Mast aft rig
Encyclopedia
A mast
aft
rig, alternately referred to as aft-mast rig, is a sailboat
sail-plan
that uses a single mast
set in the aft half of the hull
. The mast supports fore-sails that may consist of a single jib
multiple staysail
s, or a crab claw sail
. The mainsail
is either small or completely absent. Mast aft rigs are uncommon, but are found on a few custom, and production sailboats.
either by the number of staysails, with a sloop having one and a cutter more than one, or by the position of the mast, with a cutter's mast being located between 50% and 70% of the way from the aft to the front of the sailplan, and a sloop's mast being located forward of the 70% mark. A mast aft rig could, based on headsail count, be considered a variation of the sloop or cutter, or, based on mast position, a unique rig.
, the sails located in front of the mast generally deliver a higher percentage of the driving force. The stay
that supports the leading edge
of the sail causes far less turbulence
than a mast, resulting in better airflow across the lee side of the sail. To take advantage of this fact, Bermuda rigs are shifting towards larger fore-sails and smaller mainsails. Fore-sails, alternately called head-sails, include the [jib], genoas
and staysail
. The cutter, with its use of multiple foresails, achieves the same goal of placing a higher percentage of the sail area in staysails.
By moving the mast toward the back of the sailboat, designers can increase the size and driving power of the more efficient foresails. The mainsail
is reduced in size or eliminate altogether. An advantages of using foresails, also called staysails, is that they may be rigged for roller furling
. This allows the sail(s) to quickly and easily be deployed and reefed
by pulling lines. The sail rolls up around the stay. This simplicity and easy operation is one of the main attractions of the mast aft rig.
By reducing the mainsail in size or eliminating it altogether, the aft mast rig squarely minimizes or completely solves the problems associated with batten
s. Battens enable designers to increase the size of mainsails by pushing the mainsail away from the mast. However, the forces of the battens pushing against the mast make it more difficult to raise or lower the mainsail. On larger rigs, "batten cars" are needed to overcome these forces.
By eliminating the battens and associated batten cars, the material cost savings for a typical 60-ft catamaran can be as much as $12,000 AUD. Aft-mast rigs with no mainsail also require fewer winches to raise and lower sails, and no winches to move the boom. When "Hot Buoys" converted from a Bermuda rig to an aft-mast rig 5 winches were no longer required.
For rigs with no mainsail, there is also no boom
. This saves the cost of the Boom (sailing)
, and hardware and lines associated with the boom. More importantly, eliminating the boom is a matter of safety. The second leading cause of death on sailboats is the boom. Booms cause injuries and deaths directly and indirectly by knocking people overboard. Even when stationary booms represent a hazard. According to a German study, "boom strikes were the most common cause of sailing injury overall". Another aspect of safety is in regards to the elimination of the lines and hardware to control the boom. With fewer lines and less hardware on the deck there are fewer items to trip over or jamb fingers and hands.
Another disadvantage of the mast aft rig, when set up with no mainsail, is the drag on the mast. While the mast may interfere with the airflow around the mainsail, the mainsail also serves to reduce the drag on the mast. By not having a sail attached to the trailing edge of the mast, the mast becomes a significant source of drag.
The performance of the sail is dependent on having a forestay which is taught. If the forestay is allowed to slack, the sail will loose it's airfoil shape and not perform as well.
This requires heavy rigging with high tension which adds stress to the overall sail rig system. Not really a disadvantage, but a parameter to consider if rigging a sailboat to use a mast aft rig.
RB Power & Sailing of Thailand offers two aft-mast catamarans. Model "HK-40" is 40-ft long and model "HK-55" is 55-ft long. They were designed by Albert Nazarov.
Most aft-mast sailboats are either catamarans, or trimarans. An exception is the "4.8 monomaran" designed by Kees Radius's. A ""monomaran"" is a single hull with no ballast and a dagger board.
Unsuccessful commercial examples include the Delta 26 by Gary Hoyt and the CS-24 by Phil Bolger
. Prototypes of both designs were constructed, but neither entered commercial production. Ted Brewer's So-Du-It, designed for amateur home construction, had at least two examples constructed, but the anticipated offshore racing class never materialized.
.
