Thursday, January 9, 2014

Gemini designer Tony Smith reflects on 105 design following the most recent trip with wife Sue.

I was in my mid thirties when we started Performance Cruising and the Gemini project in Annapolis. Prior to that I had my own boat building company in England building several hundred Telstar trimarans and an assortment of custom boats to 70 ft. At the time Sue and I had a young family and I was more interested in ocean racing having competed in three 3,000 mile two handed round Britain races. I have stayed with just one size of 34 ft. Because of the continuous improvements and attention to detail Gemini has out sold all other catamarans to become the worlds most successful catamaran. To date we have built close to 1,100 Gemini. This success comes from the functional quality of the product. The Gemini 105's teardrop hull shapes are still revolutionary, having good load carrying, fine entry, minimum drag ,  and with the motion of a much larger catamaran. Although the overall beam is quite narrow the centers of bouyancy are far apart and quite high. The centers of gravity and centers of effort are low, which when coupled with good load carrying hulls that cannot be pushed down into the water, makes for a fast safe comfortable boat. The deck and pilot house has a low profile that reduces windage and gives a good looking boat. Gemini has the lowest draft of any sail boat with lifting centerboards , rudders and drive leg. The asymmetric centerboards are like turbo chargers to windward.
Considerable thought has also gone into the production techniques with a revolutionary interior mold for strength and lightness. The production procedures have evolved to ensure sustainable quality. The accommodations have evolved to make Gemini comfortable for any purpose, from crossing the Atlantic to cruising down the Intercoastal. The functional and attractive cockpit enclosure doubles the accommodation.
After thirty years it is time to step back from continuous development and see how successful we have been. We planned to do what lots of our customers have done and even more would like to do and travel down the East coast of America from Maryland to Florida, the Bahamas and back during the winter of 2010.

Sue and I took delivery of a standard 2010 Gemini 105 Mc in Sept 2010. The options and equipment we took  were in keeping with Performance Cruising and Gemini's philosophy of function, performance and cost. We took most of the standard options such as screecher, cockpit enclosure, davits, hammock, solar panels, helm seat, air conditioner and cabin heater. The extra PCI options we took were Garmin chart plotter, diesel hot water heater, anchor windlass, inverter and battery monitor. The additional items we added were Trackvision television, larger battery bank, salt water pump and water maker.
Although our Gemini was well equipped considerable effort went into keeping the boat light. Just before leaving we applied a fresh coat of new ablative bottom paint. As a result Gemini motored faster than most monohulls up to 45 ft. Westerbeke states that the cruising rpm of the engine should be between 2,500 and 3,000. At those engine rpm's a boat speed of 7 knots was possible with a fully loaded boat. The fuel consumption was slightly more than a gallon an hour. I kept the sails up most of the time pushing the boat speed above the 7 knots. Going down the Chesapeake bay we reach speeds up to 13.5 knots. In the intercoastal the sails gave an extra 1/4 to 1/2 a knot in winds less than 10 knots.
Gemini's dimensions of 34 ft length, 14 ft beam 18 in draft and a mast clearance from the water of 46 ft, makes a trip down the intercoastal stress free. The worst boat to have for a trip down the intercoastal is a wide catamaran or an ocean going 45 ft monohull with a 7ft keel and 64 ft mast. Most fixed bridges are 65 ft plus or minus depending on the tide. The dredged channels down the intercoastal are over 7 ft deep but these channels are narrow and not well marked. We constantly found we were in 5 ft or less of water and uncertain which side of us was the deep channel. Needless to say most monohulls at least touch bottom and at worst get stuck. We saw a power boat stuck with serious prop damage.
The days are short when going down the intercoastal in the fall. Even at 7 knots it is difficult to achieve more than 50/60 miles per day. Marinas are expensive, charging close to $2 per foot a night. The other option is to anchor at night, unfortunately barge traffic can keep going at night and the wind can come up making it important to anchor out of the channel in a protected anchorage. Here again shallow draft is highly desirable to be able to anchor out of the main channel.
Most marinas do not have wide slips. Gemini's 14 ft beam is the same as most power boats that go up and down the intercoastal making docking easy. A wide catamaran will have difficulties in most marinas, paying extra and not being able to get lifted out for emergency repairs.

