We stuck our nose outside the Golden Gate yesterday, and got slammed around. On Wednesday, the temperature is supposed to be warm and the winds are supposed to be light. But a surfing site says the swell will be 5-6 feet. I don't know how to translate that into smooth or rough for our 25 Cruiser. Can you help?
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Sea Conditions
- Thread starter dread
- Start date
dread":1fdaddxh said:We stuck our nose outside the Golden Gate yesterday, and got slammed around. On Wednesday, the temperature is supposed to be warm and the winds are supposed to be light. But a surfing site says the swell will be 5-6 feet. I don't know how to translate that into smooth or rough for our 25 Cruiser. Can you help?
That's a good question. I can't speak specifically to local conditions, but here is something that might help in general.
As an extreme example, you could have a 20' swell and not be bothered at all, IF the swells were far apart (this distance goes by the term "period"). On the other hand, you could have 2' swells that were miserable, if the period was very short (i.e. they were very close together). This is part of the reason that even 4' waves on Lake Superior are miserable: the period is almost always very short. People like me, from the Great Lakes, are initially astonished that ocean folks can go out in 15' swells (and be much more comfortable). Those would kill you in short-period conditions like are typical on the Great Lakes! So that is one thing you can look for in a marine forecast. The size of the waves AND the period.
Then there are certain areas with "local anomalies." The area around the Golden Gate bridge is not my home waters, but I've been through there once, so had to read up on it. There were certain areas to avoid, even in relatively benign conditions. So that's another thing to watch out for, especially around bridges, inlets, bars, etc.
Lost Petrel
New member
Here is a good site for info outside the gate; http://www.windfinder.com/forecast/san_francisco_buoy
As Sunbeam mentioned it would be prudent to have local knowledge as there are number of places one can get into trouble even in fairly benign conditions. You will want to stay well clear of the land because sneaker waves can get you. This just happened over the weekend; http://www.sfgate.com/news/us/article/L ... 866076.php
As Sunbeam mentioned it would be prudent to have local knowledge as there are number of places one can get into trouble even in fairly benign conditions. You will want to stay well clear of the land because sneaker waves can get you. This just happened over the weekend; http://www.sfgate.com/news/us/article/L ... 866076.php
I use this site alot. Pick your location and it will give you info on it. I go to Lawson's Landing (Bodega Bay area) and always use the below site as well as others for weather conditions. In fact going there tomorrow evening through Friday. Was suppose to go this past weekend but with the forecast on top of it being a zoo I opted to wait. There's always another day and I wanna live to see it as long as possible.
http://forecast.weather.gov/MapClick.php?lat=38.255436376379464&lon=-122.991943359375
http://forecast.weather.gov/MapClick.php?lat=38.255436376379464&lon=-122.991943359375
What I use as a crude "rule of thumb" is that I want the period in seconds to be 3 bigger than the swell in feet. So 5-6' at 9s would be fine with me provided the wind is <=15kts. As the swells get larger, I prefer a larger difference between period in seconds and the swell height in feet. For me, once the winds exceed 15-20kts, the ride can be a bit rough in a 22 or even in my tomcat (regardless of the swells). I see the 25 as being somewhere in between the two in terms of handling rougher water. Of course local structures, currents and shallow areas can take a sea state that is perfectly safe in one area and turn it into dangerous in another. Large swells in shallow areas or against strong outgoing currents at a river entrance can cause the incoming waves to break and that's something one may not expect without experience in a given locale.
I use the website swell watch to look at predicted swell heights, period and wind speeds. Its predictions are generally pretty good for 3 days and so-so for the longer term projections. Currently Swell watch is showing 11-12s period on Wed. with swells of about 5-6' just outside of the bridge. However, the swells just a few miles further out are predicted at 7-8'. The winds are predicted to be fairly light during the day in the area immediately outside of the bridge so I think it will be reasonably comfortable on Wed. That said, this is a forecast and it could change. IMHO the best way to learn how to correlate these numbers (swell height, period and wind) with the experience one feels on the water is to get out in a variety of conditions and find out what the measured/predicted swell height, period and winds are/were for the time you were out.
I use the website swell watch to look at predicted swell heights, period and wind speeds. Its predictions are generally pretty good for 3 days and so-so for the longer term projections. Currently Swell watch is showing 11-12s period on Wed. with swells of about 5-6' just outside of the bridge. However, the swells just a few miles further out are predicted at 7-8'. The winds are predicted to be fairly light during the day in the area immediately outside of the bridge so I think it will be reasonably comfortable on Wed. That said, this is a forecast and it could change. IMHO the best way to learn how to correlate these numbers (swell height, period and wind) with the experience one feels on the water is to get out in a variety of conditions and find out what the measured/predicted swell height, period and winds are/were for the time you were out.
PaulNBriannaLynn
New member
A surfing site will not give much useful information for boating. Its going to be relating the information from NOAA or Navy models and translating that for breaking waves on the beach in a particular location or surf spot.
Im not very familiar with San Francisco surfing scene but the a forecast for the break below the golden gate bridge Fort Point might require a massive swell 20' for example, to only have 5' perfect waves. It doesn't relate very well to boating!
