DIXON KEMP

Manual of Yacht and Boat Sailing and Architecture

(11th and final edition, 1913)

B. - BM.

Back.--
To back a sail, is to haul the sheet to windward.
 
Back and Fill.--
To luff up in the wind, and then fill off again. Often a vessel is worked up a narrow channel with a weather tide by backing and filling: that is, the helm is put down slowly, and the vessel kept moving until she is nearly head to wind; the helm is then put smartly up, and the vessel filled again. Care must be always taken to fill before the vessel loses way. Figuratively, to back and fill is to blow hot and cold, or assent and dissent, or to go backwards and forwards with opinions.
 
Backing.--
Timber fitted at the back of other timbers.
 
Backstays.--
The stays that support the topmast with a beam or stern wind. The topmast shrouds or rigging. (See "Shifting Backstay" and "Preventer.")
 
Backwater.--
The water thrown back when waves strike a wall or other solid object. The water that appears to follow under the stern of a ship. To back water is to move the oars of a boat so that the boat moves astern instead of ahead.
 
Baffling Wind.--
A wind that is continually shifting its direction, so that it is difficult to keep the sails full or steady; more frequently used when the vessel is close or nearly close hauled.
 
Bag.--
Sails are said to bag when they do not sit flat.
 
Bagpipe.--
To bring the sheet of an after-sail, such as the mizen, forward to the weather rigging, so that the sail forms a bag, or back sail: when head to wind useful to put stern way on a vessel.
 
Balance Lug.--
A lug sail with a boom and yard. About one-twelfth of the sail is on the fore side of the mast, and thus "balances" on the mast, requiring no dipping when going about; apparently adapted from the Chinese lug sail.
 
Balance Reef.--
In gaff sails a hand with reef points or eyelet holes for lacing, sewn from the throat to the clew. The reef is taken in by lowering the jaws down to the boom and lacing the sail along the reef band to the boom. Sometimes the gaff end is lowered down to the boom end ; in which case the reef band is laced along the gaff.
 
Bale.--
To throw water out of a vessel or boat by buckets or balers.
 
Baler or Bailer.--
A small basin-like vessel, used for throwing water out of a boat.
 
Balk.--
A hewn tree; a piece of timber for masts, &c.
 
Ballast.--
Dead weight carried to assist the stability of a vessel. A ship is said to be in ballast when she has no merchandise on board, but only sand, gravel, mud, or rubbish as ballast. A yacht in marine parlance is always "in ballast."
 
Ballast, To Keep Clean or Sweeten.--
The ballast of an old vessel should be removed every other season, scrubbed, and whitewashed with hot lime, or coated with black varnish, paraffin, or red lead. The hold of the yacht should at the same time be thoroughly cleansed and black varnished, distempered, or red leaded, or coated with one of the patent paints. A mixture of two-thirds Stockholm tar and one-third coal tar boiled together will make a good composition for the ballast and the inside of a vessel below the floor. Many vessels are regularly hauled up every year, and of course their ballast is taken out and stored. The ballast of a new vessel generally requires cleansing when she is laid up, as the soakings from the oak frames make a very unpleasant odour. (See "Distemper," "Laying Up," and "Limber Boards").
 
Ballast Bearers. (See "Bearers.")
 
Ballast, Shifting.--
To put ballast (usually duck shot in bags) in the weather side of a vessel during sailing. This practice for many years has been strictly forbidden in yacht racing, and if a man were known to practise it he would be at once debarred from racing under Y.R.A. rules. Shifting ballast is of course forbidden on account of its extreme danger.
 
Balloon Sails.--
Balloon canvas is a term applied to sails of large dimensions, made of light cotton canvas.

The chief balloon sail is the spinnaker used for sailing when the wind is aft. A balloon jib used to fill up the whole space from the bowsprit end, masthead, and mast at deck; a balloon foresail is hanked to the forestay, but the clew extends some distance abaft the mast; in a schooner a balloon maintopmast staysail has an up and down weather leech extending below the lower corner of the sail, which is hanked to the maintopmast stay. It is sheeted on to the end of the main boom. A balloon jib topsail or "Yankee" jib topsail is a useful sail ; all modern balloon head sails are cut very high in the clew, so that the lead of the sheet nearly makes a right angle with the luff of the sail. Balloon jibs have long gone out of fashion. They were succeeded by "bowsprit spinnakers," whilst the bowsprit spinnaker, a low-footed sail, has in turn given place to the higher clewed balloon jib topsail A balloon topsail is another name for a jackyard topsail, or a topsail set with two yards. The upper or "topsail yard" is a vertical continuation of the topmast. The "lower" yard or jackyard is parallel with the gaff and should act as a direct continuation or extension of it. In setting a jackyard topsail a certain amount of "drift" or "space" should be left between the gaff and the lower yard so that there may be play to take up the slack of the sheet.

