Rigs and Rigging Weight vs Drag?

[yipster]

long as there are more than unstayed rotating free masts
rigging, weight and drag would also play on this creasing mast
just an example but on a farrier with apropriate rigging, why not
looked for folding, hinging, elbow, telecopic or what do you have masts
and like to hear some opinions on shown or other alternative systems

oops, do realise opening a can of worms, start a new thread?

[grob]

Yipster,

You mean like this

http://www.transitionrig.com/

Gareth

[yipster]

interesting site with history and concepts i didnt see yet, thanks

[rayk]

Originally Posted by RHough

My hidden motive here is to arm myself with enough knowledge so I can properly advise my rigging customers. I'd like to have a good feel for when I should recommend or encourage the use of PBO rigging and when I should recommend more traditional solutions.

An easier explanation for your customers may be...

• Extra weight is only x kilograms more than your original standing rigging.
  This extra weight may be above the original CG, but the new combined CG will only be a matter of centimeters above the existing one.
• As the wind increases drag in the rig will heel the boat, and slow it down.
  As wind speed increases, drag increases exponentially.
  Drag is a force of x kilograms pushing on the CE of the rigging.
  As wind speed doubles, the drag quadruples.

Hope this helps

[RHough]

Originally Posted by rayk

An easier explanation for your customers may be...

• Extra weight is only x kilograms more than your original standing rigging.
  This extra weight may be above the original CG, but the new combined CG will only be a matter of centimeters above the existing one.
• As the wind increases drag in the rig will heel the boat, and slow it down.
  As wind speed increases, drag increases exponentially.
  Drag is a force of x kilograms pushing on the CE of the rigging.
  As wind speed doubles, the drag quadruples.

Hope this helps

Your points are well taken as they relate to static stability.

Obviously, reducing the weight of the standing rigging by 75% will have a small effect on boats where the weight of the rig is a small part of the total weight. On a 50 foot, 12,000 pound boat with a carbon mast, the weight of rod is a more significant part of the total.

The Kevlar standing rigging was about twice the diameter of the rod it replaced. The new PBO rigging is only about 30% larger than rod for the same stretch per unit load.

Where weight aloft comes into play is it's role in dynamic stability. The trade off must be in evaluating the effect of pitch and roll stability on boat speed compared to the drag penalty. AC boats use PBO as do more and more high performance racer/cruisers. I can quantify the drag, but I don't know how to estimate the effect of changing the pitch and roll period on boat performance.

I want to think that the designers that specify PBO rigging have done their homework and have come to the conclusion that the weight savings gain more than the extra drag loses. I'd like to learn how to estimate the effect on the dynamics.

[FAST FRED]

"The argument is that it reduces weight aloft. What then is the trade-off? Can reduced weight aloft more than compensate for the increased parasitic drag of doubling the rigging diameter?"

Parasitic drag doesn't increase.

The problem is that small diameter wires all have about the SAME drag.

Every single wire , halyard or lifeline "looks" about 1 inch in diameter to the breeze, in terms of induced drag.

The higher drag is because the energy required to bend the wind around the wires and return is higher in small sizes.

Thats why wires are gone from biplanes , but thick struts remain.

FF

[rayk]

Originally Posted by RHough

I want to think that the designers that specify PBO rigging have done their homework and have come to the conclusion that the weight savings gain more than the extra drag loses. I'd like to learn how to estimate the effect on the dynamics.

Maybe the best way to start is a cross section model. (Pitch can be figured out using the same process in section.)

Heel can be used to demonstrate the forces of gravity and bouyancy and the moment of increasing drag/windspeed in the rig.

Trade offs in CG/CB and rigCE/transverseCF can be compared.

A model is simple to understand, but the values of a 'typical' racer/cruiser and the wide range of conditions it sails in will undoubtably create a negative result.

Considering weight

• The weight savings aloft will be marginal in relation to the displacement to start with.
• CG will be a few cm lower. (3cm lower at 30 degrees heel is 1.5cm more righting arm.)
• Righting arm has 'lost the weight savings' from CG and CB
• Hull will ride millimeters higher. Heeled, the CB will be fractionally further from CG, increasing the righting arm.

Now drag

• Unlike AC racing the cruiser/racer is out and about in more variable windspeeds.
• If diameter of rigging has been increased 30%, your drag is greater.
• Drag is a force that acts on the CE of the rigging to heel the yacht about its transverse centre of flotation(in our tranverse model).
• When drag increases a moment occurs.Nm Kgmf ftlb take your pick
• When wind speed doubles, drag quadrules. This golden rule is vital.
  • if drag is 20lb@10knots and 80lb@20knots
    then increasing drag (not diameter) 30% is
  • 26lb@10knots and 104lb@20knots
    I made up the numbers to give an example, but whatever force you calculate is acting on a CE between the deck and masthead somewhere.
• The drag on the rigging is in the direction of the apparent wind. Over the beam it will induce the maximum heeling moment. From forward of the beam it begins robbing speed as heel decreases.

Basically this is what we are looking at,
marginally reduce total displacement

• 15000lb-100lb=14900lb
• =.0067% reduction

but marginally decrease bouyancy

• weight is lost from CG
• CG=CB

microscopically increase righting arm

• lower CG>righting arm increases
• hull rides higher>CB moves out (mono)

and lose speed/increase heeling moment by a factor

• percentage increase of drag

The question is what will make the boat faster, and quantifying the forces for a given boat is the only way to find out. To increase boat speed for a particular yacht in a variety of defined windspeeds, will give a windspeed limit, where drag has increased to cancel out the weight savings, and over come the improved stability.

AC boats might not be allowed to shed weight in some instances but can still manage a net improvement in performance if the weight is moved lower.

AC boats sail on a course that has undergone intense meteorological scrutiny.
They only race within windspeeds that are not too light nor too heavy.

As you said RHough, the scale of these boats magnifies small improvements. It is hard to replicate on a marina boat. Unless they can afford it

[brian eiland]

Haven't had time to read this thread yet, but a posting will get me on the list to receive new ones
Thanks