Re-imagining the Family Cruising Catamaran
Most, if not all, sailors who have owned or extensively sailed Atlantic Catamarans with their center cockpit, aft deck house arrangement are so impressed by their ease of handling and incorporated safety features that they never contemplate any other design arrangement.
This certainly was the case when an Atlantic 57 owner with a considerable catamaran background decided that his expanding family and desire to spend full time aboard would require a bigger boat. Mom, dad, six home schooled kids and occasional grandparents definitely had their 57'er bursting at the seams.
Using the newly launched Atlantic 72 "Skylark" as a starting point a new deck house and interior plan was developed to fit the needs of a large cruising family.
What's different?
Borrowing a concept used in the Atlantic 47 MastFoil cats, the deck house was extended sideways to nearly the full beam of the boat. That allows integration of the galley into the deck house without completely dominating the deck house layout. The galley is large by cruising boat standards. With so many mouths to feed a large pantry is integrated so the cook never needs to look far for staple items. A large professional sink system with multiple integrated functions faces a bar top counter for easy serving of snacks and lunches. A dishwasher is adjacent to the sink. On the outboard side is a 5 burner propane stove with oven and tons of deep drawers for storage. Two overhead hatches provide great galley ventilation. And of course a great view out numerous windows.
One of the interesting benefits of this arrangement is that there is a very large volume of hull under the galley floor (and similar on the port side) where nearly all of the machinery can be located. Access to the engine, desalinator, water pumps, water heater, and air conditioning is incredible. Basically it is all in one place where you can stand up to service everything. Consolidating the equipment also saves considerable time in construction and minimizes the need to lead large (and heavy) conduits full of cable and pipes all over the boat.
This is a family operation where dad is the primary operator and maintenance guy. That means systems need to be robust, easy to service, without excess complexity. Hence no gen-set. Two diesel engines is enough, why add a third? With enough solar installed additional generating capacity is not needed. The large deck house is nearly completely covered with "walkable" Solara solar panels. How much output you ask? 5.4 kilowatts! That's enough to run all the normal functions aboard including laundry, a dishwasher, 35 gph desalinator and limited air conditioning plus the usual lights, fans, winches, pumps, etc.
Sleeping Arrangements
There are three large double cabins. The two midships cabins have king size berths with lots of storage in a combination of drawers and hanging lockers. The port forward cabin has a queen size double. All three have adjacent heads with separate shower stalls.
There are three more cabins for kids (or guests) mostly with single berths each with adjacent head. The kids cabins remind me of an officer's cabin on a square rigger. Cozy and comfortable with everything necessary but little more.
There is plenty of room to spread out in the communal spaces plus a dedicated work area for home school.
The dinghy plays an enormous role in the cruising life. When at anchor the dinghy is your link to shore. Getting food, clearing customs, diving, seeing friends for happy hour, exploring the area or whatever, a capable dinghy is an essential part of the equation. Fortunately catamarans have an easy way to carry a substantial dinghy on davits behind the bridge deck. But when someone has "the" dinghy anyone left aboard is stranded, eagerly awaiting for their ride to return. To fix this problem we developed a practical way to carry two dinghies. There is not enough space aft to carry two dinghies bow to stern so we have to stack them one over the other. By extending the upper davits the high dinghy can pass aft of the low dinghy and then retract forward for sailing. The system works well and also provides a back up should one dinghy become non-operational.
Construction
Very light for her length at 43,000 pounds fully loaded the Atlantic 72 slides along on slender hulls with little resistance. Sailing 12 to 14 knots is effortless, stronger winds can generate boat speeds in the 20's. 300 mile days are common. Upwind performance is equal or better to the best monohulls. In light winds the A72 will often sail faster than the wind.
However, none of the above would be possible without careful weight control in design and construction. This is the proverbial "elephant in the room" when it comes to cruising catamarans.
The methods commonly used in factory style boat building trade low labor hours for excess weight. The need to build quickly leads them to use gel coat exterior finishes which incorporate chop strand glass mat, core types that absorb excess resin, in some cases no core, and then the need to build a boat within a boat in order to quickly cover up the inside of the raw hull and deck laminates. Given the enormous surface area in a catamaran even small increases in weight per square foot add up to significant amounts. While published weight figures for most production boats are often wildly inaccurate it would be reasonable to estimate that building an A72 in that context would add something on the order of 15,000 pounds, a 35% increase in weight. That difference alone turns a spectacular sailing machine into a ho-hum plodder.
Hull, decks and bulkheads are all vacuum bagged epoxy/carbon over thermo formed foam core. There are no cracks or gaps in the core which eliminates the possibility of water migrating withing the laminate. Hull, deck and crossbeam laminates are all on the robust side to insure long life. The result is a super stiff structure at very low weight.
Interior cabinetry is built from lightweight foam/glass panels with an AwlGrip painted surface and some varnished trim. Easy to clean and so durable that an interior re-finish might never be required.
