PHILOSOPHY Ketchup is a
23 ft-7.0m trailerable Catamaran/Tunnel-hull, suitable for home-building from readily
available plantation plywood. She offers a practical blend of performance, stability and
accommodation for a small group or family. While attractive, fast & fun, this boat has
been designed primarily to be simple to build. To this end there is maximal use of right
angles with minimal cutting & no torturing of ply.
Ketchup has been designed for
Australian conditions. As these include cruising everything from placid inland lakes to
fighting the sudden squalls and steep-pitched waves of the South-East Coast, she would be
an able coastal cruiser anywhere in the world. Ketchup is not intended for major Ocean
crossings, but because of her speed potentiaI she would be happy Island-hopping in
DESIGN & STRUCTURAL DETAIL
Ketchup is an asymmetric catamaran,
maximizing the keel to keel "track" while staying within the 2.50m (8'
2.5") legal trailerable limit. The 8' track is the same as that of a conventional cat
11' wide. The outside of the hulls are vertical and a straight line from bow to stern,
meaning that sections are fitted into a right angle between the hull and the bridgedeck.
The 10 station frames start with a quarter circle at the stern(stn 10), with the radius of
curvature increasing exponentially forward until by the front of the bridgedeck(stn 3) the
arc has become a straight line at 45deg.(see Drawing 04, 'HULL SECTIONS') This angle is
held through to the bow. This gives her a fine entry with load carrying ability increasing
aft. All arcs are 4' - the width of a plysheet. This shape also builds in 3.5" of
rocker, though this isn't visible in profile because the side/keel piece is left
protruding to its full 4 ft width. This provides a mini keel running 16 feet from 2"
depth @ station #3 to 5.5" @ the stern(#10), giving a little more bite to windward
without even using the daggerboards. It should be remembered that the straight outer hulls
also resist lee drift a lot more than conventional hull shapes, a feature employed to
great effect in the early Pacific Proas.
Frames start at width (&height) 30.5" at the transom
(station10 @ 23ft, bow=datum) and increase to 34" at station 3. Increments are half
Station spacing is 28inches with 2ft
left between 9 & 10.( A supplementary station should be added @ 1' 0", between
datum & station 1),Hull width is increased 32mm to account for the keel piece, which
is made of laminated ply or hardwood, to form an on-edge plank 200mm wide. It is shaped
right up to the bow, protruding an inch or so beyond to allow for beveling off. Below the
waterline it extends half an inch below the sides..it is not shaped but has a 50mm
aluminum or brass strip screwed to it to take the bottom for grounding, beaching,
transport etc. (Note that the fact that the rocker is hidden within the boats sides means
that it will sit firmly and level along its two 16ft side/keels, and means it can be
transported on a flatbed trailer, truck, railway wagon or ship's deck. It would even be
possible to build a detachable axle to these keels making the boat its own temporary
Battens are run along the inside
surface of the keel plank & the underside of b'deck to hold the inside sheathing ply
curve while epoxy sets. The deck is adequately supported as the tunnel "ceiling"
is 2' 6'' Max width. Joins are strengthened with strips of glass before a final
complete layer of glass, epoxy then paint is applied across the sides, bottom/tunnel & outboard pod. Painting
should include Awlgrip or equivalent on the tunnel "ceiling".
Requires no strongbacks or jigs, but simply a flat area, a few sawhorses and the sort
of tools most households already have. Necessary tools are a power hand drill, jigsaw,
sander, power saw & a dozen or more clamps. In harsh climates much of the boat can be
cut out and finished in a spare room, then outdoor assembled in a few days. The heart of
the boat is the 16' x 8' Bridgedeck made from 8 standard 9mm sheets of ply in two layers
(one laid athwartships, one bow to stern) edge glued with longitudinal stringers under and
crossways stringers on the ends of the deck. Ply bulkheads(12mm) are then stapled &
epoxied to the underside of the b'deck -some are missed out or cut out depending on the
accom plan decided upon,. Those staying are epoxy-filleted in.
