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Technical protest |
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Granite
Far too distracted from work Joined: 12 May 04 Location: Scotland Online Status: Offline Posts: 476 |
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Topic: Technical protest Posted: 20 Nov 19 at 12:50pm |
Most fences I have seen on rudders have been flat plates paralell to the flow to stop ventelation down the rudder, so only have a positive effect at very high rudder angles, or possibly very high speed. Looking at the pictures of the rudder I am not sure where the fence sits against the waterline. It looks like it could sit just above the water and be used to deflect the water cleanly away from the rudder/stock. Avoiding disrupted flow across the stock and some potential drag. Although it also looks like the bit of blade above the fence has a sharper leading edge which I think is wanted at the surface to cut the water cleanly putting the fence below the water. Whatever it does the height of the blade is going to be critical in its performance. I think it would need some very complex CFD to be sure that it is having the desired effect and not adding drag. For the rules I suspect they forgot about fences which had probably been seen before on a lot of boats. Although this rule is interesting: E.2.1 RULES The hull appendages shall comply with these class rules or the class rules in force at the time of initial hull certification. It could potentially mean you could fit full sized wings on to the rudder of an older boat |
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If it doesn't break it's too heavy; if it does it wasn't built right
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fudheid
Far too distracted from work Joined: 21 Apr 11 Location: 51.53 N 01.28 E Online Status: Offline Posts: 241 |
Post Options Quote Reply Posted: 20 Nov 19 at 8:34am |
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Cheers you
only me from over the sea...... |
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fudheid
Far too distracted from work Joined: 21 Apr 11 Location: 51.53 N 01.28 E Online Status: Offline Posts: 241 |
Post Options Quote Reply Posted: 20 Nov 19 at 8:32am |
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Edited by fudheid - 20 Nov 19 at 8:35am |
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Cheers you
only me from over the sea...... |
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Post Options Quote Reply Posted: 20 Nov 19 at 12:10am |
C.8.2 Daggerboards, bilgeboards, double rudders, winged rudders and similar contrivances are prohibited
I would have said a fence was a “similar contrivance” in as much as it is an atypical modification to conventional rudder design. That said, it seems a pity to ban it and I would be interested to know if it actually improves things or whether the increased wetted area and interference drag are more of a hindrance. |
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JimC
Really should get out more Joined: 17 May 04 Location: United Kingdom Online Status: Offline Posts: 6649 |
Post Options Quote Reply Posted: 19 Nov 19 at 11:13pm |
"Similar contrivances" is not the smartest bit of rule writing I've ever seen, but grief, you people are making a mountain out of a molehill, hell, not even as big as a molehill. A blade fence is an utterly different thing to a lifting foil. I am to say the least not biased towards the Merlin class, but I don't think the distinction presents the slightest problem. |
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davidyacht
Really should get out more Joined: 29 Mar 05 Online Status: Offline Posts: 1345 |
Post Options Quote Reply Posted: 19 Nov 19 at 10:30pm |
Surely a fence is to improve foil efficiency by reducing ventilation and hence increasing the effective span, whereas wings generate vertical lift and energy recovery from the stern wave.
I can see why a class might want to outlaw winged rudders, since the cost can be disproportionate and may limit how and where a boat may be sailed, a very different problem to tinkering around with fences. But in the end it is for the Merlins to decide if this is a worthwhile avenue to pursue.
Bear in mind that they are a restricted class and not a development class, and they have done a pretty good job in managing evolution not revolution. |
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Happily living in the past
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423zero
Really should get out more Joined: 08 Jan 15 Location: United Kingdom Online Status: Offline Posts: 3406 |
Post Options Quote Reply Posted: 19 Nov 19 at 9:42pm |
I know one thing this is the type of dealing that winds iGRF up
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Robert
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gbrspratt
Posting king Joined: 26 Sep 11 Location: Felixstowe Online Status: Offline Posts: 170 |
Post Options Quote Reply Posted: 19 Nov 19 at 9:33pm |
I think what's happened is it wasn't noticed that they may or may not be in breach of this rule. And now it's been brought to everyone's attention. But no-one is clear on why it is or isn't legal. Grandfathering the ones out there has been suggested. But not enough people can agree on an answer. It's really interesting hearing non class sailors opinions |
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gbrspratt
Posting king Joined: 26 Sep 11 Location: Felixstowe Online Status: Offline Posts: 170 |
Post Options Quote Reply Posted: 19 Nov 19 at 9:27pm |
Rockatross is legal and racing. These are Winder Merlin rudders if you really want to know . |
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Rupert
Really should get out more Joined: 11 Aug 04 Location: Whitefriars sc Online Status: Offline Posts: 8956 |
Post Options Quote Reply Posted: 19 Nov 19 at 9:14pm |
Surely it is whatever the class choose it to be? If they, as owners, decide to allow fences, or rather, to not disallow them, then they are obviously not "similar contrivences" or whatever the phrase was. Haven't they been using them for years?
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