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Old 01-10-2022, 03:03 AM   #1
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Waves at open sea

I just read Bowball's question "Weather information Vancouver to Alaska" as well as retriever's answer, which lead me to 2 very useful web sites. On the other side of the ocean I will start a similar journey in April from the Netherlands, via Helgoland and the north of Denmark to Stockholm. It is the first piece that I most worry about, especially the route from Nordeney in Germany to Helgoland and then to Thyboron in Denmark. All open seas with exposure to the west and dominating strong west winds. So far I stayed under the northern islands in the Netherlands with is sheltered by the islands and the shallow waters in-between. I have a 44 year old Ocean Marine trawler, 40 foot with twin Lehmans, all in very good condition and with a completely renovated and separated fuel supply system which I put in for this trip to avoid double engine failure due to filter plugging. My main worry is the waves. When I look at the aforementioned sites I see waves predicted to be 3 - 6 - 9 feet, even with moderate winds. For captains with similar boats on similar waters, what are your experiences with high waves and above all, what are your tips! Thanks so much!
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Old 01-10-2022, 04:41 AM   #2
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When I look at the aforementioned sites I see waves predicted to be 3 - 6 - 9 feet, even with moderate winds. For captains with similar boats on similar waters, what are your experiences with high waves and above all, what are your tips! Thanks so much!
Missing information here. Period (in seconds) and direction relative to your travel. I remember being in 12-foot seas at very long period that was glorious - like traveling down a country road in an old Buick Roadmaster. Didn't even need stabilizers turned on even though seas were roughly on the beam (generated from a major storm almost 600 nms away) . And I remember being in 6-8 foot headseas that were more or less square (8-ft at 8-secs) coming up the Caribbean from Panama that really sucked and would not have been tenable had I been on my little Willard 36. Had I been going the other direction, no problem (some corkscrewing I'm sure, but much more comfortable then headsea). And I've done a ton of sailing on SF Bay that routinely has 3-4 foot square chop every summer afternoon. Uncomfortable and wet, but workable.

Hope this gives some help.

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Old 01-10-2022, 05:52 AM   #3
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Have done a decent amount of open ocean passages in small (<55’) boats. As Peter astutely says period is critically important as regards comfort and safety for small boats. Several other things are as well.
First divid swell (waves from systems a significant distance away) from local wind waves. In general swell will have a longer period.
Second pay attention if one two or more systems are responsible for seastate. Remember wave height is reported as a average of the highest third. When several systems are in play there’s will be a harmonic resulting in the occasional wave that will be much higher in amplitude that the reported number. This even occurs with wind waves and swell. Also waves may come at you in several directions.
Then consider local wind direction and current. On this side of the pond we have the Gulf Stream. If there’s any north to the wind it comes a miserable washing machine.
Lastly consider depth and distance from land. There’s places you can be offshore but on a continental shelf. Given the surface part of a wave is 1/7-1/8 of the total wave the bottom of the wave may slow causing it to break even though not that large. I don’t know the waters you talk about but suspect much is on the shelf not truly blue water. In fact probably close enough issues of reflection, refraction, compression zones and other land effects would be in play.
This isn’t an exhaustive list of concerns. Personally find these near coastal (>25nm but <200nm off shore) trips the most difficult to sort out. So many factors to consider. Do my own weather routing but supplement it with professional weather router. When we disagree makes for interesting conversation. But continue to learn.
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Old 01-10-2022, 05:58 AM   #4
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Truly separate fuel systems should be fueled from different sources...something many don't do.
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Old 01-10-2022, 07:04 AM   #5
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Hi Hans,

you will need to follow the weather reports and wave forecasts so your trip is safe. Windy gives a reasonably good wave forecast, in addition to the previous day's swell forecast. Although the Baltic Sea is not an ocean, it can be a really nasty, short wave period and high wave. Here's a little video of the weather where you shouldn't be at sea. I put the weather forecast links that I follow in this area and that I trust, I follow several forecasts that I make decisions about.


Litle bit video baltic sea waves
https://youtu.be/DUbDwek6rAQ

the wavelength vs height can be really nasty salty and the highest wave measured is over 15 meters high, that’s a good reason to be heard ...

I actually use Windy aps and I think it predicts well the wind, the wave size and angle° of the wave and old swell angle°. In Swedish area I keep an eye on SMHI forecasts and in German waters their official forecast. And Finland area Finnish Meteorological Institute.

Windy https://www.windy.com/

Finland and Åland sea https://en.ilmatieteenlaitos.fi/weather-and-sea

Sweden off shore https://www.smhi.se/en/weather/forec...g=en,area=none

Sweden costal

https://www.smhi.se/en/weather/forec...parameter=wind

And Swedesh VHF area chart and canal number (forecast and security etc.)

https://stockholmradio.se/for-abonne...och-kanalplan/

Germany and Denmark

https://www.dwd.de/EN/specialusers/s...sea/_node.html

in finland and sweden the wind is m / s and in germany a different unit beaufort.

at sea you should get a wifi router with an external antenna that amplifies the signal.

