Wave Height?

[Gnasher]

a stupid question really as i dont take much notice of wave height, but 2moz is giving a reading of 1m on wind guru. Will that be fairly rough? Its also giving a 3 second wave reading. Is that a timed reading for the swell? Whats a good reading for wave seconds?

I will be launching out of mudeford fishing the xray area.

 

I will be ok, but i'm taking a mate out who has never boat fished and i dont want him over the deck

Edited August 27, 2007 by Gnasher

[Afishionado]

In the Pacific one might have a readin/forcast of 60ft wave hight but at a 20 minute period, and as far as our boats are concerned it would feel like flat calm because the top of each wave is so far away (in time) from the top of the next one. The Solent (notorious for it's choppy sea state) one could easily have just 3 ft wave hight but at a period of 3 seconds it would be very uncomfortable as the boat could easily be caught nose in a trough going down the face as the next wave face going upward bursts over it..

Another BIG factor is what they call 'fetch' which is the distance the wind has to run before it hits you. So you could be tucked up in Alum Bay in a SE or SW wind that was making the Solent quite choppy whilst you are sitting comfortably.

One moe thing if you double the LAND forcast suggested wind speed for the wind at sea you will not be far wrong.

 

I would sugest that you do venture out with the firm plan that if you feel it's dodgy you come back in. This way you will start to be able to relate forcast to fact on the day. Decide on alternate areas that will be out of the wind from the forecast direction. Fix in your mind a comfy bolt hole if you find yourself away from your home port and it turns nasty.

 

All these things any good skipper does automatically when planning a trip and it is a good habit to cultivate.

 

Afishionado

[AHoy]

A 1 metre wave height at 3 second period is likely to prove uncomfortable in a small boat when going to windward or at anchor.

 

If my sums are right a 3 second wave will be travelling somewhere around 5 to 6 knots (2.5 metres per second ish) with a wave length of something like 7 to 10 metres in shallow (non-ocean) water. i.e. a wave peak about every 1 and a half boat lengths.

 

A boat travelling at 10 knots is covering around 5 metres per second so heading into the sea there is a true speed of 15 knots into the waves and hitting the waves every 1 to 1.5 seconds.

 

Lots of bump and splash

 

p.s. take my figures with a pinch of salt as I am no expert on the theory behind this

 

For reference CHIMET was showing 0.1m height and 7 second interval for Monday (Bank Hol) which was a fairly good day.

 

AHoy.

[Gnasher]

very useful info lads. Many thanks to you both. We took a few over the top on the way back in, but it wasn't to bad in the end.

[Afishionado]

very useful info lads. Many thanks to you both. We took a few over the top on the way back in, but it wasn't to bad in the end.

The other thing I didn't mention and which I should have is wind and tide.

One might not think it would make much of a difference whether the wind is blowing with the current or against it. In fact with a small boat the difference could be deadly!

Lets say you leave the slip going out on a forcast of SE force 3 to 4 on an ebbing tide (I am talking about this area) Therefore the wind will be going with the tide and you decide to go out to the West and round Hengisbury or Old Harry on the ebb. On the way you think that the forcast 3 to 4 was a bit over the top as the wind seems light and the sea state is relatively flat.

OK 6 hours later you decide to come home. The tide has turned and is flooding strongly and as you get going the wind seems to have suddenly picked up and feels more like a 5 also as you approach the headland you past coming out the wind strengthens to a fierce 6 and the is a maelstrom of big standing waves and huge white rollers. You don't notice this till to late as all you have seen untill you got there is the relativley smooth backs of the waves. Suddenly you are in deep doodoo!!!

 

So what changed to make such a huge difference? the surprising thing is very little.

 

1/ The wind is now against the tide and against the direction of your travel. You didn't feel the wind going out because you were going with it.

2/ The wind will pick up about 50% more strength as it swirls round a headland.

3/ The wind and it's increasing speed at a headland is now working against the flow of water which also speeds up round a headland causing the water to bunch up into higher waves

4/ Your feeling that the wind is stronger is simply because you are now heading into it, so you have wind speed + your speed. This is called 'apparant wind speed'

 

So when looking at a forcast wind and wave situation work out how it may affect you coming back as well as going out.. It might pay to move back past a headland at slack water to avoid a nasty and possibly dangerous situation later on.

 

Mad Mike