Catamaran tacking angles , really that bad???

[smj]

I just watched your video on the other thread and the wind speed was showing 15-18 kts true. Do you think that’s accurate? I didn’t see any white caps and in 15-18 I would think white caps would be numerous and probably show up in the video. I may be wrong but is it possible your wind instrument is over reading the speed and needs to be adjusted? Looked like maybe 10 -12 kts of wind to me, which would make your boat speed phenomenal.

[GRIT]

I pondered the same thing. Even with 1.5 knots of current, the seas were pretty benign. I don't know why that was. They built up later, and we had some whitecaps, and we were registering similar speeds.

Last night, we were showing 8 knots of wind on the beam (100TWA), and the flag was limp.

There's no way to calibrate the wind speed; at least I haven't found one. I looked quite hard for it last night, as the seas were glass, and we showed 8 knots of wind on the beam, but only 2.5 knots of boat speed. There's no accounting for it. 2.5 knots of boat speed usually means 4-5 knots of wind on the beam.

Cheers.
Paul.

[smj]

The negative aspect is your wind speed instrument is way of. The positive aspect is your boat is significantly faster than previously thought. I’d say overall that’s a big positive!

[GRIT]

If it's true, that will be a nice surprise!

I'll start conferring with neighbouring boats, on what they're reading as wind speed. At least that should be easy to confirm, one way or the other.

Cheers.
Paul.

[arsenelupiga]

Originally Posted by GRIT

It just so happens that we had to pinch quite high today, to get to our destination. We did a few tacks, and I managed to get some of it on video.

I'll forewarn you all, the audio is terrible, I'm wearing earplugs so I can't always hear my wife, I'm not used to videoing, and I'm a terrible "multi tasker". The mainsail sheet controls are on my right, and I'm filming with my right hand, and frankly, we don't have our sh*t together yet. But that last tack was pretty well executed.

We're pinching to about 40-45 TWA, with a few minutes of slightly more, or slightly less. Some of you are experienced enough racers to be able to tell me if this is considered "good" performance, and I'd like to hear your opinions. I'm pretty sure we were tacking at less than 90 degrees, once I got her pointed in the right direction again. If I was concentrating on sailing, rather than filming, I'd have done a better job.

We've really not practiced much on this boat, and are usually lazy sailing, unless the wind is just right. We'll get there.

In the mean time, let me know if this video shows what you'd call good performance, VMG and all that jazz.

https://youtu.be/sNDzTQYxwYE

Cheers.
Paul.

Oh, and can someone tell me why this next video is mirrored? It's not taken with the selfie camera.

https://youtu.be/qUsBVVau6VY

Thanks.

looks pretty good to me. Comparing to numbers that were playing in front of my eyes the other day, i would say you arre 30% faster at same angles and true wind. So when you had 8 kn we had 6, give or take.

[Dave_S]

Originally Posted by GRIT

It just so happens that we had to pinch quite high today, to get to our destination. We did a few tacks, and I managed to get some of it on video.

I'll forewarn you all, the audio is terrible, I'm wearing earplugs so I can't always hear my wife, I'm not used to videoing, and I'm a terrible "multi tasker". The mainsail sheet controls are on my right, and I'm filming with my right hand, and frankly, we don't have our sh*t together yet. But that last tack was pretty well executed.

We're pinching to about 40-45 TWA, with a few minutes of slightly more, or slightly less. Some of you are experienced enough racers to be able to tell me if this is considered "good" performance, and I'd like to hear your opinions. I'm pretty sure we were tacking at less than 90 degrees, once I got her pointed in the right direction again. If I was concentrating on sailing, rather than filming, I'd have done a better job.

We've really not practiced much on this boat, and are usually lazy sailing, unless the wind is just right. We'll get there.

In the mean time, let me know if this video shows what you'd call good performance, VMG and all that jazz.

https://youtu.be/sNDzTQYxwYE

Cheers.
Paul.

Oh, and can someone tell me why this next video is mirrored? It's not taken with the selfie camera.

https://youtu.be/qUsBVVau6VY

Thanks.

On the Zeus 3 the yellow dot is your next way point, was this set, it was almost inline with your starboard tack so probably not, if you set it each time you will see the VMG improve (or not) as you play with the setup. Also you can see which is the favoured tack.

