Albany to Tasmania - Day 8 ‘Weather Routing and Fuel Consumption ’

Sunday, April 26th 2026.

Not much to report out here today.

The wind has remained light, mostly out of the south. We managed to sail all day and maintain a course slightly north of Kangaroo Island. With approximately 400 nautical miles to reach Kangaroo Island, we had to make a decision whether we would stop at American River on the Northern side of the island or continue South to Tasmania.

For this trip I purchased a subscription weather routing service called ‘predict wind’. Most offshore cruisers and racers use it to assist with planning the best departure time and to find the best route to take on the way to their destination.

The way Predict Wind work is by using known data about the performance of your boat in different conditions (polars) to estimate your position based on wind and wave data from a number of meteorological models. It’s clever in theory but accuracy can vary significantly based on the quality of the boat data you upload and the quality of the meteorological data in the area that you are  sailing.

Most new boats come with polar data that has been developed by the manufacturer to detail the expected performance of the boat given a particular wind angle and wind speed.

Emigre was built before polars were invented (probably) and I haven’t been able to find any data. I chose to use the polar for a Sparkman and Stephen’s SS34 which is similar in dimensions to a Duncanson 35.

Knowing Emigre is significantly heavier than an SS34, and carrying a much smaller sail plan, I chose to de-rate the upwind performance figures to 70% and downwind performance figures to 80% of the SS34 polar.

With this data set, you essentially set a start and end point on a map and leave the application to crunch the numbers for a couple of minutes. It shows results from about half a dozen models, giving a suggested route between the two points. When the models are all suggesting a similar route, this typically means that all the models agree on the accuracy of the meteorological data in the area. If they are suggesting vastly different routes, the data may not be so accurate.

In our case, some prediction models said to sail almost directly North into the bight to catch an incoming Northerly that was turning North East. Others recommended to stay South and then tack when the Easterly hit in a day or so.

My thoughts on the whole thing is whilst somewhat useful for departure planning, the variability of the conditions make it fairly inaccurate for route predictions at sea.

I prefer to look at the synoptic charts or global weather predictions such as ‘windy’ to get a macro overview of the way the systems are interacting and where best to position the boat to protect her from incoming storm systems.

I’m very new at this and certainly have lots to learn about predict wind and weather routing in general. I  welcome recommendations and insight into other cruisers weather routing processes.

I ended up deciding that a quick stop at Kangaroo Island was worth while for a couple of reasons.

We were slowly being caught by a low pressure system that expected to bring moderate winds, albeit nothing too sinister. Another factor was our diesel fuel usage to date and the expectation of another few days of motoring between our current position and KI.

I had calculated from burning about 40l of diesel that Emigre’s three cylinder Kubota D1005 engine sips a mere 1.6L of diesel per hour. With 230L of total capacity on board, that gives us nearly six days of range running at 1800rpm and giving approximately four knots of boat speed. Given an expected 24hr run of 96 nautical miles at four knots, we would have approximately 575 miles of total motoring range.

The third factor that persuaded me to stop at KI is the offer of a mooring, fuel and water facilities and a tour of the island from a new amateur radio friend Tony VK5KI.

I met Tony on air four of five months ago when calling for DX or international stations from the boat’s HF radio station back in Quindalup.

He was interested in my plans as he was also a sailor having moved to Kangaroo Island after stopping in with his previous sailboat.  We had a good conversation about my planned trip and he suggested I contact him again when I was heading East. A few days ago I reached out via email and set up scheduled contacts ‘skeds’ with Tony via HF radio.

We have since made a few great contacts  and he has confirmed his offer of a mooring and to show us around. Seems like an opportunity too good to pass up.

VK5KI Tony’s ‘ham shack’ on Kangaroo Island

At around 18:00hrs, the wind finally died completely and I started the engine. Making the most of the recharging batteries, I spent a couple of hours on the air working stations in WA, SA, NSW, VIC and QLD using voice and morse code.

Kevin caught up on a few games of solitaire on his phone before we enjoyed lasagne for dinner, heated to perfection in the oven. Not a bad way to end another good day at sea.