Takapu's old sloop rig

The sloop rig was adapted from an old
Olympic class Tornado Catamaran






















Here is Takapu on his second fit out in 1980.
By this time I had set up the roller furling jibs and as you can see by the outrigger extensions to leeward I was trialling sheeting positions and ideal jib/mainsail slot relationships.

The roller furling jib system I developed did have exactly the characteristics
you describe Kevin re partial furling at mid roll.
However when at a mooring I needed to separate the furling line to allow a
complete furl at each end. for this I used stainless steel "sister clips" do you
know what they are over there? Perhaps you have a different name for them? Two
identical "C" shaped claws that are sahped so that when you hold one at right
angles to the other presenting the mouth of the "C" to each other you can hook
them together. The furling line is spliced or tied off on a hole at the base of
each "C". We used the for cliping spinnaker sheets to the sail in dinghy racing
in the 1960's & 70's.

This arrangement allowed me to separate and cleat each sheet independently when
needed.

























Not too long after this image was taken Takapu was rolled over on his mooring at Whangaparaoa during a severe tropical storm. The mast was broken in two in the rough shallow bay so I had to splice it back together using a tubular sleeve and pop rivets.
It was then that I decided to replace the old windward strut with a longer, more rigid, tubular T6 aluminium tube and lengthen it to support the mast on an improved swivel joint at the fore and back stay hounds.

The mast attachment that I built was similar in most ways to a boom goose neck
fitting. I adapted the mast attachment plate from a cast aluminium goose neck
fitting rated for a 30 foot keel boat. The bracket had two beckets with
pre drilled holes for a pivot block. It also had a concave base in the vertical
axis so it fitted neatly to the leading edge of the mast at Jib hound level.

I made up 2 stainless straps to fit the inside of the 40mm (about 1 1/2 inch)
T6 aluminium tube that I chose for a compression strut/windward shroud. The
straps were 150mm long dinghy chainplates with predrilled hole (where shackle
pins were intended to be fastened) which I bought inexpensively at a local
marine hardware shop. The straps were riveted into the tube opposite each other
to protrude abot 50mm out of the upper end of the tube creating a gap of about
25-30mm. I then made up a block of Tuffnel (a high density resin fabric
composite that was commonly used in the electrical industry as a non conductive
distribution board panel)I'm sure that any tough composite or even ultra high
density plastic will do.

The block measured 25mm thick and 100 mm deep and 60mm wide shaped like a "D" I
drilled two holes in that block, 1 down the length of the back of the D and one
more through the side of the D in the middle of the curve. I then pinned a
stainless bolt through the chainplate strap holes in the end of the compression
tube and through the thickness of the block, (the one through the side of the D
in the middle of the curve).This attachment point also took connections for the
two forestays.

The second attachment was a stainless bolt passing vertically through the two
beckets of the gooseneck fitting on the mast and through the vertical hole
drilled down the back of the D. I made sure to not over tighten the nuts on
either bolt to allow freedom of movent. This created a kind of universal fitting
allowing mast rotation through every possible axis without the fouling problem
you describe.

With the forestays attached slightly to windward on the compression
strut/windward shroud, the mast was able to rotate freely to follow the sail
through 180 dgrees to either tack.
This gooseneck fitting never failed in the whole time it was in place.
If you build one ensure that the holes and pins are a snug fit with no slack.

The wishbone boom was built from an old extruded aluminium luff foil from a damaged racing keel boat rig which I scored from the scrap bin outside the rigging shop where I used to work in Auckland. The boom lasted for the 20 year life of that rig!


Takapu was launched as Seabird in the late 70's up until the time of the dismasting
after the rebuild he became Takapu.
In this image taken in 1979 "the second incarnation" The old shallow V stich and tape ama
still features. Note also the slender compression strut. Bloody useless!
My rudders were built to house in center board slots. These were designed to
act as both rudder and center board. The slots were built in to the hull at a
point where Mike and I felt they would balance the rig at a reasonable CLR and
would still be far aft enough to steer as well.
My rudders were ogive in cross section (flat on the lee side and a section of an
arc on the windward side) through the foil so they would work in either
direction when partially housed.

They were counterbalanced as well so that they had some almost neutral balance
when strong lateral loads came on. The stainless steel shaft was 5/8 inch round
bar on to which I had welded flat bar tangs which were bolted to the flat panel
on the lee rudder suface and imbedded during construction in the curved surface
of the blade 1/3 back from the leading edge.
The shaft was supported and pivoted in a wooden space frame which supported the
whole assembly in the center board slot through to the bolt on tiller and
extension.

They were vulnerable to being grounded when fully down though they were not very
deep (500 mmm), 2ft below the hull so I could sail close in to shore and use my
inertia to carry me in to wading depth with the rudders fully or partially
housed.

The shafts were badly bent and fatigued after a series of groundings and impacts with submerged objects by the time I retired them.