Each hull side takes 3 standard 9mm sheets, with 150mm scarf joins reducing the total
length to the desired 23ft. Keel pieces (32mm Hardwood or Layers of ply for taking the
bottom) are fitted to the inside lower edge of each flat outer side panel before attaching
to the bridgedeck & bulkheads. Where the frames are removed for berth/stowage
purposes, the floors put in place adequately compensate, especially as the entire hull
structure is made from ply 50% thicker than that used in many similarly sized production
Sheathing is simple as the only cutting required is in the front sheet. Before bending
this first sheet out to meet the sides, fit the front plywood "box beam" to
prevent bending the keel outwards and giving your cat a disastrous splay-footed look! This
beam provides emergency flotation (about 160lbs!), supports the front positioning
block/clamp which takes the removable wood or alloytube bowsprit/prodder, and lastly
supports the front net. This mesh is a great place to get a cooling splash on hot days,
and makes a comfy hammock & even bed unless there be ferocious mosquitoes! The twin
foredecks have generous overhangs to prevent pitch-poling...these are drilled as fixing
points to lash on the net.
Fitting the inside-of-hull ply cladding should, if possible, be left until the cuddy
accommodation plan has been decided upon, as bunk floors & storage areas need to be
installed, involving alteration/removal of some bulkheads.
Also flotation bags & tankage are now installed, & if required, access holes in
b'deck positioned and cut, head partition installed etc. etc. All this can be done after
turning the hull, its just more difficult! It may be covenant to build the boat over two
winters...in this case all these decisions could be left & the boat sealed up &
sailed as a large (and fast!) beach cat for the intervening summer season.
Flotation bags are air-filled 4 litre wine casks in all flotation cells. Even if a
compartment is holed it will take little water...to prevent the casks popping out of a
holed hull section they are encased in old fishing net...see your local trawler fleet!
Cuddy: Best use of this is 2 permanent
berths, a fold-up eat/cook/navigation table with seating for 3, and a dedicated head with
separate entrance & ventilation. The cook sits on the boat centerline at b'deck level,
with feet in the port hull under the table & probably resting comfortably on the
auxiliary quarter berth which extends under the cockpit! (This berth is only available if
the table is folded up against the side window). The cook and/or diner(s) use the head
wall as a padded backrest. Most cooking will be done by placing the camp stove(metho
2-burner -no gas bottle hassle) on the "cook box", under the boom tent. But
under way one needs to cook out of the weather and spray. A large flat-bottomed stainless
steel bowl is the sink - sea water can be heated for wash-up/showers directly over the
stove. A SS bucket is used for retrieving sea water.Flexible fresh water tank is in the
bilge below the Q-berth....hand pump mounted on the rear cuddy wall.
The Navigation table is a flat oblong box with a hinged lid which can be temporarily
set at any angle. It can be used anywhere on the boat. Within are charts, drawing gear,
torch, GPS, ship's log,. It slides into a rack on the inside of the rear cuddy wall. From
this position the map taped to its top is flush against the porthole in the rear cuddy
wall, & thus the helmsman can refer to it from the cockpit.
Windows indicated in drawings are in fact tinted perspex covers across two non-opening
portholes each side. This ensures that there are no leaks. The portholes siting and size
are optional - the important thing is to preserve as much "meat" as possible in
the cabin sides to retain the integrity of the monocoque structure. If ventilation thru
hatch/doorway proves in adequate a rear-facing "Dorade" vent can be installed in
the foredeck of either or both hulls.
Berths: Two arrangements possible:
(1) For max sitting headroom, two single berths are placed forward in the hulls, with
their foot extending under the foredeck.
