Which is more efficient, main or jib?

[UNCIVILIZED]

Originally Posted by DavidLGCrawford

Wow, that's a gorgeous boat. I can certainly see why you lusted one.

Pretty much just what I was thinking but interestingly they put jib 2 on a boom. Not sure why they would do that... it would limit you to a 100%, while without a boom you could go 120 or more. Still, I'm not an engineer so what do I know!

On a twin masted boat you could design the sail which flys in between the two spars in a manner akin to those found on some of Wharram's Tiki designs. Dutch Gaffed, loose footed mains. Including ones that get flown from the forward spar, & overlap the aft one when sheeted in. As found on this Nigel Irens design --> Nigel Irens 50' schooner
And shown by Steady Hand here --> http://www.cruisersforum.com/forums/...ml#post2251424

I'd certainly like to go for a spin on her. And if she needed a good home I'd trade them a $-Fiver Well, that plus a bit more I suppose

One could even build such a sail as a conventional square topped main, including using full battens except where the sail overlaps the aft spar. That way the sail's area completely fills up the gap in between the two spars & then some.

[barnakiel]

This is an odd question as it seems to confuse many variables in one query. Never a good prognostics for a sound answer.

Otherwise, dig into Marchaj.

Otherwise, given same area and only one sail deployed at a time, on the wind, the jib may provide more force as the forces on the main tend to be more disturbed by the mast (masts are thicker profiles than luff tapes).

Running, the main can deliver more power, as it tends to be set on a vertical mast while jibs are somewhat angled.

Etc.

In your specific context, deploy one sail at a time and measure the resulting speed. I think this is what you want to know.

Cheers,
b.

[hamburking]

I spent many happy days sailing under jib alone with no troubles, so I am a big fan of the jib sail. Off the wind, the jib rules. However, your best configuration relies on the slot effect of having the jib accelerate the wind over the lee side of the main. And you cannot count on sailing downwind all the time.

Its a flawed question. They work together. Each has its benefits on different points of sail. There are just too many variables. Why not include square sails too, which are optimum in the trades and dominated sailing ships for centuries?

Having said all that, I believe the junk rig is well known for its great efficiency.

[seasick]

Hands down the jib is the more versatile and perhaps efficient on all points of sail. I'll often dump the main altogether at sun down if it looks like it's going to pipe up during the night because a jib (especially a roller furling jib) can be reefed or doused in short order without leaving the cockpit.

[Hyrdflyr]

Originally Posted by Stumble

It gets very complicated very quickly and there are no pat answers. Aspect ratio, drag distribution, sail shape, all play a part.

I agree with the "it's complicated" reply. Wind direction relative to course has, I think,the greatest effect on efficiency of a given sail plan.

When I was a flight instructor, I had issues with the official FAA line that the Bernouli effect was the predominant reason that a wing created lift. I believe angle of attack is the most critical aspect of a wing in developing lift, and likewise a sail, but that's just my humble opinion. (and the older I get the more humble I get)

[ramblinrod]

Originally Posted by DavidLGCrawford

Given two sails of identical size, which would be more efficient, a jib with an angled leading edge or a main behind a mast?

Imagine a ketch. Typically, from the bow to stern, you would have:
jib, main mast, mainsail (on boom), mizzen mast, mizzen sail.
But what if you did:
jib, main mast, jib 2, mizzen mast, mizzen sail.

Assuming the mainsail and "jib 2" where identical size, would there be a difference?

I think you mean "effective" rather than "efficient".

"Efficiency" is the relationship between power out vs power in.

"Effectiveness" (in this context) by my interpretation of the question, is a boat speed comparison between 2 sail plans.


The correct answer is, "Nobody can say" without knowing more details than can be conveyed in a forum post.

The most effective sail plan (to weather), will be the one that provides the most sail area, with the least drag, with the best balance between CE and CLR.

[UNCIVILIZED]

Originally Posted by hamburking

I spent many happy days sailing under jib alone with no troubles, so I am a big fan of the jib sail. Off the wind, the jib rules. However, your best configuration relies on the slot effect of having the jib accelerate the wind over the lee side of the main. And you cannot count on sailing downwind all the time.

Its a flawed question. They work together. Each has its benefits on different points of sail. There are just too many variables. Why not include square sails too, which are optimum in the trades and dominated sailing ships for centuries?

