When would PicoMicroYacht Capsize?

When doing sea rowing I have adopted three rules about the sea that I try to follow in order to allow going on voyage. Generally, it should be neap tides, so reducing the tidal rate and therefore the likelihood of a confused or breaking sea, particularly past headlands. Secondly, there should be little or no wind. This rule tends to ensure the sea is calmer, but it also means the boat is generally manoevrable in different directions. Finally, the sea shoud be calm, with little or no swell.

Sea state defined in terms of wave height

For sea calmness, I listen out for shipping forecasts that indicate that the sea is ''smooth' or 'slight.'

I had become curious as to what makes it 'slight' and how this was judged. So I checked the criteria and found that there was also calm (glassy and rippled), with below 0.1 metre wave height, and then  'smooth'  was  between 0.1 and 0.5 metres, and slight was 0.5 to 1.25 metres.

I realised that that the online coastal wind forecasts had predictions of wave heights and by chance I had been  using a 'less than one metre' rule as well, which I now realised matched approximately the 1.25 metre limit for 'slight.'

An example is the forecast for next week in the sea area of my next voyage, given below. The wave height is along the last but bottom row and shows a convenient 0.5 to 0.6 metre range, well within my limits.

Windfinder predictions for Torbay, Devon, UK

For me, the reason to have a calm sea in PicoMicroYacht is to prevent capsize. There are generally two causes of capsize; either the wind pushes on the sails to turn the boat over, or the boat gets hit by a higher than expected breaking wave, washing against it with such force that it knocks it over. It is the possibility of the latter that concerns me.

The sort of wave height ranges that I row in are well below causing other problems, such as sea sickness.

But what wave height would cause PicoMicroYacht to capsize and is my approximate one  metre  rule reasonable?

I found out about a study by the University of Southamptom Department of Ship Science. This study indicates that a boat will tend to roll over if the wave hits you on the beam, the wave is breaking and the wave height is 30% of the hull length.

Applying this to PicoMicroYacht, this meant the waves should not be more that 1.14 metres, to avoid the 30% threshold.

However, whether a capsize will take place is of course more complicated. The criteria assume the waves will break and this depends in turn on other sea conditions, including shallowing water and races. Generally, for the sea to break on shallow water at the sort of wave height range I would encounter means I would be nearly aground, such as on a sandbank or beach. More of a problem are races, which I tend to avoid by going further out to sea or by passing through the race area at slack tide. It also depends on how the boat is being manoevred. For example, facing the boat into or away from the waves reduces the likelihood of capize.

Optimist dinghies have fun going through the Fiddlers race in the west end of the Solent. I went through this race in the dark in 2016 on my way round the Isle of Wight, but in very calm weather.

There is also the issue of  the particular boat. Each has it's own right moment, the degree to which the boat will resist being turned over. The resistance tends to increases as a monohull heals, reaching a critical point when it starts to decrease and then the boat will more likely turn turtle. Many boats have their righting moment function plotted, as shown figuratively below.

Stability shown figuratively according to angle of heel (artwork by Andrew Simpson)

Since PicoMicroYacht has no weighted keel, it is more likely to flip over, with less upright stability. Also if capsized, the crew has to right it, as with most dinghies. However, as I have posted before, the PicoMicroYacht has the advantage in this situation of being rapidly self draining and easy to get back in, with very low top sides. The daggerboard is kept down whilst at sea and can then be used lever the boat upright.

Part 1

Part 2

A Pico being righted using the daggerplate; Part 1 and 2 
 (Part 2 shows how to get back on board without falling in the water again)