A modern jackyard topsail should set as flat as a card. Formerly, the foot yard was short and the head yard was of great length -- as long as could be stowed on the deck of a yacht -- and the sail, very heavy to hoist, was quite unfit for close-hauled work. As the hoisting of these heavy yards was an operation of so much labour, they fell into disuse for some years between 1873 and 1888. After that date the sail was reintroduced with a comparatively short head yard and longer foot yard, after a pattern designed in American waters. The sail had consequently as much area as the old fashioned "balloon topsail," and the combined weight of head yard and foot yard was about half that of the old yard; beyond this, as the sail was well peaked, it sits and stands well on a wind in moderate breezes. In the present century with the introduction of hollow yards the area of the sail has been further increased, and the extreme lightness of yards has enabled the modern balloon topsail to be carried efficiently in fresh and even strong winds.

 
Bamboo Spars.--
In small boats these are often used on account of their lightness. They vary much in strength, and should be from 10 to 20 percent greater diameter than solid wood spars.
 
Bare Poles.--
With no sail set. With all the sails furled or stowed at sea for scudding before a heavy gale, or sometimes for lying to.
 
Bargee.-- A slang term for the crew of a barge.
 
Bar Harbour.--
A harbour that has a bank or bar of sand or gravel at its month, so that it can only be entered at certain hours of the tide.
 
Bark.-- A general term for a vessel.
 
Barque.--
A three or four masted vessel, square rigged on all but the mizzen mast.
 
Barquentine.--
A vessel square rigged on her foremast, and fore-and-aft rigged on her two other masts.
 
Barra Boats.--
Vessels of the Western Isles of Scotland, with almost perfect V section.
 
Barrel or Drums.--
The part of a capstan, windlass, or winch round which the cable or rope is wound whilst heaving. Sometimes termed the drum.
 
Base Line.--
In naval architecture a level line near the keel, from which all heights are measured perpendicularly to it. Generally in yacht designs the load waterline, as shown so a Sheer Plan, is made the base line, and all depths arid heights are measured perpendicularly or at right angles to it.
 
Batten.--
A long piece of wood need to lash to yards or booms to strengthen them. Thin pieces of hard wood fitted to spars to prevent their being chafed or cut. Thin splines of wood used by draughtsmen to make curved lines. A general term for a thin strip of wood. Battens are fitted to sails to keep the leach flat.
 
Batten Down.--
Putting tarpaulins over hatches or skylights, and securing them by iron bars or wood battens.
 
Beach.-- A shore. To beach is to lay ashore, or strand.
 
Beach Boats.-- Flat floored boats that can be readily beached.
 
Beacon.--
stake, boom, or post put on a sandbank or shoal as a warning for vessels.
 
Beacon Buoy.--
A buoy with a cross, ball, or triangle, &c., on the top.
 
Beam.--
A timber that crosses a vessel transversely to support the deck. The breadth of a vessel. "Before the beam" is forward of the middle part of a ship. The wind is said to be before the beam when the ship makes a less angle than 90û with the wind. A beam wind is a wind that blows at right angles to a vessel's keel. "Abaft the beam "is towards the stern.
 
Beam and Length.--
The proportion a vessel's beam bears to her length varies according to her type. In sailing yachts it is found that for cruising a good proportion is about three and a-quarter to three and a half beams to waterline length.
 
Beam Ends.--
A vessel is said to be on her beam ends when she is hove down on her side by the wind or other force, so that the ends of her deck beams are on the water, or her deck beams perpendicular to the water. However, in sea parlance, a ship is said to be on her beam ends when knocked down by a squall to say 45û, so that when a ship is described as being on her "beam ends" the meaning need not be taken literally.
 
Beam Trawl.--
A trawl whose mouth is extended by a long spar or beam, as distinct from the otter trawl, which is distended by boards.
 