(2) For couples a double berth across the beam is more suitable..this is structurally
stronger than (1) , and frees up massive storage forr'd in the hulls, but at the cost of
headroom above the bunk, which must be at bridgedeck level. This berth forms an excellent
3rd seat forward of the table. Headroom problem can be alleviated a little by a stargazer
hatch above the bed-head, though foredeck access is best achieved via the foot-wide side
Heads: 3' x 3' 6" Shower has nearly 5' HR -the head is forrd to give max
HR over the shower. Shower choices are to sit on a low bench or use a hatch swinging up
with a rose attached under its highest point. This connects to a hand pump on the wall via
hose, another hose from the pump is plunged into the water bucket sitting on the floor or
toilet, wherever it fits. Boiling a jug on the stove then mixing with sea water is enough
to give a nice hot shower. A camp shower (canvas water bag + rose) would also work well
from under this hatch (also from the boarding step, hanging the camp shower from the wing)
Head/shower floor is high enough above the sea to self-drain via a bung.
There is room for a toilet holding tank low in the hulls. Porta potty/bucket &
chuckit are options depending on local laws. (A simple hole in the bridgedeck level is
tempting as activity is hidden between the hulls! )
DECK, COCKPIT & BOOM TENT
General: The cockpit is 8' x 6' 3", and is great for sleeping, eating and
general socializing. Rear of the cockpit a bench seating 4 extends the width of the yacht.
A large hinged table splits the seating; under this is the nacelle holding the elec.
outboard. Over the table is the tiller, controlling a large kick-up rudder. This is fixed
to the 12mm ply seatback-transom. The port seat back is free from the other seats, and
hinged at deck level. When the seat-back panel is unclipped & swung back thru 180 deg.
the underseat becomes an access step between the bridgedeck & the rear boarding step.
Heaps of storage is available in the starboard hull(& port if Q-berth not used). below
the cockpit...hinged "lids" can be 45deg. bevel-cut as access. There would even
be room to slide a slightly deflated RIB in from a door in the transom-cum-seatback,
launching it off the rear boarding step.(NB -an 8ft RIB could be carried from the wing).
It would also be possible to hinge the entire backrest & drop it into the water as a
Boom tent: This waterproof canvas tent is stored in the huge locker accessed
by lifting the hinged front half of the rear wing top. The tent needs no special poles. It
extends over the boom (raised 18") & lowered mainsail, and is laced each side of
the boat thru a row of small holes in the daggerboard which form the boom tent-cum-cabin
walls. Either end the tent is cut to slope into the cuddy roof and rear wing...it can be
fixed to a row of domes along the back of the wing, meaning the storage box remains
indoors & useful. Windows are provided by the daggerboard handles! (see Dwg # 01). In certain warm climes it may behoove one to
frantically deploy the mossie net before and underneath the tent to avoid the crew being
eaten. This alone (quite apart from all your eating irons, tools & spare chain winding
up on the seabed) is a sound reason to forget slatted decks.
Side-decks : These are 12mm ply, a full foot wide ,& may be
lowered in two sections when sailing. They are supported by chains from the cabin-top
& wing. When stored for towing they fold up against the boat side below the window
(front section) and become a cockpit coaming (rear section). If racing the rear section
may be used for hiking out on a trapeze. Both are coated with grip-paint (as are all
bridgedeck/cabintop surfaces) Side decks are further supported by hinged triangular braces
which flip out & lock from flush with the outer hull sides. When side-decks are in
place a 3-ft by 1in wide leather-lined slot cut out of the inner side-deck edge guides
& constrains the......
Daggerboards: these slide down flush against the hull sides...the
other fixing point is just below the waterline - a wooden rung which will serve as an
anchor point for inflatables/dinghies/visitors, and is handy for swimmers . The front rung
support is streamlined, while the rear support is built light so the daggerboard will
blast out the back without compromising the hull should the board strike a submerged
object (such as the bottom!). Note that this is made possible by the side-deck slot being
a foot over-width - this last foot can be filled with lightly glued-in polystyrene foam or
other crushable material. Boards have a top lip (outer side only) of ply to prevent them
At anchor the boards are used as solid boom-tent sides. They lock into position exactly
above the raised side-decks and between the angled sections of cuddy sides & wing side
support (see dwg # 01). Holes in board sides are for lacing
tent roof. The boards are fashioned from epoxy-saturated 18mm ply, tapered to leading and
trailing edges, but shaped on the outer face only. A cut-out serves as both daggerboard
handle and tent side window in its dual roles.
