Headsail vs no headsail, efficiency

[dustman]

How much more efficient is the combination of headsail/mainsail than a mainsail alone of the same overall area? 10%, 20%? What other factors to consider? Complexity/simplicity and overall ease of use in adverse conditions?



This is in reference to ketches/schooners.

[Breaking Waves]

Originally Posted by dustman

How much more efficient is the combination of headsail/mainsail than a mainsail alone of the same overall area?

actually you have it backwards.

for the same total area, a single sail (mainsail) is (broadly) more efficient than 2 sails (main + jib).

this was conclusively proven in the C class, which has a fixed sail area. they run only single sails.

[wingssail]

Originally Posted by dustman

How much more efficient is the combination of headsail/mainsail than a mainsail alone of the same overall area? 10%, 20%? What other factors to consider? Complexity/simplicity and overall ease of use in adverse conditions?

This is in reference to ketches/schooners.

A headsail/mainsail is more efficient for most boats for two reasons:

1. A mainsail has disturbed flow because of the mast at the leading edge. A headsail has a cleaner entry. This is true for all but the most dead downwind points of sail. If there is flow over the sails the clean entry is better.

2. The two sails interact whenever there is flow. The wind is bent by the headsail and further bent by the mainsail.

Percentage is hard to calculate.

Modern sail handling makes either configuration equally easy.

Dividing the total area into two sails instead of one larger one means you deal with smaller sails.

For ease of handling and simplicity I prefer a single mast and two sails: easily reefable mainsail and a small, working, jib.

[psk125]

Read this book: https://www.amazon.com/Aero-Hydrodyn.../dp/1888671181 and come back to tell us what he says.

The reason that ketches and schooners are less popular now than they were is that the additional masts and rigging add expense and decrease efficiency.

[seandepagnier]

For the same sail area, a single sail is more efficient.

For a given maximum mast height, more sails are more efficient because each sail will be a higher aspect ratio than a single sail and have less induced drag.


On a typical cruising sailboat, the sails are already not very efficient especially off the wind, but the amount of wind power available at sea often far exceeds what is needed to go hull speed anyway so efficiency in terms of drive per sail area isn't really important.

On a bermuda rig, the main sail can provide most of the driving force downwind and broad reaching. On a beam reach or wing and wing running, it provides about the same power as the headsail, and beating it is providing the least amount of power, but is critical for balancing the forces of the headsail. Most sailboats do not sail efficiently upwind on only main or only jib.

[tomfl]

A-Class cats. I rest my case.

[carlosproa]

Originally Posted by tomfl

A-Class cats. I rest my case.

How about parallel rigs? Two mast side by side, each with a single sail? Bernad Kohler Duo800 catamaran has this type of rig.

[wingssail]

Originally Posted by tomfl

A-Class cats. I rest my case.

Apples to oranges. Class A catamarans are small, single handed, high speed, racing catamarans. Like any high speed single handed dingy it makes sense to have one sail. There is no crew and not time to deal with another sail. Looking to a Class A catamaran is not a validation of the correct choice for a cruising boat.

Class C catamarans, (Little America's Cup) they use wings, not soft sails. Again, not a validation of single sail for use on a cruising boat.

[wingssail]

Originally Posted by carlosproa

How about parallel rigs? Two mast side by side, each with a single sail? Bernad Kohler Duo800 catamaran has this type of rig.

Another idea to solve a problem which is non-existant on most cruising sailboats.

We have one in our area. Cat to Fold. It is semi high performance, well sailed and pretty cool. Some times it works, but it's advantages are rarely seen and it's frequently underperforming. The two sails are too far away to interact properly yet they are still close enough to interfere with each other.

The sloop rig with Marconi mainsail has been underdevelopment for centuries and it is, at this time, hard to beat.

[TrentePieds]

Dustman:

You question is NOT amenable to a brief (pat) answer, because you have NOT stated the particular parameter on which you wish to achieve "efficiency".

