ballystick 73 Posted October 25, 2012 Share Posted October 25, 2012 It seems apparent to me that the design development of the current foiling AC 72's such as ETNZ and Oracle has not provided any major mechanism for the prevention of pitchpoling - going down the mine? They seem to be designed to not have any support from the foils forward - like a 3 legged chair which will tip over easily. As the cats get higher up on the foils the chances get greater with the higher Centre of Gravity, imagine if the foils raised the hulls up 20 feet?? The wing sail has huge forces acting on it with a great leverage ratio to assist pitchpoling. Then take in to account a choppy sea state (like S. F.), one only has to observe foiling Moths trying negotiate the tidal chop in Tauranga harbour with the regular pitchpoling resulting in only minor damage. What do Crew.org engineers and designers think? Link to post Share on other sites
Guest Posted October 25, 2012 Share Posted October 25, 2012 http://riggingnews.blogspot.co.nz/2012/ ... ng+news%29 Link to post Share on other sites
Guest Posted October 25, 2012 Share Posted October 25, 2012 Why aren't the foils further forward? Link to post Share on other sites
ScottiE 174 Posted October 25, 2012 Share Posted October 25, 2012 are you referring to this thing, Oracle or TNZ? Link to post Share on other sites
Guest Posted October 25, 2012 Share Posted October 25, 2012 Referring to your original question, if they are to pitchpole wouldn't moving the foils forward help? Link to post Share on other sites
ballystick 73 Posted October 25, 2012 Author Share Posted October 25, 2012 I am referring to both cats at present, possibly Oracle's is most likely to suffer as we have seen already because their hulls, especially forward of the mast are very narrow. I think ETNZ would still have a high risk of burying the bows. A solution such as moving foils forward more sounds logical, to my way of thinking. Good ideas coming through, I suppose the designers/engineers have thought of these things, but they are always talking about unknown territory with these cats, this could be a demonstration of these territories. Link to post Share on other sites
chic014 0 Posted October 25, 2012 Share Posted October 25, 2012 Do the rudder Ts provide downforce? Link to post Share on other sites
ballystick 73 Posted October 25, 2012 Author Share Posted October 25, 2012 If the T foil rudders provide down force, then the rear wouldn't lift out of the water, they could possibly have a wand system like the Moths which adjust depending on speed etc but I not sure if that is allowed in the rules. Link to post Share on other sites
Absolution 7 Posted October 25, 2012 Share Posted October 25, 2012 Remember that the foils still have to work in a non-foiling configuration too so they are positioned to balance the centre-of-effort of the sail plan i.e you can't move them forward without moving the rig. Moving the rig forward will make the problem worse. The other thing to remember is that under "normal conditions" the apparent wind on these boats is always forward of the beam so the force on the wing is aft not forward. The problem comes when there is a sudden deceleration (which is a problem in itself) then the apparent wind swings aft and if you're unlucky you are going over i.e. Oracle's flip. Avoid the deceleration and you're ok! Which is why I think ETNZ have the right idea with plenty of volume in the bows. Link to post Share on other sites
Absolution 7 Posted October 25, 2012 Share Posted October 25, 2012 If the T foil rudders provide down force, then the rear wouldn't lift out of the water, they could possibly have a wand system like the Moths which adjust depending on speed etc but I not sure if that is allowed in the rules. The rules don't allow adjustable foils. The rudder foils are much smaller so it may have been engineered so that there is enough lift from the main foils to lift the whole boat. I have seen a few people suggest that the rudder foils are actually generating negative lift. Link to post Share on other sites
TimB 7 Posted October 25, 2012 Share Posted October 25, 2012 "The other thing to remember is that under "normal conditions" the apparent wind on these boats is always forward of the beam so the force on the wing is aft not forward" Oops finline, if the force was aft the boat would be moving backwards. The resultant force from the air moving front to rear over the wing (or sail) surface generates a forward vector which moves the boat. It also has a sideways component (which is why leaners lean) and drag (in the aft direction). The "T" foils on the rudder do create some downforce, especially when the bow starts to dip BUT as soon as it leaves the water the downforce is zero and "over she goes" THe AC72 are not meant to foil, the rule was written to avoid it but boys being boys, they are trying anyway. TB Link to post Share on other sites
RushMan 31 Posted October 25, 2012 Share Posted October 25, 2012 If the apparent wind is forward of the beam it is far easier to depower the rig, when the apparent is behind the beam the wing can only depower to the shrouds before the nose digs in and the boat slows down, the wing still catches the wind and drives the mast forward and then you "do an Oracle" Many times I have saved a hobie 14 from a pitch pole by an aggressive round up. App wind moves in front of the beam, pressure comes off the sail and the hulls pop out and continue sailing rather than swimming. Maybe some blow out panels on the wing would relieve the pressure, hit the red button and parts of the wing would "blow", lessening the driving force of the wing. Only to be used once a day but it might save a complete rebuild. Link to post Share on other sites
Guest Posted October 25, 2012 Share Posted October 25, 2012 Oracle have more sail area at the top of the wing and way skinner bows. I think they are more than twice as likely to flip than ETNZ. I think they might take more area off the top for their second wing??? Link to post Share on other sites
Absolution 7 Posted October 25, 2012 Share Posted October 25, 2012 You are quite correct Tim, the resultant force is forward but I was focusing on the force from the apparent wind only as I think this is key to what happens in the event of a pitch-pole. Under normal conditions the force from the apparent wind is acting aft and this is balanced by the drag, leeway and the resultant vector which drives the boat forward. If the boat stuffs the bows in and decelerates quickly the force vector from the apparent wind moves from ahead of the beam to behind it and if that force can't be converted into forward motion (due to drag) then it all goes in to rotation! "The other thing to remember is that under "normal conditions" the apparent wind on these boats is always forward of the beam so the force on the wing is aft not forward" Oops finline, if the force was aft the boat would be moving backwards. The resultant force from the air moving front to rear over the wing (or sail) surface generates a forward vector which moves the boat. It also has a sideways component (which is why leaners lean) and drag (in the aft direction). The "T" foils on the rudder do create some downforce, especially when the bow starts to dip BUT as soon as it leaves the water the downforce is zero and "over she goes" THe AC72 are not meant to foil, the rule was written to avoid it but boys being boys, they are trying anyway. TB Link to post Share on other sites
TimB 7 Posted October 26, 2012 Share Posted October 26, 2012 Yup and because the lifting foil is under the COG, when the rotation starts all that is holding the boat horizontal is a foil on the rudder....... Link to post Share on other sites
Guest Posted October 26, 2012 Share Posted October 26, 2012 Do you ever notice when the OR17 boat starts foiling the windward hull is still in the water? Looks like it is quite sticky to get out of the water given the windward center board is creating nevitive lift until it is clear. Wonder what they will do next? Bigger bows, smaller sail area at the top larger foiles (ETNZ copy??) Link to post Share on other sites
ballystick 73 Posted October 26, 2012 Author Share Posted October 26, 2012 I was thinking they could have retractable front foils used for bearing away, it would have to have low drag so as to avoid the problem that they are trying to avoid. Link to post Share on other sites
Recommended Posts
Archived
This topic is now archived and is closed to further replies.