Since publishing the previous article about Fleet and Fleet, and their respective performance under outboard power, I've been asked by several people to report on performance under oar power.
Flint was designed from the outset to be a dedicated rowing boat - the power and sailing options were after-thoughts. She rows beautifully in my biased opinion.
Fleet on the other hand has a hull-form which is not optimised for rowing, but because of her light-weight and lean hull, she does got surprisingly well - certainly much better than the typical aluminium outboard skiff (they are about as bad to row as you could imagine - even compared with an inflatable!
Here is Fleet in the only worthwhile clip I possess:-
Next is a nice clip from a Flint builder in Italy (I think) - such a pleasant little clip:-
These two clips should be viewed in the context of the previous post if you haven't read it already
My
introduction to “reading” the shape of a boat’s hull by viewing a lines drawing
came from watching over Dad’s shoulder as he read copies of “The Rudder”, Motor
Boating’s “Ideal Series”, Howard Chapelle’s “American Small Sailing Craft” and
other such documents. I guess I was about five years old at the time, and it
wasn’t too long before I had a practical introduction to a table-of-offsets
when Dad started to loft the lines of William Atkin’s Nancy, a 15ft 6in LOA modified sailing dory of 5ft breadth, and
13ft 6in length on the waterline. My part was to read out the offsets as Dad
marked everything on his full-size lofting. I didn’t understand what the
numbers meant, but I knew they were somehow very important.
Full-size lofting taking place in my workshop around 2003. Basically, expanding a set of lines from the scaled paper drafting to full-sized pencil and ballpoint drawing on white-painted plywood.
Full-size
lofting taking place in my workshop around 2003. Basically, expanding a set of
lines from the scaled paper drafting to full-sized pencil and ballpoint drawing
on white-painted plywood.
As years
went by my free days were spent sailing a Charles MacGregor-designed Sabot at the local sailing club and
generally living a salt-water life, enjoying the freedom afforded to kids in
the early sixties. But in the evenings I found myself drawn more and more
frequently to the stash of books about boats which lived in a particular part
of the wall of bookshelves in our TV-deprived house.
The drawings
which attracted my attention most were the outboard profiles and the
sail-plans. To me it appeared that the lines drawings were only for higher
beings than myself, and they meant little to me.
Moving on fifty or
sixty years, I now know that a boat drawing without a set of lines is like music
without notation. Yes, music can be played by ear, and a boat can be built by
eye or half-model – but for most of us, a set of lines is the key to
visualising and understanding the shape and behaviour of a particular boat.
A typical lines drawing, showing waterlines, buttock lines, and hull sections. I also draw diagonals, but they are not shown in this particular drawing
But just as
I know people who are amazed that I can’t ‘hear’ a piece of music by looking at
the notes on paper, I find myself puzzled when someone who has a set of plans
for one of my small sailing or rowing designs asks me if she will take their
15hp outboard!
Back in
about 2003 I was asked to draw a design for a fifteen-foot rowing boat which
was to be used by a very experienced waterman when he needed to row to the
mainland from his island home on Moreton Bay, Queensland, Australia. Moreton
Bay is a wonderful and varied paradise for boat people, but one of its notable
characteristics is the ability to generate a particularly short and steep wave
pattern. This new rowing boat design needed to be shaped to handle such
conditions.
The
resulting design, called Flint, has
turned out to be very popular with home-builders. In fact, I use a Flint as my recreational boat-of-choice
at the moment. Sheis 14ft 10in x 4ft
3ins and weighs in at as little as 40kg (88lbs). The boat is arranged to carry
a small outboard for those who for whatever reason need that facility, and
shortly after the plans were released, I started to receive letters and emails
about using motors larger than the 2 to 2.5 horsepower units I recommended in
the plans and instructions. Much time was taken up in writing emails to potential
builders, explaining why excess power was counter-productive
In order to
be an efficient rowing boat, and to be able to sail effectively with the
optional sailing rig, the lines drawing for Flint
shows considerable keel rocker, and the buttock lines (i.e. the bottom of
the boat in profile) sweep upward at a significant angle to the waterline,
terminating above the water at the stern transom.
In order to
satisfy the many people who still insisted on using larger outboards, I drew
another design - based on Flint - which
has almost zero keel rocker aft of amidships – she is called Fleet, and will run happily at speeds of
up to 20 knots (23 mph) in good conditions. More importantly, Fleet will run quietly and smoothly at
her sweet-spot of about 12 knots (14 mph). At such a speed she is covering
ground to windward at nearly four times that of a similar sized sailing boat. A
potent and efficient magic carpet for an explorer who has limited available
time.
Flint is
14ft 10in x a fraction over 4ft at the outside of the hull planking – Fleet is 15 ft x 4ft - and both are made from the same pile of
plywood and can carry similar loads. But from there the similarity ends. Flint is sweet as a rowing boat,
close-winded and fast under sail, and cruises nicely with a two horse-power
motor throttled back to the point where noise is not intrusive – under such
outboard power she sits in proper trim at about 5.5 knots (6.3 mph).
Late last
year my boating friend, Ian Hamilton, and I had a wonderful opportunity to
carry out a series of tests, comparing the speed and behaviour of a Flint and a Fleet while using a range of motor sizes on both boats. The
conditions were perfect, and because there were two of us, we were able to
photograph and video the action, as well as recording the GPS-derived results
in a note book. What a tough job – but I guess that someone has to spend a
couple of days on the water playing with boats in the interests of science…
Although we tried a
range of engines, I’m only going to discuss in detail the results from the two
engines which I consider to be a good match – in efficiency and utility – for each
of the designs. These engines were a 2hp Honda four-stroke; a 4hp Suzuki
four-stroke; and an old 4hp
Yamaha two-stroke. Fleet has a
planing hull appropriate for higher speed operation, and Flint has a displacement hull as is appropriate for her row/sailing
hull-form.
