Nothing to do with when proas are stationary but I found the Atlantic proa configuration is easily trimed from an aft CoE of sail area. I could get the Atlantic proa configuration to a neutral helm and sailing up wind with very little effort or input with sail set aft on mast without the use appendages in the water. Basically the direct opposite of the same finding with Pacific proa configuration achieving same sailing characteristics with sail set forward.
http://www.youtube.com/watch?v=Girz4J0sbvM
Todd
--- In harryproa@yahoogroups.com.au, Doug Haines <doha720@...> wrote:
>
> I was talking about the drift charachteristics, and used the weighing of anchor as an example of when you may be drifting.
> I have to let my boat naturally drift backwards a little untill it is side on to the wind enough to sheet in and go.
> If you had a motor and used that to weigh anchor then you couold motor around to a side on poisition.
> I wondered if an atlantic wouldn';t come to rest naturally leeward hull to lee, but would lay the other way and stop you from going sailing.
> I was informed of this I think by someone when I was considering a Bi-Harry. Which is still interesting. But it would behave differently to regular harry too.
> Is Bain going to discusss the shunting of Aroha?
>
> Doug
>
> --- On Mon, 16/8/10, Arto Hakkarainen <ahakkara@...> wrote:
>
>
> From: Arto Hakkarainen <ahakkara@...>
> Subject: Re: [harryproa] Atlantic vs HarryProa... and structural.
> To: harryproa@yahoogroups.com.au
> Date: Monday, 16 August, 2010, 23:53
>
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> You can always bridle the anchor line. Have the anchor in lw hull and rig a bridle line from ww hull.
>
> Arto
>
> --- On Tue, 8/3/10, Dennis Cox <dec720@...> wrote:
>
>
> From: Dennis Cox <dec720@...>
> Subject: Re: [harryproa] Atlantic vs HarryProa... and structural.
> To: harryproa@yahoogroups.com.au
> Date: Tuesday, August 3, 2010, 6:29 PM
>
>
>
>
>
>
> Sorry Doug, maybe it took a baseball bat to get it through a second time.
>
> I am starting to fall on the HarryProa placment anyway... but playing devil's advocate for a moment... and to see if I have all your points. I think I am hearing...
>
> In an Atlantic configuration, when on anchor, the windward hull would definitely be down wind and in the wrong place both from the righting moment and comfort in the cockpit. I got that. However, if I moved the anchor to the bows of the windward hulls instead of the beams as Rob has it, it would tend to keep the bows pointed into the wind. Any slight angle from that, I'd think it would be the lee hull, staying lee. Raising anchor and loading up the sails shouldn't cause much orientation change. I would think it would stay relatively neutral. Any attempt at yawing, I think could be easily compensated by the schooner rig balancing.
>
> Something like this????
> http://au.groups. yahoo.com/ group/harryproa/ photos/album/ 1001384692/ pic/334946044/ view?picmode=&mode=tn&order=ordinal&start=1&count=20&dir=asc
>
> Am I still missing something else?
>
> Thanks,
> Dennis
>
>
>
>
> From: Doug Haines <doha720@yahoo. co.uk>
> To: harryproa@yahoogrou ps.com.au
> Sent: Tue, August 3, 2010 10:22:43 AM
> Subject: Re: [harryproa] Atlantic vs HarryProa... and structural.
>
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> Dennis,
>
> i MENTIONED THIS RECENTLY ( AMONTH AGO)
> With atlantic, you will naturally sit with all th windage down wind.
> So your ww hull and leeward hulls are not where they should be.
> This I find when you pull up the anchor, it will blow you around if your sail on the leeward hull is raised and counteracts the windage of the ww hull cabin ...
>
> Doug
>
> --- On Tue, 3/8/10, Dennis Cox <dec720@...> wrote:
>
>
> From: Dennis Cox <dec720@...>
> Subject: [harryproa] Atlantic vs HarryProa... and structural.
> To: harryproa@yahoogrou ps.com.au
> Date: Tuesday, 3 August, 2010, 20:46
>
>
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>
> Rick,
>
> I keep a special folder of things I NEED to really dig into. Looking through it... I see Rob, Todd, tspeer... and many from you. This one is certainly among them. Unfortunately, my background doesn't give me a lot to draw from when it comes to fluid dynamics... so I just don't have the feel you obviously possess. I'm not complaining. .. I think its great. Fortunately for me, the rudders can percolate... I see you, Todd and Rob (moving them from leeward hulls to the beams) as the far more knowledgable theroticians and experimental scientists on the problem. I look forward to a interesting trip watching you all. Besides, if I screw up the first set, I can always yank them off and move them.
