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Technical protest

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Post Options Post Options   Quote Granite Quote  Post ReplyReply Direct Link To This Post 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

If it doesn't break it's too heavy; if it does it wasn't built right
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Post Options Post Options   Quote fudheid Quote  Post ReplyReply Direct Link To This Post Posted: 20 Nov 19 at 8:34am
Originally posted by fudheid

No mountain or even a molehill.
Just a discussion without beer/ginn/vino amongst 'peers' or brains trust.
To me in a open development class, open or grey areas like this are open to interpretation. Or logic chopping as you called it, or bending as other would. In IRC like the krazy k you get a year to revel in your logic before the rules are amended. Code zeros, cableless , fat head, all have been logic chopping.
So I have to spend £800 near enough on a new winder rudder to get the fence as it makes the boat quicker, it's a development class and maybe that's the price you pay annually as bits get developed.
I hear rumblings about the legality due to the 'contrivance'. As I understand it the class are wary of allowing Wings and other developments as they are expensive... They tend to be conservative, but there is a split fifty fifty (?) that wings and foils should be allowed, it's a development class after all, the rule IS grey that's why people are looking at it because they see an opportunity to push what's 'acceptable'. Rules/measurement is black and white, legal not legal.
Someone having a rudder that can make your boat obsolete nearly it becomes a reading of the rules.
That's what the rules are 'protectionist'.
Cheers you

only me from over the sea......
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Post Options Post Options   Quote fudheid Quote  Post ReplyReply Direct Link To This Post Posted: 20 Nov 19 at 8:32am
=

Edited by fudheid - 20 Nov 19 at 8:35am
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Post Options Post Options   Quote Peaky Quote  Post ReplyReply Direct Link To This Post 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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Post Options Post Options   Quote JimC Quote  Post ReplyReply Direct Link To This Post Posted: 19 Nov 19 at 11:13pm
Originally posted by gbrspratt

I think what's happened is it wasn't noticed that they may or may not be in breach of this rule.

"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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Post Options Post Options   Quote davidyacht Quote  Post ReplyReply Direct Link To This Post 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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Post Options Post Options   Quote 423zero Quote  Post ReplyReply Direct Link To This Post 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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Post Options Post Options   Quote gbrspratt Quote  Post ReplyReply Direct Link To This Post Posted: 19 Nov 19 at 9:33pm
Originally posted by Rupert

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?


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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Post Options Post Options   Quote gbrspratt Quote  Post ReplyReply Direct Link To This Post Posted: 19 Nov 19 at 9:27pm
Originally posted by 423zero

Rockatross, don't think it's class legal, so it's a blade you can buy that will fit a Merlin stock.


Rockatross is legal and racing. These are Winder Merlin rudders if you really want to know .
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Post Options Post Options   Quote Rupert Quote  Post ReplyReply Direct Link To This Post 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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