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Glossary of yacht surveying terms



Alongside of; on the beam


At, near or towards the stern; to move aft is to move back Alternator DC electrical generator.



Usually zinc or manganese casting fixed to the hull or metal item below the waterline, that will corrode instead of underwater fittings, thus providing protection against electrolytic corrosion.



A composition applied below the waterline to the bottoms and sides of all vessels to inhibit the growth of weed and barnacles



A strengthening timber behind the lower part of the stem and above the foremost end of the keel in a wooden vessel



Orientated across the vessel.



Standing or running (adjustable) wire rigging that supports the mast from the stern; a wire mast support leading aft to the deck or another mast



Timber standing proud usually around the aft quarters of a hull on pilot boats, to provide protection to the hull when pulling away from a ship.


Ballast keel

The keel of a yacht shaped from the ballast  (an additional weight carried in a ship) to give her stability under sail.


Ballast Tanks

Tanks carried in various parts of a ship for water ballast, for stability and to make the ship seaworthy.


Balsa core

Sheets of balsa wood with the grain running across the thickness, used as a core material between two skins of fibreglass, usually in decks, to provide a stiff panel. Unsuitable for use in hulls below the waterline.



A small shellfish which sticks to the bottoms of ships



An instrument that measures atmospheric pressure in inches or millibars of mercury



A thin, flexible wooden or plastic strip inserted into a pocket (batten pockets) on the back part (leech) of a sail to stiffen it and assist in keeping its form.



(1) The transverse measurement of a boat at its widest point. Also called breadth. (2) One of the transverse members of a ship's frames on which the decks are laid.



Longitudinal timber onto which deck beams are attached.



(1) A place for a person to sleep. (2) A place where the ship can tie up or anchor.


Bevel drive gearbox

A gearbox containing bevel drives enabling input and output shafts to lie at 90 degrees to each other. Used in rotating rod steering systems.



The very lowest part of a boats interior where water is likely to collect


Bilge Keel

Shallow keels, usually placed in conjunction with or in place of a centre keel. Attached to each side of a vessel,


Bilge pump

A mechanical, electrical, or manually operated pump used to remove water from the bilge


Black water tank

A holding tank used for toilet waste.



A stay from the stem of a boat to the end of the bowsprit used to counteract the upward pull of the forestay.


Bosun’s Chair

Canvas or wood seat attached a halyard to raise and lower someone to work on the mast


Bow roller

Fitting at the stem head that will carry the anchor chain, and often also the forestay.


Bow thruster

A propeller at the bow of the ship provides transverse thrust as a manoeuvring aid.



name given to any vertical partition or wall which separates different compartments or spaces from one another, also adding strength. Sometimes bulkheads are also watertight, adding to the vessel's safety.



A section of hull rising above deck level, intended to deflect seawater away from the deck when underway. 



A short spar projecting over the stern of a sailing vessel to sheet the mizzen sail when the mizzen-mast is so far aft that there's not enough room inboard to bring down the sheet and trim the sail. Also, a short spar extending from the stemhead in place of a bowsprit.


Butterfly hatch

Traditional timber framed deck hatch


Calorifier hot water tank

Hot water tank drawing heat from the engine cooling water.


Canvas sheathing

Canvas bonded onto hull and deck surfaces.



A piece of trim, usually wood, used to cover and often decorate a portion of the boat, i.e., cap rail



A drum on a windlass, used for pulling ropes.


Cardan shaft

A shaft usually positioned between the engine and propeller shaft, water jet or stern drive. Fitted with a universal joint at each end to take up a small angle changes. 



Timbers used to support the coamings of a wooden ship; also for supporting hatches.



A traditional and common method of timber planked hull construction, where the plank edges butt to each other.



Forcing material into the seams of the planks in a boat's deck or sides to make them watertight


Chain plates

A metal plate, strap, or rod bolted to the hull structure to which the lower ends of shrouds and stays are attached



A marine hardware store


Chine, hard chine

The line on the external surface of a hull where longitudinal plates, or panels of plywood meet at an angle.



A traditional and common method of timber planked hull construction where the lower edge of the plank laps over the top edge of the next plank down.



A fitting of wood or metal, secured to the deck, mast, or spar, with two horns around which ropes are made fast.



The lower aft corner of a fore and aft sail, both lower corners of a spinnaker, and the lower corners of a square sail



The cabin roof, raised above the deck to provide headroom in the cabin.



A low vertical lip or raised section around the edge of a cockpit, hatch, etc. to prevent water on deck from running below



The location from which the boat is steered, usually in the middle or at the stern of the boat.


Code of practice

MCA regulations governing the safety of small vessels when in commercial operation such as charter and sail training 



An opening in a bulkhead through which the crew may pass. Often used to refer to the entrance into the cabin from the cockpit.