The reason
that I was particularly interested in discovering the performance
characteristics of Fleet with a 4hp
motor, was because that is the size of motor I had in mind at the time of
drawing the boat – but it was one size I had no performance reports about. One
of the reasons for my curiosity is that 4hp/2.9kW is the maximum size motor one
can use in my State without having to register the boat.
Engine
Flint – one adult
Flint – two adults
Fleet – one adult
Fleet – two adults
2 hp Honda BF2
6.8 kts/7.8 mph
6.2 kts/7.1 mph
7.9 kts/9.1 mph
7.1 kts/8.2 mph
4 hp Yamaha 2-st
9.7 kts/11.2 mph
8.3 kts/9.4 mph
11.2 kts/12.9 mph
9.9 kts/11.4 mph
9.8 hp Tohatsu 2-st
-
-
21.3 kts/24.5 mph
18.5 kts/21.3 mph
The speed data shown in the table is exciting to me,
because it demonstrates just how efficient a lean, light-weight outboard
utility can be, and how the law of diminishing returns works in reverse when
the size and weight of power plant is reduced.
A spin-off which came from our testing is that we had
two boats of the same length, breadth, and weight, being powered by identical
engines, with the only significant difference being the bottom shapes from
amidships aft to the stern. This allowed a photographic comparison of the
longitudinal trim of the displacement and planing hulls under power.
Fleet above and Flint below
The drawing above shows the profile view of both hulls. Length, breadth
and depth are just about the same, but the bottom shape from the midsection aft
indicates major variations in performance.
Fleet at 8.5 knots (9.8 mph)
Above - Fleet running under the urge of
a 4hp Suzuki four-stroke, making 8.5 knots (9.8 mph) at part-throttle – the
engine being new and still in the early stages of the running-in process. Trim
is good, but in a small boat like this, crew placement is critical.
Fleet at 8.5 knots (9.8 mph)
Above - another shot of Fleet running at 8.5 knots (9.8 mph). In
both photos the boat is running cleanly, and is probably consuming around
2.5hp. Not much energy being wasted making spray.
Fleet running at 9.8 knots (11.3 mph)
In the photo above, I'm at the tiller of an old 4hp Yamaha which is pushing Fleet at a GPS-measured 9.8 knots (11.3 mph). The boat is carrying two men weighing a total of 171 kg (376 lbs) plus anchor, chain and a few gallons of drinking water. You can see just how clean and flat the wake is, and I find it amazing that the boat is doing this on 4 horse-power. Now things changed! We put the exact same motor on Flint to see what would happen with a displacement hull. Most people would not think a 4hp engine to be excessive power, but read on...
Flint being pushed by an old 4hp Yamaha
Here we
see Flint being also being driven by
a 4hp motor – in this case an old Yamaha. Note the completely different
fore-and-aft trim, caused not by crew placement, but by hydrodynamics. A
substantial amount of the engine’s power is being converted into spray and
wave-making. This is borne out when you look at my speed and power tabulation -
Fleet is fully 1.5 knots (1.7 mph)
faster than Flint with the exact same
engine and the same skipper – a 15.5% difference.
Another shot of Flint
displaying what happens when a hull optimised for displacement speeds is
provided with more power than she requires. If you look carefully at the angle
the aft gunwale makes with the water and then refer to my profile drawings, it
is easy to deduce that even though the bow is cocked high in the air, the aft
bottom of the boat is nearly parallel with the water’s surface.
Although Flint looked most inelegant when pushed
by a 4hp motor with an open throttle, she should not be written-off as a
power-boat.
Flint at 5.5 knots (6.3 mph) powered by a Honda 2 hp BF-2 at reduced throttle
Here she is looking efficient and capable, running at
5.5 knots (6.3 mph) pushed by an eighteen-year-old Honda 2hp air-cooled
four-stroke. The engine is throttled well back to a comfortablelevel of sound and
vibration, and the boat is running sweetly. I am not a powerboat person
by inclination, but there is great pleasure to be gained by running along
quietly like this, and you can cover a surprising distance in a short time –
all on a cupful of fuel.
Flint at 6.8 knots (7.8 mph) - 2 hp Honda at full-throttle
But even with the 2 hp motor, the boat starts to look
out-of-place when all two of those horses are let loose, getting the boat up to
6.8 knots (7.8 mph). One-and-a-half miles per hour faster than before, but the
pleasure has gone out of the experience – noisy and lacking the slicing motion.
Flint looking purposeful and dignified under sail.....
....and nestled into her surroundings under the gentle power of oars.
So what are the lessons illustrated by this
interesting little series of experiments?
·Two boats of similar proportions, weight
and displacement, but with differing bottom shape in profile, will operate in
vastly different ways when pushed beyond displacement speeds;
·It is folly to use a motor which is larger
than recommended by the designer, if your boat has a displacement hull (unless
she is a tug);
·A long, lean planning hull can be
extraordinarily efficient when driven by a motor which is unusually small by
current power-boat standards. Even a confirmed sailboat person such as myself
can derive lots of satisfaction from the effortless speed, economy, and low
noise-level of such a boat. A gentle way of covering distance in a short time,
without conspicuous consumption;
·Theory is wonderful, but gaining proof
through gently controlled experimentation is a powerful way to demonstrate
results.
The two boats – similar size and weight, but very
different performance.
