Simulation showing an X-35 sailing upwind in small waves.<br />
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At first, the model spinning with tell-tails "live". The simulated tell-tails behave similar to the real ones observed when sailing.<br />
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In the mid-section, vorticity (turbulence) generated while sailing upwind in waves. Note the considerable, periodic turbulence exiting from the from the slot between the jib & the main. <br />
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The last section, with the view from the windward side, reveals the reason of the turbulence from the slot: The pitching of the boat causes a periodic separation of the flow on the windward side of the sails, as witnessed by the blue areas. The flow velocity Vx in the blue areas is negative, i.e.. against the wind.<br />
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The pitching of the boat, even such a small pitching as shown here, has a great effect on the instantaneous forces: The drive and the heel vary as much as 50% in at the pitching period of about 1,5 s. However, the effect of the average forces is rather small.<br />
<br />
If you compare this with our earlier Star-simulations with pitching, you can see that the effect is much more severe here, especially on the high aspect jib. The nearly masthead-rig of the X-35 puts the upper part of the jib into a considerably larger motion than that of the 3/4 rigged Star. As most of the drive on this type of rigs comes from the jib (78% in this case), almost all drive is lost when the bow is pitching down, causing the separation on the inside. The mainsail drive actually goes negative for a while.<br />
<br />
This also explains why the 3/4-rig replaced the masthead-rig in the IOR racing scene in late 70's. The masthead rigged jib loses a lot more in a seaway than the fractional, as first showed by Bruce Farr's fractionally rigged 45° South. The current vogue for nearly masthead rigged boats is due to the ORCi rating rule, which favours high aspect, masthead jibs and penalizes genoas, running backstays and smaller mast sections, associated with fractional rigs.<br />
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Sailing aerodynamics: (c) WB-Sails 2015<i class="fa fa-language transViewIcon clickable" title="Translation"></i>
00:26Sailing aerodynamics: X-35 upwind in small waves
Sailing aerodynamics: X-35 upwind in small waves
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https://hoyatag.com/299241Sailing aerodynamics: X-35 upwind in small waves
Simulation showing an X-35 sailing upwind in small waves.
At first, the model spinning with tell-tails "live". The simulated tell-tails behave similar to the real ones observed when sailing.
In the mid-section, vorticity (turbulence) generated while sailing upwind in waves. Note the considerable, periodic turbulence exiting from the from the slot between the jib & the main.
The last section, with the view from the windward side, reveals the reason of the turbulence from the slot: The pitching of the boat causes a periodic separation of the flow on the windward side of the sails, as witnessed by the blue areas. The flow velocity Vx in the blue areas is negative, i.e.. against the wind.
The pitching of the boat, even such a small pitching as shown here, has a great effect on the instantaneous forces: The drive and the heel vary as much as 50% in at the pitching period of about 1,5 s. However, the effect of the average forces is rather small.
If you compare this with our earlier Star-simulations with pitching, you can see that the effect is much more severe here, especially on the high aspect jib. The nearly masthead-rig of the X-35 puts the upper part of the jib into a considerably larger motion than that of the 3/4 rigged Star. As most of the drive on this type of rigs comes from the jib (78% in this case), almost all drive is lost when the bow is pitching down, causing the separation on the inside. The mainsail drive actually goes negative for a while.
This also explains why the 3/4-rig replaced the masthead-rig in the IOR racing scene in late 70's. The masthead rigged jib loses a lot more in a seaway than the fractional, as first showed by Bruce Farr's fractionally rigged 45° South. The current vogue for nearly masthead rigged boats is due to the ORCi rating rule, which favours high aspect, masthead jibs and penalizes genoas, running backstays and smaller mast sections, associated with fractional rigs.
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