What boatspeed should I expect, as a percentage of True wind?

[GRIT]

Thanks for that. I hadn't seen that one.

We've got three of these deck blocks-antal mounted for halyards, and reefing lines. They can take a line lead at 40 degrees off perpendicular.

Antal really makes nice stuff. We had planned all our clutches and deck gear to be from Antal, but Covid shut down the plant, and we had to diversify our suppliers. We're happy with what we have, but some of it just doesn't measure up to the stuff from Antal.

Cheers.
Paul.

[GRIT]

In keeping with the "sailing fast" theme. We left St Mary's, on our way to Deltaville, with 20 knots on the beam. We were headed to York, but thought we should stock up on some groceries we missed in Cambridge. If we'd have kept going, I think we would have set a personal record. As it was, we averaged 8.6 knots from anchor up to anchor down. It was a slow sail out of St Mary's to the Potomac.

I think you can safely ignore the boatspeed through the water, as it's obviously showing slow. The potomac never runs at 3 knots at it's mouth, or probably anywhere along it's navigable length.

https://youtu.be/52AOiaFG1Vo

And the day before that, in 16-18 knots of wind: https://youtu.be/Op9JVnKEUwQ

One reef in the mainsail, and the code zero.

Cheers.
Paul.

[jmh2002]

Originally Posted by GRIT

In keeping with the "sailing fast" theme....

...One reef in the mainsail, and the code zero

Nice sailing

What's the AWS limit for your Code Zero? I guess it was getting up there at 22-23kn.

Boat was really trucking along though

[JustMurph]

That seems like a lot of sail to have up in 20 knots?! ��
I'm guessing your STW isn't calibrated quite right and the real STW would have been 13 knots as was your SOG?

[GRIT]

My sailmaker said 20 knots, with a small buffer. We pulled it down when it was fairly consistently at 22 knots. With the reefed main, and full jib, our speed was 10-11 knots.

It was fun while it lasted. We put the code zero back up as soon as the TWA was above 130, and the wind had dropped to less than 18 knots. For the rest of the trip the TWS was between 12 and 16 or so, with the odd gust to near 20, and the twa was between 160 and 175. SOG dropped to 7-8 knots, with surfs to 14.

It was a nice trip.

Cheers.
Paul.

[GRIT]

Originally Posted by JustMurph

That seems like a lot of sail to have up in 20 knots?! ��
I'm guessing your STW isn't calibrated quite right and the real STW would have been 13 knots as was your SOG?

Our code zero is smaller than I'd like, perhaps a little larger than a 120% Genoa, so I don't mind too much running it up to 20 knots. But 20 is my limit if it's not just gusts, which is why we took it down. That and the fact that we were in flat water, helped keep me in my comfort zone. Had we had the waves that are usual in 20 knots, we'd have had it down long before that.

The windspeeds were a few knots lower than what's on the video, until 10-20 minutes before we shot it. Since the windspeed didn't drop back to the norm, and our apparent wind was so high, we dropped the code zero.

We got caught in a 30 knot squall with it up once and hid it behind the mainsail. It was good training on how to deal with that sail. In this case, we'd have turned upwind if there was a serious gust, since we were pointed as high as we could with that sail, it would have just flogged a bit until we could get it under control. I was hand steering the entire time we were sailing above 12 knots; 12 is still in my comfort zone.

I have constant problems with the STW. At low speeds, it seems fine, but at higher speeds it's not accurate. Whether it's dirt, growth, or air, I don't know. Since we don't typically sail in the teens, I'm just going to leave it alone. We have three Speed units, and I'm thinking of getting rid of the analogue one that B&G said was the best for the autopilot, due to faster sampling... or something.

The two depth/speed/temp units we have in the hulls seem a little more accurate, even though they're further forward in the hulls. They're on centreline, whereas the autopilot unit is off centre by 25cm.

It's a mystery I haven't yet had the time to solve. That and the fact that the windspeed indicator often shows faster than reality (when the wind's aft of the beam, and being deflected off the top of the mainsail). We've yet to fill the chart to compensate for that, so it wouldn't surprise me to find the wind was actually 2-3 knots less than what shows on the screen.

The current was around 0.6 knots on the way to Deltaville, and nearly the same on the way to St Mary's. Though the STW seemed more accurate in the earlier video (chasing the bulk carrier).


Cheers.
Paul.

[jmh2002]

Originally Posted by GRIT

We got caught in a 30 knot squall with it up once and hid it behind the mainsail. It was good training on how to deal with that sail. In this case, we'd have turned upwind if there was a serious gust, since we were pointed as high as we could with that sail, it would have just flogged a bit until we could get it under control. I was hand steering the entire time we were sailing above 12 knots; 12 is still in my comfort zone.

Good that you've had that experience already, it's very useful even if you may not want to repeat it too often

[fxykty]

Originally Posted by GRIT

…
I have constant problems with the STW. At low speeds, it seems fine, but at higher speeds it's not accurate. Whether it's dirt, growth, or air, I don't know. Since we don't typically sail in the teens, I'm just going to leave it alone. We have three Speed units, and I'm thinking of getting rid of the analogue one that B&G said was the best for the autopilot, due to faster sampling... or something.

…

Does your analog speed sensor have a calibration table? If so, add calibration values for a range of speeds - we’ve set calibrations for our Raymarine unit at 4, 6, 8, 11 and 14 knots (only supports five). The values are different for each speed and don’t follow a linear pattern. Test and set in steady speed conditions without current.

[JustMurph]

GRIT: Are they all paddle wheel sensors?

[GRIT]

JMH2002: Yes; not too often... Though I try to practice as much as I can sailing in all sorts of wind conditions. That way, if the Sh*t hits the fan, I'll already have a shovel in hand.

