Downwind Catamaran Sailing

[krafthaus]

Question on sailing a Lagoon 400 (or other cats) downwind.

The Lagoon 400 manual has a section with sail trim guidelines in their owner's manual for various points of sail.

On downwind sailing it says never sail with just the jib/genoa only above a certain wind speed, and must have mainsail up anywhere between full and 2nd reef as minimum, again given certain wind speeds. (I looked for the manual online to post the details, but sorry, can't locate it.)

This is related to stability of the mast/rig and potential for damage in strong winds which I take is due to mainstays off the sides of the boat as opposed to a backstay typical of monohulls.

Manual also says not to sail directly downwind, and it recommends 30 degrees off the stern (or perhaps it was 15?). This is due to faster sailing on this point of sail I take it as VMG is better than straight downwind sailing? This is ok if you are on a larger open area of water, but not a narrower channel between islands for example, as you'd be gybing back & forth. If straight downwind is not recommended for rig stability reasons then how does a person gybe (rhetorical question)? Can't sail wing on wing either?

Anyway, I would appreciate comments from those with more knowledge and experience on this subject so I understand the reasons, risks, concerns. Thanks All.

[thinwater]

I sail a PDQ 32, which in many ways is like your Lagoon (no back stay, moderate design), just smaller.

No sailing under jib alone in strong winds. This most likely has to do with suporting the mast againts buckling faliure an pumping, not the strength of the shroud. This is not a mono-vs-multi issue. It is a mast design issue. Even the smallest amount of main will do.

Imbalance. The boat will be more responsive and steer better with a balanced sail plan. With low-aspect ratio keel, too much fore-aft imbalance will allow the sailplan to overpower the rudders, particularly in waves. Similarly, main alone in strong winds will make the boat round-up in the puffs; very bad. Better, off-the-wind reef the main before the jib and always keep a little jib. Up-wind, reef both sails together. The goal should always be relativly neutral to slight weather helm.
http://sail-delmarva.blogspot.com/20...-cruising.html

Furling. Rolling up the jib with a big load on it is stressfull for the crew and gear. With a main up, head down wind, blanket, and roll it up. No main, lots of flapping and huge loads, if it's really blowing. A double (or triple) reefed main is more dependable.

Wing-and-wing. Should work fine. Yes, reaching is faster, but it isn't smoother, it isn't always the dirrection you want to go, and it isn't faster (VMG) on cruising boats, once you are under reduced sail.
Sail Delmarva: Balance
Jibing isn't so bad: reef the main enough, tighten the mainsheet, center the boom, and ease it out on the new side. Just don't let it slam. If jibing is unmanagable, that is a hint that you have too much main up. This may take 3 people in a breeze, though 2 can manage if the jib is jibed first and the traveler eased later.

Scan the pages; we'ld love to read them. The link on "Balance" contains pages from the PDQ manual.

[Jimbo485]

V interesting topic. I don't have much time ATM, resin going off, typing with little pinkie...

Once the wind gets behind the beam, I find myself in a quandary in our present cat. Especially if the true wind is well behind the beam but the apparent wind is forward of the beam! And this seems to happen far too often!

With apparent wind behind the beam, I have no hesitation in getting rid of the main. Improves directional stability - better to have a front WD than a rear WD when going downwind without a doubt.

But the quandary is always during the crossover when there is a risk of worsening conditions. Because we then end up with a main hoisted, maybe somewhat reefed but still hoisted, and the windspeed increases. So it is difficult to reef the main without turning up. And turning up increases apparent windspeed and things tend to get a little crazy. With roller furling jibs and no main, it is not a problem because we bear off, the apparent windspeed decreases and then we furl away the jib(s).

I will start another topic another day about handling gusts in a cat. We are not experts and would appreciate sharing experiences.

Chau!

[Jimbo485]

We use running backstays, so we don't worry about only having 1 or 2 jibs up without a main.

Gotta run. Bye!

[simonmd]

Must say I was surprised to read the opening post but I guess the lack of conventional backstays does make sort of sence.

Personaly, I don't bother with the main when doing any downwind sailing, I find she'll easily reach hull speed with just the headsail in anything over a moderate wind so why bother?

[gramos]

I hit my best speed ever ,running downwind , with just 1/2 the jib out , the main was dropped but the mast was tensioned/ supported by the topping lift and full tension on the mainsheet .
This triangulates the whole rig so the forestay / jib can take the loads , in the same way that the main would if raised , so I can,t see the problem running downwind with the jib , same with a chute or spinny .

