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<TITLE>AYRS Newsletter July 1997 July 97 Newsletter text </TITLE>
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<H1><A NAME="P31_1896"></A> <IMG SRC="Aqwvblt.gif" WIDTH="9" HEIGHT="9" ALIGN="BOTTOM"
ALT="Icon" BORDER="0"><FONT SIZE="5" COLOR="#333333" FACE="Arial"><B>Hydrofoils<IMG
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<P><FONT SIZE="4" FACE="Times New Roman">The following is extracted from a report
on the Miami Boat Show (from Vance Buhler </FONT><A HREF="MAILTO:<[email protected]>)"><FONT
SIZE="4" FACE="Times New Roman"><[email protected]>)</FONT></A><FONT SIZE="4"
FACE="Times New Roman"> which appeared on the Internet Multihulls Email list:</FONT></P>
<BLOCKQUOTE>
<P><FONT SIZE="4" FACE="Times New Roman">"There were a few interesting boats.
Among them Dr Sam Bradfield's lovely 25ft carbon Foiler Tri EIFO with it's 7' daggerboards
and rudder to which were fastened 5' wide Tee foils. At the cost of some speed loss
at the top end the foils are optimised to lift the boat at well under ten knots of
windspeed! It also features a simple mechanical control system to trim the foils.
It's all very nicely done and really ought to spin your crank if you want an extra
50% of speed and have 10kt winds to sail in. Top speed until then had been 27 kts.
The pictures of it sailing at speed were impressive. No heeling, 2feet plus up out
of the water, straight and level, relatively little spray. If you threw away the
foils, etc., it would probably still do 27! Of course the crew would have to wear
snorkels and masks with windshield wipers because they'd be under water most of the
time. David Keiper of WILLIWAW fame says that we can expect a proper foiler on Ladder
foils to break 50Kts. My guess is that the foils will have to be optimised for the
high end and probably won't get up till the boat is doing at least 20."</FONT></P>
</BLOCKQUOTE>
<P><FONT SIZE="4" FACE="Times New Roman">We invited both Sam Bradfield and David
Keiper to comment and expand on their different approaches. Dr Bradfield unfortunately
was not available at the address we have, but we received the following from Mr Keiper:</FONT></P>
<BLOCKQUOTE>
<P><FONT SIZE="4" FACE="Times New Roman">"Sam Bradfield optimises his foil systems
for racing around the buoys. Using a submerged foil system helps in typical race
conditions of modest wind. One price paid by having submerged foil systems is that
you can not optimise performance over a wide speed range. He sacrifices the high
speed end in trying to get a high AVERAGE speed over a race course in typical conditions.
If his beautifully crafted EIFO has a top speed of 27 knots, it is a tribute to his
design abilities. That is about his top design speed. His boats should be judged
on boatspeed/true windspeed. I know he is doing well in that category. Sam does lots
of careful measurements of performance. I suppose it might be possible for a super-lightweight
fragile catamaran to match Sam's boat on performance, but only because his foil tri
EIFO is built to be durable, and weighs in substantially heavier.</FONT></P>
<P><FONT SIZE="4" FACE="Times New Roman">Compared to Sam, I design for a higher take-off
speed, usually around 12 knots. While that creates a moderate drag hump, there are
tricks to aid in punching through the hump in marginal wind conditions.</FONT></P>
<P><FONT SIZE="4" FACE="Times New Roman">I continue to design with ladder foils partly
because ladder foils with high aspect-ratio elements can be designed to be reasonably
optimum over a very wide speed range, probably the whole range, 8 to 50 knots. That
requires careful attention to a lot of details. Not just any ladder foil will do.