Bear, To.--
The direction an object takes from a ship expressed in compass points or by points in the vessel; as in reference to another vessel she bears S.E. or W.S.W., &c., or on the port bow, or weather bow, port beam or weather beam, port quarter or weather quarter, &c. ; or two points on the weather bow or port bow, &c.
 
Bear a Hand There ! -- An admonition to hurry.
 
Bear Away, or Bear Up.--
To put the helm to windward and keep the vessel more off the wind. Generally used in close-hauled sailing when a vessel begins to alter her course by sailing off the wind. (See "Wear.")
 
Bearers.--
The beams which carry the cabin floor or platform of a yacht, termed platform bearers.
 
Bearings.--
The direction between one object and another ; generally the direction of an object on land to a ship. The widest part of a vessel which may either be above or below water. A vessel is said to be on her bearings when she is heeled over, so that her greatest breadth is in the water.
 
Bearings by Compass.--
An object is said to bear, so many points on the port or starboard bow, or port or starboard quarter, or port or starboard beam as the case may be; or an object may be said to bear E.N.E. or E. or W., &c., from the point of observation.

The usual plan of taking a bearing is to stand directly over the binnacle, and notice which point on the compass card directly points to the object. A more accurate way of taking bearings may be followed thus on each quarter-rail abreast of the binnacle, have a half compass plate of brass fixed, or mark off compass points on the rail, and let two opposite points (say north and south) be in direct line or parallel with the keel. A pointer or hand, eight or nine inches long, must be fitted to the plate, to ship and unship on a pivot; move tire pointer until it points directly to the object, then read off the number of points it is from the direction of the ship's head. Next observe the direction of the ship's head by the binnacle compass ; if the ship's head points N., and the pointer showed the object to be, say, four points away westerly from the direction of the ship's head, then the object will bear N.W., and so on. If very great accuracy be required, and if the ship be yawing about, one hand should watch the binnacle compass, whilst another makes the observations with the pointer.

An object is said to bear "on the bow" if its direction in relation to the ship does not make a greater angle with the keel of the vessel than 45û. If the direction of the object makes a greater angle than that it would be said to bear "before the beam" ; next on the beam, then abaft the beam, on the quarter, right astern.

 
Beat.--
To beat to windward is to make way against the wind by a zigzag course, and frequent tacking. (See "Plying," "Thrashing," and "Turning to Windward.")
 
Beating to Windward.-- (See "Beat.")
 
Becalm.--
To deprive a vessel of wind, as by one vessel passing to windward of another.
 
Becalmed.-- In a calm; without wind.
 
Becket.--
A piece of rope used to confine or secure spars, ropes, or tackles. Generally an eye is at one end ; sometimes an eye at either end; or a knot at one end and an eye at the other.
 
Beef.--
Manual strength; generally the weight of the men hauling on a rope. "More beef here" is a request for help when hauling. Probably the term originated with the casks of beef used for food on shipboard.
 
Before the Beam.-- Towards the bow or stem of a vessel.
 
Before the Mast.--
A term used to describe the station of seamen as distinguished from officers. Thus a man before the mast means a common sailor, and not an officer. The term owes its origin to the fact that the seamen were berthed in the forecastle, which is usually "before the mast."
 
Before the Wind.-- Running with the wind astern.
 
Behaviour.--
The performance of a ship in a seaway or under canvas is generally termed by sailors her "behaviour."
 
Belay That.--
An order given whilst men are hauling on a rope, &c., to cease hauling and make fast to the last inch they have got in. Also slang for cease talking or fooling.
 
Belay, To.--
To make fast a rope or fall of a tackle. In hauling upon a rope the signal to cease is usually, "Belay!" or "Belay there!" "Belay that !" or "Avast hauling ! Belay!"

To belay the mainsheet in small boats where the sheet travels on a horse through a block. The block will travel on the horse by a thimble eye strop ; the sheet will he spliced to the clew cringle in the sail and rove through the block. Bring the fall of the sheet down to the pin under the stern seat, round which pin take a single torn then take a bight and jam it between the sheet and the seat, and a slight pull will release the sheet. The sheet can be belayed in the same fashion by a turn taken under a thole pin in the gunwale; or a bight of the fall can be taken and made fast round the sheet above the block by a slippery hitch. A pin for belaying a single sheet is shown in the accompanying sketch (Fig. 7). A through pin is fitted into the transom as shown The fall of the sheet is brought round the pin outside the transom, then round the pin inside the transom, and a bight jammed in between the transom and sheet.