[thinwater]

Let us know what you learn, Krafthaus.

[beiland]

Originally Posted by thinwater

Let us know what you learn, Krafthaus.

I just started reading this subject thread....and then ran across this posting. Excuse me, but don't folks bother to read the previous postings before making theirs??

Krafthaus stated in his original posting:

The Lagoon 400 manual has a section with sail trim guidelines in their owner's manual for various points of sail.

On downwind sailing it says never sail with just the jib/genoa only above a certain wind speed, and must have mainsail up anywhere between full and 2nd reef as minimum, again given certain wind speeds. (I looked for the manual online to post the details, but sorry, can't locate it.)

This is related to stability of the mast/rig and potential for damage in strong winds which I take is due to mainstays off the sides of the boat as opposed to a backstay typical of monohulls.

Manual also says not to sail directly downwind, and it recommends 30 degrees off the stern

[beiland]

Originally Posted by krafthaus

This is related to stability of the mast/rig and potential for damage in strong winds which I take is due to mainstays off the sides of the boat as opposed to a backstay typical of monohulls.

Manual also says not to sail directly downwind, and it recommends 30 degrees off the stern (or perhaps it was 15?). This is due to faster sailing on this point of sail I take it as VMG is better than straight downwind sailing? This is ok if you are on a larger open area of water, but not a narrower channel between islands for example, as you'd be gybing back & forth. If straight downwind is not recommended for rig stability reasons then how does a person gybe (rhetorical question)? Can't sail wing on wing either?

Anyway, I would appreciate comments from those with more knowledge and experience on this subject so I understand the reasons, risks, concerns. Thanks All.

I suspect this manual was written by a young lawyer whos looking to protect the manufacturer from ANY mast damage on their vessels.

Certainly the 'backstaying' on a 3-point multihull type rig is lacking in good support for an all-headsail arrangment....look at that shallow angle (in the fore-to-aft plane) of the backstay/shroud with respect to the forestay.

But one must account for the bigger angle provided this backstay/shroud as it spreads out to the beam of the vessel (much better). To be considered as well is that most mast on these production boats are more heavily speced as it is a multihull vessel with much higher righting moments.

When I visit the shows and look at some of these charter multihull vessels (and retail ones) I'm continuosly amazed at the amount of rigging they seem to find necessary to hold up these rigs. I believe a lot of this over-rigging stems from the real lack of engineering analysis of sailing rigs on production vessels. Instead they simply follow the leader with rigging solutions similar to the older assumed standard. I address this situation in this subject thread:
Sail Loading on Rig, Rig Loading on Vessel


Meanwhile look at this guy who believes in ONLY jib sailing:
Lyra's Rig

Or here is another fellow who uses two genoas in a unique fashion:
Catbird Suite

[beiland]

Originally Posted by thinwater

No sailing under jib alone in strong winds. This most likely has to do with suporting the mast againts buckling faliure an pumping, not the strength of the shroud. This is not a mono-vs-multi issue. It is a mast design issue. Even the smallest amount of main will do.

It is a monhull verses multihull issue in that monhulls don't general use a 3-point rigging arrangement as multihulls do.

Imbalance. The boat will be more responsive and steer better with a balanced sail plan. With low-aspect ratio keel, too much fore-aft imbalance will allow the sailplan to overpower the rudders, particularly in waves. Similarly, main alone in strong winds will make the boat round-up in the puffs; very bad. Better, off-the-wind reef the main before the jib and always keep a little jib. Up-wind, reef both sails together. The goal should always be relativly neutral to slight weather helm.
http://sail-delmarva.blogspot.com/2010/09/simple-jib-lead-adjustment-for-cruising.html

Boat will steer more easily downwind under jib alone.

Furling. Rolling up the jib with a big load on it is stressfull for the crew and gear. With a main up, head down wind, blanket, and roll it up. No main, lots of flapping and huge loads, if it's really blowing. A double (or triple) reefed main is more dependable.

True rolling the jib in the blanket of the main will be easier. ...BUT the who wants a big full battened main pressed up against the spreaders and other rigging as the wind picks up and you either haven't reefed in time, or you follow that manual and leave the main up...bull (/QUOTE]

Jibing isn't so bad: reef the main enough, tighten the mainsheet, center the boom, and ease it out on the new side. Just don't let it slam. If jibing is unmanagable, that is a hint that you have too much main up. This may take 3 people in a breeze, though 2 can manage if the jib is jibed first and the traveler eased later.