Having said all that, I believe the junk rig is well known for its great efficiency.

How do you define a junk rig as being efficient? Low cost maybe, but not efficient. Especially when compared with the Bermudan rig, in it's many variations.
Speciically, I'd love to see the Polars for a boat fitted with a junk rig, as compared to those of a Bermudan rigged sistership or cousin. And yes, this is coming from a genuine, unflinching, Pete & Annie Hill fan. Since about 1990. Meaning their junk rigged dory, Badger.

There's always been a strong temptation to build a similar boat myself. But then logic kicks in, & grabs me by the neck. Firmly telling me to tilt at a different windmill.

[ramblinrod]

Originally Posted by ramblinrod

I think you mean "effective" rather than "efficient".

"Efficiency" is the relationship between power out vs power in.

"Effectiveness" (in this context) by my interpretation of the question, is a boat speed comparison between 2 sail plans.


The correct answer is, "Nobody can say" without knowing more details than can be conveyed in a forum post.

The most effective sail plan (to weather), will be the one that provides the most sail area, with the least drag, with the best balance between CE and CLR.

Correcting myself before someone else does, in post above, shoulda be'ed, ...will be the one that produces the most drive, with the least drag...

[TeddyDiver]

Originally Posted by StuM

My first thought is that you won't get the slot effect with two jibs that you would with jib+main.

Slot effect is a myth what comes to soft sails..

[reed1v]

depends on size of jib, cut of the main, point of sail, sea conditions, and strength of the winds. Also what kind of boat are you talking about. For us with a heavy blue water ketch, we used all our sail inventory as conditions changed.

The jib normally gives drive while the main gives direction, with the mizzen giving stability. Hard on the wind the mizzen is useless; direct downwind everything but the jib are more or less useless(assuming you changed to a 160 or more cut jib. In between, they all add something.

In a blow(45+ knots), then jib+mizzen, beyond 55knots then just the staysail(inner jib) and reefed mizzen. Hurricane conditions then either nothing or a tri sail off the mainmast to keep steady.

No wind or very little wind, go with very light jib.Or if you are motoring, then put up all three sails since they do help conserve fuel and will add about a knot to the boat. Hope that helps.

[Cheechako]

I say the angled foresail. Because the mast interferes with wind flow.

[Adelie]

Ignoring any secondary influences the jib would be more "efficient" due to higher aspect ratio and cleaner air over the sail (no mast).

That said, in the real world you can't ignore the secondary influences:
Balance
Synergy between sails
Ease of handling
Ease of reefing

[Stumble]

Originally Posted by Adelie

Ignoring any secondary influences the jib would be more "efficient" due to higher aspect ratio and cleaner air over the sail (no mast).

That said, in the real world you can't ignore the secondary influences:
Balance
Synergy between sails
Ease of handling
Ease of reefing

It just depends, mains are typically higher aspect than jibs on cruising boats. But if you go with a non-overlapping fractional jib...

Is the mast rotating or not? A rotating main gains power from the mast, so much so that on sail area limited classes rotating masts are typically counted as part of the main's sail area. A non-rotating mast just generates drag.

How much roach is there on the main? The more there is the more efficient the main is, and a square top is even better as the top cuts votes drag substantially.

What's the angle of the forestay? Drag goes up as the angle decreases from verticle.

Are we discussing the jib in isolation, or are you also counting the drag created by the mast needed to hold I think up.

Like I said it's complicated. But if you have a limited amount of sail area to play with then a unirig will always be preferable over a sloop.

[Kinta Ray]

Starting from scratch a rotating wingmast main would kill either sail. In the example you give ( and this is just my opinion) I would go Jib/jib mainly because although the perpendicular luff of a main should be more efficient than the angled jib its advantage is negated by the disturbance of the mast on laminar flow. The other advantage of the jib/jib lies in its ease of handling (talking furling here). Unless you are changing the rig completely I would be putting up as much sail as possible for the conditions and that includes jibs, mains and mizzen. There is no substitute for water line length or sail area. On a broad to close reach my catamaran sails about 1.5k slower under jib in 8-10k true wind but I have a 3/4 rig with a roachy main (don't know the sail areas). I mainly sail alone so use the jib a lot(the main takes effort to put up and I'm old and lazy).

[Redpcx]

There never is a correct answer to a rigged question.