SCHOONER/ KETCH-CUTTER RIG & SAIL PLAN as Ketch-Cutter. (But could also be classed as a Schooner)
Foremast 21' with ft2 fully battened square-topped loose-footed Foresail, with see-thru
37 ft2 Jib/staysail on three-quarter
forestay with bridle to bows and furler above this.
107 ft2 Masthead semi-Genoa (extends 1ft
behind mast) on furler. Attached to demountable 11ft prodder clamped into seats on front
beam & foredeck forr'd of mast. This sail is not necessary, but it or an asymmetric
spinnaker would be great in light airs.
For downwind racing the 2 jibs can be replaced by an
asymmetric spinnaker of 285 ft2 (490ft2 tot)
Full spinnaker seems futile as the two mains running wing
& wing downwind would rob it.
Twin backstays clip to chainplates ss-bolted thru outer hull
sides with 12mm ply backboards.
Mainmast 23' (constant diameter) carries ft2 fully battened square-topped main with 8' boom doubling as tent
Twin backstays run to eyes bolted thru the bridgedeck (again
mountings strengthened by ply backing plates).
All stays on the boat have spring-loaded clip-ons, and screw adjusters are
replaced by tensioned springs.
Both masts are aluminum sections with sail -track and halyard pulley built in
below welded-on mast-head containers each housing a standard automotive airbag pack. (See
Masts are stepped in tabernacles comprising a 2ft alloy pipe with diagonal braces to
deck plus an upper leather-lined collar clamp braced to the cabin roof. Beneath the pipe
an equivalent diam.hole is cut in the bridgedeck...a hardwood block or alloy pin prevents
the mast falling thru the deck (more on this below)
Anti-Capsize Features: The boat is unlikely to go past 90 deg as when the
mastheads strike the water they set off masthead air-bags (pinched from automobile
technology). The bags are packed into a special aluminum masthead containers welded above
and independent of the halyard pulley. They are identical to the car version except they
remain inflated once triggered. Two low aspect mainsails instead of one (high-aspect in
most cats) produces a lower Centre of Effort (Encircled "x" in Sail Plan -Dwg # 01) 260lbs of batteries low in each hull will be
extremely effective ballast. These would be removable for racing.
Recovery: Beneath the tube holding the mainmast foot is a hole in the
bridgedeck large enough to push the mast thru. Standing on the deck side (1ft wide), (prob
up to your knees in water), drop the main & loosen the mast clamps. Pass the main
right thru the boat till the air-bag container stops you. Tighten the tabernacle clamp
just below the air-bag housing (large wing nuts with welded on extensions) and get the
crew swinging on the wrong-way mast plus dagger boards. As a last resort you could tie a
few batteries on the end of the main, but they are pretty helpful where they are. Dropping
all other sails would help. The foremast could be freed to float about on its airbag at
the end of a line. The really serious type could fix pipes into the angled sections of the
cabin side and wing for someone to swing on! The spar from the cabin would make a great
hand-hold while leaping up & down on the slippery daggerboard.
Storms: If caught out and in trouble with windage in the bare rig the main
mast could be dropped through the cockpit deck to act as a bizarre 18-foot keel.
Single large spade rudder mounted on the transom-cum-seat back. Kicks up for beaching.
SOL-Z electric outboard acts as an emergency rudder(it is designed for this) Also rudder
control may be linked to the motor. Anchor and drogue can be carried one each hull in the
compartment between stations 1 & 2. There is adequate room for chains & warps.
Deployment is via a pulley in the centre of the triangular box forebeam. No winches are
needed as no sail is over 10 sq. meters. The usual 2:1 or 4:1 sheeting as used on beach
cats is adequate. All sail lines are led back thru blocks to the centre rear of the cuddy
roof. Rope ends disappear into a large canvas bag between the doors.The mainsheet is left
aft with the helmsman, who can cleat it off or use it for more effective sailing. The main
is also controlled by a vang plus an 8' radius curved traveler to the rear of the flat top
surface of the wing.
