Rick,

 

I am a bit unclear. Did  you just add the span efficiency to the model and sailplan  you already have for ToyyoT, or did you change the sailplan to match the Visionarry sailplan? I am all in favor of being able to match the numbers you have listed below! 12.2kts into a 15kt breeze would be awesome!

 

Can  you tell where the boom would be positioned for a 50% true wind angle? If it is over the lw hull, your idea of a tarp joining the hull to the boom to increas the span seems doable. Not for short-tacking, but if there is a long upwind run while island hopping in the Bahamas, it might be worth the effort to get that extra 1.4 kts of speed. If it is angled out over the water, that is more problematic.

- Gardner

 

On Tue, Jun 7, 2011 at 4:40 AM, Rick Willoughby <rickwill@bigpond.net.au> wrote:

 

Arto

Using your numbers with a sail area of 72sq.m the L/D improves from about 21 to 26.   These values are quite high because the rig is high aspect.   

This does not mean much unless you are looking at the VMG to windward.

I have not yet made a VPP for the Visionarry design so I have used Gardner's ToyyoT as an example.  Just changing the span efficiency to the values you have provided gives the following data for his boat:

With wind of 15kts at 50 degrees true the lower value gives boat speed of 9.8kts while the higher value gives boat speed of 12.2kts.  So significant gain in VMG.   This is about as high as his rig will get as they correspond with 31 and 28 degrees to apparent wind.  I expect a single wing will point higher but have not checked it.

As the boat bears away the benefit diminishes.  For example with wind at 15kts, 90T the respective speeds are 14.9kts and 15.9kts.

Sailing at 50 degrees to the true wind does not sound too good but remember the boat is going fast so the apparent wind swings a long way toward the nose.  Also sailors are used to making observations of the wind direction from the boat - in this case it would seem the boat is capable of tacking through 56 degrees viewed from the boat when in reality it is 100 degrees or a bit less if you look back at the tracks.  It gets more realistic looking at what the angle between two windwards tacks look like.  Not many boats get within 90 degrees particularly if they are capable of achieving wind speed with boat speed.

With the higher span efficiency the boat will pinch up to about 42 degrees true while it goes out to 48 degrees with the lower value.   In both case the speed is around 8.8kts.  I have not checked if these values give better VMG.  

In all these cases I have not fiddled with any sail trim to see if there are better options by tweaking the sail set.  As they would benefit both cases in similar ways.  First thought is that flattening sails may benefit at higher wind speed but ToyyoT is not overpowered in 15kts.

Rick

 

On 07/06/2011, at 5:14 PM, Arto Hakkarainen wrote:

 

Rick,   So to consider what this means in reality let's think about visionarry size boat. If the mast is 18 m high above water and the boom sits about 2 m above deck meaning boom is about 3 m above water we get 15 m span on the rig? Right? And 10 % of span means then 1,5 m between sail and deck to have the span efficiency of 1,3? And recuding it from 1,5 m to 0 m increases the span efficiency by 54 % (1,3->2)? Does this mean that with no end plate at all span efficiency is 1? Did I get it right?   With such increase in span efficiency how much is L/D improved? If I understood the Tom Speer figures correctly already 1 % gap (15 cm in the example above) increases the induced drag significantly and moving from 0 % to 1 % has biggest effect on the efficiency. Or am I reading it wrong?   Arto --- On Tue, 6/7/11, Rick Willoughby <rickwill@bigpond.net.au> wrote: From: Rick Willoughby <rickwill@bigpond.net.au> Subject: Re: [harryproa] Span Efficiency - Another Harryproa Opportunity To: harryproa@yahoogroups.com.au Date: Tuesday, June 7, 2011, 9:40 AM   Arto Basically your last statement is true. Tom Speer has published some charts on it from 3D modelling on his web site. The span efficiency rapidly drops from near 2 at full end plate to about 1.3 with a gap that is 10% of the span above an effective end plate like a deck or water level. Improving the span efficiency has a small impact on the coefficient of lift of the rig but a direct inverse correlation with the induced drag.  So doubling the span efficiency halves the induced drag.  It is really significant in improving the windward performance of low aspect rigs. Rick On 07/06/2011, at 4:16 PM, Arto Hakkarainen wrote:   Rick,   Next question is how close to the deck it must be to be useful as end plate? I remember discussion in the monohull racing circuits about jibs and how close to the deck they must be to have end plate effect but cannot recall any clear answer. Or is the answer closer the better or something similar?   Arto --- On Tue, 6/7/11, Rick Willoughby <rickwill@bigpond.net.au> wrote: From: Rick Willoughby <rickwill@bigpond.net.au> Subject: Re: [harryproa] Span Efficiency - Another Harryproa Opportunity To: harryproa@yahoogroups.com.au Date: Tuesday, June 7, 2011, 2:04 AM   Arto Anything that creates flow resistance from the pressure side to the low pressure side helps with span efficiency.  Adding bits to achieve it gives diminishing return because the added bit adds drag.  The deck of the lw hull is there anyhow.  Bringing the boom down to the hull does not add more drag area. Rick On 06/06/2011, at 11:52 PM, Arto Hakkarainen wrote:   I suppose that a really wide boom such as "park avenue boom" is not sufficient to end plate the main? Or is it?   Arto --- On Sun, 6/5/11, Rick Willoughby <rickwill@bigpond.net.au> wrote: From: Rick Willoughby <rickwill@bigpond.net.au> Subject: [harryproa] Span Efficiency - Another Harryproa Opportunity To: harryproa@yahoogroups.com.au Date: Sunday, June 5, 2011, 5:50 AM   Looking at the mast and boom on Peter's boat yesterday the topic of span efficiency came up. Also when I was working on the parameters for Gardners schooner rig to plug into the VPP I had to take at stab at the span efficiiency of his proposed sail plan. This is something that I have discussed with respect to rudders and daggers but I don't think it has been discussed with sails.  Although I have referred to aspect ratio rather than span efficiency.  In effect the induced drag is halved if the blade is effectively end plated against the hull or if a surface piecing blade is at high speed and non-ventilating.  End plating is equivalent to doubling the aspect ratio or span efficiency is 2.     Anyone who has sailed on a sloop rigged keel boat knows how the pointing ability improves when the genoa is sheeted down against the deck.  This increases the span efficiency of the rig.  There is little or no air spilling under the sail.  Another good example is Macquarie innovation.  They went for a low aspect wing but were able to improve the span efficiency by setting it close to the water: http://www.sailinganarchy.com/fringe/2009/macquarie.jpg Wing end plating is something I proposed for my beach proa.  It can also be achieved with the schooner rig Gardner is proposing.   The sail efficiency is most important when sailing close to the wind and in these angles just the lw hull provides reasonable end plating. Gardner -  For the VPP I produced I selected a span efficiency of 1.3 based on what I have read about bi-planes.  If you "end plate" at the bottom the span efficiency lifts to 2.   There is some work being done with winggrid winglets that get span efficiencies above 2: http://aero.stanford.edu/reports/nonplanarwings/AIAA-2004-2120.pdf    Rick Willoughby rickwill@bigpond.net.au 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