DESIGN HISTORY
Two early pintail design precedents were shaped for Nat Young by Harold Iggy at Weber Surfboards for the Hawaiian winter of 1968-1969 and ridden to 5th place in that year's Duke Kahanamoku Contest.
The two boards had identical large sun decals on the deck.

The following winter (1969-1970):
"We ended up in Hanalei Bay and got to witness Joey Cabell surf Hanalei at 18 to 20 feet. 
I stood on the deck of the Princeton Hotel and watched him, 800 metres off- shore on the board that he'd shaped himself called "White Ghost", 9- foot 6-inches long with down rails tucked under to an edge and a completely flat bottom. 
It was a memorable experience indeed, and for the next few years Joey was to be my hero and guiding light as far as equipment was concerned.
...
The Smirnoff contest kicked off at Makaha Beach in the last week of November (1969)and I was using a beautiful 8-foot 6-inch down-rail gun inspired by Cabell, with a 9-foot board as backup. 
With no surfboard company to appease I'd got Cabell's shaper Steve Teau to shape both of the boards before I left Kauai." 
-Young: Nat's Nat (1998) page 228.

In early 1971, Nat Young had relocated to a rural acreage outside Byron Bay on the NSW North Coast where he:
" turned the property's old farm-machinery shed into a surfboard factory, building the glassing stands myself and, with Garth Murphy's help, a shaping stand. 
It was really satisfying building boards at home; I did everything myself and there were always plenty of orders, what with sales to a growing number of local friends and Ray Richards, from Newcastle, who asked me to make boards for his shop whenever I had time between custom orders. 
I modelled them on the board I was riding at that time, a scaled-down version of those Cabell had been surfing in Kauai; 7-foot long by 201/2 inches wide, a double-ended pintail with soft, low rails tucked under to an edge. 
I coloured them all in soft pastels and used very small pivot fins, as with that design I found that I didn't need to use much fin at all, the drive coming from the bottom shape and low rails. 
Over the course of twelve months I kept reducing the fin size until I'd got it down to only 7-inches deep and 3-inches wide at the base.
...
I believe that this period in Byron was the best I've surfed in my life."
-Young: Nat's Nat (1998) page 236.

It was at this time that the footage of Nat at Broken Head was shot by Alby Falzon for inclusion in The Morning of the Earth, see below.

The design featured a compressed pintailgun template, 2nd phase concave bottom, soft box rails with a hard edge, large nose lift and a small Greenough single fin.
The early models Byron Bay models usually featured grey/blue pigment laminate and this was continued when the boards were initially manufactured for Bennett Surfboards in Brookvale.
Later Sydney models, first at Bennetts and later at Nat's Mona Vale factory, had sprayed blanks.
While the early models often had, as on this example, one of several large Oriental decals (see below), by the mid-1970s this was replaced by a large naked female and floral illustration, see #151.

These design was manufactured, virtually unchanged until 1981, thereafter it was reconfigured by inverting the position of the wide point, widening the tail and installing a tri-fin set up. 
See Nat Young Tri fin # 57.

OTHER NAT YOUNG BOARDS
Pintails #20, #151 and #174 -  images below.

Also see Nat Young Tri fin # 57, 1981 and Nat Young Tri fin # 27, 1981

COMMENTS : Replacement board for #20

REFERENCES
Magazine Article :
1. Falzon, Albert and  Murphy, Garth (Photographers) :"Nat and His Boards and His Surfing"
Tracks magazine October 1971, page 14. 
Note Pintail and Squaretail ("Backhand") model.
2. Nat Young : ''Ten Years in the Planning''
Surfing World magazine Vol 26 #4 1978 pages 24 - 26
Photos by Bruce Channon, image below.

Books:
1. Nat Young’s Book of Surfing  page 64.
2. Nat : Surfing Fundamentals    Pages 100 - 101.
Same text as # 1. above. Includes reprint of Pintail/Backhand photograph in Magazines # 1, noted above.
3. Nat’s Nat and that’s that
 Extensive references and photographs, note pages 228 to 236.

Film :
1. Alby Falzon:  The Morning of the Earth,  1972.
http://www.youtube.com/watch?v=mRJu4KjATKA

While MOTE is packed with an incredible amount of high quality surfing performances, the sequence featuring  Nat Young (in his regulation red boardshorts/longsleeve vest) at Broken Head, NSW, is arguably the most outstanding.
In extremely fast breaking waves, Nat fails to make his first two when he attempts to speed trim though sections.
Subsequently, he is more successful by forgoing the straight line approach and rides at the curl speed by maintaining a series of fluid turns whereby the board is constantly accelerating coming out of the top turns.
This effectively was the ultimate expression of McTavish's Break Out From the Straight Line Theory, formulated in  late 1967.
See Source Documents: "LADIES AND GENTLEMEN AND CHILDREN OF THE SUN.."

Through the 1970s this approach would typify shortboard surfing, with straight-line surfing generally confined to riding deep in the curl.
Towards the end of the 1970s, South African Shaun Tomson extended performance levels by advancing the method whereby he was "turning inside the tube", see  Bill Delany's Free Ride (1977).

2. Alby Falzon: Crystal Voyager,  1973
Nat in California on green 8 ft Pat Morgan Surfboard (three circles decal) with a long base keel fin.
3. David Sumpter: On Any Morning, 1974
Nat Young in Bali and 1972 Coke Contest, Fairy Bower.
4. NatYoung: Fall Line, 1979
Victoria with Wayne Lynch.

CONDITION: 9.