The sailboat now shuttles tourists to Monkey Mia
. A resort area near Perth Australia.
Hot Buoys is a 65-ft long cruising trimaran with a 40-ft beam. It was designed by Jay Kantola, and built by Richard and Kris Barrie of California. In 2010 it was converted by Philip Maise to an aft-mast rig with a self-tacking crab-claw sail. Video in External Links
Warick Collins, experimental boat builder, and inventor of both the tandem keel
and the universal hull, now uses an aft-mast rig. "I believe that in due course this will have wide applications for motor-sailers, commercial vessels and sail-assisted passage-making on larger vessels of different types.
Mast
-Engineering:* Mast , a pole that holds a sail on sailing ships and boats, or radar and telecommunication antennas on modern warships* Guyed mast, a type of tall structure supported by guy-wires...
aft
Aft
Aft, in naval terminology, is an adjective or adverb meaning, towards the stern of the ship, when the frame of reference is within the ship. Example: "Able Seaman Smith; lay aft!". Or; "What's happening aft?"...
rig, alternately referred to as aft-mast rig, is a sailboat
Sailboat
A sailboat or sailing boat is a boat propelled partly or entirely by sails. The term covers a variety of boats, larger than small vessels such as sailboards and smaller than sailing ships, but distinctions in the size are not strictly defined and what constitutes a sailing ship, sailboat, or a...
sail-plan
Sail-plan
A sail-plan is a set of drawings, usually prepared by a naval architect. It shows the various combinations of sail proposed for a sailing ship.The combinations shown in a sail-plan almost always include three configurations:...
that uses a single mast
Mast (sailing)
The mast of a sailing vessel is a tall, vertical, or near vertical, spar, or arrangement of spars, which supports the sails. Large ships have several masts, with the size and configuration depending on the style of ship...
set in the aft half of the hull
Hull (watercraft)
A hull is the watertight body of a ship or boat. Above the hull is the superstructure and/or deckhouse, where present. The line where the hull meets the water surface is called the waterline.The structure of the hull varies depending on the vessel type...
. The mast supports fore-sails that may consist of a single jib
Jib
A jib is a triangular staysail set ahead of the foremast of a sailing vessel. Its tack is fixed to the bowsprit, to the bow, or to the deck between the bowsprit and the foremost mast...
multiple staysail
Staysail
A staysail is a fore-and-aft rigged sail whose luff can be affixed to a stay running forward from a mast to the deck, the bowsprit or to another mast....
s, or a crab claw sail
Crab claw sail
The crab claw sail or, as it is sometimes known, Oceanic lateen or Oceanic sprit, is a triangular sail with spars along upper and lower edges. The crab claw sail is used in many traditional Pacific Ocean cultures, as can be seen by the traditional proa and tepukei.-Construction:The crab claw sail...
. The mainsail
Mainsail
A mainsail is a sail located behind the main mast of a sailing vessel.On a square rigged vessel, it is the lowest and largest sail on the main mast....
is either small or completely absent. Mast aft rigs are uncommon, but are found on a few custom, and production sailboats.
Comparison to other single mast rigs
Many mast-aft rigs utilize a small mainsail and multiple staysails that can resemble some cutter rigs. A cutter is a single masted vessel, differentiated from a sloopSloop
A sloop is a sail boat with a fore-and-aft rig and a single mast farther forward than the mast of a cutter....
either by the number of staysails, with a sloop having one and a cutter more than one, or by the position of the mast, with a cutter's mast being located between 50% and 70% of the way from the aft to the front of the sailplan, and a sloop's mast being located forward of the 70% mark. A mast aft rig could, based on headsail count, be considered a variation of the sloop or cutter, or, based on mast position, a unique rig.
Advantages of the mast aft rig
In the typical Bermuda rigBermuda rig
The term Bermuda rig refers to a configuration of mast and rigging for a type of sailboat and is also known as a Marconi rig; this is the typical configuration for most modern sailboats...
