Help best VMG Downwind this time

[Dave_S]

I enjoy upwind more than downwind, maybe I'm doing it wrong (in fact as I write/process this I am realising that I am doing it wrong) I haven't had to do much/any that I can think of direct downwind sailing. My targets have always been reachable downwind on a single run so I just point it at the target and make the best of it, but that is probably why I haven't found it exciting with flapping sails and no apparent.

I spoke to a guy on a similar boat who gibes at 145* TWD and sails at 80* apparent. So he is actually sailing upwind anyway. That's about wind speed so it sounds close to do-able for me ???

Just looking for some other people's experiences to give me an idea of what to aim for and some short cuts on the best VMG.

I worry about not reefing and what is the best approach if I miss my reefing point and find I have too much sail up. Can I turn direct down wind, let out more Genoa and align the main backwards directly into the wind and bring it down a couple of reef points ? Or is it just going to ballon out.

[Dsanduril]

Dave,

there are two approaches to sailing dead downwind (DDW) - putting up a large sail and going straight, or gybing both sides of the course as you describe. Every boat is a little different as to which is most effective and easiest.

We recently did the trip from Gloucester Passage to Cape Upstart in company of a Schionning 1500 - so about the same size and type of boat although he is probably lighter (definitely much newer). We opted for the DDW option using our Asym spinnaker. Gybed once as the wind shifted. Made 7 knots and change. He opted for the downwind tacking with large headsail and main. Did about 9 knots over the ground, but his VMG was about the same as ours. He was gybing between 70 and 80 degrees each time.

In the end, after ~45 miles we got into the anchorage about 10 minutes before he did - and we had left about 10 minutes before as well. So, it was a wash, he definitely got extra speed but also sailed significantly further. I'd kind of wondered exactly the same question on real world sailing (vs. polars and computed sailing) VMG. It's only one data point, but in this case it was pretty even. So then it comes down to personal decisions, I don't mind running the spinnaker even singlehanded in mild conditions but you have to to get the DDW speed vs. doing the work of gybing with plain white sails and keeping up the boat speed.

As to the other question, we don't have much trouble reefing downwind. Yes, the main/battens will fall against the rigging and you may have to pull the sail down a bit but we've never found it difficult. We do center the boom to make it as easy as possible. If necessary and you aren't carrying a big/light headsail you can always round up to reef (unless you've really missed the mark and wind is that strong).

If we opt for the DDW option rather than tacking downwind then we generally put up the spinnaker (or the big genoa if TWS > ~20) and drop the main entirely. No worries about reefing, or slatting and we find speed to be pretty much the same by getting free air to the headsail. Makes the steering easier too. I know that's antithetical to many cat sailors, but we find we don't lose much DDW by dropping the main (I suspect it might be different with an accommodation biased cat but that's not your boat or ours and I've never really sailed one for a much time so can't speak to it).

[44'cruisingcat]

If you have a spinnaker and your destination is DDW, then sailing DDW is very hard to beat.

To give an example, our sistership left Pancake creek about 10 minutes ahead of "Zero" one of the megabuck all carbon 50+' Schionning G forces.

They set their symmetrical kite, Zero started tacking downwind under a big carbon screecher and main. By Bundaberg Zero was about 5 miles behind .

It takes an extremely fast boat to benefit from tacking downwind.

[44'cruisingcat]

I've always reefed on whatever point of sail we happen to be on, it's never been a problem.

[Pete7]

When we first got our yacht I watched one of our sister yachts sail right past us with white sails, tacking down wind. It was an interesting lesson.

Pete

[Chuck Hawley]

The additional distance sailed when sailing 10-15 degrees above the desired course is really insignificant. Even at 30 degrees off-course, it's only, what, about 15% longer? That would be the speed difference between about 6 knots DDW and 7 knots reaching. I can't answer this for your boat with your sails, but I would submit that many boats can exceed 15% distance disadvantage when they reach up.

Chuck

[multihullsailor6]

Dave,

Besides the boat and your choices of sailing here's the tactical tool:
- draw on a sheet of paper a line of say 10cm = 10 SM, that's your downwind course and boat speed
- then from the starting point draw a line at 10 degrees to right/left to the half way point line from above and back to the 10 SM point.
- Repeat above at 10 degrees until you reach 40 degrees.
- Now measure the total distances
So if you sail DDW at 10kts any course deviation in order to be at your final ( 10 SM ) destination to be beneficial to you will have to be at greater speeds.

[Dave_S]

Dsanduril and 44'Crisingcat.....

Do you just align the sail to the wind backwards, let the wind out and let it lower down, or do you just pull it down with the wind in it. Anything I should be careful of, what could go wrong.