>
> Right at the moment, I'm working on one Rob and Robert unknowingly kicked me off with... I was happily making saw dust in the basement, believing I had everything decoupled and I could lazily build my leeward hull in a vacuum. That's pretty much true... up to a point. Between Rob's obvious leaning, his ergonomics observation and Roberts racking issues, I've decided to attack my fence-riding on the sail and rudder placement issue head on. And per SOP... brute force is required.
>
> To that end, I'm first getting back up to speed in my old area of expertise (Jeeze... its been 17 years) . I've downloaded the CAELinux series of finite element analysis and CAD programs. So far, its staggering what these people are releasing as Open Source. Twenty years ago, I was using the crown jewels of FEA and this things depth and breadth and integration. .. just blow it away. Its HUGE! I'm getting spun up on three more forums to help with my learning curve.
>
> As I see it, I want to study the racking forces, natural frequencies and driving frequencies of the wave trains and how badly they drive the structural weight of the beams and hulls. My belief... is that I'm going to join the choir... and sing HarryProa. Of course, I'll feed back to this forum my results and observations.
>
> Hey Doug... you thought I was getting too theoretical before. Besides, the Admiral thinks you all are great... you keeps me off the street chasing younger women, out of bars swapping lies and off really expensive past times. No drugs, sex and rock and roll for Dennis. Not that it was an issue... before.
>
> Dennis
>
>
>
>
> From: Rick Willoughby <rickwill@bigpond. net.au>
> To: harryproa@yahoogrou ps.com.au
> Sent: Mon, August 2, 2010 10:42:53 PM
> Subject: Re: [harryproa] Re: Leeway Prevention
>
>
>
> Dennis
> You should take the time to look ALL the way through Todd's clip. It gets more interesting in the shunts.
>
>
> You should also take a look at rudders designed for higher speed applications. Above 15kts or so cavitation becomes an increasing factor and eventually dominates performance for water foils. You may find this interesting:
> http://books. google.com. au/books? id=euQZ16elT5kC&pg=PA172&lpg=PA172&dq#v=onepage&q&f=false
> You will see that the entries get sharper and the tails get chopped. The tight radius twin nose foil I proposed will performa better than a symmetrical 4-series NACA for speeds where cavitation is a consideration.
>
> Reducing appendage drag by 30% through one single change like use of an asymmetric section will be even more beneficial when it is accounted for in the next loop of the design spiral. 30% drag reduction on the appendages is equivalent to maybe 10% reduction in hull drag or 15% reduction in weight - again these benefits are only the first time through the spiral. The benefit will amplify second time through.
>
>
> The proa as sailing configuration has not undergone a lot of development. There is a whole lot of unexplored potential. The asymmetric rudders seem to be one such area but good to see some have actually tested them.
>
>
> The twin rudders would be more aptly termed articulating keels. They are larger than conventional rudders need to be and will have a narrower angle of operation because they have more power. You would design them to operate around the point of maximum L/D, which is closer to a keel or centreboard criteria than conventional rudders. With conventional rudders you have an interest in the maximum lift but for articulating keels it is a different requirement. Under way they will have ample turning power with only small changes in AoA so they do not require a wide working range and the maximum lift is really well above any steering force you would need.
>
>
> Suggesting that you would only use symmetrical foils on a proa is akin to saying that airplanes should only use symmetrical section wings. Those that are meant to fly well upside down like stunt planes often use symmetrical sections but most use asymmetric wings because there are huge advantages in reducing drag by doing so. Like proas most planes are designed to lift in only one direction. (I wonder if the early aircraft designers had a discussion on merits of asymmetric and symmetric wings. Maybe they looked at what birds used. Like a proa, birds are intended to lift only upwards. )
>
>
> Rick
>
>
> On 03/08/2010, at 11:01 AM, Dennis Cox wrote:
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> Yes, I took the time... the first minute or two. Maybe, I didn't watch enough. It certainly shows packaging and mechanical efficiency. However, I don't recall if tsstproa makes any claims nor testing (yet) that shows it was faster or prevented leeway more efficiently. What happens at higher speeds when vortex shedding and flutter gets involved on a larger and/or faster scale?
>
> The rudders on my POS are accidentally assymetric (bad molding) and have rounded trailing edges... and they stall and miss behave. A friend with a similar boat who contoured his to a NACA symmetric foil behaves beautifully. .. it stalls predictably in both directions and there is no shimmy in the wheel. The before and after were night and day.
>
> Back to tsstproa... does it stay stable with a hinge at 50% of the chord? At slow speeds, looks great...
>
> If higher speeds were run... I might try playing arm chair quarterback and suggest that he allow it to pivot rearward (whichever rearward applies) to allow the center of effort to "guarantee" being behind the pivot axis. It seems like several degrees is all that it would need.
