Sailing downwind techniques

[moreton99]

Reading a book by Gregor Tarjan - Catamarans. I have attached two excerpts from this book. He has a diagram in there saling downwind that I hope you can see and its driving me nuts. Tried it sailing the other day but obviously I have massive gaps in my understanding of sailing and nothing happened.

Not sure if you will be able to read the text but I'm sure it will make sence to some.

In the third pic of the boat in the series he turns the boat to run directly downwind. The text says "Main sheet is trimmed to adjust for new apparent wind angle which accelerates boat" He has the arrow still coming from abeam a little because of the apparent wind created? Hang on, if you run with the wind how can the wind come from the side?

Next image down even drives me crazier. text says "Gradually keep bearing away to keep apparent wind drawing" What! the true wind is coming from the starb side?

I am getting the idea of the "slot" a bit but I can't visualise how you can bend the wind that much.

Apprechiate any suggested reading on this or explanations.
Paul.

[44'cruisingcat]

He makes it look more complicated than it is. Actually if you tried it as dedcribed you'd have a couple of gybes to deal with.

When you find yourself sailing quite deep angles and going slow you can often sail a better AWA, develop more boatspeed and still be sailing the same course.

As an example, we were recently sailing at around 4 kts in around 7 kts TWS at about 155 TWA, giving us about 4 kts AWS at around 120 AWA.

I gradually steered the boat to higher AWA s, trimming sails (assy and main) as I did. (Using AWA steer on the autopilot)

As the boatspeed increased, the difference between AWA and TWA increased.

I ended up sailing at around 55' AWA, with about 7 kts boatspeed and around 8kts AWS.

But still sailing on the same heading, with the same TWA.

https://youtu.be/eRAOQb0JwaI

[thinwater]

The other problem is that most of the images are physically impossible. The first 2 could be true, but the rest are fiction as drawn. You can't sail by the lee and have the apparent wind on the opposite side. It doesn't work that way. And even boats on foils can't generate as much apparent wind as he illustrates farther down, and certainly not a cruising cat.


I suggest crumpling that image up and starting with a different book. Don't get frustrated by it.


Yes, apparent wind changes as a boat accelerates, but he's acting like cruising cats are super fast like foiling AC cats. In fact, they sail about like large monos, only less weatherly (I'm not anti-cat--I've sailed many and owned a cruising cat for years).

[fxykty]

Originally Posted by thinwater

The other problem is that most of the images are physically impossible. The first 2 could be true, but the rest are fiction as drawn. You can't sail by the lee and have the apparent wind on the opposite side. It doesn't work that way. And even boats on foils can't generate as much apparent wind as he illustrates farther down, and certainly not a cruising cat.


I suggest crumpling that image up and starting with a different book. Don't get frustrated by it.


Yes, apparent wind changes as a boat accelerates, but he's acting like cruising cats are super fast like foiling AC cats. In fact, they sail about like large monos, only less weatherly (I'm not anti-cat--I've sailed many and owned a cruising cat for years).

Well, 44C’s video shows that your last sentence is not quite right. Heavier cruising cats are probably best served, like their cruising monohull brethren, running DDW under wing and wing or spinnaker alone. But lighter cats can certainly use apparent wind to their advantage to reach up, gain speed, then soak down as far as the increased apparent is maintained. VMG DDW probably isn’t much better, but it is more fun.

You’re right about Tarjan’s book though - he is too loose technically and too much marketing fluff. Though I confess I liked all the first generation Outremer images :-).

[Factor]

There is an extra issue here and that is whether the boat has boards or not, if it has you can steer for better speed with the board up and use the leeway to still have your CMG as you would prefer it.

Your oram would certainly have board/s? Short story - talk to 44C I am sure he will help.

[thinwater]

Originally Posted by fxykty

Well, 44C’s video shows that your last sentence is not quite right....

Agreed. I exaggerated a little. My cat was not that slow either.
But some of those pics represent ridiculous exaggerations. Surfing, shifts, and gusts all play a part. Surfing can really change things. But not AW from the wrong side!

