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YOU ARE HERE Information / Kayak Design / Kayak Design Terms

Kayak Design Terms

A description of boat design terms and how they relate to boat performance.

ParticularsParticularsParticularsParticulars Just a fancy term for the

measurements and characteristics of aboat.

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Over All L engthOver All LengthOver All L engthOver All Length(ft)(ft)(ft)(ft)

Also known as Length Over All (LOALOALOALOA).The total length of the kayak frombow to stern

Over All WidthOver All WidthOver All WidthOver All Width(in)(in)(in)(in)

Also known as Beam Over All (BOABOABOABOA).The width at the widest point of theboat.

Water LineWater LineWater LineWater LineLength (ft)Length (ft)Length (ft)Length (ft)

Also known as Length Water Line orLoad Water Line (LWLLWLLWLLWL). The length ofthe boat measured at the waterline.Used to determine "hull speed". Ingeneral boats with longer LWLs will bemore efficient at high speeds. In other

words long LWLs general make boatsfaster. As the term "Load Water Line"implies this is the length of thewaterline when the boat is loaded thedesign displacement.

Water LineWater LineWater LineWater LineBeam (in)Beam (in)Beam (in)Beam (in)

Also known as Beam Water Line(BWLBWLBWLBWL). The width of the boatmeasured at the waterline. This is aprimary determinant ofinitialstability.

Design WaterDesign WaterDesign WaterDesign WaterLineLineLineLineDisplacementDisplacementDisplacementDisplacement(lbs)(lbs)(lbs)(lbs)

The Design Water Line (DWLDWLDWLDWL) determines the total amount ofweight the boat was designed to carry. This is a some whatarbitrary number. The boat can carry more or less, but the otherparticulars are only completely accurate when the combined weightof the boat, paddler and the gear it is carrying is the same as theDWL displacement.

Draft (in)Draft (in)Draft (in)Draft ( in) How far below the waterl ine the boatreaches. This does not includerudders or retractable skegs.

Wetted AreaWetted AreaWetted AreaWetted Area(sq. ft)(sq. ft)(sq. ft)(sq. ft)

The surface area of the part of theboat that is under water. Lower wettedarea means less frictional drag.

Waterpl. AreaWaterpl. AreaWaterpl. AreaWaterpl. Area(sq. ft)(sq. ft)(sq. ft)(sq. ft)

The area of the water plane. Thewaterplane defined by the waterlineoutline.

Total surfaceTotal surfaceTotal surfaceTotal surfacearea (sq. ft)area (sq. ft)area (sq. ft)area (sq. ft)

The total surface area of the skin of the boat. You can get anapproximation of the weight of the bare boat by multiplying by thedensity of the wood strip and fiberglass layupyou are using. A goodstarting point is 0.7 pounds per square foot for a typical 1/4" layupwith 6 ounce glass.

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ak Design Terms | Guillemot Kayaks http://www.guillemot-kayaks.com/guillemot/information/kayak_design/...

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ApproximateApproximateApproximateApproximateBare BoatBare BoatBare BoatBare BoatWeight (lbs)Weight (lbs)Weight (lbs)Weight (lbs)

The weight of the boat before adding seats, hatches, rudders or anyother outfitting. This is approximated by multiplying the TotalTotalTotalTotalsurface areasurface areasurface areasurface areaabove by 0.7. and assumes 1/4" western red cedarstrips with 6 ounce cloth.

Volume (cu ft)Volume (cu ft)Volume (cu ft)Volume (cu ft) The total volume of the kayak. The volume of water that the boatwould displace if it were totally submerged.

VolumeVolumeVolumeVolume(Gallons)(Gallons)(Gallons)(Gallons)

Same as above in gallons.

Prismatic Coeff.Prismatic Coeff.Prismatic Coeff.Prismatic Coeff. Prismatic Coefficient (CpCpCpCp) or

Longitudinal Prismatic Coefficient:

(The displacement volume) divided by(the volume of a prism equal in length

to the LWL whose cross sectional area

equals the Midship section area)

This is a rough measurement of the

"fineness" of the boat shape. A boat

with a "fine" shape has quite sharp

ends. It is used to estimate drag. The

typical range is roughly 0.5 to 0.7.

