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Old 03-09-2015, 03:28   #1
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Headsail versus Mainsail

I'd be interested to hear members opinions on which produces more power in a catamaran-the headsail or the mainsail?
I note that cats like the Lagoon 39 have moved the mast aft, resulting in a bigger headsail and smaller main. Does this arrangement produce better performance?
My experience in catamarans is very limited; however I have been heavily involved in windsurfing almost from it's inception to the modern day wave board. When windsurfing sails eventually became fully battened their performance increased substantially. Therefore I'm puzzled as to why in some quarters it is considered desirable to increase the headsail at the expense of the main. However, I note that this opinion is not universal, as I have come across one website touting itself as a guru on catamarans which says just the opposite.
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Old 03-09-2015, 06:21   #2
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Re: headsail versus mainsail

Hi Geoff - right off the bat, I think it depends a lot on the relative sail areas. It's easy to conclude that the main is the biggest driver for rigs with smallish head sails, like self tacking jibs. For big, overlapping genoas, the difference gets less and may depend a lot on the point of sail. Finally, for rigs with the mast set back and smaller mains vs headsails (new Lagoon 39) it's easy to conclude that the headsail is the biggest driver. Actually, I think the L39 approach is a good idea for a cruising boat without boards sailed by cruisers who have little need or desire to go upwind.

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Old 03-09-2015, 07:27   #3
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Re: headsail versus mainsail

Quote:
Originally Posted by geoff326 View Post
I'd be interested to hear members opinions on which produces more power in a catamaran-the headsail or the mainsail?
I note that cats like the Lagoon 39 have moved the mast aft, resulting in a bigger headsail and smaller main. Does this arrangement produce better performance?
My experience in catamarans is very limited; however I have been heavily involved in windsurfing almost from it's inception to the modern day wave board. When windsurfing sails eventually became fully battened their performance increased substantially. Therefore I'm puzzled as to why in some quarters it is considered desirable to increase the headsail at the expense of the main. However, I note that this opinion is not universal, as I have come across one website touting itself as a guru on catamarans which says just the opposite.
Lagoon very carefully recognised that most of their boat owners don't do upwind and catered the sail plan to suit. As for performance, if the Lagoon 37 (its not 39) would not be in the top end of the performance stakes, hell you couldn't even see the top end from there, but it suits those who motor more than they sail
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Old 03-09-2015, 11:20   #4
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Re: headsail versus mainsail

Geoff,

As mentioned it very much depends on the boat, the size of the rig, the loads you can tolerate, and any design limitations. There simply isn't enough information in the question to give a meaningful answer across all boat types.

If you restrict sail area, then the most efficient design is a single high aspect main, ala an A-Cats. But this has serious limitations, specifically massive sheet loads, and compression loads under the mast.

If you restrict mast height, then a big main, and a big head sail has more sail area and thus power.

If ease of use is important then a self tacking jib and a big main are probably the easiest to deal with.

To limit cost, low aspect sails with a short mast is cheaper...

The question as asked is a lot like asking 'what generates more hp, a gas or Diesel engine? The only appropriate answer is 'depends on the engines involved'.
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Old 03-09-2015, 16:51   #5
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Re: headsail versus mainsail

Thanks for the replies.
Is a reasonable assumption then that by moving the mast aft, upwind performance, particularly on a tight reach, is lessened, while downwind performance is increased?
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Old 03-09-2015, 17:02   #6
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Re: headsail versus mainsail

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Is a reasonable assumption then that by moving the mast aft, upwind performance, particularly on a tight reach, is lessened, while downwind performance is increased?
Particularly at your best upwind angle. Usually, upwind angle is limited by the sheeting angle of the headsail (on cruising boats). Make the headsail your most powerful sail and this just exasperates the problem. IMHO. If you like or need to sail upwind, you need the main as your principle driver.

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Old 03-09-2015, 17:21   #7
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Re: Headsail versus Mainsail

Could another factor be large mains can be intimidating/difficult for short handing whereas roller furlers for large headsails aren't (so much) ?
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Old 03-09-2015, 17:31   #8
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Re: headsail versus mainsail

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Particularly at your best upwind angle. Usually, upwind angle is limited by the sheeting angle of the headsail (on cruising boats). Make the headsail your most powerful sail and this just exasperates the problem. IMHO. If you like or need to sail upwind, you need the main as your principle driver.

Dave
So it makes one wonder why Cats with dagger boards don't have aft positioned masts and then one could get the best of both worlds?
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Old 03-09-2015, 17:48   #9
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Re: headsail versus mainsail

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So it makes one wonder why Cats with dagger boards don't have aft positioned masts and then one could get the best of both worlds?
That would be like putting finely tuned suspensions and Perelli tires on a Winnebago. While the best of both worlds, it doesn't make the compromise disappear. IMHO.

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Could another factor be large mains can be intimidating/difficult for short handing whereas roller furlers for large headsails aren't (so much) ?
Certainly a factor for the Lagoon 39. It comes down to this question: Do you want a sailing machine that you can live on, or a house that also sails?

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Old 03-09-2015, 18:04   #10
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Re: headsail versus mainsail

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That would be like putting finely tuned suspensions and Perelli tires on a Winnebago. While the best of both worlds, it doesn't make the compromise disappear. IMHO.



Certainly a factor for the Lagoon 39. It comes down to this question: Do you want a sailing machine that you can live on, or a house that also sails?

Dave
Do I take then that you consider a Lagoon 39 a house that also sails?
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Old 03-09-2015, 18:34   #11
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Re: headsail versus mainsail

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Do I take then that you consider a Lagoon 39 a house that also sails?
No - its a 37 foot house that occasionally sails
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Old 04-09-2015, 00:41   #12
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Re: Headsail versus Mainsail

Geoff,

You were right when you said about an aft mast boat with daggerboards. It does give good upwind performance DEPENDING on the design. Making blanket statements about aft mast designs not sailing well to windward is just wrong.

Many factors are involved in a good design, and how well it performs under various conditions and wind angles. You'll have to investigate a bit deeper. Look at the SA/D of the Lagoon 39. Also look at the hull design basics. What is the Lwl/Bh for starters?
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Old 04-09-2015, 07:00   #13
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Re: Headsail versus Mainsail

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You were right when you said about an aft mast boat with daggerboards. It does give good upwind performance DEPENDING on the design. Making blanket statements about aft mast designs not sailing well to windward is just wrong.
Of course BigBeakie is correct. My statement was overly broad and made in the context of production boats principally made for the charter market.

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Old 04-09-2015, 16:26   #14
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Re: Headsail versus Mainsail

The mast aft position of the L39 is not done for performance reasons as its not a performance boat. It's probably to make the main easier to handle. In my opinion, it would have been better to go with a mast in its normal position and go for an in-mast furling main, back stay (no back-swepth spreaders), and have a main that is better for downwind sailing.


I also don't think a mast aft is good for performance. Look at open design classes like 18 foot skiffs or real racing multis. Luff length is much more important than overall size (width). For a non gennaker rig, I think 1-to-3 ratio jib-main is good (I have experience in such racing design class). For a class with gennaker, probably closer to 1-to-2
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Old 04-09-2015, 17:22   #15
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Re: Headsail versus Mainsail

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Make the headsail your most powerful sail and this just exasperates the problem.
And ya really don't want an exasperated problem on your boat... the calm ones are bad enough!

(sorry.... couldn't help myself!)

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