Lanzarote to Grenada, day 12

Stravaig'n the Blue
Thu 21 Jan 2021 22:11
End of day 12 position: 18:59.6 N 041:11.1 W
Position timestamp: Thursday 21 Jan 2021 12:00 UTC-2
Distance travelled last 24 hours: 174 NM (7.25 knots average)
Reduction in distance to destination last 24 hours: 168 NM
Distance travelled total: 1846 NM
Average speed since departure: 6.4 knots
Shortest distance to destination: 1271 NM
ETA based on shortest distance and average speed so far: 6pm on 29 January (20.25 days in total)

Another record breaking 24 hours. Three records broken this time. Was this our super Saturday? Distance travelled 174 NM beat day 5’s 171. Reduction in distance to destination 168 NM beat yesterday’s 157. The third record was least hours slept. We don’t log hours slept. I’m not sure why; we log everything else. So you’ll need to trust me that last night was the worst so far. The first two records were obviously and simply due to going faster. And going faster was a significant contributor to the least hours slept record. Let me explain.

The Blue Water Runner was back in action on Monday. On Monday evening we took the decision to furl the BWR overnight and deploy our regular headsail which is a little over one quarter the size of the BWR. That made for a slow but comfortable night. On Tuesday evening, we dropped the BWR to the deck, retied the sheets and redeployed in asymmetric mode, half of the maximum size, so twice the sail area we had on Monday night. Another comfortable night but much faster.

Yesterday, with the winds easing, we decided to leave the full BWR up overnight knowing that the winds would pick up a bit after dark. This is contrary what happens almost everywhere else where, typically, winds drop overnight as the sun’s heat that has built up during the day dissipates; it would interesting to find out why the reverse happens in these waters. After dark, the wind duly built from the mid teens to the low twenties and so last night was very fast but not at all comfortable.

The problem wasn’t the speed itself. It was a combination of the speed, the following seas (waves overtaking us directly from behind) and the autopilot doing the steering.  Had the water been flat, it would have been fine. The overtaking waves lift the boat up as they pass underneath and cause the boat to slew one way or the other, the autopilot adjusts for this and brings the boat back on course just as the next wave comes along. The slewing increases as the boat’s speed increases and as the wave height increases. During the day, the slewing about had been, as always, an irritation but, in the dark with the wind, waves and speed all up it made for very uncomfortable sailing and made getting to, and staying, asleep difficult to say the least.

Why do boats behave like this and isn’t it possible to design them so that they don’t? Older yachts with their long keels, narrow hulls and low topsides are, I am told, much better at handling sailing downwind in following seas. These boats sit lower in the water so the waves pass around them rather than lifting them up and spinning them like a cork. It would certainly be interesting to do an offshore passage in one of these older boats to discover the extent of their superiority in downwind sailing.

As yachting has grown in popularity, the yacht buying public and the charter companies have increasingly asked boat builders to provide more and more accommodation but without making the boats any longer. Unable to increase the length, the boat builders have increased the beam and modern production yachts are now very wide from fairly far forward all of the way to the stern, very different from traditional designs. There is also much less of the boat in the actual water so they float on top rather than sit in it. The increased accommodation requirement has been met but the downwind boat handling has been compromised.

Short of going back to the older designs with their cramped quarters, what are the options? One option is to sail slightly across the waves rather than directly before them. The boat is still lifted by the waves but the slewing is much reduced and is always in the same direction. This is what we did on Monday and Tuesday (primarily because our sail configuration didn’t allow us to sail directly downwind) and is what we will be doing again tonight!

Another option is to switch off the autopilot and have someone actually steer the boat. A good helm will sense the boat rising on a wave, anticipate the likely direction of slew and steer into it to keep the boat going in a straight line. An autopilot can’t, yet, do this; it can only react once the slewing has started. During the day, with the BWR out, we have been taking turns at the helm.   On our 2016 crossing, when there were three of us on board (thank you Ted), there was always someone at the helm, 24*7, unless we were motoring or the steering linkages had failed. But that’s another story.

I said that autopilots can’t yet do what a human helm can do and deal with following seas in a preemptive rather than reactive way. But this may be about to change. B&G, the marine instrument maker, has been working with Alex Thomson Racing to enhance B&G’s autopilot computers to do exactly this. (Like many boats we have B&G kit.)

The work was being done as part of Thomson’s now long abandoned fourth attempt to win the Vendée Globe but hopefully the work is continuing.  I am not sure I want to sign up to beta releases of this feature, testing could be messy, but I do look forward to the day the latest release of my autopilot computer software contains a fully tested following seas component that will ensure comfortable sailing downwind in all conditions.

We are putting the clocks back another hour tonight so will each get an extra 30 minutes kip (and an extra 30 minutes on watch). We should have put the clocks back last night but forgot. I’m glad we didn’t; we’d just have had two extra 30 minutes of discomfort.

Footnote to yesterday’s encounter with Charlie Dalin on APIVIA. It was clear from the encounter that there was a problem with APIVIA’s AIS system. The boat should have shown up on our chartplotter from about 12 miles away but it didn’t appear until it was about 2 miles distant. That isn’t much warning of a boat approaching at over 20 knots. We also noticed that the AIS updates we received subsequently were intermittent as was evident from the jerky progress of APIVIA on our plotter. I’m not sure why I didn’t mention the problem when I spoke to Dalin but it has now been passed on to him via our after sales support contact at Allures Yachting and from there to Vendée Globe race management.

All is well.