[s/v Jedi]

The diagram is stupid. If you have a nice performing boat (doesn't matter how many hulls) and have a long downwind run, then you have two choices (assuming cruising, not competition):

1. Get there the easiest way possible: this is done by flying just a big symmetric spinnaker using -two- spinnaker poles and set AP for wind mode downwind steering.

2. Get there the fastest way possible: Use your best sails for broad reaching (asymmetric spinnaker, code zero), use wind mode on the AP set to broad reaching, set waypoint in the plotter, watch VMG and lay lines on the instruments and gybe when instruments indicate it's time to.

I used to be #2 but with all the boat projects I'm currently doing I'll be happy with #1 for a while... need to get another spinnaker pole though

[Factor]

Originally Posted by s/v Jedi

. need to get another spinnaker pole though

Whats a spinnaker pole? Haven't used one for many many many years

[s/v Jedi]

Originally Posted by Factor

Whats a spinnaker pole? Haven't used one for many many many years

Yes but you have three times as many hulls as me :-)

BTW, I also have a mizzen spinnaker that I can fly without spinnaker poles :-)

[catsketcher]

Yeah the diagram is incorrect in the angle the true wind is aligned at. As has been stated above it is impossible to bring the apparent forward at a square run or by the lee.

I wrote an article about this about 15 years ago called assymetric arguments. In it I researched the power to weight ratio or a typical performance cat and racing monos with spinnaker poles, like the Sydney 38 and Farr 40. My pretty fast cat has a lower power to weight ratio than these boats and they both use a symmetrical kite on a pole to run deep.

Having sailed skiffs and fast cats, there is a huge difference between what they can do and what our cats can do. That said it can be really good to understand your boat and work out when to head up a bit, generate apparent and then bear away.

For us, we often head up off course by about 20 degrees in a light easterly when heading south in summer. This gets us up to about 7 to 8 knots in a light breeze under reacher. If we were to bear away the 20 degrees and stay on course we would sit there are wallow at 2-3 knots, but head up and we can do windspeed. Then after a while the breeze comes in and we can bear away and get head for our destination with more breeze and deeper angles.

So for your boat, go out in light winds and head up onto an angle of about 90-120 true. The boat will start to glide along. The trick is then to ease the sails a little and bear away to bring the course closer to the desired heading. When the boat slows down, gently head up again. Eventually your boat will let you know where it is happy. For me I love sitting on the coachroof in 8 knots lilting along at 8 knots with the autopilot hardly working and only 8 knots of true wind. The apparent is at 90 degrees which is a typical angle skiffs sail at.

In more wind we sail less apparent. In moderate to heavy we sail dead downwind with an assy connected each clew to each bow - easy as.

cheers

Phil

[TeddyDiver]

Originally Posted by moreton99

snip..
I am getting the idea of the "slot" a bit but I can't visualise how you can bend the wind that much.

Apprechiate any suggested reading on this or explanations.
Paul.

There's no such thing as "slot" with soft sails, and there's no explanation to the picture except imagination.

[mikedefieslife]

Originally Posted by Factor

Whats a spinnaker pole? Haven't used one for many many many years

I actually just bought one. On my narrow beam cat it is impossible to use the genoa with any effect downwind without one.

I imagine it's similar even on slightly wider cats. If your cat has a 5.5m beam and the genoa has 6m foot, it's going to be a floppy unshapen mess downwind.

[boatman61]

Sailing techniques downwind..?
1/ Drop main..
2/ Roll out genoa..
3/ Set autohelm..
4/ Pour large Tanqueray and tonic..
5/ Sit back and chillax..
Screw Tarjan..

[moreton99]

Thank you all for comments. Very helpful explanations.
Factor, I try not to bother 44c too much. He has been such a great help to me from when I first bought the boat.
Boatman61, i often run straight downwind and enjoy the easy passage but I am worried the boat will get the shits that I am not at least trying to use her to potential.

[maxingout]

This is how I sail downwind. Crossed the Atlantic from Cape Verde to Barbados in this configuration.