. . . In designing Williwaw, I optimised for the 10 to 20 knot speed range, since,
in that day, no one even thought that sailing yachts could fly. In ideal conditions,
strong wind and flat water, Williwaw got up to about 30 knots. Hydrofoil surfing
out at sea, she probably had speed bursts to 25 knots.</FONT></P>
<P><FONT SIZE="4" FACE="Times New Roman">Another reason I've stayed with ladder foils
is that the elements can be built into truss arrangements that can withstand the
worst punishment the sea can give. Submerged foils are necessarily cantilevered,
and have a lower strength-to-weight ratio. Also, submerged foils require moving parts,
which I don't like at sea.</FONT></P>
<P><FONT SIZE="4" FACE="Times New Roman">There are foil sections that are free of
cavitation up to about 50 knots , so such a sailing speed is a reasonable goal in
ideal conditions. Just remember that Alexander Graham Bell pushed a power hydrofoil
with ladder foils up to almost 62 knots in 1919. His foils were a bit crude- --flat
plates, I believe.</FONT></P>
<P><FONT SIZE="4" FACE="Times New Roman">Rather than just giving words or drawings,
I would be happy to develop the ultimate sailing-speed machine that would do 50 knots.
Unfortunately, I've never had the capital to build and campaign such a boat. I think
I could do it with a small fraction of the capital that some other hydrofoil designers
have had to play with."</FONT></P>
</BLOCKQUOTE>
<P><FONT SIZE="4" FACE="Times New Roman">We perhaps ought to mention that Dave Keiper's
book "Hydrofoil Voyager" is available from: 1) Multihulls Magazine; 2)
Multihull International magazine, which has the lowest price for UK buyers ( they
also carry the video tape of Williwaw in action, in PAL format); 3) Philip Thompson,
in Australia (e-mail: </FONT><A HREF="MAILTO:[email protected]),"><FONT
SIZE="4" FACE="Times New Roman">[email protected]),</FONT></A><FONT SIZE="4"
FACE="Times New Roman"> who writes for Multihull World; and 4) from the publisher:
Hinsdale Press, 123 South Pacific St., Cape Girardeau, MO 63703, USA.</FONT></P>
<H2><A NAME="P53_6526"></A> <FONT SIZE="4" COLOR="#006697" FACE="Arial"><I><B>HYDROFOIL
KITS</B></I></FONT></H2>
<P><FONT SIZE="4" FACE="Times New Roman">Since then we have also received the following
announcement of the availability of beachcat hydrofoil kits from Dave's company DAK
Hydrofoils:</FONT></P>
<BLOCKQUOTE>
<P><FONT SIZE="4" FACE="Times New Roman">We can now report some good news. Our 3"-chord
aluminium hydrofoil extrusions are being manufactured. With my assistant, who has
a Hobie-18, we'll be testing the foils this summer. The test results will be applicable
to most other beachcats.</FONT></P>
<P><FONT SIZE="4" FACE="Times New Roman">We should be able to ship foil kits by late
summer. We hope you continue to be interested. In the Multihulls magazine article
(Nov/Dec '96, page 41), we said we could provide, in a do-it-yourself kit for under
$600, the necessary hydrofoil hardware to get your boat flying on foils. We will
stick to our promise on price, setting it at $595 plus shipping costs from Cape Girardeau.
However, this price applies only to those who order the kit in the next 30 days or
so, and also send us a deposit of $200 for the kit. [Note: We acknowledge receipt
of all deposits. Deposits are fully refundable, if you change your mind about wanting
a kit. Also, anyone who buys a kit and then changes their mind, we will help locate
another purchaser so that you'll get your money back.] . . . At our low foil-kit
prices, you won't need to take out a home equity loan to get flying on hydrofoils,
as you might for buying a production hydrofoil sailboat on the market. You may even
get some friends out sailing again with hydrofoils, because of the smoother ride,
which gives a big-boat feel.</FONT></P>
<P><FONT SIZE="4" FACE="Times New Roman">Our foils should be suitable for the Hobie
14, 16 and 18, Nacra 5.2, Prindle, Sea Spray, A-class, others, plus some home-built
catamarans. Kits will differ in the attachment hardware. These kits are most suited
to 14 to 21 foot catamarans that are lightweight. Heavy catamarans, usually of deeper
draft and higher freeboard, are not well suited for foils. Our ladder foil unit also
happens to be suitable for small powerboats.</FONT></P>
<P><FONT SIZE="4" FACE="Times New Roman">The kit comes with step-by-step plans, and
includes many construction tips. The most difficult part of construction has already
been done--- the cutting and fitting together of the elements of the foil units at
the proper angles, and the drilling of the pilot holes for screws. Thus , the builder
does not have to do much metal working. The builder taps thread for the screws, roughs
up the metal next to the joints to make the epoxy hold better, and epoxies the foil
elements together. After the epoxy sets, there is some filing to streamline the joints
that will be underwater. Additional epoxy filler will be added to make good fillets.
