Dashew's Unsailboat
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Long-distance sailing aficionados are familiar with
the names of Steve and Linda Dashew. The
couple has sailed around the world several times
and over the last several decades developed a
series of long, slender sailboats that define
performance at sea. Their most recent sailboat,
Beowulf, is a 78-foot speedster that can surf at 25 knots
when running in seas with a full press of its 6,000
square feet of sail area. No
strangers to passagemaking
on the edge, the
Dashews seek adventure
in vessels noted for
comfort, safety and speed.
I’ve been bugging Steve
about doing a powerboat
for years, as I knew it was
only a matter of time
before he and his wife
made the decision to
move into the trawler
lifestyle. As a generation
of sailors ponder the
reality of aging backs and
muscles, the desire for
quality grandchildren time
and a growing acceptance
of comfort and its
systems, we’re seeing
more and more sailors
make the switch, however
reluctantly. And in the
case of Steve Dashew, it is
very reluctantly.
As a boat designer who
spends much of his time
thinking outside the box,
Steve is fascinated by
efficiency, design and
speed. Sailboats that come
from his mind routinely
cross the world’s oceans on speedy passages and
gunkhole among the world’s best cruising grounds
without compromise. High-end vessels with
enormous speed potential and extended range under
power or sail, Dashew’s boats are long and lean, and
he considers them ideal for the experienced couple.
I spent some time with Steve and Linda in the
mountains of Arizona and got the latest update on
their newest project, an aluminum ocean motorboat
of major proportions. Now under construction in New Zealand, it is expected to splash sometime in
2005. And it is as different from a traditional trawler
as the Dashew sailboats are from a traditional gaffrigged
Tahiti ketch. It’s going to turn some heads,
that’s for sure.
The new boat, which Dashew calls his “unsailboat,”
is big for a two-person boat, with an overall length of
83 feet and waterline length of 81 feet. The boat
draws five feet. With a
displacement of between
75,000 and 105,000
pounds, depending on
load, the displacement-tolength
ratio is between just
65 and 75.
DESIGN
REQUIREMENTS
With more than 2,000
hours invested in the
creative design process
prior to developing
working drawings, Steve
explained that his
important requirements
were specific. “My design
targets were three-fold,”
Steve said. “First is heavyweather
capability; that is
the most important.
“Second is comfort at
sea in heavy weather.
The third is getting there
quickly. A distant fourth
is what it looks like and
living at the dock.”
This boat is to be their
own personal boat, not a
prototype of another line
of custom yachts. At this
stage in their lives, there
are simply too many other things to occupy their
time, with grandchildren on both coasts and Steve’s
passion for long distance soaring in a glider.
The Dashews have a huge database of calculations
and technical information gathered over the years of
building high-performance sailboats, and he figures it
should help even more on his new powerboat.
The slender shape of this vessel is important for
his ultimate two-person passagemaker. The fact that
the boat is 83 feet long doesn’t faze Dashew at all.
“I can’t get the hull shape
I want for going uphill in a
shorter boat. You need a long,
skinny boat.
“You have to balance what’s
happening in the bow with
what’s happening in the stern.
I want the bow to slice into a
wave a certain distance before
it starts to lift, but still have
enough buoyancy to lift the
bow in a really big wave.
“At the same time, if the
stern is too wide and too
buoyant, the passing wave
will lift the stern, which
pushes the bow down. So we
keep the ends fine.”
The boat has great
longitudinal stability due to
her length, so he can afford to
sharpen the ends and reduce
reserve buoyancy to improve
pitch resistance.
Interestingly, the long hull
does not translate into
maximum accommodations,
rather maximum comfort at
sea. The forward 17 feet of the
boat is an empty chamber,
providing reserve buoyancy.
The stern 18 feet is reserved
for the boat’s engine room.
This keeps interior living
spaces centered in the hull,
with all accommodations just
a few feet from the pitch center of the boat.
This central location translates into minimal
acceleration and deceleration and motion, even in
heavy weather. It is essentially a 50-footer’s interior
inside an 83-foot hull. No one will have to work or
sleep more than 10 feet from the center of the boat.
