Down wind sailing with monitor windvane

[The Smokester]

I think one needs to specify the boat and its characteristics when discussing the performance of windvane steering. From your blog, I see that you sail s/v Lexington which is a 46’ Morris with 24,000 pounds displacement. This is a heavy displacement boat which does not plane (or surf much) and therefore has a limiting “hull speed”. This implies that when traveling down (the true) wind, the apparent wind will always be from the stern and relatively constant. Under these assumptions, a windvane, and particularly a Monitor, is an excellent option for long passage downwind sailing.
Using the large-size Airvane (Part #1.1) on the Monitor I have found that it (the Airvane) responds to only a few (<3) knots of wind. In such a light breeze, for a heavy displacement boat, the wind passing by the Airvane is not the main issue. Rather, it is the lack of forward boat motion that is the problem.
The Monitor translates the pressure of water flow against a Paddle (Part #61) into steering force at the wheel. I have found that it is the lack of pressure on the Paddle at very slow boat speeds that limits the Monitor’s ability to steer. This places a premium on reducing friction in the Pendulum Lines (Part #820) which transmit the force into steering control. These lines should run cleanly and as directly as possible to the (in your case) Wheel Adapter (Part #100). This is not the place to skimp on the turning blocks. In my case, I have replaced relatively inexpensive turning blocks with 2” Harken Carbo Airblocks’s and noticed an improvement in light wind performance.
Also, Monitor has recently changed very slightly the design of the Internal Pullies (Parts #49) to reduce a poorly understood chafing problem with the Pendulum Lines. This problem occurred on my Monitor after many thousand miles. I changed out Parts #49 for the new design, and also have been careful to allow very little slack (but not too much tension) in the Pendulum Lines. The problem has not recurred in the past 5000 nm.
There are a few issues that can emerge in more extreme downwind sailing conditions. Steering downwind in ocean swells can be intensive for most displacement boats since the stern is constantly being knocked sideways. The Paddle of the Monitor reacts to counter this tendency of the stern to swerve thereby providing negative feedback which easily and impressively corrects the boat back on course. That’s the good news. The issue to watch here is that the restoring forces generated by the monitor can become quite high as the following waves increase in size. I am talking here about large waves that sometimes poop the boat. It is not unknown for the Monitor-supplied clamps holding the Wheel Adapter to be broken or for the entire Wheel Adapter to be ripped from the helm during more extreme conditions. Personally, I (and Monitor) regard this to be a positive failure mode since it is easier to replace at sea three commonly-available hose clamps than refit bent or broken steering gear. Everything has its limits and these hose clamps represent an important mechanical fuse to protect the rest of the steering chain. But have spares at the ready when the wind and waves pipe up.
Another uncommon failure mode in downwind sailing with the Monitor is the un-meshing of the Ring and Pinion Gears (Parts #36 and #37). In this case, the gears jump out of mesh and the pendulum is locked. This can happen in heavy following cross seas (i.e. ones that frequently poop the stern) where the Paddle is being slapped violently from one side to the other. Again, what would you rather have? A broken mangle of tubing or (what turns out to be) a minor at-sea repair. If you are doing a long passage (beyond the horizon of the departure weather forecasts) it would be wise to know how easily this can be fixed (described in the manual) or satMail Scanmar (the Monitor manufacturer). The gears can be re-meshed in about 5 minutes without fear of losing any loose parts…Again a tribute to the thoughtful engineering of the monitor.
This is already too long, but briefly, let’s talk about sail plan. With a windvane, it needs to be balanced. For downwind, the choices are spinnaker, wing-on-wing and butterfly (two large genoa’s poled out).
The fastest is the spinnaker but that is the least stable when the wind pipes up. Wing-on-wing with a poled-out headsail is the quickest to set up when your point-of-sail lasts for a short time. And lastly, butterfly (twin poled-out head sails) which is the most stable and, depending on your rigging, can be adjusted to increasing wind speed.
Finally, beware of Bimini’s and other structures near the stern of the boat. These may confuse the wind near the Airvane and also exacerbate a tendency of the stern to swing to weather.
I hope this helps. I am not a Monitor shill but just a happy user. Also, their customer service is the greatest.

[Paul Elliott]

Originally Posted by RDW

Paul, is this a general statement or would stuff ahead {down wind} of the windvane sailing downwind or dead down wind affect how the wind vane would perform?
rdw

It's a general statement. I've seen airflow interference cause problems on several points of sail. My bimini has caused it both upwind and downwind, and my outboard that I stow on the stern rail has caused it as well. Obstructions to windward of the windvane are probably worse, but leeward obstructions can also affect the airflow. Sometimes only a few degrees difference in the apparent wind can make a big difference, as the eddies can be pretty tight.

Downwind, the lessened apparent wind generally gives the windvane less to work with, and I agree with smokester that very slow boat speed significantly reduces the power that the oar generates.

[Paul Elliott]

Originally Posted by The Smokester

Also, Monitor has recently changed very slightly the design of the Internal Pullies (Parts #49) to reduce a poorly understood chafing problem with the Pendulum Lines.