Gemini does not heel like a monohull and therefore has been designed with an interior like a small apartment. It is perfect for a couple with a Queen size double master cabin and two smaller guest cabins aft. The master bedroom has plenty of storage with a large hanging closet. The dinette can also be made into an extra double bed.  The galley and navigation are large with plenty of storage down in the starboard and port hull, with just two steps up to the dinette and cockpit. The dinette seats 6 on the bridge deck with an extra seat just inside the cockpit door. The head is in the forward end of the port hull and has a large shower area separated from the head by a fold away door.
The cockpit enclosure almost doubles the boat with most of the day spent there. We call this area our Florida room. On a winter trip down the intercoastal this area is just as warm as the cabin with the heat coming through the open windows and doors. The enclosure design has easy entry aft doors. The hammock serves as a safety device and prevents falling over board when exiting the enclosure or walking across the aft deck at sea.
To enhance the living comfort of Gemini making it just like home we have a cabin heater that puts out 29,000 btu of free heat when the engine is running. When at anchor and the engine off we have a thermostatically controlled  Espar diesel hot water heater in the line. This heater is very small weighing just 7 lb and fits in the cockpit locker. The fuel use is less than 1/10 of a gal per hour. Our Gemini also has the standard 16,000 btu air conditioner that is also a heat pump for heat at the marina. The cabin heater that runs off the engine is powerful enough to heat the cockpit enclosure. Most other power and sail boaters are very jealous when they see  us sitting in the cockpit in shirt sleeves motoring down the intercoastal in freezing cold weather.
Many marinas do not maintain their cable TV. Over the air tv reception is practically nonexistent down the intercoastal. To maintain the like home conditions I added a Trackvision TV from KVH using "direct" satelite TV. A  thin 19 in led TV weighed only 6.5 lb as did the Trakvision. The electrical consumption is only 3.5 amps. This unit worked well except for the loss of local net work TV when we moved away from our local area. We had over 100 channels including CNN, BBC America, Weather channel, USA etc
The 100 watt solar panels are at the rear of the boat where they are least likely to be shaded. The standard Westerbeke engine alternator puts out over 40 amps when the batteries are at 50% charge. The two standard 24 series house batteries were changed to 6 volt golf cart batteries with the third 24 series battery being changed to a smaller 12 volt starter battery. The main battery switch had a battery combiner to keep all batteries charged but seperate. The house battery storage went up from 170 Ah to 255 Ah the starting battery went down from 85 to 50 Ah the weight penalty was 24 lb. The 2000 watt inverter I used had a battery charging capability of 100 amp and only weighed 25 lb. AGM or gel cell batteries are considerably heavier for the same storage but have the advantage of no maintenance. More batteries obviously add weight and need extra charging capabilities. The inverter was only connected to the 110 volt outlets, although it could run the air conditioner and the fridge. In this way we could use 110 volt appliances such as vacuum cleaners and battery chargers.
Using the battery monitor we were able to see that during the night at anchor with the Espar diesel heater running, several hours of television and normal living including cooking and showers the total current used was 140 Ah. This is about half the available storage. The batteries were quickly filled back up with the 40 amps output from the engine alternator. Tests showed that the Espar heater took 12 amps every time it started and 4.5 amps when running. The heater fan that run continuously took 5 amps on full. The Espar heater was on a thermostat but the heater fan was not. I plan to hook the heater fan up to the thermostat. The Track TV uses 4 amps. The 3 phlorescent lights used .8 amps each but the 5 other incandescent lights used 1.5 amps each. The anchor light used 1.5 amp. I plan to change to all phlorescent lights for use inside the boat and Led for anchor lights and mast lights that use .5 amps.
The galley works well with several feet of counter surface, a double sink with an additional salt water pump for use at sea. The stove has two burners a broiler and oven with battery ignition. The eye level fridge automatically switches from 110 volt to propane when at sea with automatic shut off, if leaking propane  is detected by the gas monitor. The fridge is a well insulated 4.5 cu ft that makes ice. The propane use is less than 20 lb in 2 weeks. There is a small on or off computer fan to make the fridge more efficient. There are a lot of safety devises with very low current draw for the propane. Two light weight 20 lb fiberglass propane tanks are standard. The galley storage under the starboard side of the dinette is large. There are several drawers for cutlery etc. A shelf along the back of the galley is for cups, glasses and kitchen roll holder. A microwave will fit under the dinette or on the counter top. The area behind the centerboard is for bulk storage accessible from the galley top.
The navigation area in the port hull has a chart storage desk and bulk storage under the dinette and behind the centerboard case. I added a book rack behind the dinette seats.
The large shower in the port hull works well with a fold away door in front of the toilet. The area behind the door keeps the towel, clothes and toilet area dry when showering. The toilet has two Y valves so that waste can go over board when off shore or into the holding tank. The holding tank can be gravity drained or deck pumped out. The inlet water can come from the sea or fresh water from the sink. The holding tank is 18 gal. 10 pumps of the toilet handle is approx a gall. The level of fluid in the holding tank can be seen in the sail locker through the plexiglass wall.
The level of water in the two 30 gal tanks under the aft beds can be seen through the translucent tank material. A gauge would be a good addition for family use. A power survivor 40 water maker was also added in the starboard aft cabin. This unit produces 1.5 gal water an hour. This unit weighs 24 lb roughly the same as 3 gal water. This unit can only be used in clean sea water and is ideal for trips to the caribbean.  The unit uses less than 5 amps  and  can be used manually in an emergency. Hopefully the solar panels will provide enough power to run the water maker.