, the sails located in front of the mast generally deliver a higher percentage of the driving force. The stay
Stays (nautical)
Stays are the heavy ropes, wires, or rods on sailing vessels that run from the masts to the hull, usually fore-and-aft along the centerline of the vessel...
that supports the leading edge
Leading edge
The leading edge is the part of the wing that first contacts the air; alternatively it is the foremost edge of an airfoil section. The first is an aerodynamic definition, the second a structural one....
of the sail causes far less turbulence
Turbulence
In fluid dynamics, turbulence or turbulent flow is a flow regime characterized by chaotic and stochastic property changes. This includes low momentum diffusion, high momentum convection, and rapid variation of pressure and velocity in space and time...
than a mast, resulting in better airflow across the lee side of the sail. To take advantage of this fact, Bermuda rigs are shifting towards larger fore-sails and smaller mainsails. Fore-sails, alternately called head-sails, include the [jib], genoas
Genoa (sail)
The genoa or jenny was originally referred to as the 'overlapping jib' or the Genoa jib, being named after the city of Genoa as explained below. It is a type of large jib or staysail used on bermuda rigged craft that overlaps the main sail, sometimes eliminating it. It is used on single-masted...
and staysail
Staysail
A staysail is a fore-and-aft rigged sail whose luff can be affixed to a stay running forward from a mast to the deck, the bowsprit or to another mast....
. The cutter, with its use of multiple foresails, achieves the same goal of placing a higher percentage of the sail area in staysails.
By moving the mast toward the back of the sailboat, designers can increase the size and driving power of the more efficient foresails. The mainsail
Mainsail
A mainsail is a sail located behind the main mast of a sailing vessel.On a square rigged vessel, it is the lowest and largest sail on the main mast....
is reduced in size or eliminate altogether. An advantages of using foresails, also called staysails, is that they may be rigged for roller furling
Roller furling
Roller furling is a method of furling or reefing wherein a sail is rolled around a stay or rotating spar. Roller furling is most commonly encountered on foresails, such as jibs, with mainsails a distant second.-Furling methods:...
. This allows the sail(s) to quickly and easily be deployed and reefed
Reefing
Reefing is a sailing manoeuvre intended to reduce the area of a sail on a sailboat or sailing ship, which can improve the ship's stability and reduce the risk of capsizing, broaching, or damaging sails or boat hardware in a strong wind...
by pulling lines. The sail rolls up around the stay. This simplicity and easy operation is one of the main attractions of the mast aft rig.
By reducing the mainsail in size or eliminating it altogether, the aft mast rig squarely minimizes or completely solves the problems associated with batten
Batten
A batten is a thin strip of solid material, typically made from wood, plastic or metal. Battens are used in building construction and various other fields as both structural and purely cosmetic elements...
s. Battens enable designers to increase the size of mainsails by pushing the mainsail away from the mast. However, the forces of the battens pushing against the mast make it more difficult to raise or lower the mainsail. On larger rigs, "batten cars" are needed to overcome these forces.
By eliminating the battens and associated batten cars, the material cost savings for a typical 60-ft catamaran can be as much as $12,000 AUD. Aft-mast rigs with no mainsail also require fewer winches to raise and lower sails, and no winches to move the boom. When "Hot Buoys" converted from a Bermuda rig to an aft-mast rig 5 winches were no longer required.
For rigs with no mainsail, there is also no boom
Boom
-Pole or spar application:* Boom , spar at the foot of a sail on a sailboat* Boom , a wishbone shaped piece of windsurfing equipment* Boom barrier, a barrier used to block vehicular access through a controlled point...
. This saves the cost of the Boom (sailing)
Boom (sailing)
In sailing, a boom is a spar , along the foot of a fore and aft rigged sail, that greatly improves control of the angle and shape of the sail. The primary action of the boom is to keep the foot of the sail flatter when the sail angle is away from the centerline of the boat. The boom also serves...
, and hardware and lines associated with the boom. More importantly, eliminating the boom is a matter of safety. The second leading cause of death on sailboats is the boom. Booms cause injuries and deaths directly and indirectly by knocking people overboard. Even when stationary booms represent a hazard. According to a German study, "boom strikes were the most common cause of sailing injury overall". Another aspect of safety is in regards to the elimination of the lines and hardware to control the boom. With fewer lines and less hardware on the deck there are fewer items to trip over or jamb fingers and hands.