[Dave_S]

I have a symmetrical spinnaker but it's in the shed :-)

I'll get more comfortable with everything else before I try it out. It does have a sock.

[Dave_S]

Originally Posted by Chuck Hawley

The additional distance sailed when sailing 10-15 degrees above the desired course is really insignificant. Even at 30 degrees off-course, it's only, what, about 15% longer? That would be the speed difference between about 6 knots DDW and 7 knots reaching. I can't answer this for your boat with your sails, but I would submit that many boats can exceed 15% distance disadvantage when they reach up.

Chuck

It gets worse the more you come around, 35* off the wind becomes a 22% increase in speed required, not accounting for gibing times. I would think gibing would be faster in my boat than the reacher DDW but maybe not faster than a spinnaker as 44 says.

A lot like upwind, it seems to be a fine line the compromise between boat speed and VMG.

[Dave_S]

Originally Posted by multihullsailor6

Dave,

Besides the boat and your choices of sailing here's the tactical tool:
- draw on a sheet of paper a line of say 10cm = 10 SM, that's your downwind course and boat speed
- then from the starting point draw a line at 10 degrees to right/left to the half way point line from above and back to the 10 SM point.
- Repeat above at 10 degrees until you reach 40 degrees.
- Now measure the total distances
So if you sail DDW at 10kts any course deviation in order to be at your final ( 10 SM ) destination to be beneficial to you will have to be at greater speeds.

Thanks, good idea.

I might do up a chart of angles V's %'s to show the increases required to = the additional distance covered.

[catsketcher]

Whether to tack downwind can depend on conditions.

I did spend about two thousand miles using our assy and tacking downwind only to find out that in reality it was not worth it. These conditions were usually when the wind was 10 knots and above and the sea state was fine for letting the sails fill. In the end I stopped using the assy and now use the reacher/Code 0 or a symmetrical with the main down. We just head the boat downwind, pretty much straight to the destination.

But there are times when it really is worth tacking downwind - sort of. In some light winds, say a developing sea breeze, I will often sail rather high, maybe 15-30 degrees above the course. If I can get the boat moving under reacher she will sail along like a magic carpet - doing 8 knots in 8 knots of wind. The trick is to come up until the apparent wind is abeam. Then as it builds, and goes forward, you bear away slightly, keeping the apparent abeam. We have had some magical sailing like this when others are motoring and we slip along on flat seas.

Then usually the seabreeze will come in and we can then bear away with a stronger breeze further aft. Watch racing sailors go downwind - they go all over the place to keep speed up - so check the weather forecast and don't be afraid to get the boat breathing if the breeze is shifting and changing strength later in the trip.

Your boat will really like generating apparent so put the reacher up and try out the angles, get that light wind on your hip, with the apparent abeam and she will eat up the miles. Doing this to go straight downwind is often a pain though, but it works well if you can postpone the change in course till later on.

cheers

Phil

[44'cruisingcat]

To reef when going downwind or deep reaching, I'd first make sure the gybe preventer is off, then move the traveller up toward the centre then sheet on a bit, but still leaving some mainsheet out.

This allows the boom to lift.

Ease the halyard a bit, the sail will rest on the spreaders and shrouds, don't let out so much halyard that it wraps around them, then start winching in the leech reefing line. When there starts to be a bit of load on the mainsheet again, ease the halyard some more, winch in more reefing line, etc. Until you can get the luff reefing point secured. Then retension the halyard. The mainsheet might need easing a little to get that done..

Takes a couple of minutes but gets the job done and is a lot less stressful than rounding up if you've left it a bit late or there's a bit of a sea running. And you stay on course.

I always make sure there's plenty of headsail out and it's driving well, which keeps the apparent wind speed down.

[44'cruisingcat]

Originally Posted by catsketcher

Whether to tack downwind can depend on conditions.

I did spend about two thousand miles using our assy and tacking downwind only to find out that in reality it was not worth it. These conditions were usually when the wind was 10 knots and above and the sea state was fine for letting the sails fill. In the end I stopped using the assy and now use the reacher/Code 0 or a symmetrical with the main down. We just head the boat downwind, pretty much straight to the destination.

But there are times when it really is worth tacking downwind - sort of. In some light winds, say a developing sea breeze, I will often sail rather high, maybe 15-30 degrees above the course. If I can get the boat moving under reacher she will sail along like a magic carpet - doing 8 knots in 8 knots of wind.

cheers

Phil

Agreed, in very light wind, tacking downwind will generate apparent wind that can get the big downwind sails working, when running DDW might not.

[Dave_S]

The nice people at oceansail.co.uk have done it for me.....

The JPG might be too small to see so the PDF of the same file is attached.