NBs
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Old 01-10-2022, 10:59 AM   #6
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Will note virtually all apps use information that’s available from government sources for free. I trained in the era of arrows not colors and still find arrows give the information in a manner easier to interpret without confusion. Also arrows require no scale to look at and can be transmitted at a lower baud rate without degrading.
I refuse to pay for something twice. I pay my government to to generate this data. My government has agreements to share datasets with other governments. Therefore I use passageweather and voluntarily give them a donation annually.
Unfortunately find such datasets show the predominant wave train only. It’s rare there’s only one wave train so such datasets are not infrequently misleading. North Baltic notes a windy does report prior swell and current wave train so after minimal experience you can interpolate what you will face to some degree. How ever this is also available for free elsewhere.
Here think how long your transit will take becomes important. Here on the US east coast people often do multi day near shore transits making use of favorable windows. My understanding is given the potential for significant weather across the bay of biscay and the difficulty entering ports with a east wind or wave train across Portugal the same occurs. This is not uncommonly done in “B” boats. Hence find it’s always worthwhile to correlate gribs to a chart. The files offered by windy or passage weather do not have the granularity as to present the details of the local seastate. But by looking at a chart as you look at files you generally can get a good idea what you will face.
For anything over a day sail (and sometimes for those) like to look at a 500mb and a regional (and larger) weather chart. In recent years the errors in predictions are as often when things will arrive as in intensity. Find the loops you see on windy and similar apps can be quite misleading. It’s here I’m most frequently disappointed.
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Old 01-10-2022, 01:19 PM   #7
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Hi Hans!

I think your boat is more than capable of the trip you desire, if you keep an eye on the weather forecasts. The posters here have already given some great weather info suggestions. As for myself, I use the Windy Pro app. Well worth paying for. It gives you simultaneous overview and "average" of about 8 different weather models. By the hour.

I find that in the Baltic and North Seas, that bad weather is considerably less "spontaneous" than it can be in the Mediterranean, where I am cruising now. It is my experience in the north that if you wait for an optimal "weather window" in the near term forecasts (checking many), you have 95%+ probability of not being surprised by weather.

We did roughly the trip you are contemplating in our Greenline 33 (single engine) in 2015. We were going the opposite direction, however: Malmö>Kiel Canal>Eider>Tönning>Helgoland>Norderney>Delfzijl. The weather was absolutely glorious. Hardly a ripple -- but we did wait in Tönning for a couple of days for this weather window. Our biggest stresses on this journey had nothing to do with the weather. They were 1) Crossing the commercial traffic separation zone going into the Elbe and 2) the leg from Norderney to Delfzijl, where we took the small channel marked with "sticks" that is only navigable for a few hours at high tide. I had bought local charts prior to this, which gave me the courage to try this. In the end, however, we ended up following some small local work boat and I never needed the charts. Along the way, I noted that had I used the charts, I probably would have had less success than I did following the local boat. He took some twists and turns that were NOT on the charts and NOT where the so-called markers said we should be.

It's only about 40nm from Norderney to Helgoland and much less than that from Helgoland to Tönning. Easy day trips for your boat!
If you can find a way to do it, I would recommend trying to make some type of booking for the marina at Helgoland. We did not and ended up rafting to another boat. This is not usually a problem and is quite common in this region – except, in this case, the boat we were rafted to was, itself rafted to FIVE boats. So, we were number seven in the raft. Thankfully, we did not need to string a power cable ;-)


The two pictures below are for inspiration:
1) A picture of us sitting in the mud at low tide in Tönning
2) A typical view in Helgoland!
Attached Thumbnails
tonning.jpg   Helgo.jpg  
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Old 01-10-2022, 01:29 PM   #8
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P.S. If you're going to Thyboron to experience Limfjord, great. If you have little interest in Limfjord, then I would highly recommend going in at Tönning and taking the Eider to Kiel canal. (Kiel canal is easy and fascinating.) This way, you will avoid a whole lot of possible North Sea weather exposure on the west coast of Denmark, where there is little in the way of shelter.
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Old 01-21-2022, 05:36 AM   #9
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Thanks to all