The designed roll period of 4–4.5 seconds is faster
than in traditional trawlers, but shorter duration
because the accommodations are closer to the pitch
moment.
Unlike massive expedition trawlers that derive
comfort from mass, the new Dashew boat takes an
opposite tack, a displacement boat that handles
rough weather through hull shape. Dashew’s goal is
to maintain 10 knots going uphill into 20–25 knots of wind with good control,
with enough range to go
anywhere in the world.
Another design goal was
the ability to avoid a capsize.
Steve’s research on similarshaped
sailboats has led him
to believe he could build in
self-righting capability, while
designing a hull that avoids
capsize in the first place. The
relatively short keel will allow
the boat to slip sideways in
beam seas as the hull heels up
to 40–45 degrees, dissipating
the wave energy and
recovering before another
wave hits the boat. The shape
of the hull adds tremendous
buoyancy as the boat heels,
going from a waterline beam
of 13 feet to almost 18 feet at
deck level. And the resistance
of the underbody to beam
seas is minimal.
To reduce rolling, Dashew
worked with engineers at
Naiad and the boat’s fin
stabilizers each measure
12 square feet. Normal
conditions would dictate fins
of only 9 square feet, but
Dashew wants them to be as
effective in the rare instances
when he slows down to
7 knots in really horrible
conditions. Again, he is designing for bad weather,
not the majority of the time in ideal conditions.
But his emphasis on heavy-weather capability
adds to comfort levels in all major areas of the boat.
To provide additional stability when traveling light
on fuel, he has incorporated 1,700 gallons of water
tankage, which can be filled with either fresh or
saltwater to further lower the center of gravity in
bad weather. The resulting motion would be
uncomfortable, for sure, but safety is more
important. Dashew has spent an enormous time
thinking through every scenario and is confident the
boat will handle the most difficult conditions.
The boat carries 3,600 gallons of fuel and at 10
knots should make 10,000 nautical miles. The boat will have two diesel engines, each a John
Deere 4054TFM rated at 150 hp.
NO ROOM FOR SURPRISES
In an office filled with technology and
sophisticated computer software, such as Fast
Ship, Rhino, Autocad and Swift Craft, Dashew
developed prediction models of various sea
conditions and knows, for example, that at
12 knots in calm sea conditions, the bow will
come up just 0.6 degrees.
Another benefit of the long hull and low
house is that he can be even more conservative
in specifying classification for use in all
oceans, something that would not be
practical in a conventional trawler. A 4-foot
structural member of the deckhouse, for
example, might need to be made really beefy
and robust, where in a more traditional
trawler that same member might be 9 feet long. If it
was built to the same “all ocean” requirement, that
structure and others might be so heavy and
unwieldly that the resulting boat would be so heavy
as to not be practical to build or operate.
The long engine room has standing headroom
and the saloon is the length of the house, 22 feet
long by 14.5 feet wide, with 6' 6" headroom. The
owner’s cabin is 20 feet long and features a walk-in
closet. Under the saloon are six fuel tanks, over top
of which is a 39-inch high space for bulk storage of
provisions, freezers and other gear. Between that
virtual basement and the massive walk-in closet, the Dashews won’t need to build in lots of cabinets and
lockers and can leave most living spaces open.
The boat is under construction in New Zealand
at Circa Marine in Whangarei, through aluminum
fabrication. Kelly Archer Boat Builders in Auckland
will finish the interior woodwork and systems.
The choice of aluminum and double bottom construction
is no minor preference choice, as Steve is
well aware that over 10,000 shipping containers are
lost off merchant ships each year, and grows yearly.
These represent a serious risk to the modern
cruising boat.
Like I said, he’s thought of everything.
STAY TUNED
I think this is an exciting project and certainly
promises a different direction in passagemaking
design. When I get free long enough to entertain
thoughts on my own future passagemaker, visions
of the South Pacific dance in my mind. And when
that comes to pass, I know I’ll be looking for a
boat as safe and comfortable as the unsailboat
design penned by Steve Dashew.
It will be some time before the boat is completed
but time does fly. Speaking of which, Steve is
waiting patiently through the construction by
flying his glider to longer and higher personal
records.
