Boat measurements and terms
What is it all the boat things called FAQ

Boat measurements and terms

What is everything called FAQ

Introduction to the boat measurement FAQ

There are so many names for rig- and sail measurement, sail parts and boat equipment where many in daily use just have short cuts like J, LP, AWA, COG etc. Below here we will try to list them in sections for rig and sails with a short  description for each. They will be listed alphabetic in each section. Just click on eac headline to unfold the answers.

👉 What are the boat measurements terms on a sailboat rig. ->
  • E: The max mainsail outhaul mark on the boom.
  • I: Distance from head stay top attachment to the deck.
  • J: Distance from head stay bottom attachment to front of the mast measured.
  • J2: Base of staysail / cutter stay triangle
  • JLRH: Distance from front of mast to the eye on the end of the bow sprit.
  • ISP: Spinnaker halyard above the deck.
  • P: The max mainsail top mark on the mast.
  • SPL: Length for the spinnaker boom.
  • STLFm: Length of the bowsprit from headstay attachment.
  • T: Length of the head stay.
  • TSP: Distance from front of mast to the eye on the end of the bow sprit.
  • Aft stay: Is attached from the mast top to aft on the boat. On masthead rigging it controls the tension on the head stay and also the bend of the mast interacting with the cutterstay. On fractional rigging boats it controls the bend of the mast interacting with the runners and checkstays.
  • Angled spreaders: Is when the spreaders are angled backwards. This is more and more common even on race boats.
  • Baby stay: Is a short stay from lowest spreader to the deck to control the mast forward aft. movement.
  • Boom nock: Rear end of the boom.
  • Boom vang: Also called kicker or kicking strap, is a line / piston system that pulls the boom up and down to control the shape / twist of the mainsail.
  • Bowsprit: A fixed or retractable extension of the bow.
  • Checkstays: Are part of the runners and used for stabilise the mid part of the mast and control the max bend of the mid and lover part of the mast. 
  • Continues rig: Is when all side stays goes from the mast to the deck passing the spreader ends.
  • Cutter stay: A inner foresail stay aft from the head stay, often used for a jib 
  • Discontinued / linked rig: Is when the intermedium vires are connected to the top side stay at each spreader end. 
  • Fractional rig: Is a rig type, where the head stay is attached lower than the the mast top. 7/8 is quite normal on racing boats and 9/10 on cruising boats.
  • Gaff: The top boom on a gaff rigged boat.
  • Gooseneck: The pivoting part that connects the boom to the mast and also contains the attachment point for the mainsail clew.
  • Inner forestay: Is a not sail carrying stay for stabilising the mid part of masthead mast.
  • In-line spreaders: Is when spreaders straight across each others 90° on a boats centerline.
  • Luff rake: Distance from mainsail tack to a vertical line from the mainsail head (mast heel).
  • Mast head rig: Is a ri type where the head stay is attached at the top of the mast.
  • Triatic stay: Is the forestay on a mizzen mast attached to the top of the main mast and the top of the mizzen mast, or lead down the mizzen mast.
  • Runners: Or running backstay as they are also called has different functions on masthead and fractional riggings. On masthead they work together with cutterstay’s to controle the mast bend and movement. On fractional rigging the control the tension on the head stay.
  • A: The length of the head sails aft leech.
  • E: The mainsail foot length.
  • EY: The mesan sail foot length.
  • FSA: Asymmetric spinnaker area (calculated).
  • FSHW: Mid width width on a asymmetric downwind sail.
  • HSA: Head sail area (calculated).
  • HHB: Head sail head board.
  • HHW: Headsail lower width.
  • HQW: Headsail lowest width.
  • HTW: Headsail mid width.
  • HUW: Headsail upper width.
  • LP/HLP: The perpendicular length from the clew (sheet corner) to 90° on the head stay.
  • MHB: Mainsail head board width.
  • MHW: Mainsail half width.
  • MQW: Mainsail quarter width.
  • MTW: Mainsail tre quarter width.
  • MUW: Mainsail upper width.
  • P: The max mainsail luff length.
  • PY: The max mizzen sail luff length.
  • SF/FSFL: Length of the foot on a symmetric spinnaker.
  • SHW: Spinnaker half with.
  • SL: Length of the side leech on a symmetric spinnaker.
  • SLE: Length of the aft leech on a asymmetric spinnaker and both leech on a symmetric spinnaker.
  • SLU: Length of the luff on a asymmetric spinnaker.
  • SMW: Spinnaker max width.
  • STLFm: Length of the bowsprit from the head stay attachment.
  • U: Length of the bottom leech of the head sail.
  • AWA: Average wind angle is the wind angle passing your boat, affected of your boat speed over ground.
  • AWS: Average wind speed is the wind speed passing over your boat, affected of your boat speed over ground.
  • BTW: Bearing to waypoint is the course you must sail to approach the waypoint. 
  • COG: Course over ground is the compas course the boat is moving over ground.
  • DTW: Distance to waypoint.
  • HDG: Heading is the compas course the boat is pointing relative to the magnetic or true north.
  • TWA: True wind angle is the real wind not affected of your boat speed.
  • TWD: True wind direction is the compas direction of the wind.
  • TWS: True wind speed is the real wind, not affected of your boat speed over ground.
  • SOG: Speed over ground is the speed the boat is moving over ground.
  • STW: Speed through water, the speed the boat moves relative to the water, usually measured with a paddle wheel.
  • VMC: Velocity made good on course is the speed the boat are moving towards a windward or leeward when its possible to steer direct to the mark.
  • VMG: Velocity made good is the calculated speed the boat moves directly towards a windward or leeward mark. The VMG is one of the most important velocity scales.
  • XTW: Cross track error, is the distance your boat have drifted of the intended line to the waypoint.
  • Clew: Rear bottom part of sheets attachment point on sails.
  • Headbands: A sewn in profile on headsails for use en head foils.
  • Headboard: The top of the sails for halyard attachment. It can be a simple ring, but also made of aluminium or carbon fiber plates to make the of sails wider as on Fathead or square head sails .
  • Leech: Aft part of mainsails, head sails, asymmetric sails and both side leech on symmetric spinnakers.
  • Leech line: A thin adjustable line sewn in the aft leech to prevent the sails aft leech to flap rapidly. On mainsail it can be practical to have it over top.
  • Luff: Front leech on mainsails, head sails and asymmetric downwind sails 
  • Piston hanks: Is small hooks to hook on headsail on wire head stays and can be made of bronze, stainless steel or plastic.
  • Self-tacker sheet board: A quarter circle board made of aluminium or carbon fiber plates with a series of holes. That will allow to change the twist in the sail by moving the sheet block between the holes.
  • Tack: The front bottom part of head sails and asymmetric downwind sails.