Cruisers Forum

Join CruisersForum Today

Thread Tools Rate Thread Display Modes
Old 29-05-2012, 06:09   #16
Senior Cruiser
s/v Beth's Avatar

Cruisers Forum Supporter

Join Date: Oct 2008
Location: Coos Bay, Oregon
Boat: Valiant 40 (1975)
Posts: 4,064
Re: What does swell do to boat speed

Hmmm, in the swells I went through recently you couldn't see the horizon at the bottom of the swell. I thought the green flash you were talking about was the sun glinting through the ocean water!
Swells for me are never as swell as I thought they would be...

s/v Beth is offline   Reply With Quote
Old 29-05-2012, 06:15   #17
Senior Cruiser
maxingout's Avatar

Cruisers Forum Supporter

Join Date: Dec 2006
Location: Fort Pierce, Phoenix
Boat: Privilege 39 Catamaran, Exit Only
Posts: 2,367
Re: What does swell do to boat speed

Our catamaran creates a very stable platform when sailing downwind, and that may be one of the reasons why I like the large swells so much in the Pacific.

Dave -Sailing Vessel Exit Only
maxingout is offline   Reply With Quote
Old 29-05-2012, 07:51   #18
CF Adviser
Bash's Avatar

Cruisers Forum Supporter

Join Date: Dec 2008
Location: sausalito
Boat: 14 meter sloop
Posts: 7,256
Re: What does swell do to boat speed

Originally Posted by Nostrodamus View Post
I believe it has something to do with swell height and the time period between swells but i'm not sure.
You are correct. Wave height is meaningless unless you know the interval. A swell of 12' every 17 seconds is far more benign than a swell of 8' every 8 seconds, the latter of which will entail steeper waves and will thus affect the boat more.

Realize that swells tend to spread out the further they get from the source of energy that generates them. A long swell interval indicates that they may have traveled for days from away from a low pressure system. This can create frustrating conditions for sailing because you may not have the necessary pressure to deal with the swells. Upwind this means you won't be able to point as high, downwind this means that your sails will not be able to hold their shape much of the time, even if using a preventer.

A following swell will have the greatest effect on a boat that is able to surf. That same boat will have greater difficulty carrying its momentum into the swell, especially when the waves get square. In other words, swell will have more effect on a sailboat that accelerates well than a sailboat that doesn't.

I used to race for a syndicate that actively campaigned two boats. One was light displacement, the other was an ultralight. We could look at the wind forecast and wave report and know which boat was more likely to win on any given day. Unfortunately, what this means in terms of the OP's original question is that how swell affects boat speed is highly dependent upon the boat. It's ultimately a question of VMG, and this not only becomes highly complex, but it becomes highly variable. The only real answer is: it depends not only on the swell, but upon the boat.

Regardless, there's no way someone could answer, "Add or subtract 10% of boat speed for any swell over 6'." It just doesn't work that way.
cruising is entirely about showing up--in boat shoes.
Bash is offline   Reply With Quote
Old 29-05-2012, 10:07   #19
Registered User

Join Date: Sep 2011
Location: Med.. currently Greece
Boat: Oyster 45
Posts: 338
Re: What does swell do to boat speed

Thank you for your very well explained answer which I totally understand leaves me with no answer but more of an idea on the subject.
Who said sailing was easy.... certainly not me.
Thanks again for all the replies both on and off subject which I and hopefully others found interesting.
If it works you did it right, if it doesn't you did it wrong.
Nostrodamus is offline   Reply With Quote
Old 04-06-2012, 18:26   #20
Registered User

Join Date: Nov 2010
Location: San Francisco Bay
Boat: Hunter Legend 40
Posts: 291
Re: What does swell do to boat speed

Pardon the interruption, but I'm checking on sea conditions and I was curious about wave height and frequency in trip planning. I've been looking at grib lines and calling dial a buoy.
If you want to get beat up, sail into the swell?, if you want to sail leisurely sail with the swell? The swell is usually with the wind? when does the wave height and frequency start getting dicey? 6 feet 6 seconds? Do you guys use this criteria in planning trips?


I'm wet nurse to a last place dead to the neck up ball club and I'm choking to death.
gpshephe is offline   Reply With Quote

Thread Tools
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

Our Communities

Our communities encompass many different hobbies and interests, but each one is built on friendly, intelligent membership.

» More about our Communities

Automotive Communities

Our Automotive communities encompass many different makes and models. From U.S. domestics to European Saloons.

» More about our Automotive Communities

Marine Communities

Our Marine websites focus on Cruising and Sailing Vessels, including forums and the largest cruising Wiki project on the web today.

» More about our Marine Communities

Copyright 2002-2015 Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 23:47.

Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2016, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2016, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.