We’ll stay in touch during the project and bring
you an update when she progresses further along
in New Zealand. Hopefully by then he’ll have
come up with a name for his new creation.
It will be well worth the wait.
Concept Notes by Steve Dashew
DESIGN REQUIREMENTS
• Be at least as comfortable as
our sailing designs for long
ocean voyages.
• Capable of making 4,000- to
6,000-nautical mile passages at
reasonable speeds.
• Ability to make fast passages
uphill, against wind and waves,
with tolerable comfort levels.
• Heavy-weather capability at
least equal to our sailing
designs, but with less work
required from the crew.
• Put to bed for long-term
storage in a half-day (wake up
from long-term storage in same
time).
• Minimal maintenance,
maximum reliability.
• Operation by a crew of one
or two.
OUR PHILOSOPHY
In the past 30-plus years we’ve
sailed more than 250,000 miles.
The majority of this has been in
our own designs. We go to sea
because we love the cruising
lifestyle and crossing oceans.
We’ve found that truly dangerous
weather is a rarity. In all of our
offshore miles, we’ve only been
exposed to dangerous weather for
maybe 72 hours total. And the
majority of this exposure took
place in the “olden days” before
weather faxes, satellite images
and routers.
For us the bottom line in
making the ocean-crossing
experience enjoyable is being
mentally comfortable. This means
knowing that the vessel we are on
can deal with virtually anything
encountered—from heavy weather
to floating logs. Adding physical
comfort to the equation allows us to enjoy the serenity that comes
with long ocean passages.
Every aspect of this new design
is based on this philosophy. We
want to be able to make long
passages in comfort and safety.
Our sailing designs are easily
steered by their autopilots at high
speed down wind, running and in
quartering seas. The combination
of hull, rudder and keel factors
that allow this capability in our
sailboats are present in this
power design. Many years ago
we learned how to take
broaching out of the downwind
equation. In fact, designs like
Sundeer and Beowulf are
comfortably handled by their
autopilots surfing at speeds over
25 knots. We expect this design to
be able to maintain a comfortable,
normal turn of speed in brisk
quartering trade winds.
I know that at least a quarter of
the time this boat will be heading
upwind, against prevailing wind
and seas. This will take place in
16 to 30 knots of wind and seas
of 4 to 12 feet. To have maximum
flexibility in voyaging, one must
be able to make good progress
upwind, keeping the crew happy
in the process.
Uphill comfort comes down to
three factors: how volume is
distributed throughout the hull,
particularly above the waterline;
how the weight of the boat is
distributed throughout the boat,
and the speed of the boat relative
to wave shape and period. There
is a careful balance that must be
struck between a fine bow shape,
able to penetrate into seas with
little apparent motion, and one
with enough volume to lift as the
waves become larger and/or steeper. This volumetric
relationship is confirmed with
CFD (computational fluid
dynamics) analysis.
The final comfort issue is
transverse (beam) seas. The
design is inherently stable at
speed. For example, with no
stabilization system, CFD analysis
indicates an average roll in a
beam sea state five, of plus or
minus 4.9 degrees. With active
stabilizers turned on we expect
little discernable motion.
The aft deck has 21 feet of
storage space for dinghies, easily
launched or retrieved using prerigged
boat booms.
HEAVY WEATHER CONSIDERATIONS
The best way to avoid
problems is to stay out of heavy
weather in the first place. A
premium is placed on good
routing and boat speed. A vessel
capable of 275 to 300 miles a day
has significantly more flexibility in
regard to weather options than
one cruising 180 to 220 miles
per day.
Once heavy weather is
encountered steering control
becomes the key ingredient. This
is true whether running with the
storm or heading into the waves.
The main risk is from
knockdowns or capsizes induced
by breaking waves. Our
approach is to design the hull
and fins in such a way that they
tend to slip sideways once a
certain angle of heel has been
reached. Slipping allows the hull
to move with the breaking wave
crest, dissipating wave energy
over time and reducing the
tendency for the hull to roll over.
The alternative with deep heavy designs is to sit in place like a
breakwater. In this case all of the
wave’s power is converted into
rolling motion which can lead to
a capsize.