Hull Shape
The A72 has a conventional raked stem. This provides more jib area due to the tack being further forward and importantly provides much more buoyancy forward. This is contrary to the fad of "reversed bows". I understand the reverse bow logic in some designs such as the floats of a large racing trimaran where the bow is frequently driven deep through waves but in that case there are no obstructions to 25 kts of water racing aft along the deck save for a well streamlined crossbeam that may be 30 feet aft of the bow. The cruising cats emulating this hull form typically have all manner of obstructions to that high speed water flow; crossbeams with nets and anchors attached, blunt wing deck fairings, vertical deck houses with large windows just to name a few. And these structures are not nearly far enough aft to avoid being violently slammed by water if you stuff the bows. You can make the argument that many of the mainstream cruising cats can't go very fast but there are times when it is hard not to surf waves at high speed no matter how tubby the cat is. Further, raking the stem aft will subtract a huge amount of hull volume which can be critical buoyancy forward as you surf down a large steep wave into the trough. The whole mission of the hull bow when sailing fast down wind is to keep the non-bow portions of the boat out of the rushing water. Failure in that mission can lead to some nasty experiences.
The hull bottom carries a V-section well aft to avoid pounding under the forefoot in waves. If you have any doubt how important this is look at the videos of the cats emulating racing cat hulls with full or even flat U sections forward and pay attention to all the spray being ejected sideways on every wave. Realizing that inside the hull every wave impact is experienced as a BANG! rather than a Woosh.
There is a shallow fixed fin on each hull, thru which the daggerboard exits. The fin and dagger case are super strong so that hitting a rock at speed will only damage the dagger board and not damage the dagger board case. In a grounding, the fins protect the hulls from damage and, critically, protect the props and rudders. Props and shafts don't take the ground well but to function properly they need to be deeper than the hull and hence are vulnerable without the hull fins. Much the same can be said for rudders. Cruising far from home, often with sketchy charts, any damage becomes a big deal to repair and can totally disrupt a cruise.
Underwing Clearance
Wave slap beneath the bridge deck is uncomfortable and needs to be minimized as much as possible. There really is only one way to do that and that is by using generous clearance between the large flat surface and the water. Keep in mind that cats do heel, not a lot but they do, and that will depress the leeward side reducing the clearance. The A72 has nearly four feet of clearance which has proven to almost completely eliminate getting kicked from below. When that does happen the bridge deck (deckhouse floor) is an extremely stiff carbon skinned laminate with large carbon fiber box beams on the underside. Under wave impact the deflection of the floor is extremely small.
Sail Plan/Rig
The majority of catamarans still use a beach cat style sail plan. This is dominated by a large fully roached mainsail and small jib, the top of which is well below the masthead. This makes little sense to me since there are gigantic differences in form and function between a beach cat and a cruising cat. Some new thinking here would be beneficial.
Between the mainsail and jib the mainsail is by far the more difficult sail to handle. Roller furling jibs are easy to deploy, easy to reef or roll away completely. Jibs are simple and safe to gybe in lots of wind. And quite a bit less expensive to buy than mainsails.
The mainsail, on the other hand, is more work to raise, reef and put away. As the mainsail increases in area due to adding roach or square tops it adds yet more weight and complexity. Further, the extra large roach eliminates the use of a fixed back stay. Instead of a backstay the mast must be supported by moving the shroud chainplates further aft. Unfortunately when the shrouds are lead aft the amount you can ease the main sheet becomes quite restricted. Sailing a reach the typical cat mainsail is almost always considerably over sheeted and stalled. If not the battens will be sawing themselves in half as they rub against the leeward shrouds. Sailing with the mainsail over trimmed is not efficient and also causes weather helm which takes more rudder angle to correct, further slowing the boat. What good is an oversize mainsail if you can't trim it correctly?
In a beach cat this isn't typically a problem because the little boat's power to weight ratio is so great that it is easy to keep the apparent wind forward far enough that the mainsail never needs to be eased very far. Cruising cats are a whole different story and even the fastest ones can't replicate what happens on a beach cat.
Yet another reason the beach cat rig makes so little sense on a cruising cat is that beach cats use rotating masts to minimize the air flow turbulence over the mainsail. Extremely few cruising cats use a rotating mast and there are many good reasons not to in a cruising boat. A fixed mast really hurts the mainsail performance, a jib with no obstruction on the luff is much more efficient since the majority of driving force comes from the most forward part of the sail.
But pounding square pegs into round holes seems to be the order of the day. As I sit at anchor in George Town, Bahamas looking at the multitude of cruising cats (over 80 at last count) I see this same generic rig in boat after boat after boat.
So where does that leave us? My take has been steadily evolving toward less mainsail and more jib area. In the A72 a permanent backstay is used and the shrouds moved forward to allow easing the main sail further when reaching. A fixed backstay provides more headstay tension when sailing upwind which improves the jib performance. With a fixed backstay the mainsail needs to have an older style "pin head" reducing its area but that's fine with me. The sail is lighter, the battens can be lighter and fewer in number. And the mast is better supported.