A term usually associated with light weight craft that are built using high strength reinforcements such as Kevlar and carbon fibre, in association with structural core materials such as PVC foam and aluminium honeycomb. These materials are usually bonded with high performance resins such as epoxy.



Panel on which controls, switches, and instruments may be mounted, usually at the helm position.


Constant velocity joint

A joint in a shaft that will accommodate a small amount of change in direction, without causing a variation in the angular speed during a single 360 degree revolution. It will not transmit thrust and therefore should be used in conjunction with a thrust bearing in a propeller shaft train.


Copper tingles

A patch of copper sheet, nailed over a minor defect on a timber hull



Surface cracks usually caused by weathering process


Cruising chute

Large lightweight foresail set with a loose luff.


Cutlass bearing

The water lubricated bearing surrounding the propeller shaft where it exits the hull and also in P brackets.



A single masted sailboat similar to a sloop except sails are arranged so that many combinations of areas may be obtained. A sail plan with two headsails, a main jib and a smaller staysail set between the jib and the mast.



A buoy that may be thrown in the event of man overboard, and which carries a pole standing above the surface of the water, and showing a bright flag and light.



Small fixed cranes that are used to lift heavy items from the water such as tenders.



Heavy longitudinal timbers fastened under the keelson. The timbers of the bow and stern are fastened to the deadwood.


Deck cleat

A cleat on deck used for mooring.



The underside of the deck, viewed from below the ceiling.



The separation of layers of fibreglass, or of laminations of timber. Also the separation of layers of veneer in plywood.



Screen of cloth or other material to give the crew protection against the weather, wind and water spray.


Drive belt

Rubber belt usually externally fitted on an engine and which drives from and to a drive wheel. 



Large nails used for fastening planks.


Electrolytic action

Corrosion set up by an electro-potential field, usually caused by different metals below the water line, and by battery earth leaks.


Encapsulated ballast

Ballast within a fibreglass or metal keel.


Engine mounts

Supports between the engine and hull structure



A nautical version of the national flag of the country usually flown at the stern.


Epoxy compound

A paint or resin that is based on epoxy resin.



(1) In good condition. (2) To adjust to proper shape or size.



A fitting used to guide a line in a particular direction without chafing.


Fiddle rail

A low rail used at the edge of horizontal surfaces in the vessel’s accommodation furniture, intended to prevent items from sliding off.


Flexible glands

A water seal that is mounted flexibly on a tube, usually with a rubber hose.


Float switch

A switch that activates an electrical circuit when the water in which it sits, rises above a certain level. Used often to activate bilge pumps.



A transverse frame running each side of the keelson to the bilges. Its structural function is mainly to distribute the loads applied to the keel, into the hull shell.


Fly bridge

The highest navigation bridge. It usually includes an added set of controls above the level of the normal control station for better visibility.



Aluminium section on the forestay that takes the luff of the sail



The lower edge of a sail.



Towards, near, or at the bow; Prefix denoting at, near, or toward the bow.



A structural member of a hull running from the keel to the side rail; the transverse strengthening members in a ship's hull that extend from the keel to the deck or gunwale. The frames form the shape of the hull and act as a skeleton on which the hull is secured.



folding or rolling a sail and securing it to its main support


Furling system

A system for rolling the sail away.


Galvanic isolator

A device that is designed to prevent electrolytic corrosion. A galvanic isolator is fitted in series with a shore supply AC earth conductor, to block low voltage DC galvanic current flow of up to 1.2 volts.



The first plank on the outer hull of a wooden vessel next to the keel. In steel ships, the plating next to the keel, or what is known as strake A.


Garboard plank

The first plank above the keel


Gearbox output flange

The flange onto which the propeller shaft is attached to he engine gearbox



The outer resin surface of a fibreglass boat, usually coloured.


Genoa tracks

The track fastened to the deck to which the genoa sheets are led, before leading to the winch



A system by which an object such as a compass is suspended so that it remains horizontal as the boat heels.



An adjustable fitting used for providing a seal on a shaft. Also a means of providing a seal for cables or pipes through a bulkhead or deck.



The fitting which connects the boom to the mast.



Global Positioning System



Timber board made from a grid of narrow planks


Graving piece

A small piece of timber let into a timber member as a local and non structural surface repair.


Grey water tank

A holding tank used for storing washing waste water.


Grit blasting

Method of aggressively abrading a surface using sand or similar material, propelled onto the surface in a high pressure spray.



The action of a vessel striking the sea or river bed.



Glass Reinforced Polyester. Commonly called fibreglass



The upper deck rail along both sides of a vessel to prevent anyone on board from falling overboard.



A ring-shaped fitting into which the rudder pintle is inserted which allows the rudder to pivot.



The upper edge of a boat's side; the part of a vessel where hull and deck meet.



The part of a windlass around which the chain is driven.