Then you mount the main foils to the forward crossarm and deck edge with the hardware
provided. Stainless-steel bolt hardware is provided. Stabilising fins will be attached
to the bottoms of the rudder blades. On some boats, there may be some looseness in
the rudder assembly, which needs to be corrected before you can go foiling. Kit construction
will require a weekend or two of time.</FONT></P>
<P><FONT SIZE="4" FACE="Times New Roman">We also offer a ready-to-install set of
foils for a few of the most common beachcats. The price on that will be $1250, with
a $400 deposit. The ready-to-install foils will already be coated for salt-water
protection. (Those who build from our kit, and plan to sail in salt water, will want
to take the foils to a local shop where they do "powder coating," which
gives a slick, durable finish in the colour of your choice.)</FONT></P>
<P><FONT SIZE="4" FACE="Times New Roman">We expect a catamaran with these foils to
be able to get flying in a true wind of 9 to 10 knots, depending upon boat weight
(number of crew), sail area, and the heading relative to the wind. In marginal winds,
it is easiest to get flying while close reaching. However, the top speeds will be
achieved with a stronger wind, and the true wind a bit aft of the beam. In ideal
conditions, foils may double the speed. Mostly, foils will add 50% to speed when
there is wind for flying. In light airs, one retracts the main foils, and sails the
boat conventionally. The rudder stabilising fins are set to zero degrees angle of
attack, and add only slightly to drag in light airs.</FONT></P>
<P><FONT SIZE="4" FACE="Times New Roman">There is a smooth transition between hull
buoyancy and hydrofoil lift. As the boat picks up speed and gains hydrofoil lift,
the bow comes up, augmenting angles of attack and lift on the foils. Crew can also
move aft to further augment lift off in marginal winds. Just before becoming fully
foilborne, there is a modest drag hump. It is easiest to break through the drag hump
while sailing 60 to 70 degrees from the true wind. If one turns the boat suddenly
away from the wind by 10 or 15 degrees, suction on the lee hull stern is broken,
and also the sail gets "pumped. " That usually gets the boat through the
drag hump in marginal winds. There is a noticeable acceleration as soon as the boat
becomes fully foilborne. As it accelerates to higher speeds, the bow comes back down
to about level trim. If you find that the boat flies either bow up or bow down at
high speed, you should change slightly the angle of attack of the rudder stabiliser
fins.</FONT></P>
<P><FONT SIZE="4" FACE="Times New Roman">The foils not only increase speed potential
in moderate to strong winds, they increase stability markedly, making the boat much
easier to manage. Foils reduce rolling, pitching, yawing and heaving. There is reduced
hull pounding and rigging fatigue. Foils drastically reduce the likelihood of lee-bow
burying or capsize. Not only that, crew comfort is increased, with a drier, smoother
ride.</FONT></P>
<P><FONT SIZE="4" FACE="Times New Roman">In case you are not familiar with our hydrofoil
sailboat research and development, we should mention that our first creation, back
in the late 1960's, was the awe-inspiring 31-foot hydrofoil trimaran "Williwaw,"
which successfully cruised 20,000 miles around the Pacific in all kinds of conditions.