The green and red dotted lines are your laylines for tacking (I'm not sure how they are set, I think it learns but I'm not sure about that). If the silhouette of the boat is pointing inside of those laylines it is telling you that you are pinching and loosing VMG and your boat speed to wind speed will drop. You might be quicker not to pinch and do another tack.

You seemed to have a fair amount of rudder angle, best speed (less drag) will come from a balance between your dagger boards and your rudders. Every boat is different because ratios of lift between rudder profiles and dagger boards will change from boat to boat but maybe try a bit more dagger board if your rudders get out more than say 5°. You might find it's slower and your boat just needs it but it might be better.

[GRIT]

Thanks Dave, for those suggestions.

I hadn't noticed the rudder position. I was having a hard time just pointing the camera. It was quite distracting.

The waypoint was set, we could almost get there, but there was a shoal in the way, so we were just tacking to get a little distance from the shoal. I hadn't noticed that dot, so thanks for that too.

I've a lot to learn about sailing efficiently. No doubt there, but we'll practice, and get better at it.

Cheers.
Paul.

[Joli]

Originally Posted by AllenRbrts

I'm a little nervous about commenting on this thread given that folks have some strong opinions, but here goes.

It seems to me people are making unequal comparisons. arsenelupiga post was about sailing angles with TWS at 22K, and yet others were comparing monohull performance at 10K TWS. Certainly tacking angles will be very different between those conditions. At 22K TWS and SOG at 8K, AWA of 40, tacking angles of 100 would seem to be possible, but at 10K TWS those angles would become more like 160 (assuming SOG is still 8K).

I certainly don't what arsenelupiga's actual conditions were, but on our production cat (FP44), when sailing upwind, we typically will have a reported adverse current of about 2K. That is not real current, but instead a calculated current based our heading being higher than our COG and that our water speed is higher than our SOG. This "current" is due to leeway due to our minikeels. Again I don't know what arsenelupiga's conditions were, but some folks they might think they had adverse current, but it actually only the effects of leeway.

We can usually keep pace with our buddy boat which is a Hylas 49, but we have feathering props, very clean bottom and carbon sails. I do know that Joli at 61' sails circles around us

Hi Allen,
Are you guys still in the Bahamas? Watched your track, you made great time!
Coming down to the Caribbean this year was one tough beat, 25 to 45 TWS at 30 AWA for 7 days. We were all sore and tired and happy to be at anchor after that one.
Hope the season is going well and we catch up again.
Bryan

[wingssail]

Originally Posted by GRIT

It just so happens that we had to pinch quite high today, to get to our destination. We did a few tacks, and I managed to get some of it on video.

I'll forewarn you all, the audio is terrible, I'm wearing earplugs so I can't always hear my wife, I'm not used to videoing, and I'm a terrible "multi tasker". The mainsail sheet controls are on my right, and I'm filming with my right hand, and frankly, we don't have our sh*t together yet. But that last tack was pretty well executed.

We're pinching to about 40-45 TWA, with a few minutes of slightly more, or slightly less. Some of you are experienced enough racers to be able to tell me if this is considered "good" performance, and I'd like to hear your opinions. I'm pretty sure we were tacking at less than 90 degrees, once I got her pointed in the right direction again. If I was concentrating on sailing, rather than filming, I'd have done a better job.

We've really not practiced much on this boat, and are usually lazy sailing, unless the wind is just right. We'll get there.

In the mean time, let me know if this video shows what you'd call good performance, VMG and all that jazz.

https://youtu.be/sNDzTQYxwYE

Cheers.
Paul.

Oh, and can someone tell me why this next video is mirrored? It's not taken with the selfie camera.

https://youtu.be/qUsBVVau6VY

Thanks.

Great sailing, Grit!

It is fun seeing someone tacking to a destination. You must have been in a channel or you could have just sailed directly to it on stbd.

