Ocean conditions query

hi Folks

Just need some advice and clarification on what the ocean will be when the following are predicted.

- winds E 12 knots

- swell SW 1.5m

Wil it be uncomfortable on the ocean?

 

I'm thinking because the winds are easterlies it may level out the swell a little? Is this correct?

Or am I totally wrong and it'll somewhat uncomfortable with a 1.5m swell?

 


mjohns's picture

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what size boat ? and how far

Fri, 2017-02-17 09:20

what size boat ? and how far out are you going?

 

inshore with a easterly is generally pretty okay, further out you go the worse it gets, 1.5m swell is nothing to worry about though

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Let's say if I'm heading out

Fri, 2017-02-17 09:25

Let's say if I'm heading out to the 5 fathom bank on a 6.5m vessel... 

Jackfrost80's picture

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I've headed out 14 mile off

Fri, 2017-02-17 09:43

I've headed out 14 mile off Mindarie in a 5m glass boat in similar conditions but with a NE. The old man wasn't a massive fan when hitting chop then swell or visa versa so we stuck him up back. Once out it was fine.

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Auslobster's picture

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Easterlies...

Fri, 2017-02-17 10:29

 ...blow into the face of the swell, making the waves stand up more...it's why surfers love it when it's blowing offshore. However, as mentioned, 1.5m is generally nothing to worry about. FFB will be safe as houses, especially in a +6m boat. Planning to go there, and beyond, in my 5.8 on Sunday.

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Auslobster - what will be the

Fri, 2017-02-17 10:49

Auslobster - what will be the chop like at FFB when winds are E 12-15 knots?

 

Hutch's picture

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 Inshore will be calmer than

Fri, 2017-02-17 11:37

 Inshore will be calmer than usual. Slightly more offshore becomes more uncomfortable than winds from the opposite directions and it can get very messy. In a bigger boat it shouldn't matter tho

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Paul H's picture

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 to judge swell you need to

Fri, 2017-02-17 12:01

 

to judge swell you need to also look at the swell period (in seconds) a 1.5m swell at 6 second intervals (steeper) is a totally different animal to a 1.5m swell at 15 second intervals

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amen brother 

Fri, 2017-02-17 17:45

amen brother

 

sonofdarryl's picture

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Ocean Conditions

Sun, 2017-02-19 22:24

 

G'day Stumpie.

Im sure everyone has different and valid ideas but ill explain how I normally assess the conditions.

You'll have to excuse the rant I have had a couple.

Ideally you want the wind under 10kn for a pleasant ride. This can be in any direction.


But if its stronger than 10kn, it will still be bearable if its offshore (any E in it) if you stay relatively close to shore. But like others have said it will get worse as you head out, and will get worse quicker the stronger the wind. 15kn offshore but within 5km is normally comfortable. This still gives you the opportunity to get out behind the reef and also the waves are cleaner and easier to read if attempting a dodgy passage in an offshore.

Westerly (or any onshore) will make the surface look worse from the shore, but the sea surface wont really worsen as you head out. This is due to fetch, the further wind has travelled over WATER (not land), the choppier it will be. Easterlies 'start their fetch' from say Cottesloe and as that wind line tracks out to sea (at say 20kn) it turns from a flat surface to calm ripples, to white caps and eventually a fairly choppy sea (...but if it was only 10kn it wouldnt even make the white cap stage) After 20km it gets to rotto and transits is choppy as shit. The wind continues to blow over the island and then starts its ocean ride again at West End, but since it went over land in between, the fetch is 'reset' so we have calm water again at West End until you get outside the protected zone and into the 'path' of the fetch again.

If it was a 20kn Westerly, the wind has blown over the ocean basically since that wind originated and with zero land in between you will cop the full 20kn whitecapping sea.

So with an onshore you get what you get, an offshore you have a grace period depending on how far out you go. But again as long as its under 10kn youll generally be fine no matter how far out.


The offshore only makes the waves standup when theyre about to break, ie their wavelength touches the seafloor, so deeper than 15/20m you won’t notice a thing. Same goes for periods, they don’t matter in deeper water (when comparing big periods to medium periods) but to put it simply they have the effect of making a medium swell act like a big swell. A longer period wave has more water behind the crest than a shorter period of the same height, so when it slows down to break there is more water pushed into a smaller area hence a taller wave. But out to sea they are both the same height so meh. Makes a difference to a surfer but not a deep sea fisherman. It does however pay to see what the winds were doing the night/day before as a howling wind the previous night will leave the ocean hungover and medium period swells crossed up everywhere making for a sore backside, even if its 0knots at the time. But be patient as they do subside after decent period of low wind. These are technically small period swells but there usually isnt much point looking for these on the average forecast websites as they generally only show the primary swell period. You can find secondary/tertiary swell periods but for what its worth its easier looking at the pervious days wind.


Swell is more of a personal preference, I never mind a big swell if its low winds, but a really small swell can make a 15kn sea more bearable. Just means you need to chose a deeper passage as you head out and you will get more waves imitating lumps on your sounder! Waves don’t break until the depth is about 1.3 times the height of the wave, so keeping that in mind you’ll be safe picking a passage that never gets shallower than about 15m. You can always scoot over those 7m sections if the swells not maxing and you know how to read a set - just don’t stick around.

Tide has minimal effect in the SW to the surface conditions.

For anything above above 12kn i like to either sea anchor or idle in reverse. The sacrifice for this is your sounder not reading as well as it should. If you'd prefer to not then prepare to lose alot of gear to snags and bring heavy lead.


In summary for a smallish boat like mine:

wind under 10kn, any swell, didnt blow over 12kn all night = you beauty just watch the passage on the way out to the shelf

wind 15kn offshore, small - med swell = stick to within 5km, bring the sea anchor.

wind 20kn offshore, small - med swell = 1-2km out.

wind 10-15kn onshore, very small swell = bearable but not pleasant.

wind 10-15kn onshore, big swell = white caps can spill over when they stand up with the SW swell. not much fun, stay alert.

wind 15kn+ onshore = liquorland.

Any conditions but 20kn+ winds for the night / day(s) before in surrounding areas = will be more bumpy than expected

 

 

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 Awesome info thanks for the

Mon, 2017-02-20 04:56

 Awesome info thanks for the comprehensive write up. I'm sure this will help others too.