Mike and I discovered that the ogive section was so efficient as a lifting foil
that the pivoting action was not needed at all to steer the boat so we went to
fixed ogive section foils that were controlled by small tackle lines. Instead of
a tiller Toroa had a second sheet.
The control line allowed me to pull the foil down through the hull against the
tension of a bungy cord which always retrieved the board flush into the hull
when there was no tension on the control line. The method proved far superior
to the old one so I adapted the idea for the new proa Toroa as well. Now though,
since I have extended the length of that boat Toroa no longer needs rudders at
all. I'm on a perpetual quest to remove moving components and on
towards my goal of simplicity in all things.
It has been that initiative that persuaded me to abandon the sloop rig in favour
of the lateen on my proa which I now favour over all the other rigs I have
tried.

Hull asymmetry

"I saw the new pics this morning. It must be exciting to see it that way at last. In one photo I can even see the "Kiribati dimple". Isn't it time for you to release this dirty little secret into the blogosphere?" Gary Dierking

O.K. Gary you asked for it!

I've been asked this question many times, over many years and after much practice, research and reading I think I'm ready to answer.

The so called Kiribati dimple is a feature of some of the variants of proa characteristics found around the Pacific past and present and is most pronounced in the proas of Kiribati.

In the late nineties I was fortunate enough to have been able to converse with several of the great aero-hydro dynamics experts of our time. In Auckland these were professor Peter Jackson and Tom Schnackenberg. These conversations lead to hours of reading in the engineering library at the University of Auckland. I was preparing research material for my thesis to contribute to an advanced degree in design.

Kuchemann was a German professor of aerodynamics invited to continue his research in the United States after the Second World War. During the 1950's he was experimenting with supersonic aircraft design for McConnell Douglas. One of his papers talked about delta wing flow dynamics. This was interesting enough to me however I then came across some experimental wind tunnel work on supersonic fuselage design. The "Coke bottle" profile of several jet fighter bombers solved the problem of shock wave development at the wing root where the wings joined the fuselage. This is an area of dramatic increase in fluid displacement. It was found that where this secondary drag inducing shock wave developed, the fuselage could be "waisted" or reduced in circumference to improve the overall aerodynamic efficiency of the airframe at sub and supersonic speed. It was explained to me that supersonic air has similar flow characteristics to water when compared to fluid flow over a hull.

I made the assumption that a hull with significant rocker and combined proximity to the widest section of the hull of an asymmetric proa (or any displacement sailboat hull for that matter) would benefit from a waist on the high pressure (or leeward) side in order to reduce drag.
I had already had my curiosity aroused on this subject by J.S. Taylor many years before when Mike and I were building Takapu. Taylor published a series of articles in the NZ Seaspray Magazine in which he wrote about his experiments on the hull of a proa with just such a dimple. I recall him relating his experiments which involved the filling and fairing of the dimple on his trial hull. The hull was slower and lifted less after the treatment than before!

Mike and I have since that time incorporated the dimple in our proa design work with good and satisfying results. Both Takapu and Toroa are faster than their predicted maximum hull speed, based on prismatic coefficient calculations, by a significant factor. Furthermore we have found that our hulls are not as susceptible to broaching when sailing down wind in a following sea.

Of course the artists right side of my brain also has a say. Intuitively I know that in nature pure symmetry is anathema in living organisms. Where symmetry appears to present itself there, on closer detailed inspection (on the other side of the coin), you will find variation.

Both the United States Navy and Jaques Cousteau carried out experiments on the form drag of fish and marine mammals. When towed (dead) at their known respective speeds, the from drag of their streamlined bodies was far greater than their musculature could possibly propel them.
I believe that we have been looking at the dynamics wrongly.
No fish dolphin, shark or seal is ever symmetrical when swimming at speed. They are always at any given moment either asymmetric one way, or the other. Whilst asymmetric at the extreme extent of flex the body is curved on one side and hollow on the other (in the case of a dolphin the same is true though of course the asymmetry is in the horizontal plane). Whilst in the fully curved stage of motion, at speed the lift generated is slightly forward of lateral in a similar way that a sail generates lift. The body is inclined to generate a zone of low pressure on each oscillation which reduces drag and effort.

I believe that the canoe builders of Oceania either observed this phenomenon or generations of builders stumbled on the benefits of asymmetry thousands of years ago. Either way the fact remains that it works and it works very well. I would not consider building a shunting proa without this feature when there is so much to gain and so little to loose.

Harmen R Hielkema.

Madagascar outrigger canoe

And now a small break from the Toroa surgery






















My brother found this in a Dutch "Zeilen" magazine, January 08 (photo by Edo & Joanne Ankum)
I always understood from my friend Steven (who's father was a military courier in Africa During the second World War) that outrigger canoes were common in Madagascar, he viewed them from the bubble observation window in the PBY Catalina in which he flew regularly
Here's a nice example of a tacker (not a shunting proa)
What's revealing for me is the way the lateen sail is set down wind.

Back to work, finishing the coving and glassing on the interior of Toroa's hull today.

More soon.