Watching your instruments I have a few observations (guesses, actually).
at

1. Your tacking angles based on COG, were about 102 degrees.
2. It might be easy to attribute this to negative current, but the current pointer is consistently against you, almost directly. If it were actually current it would remain constant in compass direction. I think the Zeus is calculating that based on the difference between STW and SOG, meaning it is not current but optimistic STW. (boat speed is reading high).
3. And your TWS which is based on AWS and STW, is off due to optimistic STW. It is a boat speed problem not a wind speed problem.
4. Notice that the TWD changes when you tack? This is also calculated using STW. If everything was accurate the wind would remain constant as you tack.
5. It was hard to calculate the VMG to windward from the instruments, I only saw VMG to the waypoint, which was heavily favored to stbd tack, and in 15 minutes the distance went from 12.4 miles to 7.9 which is a VMG of 18kts, so I don't get what is happening there. If we had Lon/Lat we could caclulate the distance sailed and come up with a better VMG figure.

On my boat we have OpenCPN running while sailing and inspection of the track allows us to get lon/lat after the fact and we can do several calculations including actual SOG over time. It also helps us create accurate log book entries (actual time, speed, heading at various points on the passage).

[GRIT]

Thank you Wingssail.

Those are some fantastic observations.

I've been hesitant to mention STW, since I suspected my numbers were exagerated. So I always try to stick to SOG, which I assume should be accurate.

I've made adjustments to the speed already (75%) which I hoped would have been enough. The Vulcan seems to take the adjustment, and use it, but the Zeus just ignores the calibrations I input, so I don't video with the Zeus anymore.

I never noticed the distance to waypoint changing, I'll look at the video again, and I'll watch for that today.

Today, we're going to do some short tacking, and I'll watch the current closely. Thanks for mentioning that, it's been on my mind, and I've got to get the Zeus to accept the changes.

The Vulcan used in the video has been adjusted/calibrated, to 75%, but perhaps it's not actually taking it out. It does show a different speed than the Zeus, but it's got it's own sending unit, so I didn't think much of it.

And tacking through 100 degrees? Wow, that sucks pretty bad. I thought I was doing so well.

Thank you so much for your insight. I'll study those issues today and report back later.

Cheers.
Paul.

[fxykty]

Originally Posted by GRIT

...

And tacking through 100 degrees? Wow, that sucks pretty bad. I thought I was doing so well.

...

There is nothing bad to be tacking through 100 degrees and why do you say it sucks? The AC75s tack through well over 90 degrees - looks like 115 or so - and no one would argue that they’re not phenomenally fast upwind (or downwind, gybing through 130-140 degrees).

It is the VMG that matters and that is a combination of boat speed and angle. As a performance cat (with daggerboards I assume) you will likely get best VMG with higher boat speed and larger TWA. Pinching up will slow you down and disproportionately increase leeway, negating the better AWA and resulting in poorer VMG.

As you build experience with your boat you will be able to figure out whether she likes to point high and slow or low and fast, or somewhere in between, for best VMG. In certain conditions high and slow may be best (e.g. high wind and flat water).

As wings points out, use your actual tracks for analysis rather than your instruments. Mark your sail controls so that you can replicate settings, irrespective of your possibly miscalibrated instruments.

[GRIT]

Thanks Fxykty.

You're right of course. I was focused on getting 90 degree tacks, and I'm not sure why. The important thing is to get upwind as quickly, and comfortably, as possible.

Yes, we do have boards. They're pretty fat, so should theoretically work fairly well in lower boat speeds.

I've sent an email to my B&G guy, to try and sort out the STW issue, we'll see how that goes.

I have Open CPN, and will work on getting it hooked into the nmea 2000 system, so I can start using it for this sort of stuff.

Thanks for nudging me back to what's really important.

Cheers.
Paul.

[GRIT]

We went out today, to study our tacks again.

It was blowing up to 25 knots and, trying to point high, ceased being fun. So after the second tack, we headed to the beach. We saw no point in trying, with the instruments showing make believe numbers.

I looked at the video again, and saw the DTW changing fairly randomly. Thanks Wingssail.

I changed the source GPS to the one built into the AIS. I'll get an NMEA 2000, external gps to feed the system. These new fangled systems are really needy! Sometimes I miss my old mono, with the Aries on the stern. But not often.

The beach was nice though.

Cheers.
Paul.

[jdazey]

I don't think Opencpn works directly with N2K. Possibly an N2k->0183 converter will help, but that's one of the reasons I don't use Opencpn very much.

[GRIT]

Yes, I'm pretty sure I'll need a converter.

I must have a kilometer of wire for the electronics already. That's just what I wanted, another kilo of cable, and another wire to pull.

Cheers.
Paul.