Higher numbers tend to be more

efficient at higher speeds and lower

number more efficient at lower

speeds.

The prismatic coefficient was

originally developed as term for hull

design analysis by Admiral David W

Taylor in 1943.

Block Coeff.Block Coeff.Block Coeff.Block Coeff. Block Coefficient (CbCbCbCb)

(the displaced volume) divided by

(LWL * BWL * Draft)

This a rough measurement of how "V"

shaped the bottom of the boat. It is

useful in determining how well a boat

tracks

Midship AreaMidship AreaMidship AreaMidship AreaCoeff.Coeff.Coeff.Coeff.

Midship Coefficient (CmCmCmCm)

(The area of the section at midship)

divided by (BWL * Draft)

Waterpl. AreaWaterpl. AreaWaterpl. AreaWaterpl. AreaCoeff.Coeff.Coeff.Coeff.

The area of the waterplane divided bythe length and width of the boat at thewaterline.

Lateral PlaneLateral PlaneLateral PlaneLateral PlaneCoeff.Coeff.Coeff.Coeff.

The lateral plane is what you seebelow the waterline when looking atthe boat from the side. Thiscoefficient is the area of the lateralplane divided by the LWL times theDraft.

LongitudinalLongitudinalLongitudinalLongitudinalCenter ofCenter ofCenter ofCenter ofBuoyancyBuoyancyBuoyancyBuoyancybehindbehindbehindbehindAmidship (in)Amidship (in)Amidship (in)Amidship (in)

The fore and aft location of the Centerof Buoyancy relative to the middle ofthe boat. Here it tells you how farbehind the middle of the boat theCenter of Buoyancy is. Oftenabbreviated as: BBBB, CBCBCBCB, or COBCOBCOBCOB.

LongitudinalLongitudinalLongitudinalLongitudinalCenter ofCenter ofCenter ofCenter ofFlotationFlotationFlotationFlotationbehindbehindbehindbehindAmidship (in)Amidship (in)Amidship (in)Amidship (in)

The location of the geometric centerof the waterplane area relative to themiddle of the boat. This is where youwould add more weight for the boat tosink straight down. Often abbreviatedas:FFFF, CFCFCFCF, COFCOFCOFCOF, or LCFLCFLCFLCF.

Center LateralCenter LateralCenter LateralCenter LateralArea behindArea behindArea behindArea behindAmidship (in)Amidship (in)Amidship (in)Amidship (in)

The location of the geometric centerof the lateral plane relative to themiddle of the boat.

Sinkage (lbs/in)Sinkage (lbs/in)Sinkage (lbs/in)Sinkage (lbs/in) An approximation of how muchweight you would have to add to sinkthe boat another inch. It will generallyrequire more weight to get a full inch,but if you want to go up or down1/10th inch, one 1/10th of theSinkage added or subtracted will bepretty close.

Moments toMoments toMoments toMoments tochange trim 1change trim 1change trim 1change trim 1inch (lbft)inch (lbft)inch (lbft)inch (lbft)

The amount of torque required topush the bow or stern into the waterabout 1 inch. This is an indications ofhow quickly the boat will rise over


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How a Paddle Works up Kayak Stability

waves.

RightingRightingRightingRightingMoment at 1Moment at 1Moment at 1Moment at 1degree (lbft)degree (lbft)degree (lbft)degree (lbft)

How much torque is required to tipthe boat a small amount. Anindication ofinitial stability.

Vertical CenterVertical CenterVertical CenterVertical Centerof Gravity aboveof Gravity aboveof Gravity aboveof Gravity above

DWL (in)DWL (in)DWL (in)DWL (in)

The VCGVCGVCGVCG is used to calculate the"Moment to change Trim" and the

"Righting Moment" above and isimportant for determining stability.Most of the data on these pagesassume a VCG that is 10.5 inchesabove the bottom of the boat.

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block coefficient

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