This thread has been very useful for me, thanks for your links and all contributions. I am sure that as soon as I am at sea I will relax again but I am just curious how my trawler will behave. I did cross seas in sailing ships, sometimes even with strong winds, but the design of these ships and the power of the sails give a strong stabilising effect. We'll see this summer.
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Old 01-21-2022, 09:36 AM   #10
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Originally Posted by Hans Rovers View Post
I just read Bowball's question "Weather information Vancouver to Alaska" as well as retriever's answer, which lead me to 2 very useful web sites. On the other side of the ocean I will start a similar journey in April from the Netherlands, via Helgoland and the north of Denmark to Stockholm. It is the first piece that I most worry about, especially the route from Nordeney in Germany to Helgoland and then to Thyboron in Denmark. All open seas with exposure to the west and dominating strong west winds. So far I stayed under the northern islands in the Netherlands with is sheltered by the islands and the shallow waters in-between. I have a 44 year old Ocean Marine trawler, 40 foot with twin Lehmans, all in very good condition and with a completely renovated and separated fuel supply system which I put in for this trip to avoid double engine failure due to filter plugging. My main worry is the waves. When I look at the aforementioned sites I see waves predicted to be 3 - 6 - 9 feet, even with moderate winds. For captains with similar boats on similar waters, what are your experiences with high waves and above all, what are your tips! Thanks so much!

I found this interesting chart as well to help when planning for open water and trying to figure out swell+wind wave actuals.

Click image for larger version

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Old 01-21-2022, 02:49 PM   #11
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Wifey B: We did our brief tour of Scandinavia last summer and had an incredible tour advisor from this forum, who has even posted in this thread and to whom we're so grateful.

Now, we have weather services but still we find Windy to be an incredible resource and most users only touching the surface of it's capability. Their free is great and premium even better. A few things I'd like to point out.

1. You have three different forecast models to choose from. A few days out they will often have significant differences. We consider the worst forecast in planning.

2. There are many more layers available and some are very useful. For instance, wind and wind gusts, but the ones we find most useful are for waves. The waves are broken down into Wind Waves, Swell 1, Swell 2, and Swell 3. As pointed out above, height without period is of virtually no meaning.

I just did a little exercise of the coast of Paradise, otherwise known as Fort Lauderdale, Sunday at 11 AM. ECMWF has 6' at 8 seconds, GFS has 5' at 9 seconds and Icon has 5' at 7 seconds. All show it from the North. If you look closely and move a few hours, you see that the difference is ECMWF simply has the conditions arriving sooner.

But there is more. Looking at ECMWF, wind waves are N 3' at 4 seconds, not bad but a bit choppy. However, there is a primary swell on top of that which is 5' at 9 seconds. No other swells. The swell is also from the north. A 5' swell at 9 seconds isn't bad at all. Wouldn't concern me at all. Wind waves of 3' at 4 seconds are a bit rough, but I'd just speed up a bit and be fine. However, these combining as they are appearing to do throws an entirely different look and I'd prefer to wait rather than let them double team me.

As a comparison if I was looking at Palm Coast, it shows NE 5' at 8 seconds but only NW 2' of wind waves at 3 seconds, a NE Swell 5' at 9 seconds, and E Swell 1' at 7 seconds. I find the Palm Coast conditions much more acceptable even though at first glance they look much the same. Why? The overriding contributor in Palm Coast is the swell, not the wind waves.

Now I wouldn't head out in either in a 39' CC, but in an 85' MY I'd likely head on out at Palm Coast and wait at Fort Lauderdale. If I was really looking at this I'd research further.

Just pointing out that there's a lot of available information and one needs to learn to use it all together. As to Windy in Scandinavia, found it very accurate and useful.

Someone once said to me, "I can't figure it out. One day 4' is ok and another day it's horrible." I said, "Not all created equal" and laughed but then showed them the underlying data. They'd never looked at periods.

My first time going out off the coast of Washington, I saw the 10' waves forecast and I was concerned but that's when I really learned about Pacific Coast swells and it was nothing. Meanwhile, the Chesapeake can be horrific at 4' and even at 3'. I've seen 3' at 2 and 3 seconds and that's torturous if going slow. It's like someone beating you at 2 second intervals. Actually sending you opposite at 1 second intervals.

