Downwind trim?

[Quoddy]

Two opinions on trim?
The situation is you are sailing downwind with 110 fractional sloop on a broad reach. The wind picks up 5k to 15k and you want to reduce power. You release the vang and the boom rises.
One opinion is that this will automatically cut power because the twist will allow the air to spill from the sail.
The other opinion is that the rising boom will allow more depth in the sail and therefore increase its power as well as slacken the forestay which will power up the jib.
What do you do to cut the power?

 

[Don Guillette]

Quoddy: Good question. Let's see what some of the other listers come up with.

For starters, the 110 is not a factor. When sailing DDW some of the sail trim factors that are used for closehauled and reaching are not a factor. Think of sticking a boom stick and a bed sheet on a 55 gal drum and you get an idea of what it is like to sail from Long Beach, Ca to San Diego or Ensenada, Mexico. Think of what the wind is doing to your main and jib while sailing DDW. Your sail is like a kite.

Think also of the "4 elements of sail trim" - draft depth, draft position, twist and angle of attack and decide which elements do not come into play when sailing DDW.

Let's see what develops on this thread?

 

[BobM]

Interesting question Quoddy. On a broad reach your main is all the way out, so there is no easy way to dump wind from it in typical fashion.

After thinking about it, the best way may be to actually flatten (sheet in the vang outhaul and cunningham) and sheet the main in a bit, but you would probably be best to rig a preventer too. That should allow the wind behind you to flow more easily over the sail and forward, depowering the boat. Of course you would unshadow your jib a bit, perhaps defeating this approach somewhat. But I can see that letting the vang out could help dump the air out. I look forward to seeing other opinions.

This type of situation can get pretty hairy if you depower too much. I was sailing with just my main up in ~10 knots and turned onto a run to get out of the harbor. Without the jib up and now traveling with the tide I realized that I had lost steerage, as essentially no water was moving over the rudder. I deployed the 135, reefed to about a 110 to regain control. It could have been fun if I had cut closer to Deer Island Light!

 

[Broke sailor SV Marcell]

Maybe Quody has swept back wpreaders in which case you can't let the main all the way out. So the boom is essentially still over the boat. Without tightening the vang you end up with incredible twist.

 

[Quoddy]

Mainsail power

Thanks for the responses. The boat has sweptback spreaders and I was on not to deep a broad reach. The basic question is about cutting the power of the main and what’s effective and what isn’t. When you are going downwind, being able to let of the gas effectively with out a major heading change seems quite important.

 

[shemandr]

I think depowering downwind is one of the weaknesses of swept back spreaders. It is fortunate that the need to depower on a deep angle is not common for coastal sailors. But, if caught in that situation I would first release the main sheet quite a bit and then raise the traveler to hopefully keep the sail off the spreaders or minimal contact with the spreaders and create as much twist as possible. After that I would reduce sail area. Probably in a downwind mode by rolling up the jib and then reefing the main. On my boat the vang is not that useful but I would have it released, as you said, to spill off wind in the top of the sail. I'm not sure flattening the sail has that much meaning in a downwind - barndoor - mode since flow over the sail isn't the main driving force. In fact, the J-world videos recommend outhaul tight for downwind to maximize barndoor size. Following that reasoning you would release the vang and outhaul and even the halyard to make the effective sail area smaller. I would not actually do that for other reasons but in principle that would be the direction to go.

 

[Don Guillette]

Let’s start with how we get the most power from our main and jib while sailing downwind. Once we understand how to get max power then it is easy to understand how to de-power. Because the jib in this case is a 110, I’m going to focus on the mainsail only.

The more shape you have in the mainsail going downwind equals the more sail area you have exposed to the wind. Lift is not a real factor as you are being pushed by the wind.

This is how I set up for downwind. It is not the only way but the way that works for me.

First, I ease out the main until it starts to luff and then sheet in until the luffing stops. Next, I ease the outhaul to expose more sail area. Next, I ease the Cunningham and also ease the main halyard about ½”. Next, I ease the boom vang. The key word is EASE. What I’m trying to do with the boom vang is get the top batten to be parallel with the boom. In other words, eliminate as much twist as I can. If you have a back stay adjustor it should be off. The crew should be centered in the boat,

Now, if I wanted to kill the power I’d reverse these functions but before I did that I'd try one thing. I’d turn slightly away or “bear off”. Why wouldn’t I “head up”? If I did that the boat would take off. Actions taken downwind are the opposite of closehauled. To kill the power closehauled I’d head up.