Disadvantages of the mast aft rig
Mast aft rigs are viewed as unconventional, and since recreational sailors often choose boats based on what "looks" right, mast aft rigs face resistance in the recreational market. Racing sailors will use whatever is fastest within class rules, and class rules are generally very closely tied to the conventional Bermuda rig.Another disadvantage of the mast aft rig, when set up with no mainsail, is the drag on the mast. While the mast may interfere with the airflow around the mainsail, the mainsail also serves to reduce the drag on the mast. By not having a sail attached to the trailing edge of the mast, the mast becomes a significant source of drag.
The performance of the sail is dependent on having a forestay which is taught. If the forestay is allowed to slack, the sail will loose it's airfoil shape and not perform as well.
This requires heavy rigging with high tension which adds stress to the overall sail rig system. Not really a disadvantage, but a parameter to consider if rigging a sailboat to use a mast aft rig.
Commercial Production Examples
An early successful mast-aft design was built by Prout Catamarans, Ltd. The Snowgoose models were offered with a mast-aft rig, and it boasted a number of features that made short-handed sailing easier than with a standard Bermuda rig. Broadblue Catamarans Ltd. now owns and makes two of the Prout designs, which still come standard with the mast-aft rig.RB Power & Sailing of Thailand offers two aft-mast catamarans. Model "HK-40" is 40-ft long and model "HK-55" is 55-ft long. They were designed by Albert Nazarov.
Most aft-mast sailboats are either catamarans, or trimarans. An exception is the "4.8 monomaran" designed by Kees Radius's. A ""monomaran"" is a single hull with no ballast and a dagger board.
Unsuccessful commercial examples include the Delta 26 by Gary Hoyt and the CS-24 by Phil Bolger
Phil Bolger
Philip C. Bolger , prolific boat designer, was born and lived in Gloucester, Massachusetts. He began work full time as a draftsman for boat designers Lindsay Lord and then John Hacker in the early 1950s. Bolger also cites being influenced by mentors L.F...
. Prototypes of both designs were constructed, but neither entered commercial production. Ted Brewer's So-Du-It, designed for amateur home construction, had at least two examples constructed, but the anticipated offshore racing class never materialized.
Custom Yacht Examples
Shotover is a 60-ft long racing catamaran with a 31-ft beam designed by Lock Crowther and built for Sir Douglas Myer. This sailboat utilizes a mainsail and a small boom. For several years it held the fastest time in the Brisbane to Gladstone yacht raceBrisbane to Gladstone yacht race
The Brisbane to Gladstone yacht race is held annually, starting on Good Friday. The premier blue water classic begins from Shorncliffe in Moreton Bay, Queensland, Australia and finishes in Gladstone Harbour. It attracts competitors from interstate and usually attracts a fleet of 40 to 100 boats....
.
The sailboat now shuttles tourists to Monkey Mia
Monkey Mia
Monkey Mia is a popular tourist resort located about 800 km north of Perth, Western Australia. The resort is 25 km northeast of the town of Denham in the Shark Bay Marine Park and World Heritage Site....
. A resort area near Perth Australia.
Hot Buoys is a 65-ft long cruising trimaran with a 40-ft beam. It was designed by Jay Kantola, and built by Richard and Kris Barrie of California. In 2010 it was converted by Philip Maise to an aft-mast rig with a self-tacking crab-claw sail. Video in External Links
Warick Collins, experimental boat builder, and inventor of both the tandem keel
Keel
In boats and ships, keel can refer to either of two parts: a structural element, or a hydrodynamic element. These parts overlap. As the laying down of the keel is the initial step in construction of a ship, in British and American shipbuilding traditions the construction is dated from this event...
and the universal hull, now uses an aft-mast rig. "I believe that in due course this will have wide applications for motor-sailers, commercial vessels and sail-assisted passage-making on larger vessels of different types.
External links
- Boats featuring an innovative "wishbone" mast, in both tall and short versions. Another photo of the tall rig. These may or may not have been constructed for the Proycyon project.
- Revisiting a mast-aft sailing rig
- Mast aft on a puddle duck racer a plywood boat you can build. Here are other unusual sails at pdracer.com
- Sail power calculator
- Video "Hot Buoys" Self-Tacking Aft-Mast Trimaran