Part One - Part Two - Part Three - Part Four
When I ended the last tale the rains were beginning, before the
rains really came I managed to get several coats of paint on the
pram and then finished my grandson's train table, you know, Thomas
the train etc., before Christmas. During my spare time I worked
further on the design and looked for a space to build the boat.
The last illustration in my previous article looked like this.
Junkish but not really, so back to the computer.
The basic hull remained the same, it was the sheer line that
changed to give that junk like look.
I spent quite a bit of time going from design page to design
page to junk page looking for inspiration. One which caught my
eye was this one, Jonque
I liked the sheer dipping to the bow and so I modified my design
to make the cuddy lower and the sheer line run the entire length.
I also added false davits to get the attachments for the mizzen
sheets well aft.
I looked at the enormous cockpit and decided to have buoyancy
tanks along the sides and also a self draining cockpit well (which
I've had to forego in the actual vessel as money started to run
out, maybe after the first season of actually sailing we can make
a decision as to whether that little modification is necessary).
The final design is almost this.
Note the change to the rudder. I decided that I didn't want all
those bungy cords and tried to devise a way of doing the same
thing more subtly. I was on the Lee Valley site one day drooling
over tools I can't afford and really would only use once or twice
in what remains of my lifetime and I noticed these things called
rare earth magnets. So I thought why not replace the cords with
magnets and washers. That required a complete rethink of the rudder
and since this drawing I've rethunk it again finally coming up
with a sliding control system that will stand up to being bashed
about in a seaway, I hope.
I also changed the davits, they are higher and come off the gunnel.
The end result is a boat that's 20 feet LOA but only 12.5 feet
LWL with a cockpit 7.5' long with a 6.5' foot cuddy. I've called
her Kuai Le which means joy in Mandarin. I got the name from a
Yoyo Ma Christmas melody. Kuai Le is 20' LOA, 6'6" beam,
9" draft with water ballast tanks full.
Ah yes, ballast tanks. In the last article I said I was toying
with the thought of ballast tanks, no longer. The tanks are right
amidships one on either side of the keelson 3'x2' by 9”
or 4.5 cubic feet each, about 250lbs each. The tanks fill from
the outboard side so when heeled there is no drainage from the
drain hole on the windward side. I'm playing about with self draining,
if I put her on the hard as the tide goes out the ballast will
drain and the air vent will let air in but not out and on refloating
she'll float higher than when we beached as no water can get back
in the tank until the airvent is released.
I was thinking of using the VacuVent wine stoppers. The old ones
are much like a miniature dinghy bilge drain. You put them in
the mouth of an open wine bottle and using a pump pull the air
out of the bottle. I was thinking that if you put them into the
ballast tank upside down you could let the air out using a straw
or something similar to fill the tanks and then when the tank
drained air would be pulled in but the lips of the vent would
seal and not let air out.
Anyway, we'll see how that goes. I might have to “borrow”
the old ones and buy new ones, which aren't the same design, for
you know who for Christmas.
I any event she'll be big enough to carry four adults for day
sailing and two for over night. The cuddy cabin is 6'6" long
with just under 4' headroom at the center line. The cabin top
is open, ala Bolger and Michalak,
all the way to the main mast and is canted to the gunnels which
increases visibility forward.
I completed a table of offsets and did some very basic math.
With the designed waterline the displacement is just under 2600
lbs. Of that 500 lbs is water ballast, 200ish lbs is me, the hull
is 750lbs, rudder and dagger board 50lbs, masts, spars and sails
80 lbs leaving just over a 1000 lbs for gear, passengers etc.
The pounds per inch immersion is 390 lbs so she'll probably sit
2” above the designed waterline for solo day sailing.
I also did some stability calculations. The gunnel goes under
somewhere between 30 and 45 degrees and she's pretty stable to
about 65 degrees. In fact the center of buoyancy is well outside
the center of gravity up to 90 degrees. Because of the buoyancy
tanks she'll float well beyond 90 degrees but the center of gravity
passes over the center of buoyancy at 95 degrees at which point
the masts should be in the water stopping any further roll.
It looks like her best angle for sailing will be 25 degrees,
that would be interesting. The weather chine will be clear of
the water at the midsection, half of one ballast tank will be
in the air, there's lots of reserve stability at that angle and
the lee chine is clear of the water at the bow.
It also appears that fore and aft placement of crew in the cockpit
will have minimal effect. The moment to trim is 210 lbs so me
wandering around, if one can do that in a small boat, won't change
The rest of the numbers are,
Center of buoyancy Aft .0417 ft
Vertical center of buoyancy Below LWL .3033 ft
Center of flotation Aft .0875 ft
Block .6566 (what do you expect from a
Prismatic .6623 square boat?)
Moment of inertia 223.8354 lbs
Metacentric radius 5.6669 ft
Actually, the only really important numbers, other than displacement,
are the centers of buoyancy, flotation and the metacentric radius.
The coefficients will all change significantly once she heels
and immerses the lee chine.
I'm hoping that the end result will have that same big boat feel
that the Bolger Micro has, lots of momentum.
I've also started designing other boats and I'm making models
of those boats in cardboard and basswood. One of the things I've
relearned is that weights in scale times scale cubed equal weights
in the real world, thank you Weston Farmer. In Canada we have
a $2 coin referred to as a twoonie, the $1 coin had a loon on
it hence loonie, you see the logic, and a twoonie weighs a smidge
under 5 grams. This is a useful thing to know. I built a 1/24th
scale model of one of my designs and marked the designed LWL on
the side. Following Weston Farmer's advice in his book, I floated
the model in the sink and added weight until it hit the LWL. Two
twoonies, 10 grams, times 24 cubed, divided by a thousand equals
a displacement of 138 kilos or roughly 300 lbs. The picture below
is the model, it's wrinkled because not being satisfied with determining
displacement I kept adding weight to see what it would carry,
four twoonies and a loonie and it sank. It looked so nice before,
Back to Kuai Le, I was satisified with the numbers and the look,
had a name and so it was time to build, but where? Next time!
Experience starts when you begin - R.D. Culler