Poll

If the hull were as slick as, say a tuna or other quick fish, would it glide faster?

no
4 (36.4%)
yes
2 (18.2%)
maybe
1 (9.1%)
i don't know
3 (27.3%)
yes but how?
1 (9.1%)

Total Members Voted: 11

Voting closed: January 29, 2011, 01:43:22 AM

Author Topic: "hull scale" design  (Read 2937 times)

LB

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"hull scale" design
« on: December 30, 2010, 01:43:22 AM »
I'd like the opinion of experienced watermen, kayakers, boatman, as to whether
you think the slick nature of a fish body could benefit boat hull hydrodynamics

colas

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Re: "hull scale" design
« Reply #1 on: December 30, 2010, 02:47:49 AM »
Fast fishes do not have smooth skins, on the opposite. See:

http://wings.avkids.com/Book/Animals/advanced/marine-01.html

Quote
Fish have several different ways of dealing with friction drag:

    Slimy mucous layer
    Denticles (small teeth) on the skin
    Flexible skin movement

Barracuda secrete (release) slimy mucous from glands under their skin. This reduces drag by 60%! Sharks have denticles on their skin that cause the water to form a thin film that reduces drag in much the same way as the slimy mucous. Dolphins and whales have the ability to adjust their skin tension (pressure) to reduce drag. As a result all of these fish are fast swimmers.

On my SUPs I use the "shark" method: rough sand the bottom (400 grit)

PonoBill

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Re: "hull scale" design
« Reply #2 on: December 30, 2010, 08:17:15 AM »
Take a look at an Ono (wahoo) sometime. One that's not gently steaming on a bed of coleslaw and dirty rice (hmmm, maybe the Fishmarket for lunch). Looks like a kids drawing of an armored fish. Goes like stink in the water. Hydrodynamics never works like you'd think it would.
Foote 10'4X34", SIC 17.5 V1 hollow and an EPS one in Hood River. Foote 9'0" x 31", L41 8'8", 18' Speedboard, etc. etc.

LB

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Re: "hull scale" design
« Reply #3 on: December 30, 2010, 10:40:27 PM »
hey colas, found another worth reading after I checked yours out.  Very interesting yours is.  I looked a bit deeper check it out:

 How strategic roughness can yield aero- and hydro-dynamic benefits has elicited a great deal of research in recent years. Consider the humble golf ball. Those characteristic dimples are not created equal: the indentations around the equator of the ball are actually slightly deeper than those at the poles. This deceptively simple design feature grants a golf ball in flight and with the proper backspin an additional two seconds of 'hang-time' — increasing driving range by as much as 80 feet (24 metres) — and reduces the incidence of hooks and slices by as much as 75%. Similarly, in fighter jets or fast ships, the secret to their phenomenal speed lies in fine, V-shaped grooves. These grooves must be very closely spaced — about as close together as the grooves on an old-fashioned phonograph record (Anyone remember those?). Such closely-spaced grooves appear to reduce drag by preventing eddies from coming in contact with the surface of a moving body. Nowadays, there is hardly an American military aircraft or vessel that does not somehow benefit from the fluid dynamic efficiency of incorporating strategically-placed, V-shaped grooves along the fuselage, hull, and foils. But, whenever there is a physical principle that provides an elegant solution to a practical environmental challenge, it seems that Nature always beats us to the punch. Collectively, the tiny, three-ridged dermal denticles of the White Shark create closely-spaced grooves similar to those on high-speed air or water craft. These denticles very probably impart similar drag-reducing properties to the shark. Thus, without understanding the first thing about golf balls or military craft, the White Shark has been employing many of the same fluid dynamics principles for millions of years.

Raschi and ichthyologist Jack Musick discovered that the longitudinal ridge system created by shark dermal denticles is responsible for drag reductions

did you notice a difference in glide (before I sand away)?

stoneaxe

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Re: "hull scale" design
« Reply #4 on: December 31, 2010, 12:31:52 AM »
There's been a bit of discussion of this previously. The Boardlady recommends using a scothbrite pad or wetsanding (400 grit I think) to make a windsurfer faster.
Bob

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colas

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Re: "hull scale" design
« Reply #5 on: January 01, 2011, 12:55:28 AM »
did you notice a difference in glide (before I sand away)?

Yes, both on my SUP and Windsurfing. I feel it when going onto planing mostly: for instance in SUP, when you are on weak waves that are closing, and you move high in the curl and get as much angle as possible to make the section, in this situation where you are at low speed and want the max acceleration, the rough-sanded bottom & rails makes the board "squirt" forwards noticeably easier, with the smooth hull I often was stuck in the lip.

On the same subject, apparently there have been a breakthrough in torpedo speed by having a stream of air bubbles emitted at the tip of the torpedo, so that the torpedo actually glides in a thin layer of air/mush. They are implementing it by having a special shape of the tip that at high speed vaporizes water from the shock wave pressure...

PS: The golf ball is another story: the dimples are there not to actually provide less drag, but to prevent instabilities to happen: without the dimples, the air flow will hesitate betweeen sides, and risk choosing one side, putting your ball onto a very curved - and unpredictable - path. It is a case of "better go a tad slower but straight".
« Last Edit: January 01, 2011, 12:58:01 AM by colas »

 


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