How do they measure the swell offshore

[toga]

I went offshore a few weeks ago when all that rain started.My luck as usual,we had so much good weather and when i go offshore the weather turns to crap. Anyway the forecast was for 1.5 metres of swell i thought that couldn't be to bad so we all head off to the coast.While we were out there some of the waves or swell would of had to been well over three metres from bottom to top.It was hard just to stand up the deckies had no problem though i guess they are use to it.I have only been once before i figure we went on a good day that time.

[John_R]

Toga,

I understand you have seas and swells. The seas are local wind generated waves and the swell is from a more distant disturbance. Anyway a 1m sea on a 1.5 m swell can add up to a 2.5m wave.

I find the seas are more of a problem than swell because seas are usually at short intervals like 4 sec between crests, while swell can be 10-14 sec.

Therefore a day with a 1.5m swell but no wind seas can be comfortable offshore while 1m seas with no swell like moreton bay often gets, can be awful.

Hope this helps.

John

[seatime]

G'day toga,

As John_R has noted you may have experienced a combined sea and swell. When there has been lots of Sthly wind the sea sits on top of the swell.
The BOM site has some tutorial type info on waves. http://www.bom.gov.au/info/marine/marpamp.shtml

Have a look at the EPA wave and swell plots.
http://www.epa.qld.gov.au/projects/w...id=13&noback=4

regards.

[Ben@Tamworth]

I went offshore a few weeks ago when all that rain started.My luck as usual,we had so much good weather and when i go offshore the weather turns to crap. Anyway the forecast was for 1.5 metres of swell i thought that couldn't be to bad so we all head off to the coast.While we were out there some of the waves or swell would of had to been well over three
metres from bottom to top.It was hard just to stand up the deckies had no problem though i guess they are use to it.I have only been once before i figure we went on a good day that time.

Heya Toga,

When you look at the forecast get both the seas and the swell forecast.

Swell is the rolling in waves with a few seconds between and comes from weather systems 100's or 1000's of kilometres away (remember the surf in Sydney a couple of weeks after Cyclone Larry? - that was a direct result of the cyclone)

Seas are the general slop that happens from local winds - you can be out on a calm day when a squall blows in and then the water chops up and gets nasty.

A forecast of 1m seas and 1.5 swell isn't bad and I have no hesitation myself in going out in that. A 3m swell is also fine if there is no wind or seas - it'll get very nasty very quickly if any wind picks up though!

The Bureau of Meteorology states on their website

Please Be Aware:
Wind gusts may be a further 40 per cent stronger than the averages given here, and maximum waves may be up to twice the height.

Also keep in mind that the forecast is an average wave height, so some waves can roll in practically flat, others tower. Usually the bigger ones will come in groups. If you count them you might find there is 3 big waves coming in every 20 or 30 smaller ones.

When you want to go out, have a look at the forecast for seas and swell, but also look at what is going on with weather patterns. I live on the Mid north coast so when deciding if I am going to sea I also look at the forecast for Far North Coast and Hunter to see what is happening there, both in seas and actual weather, wind etc.

I only have a 4m tinny so checking the weather forecast is of greater importance than if I had a 9m platey

Oh yeah, another thing to look out for is bommies. A local bommie here rises to only about 2m under the surface from 17m surrounding area. Anything above 2m swell really pushes up on the bommie and can give a peak breaking wave well over 3-4m - Bommies are dangerous and you need to learn the characteristics of the one you fish to know how the sea will behave

Hope this helps!