Forward of the mast there are two jibs, a masthead genoa which can be used upwind in light air but is mostly intended for reaching.
A regular genoa jib on a robust conventional furler is, in my opinion, far more practical and safer in a cruising cat than trying to achieve the same function with a screacher, particularly in a cat the size of the A72. A rolled up screacher for this boat would resemble a 100' long, 200 pound Anaconda which would have to be dragged out of the fore-peak locker, or hoisted (wet) from a large bag living on the tramp, every time it was used. Sure, you can be lazy and leave a screacher up for protracted periods but neither the sail or its furler is designed to be bouncing around while sailing upwind or even weather a squall at anchor. Absolutely the last thing you want is to have a large sail unfurl on its own, or worse, hourglass in a squall.
The inner fore stay carries the workhorse of the sail plan, a robust self tacking jib. The clew is fixed to a boom in such a way that when the sail is rolled to reef the sheet lead automatically moves forward providing an efficient sail shape. There is no limit to how deeply the sail can be reefed. While there may be times when a storm jib is preferable the usual situation is, "I need to reduce sail now!" The self tacking jib is always there are ready to serve in winds up to 40 knots or more.
On the A72 we selected "manual" furlers for the jibs. The furling lines are led to an electric winch in the cockpit so they are very easy to handle. This avoids having a vulnerable furling motor on the bow being blasted by salt water. And allows the furling line to be led to any winch in case its primary electric winch has a problem. A cruising boat always needs to have a back up plan, things break occasionally and that can't jeopardize the utility of the entire boat. There are six winches in the cockpit, any one can be used to furl the jibs if need be.
Sailing deep downwind in strong tradewind conditions the two jibs set wing and wing works really well. The staysail boom is set to the weather side and the genoa sheeted to the rail opposite. The mainsail needs to be deeply reefed or furled. In 25 knots wind and more it's like a magic carpet ride.
There was considerable discussion about what sail best fills the gap for light wind, deep off the wind, sailing. Ultimately, nothing works as well as a spinnaker. Since we already have a large genoa in the sail plan a screacher, even though it is somewhat larger, doesn't really solve the problem. The spinnaker is lighter and more compact to stow when not being used than a rolled screacher. And by modifying the sock so that it is truly unbreakable the sock downhaul line can always be put on a winch ensuring the spinnaker can be put away when the time comes.
Sailing Performance
For this I will defer to Alan Weeks skipper of the A72 "SKYLARK". Alan has been at the helm for nearly 4 years and has sailed her over 21,000 miles.
"Skylark is a true world voyager that routinely covers 300 plus miles a day. Using the right sail plan she sails at the speed of the wind, remarkable for such a big boat. With 8 knots of wind going to weather we're doing 8 knots of boat speed.
In passage making speeds of 12 to 16 knots is the norm. With enough wind, 14 to 20 kts of boatspeed is common. During one passage we kept the speed between 20 and 25 for about 5 hours straight. All of this is achieved easily and safely with 2 crew just as it is on the A57."
Various Safety Features
Batteries
For a number of well known reasons Lithium batteries have become common on cruising boats. However they store tremendous energy and if some part of the battery or battery management system fails a battery can go into a thermal runaway. This basically is a fire that can't be put out with a fire extinguisher. People familiar with the problem say the only way is to flood the battery with enough water to cool it. But if your house battery bank is burning its likely there will be no electric power for pumps. The solution incorporated in the A72 was to locate the batteries low in the hull (where the weight belongs anyway) in a special compartment that can be flooded with seawater just by opening a dedicated seacock, located 15' away. Hopefully this will never need to be tested. Knowing it is there certainly helps me sleep better.
Automatic Main Sheet Release
Experience has shown that capsizes, although rare, are usually caused by simply not easing the sheets in time. As a last line of defense an automatic sheet release was included on the dead end of the main sheet. This unit uses a very sensitive rate gyro/ GPS and is programmable to whatever heel and pitch angles are selected. In the whole scheme of things it is pretty cheap insurance and seems like a good idea to incorporate. The main sheet uses fixed vang/preventers as standard so even with the sheet fully disconnected it is still possible to control the boom well enough to reconnect the sheet once the dust settles.
Watertight Divisions
This cat cannot ever sink due to the inherent buoyancy of the structure. Even so, a bad collision with another vessel or running hard into a stationary object may result in breaching the hull. There are two watertight bulkheads forward in each hull which should effectively deal with any sort of collision. There is also a bulkhead watertight to well above the waterline just forward of the rudder and engine shaft stuffing box, two items that could potentially spring a substantial leak. That give four sections in each hull where flooding can be contained.
Finally
Creation of a spectacular cruising machine is a large undertaking that is only successful when owner, designer and builder can work together to find the best solutions to the numerous compromises required. Nothing in our world is ever perfect, but that should not deter us from the quest!