Reply
 
Thread Tools Search this Thread Display Modes
 
Old 02-13-2019, 09:00 AM   #1
Senior Member
 
BrianSmith's Avatar
 
City: Wherever Smartini is
Country: USA
Vessel Name: Smartini
Vessel Model: 2002 Kristen 52' Flybridge Trawler
Join Date: Mar 2014
Posts: 345
Wave height and period: what's "comfortable"?

We're in Providenciales, TCI, getting ready for out next move, to San Juan, PR. We expect it to take 56 hours at 7 kts. We're looking for a nice 3 day weather window, but the REALLY nice windows are few and far between this time of year. You know - the ones with wind under 10kts, 2-3 ft waves, and a 10 second wave period.

So we're trying to figure out some "cut off", below which it is likely to be fairly comfortable, and above which, we just won't go. But we don't have that much "big water" experience - back and forth from FL to Bahamas several times, but those are 8 hour crossings, and we're looking at 56 hours.

We use PredictWind and Windy to get forecasts. If you want to play along at home, you can look at Windy for free (windy.com). Pick a point midway between Provo and San Juan, and look at the Waves forecast. You'll see, this coming Saturday, Sunday, and Monday a stretch in which the waves are forecast to be (at worst) 5 ft. with a 7.6 second "swell period", and (most common) 4 ft. with a 7.8 - 8.2 second "swell period". Waves are from the East that whole time. Wind during that period is from SE then E, up to 14 kts with gusts as high as 20 kts.

PredictWind shows 3 different model forecasts: one mostly in agreement with Windy, the other two are as bad as 6 ft. waves with a 7 second period.

Go, or no-go? (We are stabilized, but with the waves from that direction, won't be doing much.)
__________________
Advertisement

BrianSmith is offline   Reply With Quote
Old 02-13-2019, 09:15 AM   #2
Guru
 
caltexflanc's Avatar
 
City: North Carolina for now
Country: USA
Vessel Name: Small Incentive
Vessel Model: Boston Whaler 130 Sport
Join Date: Aug 2011
Posts: 5,050
I don't know your and your crews tolerance for boat motion, nor the characteristics of your boat, so have no idea what's "comfortable" for you. Personally, those are no go conditions for me given my tolerances and boats I have run, such as 49' Grand Banks and a stabilized Hatteras 56MY, especially at night.
__________________

__________________
George

"There's the Right Way, the Wrong Way, and what some guy says he's gotten away with"
caltexflanc is offline   Reply With Quote
Old 02-13-2019, 09:27 AM   #3
Guru
 
djmarchand's Avatar
 
City: Litchfield, Ct/Punta Gorda, Fl
Country: USA
Vessel Model: Atlas Pompano 23
Join Date: Aug 2012
Posts: 4,645
When we kept our boat on the west coast and often made the trip to Catalina Island, a forecast of 5-6' seas was our limit. This was on a 34' Mainship Trawler with no stabilizers. I would think you would be fine up to 7'.


YMMV of course.


David
djmarchand is offline   Reply With Quote
Old 02-13-2019, 10:11 AM   #4
Grand Vizier
 
Delfin's Avatar
 
Join Date: Jan 2010
Posts: 3,411
It's real complicated. For example, at 7 knots you'll cover 11 ft/second. For my boat at that speed, I'll cover a boat length every 5 seconds. If the period of the waves is 6 seconds, but the waves are traveling at 3.5 knots (common), which direction they are traveling plus wave height determines the comfort of the ride. If they are nose on, I'm straddling them and pounding. If they are moving away, I'm riding up and down and the motion is just fine. In the first case, waves over 3 ft might be an issue. In the latter they could be 10' and be no issue.

Knowing boat speed, length, wave height, wave speed and direction, you can figure it out for a particular crossing easily enough.
Delfin is offline   Reply With Quote
Old 02-14-2019, 09:20 AM   #5
Senior Member
 
BrianSmith's Avatar
 
City: Wherever Smartini is
Country: USA
Vessel Name: Smartini
Vessel Model: 2002 Kristen 52' Flybridge Trawler
Join Date: Mar 2014
Posts: 345
Quote:
Originally Posted by Delfin View Post
It's real complicated. For example, at 7 knots you'll cover 11 ft/second. For my boat at that speed, I'll cover a boat length every 5 seconds. If the period of the waves is 6 seconds, but the waves are traveling at 3.5 knots (common), which direction they are traveling plus wave height determines the comfort of the ride. If they are nose on, I'm straddling them and pounding. If they are moving away, I'm riding up and down and the motion is just fine. In the first case, waves over 3 ft might be an issue. In the latter they could be 10' and be no issue.

Knowing boat speed, length, wave height, wave speed and direction, you can figure it out for a particular crossing easily enough.
Wow - that seems like a great way to evaluate this! Thanks!
BrianSmith is offline   Reply With Quote
Old 02-14-2019, 04:30 PM   #6
Guru
 
caltexflanc's Avatar
 
City: North Carolina for now
Country: USA
Vessel Name: Small Incentive
Vessel Model: Boston Whaler 130 Sport
Join Date: Aug 2011
Posts: 5,050
Quote:
Originally Posted by djmarchand View Post
When we kept our boat on the west coast and often made the trip to Catalina Island, a forecast of 5-6' seas was our limit. This was on a 34' Mainship Trawler with no stabilizers. I would think you would be fine up to 7'.


YMMV of course.


David
That's with pretty gentle long period swells. Out these parts that's a Small Craft Advisory.
__________________
George

"There's the Right Way, the Wrong Way, and what some guy says he's gotten away with"
caltexflanc is offline   Reply With Quote
Old 02-14-2019, 05:11 PM   #7
Grand Vizier
 
Delfin's Avatar
 
Join Date: Jan 2010
Posts: 3,411
Quote:
Originally Posted by BrianSmith View Post
Wow - that seems like a great way to evaluate this! Thanks!
The route you mentioned, the direction from TCI to PR, wave height and period, makes this look like kind of an uncomfortable ride.
__________________
Delfin
"Dad always thought laughter was the best medicine, which I guess is why several of us died of tuberculosis." - Jack Handy
Delfin is offline   Reply With Quote
Old 02-14-2019, 10:12 PM   #8
Guru
 
Crusty Chief's Avatar
 
City: Las Vegas/West Coast
Country: USA
Vessel Name: Pairadice
Vessel Model: Selene 47
Join Date: Jul 2014
Posts: 1,461
This could get into a rather lengthy and somewhat technical conversation.

As a general rule (I use that term rather loosely) if the duration of the Swell is 2 times the height, I.E. 5 ft at 10 seconds and the wind is not a factor, its a go. Now, when does the wind become a factor? Dont remember if the wind and swell have ever come from the same direction, but if the winds are 10-20 knots and low swells its a fairly comfortable ride. Get over 20 knots and things can change rather quickly, cuz now the wind waves are effecting things.
Since we are not stabilized, an ideal day for traveling south or north is 3ft swell from the west at 12 seconds with 5 knots of wind from just about any direction. Oh, and the sun is out with no clouds and 75 degrees, and the moon is gonna be a full one and bright.
Nice dream right?

Cheers
__________________

Crusty Chief is offline   Reply With Quote
Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

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





All times are GMT -5. The time now is 04:24 AM.


Powered by vBulletin® Version 3.8.8 Beta 4
Copyright ©2000 - 2019, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2006 - 2012