A line used to hoist or lower a sail, flag or spar. The tightness of the halyard can affect sail shape.



The top of a sail or mast.


The toilet compartment.


Highfield levers

A lever usually used to tension a piece of rigging


HIN number

A unique number imprinted into the hull on or near the transom, which identifies the vessel, and indicating country of origin, manufacturer, model, date of hull manufacture, and model year.


Holding tank

A tank used for storing liquid waste before discharging overboard at sea or to a land waste station. Often used in toilet systems.


Isolation transformer

A device fitted immediately in line with the shore supply inlet, that will prevent galvanic DC leakage of any voltage in the earth connection, from being transferred from the shore supply into the vessels circuits. It will also eliminate polarity problems, and other disruptive elements from the shore supply such as voltage surges and spikes.



A line or cable secured between two points and used as a support for various purposes and usually on deck for attaching a safety harness.



A beam attached to the top of the floors to add strength to the keel on a wooden boat.



A sailboat with two masts, where the aft mast, the mizzen, is the shorter mast, positioned forward of the rudder post.



An angle or channel from deck beam to shell frame taking the place of a bracket.


Lap joints

An overlap joint usually in timber or metal.



Compartment in the stern of a vessel used for storage; a storage space below the deck in the cockpit.


Lead car

Turning wheel for the jib sheet that is attached to the track on deck and which may be adjusted for position.


Lee board or lee cloth

A board or canvas sling, arranged longitudinally at the inboard edge of a berth, to help prevent the occupant from falling out, when the vessel is heeling.



The trailing edge of a sail.


Limber holes

Holes in the bottoms of floors or floor timbers for drainage; holes in the bilge cross frames to allow bilge water to drain to the lowest point,



1. An instrument that reads the speed and records distance travelled of the vessel.   2. A journal that’s kept by the watch keeper to record all significant navigational details during a passage.



The leading edge of a sail.


Mascerator pump

A pump that will pump liquids and soft solids that can be broken up. Usually used to discharge waste from holding tanks.


Mast partners

Reinforcements for a mast where it passes through a deck



Miniature Circuit Breaker.



Marine Coastguard Agency



On the centreline of the hull


Mimic panel

A panel engraved with the outline of the vessel, in which small lights are set, that will illuminate when an electrical circuit is activated. Often used to indicate when navigation and deck lights, and electric bilge pumps are working.



A small sail set on the mizzenmast, which is positioned forward of the rudder post



The mast aft of the mainmast in a sailing ship - the shorter mast behind the main mast on a ketch or yawl


Moisture meter

A meter used to measure the amount of moisture in a material


Instrument that receives public messages broadcast by the coastguard.



Process by which water passes through a membrane such as gelcoat, to form a solution under a higher pressure than the originating source of water, causing blisters to form.



A removable walkway that is used to board a vessel from the quayside, also called a gang plank.


P bracket

A strut that supports the outboard end of the propeller shaft



Timber plugs fitted over the head of screws in planking



A tapered metal pin which fastens the rudder to the stern by dropping into gudgeons


Polyurethane foam

A closed cell foam material with very little strength and often used to form buoyancy. Also used to make shapes over which fibreglass may be laminated to form frames etc.



The left side of the boat when facing forward. The opposite of starboard


Prefilter units

A fuel filter in the fuel supply line, that does not have a glass bowl.



1. European Recreation Craft Directive who publish a set of standards to which recreational craft of less than 24 meters length, must be built and certified.  2. Residual Current Device, that will trip the mains AC supply in the event of a leak to earth.


Roller Furling

A method of storing a sail, e.g., by rolling the jib around the headstay.


Roller Reefing

A system of reefing a sail by partially furling it. Roller furling systems are not necessarily designed to support roller reefing.


Rubbing strake

A longitudinal member standing proud on the topsides of a hull, to provide protection to the hull when coming alongside.


Rudder stock

The shaft or post onto which the rudder is made


Sampson posts

A strong vertical post used to attach lines for towing or mooring.



Deep corrosion in mild steel, characterised by hard layers of oxidised steel.


Scarf joint

A joint between to lengths of timber with each end cut to a long mating wedge. 



A fore-and-aft rigged sailboat with two or more masts. The aft mast is the same size or larger than the forward ones.



An opening in a deck, cockpit, toe-rail or bulwark, to allow water to run off the deck and drain back into the sea.


Sea cock

A through hull valve, a shut off on a plumbing or drain pipe between the vessel and the sea

Servo valve

A valve that is operated electrically


Shaft bearings

Bearings that support a rotating shaft such as the propeller shaft.


Shaft brushes

Electrical contacts on a shaft usually used to electrically connect the hull anode to the shaft



A transverse or longitudinal crack in timber, usually caused by shock loads, such as those sustained when the tree is felled.



The straight or curved line of the deck line; curvature of the lines of a vessel toward the bow and stern.