At the moment, we're in the Exumas where conditions are 1' at 4 seconds. Been playing around with water toys and the RIB's and exploring small islands. Snacking on leftover chicken at the moment.
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Old 01-30-2022, 08:26 AM   #12
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Thanks Tozz and BandB, I feel more and more confident! Very helpful indeed.
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Old 01-30-2022, 10:29 AM   #13
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Too much detail.
Simply put, you need to wait for a strong High over the area, so that the winds are light, less than 7 knots. Otherwise stay in port.
There are plenty of days like that in the summer, BEFORE August.
I find and use Windy for winds and don't even bother looking at wave forecasts.
Good luck
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Old 01-30-2022, 11:27 AM   #14
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Strongly recommend learning from Lee Chesneau or other expert in marine weather. The best money and time I ever spent was under his tutelage. Consider taking a marine weather course of some type as it will do more to improve your safety than a safety course, your comfort than any ASA or Power Squadron course and allow you to know when to judge any computor generated model (American or European) with a jaundiced eye. All weather is local. All you care about is the weather and waves exactly where you are. Understanding the interactions between shore, bottom, depth, distant perturbations , fundamental wave dynamics and the limitations of computer generated modeling will do much to make you a better captain. Gribs aren’t granular enough. This is particularly true in coastal settings. All weather predictions are probabilities and it’s generally hard to abstract those probabilities from the common commercial pictographic presentations like Windy or passage weather. Even when contemplating a weeks vacation coastal cruise understanding how waves and weather are generated will make the difference between pleasure and discomfort. Reading weather charts and especially the 500mb will help you decide where to go . This is especially important when you have a fixed time frame for boating. Schedules kill but sometimes you can keep your schedule if your willing to change your plans.
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Old 01-30-2022, 01:00 PM   #15
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There's 2 parts to marine weather.... reading major forecast data.... then knowing how they will affect the localized weather you are likely to encounter.

That comes from experience...all the classroom time in the world only really teaches you half the equation.

Like Richard on Dauntless highlighted there is usually one safe bet.... if you can stay in that weather window.
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Old 01-31-2022, 08:07 AM   #16
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PS although I agree experience is important understanding the principles of what causes weather and waves allows you to take that experience and put it to good use.
As they say “there’s ten ways to do anything on a boat and nine of them are wrong “. Been on boats with very experienced people who could not predict local coastal sea state nor hyper local T-storm risk. They just toughen up and get through it learning nothing about why it occurred there and why it occurred then. Similarly inability to read clouds or a recording barometer has lead to some interesting conversations with these old salts.
So don’t disagree with you but view experience as necessary but insufficient. Do a formal weather course. Read a few marine weather books.
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Old 01-31-2022, 08:33 AM   #17
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.....
So don’t disagree with you but view experience as necessary but insufficient. Do a formal weather course. Read a few marine weather books.
Perhaps the best book on marine/cruising weather is by Steve Dashew. Gratefully available for free PDF download. His books are an amazing gift to the cruising community.

https://setsail.com/free-books/

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Old 01-31-2022, 10:36 AM   #18
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PS although I agree experience is important understanding the principles of what causes weather and waves allows you to take that experience and put it to good use.
As they say “there’s ten ways to do anything on a boat and nine of them are wrong “. Been on boats with very experienced people who could not predict local coastal sea state nor hyper local T-storm risk. They just toughen up and get through it learning nothing about why it occurred there and why it occurred then. Similarly inability to read clouds or a recording barometer has lead to some interesting conversations with these old salts.
So don’t disagree with you but view experience as necessary but insufficient. Do a formal weather course. Read a few marine weather books.
I never said understanding how weather phenomena is generated isn't important...but it's understanding where you are with marine effects that many weather forecasts don't get right or at all that ultimately is important.

I lean towards the experience factor than training in this area.
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Old 01-31-2022, 11:11 AM   #19
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When a resident got invited to a sail with a senior attending on a 42 center console ketch. Was on the night before so sleeping below although it was a beautiful day. 10-15kts. 2-3’. Going from Marion MA to Stonington CN with all the rags up.
Told by wheel man boat on AP with others chatting and snacking in cockpit. Approaching the L.I. race (~2-5m off Port Judith) boat knocked down. Lost the mizzenmast but no other damage to boat or crew.
Mistake was lack of knowledge not experience. Strong system had passed several hundred miles offshore. It produced swells coming from east but refracting around tip of L.I. and reflecting off R.I. Rising tide out of LI sound. Local wind southerlies to southwesterlies but northwesterlies night early morning and night before. Multiple waves trains from multiple directions. In the open waters of block island sound a very modest swell with very small wind waves on top. When I came up after the event conditions were very modest. A 2-4’ swell with maybe 1-2’ on top. Nothing breaking. Told all different descriptions of the”rogue “ that knocked us down. Was told there was a period of 5-15m before event there was an occasional non breaking 5’-6’er that would occasionally come through but background sea very benign.
Knowledge would have raised the awareness that close to the RI shore could raise the possibility of synchronization of the wave fronts. Looking at the history of prior days and regional outlook would have lead to a better assessment. The prudent captain would have taken the cut nearer to the NY side even though a bit longer trip. This occurred in local cruising grounds. Everyone onboard had plenty of experience in that area and plenty of boating years/decades.
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Old 01-31-2022, 11:28 AM   #20
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I am not saying one or the other...but have seen where experience over book/classroom knowledge wins more often....especially for coastal and inland cruising...offshore less so because of less effects of local issues.

All points can be countered with the occasional experience we have had that contradict.

Anyway, offshore swell issues often are learned well in general experience...really don't need classroom stuff to see it up close first hand on a regular basis.
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