The wind and swell interval are what you'll want to pay attention to. The wind is what will cause the uncomfortable seas. A marine forecast may call for a 1 -2 ocean swell but will not take into account the waves generated locally by the wind. Those locally generated wind waves are what can cause problems fast, or at least make things miserable.
Swell interval is important and is what Sunbeam was getting at above. This is the period or space in between the waves. Anything above a 14 second interval is what I would consider a longer interval and much easier and comfortable to navigate. Say the forecast was for 10 foot swells at 19 seconds. That is not going to be nearly as uncomfortable as a 6 foot swell at 8 seconds.
As a surfer in a previous life(style), the longer intervals between sets meant alot larger set waves to surf. A 6' at 18 sec swell could generate 10' breaking waves on the beach, where 6'at 9 sec swell may be barely 4'. The trough between the waves isn't as deep and produces a smaller wave. Not relevant in a boat, because we all try to avoid areas where the waves are breaking for safety
Im not very familiar with San Francisco surfing scene but the a forecast for the break below the golden gate bridge Fort Point might require a massive swell 20' for example, to only have 5' perfect waves. It doesn't relate very well to boating!
The wind and swell interval are what you'll want to pay attention to. The wind is what will cause the uncomfortable seas. A marine forecast may call for a 1 -2 ocean swell but will not take into account the waves generated locally by the wind. Those locally generated wind waves are what can cause problems fast, or at least make things miserable.
Swell interval is important and is what Sunbeam was getting at above. This is the period or space in between the waves. Anything above a 14 second interval is what I would consider a longer interval and much easier and comfortable to navigate. Say the forecast was for 10 foot swells at 19 seconds. That is not going to be nearly as uncomfortable as a 6 foot swell at 8 seconds.
As a surfer in a previous life(style), the longer intervals between sets meant alot larger set waves to surf. A 6' at 18 sec swell could generate 10' breaking waves on the beach, where 6'at 9 sec swell may be barely 4'. The trough between the waves isn't as deep and produces a smaller wave. Not relevant in a boat, because we all try to avoid areas where the waves are breaking for safety
Nonsense - you must not have looked at the site as this site provides a heat map of swell height, swell period and wind over a large area - e.g. well outside of the beach. I've used it for many years and find it quite useful for my boating. The heat map format (with vectors for direction) combined with projections for every 6 hours provides a level of visualization that you simply don't get from many other sites.PaulNBriannaLynn":2qn7scpw said:A surfing site will not give much useful information for boating. Its going to be relating the information from NOAA or Navy models and translating that for breaking waves on the beach in a particular location or surf spot.
PaulNBriannaLynn":2qn7scpw said:Im not very familiar with San Francisco surfing scene but the a forecast for the break below the golden gate bridge Fort Point might require a massive swell 20' for example, to only have 5' perfect waves. It doesn't relate very well to boating!
The wind and swell interval are what you'll want to pay attention to. The wind is what will cause the uncomfortable seas. A marine forecast may call for a 1 -2 ocean swell but will not take into account the waves generated locally by the wind. Those locally generated wind waves are what can cause problems fast, or at least make things miserable.
Swell interval is important and is what Sunbeam was getting at above. This is the period or space in between the waves. Anything above a 14 second interval is what I would consider a longer interval and much easier and comfortable to navigate. Say the forecast was for 10 foot swells at 19 seconds. That is not going to be nearly as uncomfortable as a 6 foot swell at 8 seconds.
As a surfer in a previous life(style), the longer intervals between sets meant alot larger set waves to surf. A 6' at 18 sec swell could generate 10' breaking waves on the beach, where 6'at 9 sec swell may be barely 4'. The trough between the waves isn't as deep and produces a smaller wave. Not relevant in a boat, because we all try to avoid areas where the waves are breaking for safety
Also, it's the difference between the height and period that matter most IMO. For example, 4' swells at 4s will be a washing machine where as 4' at 7s will be just fine and 4' at 12s will be like a lake. I agree that the wind is perhaps the most important factor though and I just don't like wind much above 15kts. The vector display of the site I referenced allows you to see when and where the wind is aligned with, opposed to or cross to the swells and of course that matters also. That said, my crude rule of thumb has served me pretty well in 12 years of offshore boating on the west coast.
There are several items not mentioned by folks perp has unfamiliar with the SF area--or perhaps any area where there is a huge volume of water gong in and out of a narrow channel.
One is the current. SF bay is notorious for its currents--and the swells defracting around Point Reyes, into the outer bay entrance. You are going to have the least wave problem during a high slack water--if all other things are equal. But of course they are are not always equal.
The wind can accelerate, and increase the steepness (as Roger points out the importance of this)--and wind/waves against current will make the waves much steeper--waves with current behind will smooth the waves out and give a longer period.
Also in the entrance to SF, it depends on where you go. I'll let those with much more local knowledge, comment on those specifics. Most of our experience is with boats 38 to 60 feet in length, and a draft of 7 feet. We tend to follow the ship channel and not turn North or South until we are at the Sea Buoy.--and avoid the "Potato Patch" and other shoal areas, both North and South of the main channel.