A line that controls the angle of the sail in its relation to the wind; attached to the clew of a sail to adjust its trim


Shore supply system

An electrical system on board drawing supply from alongside the berth.



Part of the standing rigging that helps to support the mast laterally by running from the top of the mast to the side of the boat


Shroud Plates

Attachment fitting for the shrouds to the hull of deck


Signalling shapes

Anchor ball and steaming cone signalling shapes, displayed on the mast or rigging



An extension of the keel for protection of propeller and rudder.


Skin fittings

Fitting in the hull onto which a valve and/or hose or pipe may be attached



A single mast vessel with fore and aft rigged sails.


Sole board

Cabin or salon deck or floor; the inside deck of the ship


Solenoid switches

A switch operated by an electric solenoid that is switched elsewhere


Sound condition

The condition is functionally intact.



A pole used as part of the sailboat rigging, such as masts, booms, gaffs, yards, etc



A large lightweight symmetrical sail used for sailing downwind. The windward clew sets on the spinnaker pole, and the leeward clew is sheeted to the aft end of the deck.


Spinnaker pole

A spar that is set up horizontally between the mast and the windward clew of the spinnaker.


Spray hood

A canvas screen at the forward end of the cockpit, providing shelter from sea spray. Usually fitted on a folding tubular framework.


Spray rails

External stringers of a triangular section, on the bottom of a planing hull, which provide additional lift.



Small struts or spars extending toward the sides from one or more places along the mast. The shrouds cross the end of the spreaders, enabling the shrouds to better support the mast.


Stanchion base

The fitting into which a stanchion is secured



A vertical support for guardrails and lifelines


Standing rigging

Stays and shrouds that support the mast.



The right side of the boat when facing forward.



A line or wire from the mast to the bow or stern of a ship, for support of the mast; rigging used to support the mast from forward or aft.



A triangular fore-and-aft sail carried on a stay. A sail that is set on a stay, and not on a yard or a mast. On a cutter this is the sail located between the jib and the main sail



The forward edge of the bow. On a wooden boat the stem is a single timber.



Top of the stem 


Stern gland

Water seal where the propeller passes into the stern tube, exiting the hull.


Stern post

1) A large casting shaped to allow the propeller blades to revolve. The rudder is fitted on the after post. (2) The principal vertical timber in a ship's stern, upon which the rudder is fastened.



On wooden boats, a line of planking running from the bow to the stern along the hull.


Strip plank

A more recently developed method of hull construction, where narrow planks are used which are edge nailed and glued to the edge of the previous plank.


Structural floor

Structural cross member passing over the top of the keel in side the hull.



A rotating fitting used to keep a line from tangling.



A gauge that measures engine revolutions per minute.



1. The point in a sail where the luff and foot meet.   2. To change direction by pointing the sailing vessel into and beyond the upwind direction.



A clenched copper fixing on rigging wire



1. A small boat used to ferry the crew to and from the mooring, and which may be carried on board.  2. A term used to describe a sailing boat that will heel over easily.



A bar or handle for turning a boat's rudder or an outboard motor, thereby steering the boat.



On wooden vessels, the ribs of a wooden vessel, connected to the keel, which give shape and strength to the ship's hull. Usually formed out of straight timber by steaming and bending to shape.



The sides of a vessel between the waterline and the deck


Tramex meter

A moisture meter



The athwartship portion of a hull at the stern. The flat, vertical aft end of a ship.


Trim tab

An adjustable section of the rudder that allows the rudder to be corrected for lee helm or weather helm.


Tumble home

The distance the ship's side falls in towards the centre line above the point of maximum beam. Opposite of flare.


Universal joint

A joint in a shaft that will transmit torque through a minor angle change, but will cause a variation in angular speed during a single 360 degree revolution, thus sometimes leading to vibration if used in a propeller shaft train. Not suitable for transmitting thrust. Most often found in vessels in their rod steering systems.


Vinyl linings

Decorative linings within the accommodation space.



Mooring ropes.


Webbing jackstays

Straps lying full length on deck onto which a safety harness may be clipped



Surface distortion of the gelcoat below the waterline, caused by water absorption in strands of fibreglass, and usually leading to osmosis.


Wind deflector

Screen on the flybridge to deflect wind from the helm position when underway.



Arrow shaped vane on the mast head indicating the wind direction



A special form of winch used to hoist the anchors.


Woven rovings

Straight filaments of fibreglass that are arranged in strands, and woven to form a fibreglass cloth for use in GRP.



A foresail used on yachts similar to a genoa, but cut narrower, with its leech not overlapping the mainsail, and a higher clew.




A sailing boat with two masts, the aft mast being shorter, and positioned aft of the rudder post.


If you would like to help improve this glossary, please email your suggestions to 


Jim Pritchard 

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