The sailing performance of Gemini is better than most other cruising catamarans and monohulls with the large roach fully battened main and 150% overlapping genoa. The optional screecher on a curved track between the bows is easy to use in light airs. The asymmetric lifting centerboards, low windage cabin and lifting drive leg add to the all around performance of Gemini.
Unlike most other catamarans that have a large fully battened mainsail and a small jib, Gemini has a conventional rig. The mainsail is uniquely designed with a head board that fits under the mast crane allowing for a large roach fully battened main that goes 30 in behind the back stay and easily tack through. Having a back stay allows for a balanced rig with the mainsail and roller genoa being of equal area. The large mainsails of other catamarans are difficult to handle, particularly in offshore conditions. Gemini's small main and roller genoa can easily be handled by one person. Taking advantage of the back stay and beam we have added a curved track across the bows to which we add a large roller furling screecher that can be used hard to windward with the car amidship or with the car to one side for down wind.
The pilot house and canopy are designed for minimum windage. The pilot house and ridged canopy act as an end plate to the mainsail. The sloped pilot house windows leading to the horizontal ridged canopy that is just a few inches below the boom directs the air from over the deck into the main sail and produces forward drive. The entire cabin would be windage if the boom was raised so the air flowed under it.
With everything raised, Gemini's draft is 18 in. The lifting centerboards are asymmetric, giving lift to windward when the leeward board is down 5 ft 6 in . When motoring the boards are up for minimum resistance. When docking, the boards are down, dramatically improving maneuverability in strong winds. The rudders are under hung for efficiency and can be lifted when in shallow water or to service. Just like the centerboards the rudder will come up if they touch ground. The lifting rudders do not load up when lifted and will still steer the boat in the up position.
On the bridge deck at the back of the cockpit in a locker is the 27 hp three cylinder Westerbeke diesel, with a reduction gear box and connected to a sonic drive leg. The sonic drive leg can be steered and can be pumped up out of the water when sailing or at a marina to prevent corrosion or fouling of the propellor. There are no through hull fittings such as shaft logs with the drive leg up or down, consequently there is no chance of the boat leaking because of the engine. There is only one engine keeping the weight and maintenance to a minimum. With the engine on the bridge deck there is no loss of accommodation in the hulls. The diesel is very safe, economical and reliable with good battery charging and water heating. We use the Westerbeke because it is a very reliable mitsubishi diesel having the lightest weight and the best hot water heating system of any Diesel. Westerbeke worked with us for the best installation with the Sonic drive and least vibration and noise.
When designing the revolutionary screecher the bow sprit was also redesigned so that the anchor went through the bow sprit. The anchor roller is angled down so that the anchor self stows when being raised. This makes an anchor windlass an easy option. The choice of anchor windlass and location of switches, has to be considered to keep the weight down and least power usage. I chose a  Windlass 36 that is low cost and light weight that does not need to be powered out and uses less than 15 amps for a 700 lb pull. the switch is in the anchor locker so that the amount of chain and rope deployed can be monitored as well as the retrieval. The anchor is a 25 lb Delta with 50 ft 1/4 in high tensile chain and 100 ft 1/2 in rope. My spare anchor is a fortress anchor.
A chart plotter is a must for any voyage. Even down the intercoastal it shows you exactly where you are in the channel.  The garmin we used had a 12 inch touch screen and could have a radar. I do not think a radar is of any use going south. Even off shore it uses too much power to be used effectively.

The engine only had 12 hours on it before we left. I took everything necessary to service the engine with plenty of spare parts. The initial running of the engine was with constant changing of the throttle. After about 50 hours we were in Oriental so I serviced the engine. I changed the oil and filters. I also checked the cylinder head bolts and adjusted the valve clearances. Going down the Cape Fear river I struck an under water object. After a thorough inspection I thought there was no damage. When going into Southport it became obvious that I had broken the steering yoke. First thing the next day I got hauled out. I had a spare Yoke which took me 2 hours to change. At the same time I did the routine service of the drive leg which would have taken a haul out anyway. I changed the oil in the drive leg and greased the bearings.
The sonic drive is the best performance and cost option for a Gemini. We only have the weight of one engine which is on the bridge deck. The sonic drive leg is the way to get the drive to the propeller in the water. The Sonic drive gives fantastic maneuverability with the ability to steer the propeller in parallel with the twin rudders. The propeller can be pumped up out of the water to reduce drag when sailing or at the marina to prevent corrosion. With the engine and drive on the bridge deck there is no chance of sea water leaks and the engine is easy to service. With the engine in the cockpit there is less engine noise and smell in the cabin. The weakness to the sonic drive is the long lever arm from the prop to the transom, something has to give if an underwater object is struck. The steering Yoke is the easiest thing to change so has been made the weakest link.
It took us 2 days to go 130 miles down the Chesapeake bay and a total of 9 days to Charleston SC. We, anchored three nights and spent 6 nights in marina's. We have travelled 562 miles and purchased 86 gal diesel, at an average speed of 7.1 knots. We have used about 60 gal water showering on the boat most of the time. We started with 2x 20 lb propane bottles and have used about 12 lbs. Buying provisions is quite difficult so we took a lot of supplies with us.

Wednesday, January 1, 2014


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