M – Mike (phonetic)

Two dashes in Morse code, and means, ‘My vessel is stopped and making no way through the water’ in the International Code. Mike in phonetic

M Magnetic

M – Magnetic – Of bearings, courses and the like, means that the direction is measured as an angle related to Magnetic North rather than True North. (Please see North.)


Marine Accident Investigation Branch – examines and investigates all types of marine accidents to or on board UK ships worldwide, and other ships in UK territorial waters.

Main mast

The taller of two masts is the Mainmast. If it is the after of two then the forward one is the Foremast, but if the main is to the fore then the lower after mast is the Mizzen.

Make sail, to

To set sails. And to make more sail is to add a sail here and there as to set a Topsail or a Watersail.

Man overboard (MOB)

‘Man over­board!’ is the most important and serious order you can ever hear, and it is an order which means instant action by everyone no matter who gives it. Devise a plan which will suit your boat and your crew.


A natural rope fibre much used in the past for warps and general pur­poses, but now displaced by the synthetics.

Marconi rig

Though not much used now the word refers to tall-masted Bermudan rig, which in contrast to the old gaff mast needed sophisticated wire bracing akin to that of a wireless-mast ashore.


Artificial yacht harbour

Marine glue

An old term for caulking material for the seams of Laid decks that would consist of rubber, pitch, naphtha and

Marker buoy

Usually a racing mark rather than a navigational buoy. The latter tend to be called buoys – others have the prefix, mooring, marker, wreck, telephone, DZ or the like.


Small line (like twine), properly made of two tarred strands laid up loosely. Can be used for Whipping or Serving.

Marline spike

A fat bodkin with an ogival taper to its point, used for opening the strands of wire or rope cable when splicing. Some people use the pointed end to turn shackle pins, but the curved taper is not appropriate to that application and the spike is likely to slip out of the pin and into your flesh. A shackle-key is better, and some good hands prefer a pair of pliers. (See also Fid)

Marling hitch


Mini-ARPA. A version of ARPA for small boats. Typically limited to around 10 targets.


International Convention for the Prevention of Pollution From Ships


On a sailing boat, this refers to the pole from which the sails are rigged. A motor cruiser may have a mast that is no longer than a sailing cruiser’s ensign staff, but it is still called a mast. A mast has a Head at the top and a Foot at the bottom. The head of a wooden mast is usually capped with a disc called the Truck which covers the exposed end-grain of the mast itself against water. A mast is supported by Shrouds and Stays, and it may have Spreaders to spread the shrouds and widen their angle of pull. Lower shrouds meet the mast at the roots of the spreaders, and this region is called the Hounds. The foot of the mast may step on deck in a large socket structure called a Tabernacle, or it may pass right through the deck and be stepped on the keel itself. Note that a mast steps on things with its foot, and that the after part of the underside of the foot is even called its Heel.

Mast coat

A sleeve of canvas designed to prevent water from passing down below decks. Both the lower and upper edges of the coat must be well sealed, the upper to the mast and the lower to the deck.


The chief officer of the vessel. The one who does the wor­rying.

Masthead float

Catamarans and trimarans, being normally unballasted, float with great stability either way up. A float at the masthead should prevent the im­mersion of the mast, and thus ensure that the craft never gets into the stable, in­verted attitude. Some floats are made of lightweight foamed plastic, or are air-fIlled hollow chambers. Others are bladder-like, to be inflated automatically from a carbon dioxide cylinder if the boat goes beyond a certain angle of heel.

Masthead light

Please see Steaming light

Masthead rig

A rig where the forestay attaches at the masthead.


The international spoken word of distress, corresponding to SOS. It derives from the French m’aidez, help me. The acepted format of a Mayday call is to repeat the word ‘Mayday’ three times in succession and without haste, then give the name of your boat, her position, the nature of the trouble, and what action you are taking. In short, tell them what they are to look for, and where they are to look.


Maritime and Coastguard Agency. Implements UK Government’s maritime safety policy co-ordinating search and rescue at sea, inspecting ships and preventing pollution.

Measured distance

An accurately measured distance marked by two pairs of beacons ashore. Sometimes it is exactly a sea mile, but the actual distance will be shown on your chart. The chart will also show the correct course to sail when checking speed – you must sail parallel to the measured line, of course.

Mercator’s projection

Most commonly used method of showing the spherical world on flat paper, it shows parallels of latitude parallel. It also shows meridians of longitude as parallel, which they are not, because in practice they meet at the north and south poles.


One of the imaginary lines which run due north and south between the poles of the earth, denoting longitude. The meridian which passes through Green­wich (England) is zero longitude and all others are measured as so many degrees east or west of that.


In naval architecture the metacentre shows the relationship between the Centre of gravity of a vessel and her Centre of buoyancy when heeled. By relating those two centres it provides an index of her righting or restoring tendency. By plotting the positions of the heeled metacentres for sections along the length of the hull, the designer traces a curve called the Metacentric shelf. This curve is considered to give a good guide to the fore-and-aft Balance of a boat under sail.


MHWN Mean High Water, Neaps.


MHWS Mean High Water, Springs.


Sometimes called ‘microballoons’, these are tiny bubbles of air, encased in shells of glass or resin. So small that the resultant material looks and feels like powder, they are mixed with resin to make a relatively low-density filler for cavities in moulded or foam sandwich hulls.

Middle ground

A shallow bank which divides a channel or fairway into two parts. It is marked with Middle-ground buoys which usually indicate the deeper of the two channels so formed.


A unit of pressure as marked on a barometer, which is itself one thousandth of a bar (one bar is a pressure of one million dynes per square centimetre).

Miss stays, to

To fail to Go about. A sailing boat misses stays when she Luffs up into the wind and then falls off on the same tack instead of on the intended new tack.