This is interesting to learn. I've had chafing problems -- a parted pendulum line isn't fun at 4:30AM! I ended up putting external turning blocks on my stern rail, positioned to keep the lines running true as they leave the vane tubing. This cured the chafing. I will take a look at the design changes.

[The Smokester]

Originally Posted by Paul Elliott

This is interesting to learn. I've had chafing problems -- a parted pendulum line isn't fun at 4:30AM! I ended up putting external turning blocks on my stern rail, positioned to keep the lines running true as they leave the vane tubing. This cured the chafing. I will take a look at the design changes.

Mine chafed where the Pendulum Lines enter at the bottom of the tubing. The actual chafe was hidden up inside the tube but I managed to notice some fluff hanging out the bottom during daily inspection and changed out the line mid-ocean before it parted. Bullet dodged.

My understanding from SCANMAR is that this chafe happens only on some installations, occurs after many thousands of miles and is not definitively understood. The changes in the new pulleys are subtle...almost imperceptible to my eye, but the changeout is easy (done at anchor) and I haven't had a problem since. My monitor is about three years old and more recent ones apparently have the modified turning blocks.

Also, using fixed and/or double blocks on the run to the Wheel Adapter can cause chafe. Make sure that the individual turning blocks for each side move freely from each other and from the mounting surface.

[Paul Elliott]

Originally Posted by The Smokester

Mine chafed where the Pendulum Lines enter at the bottom of the tubing. The actual chafe was hidden up inside the tube but I managed to notice some fluff hanging out the bottom during daily inspection and changed out the line mid-ocean before it parted. Bullet dodged.

My understanding from SCANMAR is that this chafe happens only on some installations, occurs after many thousands of miles and is not definitively understood. The changes in the new pulleys are subtle...almost imperceptible to my eye, but the changeout is easy (done at anchor) and I haven't had a problem since. My monitor is about three years old and more recent ones apparently have the modified turning blocks.

Also, using fixed and/or double blocks on the run to the Wheel Adapter can cause chafe. Make sure that the individual turning blocks for each side move freely from each other and from the mounting surface.

My chafing was similar, and it chafed through a couple of times, and I've noticed it and replaced the line (or turned it end for end) a few more. I think the problem was flex in the bracket holding one of the blocks. This hasn't been a problem since I rigged the external blocks.

[Sailormantx]

Following. I have had severe chafing problems in the same places. After experiencing a broken line once, I know to watch for it and tie a new stopper knot when it starts showing a lot of fuzz. It seems to only last for about two weeks before needing to be reset again. I also get a lot of chafe at the turning block going to the wheel adapter even after changing to a larger block. It is a double block going to the wheel, so I will change it to a pair of singles before the next trip to see if that helps.

[The Smokester]

Originally Posted by Sailormantx

... I also get a lot of chafe at the turning block going to the wheel adapter even after changing to a larger block. It is a double block going to the wheel, so I will change it to a pair of singles before the next trip to see if that helps.

This seems serious. What size boat and is there a lot of friction at the wheel?

I was told when I did the installation that double blocks caused friction so I use single blocks on each individual line.

Maybe also call Scanmar regarding the latest pulley version.

[01kiwijohn]

My ol' boat has a really big main. Downwind, I find it runs better with the light air vane (a must have), a 150 poled out one side and a similar sized, light weight sail with the sheet fed through a snatch block on the end of the boom. Stow the main. If the wind is really light, I use a light bungee and clip it to the counterweight and then the monitor frame cross tube, underneath. DDW it still wanders a bit, but it's tolerable.
Enjoy the ride.

[Sailormantx]

Nomad is a 42' LOD schooner. Not a lot of friction in the steering, but long lines to the wheel with an center cockpit configuration. Even using the recommended sta set lines, I have to take up the slack every few days but that shouldn't be the source of chafe. I will be checking out those new blocks from Scanner.

[Jim Cate]

Originally Posted by Sailormantx

Nomad is a 42' LOD schooner. Not a lot of friction in the steering, but long lines to the wheel with an center cockpit configuration. Even using the recommended sta set lines, I have to take up the slack every few days but that shouldn't be the source of chafe. I will be checking out those new blocks from Scanner.

Faced with that issue, I'd be looking at Dyneema for the control lines. The stretch issue would vanish, and friction would likely be reduced everywhere.

Jim

[Sailormantx]

Originally Posted by Jim Cate

Faced with that issue, I'd be looking at Dyneema for the control lines. The stretch issue would vanish, and friction would likely be reduced everywhere.

Jim

Jim, that's a great idea! Could probably go down a size as well making for a nicer fit in the blocks.

[double u]

"...The Paddle of the Monitor reacts to counter this tendency of the stern to swerve thereby providing negative feedback..."
in theory< yes, what we found though that during the sudden swing to the side of the stern the apparentwindangle changes too leading to a correction of the pendulum into the wrong direction.
from a performance point of view the Atoms (sadly no longer made) was excellent: very sensitive in light winds & powerful enough for our 37'er