Designs comparison page
|Perhaps the easiest way to size a kayak is to have a visual frame of reference such as other kayak designs. This page brings all One Ocean Kayaks together, side by side, for relative comparison of scale as well as the technical stuff such as wave and viscous resistance.|
The kayak profiles below show the exact scale and proportion of the designs relative to each other.
Resize your browser to full screen for better viewing. Click on images for kayak technical specs (particulars).
Cape Ann Double
Cape Ann Expedition
Cape Ann HV - scaled from Cape Ann
Cirrus and Cirrus Hybrid
Expedition Sport - scaled from Expedition
Storm LT - scaled from Storm
Cirrus LT and Cirrus LT Hybrid - scaled from Cirrus
Storm SLT - scaled from Storm
Cirrus SLT - scaled from Cirrus
resistance and friction drag charts|
The charts below represent the theoretical performance potential of One Ocean Kayaks hullforms. The input of all the variables into the 'drag prediction algorithm' allows quite a bit of flexibility and interpretation. Therefore, the results should be taken less for their absolute value than as an insight into the kayaks performance relative to each other. Comparisons to other kayak designs can be considered absolute only if the same criteria were applied in all instances. The analogy of two cooks preparing a meal from an identical recipe and both dishes come out tasting totally different is very apt in a case like this.
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NOTE: Some of the graphs are too close together for visual comparison. The table of numbers below the chart indicates the 'y axis' values for each kayak.
drag) Since viscous resistance
in the graph is plotted against speed the most significant difference among
the kayaks is their wetted surface. It is therefore not surprising that
the viscous drag will be the smallest for the smallest kayak (Storm SLT)
and progressively larger with each larger kayak design.
As the hull plows through the water, a thin layer of water trapped in
the 'roughness' of the surface is dragged along with the hull. Since the
'trapped' water molecules are in contact with many other molecules further
from the hull, their kinetic energy is transferred progressively through
'layers' further from the kayak skin. This viscous interaction of water
molecules is confined in a space called the boundary layer. The
boundary layer is where water causes 99% of Frictional resistance.
in units -> kg/m^3 x (m/s)^2 x m^2 = kg x m/s^2 = mass x acceleration = force
Cf = 0.075/(log (R)-2)^2
R (Reynolds number) = (V x L)/(nu)
(nu)kinematic viscosity = (mu)/(rho)
(nu) is a constant for water salinity and temperature
Unlike viscous drag, wave resistance is far more complicated to calculate
for it takes into account many more hull parameters as well as other factors
which are beyond the scope of this page (at this point).
Total resistance is the sum of frictional and wave resistance. (If you added the Frictional resistance graph to the residual drag graph you would get the chart on the left)
The blue line for the double shows the largest resistance but remember
there are two people to share the load, so if you divided the total resistance,
each paddler would need to exert less energy than in any of the single
Coefficient of total resistance vs. volumetric Froude number
The lower the graph at each point, the more efficient the kayak. The blue line of the Double has practically the highest efficiency across the entire speed range with the Expedition following second but the Cape Ann HV is by far the most efficient kayak up to the Fn = 0.8 and second best up to the 0.9 mark which corresponds to a cruising speed of about 4 knots. This is not surprising since its wetted surface relative to the volume below the waterline (the Area/ Dispacement ratio) is currently the lowest of all the kayaks. Consequently, the HV as well as the Double and Expedition perform very well at moderate speeds with generous loading. The Storm is very close to the Cape Ann at lower speeds but becomes far more efficient at higher speeds beyond the Fn = 0.9 mark.
The Expedition Sport shows the second lowest Total resistance between 3.5 - 5.5 knots. It also ranks as a relatively efficient kayak (after the Expedition and the Double) between Fn 0.85 and 1.05 (3.5 to 4+ knots)
Total drag vs. Efficiency distinction
It is quite clear from this chart that kayaks with longer waterline and larger displacement (or any boat for that matter) will generally be more efficient, that is, they will experience less drag with respect to the amount of 'stuff' they can carry. Take for example a long ship carrying many tons of cargo. The drag on such ship would be obviously enormous but it would still take less energy to transport all this cargo than having it transported in hundreds of same shape, kayak-sized boats. The drag on the small boats together would far exceed the total resistance of the large ship, thus the large ship would be more efficient. This is a very extreme example, but it illustrates the concept more clearly than cases in which subtle differences do not provide much insight into the principles at play.
This chart really shows the relative efficiency of the hulls adjusted
for displacement (that is why the volumetric Froude number as the horizontal
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Last page update: 12 May 2013