 

Fig. 7

Belaying Pins.--
Pins in racks, in cavels, spider hoops, &c., to make fast ropes to.
 
Belaying the Binnacle.--
A slang term applied to the acts of a greenhorn or sham sailor who uses unseamanlike terms, or misapplies well known terms, or makes unseamanlike or impracticable suggestions.
 
Bell Buoy.--
A buoy with an iron cage upon top of it, containing a bell which is struck by a hammer or hammers moved by the heave of the sea.
 
Bells.--
The manner of keeping time on board ship by striking a bell every half hour. Thus one bell is a half hour, as half-past twelve; two bells one o'clock ; three bells half-past one, and so on until eight bells are struck, which would be four o'clock. One bell would then be begun again and proceed up to eight o'clock. Thus eight bells are struck every four hours, the duration of a watch. Except in the afternoon when, to change the order of the watch, one bell is struck at six p.m., dividing the time from 4 p.m. to 8 p.m. into two dog watches of two hours each.
 
Below.--
A general term for the under-deck space. To go below is to descend from the deck to the cabin, or to under the deck. A seaman always goes "below," and never "downstairs." It is considered very green and landsman-like to hear a person on board a vessel speak of going "downstairs" for below, or upstairs for "on deck."
 
Below! or Below There ! --
A mode of hailing or attracting the attention of the crew below by those on deck.
 
Bend.--
To fasten a rope to another I to fasten a rope to a spar; to bend a sail to a yard, &c. A knot, a mode of fastening a rope to a spar, &c.
 
Bends.-- The wales of a ship. Stout planks on the side of a ship.
 
Beneaped.--
Aground for want of water, owing to neap tides. The rise and fall of neap tides during quarter moons are lees than during the full and change; consequently, if a vessel got ashore during a high water spring tide she might have to remain all through the neap period.
 
Bermudian Rig.--
The mast of a Bermuda rigged boat is very long, and is often placed far forward with a considerable rake aft, and the sail set upon it is of the well-known sliding gunter shape. The objection to the rig before hollow spars were invented is the long heavy mast placed in the eyes of the boat, and although the sail stands well when hauled in on a wind, yet off the wind it causes some trouble, as it is often very difficult except in very strong breezes-to keep the sail from falling on board.
 
Berth.-- A place to sleep in; a cabin. Employment.
 
Berthed.-- The situation of a ship when anchored.
 
Berthon's Logs, or Speed Indicators.--
A log invented by the Rev. E. Berthon. A tube passes through the keel, and the water rises in this tube in proportion to the speed of the vessel through the water. A simple mechanical contrivance of weight, line, and pulley serves to indicate the speed on a dial.
 
Bevel.--
In shipbuilding, the departure from the square a timber is made to take to suit the inclination of a plank. An oblique edge of a piece of timber or plank.
 
Bevelling Board.--
A piece of wood used by ship builders on which the angle of the bevels for timbers are marked in lines.
 
Bibs.--
Pieces of timbers fastened to the hounds of ships' masts to support the trestle trees.
 
Bight.--
A loop or part of a rope doubled so as to form a loop, thus:
 
xxx
 
or, the deepest part of a bay.
 
Bilge.--
The round in a vessel's timbers where they begin to approach a vertical direction.
 
Bilged.--
A vessel is said to be bilged when her framing is broken in, or damaged along her bilge by grounding, or falling down when shored up by the side of a wharf.
 
Bilge Keels.--
Pieces of timber or steel plates (sometimes termed rolling chocks) fitted longitudinally on a vessel's bottom, so that she may take the ground readily and not damage her bottom. Bilge keels, however, now fulfill different offices and are fitted to large ships to assist in checking their rolling. Nearly all beach boats are fitted with bilge keels, and to some extent they prevent a boat making lee way; of course only the lee bilge keel can so operate to any useful extent, and the effectiveness of this one would be interfered with by the disturbed state of the water near it. Bilge keels, if very deep, would affect very greatly a boat's handiness in tacking; also the lee one would assist in heeling the boat to an extent dependent upon the force of the lee way, and the area of the bilge keel; on the other hand, bilge keels will tend to check the sudden heeling of a boat, for the same reason that they cause the process of rolling to be more slowly performed, because they have to move a body of water. In steel and iron built steam yachts, bulb iron bilge plates are often fitted and check the rolling.
 
