Mon, 5 Nov 12 12:53
The Walvis Bay wind machine remains on safari... although we might get a chance to get out over the next couple of days. It has now been 16 days since we last had enough wind to get going. It's going from 'unusual' to ridiculous. The walls of the container begin to close in on us.
The WSSRC are now on-site so any runs we do from here will be officially ratified ones. Our record attempt period has started. The big TRIMBLE 5700 GPS is mounted on the boat. The gig is on!
The standby time has allowed us to think long and hard about our current performance predicament. We had our design meeting where Chris, Malcolm and myself had a long Skype discussion about likely scenarios. Basically we tried to reverse engineer the problem and our train of thought was as follows...
-The most likely candidate that would be giving us a sudden, large loss of performance regardless of power input is cavitation.
-The rudder is not loaded highly enough nor does it have the base area to give us such a sudden drop in performance... although we will continue to put sensors on it to make sure it isn't contributing.
-So... the most likely candidate for caviataion is the suction surface of the main-foil.
-The main foil shouldn't begin to cavitate around 52 knots unless it is 40% overloaded.
- How could the main foil be 40% overloaded at such a relatively low speed?
- If the upper portion of the foil, the part that enters the water, was ventilating (highly likely as it is at the surface), then what effect would that have on the boat?
- On checking the numbers, AEROTROPE deduced that if the transition (curved part of foil) was ventilating down its suction side... then we would lose about 30% of our lateral loading area. At 52 knots... this would lead to the lower section of the foil being overloaded by... wait for it... 43%!
-It would cavitate
- AND... the back of the boat would ride very low... as it has been doing...
- AND... pitching the foil up would most likely have little effect and may actually make it worse by leading to more upper surface ventilation (as we have often seen)
more here
The WSSRC are now on-site so any runs we do from here will be officially ratified ones. Our record attempt period has started. The big TRIMBLE 5700 GPS is mounted on the boat. The gig is on!
The standby time has allowed us to think long and hard about our current performance predicament. We had our design meeting where Chris, Malcolm and myself had a long Skype discussion about likely scenarios. Basically we tried to reverse engineer the problem and our train of thought was as follows...
-The most likely candidate that would be giving us a sudden, large loss of performance regardless of power input is cavitation.
-The rudder is not loaded highly enough nor does it have the base area to give us such a sudden drop in performance... although we will continue to put sensors on it to make sure it isn't contributing.
-So... the most likely candidate for caviataion is the suction surface of the main-foil.
-The main foil shouldn't begin to cavitate around 52 knots unless it is 40% overloaded.
- How could the main foil be 40% overloaded at such a relatively low speed?
- If the upper portion of the foil, the part that enters the water, was ventilating (highly likely as it is at the surface), then what effect would that have on the boat?
- On checking the numbers, AEROTROPE deduced that if the transition (curved part of foil) was ventilating down its suction side... then we would lose about 30% of our lateral loading area. At 52 knots... this would lead to the lower section of the foil being overloaded by... wait for it... 43%!
-It would cavitate
- AND... the back of the boat would ride very low... as it has been doing...
- AND... pitching the foil up would most likely have little effect and may actually make it worse by leading to more upper surface ventilation (as we have often seen)
more here
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