Isn't gybing a full battened main fun??....even a reefed one, in a good breeze??

[ggray]

Couple of points to add to the discussion; comments appreciated.

I'm guessing that mast pumping must be more the issue, if there really is one. When the main is eased when off the wind, it no longer braces the mast in the direction needed. If the mainsheet is eased as well, even less bracing. I've always thought the help of a raised main in bracing the rig was more important close hauled, when the main would certainly act like a backstay.

Since apparent wind moves forward with boat speed, it is surprising how close together a course of 150* off the wind is to same course on opposite tack, especially with a gennaker up. It's not 60*, but more like half that. So while you are 150* off the wind, you aren't far off from DDW anyway.

Once while sailing with gennaker I was forced by obstructions to sail DDW. I jibed main, and continued wing and wing very well. Not sure I'd make a practice of this, but it worked for the 1/2 mile we were restricted.

[Cruisin Cat]

Interesting discussion...I didn't realize there was a problem sailing down wind with no main.

I sail down wind in my cat with just genoa or asymetrical spinnaker quite a lot. I just don't like the boom banging about, and I'm cruising not racing.

Seems the problem must be more pumping as ggray said....but what exactly is pumping?

[thinwater]

Originally Posted by beiland

I just started reading this subject thread....and then ran across this posting. Excuse me, but don't folks bother to read the previous postings before making theirs??

Krafthaus stated in his original posting:

Why a post like this; just to stir things up and to draw attention?

I spoke in very simple terms to why the mast could be unstable, but didn't feel an engineering analysis was called for, nor do I have specs on the boat. I know that some boats can have the masts pulled out of column aft by a deeply reefed main, so in absence of more information, all we can make is conversation. Clearly the OP had read the manual but found it unclear. Perhaps you would have understood me more easily had I asked the OP to request clarification from the factory. I would like to hear if bracing the mast up with a tight back stay changes things. Moreover, I can make some fairly educated guesses as to their reasoning, but that does not mean I would not like to hear THEIR reasoning, particularly if I was the owner of a late model boat.

Yes, every rig is a compromise. Obviously. As for your refferenced post, I saw lots of ornate wording, but not much meat. As much as a rigging can be analyzed, there will always be the variables of wind, wave, and skipper handling that will defy numerical analysis. A rogue wave type situation matched to an ill timed jibe.

Or as engineers say, "calculate to 6 significant digits, measure with a micrometer, mark with chalk, and cut with an ax." Heavy weather designs ask for expereince. Smooth waters invite calculation from first principles. I do refinery engineering, and there are places where calculations from first principles are dependable, and there are times when take-offs from existing processes are a more conservative bet (not always better or safer, but safer from a CYA view).

------

As for the rest, it's just opinion and much can be boat specific. I'm guessing most of your expereince is on monohulls, but correct me if I have guess incorrectly.

a. Yup, there are monos with 3-point rigs. My point was that it was a mast-in-column issue, not a boat issue.
b. No, not on some cats with LAR keels. In fact, some cannot steer much at all if so unbalanced. Different answers, different boats. Having some main up is not a problem off the wind on cats.
c. I'm assuming reefing was done in time and I said as much. At least on my boat, the main will still come down in a blow.
d. Never had a problem, up to 35 knots with 2 reefs in and careful procedure. But again, I suppose this is boat-specific.

On every boat, the skipper needs to learn when to get the laundry in. Down wind can be the trickiest call, cause she's going like a bomb and life is good!

[thinwater]

Originally Posted by Cruisin Cat

pumping as ggray said....but what exactly is pumping?

The mast can begin to bend fore and aft. The main tends to inhibit this, but it can happen with the main up, particularly with slender sections.

[Dave852]

On my last boat I used a 22' carbon whisker pole and on two Pacific crossings spent a lot of time wing and wing if the wind was 20 knots or above. If under 20 knots flew the kite with the main up as well but with 3 reefs so as not to shadow the kite. The reason I always kept the main up was because if I dropped it completely I would have to turn into the wind to raise it again. As long as I never lowered it below three reefs then it could be raised back up while still downwind because the battens were up past the lazy jacks. On a cruising cat I can see no reason not to sail directly down wind which is usually directly down wave and a sweet ride. Of course more effort is required to set the boat up to maintain a good speed directly downwind but I feel it's worth it for the smooth ride.