Bilge Kelsons.--
Stout pieces of timber fitted inside a vessel in a fore-and-aft direction along the bilge to strengthen her.
 
Bilge Strakes.--
Thick plank worked longitudinally in the ceiling of a vessel inside along the bilge, or over the heads and heels of the frames, to strengthen her-used instead of bilge kelsons, and through fastened.
 
Bilge Water.--
The water inside a vessel, which in flat-floored crafts may rest in the bilge.
 
Bill.--
A point of land ; also the extreme points of the flukes of an anchor.
 
Bill Boards.--
Pieces of wood fitted to the head of a vessel to protect the plank from the fluke of the anchor.
 
Bill of Health.--
A document wherein it is certified that the condition of the crew is healthy or otherwise. Hence a clean bill of health means that all the crew are free from disorders, and a foul bill of health the contrary.
 
Bill of Lading.--
A document setting forth the cargo of a ship, certified by the master.
 
Bill of Sale.--
A document by which a vessel is transferred from one owner to another. A "Bill of Sale" must be produced before a register can be transferred. Forms of Bill of Sale can be procured from Waterlow and Sons, printers and stationers, London, E.C.

There are several points to which attention should be given before concluding a purchase. Wages form a prior claim on every vessel. It is therefore essentially necessary that a purchaser should satisfy himself that no claims of this description exist; or be may find, after he has completed his purchase, that he has some further large amount to pay before be can call the ship his own. In 1890 a case occurred in which the mortgagee of a large steam yacht, after taking possession, had to defend an action in the Admiralty Court, brought by the late master for wages and necessary payments, and eventually had to pay a large sum to settle these claims. It should also he seen, before a purchase is completed, that possession of the yacht can be given, and that she is in the hands of no shipbuilder who has a lien upon her and a right to detain her for work done. With regard to yachts, of course claims for salvage seldom arise ; but it is just as well to remember that, if they do exist, they form a claim against the vessel.

As to the sale of yachts, very little need be said, but there are one or two simple rules which it is absolutely necessary to follow. A vendor should never, under any circumstances, give up possession of his vessel until he has the purchase-money in hand. A breach of this rule has not infrequently produced rather serious consequences. In 1890 an owner sold his vessel to an apparently rich man, and very weakly gave him possession. He had to sue for the purchase-money, and to get the sheriff to seize and sell the yacht again, at a considerable reduction in price, before he was paid. Fortunately for him, he did get his money eventually, although the purchaser became bankrupt within a few months after the transaction.

It is necessary to be very guarded in dealing with foreigners. A case occurred, some few years since, in which an American gentleman bought a schooner yacht, and was given possession before payment of the purchase-money. The purchaser thereupon proceeded to get under way for America, and neglected to pay for the ship. The owners pursued him in a tug and brought him back to Cowes; thus securing the vessel, but not the money.

Another rule which should be observed is never to send a vessel out of the country to a foreign purchaser until payment has been made in England. An owner may find it a very difficult matter to enforce payment in a foreign court. The purchaser may raise difficulties and objections to the yacht after she has got abroad, and the owner may have to bring his yacht home again, with the expenses of his crew and his outfit to pay.

Another point with regard to which vendors require to be careful is the commission payable on a sale. Few sales are effected nowadays without the intervention of an agent, and it is an ordinary practice to put a yacht into the hands of several agents for sale. A purchaser frequently writes round to every well-known agent for a yacht likely to suit him, and perhaps lie gets particulars of the same vessel from three or four different agents. It is often very difficult to say which of them first introduces the vessel to him, and who is entitled to receive the commission on the sale. It is not an uncommon occurrence for two or three claims to be made for commission on the same vessel ; and it is very needful for the owner, before he completes his contract, to satisfy himself on this point, and to make sure that he will not be called upon to pay more than one commission on the sale of his yacht.

 
Billy Boy.--
A bluff, round-ended vessel, common in the north, often rigged as a cross between a ketch and schooner, usually with a single square topsail.
 
Binnacle.--
A ease wherein the compass is contained. (See "Compass" and "Fluid Compass.")
 
Bird's Nest.-- (See "Crow's Nest.")
 
Birlin.-- A rowing and sailing boat of the Hebrides.
 
Bitter End.--
The end of a cable left abaft the bitt a after the turns have been taken. Sometimes the anchor is shackled to the "bitter end" when the used end has become much worn. The extreme end of a rope.
 