When using the boom vang to de-power you should proceed slowly. Watch the top of the sail as it opens up. Don’t release it all the way. The idea is to keep enough tension so the boom does not rise.

Next time you are on the water try the above and see if it works for you.

 

[Todd Smith]

How about a reef ?

De-powering options are limited going downwind.

 

[Don Guillette]

Todd: Yes, reefing is an option but I'd try the other stuff suggested first. You would have to come up to head to wind to do the reef. Reefing is your last resort.

Here's the rule of thumb on when you reef - you reef when the first thought of it crosses your mind!!! You don't wait because things just ain't going to improve.

 

[Todd Smith]

Don,

I agree that the other stuff is the 1st option, but doesn't seem to have as much effect downwind as those same options upwind. Maybe that's because most of my sailing is racing and we almost NEVER try to depower downwind.

And I have been quit successful putting reefs in on various points of sail. From close hauled to beam reaching, slacking the sheet enough to release the pressure seems to work pretty well. Dead downwind I have managed, but it is more of a struggle.

Todd

 

[tomgrigsby]

"Next, I ease the boom vang. The key word is EASE. What I’m trying to do with the boom vang is get the top batten to be parallel with the boom. In other words, eliminate as much twist as I can. If you have a back stay adjustor it should be off. The crew should be centered in the boat,"

I'm confused. How does easing the vang which allows to boom to rise reduce twist? I would think you would tighten the vang to increase power, and ease it to induce twist to dump air.

 

[Alan]

tom, what Don is trying to say is that the vang has multiple positions. It's not either full on or full off. Adjusting the vang (and therefore twist) is done to make the top batten match the boom's relative position the the breeze for maximum projected sail area. That results in the greatest amount of force being translated to the sail. When sailing down wind your sail is no longer an air foil, it becomes a barn door. The more perpendicular it is to the breeze the greater the force it exerts.

 

[tomgrigsby]

Thanks Alan, that makes sense.

 

[paphman]

I find this topic to be very interesting. We sail a Catalina 22 on Lake Ontario, so there are days that have strong winds. The C-22 is a mast head rig, and the spreaders are not swept back. On our boat I find that sailing more than about 150 to 160 degrees down wind, the jib is in the lee of the main and is of little use. If the wind is not strong we will pole it out to the other side. Is this the same for a fractional rig? It seems to me that if the wind is to strong on a run, it was very strong on the other points of sail. Maybe we small boat sailors are more sensitive to this than the larger boat sailors. I always reef when I feel the wind is going to be an problem. It is real easy to shake it out if needed. I know this goes against the grain a little but when not sure put in a reef.

Dale

 

[tomgrigsby]

From all I've read, you are not going against the grain. Every recommendation on this forum that I've read states more or less that if you wonder if you should reef, you should already have done it. Sounds like excellent planning to me. I haven't reefed my main yet. I need to verify how the lines work and practice it. In the mean time, I've mostly avoided going out in conditions where one would be necessary. See my mainsail bubble post for a time when I probably should have reefed the main. Learning the reefing system is high on my to-do list now. BTW my previous boat was a 73 Catalina 22. I loved it. Mine had the swing keel. I sailed one with a fixed keel across the bay from Rota to Cadiz in Spain one time. Great boat

 

[Alan]

Tom, while you're sailing on your boat you almost never experience 'true wind' speed. You and your sails are under the influence of 'apparent wind'.

While sailing off the wind (running) the apparent wind feels less than the true wind. A true wind of 12 knots could feel like 8 or 9 knots. This becomes deceptive when turning up wind where the "new" apparent wind will feel like 15 or 16 knots. If you are sailing down wind with a large headsail flying you will want to reduce sail area BEFORE you turn up into the new breeze. All the time the true wind speed could have remained constant.

Reefing your main is something that you should do before you go out again. Practice doing it while you are still at the dock if there is little or no breeze there. I you're motoring out to your sailing area, this is another opportunity to practice setting a reef. Your goal is to be able to put a reef in in under a minute. When you can do that you have become proficient at reefing. This is one skill that you really must master.

 

[tomgrigsby]

Alan
That is exactly my plan to work out the reefing system before I go out again. It's been so dang hot lately that I haven't been out at all in the last 2 months. I'm going to go down to the boat early one morning when there's no wind and giver 'er a go. My boom is fitted with 2 reefing lines, so I can set up for a first and a 2nd reef.
And I apologize for the thread hijack.
I see the wisdom in putting in a reef before turning upwind should conditions dictate.