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Old 26-04-2011, 19:47   #1
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Swell Size , Period and Boat Comfort ?

Coming south back from Broken Bay (NSW, Oz) yesterday we had a forecast 10-20kts of SE wind, a 1.5m swell and (from memory) a 1.5m sea.

It was the most uncomfortable ride I have ever had. The boat pitched and rolled violently coming out of Broken Bay, there was a slight improvement as we moved away from the coast, and then things got worse again as we turned to enter Port Jackson. Spray was coming across the deck often.

The movement of the boat was so violent it was almost impossible to go below.

We had the wind against the east Coast Current (probably about 0.5kt), and one of the VHF weather reports had the wave period at 5.8 seconds which sounds very short.

I do know it would have been better not to go, but the forecast for the rest of the week was no better so the alternative was to leave the boat in Pittwater or Broken Bay and to bring it down later.

Has anyone had much experience of these conditions, how common they are and how well different boats handle them?
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Old 26-04-2011, 20:08   #2
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Re: Swell size, period and boat comfort?

LOL welcome to our world. 6~8 footers with a 3.5 to 4.5 sec period.

Ain't nothin comfy but a lake freighter.
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Old 26-04-2011, 20:23   #3
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Re: Swell size, period and boat comfort?

Quote:
Originally Posted by Boracay View Post

Has anyone had much experience of these conditions, how common they are and how well different boats handle them?
Yes.
Very, outside the gate.
the Cal just climbs up and down the mountains of water...

*I* on the other hand...

man... the admiral musta been loving THAT trip!
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Old 27-04-2011, 15:53   #4
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Another check before leaving...

Now I know to check wave height and period before leaving.

They are available from the Sydney Ports website.

These are today's graphs.
Notes:
  • Hs is the Significant Wave Height in metres and is the average of the highest one third of all waves in the record.
  • Hmax is the Maximum Wave Height in metres in the record.
  • Tp is the Peak Energy Period in seconds, or the period of the dominant waves in the record.
  • Tz is the average time in seconds between all waves in the record.
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Old 27-04-2011, 16:03   #5
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Re: Swell Size, Period and Boat Comfort?

Don't these all depend upon the phases of the moon?
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Old 29-04-2011, 12:00   #6
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Re: Swell Size, Period and Boat Comfort?

Bora, I have experienced this ride lots of times whilst making that short trip. I believe that it is mostly due to backwash or reflected waves off of the cliffs that surround both entrances. The resulting chaotic wave patterns give rise to a horrid jerky and unpredictable motion. Yuck. One often experiences the same conditions around the entrance to Jervis bay... also surrounded by sheer cliffs. Down there, if just passing by, we try to stay at least 5 miles off to reduce this nastiness

The good news is that it only lasts a couple of hours...

Cheers,

.
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Old 29-04-2011, 12:10   #7
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Re: Swell Size, Period and Boat Comfort?

In reality the size of the boat is inverse to the size of the wave.
Or in other words; The smaller your boat is, the bigger the waves are.
Any questions??
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Old 29-04-2011, 17:59   #8
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Re: Swell Size, Period and Boat Comfort?

I think each boat design has a natural harmonic and if wave period syncs with that you will be uncomfortable. A slight change of course will often offset this.
Regards,
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Old 29-04-2011, 18:10   #9
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Re: Swell Size, Period and Boat Comfort?

Sounds like the Great Lakes.
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Old 29-04-2011, 18:12   #10
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Re: Swell Size, Period and Boat Comfort?

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Originally Posted by boasun View Post
In reality the size of the boat is inverse to the size of the wave.
Or in other words; The smaller your boat is, the bigger the waves are.
Any questions??
Sounds like a good argument in favour of bigger boats.
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Old 29-04-2011, 18:30   #11
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Re: Swell Size, Period and Boat Comfort?

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Sounds like a good argument in favour of bigger boats.
Yeah, the last time I went "boating" there were 50-foot-something waves and 60-70 knot winds. The 900-something-foot ship handled it fine.

On smaller craft, I found that changing direction slightly to meet the waves at a more favorable angle often helps. Short, steep waves are the worse as they can stop all forward movement of a boat.
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Old 29-04-2011, 18:38   #12
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Re: Swell Size, Period and Boat Comfort?

glad to hear anther pacific coast sailor stating wave height factoids here--thankyou!!! gets large out there....
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Old 29-04-2011, 18:40   #13
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Re: Swell Size, Period and Boat Comfort?

Quote:
Originally Posted by Boracay View Post
Coming south back from Broken Bay (NSW, Oz) yesterday we had a forecast 10-20kts of SE wind, a 1.5m swell and (from memory) a 1.5m sea.

It was the most uncomfortable ride I have ever had. The boat pitched and rolled violently coming out of Broken Bay, there was a slight improvement as we moved away from the coast, and then things got worse again as we turned to enter Port Jackson. Spray was coming across the deck often.

The movement of the boat was so violent it was almost impossible to go below.

We had the wind against the east Coast Current (probably about 0.5kt), and one of the VHF weather reports had the wave period at 5.8 seconds which sounds very short.

I do know it would have been better not to go, but the forecast for the rest of the week was no better so the alternative was to leave the boat in Pittwater or Broken Bay and to bring it down later.

Has anyone had much experience of these conditions, how common they are and how well different boats handle them?
Welcome to open-water boating. Such conditions are relatively mild. Spray over the deck? That's nothing. What you goin' to do with serious weather?
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Old 30-04-2011, 08:46   #14
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Re: Swell Size, Period and Boat Comfort?

Quote:
Originally Posted by markpierce View Post
Welcome to open-water boating. Such conditions are relatively mild. Spray over the deck? That's nothing. What you goin' to do with serious weather?
Mark, in this case the cause of the unpleasant ride is the chaotic nature of the reflected waves from the sheer cliffs that abound in this particular bit of the Aussie coastline. We've transited the area quite a few times and have indeed found the conditions unpleasant, even when the sea conditions a few miles away are ok.

I've no idea how Boracay deals with harsh wx, but can sympathize with his dislike of this area.

Cheers,
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Old 30-04-2011, 10:55   #15
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Re: Swell Size, Period and Boat Comfort?

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Mark, in this case the cause of the unpleasant ride is the chaotic nature of the reflected waves from the sheer cliffs that abound in this particular bit of the Aussie coastline.
Oh! Sorry I came off as a sm..t a.. ignoramous.
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