>
> However, for a boat designed to be stretching for top end speed, my I'd think that its going to have more drag than a standard type foil (symmetric or not). So, I guess its a decision of what one wants to optimize... mechanical simplicity (pivot +/- 20) or ultimate speed (with more complexity by pivoting through 270+.
>
>
> On a cruiser, it might be the way to go... on a racer... doubtful. On a racer/cruiser. Hmm... I'll definitely curuous and will look into it more.
>
> Dennis
>
>
>
>
> From: Rick Willoughby <rickwill@bigpond. net.au>
> To: harryproa@yahoogrou ps.com.au
> Sent: Mon, August 2, 2010 8:10:09 PM
> Subject: Re: [harryproa] Re: Leeway Prevention
>
>
>
> Dennis
> Did you take the time to watch the video that Todd linked to:
> http://www.youtube. com/watch? v=eEevSrV04EQ
> The rudders are bi-directional. What surprises me is that they happily work swinging free with the side pivot. I did not expect this but it is possible with the large radius nose he is using.
>
>
> I have not gone through the moment analysis thoroughly but the stable angle of operation gets smaller as the nose/tail becomes pointier. A nose radius of 0.3% of chord gives a stable working range of 10 degrees at Re# 10E6. Going larger radius increases the stable range but there is a point where the L/D will suffer due to trailing edge turbulence.
>
>
> Irrespective of the stable working range it gets down to whether you want to allow the rudders to float or not. This runs the risk of a rudder suddenly becoming a brake. Rudder stops could be used to limit the range.
>
>
> Rick
>
>
> On 03/08/2010, at 8:58 AM, Dennis Cox wrote:
>
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> I think the biggest issue would be... reversing them. Rotating (as Rob does now) during the shunt gives you the asymmetric on the wrong side going one of the directions. You'd have to have a rudder that is twice as long with half out of the water and rotate the other end into the water going the other way. If I were to use Rocket Science... I'd say something like aero-elastic tayloring (well fluid-elastic tayloring) and have the foil adaptive. Hmmmmm.... don't get me started. It might be painful.
>
> Dennis
>
>
>
>
>
> From: Rick Willoughby <rickwill@bigpond. net.au>
> To: harryproa@yahoogrou ps.com.au
> Sent: Mon, August 2, 2010 6:42:26 PM
> Subject: Re: [harryproa] Re: Leeway Prevention
>
>
>
> Ben
> Leeway on a hull is added drag and loses VMG. Some keel boats are using flaps or even adjusting the keel or board angle on each tack to overcome leeway. If you have two large rudders rather than a keel/ boards and rudder then you can set rudder angles to avoid leeway.
>
>
> Using asymmetric rudders means you can get the lift more efficiently with a smaller area than symmetrical sections that have to work in both directions. At zero lift (negative AoA) they have less drag than a symmetric section capable of generating the required lift on the wind. So downwind they will have less drag than symmetrical rudders and keels/boards. . You could also lift the leading one if set up to do so.
>
>
> The rudder drag will be a significant portion of the overall drag on a harryproa using a long slender lw hull so anything to reduce it can have a significant impact on performance. You could reasonably expect to reduce the rudder drag by 30% using an asymmetric section compared with a symmetric section for the same lift.
>
>
> I do not know how common asymmetric rudders are on proas but it seems the logical choice and another natural advantage of the breed.
>
>
> Rick
>
>
>
>
>
> On 03/08/2010, at 12:24 AM, bjarthur123 wrote:
>
>
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>
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> > The unique feature offered with two large rudders on a proa is the potential advantage of using asymetric sections for the rudders.
>
> what a brilliant idea! by "potential", do you mean to say this is NOT customary on modern proas? if so, why not!?
>
> so upwind the more curved surface faces upwind. lift is generated even when the angle of attack is zero. so less leeway and drag. course is more upwind even though heading is the same.
>
> but what about downwind? you maximize VMG by sailing on a broad reach re. true wind, which on a boat that can sail windspeed is a beam reach re. apparent. you don't want to prevent leeway (correct?), so do you flip the asymmetric rudders around so that the more curved surfaces point downwind? this would then generate more leeway, which when trying to go downwind is good. am i getting this right?
>
> new member by the way. just bought a weta trimaran, and am dreaming about retiring on a larger boat. maybe a harryproa!
>
> ben arthur
> weta #358, "gray matter"
> ithaca, new york
>
>
>
>
> Rick Willoughby
> rickwill@bigpond. net.au
> 03 9796 2415
> 0419 104 821
>
>
>
>
>
>
> Rick Willoughby
> rickwill@bigpond. net.au
> 03 9796 2415
> 0419 104 821
>
>
>
>
>
>
> Rick Willoughby
> rickwill@bigpond. net.au
> 03 9796 2415
> 0419 104 821
>