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Owners Group Reply: Polar File for weather routing

Owners Group Reply: Polar File for weather routing

Has anyone managed to put together a realistic ‘polar file’ for the Nicholson 38? It enables one to interact with weather routing software like Fastseas etc. Any info appreciated, thanks

Czarina Blue

A bit of a long post and reply, but I hope some folks find it useful :).

A while back we tried looking at some of our sailing data to try to create a custom polar but struggled.

For our last few trips, we have used Fast Seas with one of the default polars by just setting some variables.

  • Sailing Vessel
  • Performance Adjustment 70%
  • Start Motoring When Speed Falls Below 2
  • Motoring Speed 4
  • Vessel Waterline Length (LWL) 36.2
  • Closest Point of Sail (True Wind Angle) 60

The polar looks something like this.

TWA\TWS; 0; 5; 10; 15; 20; 25; 30
0; 0.0; 0.0; 0.0; 0.0; 0.0; 0.0; 0.0
40; 0.0; 1.4; 2.5; 2.9; 3.0; 3.0; 2.9
60; 0.0; 3.0; 4.7; 5.2; 5.3; 5.4; 5.4
90; 0.0; 4.2; 5.7; 6.1; 6.4; 6.6; 6.8
135; 0.0; 3.2; 5.2; 6.0; 6.6; 7.1; 7.7
180; 0.0; 1.9; 3.6; 5.1; 5.7; 5.9; 6.4

As I said we have been testing this out with some routes, and had a few learnings.

The main one of those is that if you are fighting against swell, or “larger” waves and chop everything becomes less accurate

Plymouth to Falmouth

This was up wind all of the way with a single tack part way along as the wind changed slightly.
We were sailing on our closest point of sail the whole way, so 60 degrees for the conditions we were in is pretty accurate. This was 1m swell from the west and 15-25 knts generally from the west.
With less swell I imagine we could get closer to the wind that 60 degrees.

The route planned was 12h17m and our track for the routed part was 13h, so pretty close

On this screenshot, you can also see 2 other waypoints (blue pins). These were the tacking points for 2 other polars.
The right most of these was our custom polar that we made a while back, this it turns out would have been too pessimistic.
The leftmost of these was with a 45 degrees as the closest point of sail.

Penzance to the Isles of Scilly

Routed time 8.5h, Tracked time 8 hours
We cheated slightly here between points 5 and 6 on the route where we found ourselves with no wind and we motored around the corner a little to find it again. This might explain why we beat the routed time.

Isles of Scilly to Brest

We had a pretty simple route for this which was mainly downwind.

We ended up hacking to do the odd gybe and gull-winged at points.

The route here was 1d5h and our track along the route was actually only 24h.

At a guess, this was due to the following 1-1.6m swell the whole way pushing us a bit faster. Max land speed here for us was actually 11knts