There is a good site about the SF bar:
http://coastsidefishingclub.com/grey-be ... cisco-bar/
one of the first comments is:
Many times I have left SF timing with the tide/current, and see boats coming back-and have them yell"it is not passable"--Invariably they have tried to cut a corner. There are plenty of boats which have met their fate in these areas So this is nothing to mess with--and if you are not comfortable- as you start out,-make it a day in some other part of the bay.
The Channels leading to the Delta can also be very rough--again often related to local winds and velocity of current, as well as the underlying wave conditions. A few hours can make all of the difference in the world in the roughness in many parts of the bay.
A most interesting historical exhibit is in Sausalito, where the Army Corp of Engineers has a 200 yard long physical working hydrological model of SF bay system. Definitely worth a visit (especially on a rough day).
Today, you only have to go to:
http://l-36.com/sf_current_new2.php?menu=9 Put in the place, the date and time--and you have an excellent computer model of the current. Many of our chart plotters have current points which you use to see the state of the current--and choose a better time if necessary.
One is the current. SF bay is notorious for its currents--and the swells defracting around Point Reyes, into the outer bay entrance. You are going to have the least wave problem during a high slack water--if all other things are equal. But of course they are are not always equal.
The wind can accelerate, and increase the steepness (as Roger points out the importance of this)--and wind/waves against current will make the waves much steeper--waves with current behind will smooth the waves out and give a longer period.
Also in the entrance to SF, it depends on where you go. I'll let those with much more local knowledge, comment on those specifics. Most of our experience is with boats 38 to 60 feet in length, and a draft of 7 feet. We tend to follow the ship channel and not turn North or South until we are at the Sea Buoy.--and avoid the "Potato Patch" and other shoal areas, both North and South of the main channel.
There is a good site about the SF bar:
http://coastsidefishingclub.com/grey-be ... cisco-bar/
one of the first comments is:
the second most dangerous major port entrance on the west coast behind the Columbia River bar.
Many times I have left SF timing with the tide/current, and see boats coming back-and have them yell"it is not passable"--Invariably they have tried to cut a corner. There are plenty of boats which have met their fate in these areas So this is nothing to mess with--and if you are not comfortable- as you start out,-make it a day in some other part of the bay.
The Channels leading to the Delta can also be very rough--again often related to local winds and velocity of current, as well as the underlying wave conditions. A few hours can make all of the difference in the world in the roughness in many parts of the bay.
A most interesting historical exhibit is in Sausalito, where the Army Corp of Engineers has a 200 yard long physical working hydrological model of SF bay system. Definitely worth a visit (especially on a rough day).
Today, you only have to go to:
http://l-36.com/sf_current_new2.php?menu=9 Put in the place, the date and time--and you have an excellent computer model of the current. Many of our chart plotters have current points which you use to see the state of the current--and choose a better time if necessary.
PaulNBriannaLynn
New member
rogerbum said:Nonsense - you must not have looked at the site as this site provides a heat map of swell height, swell period and wind over a large area - e.g. well outside of the beach. I've used it for many years and find it quite useful for my boating. The heat map format (with vectors for direction) combined with projections for every 6 hours provides a level of visualization that you simply don't get from many other sites.
You're right Roger I hadnt looked at the site you posted because I was typing my response and multitasking but I've been there before. The site is good, and has the basic map that you will find at all the surfing websites, magicseaweed.com, surfline, swell watch, etc. For northern califoria it even has a written synopsis which is good. When looking at our local waters of the PNW, there is alot less information but the map shows most of the info I would want. I like a written synopsis like the NWS/NOAA provides including the size of the surface lows arriving
along with a good model:
http://polar.ncep.noaa.gov/waves/viewer ... US_wc_zm1-
This map is down to 3 hr updates out to 180 hrs showing both predicted swell, interval and wind. I believe the information from most of the surfing sites is taken directly from this model.
Many of the surfing websites have links to this information such as http://westportgrayland-chamber.org/surfing_info.php but the links dont always work as web addresses change
The reality is, without local knowledge and experience a person is not going to know what to expect from a forecast without actually experiencing it and its better to be on the safe side.
1TUBERIDER
New member
I use the noaa near shore reports to get an idea. Surf sites can be good but I usually look at them for the cam corder view. Some surf sites have very accurate wave forecasting models. Great for surfing. I use noaa because it is fairly accurate and local.
Before I launch I use my eyes and experience. Launch ramp is next to beach.
And as a last chance sort of I evaluate conditions as I exit the harbor.
The main barrier to pleasant boating for this area is wind. Add close period swell and wind, conditions change fast. Try not to be set on a schedule when boating, or at least make allowances for conditions. When the ocean conditions suck it might be a good time to do something else. I have lots of options.
Before I launch I use my eyes and experience. Launch ramp is next to beach.
And as a last chance sort of I evaluate conditions as I exit the harbor.
The main barrier to pleasant boating for this area is wind. Add close period swell and wind, conditions change fast. Try not to be set on a schedule when boating, or at least make allowances for conditions. When the ocean conditions suck it might be a good time to do something else. I have lots of options.