The SOL-Z 8hp electric outboard was chosen for:
- Efficiency (as much thrust as a 15hp conventional internal
- Running cost. Twenty percent of diesel inboard or petrol
- Environmental reasons (zero emissions + very quiet -this has
a huge effect on fish/bird sightings).
- Size, shape, design. It is small (easily built into a pod)
and light (28k), Best of all the long shaft is blade shaped it not only steers well it
would make a fine back-up rudder.
- Practicality. Most marinas have shore power.
- Also batteries can be charged by wind, solar power (try
cells on cuddy& wing) or towing a prop unit (I've ruled out petrol generators as they
defeat the Principle!)
SOL-Z make even more compact inboard/saildrive units but
they are unsuitable for beaching.
The SOL-Z 8hp electric outboard was NOT chosen for the weight of its power source - 4
Lifeline 4D batteries in sealed plastic boxes. However these are small enough to mount low
in the hulls (2 in each) giving 260lbs ballast in each hull. These don't need much
attention but would be accessible from beneath the bunks. Further, a lot of weight in this
yacht would be carried aft. This is countered in part by the hull sections, but final trim
for unusual circumstances can be achieved by mounting the batteries in a long wooden
trough with a clamp each end, and sliding them fore & aft to fine-tune the trim.
Setting up for a weekend cruise, this would be worth the few minutes it takes.
The SOL-Z was NOT chosen for its price! Landed in the USA
it is $3900 plus $840 for batteries(see below), however this does beat $7000 for an
equivalent Diesel. Cheaper electric motors are available, but the SOL-Z has the right
combination of reliability & size for this design. It is manufactured in Switzerland,
so in Europe it should be cheaper than the above quote.
items include foredeck railings, liferings in cockpit and there is plenty of space to
carry a liferaft in the cockpit, on the foredeck, on cuddy roof, or in the starboard hull.
To prevent pitchpoling we have high bows, devoid of storage and sealed off as dedicated
buoyancy areas. The 45 degree hull line plus the 3" overhang of the deck further
discourage plunging. The underside of the forebeam is also angled as the bows to force its
way upwards. The 3/4 staysail provides plenty of lift.
The 4 batteries for the SOL-Z , radio, stereo, Nav lights etc. are seen as a danger.
I've specified Absorbed Glass Matting batteries by Lifeline -these are guaranteed to have
the following qualities: sealed, nonspillable, install in any position, submersible
without damage, maintenance free, 2xnormal life, fast recharge with no voltage limit, deep
cycle, 3% per month unattended discharge, shock & vibration resistant.
For storms a set of reefing tapes is sewn on each main to drop them 40%. The
flexibility of the sail plan is of great help in changeable conditions.
||1500 lbs (2 crew)
||.2220 lbs (2 crew,
batteries &ob -weekender setup...b'deck 23" clear of water)
||3180 lbs (kitchen sink
etc -drops the bridgedeck 3" to 20" clearance )
(increasing each inch)
||33 / 27 (Design WL / Cruise)
|Expected Speed (15k wind)
|Expected Speed (SOL-Z)
||10 kts cruise, 15 max
PS: -a final question:
- Jeff Gilbert
- 9 Birbai Place, Waramanga, ACT 2611 , Australia. Ph (02)6288.9450
- Quals: BSc (applied maths)
Q: The Design Brief stresses simplicity & ease of handling. Yet
Ketchup has up to 4 sails?
A sudden gybe, or badly torn sail is no longer a disaster!
- The sail plan divides the sail area into manageable chunks which need no winches; masts
are easy to rig.
- The centre of effort is low, but more importantly almost identical for the entire plan
& the forward main alone, thus...
- The beginner can sail with foremast alone, the boat will sail the same as with all 4
sails (just more slowly!)
- In sudden changes it is easier to drop a sail than to struggle losing an equivalent area
On the other hand one will never experience the thrill of dropping the only winch