Originally Posted by fxykty

Does your analog speed sensor have a calibration table? If so, add calibration values for a range of speeds - we’ve set calibrations for our Raymarine unit at 4, 6, 8, 11 and 14 knots (only supports five). The values are different for each speed and don’t follow a linear pattern. Test and set in steady speed conditions without current.

I don't know. The wind sensor has a table, which I'll have to sort out. Perhaps the speed sensor has one too. Thanks for the hint, I'll find out.

We've been ignoring the STW and just looking at the SOG, which, with VMG is all we really care about. But, these instruments are expensive, and I'd like them to work. Without accurate boat speed, and windspeed, windvane mode is a bit wonky.


JustMurph: Yes, all three use paddle wheels. The front two are digital units, and the third is analogue (I believe).

Cheers.
Paul.

[JustMurph]

Originally Posted by GRIT

We've been ignoring the STW and just looking at the SOG, which, with VMG is all we really care about. But, these instruments are expensive, and I'd like them to work. Without accurate boat speed, and windspeed, windvane mode is a bit wonky.

So you have all B&G yes? I'm interested, as I'm looking to replace my instrumentation and autopilot soon with B&G.

What exactly is happening when windvane mode goes wonky and what do you think it causing it? Is it mainly the upwash on the wind sensor throwing that off when sailing down wind? Having the capability to sail down wind under auto pilot to the TWA reliably is a big one for me.

What is your wind sensor? Should I be looking at mounting mine higher while I have the mast off the boat?

[jmh2002]

@Dockhead has been chasing the path of getting accurate TWS and has a number of threads on this subject.

You can find them here: https://www.cruisersforum.com/forums...rchid=34591146

But here is a particularly detailed one: https://www.cruisersforum.com/forums...nt-255198.html

and here a general overview: https://www.cruisersforum.com/forums...ta-255357.html

From my racing days I can say that yes the height of the Mast Head Unit is very important and it's why of course you can get quite tall extended models from the likes of B&G, etc. You could also make you own too of course.

Also there needs to be a serious overview of the whole setup and integration. It's no point having accurate wind if you don't accurate speed because then TWS and TWD won't be accurate.

And all of this requires a lot of calibration to get right, and to get right for various conditions. At least on a Cat you don't have angle of heel to deal with like on a mono, but you do still have motion to consider.

A lot can be done yourself, but once you reach a certain point the next step is to get a B&G tech onboard to get the calibration really right. Not just a 'repair guy' but a tech who specialises in doing this.

At one point I actually had a guy who I referred to as the 'B&G whisperer' - we had a good setup, but he took it to another level. It was worth flying him in once a season / year to go over things. On a cruising level that would excessive, but the point is that the instruments should also be treated like any other mechanical device onboard. They need attention, they need maintenance, they need adjustment, etc.

Proper calibration is time consuming and expensive but the results pay off in many ways. For racing, well it's obvious. For cruising as you said it follows on into such things as being able to sail down wind under auto pilot with full confidence, etc. Especially so on a multihull with increased speeds, and sometimes rapid changes in the AWS and AWD.

I suspect that from a cruising perspective many sailors who don't have a racing background are a bit in the dark about what is important, and even what is possible in relation to instruments and data.

You'll even see many posts on this forum saying that you don't even need accurate TWS/TWD.

That may have been the case when everyone was cruising on heavy, slow, 35ft double ended monohulls, but things are a bit different now!

I guess everyone mostly just makes do somehow but having a really well setup system is very nice and allows you to take best advantage of the expensive set of sails often found on a performance catamaran.

[Tupaia]

Originally Posted by JustMurph

So you have all B&G yes? I'm interested, as I'm looking to replace my instrumentation and autopilot soon with B&G.

What exactly is happening when windvane mode goes wonky and what do you think it causing it? Is it mainly the upwash on the wind sensor throwing that off when sailing down wind? Having the capability to sail down wind under auto pilot to the TWA reliably is a big one for me.

What is your wind sensor? Should I be looking at mounting mine higher while I have the mast off the boat?

You should seriously consider an ultrasonic wind sensor.

https://lcjcapteurs.com/en/girouette...-vent/cv7-c-2/
There are adapters for all instruments systems.
The consistency of data is far superior to mechanical units especially in any sea state.

[Tupaia]

Originally Posted by GRIT

One reef in the mainsail, and the code zero.

Cheers.
Paul.

A cautionary note:

Assuming your code zero flies from the mast head you might need to be concerned or at least be aware of using it with a "reefed" main.

A headsail flying from the mast head on a fractional rig usually relies on the mainsail leach loads to counteract forces on the unsupported top part of the mast.

How is your top mast supported?
Running backstays?
Jumper stay?

Sailing looks good in the vids BTW.

[GRIT]

Originally Posted by JustMurph

So you have all B&G yes? I'm interested, as I'm looking to replace my instrumentation and autopilot soon with B&G.

What exactly is happening when windvane mode goes wonky and what do you think it causing it? Is it mainly the upwash on the wind sensor throwing that off when sailing down wind? Having the capability to sail down wind under auto pilot to the TWA reliably is a big one for me.

What is your wind sensor? Should I be looking at mounting mine higher while I have the mast off the boat?

Yes, we're using B&G instruments.

We have the H5000 autopilot, which I think was probably overkill, but it works well.

The wind sensor is their "standard" one, which we'll be upgrading soon. I'm 80% certain the issue is with upwash from the mainsail. For example, when I gybe 100 degrees, it's likely the apparent wind direction doesn't change by 100 degrees.

When I say wonky, I mean that it roams a lot, searching for the right course to steer.

YES, mount the sensor higher than standard. I'd personally love to install two sensors on the stern, and have the pilot always use the windward one, but I don't think that's an option.

Cheers.
Paul.