The other issue is to have
plenty of range of positive
stability so the boat can recover
quickly. The limit of positive
stability (LPS) is a function of
several design factors, such as hull
and topside shape, distribution of
volume in structure above the
deck, and center of gravity. Most
of these are fixed. However, the
amount of liquids on board and
where they are placed has a big
impact on how the boat will react
in a rollover situation.
In our worst-case offshore
configuration (in terms of liquids)
LPS should be at least 120 to
125 degrees—about the same as
one of our larger sailing designs.
However, if this vessel is
configured for heavy weather,
with fuel tanks filled (or fresh
water tanks filled when fuel tanks
are at 40 percent), LPS can go to
160 degrees or more.
It is usually when something
goes wrong with the boat in
heavy weather that events begin
to cascade out of control. A
majority of risk can be eliminated
with good systems design and
installation. Even more can be
eliminated with proper maintenance.
But we still have to
consider what happens if the
engines are disabled in dangerous
weather.
Should this happen we’ve
designed in the necessary
fairleads and handling gear to
deal with a parachute anchor
off the bow, and a Jordan Series
Drogue, or Galerider off the
stern. The “breakwater” across
the aft deck is designed for use
with the latter, so that the dinghies and aft end of the house
are not totally open to boarding
seas.
Finally, it is possible to make
the boat totally watertight. All
dorade vents have internally
closable seals. Engine-room vents
are designed to be watertight
with the boat inverted. And the
aft, starboard cabin will be set up
so that if we are in one of the two
bunks, and the boat is knocked
down or rolled, our bodies are
constrained in a small area.
DESIGN DETAILS
We used the considerable
database of our recent sailing
designs, which exhibit excellent
powering capabilities. Our 67-foot
Sundeer and 78-foot Beowulf are
the closest in hull configuration.
Beowulf has better than a 2000-
mile range at 11 knots. Both
boats have exhibited excellent
powering capabilities into steep
head seas.
Removal of the rig and the
requirement for hull form stability
to offset the power of the sails
opens a number of areas for
improvement in hull efficiency
and comfort.
We tested different configurations
to find a combination of
comfort and sea-keeping abilities
that best met our requirements.
Open-ocean conditions up to sea
state seven, significant wave
heights of 24.3 feet with
occasional waves of 31 feet, and
up to 40.7 feet, were run. The
runs were done at speeds from
6 to 11 knots heading into the
waves, quartering the waves and
running before them. Other runs
were done at various speeds and
headings, with waves in the sea
state 4, 5 and 6 ranges.
Tank testing confirmed our
predicted drag figures, as well as variations based on changing
the center of buoyancy and
different levels of bow and stern
immersion. We were pleased to
find that the drag data from
Oceanic Consulting agreed
closely with our in-house drag
analysis.
For this project we are using
the Lloyds Special Service Class
rule, All Oceans Rating. The rule
defines the plating and framing
requirements throughout the
boat. Part of the rule input is boat
speed, wave size and G-loading.
We are framing and plating to
much higher factors of safety than
the SSC requires—in some cases
to twice the stiffness the rule
looks for.
We take this approach for two
reasons. First, we want the
ability to beat into difficult
conditions at high speed and not
worry about the boat. Second,
we are more concerned with the
risk from flotsam than we are
from waves.
As is standard on our
aluminum structures, this design
has a double bottom, forming
fuel and water tanks along with
a series of watertight bulkheads.
The systems on board also will
follow the philosophy we’ve
refined over the years with our
sailing designs. We expect to be
able to sit at anchor for a week
without resorting to auxiliary
power generation. Electrical
power will be supplied by 3,000
pounds of traction batteries. A
pair of 4kW Electrodyne DC
alternators, one on each engine,
will charge the batteries while
under way.
There is an 8kW genset
aboard, but this will be used
primarily for air conditioning and
for days when the clothes dryer
is used.
Reprinted with permission. Copyright 2003 © Dominion Enterprises (888.487.2953) www.passagemaker.com
You are reading the text-only copy of this article. To access the article as it appeared in PassageMaker Magazine, please log in to purchase and download the PDF version of this article.