"Lift generated" (i.e. the equivalent of horsepower in a car) is certainly one parameter that can be considered, and it is presumably the one you mean. If so, the posts above are right enuff, but maximizing lift generated by the sails is NOT the only parameter that needs to be considered in boat design. "Sacrificing lift" is often necessary in order to achieve "efficiency" on other parameters so that, when ALL parameters have been considered and OPTIMIZED in terms of the design objective, the boat may be "efficient" as in being fit for her purpose.

But you are off to a good start. If you really want to get a grip on the "efficiency" of sails, then read the sundry books on the topic authored by C.A.Marchaj. He is the aerodynamics guru of the sailing world :-)

All the best.

TrentePieds

[Don C L]

In terms of actual numbers, that’s a good question. In terms of practicality, I think we are seeing it in various modern racing rigs. I’m pretty sure it is settled that the maximum lift to drag is achieved by a single wing, (biplanes vs monoplanes might apply here) but in sailing we have change wing area and shape occasionally, and it is advantageous to keep the center of effort low to minimize heeling in some designs. Ketches have other advantages to be considered in spite of added complexity. In rougher weather many folks like the increased number of options afforded by multiple sails available. Maybe inefficient, but more practical and useful to some.

[Breaking Waves]

Originally Posted by wingssail

Class C catamarans, (Little America's Cup) they use wings, not soft sails.

back before wings, the C-class used soft sails, and a single mainsail was still proven the winning solution - look up 1976 Aquarius V

The physics is pretty clear, for a given area, a single foil is most efficient. . . . and higher aspect is more efficient than low.

Now what limitations the Op add are a bit unclear, but unirigs can be pretty easy to handle (see the Freedoms) in a cruising context.

[Cadence]

More info. might get a sensible response.

[TrentePieds]

Quote: " ...unirigs can be pretty easy to handle."

Absolutely. The catboat originated among poor inshore fishermen in New England. Its merit was that it was cheap to build and easy for one man to handle while doing his REAL job, which was that of catching fish. Not that of sailing. Sailing was merely a means to an end.

Thus it was "efficient" on those parameters. It was NOT efficient in terms of aero/hydro dynamics. It was not its objective to be so.

Dustman might like to contemplate that the current thinking in regard to a SINGLE sail is that for sailing ON the wind, an aspect ratio of 1:6 is OPTIMUM (i.e. "best" having had regard to all relevant factors) including the AIRFOIL (cross sectional shape when full of wind and correctly trimmed in respect of Angle of Attack). Traditional catboats were more like 1:3 because THAT is optimum when OFF the wind in a sloppy sea.

TrentePieds

[dustman]

What I am gathering so far is that there is not enough difference in efficiency to make it a deciding design factor.


Not sure exactly what additional info you need, but I will give a brief description of the boat I plan to build.


My first boat will be for cruising the Bahamas and perhaps more of the Caribbean, I'll likely be dropping it in the water at Corpus Christi and working my way over. Later, after having gained experience, I will be building a much larger version for ocean crossings.



It will certainly be a catamaran, approx 30' waterline, 12' beam, either a schooner or ketch, leaning towards a gaff rigged ketch with freestanding masts. Since I am limiting the beam so much I want to split the sail plan up to keep the center of effort low. A ketch, in my limited experience but abundant research, seems like it gives you a lot of options and control. The hulls will have no storage or accommodations, being something like scaled up versions of hobie 16 hulls but not quite as skinny, there will only be a very small, highly aerodynamic cabin on deck, everything mounted on an aluminum frame. The whole idea is simple, cheap, light, minimal windage, minimal draft, and easily handled by myself alone and an eye to reducing/eliminating potential maintenance and failure points. The loaded displacement for myself alone should wind up being about 1200 lbs, with a sail area of 120-150ft2, divided between fore and aft masts, thinking about a 60-40 sail area distribution, with sails of 3 to 1 aspect ratio.


I hope you guys can make sense of all that, writing is not my strong suit.