A seam in a sail where the cloths meet at an angle, usually approaching a right angle.

Mizzen (mizen)

The fore-and-aft sail set on the after mast of a Ketch or Yawl. The mast is called the mizzenmast, and associated rigging and fittings take the same prefix when necessary, as in ‘mizzen boom, mizzen halyard’ and so forth. (See also Jigger)

Moderate (in shipping forecast)

Visibility between 2 and 5 nautical miles. Wave height of 1.25m to 2.5m


A stone pier or breakwater protecting a harbour from seaward, and nor­mally one against which vessels may lie. Would not be used of a breakwater of roughly-heaped boulders, for example.

Monkey’s fist

An easily-made knot which has many turns so as to build up into a ball of rope. Used to weight the end of a heaving-line, sometimes with a piece of lead or a stone buried within the ‘fist’.


To make a vessel fast to a laid mooring, alongside a quay, or to the bottom by means of two of her own anchors. The first two uses of the word require no further explanation, but the third always denotes a clear distinction between ‘anchoring’ with only one anchor, and ‘mooring’ with two. If a boat lies to a single anchor there is a likelihood that the pull on the anchor will be reversed from time to time by changes in wind and tide. An anchor is designed to support a directional pull, and those changes mean that it may have to re-bed itself several times a day. Thus if a boat is to be left unattended for longish periods, it is prudent to moor her with two anchors, placed in up- and down-stream positions. There are several ways of doing the job, of which this is but one: drop the main or the normal length of cable, then take out the Kedge in the opposite direction in the dinghy and drop it at the extremity of its cable. Now make fast the kedge cable to the bower cable (normally with a Rolling hitch) and veer a couple more fathoms of the bower cable so that the hitch is well below the boat’s keel and rudder. If you have plenty of bower cable you can manage the job without a dinghy, by first veering at least double the normal amount of cable, then dropping the kedge Underfoot and hauling in half the main cable again before making the rolling hitch.


An arrangement of anchors, Clumps and chains which are left permanently in position so that a boat may lie to them. There is commonly a ground chain running along the bottom between anchors, clumps or the like, and a riser chain leading up from a Swivel on the ground chain to a mooring buoy. In some cases the boat makes fast to the buoy, in others the buoy is brought aboard so that the riser may be made fast to the cleats, bitts or samson post.

Morse code light

A beacon light which flashes a letter of the Morse code. Rather rare.


To sail, usually to windward, with the motor providing some additional push. A very sensible way of making progress, quicker and easier than sailing, quicker and more comfortable than just motoring.


Most modern sailing cruisers have at least as much mechanical power as the motor-sailers of the past, and many have more. They also have more sail area. Perhaps the main distinguishing characteristic of most motor-sailers is that they retain the sort of shelter and comfort that motor cruiser owners are sensible enough to demand but which sailing people seem to think degenerate.

Mould or mold

The spelling is different in England from that in the USA. To a real boatbuilder a mould is a pattern or template of an internal hull section. Moulds are set up along a centreline in the builder’s shed, and braced to the roof. The hull is then built around them and they are eventually removed. On the other hand, a mould to a modern slush-bucket boatbuilder is hollow, like a jelly-mould, inside which laminates of glass and polyester resin can be laid up. That kind of mould has the dimensions of the exterior of the boat, and is itself made by ‘moulding’ over a solid wooden Plug which has to be made as accurately as is humanly possible. A hull laid up of resin and glass inside a mould is said to be ‘moulded’. But so is one made from strips of wood veneers glued in layers over a male plug. A wooden boat may be Cold moulded, as is usual, which means that the glue sets at ambient temperatures without heating. More rarely it may be Hot moulded, which involves baking the glue at quite a high temperature. Anything made in or over a mould is called a Moulding, whether it be as large as a hull or as small as a ventilator. By contrast there is the more ancient moulding, the half-round or quarter-round timber strip used by a traditional boatbuilder to fit into such corners as that between a hatch coaming and a deck.

Moulded and sided

Boatbuilders’ usage, meaning the dimension of a timber between its curved faces. Thus a frame or rib might be described as ‘four inches moulded, and three inches sided’, meaning that it is four inches between the curved faces and three inches between the straight faces. In a deckbeam ‘moulded’ is the thickness top to bottom, and ‘sided’ is the fore-and-aft dimension. In a keel ‘moulded’ is the vertical dimension, ‘sided’ is the lateral or side-to-side.

Moulded depth

This term is one whose meaning has changed slowly over the years. Except in strictly technical parlance, it would nowadays be taken to mean the body depth of a hull. That is to say the depth between deck and keel. The term is used of any type of boat, whether of moulded construction or not.


To close the open mouth of a hook by taking several turns of a lashing across it. Double, or sister hooks are moused with a lashing of mar line to keep them closed.


Member of the Royal Institute of Naval Architects.


Maritime Safety Information. Weather, navigation and tidal warnings broadcast on the BBC, Navtex, VHF and other media by the MCA.


A hollow in the shore near High-water mark where a boat may lie when laid up. When the mud is soft she may create her own berth by the combined action of her weight and of the water flow around her bottom.


A boat with more than one hull, such as a catamaran (two hulls) or trimaran (three hulls)

Mushroom anchor

An anchor used in soft mud, sometimes as part of a laid mooring. It is shaped like a mushroom with a very hollow crown.


A headwind. A wind on the nose. A wind on your muzzle – if you happen to be a sea-dog. See: Eye Of The Wind).


To restrain and hold down a sail or other piece of flapping canvas. (See Dowse.)


Polyester film used for sails. Has high strength for its weight. Mylar is in fact a trade name of its American maker. The same stuff made in Britain goes under the name Melinex. Polyester fibre when woven into cloth for sails has the trade name Dacron in the USA, Terylene in the UK.