You can get an idea of the high hydrodynamic efficiency of our foil designs when
you consider that a 10 to 12-knot wind is able to lift a yacht weighing 1.5 tons
right out of the water with only 380 square feet of sail in a conventional sloop
rig. . . . Later, in the early 1970's, we developed and test-marketed foils for the
smaller beachcats, using 2"-chord foils. We stopped marketing during a recession,
but continued research. Our new improved beachcat foil kits are the result. You can
read about all our previous developments in the book, "Hydrofoil Voyager."</FONT></P>
<P><FONT SIZE="4" FACE="Times New Roman">We invite you to visit our website if you
haven't already. The website URL appears below.</FONT></P>
<P><FONT SIZE="4" FACE="Times New Roman">We hope you are persuaded to get in on the
great fun of hydrofoil sailing. It is definitely more fun to fly both hulls of your
catamaran. Call or write if you have questions.</FONT></P>
<P><FONT SIZE="4" FACE="Times New Roman">Sincerely,</FONT></P>
<P><FONT SIZE="4" FACE="Times New Roman">David A. Keiper DAK Hydrofoils, 123 South
Pacific Street, Cape Girardeau, MO 63703, USA; phone: 573-651-6582; e-mail: </FONT><A
HREF="MAILTO:[email protected];"><FONT SIZE="4" FACE="Times New Roman">[email protected];</FONT></A>
<BR>
<FONT SIZE="4" FACE="Times New Roman">Website URL: </FONT><A HREF="http://www.igateway.net/~dakh"><FONT
SIZE="4" FACE="Times New Roman">www.igateway.net/~dakh</FONT></A></P>
</BLOCKQUOTE>
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<P><IMG SRC="797-1.gif" WIDTH="374" HEIGHT="230" ALIGN="BOTTOM" ALT="Beach cat with Keiper foil kit"
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<CENTER>
<P><FONT SIZE="4" FACE="Times New Roman"><B>DAK Hydrofoils Beachcat Foil Kits</B></FONT></P>
</CENTER>
<P><FONT SIZE="4" FACE="Times New Roman">Further correspondence elicited the following:</FONT></P>
<P><FONT SIZE="4" FACE="Times New Roman">The extrusion sections for the lifter is
Clark-Y with thickened trailing edge. That has a rounded nose, and max. thickness
almost 12% at 30% of chord from leading edge, and a flat surface underneath from
30% to 100% of chord. It is not suitable for reversing (shunting) proas. This section
features a wide angle of attack range with good L/D, and can get fairly high lift
without stalling.</FONT></P>
<P><FONT SIZE="4" FACE="Times New Roman">For the strut, they are using the NACA 16-008
section with thickened trailing edge. A fairly thin strut, at 8% max. thickness,
which minimises surface-piercing drag and ventilation. This strut section is suitable
in the truss arrangement ladder-foils they design, where stresses are mainly tension
and compression. It is not suited to cantilevered foils, where there may be a sizeable
unsupported span subjected to bending stresses.</FONT></P>
<P><FONT SIZE="4" FACE="Times New Roman">The foils retract on pivot axes running
fore and aft. Thus the foil unit swings out to the side and then up. The main pivot
axis is along the edge of the deck, at the apex of the foil unit, and the apex of
two braces going forward from the foil unit. Looking at the drawing (above), you'll
note a horizontal bar laying on top of the main crossarm. There are pivots (fore-and-aft
axes) at each end of that bar. The middle of that bar clamps to the outer end of
the crossarm.</FONT></P>
<P><FONT SIZE="4" FACE="Times New Roman">As to the rudder and stabilising fin arrangement,
the simplest is to have stabilising fins at the bottom of the rudder blades. They
do not need to be retracted, as the fins have zero angle of attack. Keiper tells
us he has also been trying to work out another more-complex arrangement, similar
to that he had on his boat Stormy Petrel, in which the rudder and fin can be retracted
(on a longitudinal axis), with a shallow rudder blade going in the water when the
foil rudder is retracted.</FONT></P>
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