Bitts.--
Stout pieces of timber fitted in the deck to receive the bowsprit ; also stout pieces of timber fitted in the deck by the side of the mast, to which the halyards are usually belayed.
 
Black Book.--
A book kept at the Admiralty, or said to be, wherein is recorded the offences of seamen. Several yacht clubs have kept "black books," but they have been of little use, as owners showed a disinclination to insist that no man should be engaged in his yacht who was on the "black book."
 
Blacking Down.--
Painting or tarring the rigging, or sides of a ship.
 
Black Jack.--
The black flag hoisted by pirates.
 
Black Leading a Boat's Bottom.--
It was formerly a common practice to black lead the bottom of boats, especially for match sailing, and the custom is still much followed. There were several methods of getting the lead on, and the following is as good as any:

First scrape the bottom clean of old paint, tar, &c., and stop open seams, nail holes, shakes, &c. Then put on a thin coat of coal tar, reduced by turpentine or naphtha until quite liquid. When dry and hard put on another coat, and if the boat is a large one this second coat should be put on by "instalments." When nearly dry, but yet sticky, put on the black lead, in fine powder. To get the powder on a dabber must be used; a sponge tied up in a soft piece of cotton cloth is the best thing for the purpose. Care must be taken not to attempt to put on the black lead in the sun or the tar will come through. On the other hand, if the tar is hard the black lead will rot "take hold." When the whole is thoroughly dry and hard, polish up with the ordinary brushes used by housemaids for grates.

 
Black Paint.--
A good mixture for the outside of a boat is thus made: to 6lb. of best black paint add half pint of good varnish and 1/2-lb. of blue paint.

Or, black 9lb; raw linseed oil 1 quart ; boiled linseed oil 1 quart ; dryers 1/2-lb.

For an iron yacht : 1cwt. of Astbury's oxide paint ; 6 gallons of boiled linseed oil; 1 gallon of turpentine ; 3 gallons of varnish; 21 lb. dryers. (Messrs Astbury's, King-street, Manchester.)

 
Black Varnish.--
Modern racing yachts are generally coated on the bottom with a mixture known as black varnish (See "Varnish"). When the varnish is well mixed and put on by a skilful man it is generally considered the best bottom for racing. In hot weather, however, a black varnished bottom must he wiped off, touched up, and repolished (about every two weeks) or it will become slimy.
 
Blackwall Hitch.--
A hitch used to jam the bight of a rope to a hook, &c. (Fig. 8.)
 
Fig. 8.

 

Blade.-- The flat part of an oar or screw propeller.
 
Bleaching.--
An American plan for bleaching sails is as follows:
Scrub with soap and fresh water on both sides, rinse well, then sprinkle with the following solution : slacked lime, 2 bushels; draw off lime water and mix with 120 gallons water and 1/4-lb. blue vitriol. This also preserves the sails. (See "Mildew.'')
 
Blind Harbour.--
A harbour whose entrance cannot readily be made out from a distance.
 
Blisters.--
Unsightly blisters on paint are generally caused by putting new paint upon the top of old, or using very thick paint. The old paint should be burnt or scraped off.
 
Block.--
A pulley. A single block has one sheave; double, two ; three-fold or treble, three ; and so on. (See "Fiddle Block" and "Sister Block.")
 
Black and Block.--
Chock-a-block. Two-blocks. When the blocks of a tackle are hauled close together. A vessel is said to take her main sheet block and block when the boom is hauled so much aboard that the two blocks come close or nearly close together.
 
Blow, A.-- A gale of wind.
 
Blue Jackets.-- Sailors.
 
Blue Peter.--
A blue flag with a white square in the centre; hoisted at the fore truck as a signal that the vessel is about to go to sea, and five minutes before the start of a race.
 
Blue Water.-- The open sea or ocean.
 
Bluff.-- A wall-like headland.
 
Bluff-bowed.-- Very full bowed, thus: xxx
 
B.M.--
Abbreviation for builders' measurement or tonnage, the formula for which is ((L - 3/5 B) x B x 1/2 B) / 94 . The length is taken from the after side of the sternpost in a line with the rabbet of the keel to a perpendicular dropped from the tore side of the stem on deck. This is "length between perpendiculars.'' O.M. is sometimes used, that being an abbreviation for "Old Measurement," which is the came as B.M.

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