------------
sTupider than tee

mark ricketts · Post by **mark ricketts** » Mon Apr 07, 2008 12:02 pm

I guess I'm with parkes on this on - check out farrer's surfing - he generates ridiculous speed through his turns - we rarely are after flat out straight line speed. of course, when we are, we want all we can get!!! but i resisted multi-fins for years because of the drag until I finally weakened and put in two small rail fis which allowed me to turn in completely different places and utilise power that I'd never had access to before.

its all a balance of course - the old schoool fish go flat out and turn like dogs and some of the modern boards are slow but can milk everything. i've also noticed the "mushing" nose in some photos and it must be bad. i 've tried bogging up a small nose vee in an old board to try to eliminate it but.... found no appreciable difference.

Kneeboard Surfing USA Community Forum

HULL HYDRODYNAMICS 101, DISCUSSION

HULL HYDRODYNAMICS 101, DISCUSSION

hull?

hull

hull design