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How to steer with a following sea

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kevinmac
Admiral

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USA
732 Posts

Initially Posted - 06/26/2006 : 15:46:15

Arlyn, or some other knowledgeable person out there:

I read a post where Arlyn described "precised helm control" being necessary when running or reaching with a following sea of significant size. I have only experienced this condition once, in a C25, and I just steered the boat to maintain course, which meant a lot of pushing and pulling on the tiller. But I don't know if I was doing it right.

Can someone out there precisely describe the correct helm technique in this sea condition?

Also, I was out in 2' waves yesterday (for the first time) in my boat. These are short period waves in the channel near my marina. As I was sailing into them, the prop would cavitate periodically, and the motor would rev higher. Do I need to mess with reducing throttle when it does this for a second or two? Will it hurt the motor?

Thanks in advance for your help.

Kevin Mackenzie
Former Association Secretary and Commodore
"Dogs Allowed"
'06 C250WK #881
and
"Jasmine"
'01 Maine Cat 30 #34

Edited by - on

John G-
Admiral

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793 Posts

Response Posted - 06/26/2006 : 16:55:31

Kevin,
It's not an easy question to answer in words. Experience at the helm is the best teacher.
I will try to start a conversation that I am sure some will amend, dispute and mostly have more to add to.
Here is a page from [url="http://www.boatus.com/husick/bh_autopilot.asp"]Chuck Husick from Boat US [/url]on auto helms;
 

 “Following seas can rapidly slew the stern of the boat, often at a rate beyond the steering correction ability of the autopilot. A competent human helmsman has the advantage of being able to sense acceleration, the beginning of boat movement that precedes a readily measured change in heading. Experienced helmsmen will constantly and usually unconsciously correct for the impending heading change. The boat maintains a more constant heading and is less likely to roll excessively.”
 

Heading downwind can be the most challenging direction because your boat wants to head upwind. You noticed that you had to work the tiller constantly and that was the right thing to do. Holding the helm over will result in the rudder losing steerage and then you’ll spin up into the wind and broach. Working the nose of the boat back downwind with short and deliberate tugs on the tiller will keep you from rounding up. After awhile you’ll get the hang of it and as you reach the top of a wave a quick tug and you’ll literally be surfing your boat down the face of the waves. Watch the speedo, if you have one, it will zip up a couple of knots in big seas. It’s fun but pay attention, too much and you’ll spin out the other way, a little late and you have a chance of slapping your mast on the surface.
Be carefull and keep you head down.

Underlined words are a HOT link.

Edited by - on

Tom Potter
Master Marine Consultant

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USA
1913 Posts

Response Posted - 06/26/2006 : 17:19:52

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by kevinmac
 Also, I was out in 2' waves yesterday (for the first time) in my boat. These are short period waves in the channel near my marina. As I was sailing into them, the prop would cavitate periodically, and the motor would rev higher. Do I need to mess with reducing throttle when it does this for a second or two? Will it hurt the motor?<hr height="1" noshade id="quote"></blockquote id="quote">

Kevin,
Last November I went on a cruise with Fleet25 in Jacksonville Fla. on a trip to Cumberland Island,Ga. It's there that I had a problem with my prop coming out the water. I have (had) a 8hp long shaft and knew all along that the motor was not down in the water far enough. It worked well on the lake but once I got in some seas and with a good wind blowing on the starboard the motor spent more time out the water than in. When I got back from the trip I contacted Tohatsu and bought a lower unit extension kit that extended my (motors)

lower unit another 5 inches.
All that being said, running you motor out of the water is not good for your water pump impeller. But... I wouldn't cancel my trip for that. If you get in a situation where you start cavitating a lot, shift your crew aft and to the starboard and have fun. If that don't work cut the motor and raise the sails!

Edited by - Tom Potter on 06/26/2006 17:25:25

kevinmac
Admiral

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USA
732 Posts

Response Posted - 06/26/2006 : 17:40:36

Thanks Tom. Actually, I already HAVE an extra long shaft. Still cavitates on these steep, short period waves... Sigh.

Cancel my trip? NO WAY! I am counting the minutes until I leave...

Edited by - on

Tom Potter
Master Marine Consultant

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USA
1913 Posts

Response Posted - 06/26/2006 : 18:10:36

Kevin, Drink plenty of water and charge you camera batterys cause we want pictures. (of your trip too)

Edited by - Tom Potter on 06/26/2006 18:12:05

kevinmac
Admiral

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USA
732 Posts

Response Posted - 06/26/2006 : 19:30:52

Aye Sir! -Kevin

Edited by - on

atgep
Master Marine Consultant

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1009 Posts

Response Posted - 06/26/2006 : 22:29:39

Kevin, are you leaving the Everett area? I am up in Whidbey island. A nice place to stop over would be Coupeville. They have a great floating dock and fine resturants. Let me know if you are heading up this way.

Tom.

Edited by - on

Russ.Johnson
Commodore

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USA
855 Posts

Response Posted - 06/27/2006 : 01:12:17

Kevin,
I'm no expert and I'd like to hear what others have to say.
Here's what I've experienced.
Let's say the following seas are 20 degrees to port.
If you don't want to run dead downwind, the best solution is a short zig-zag course.
When the boat is rising, turn with the swell.
When the boat is falling, turn across the swell.

There are 2 factors to be aware of.
1) The swell hits the stern first and wants to push it to starboard.
2) Sometimes, the swell is actually moving faster than your boat, so the rudder works in reverse.

The first part is easy. The second part takes practice.
When the swell starts to lift the stern, the boat speed and water speed will be the same.
Just for an instant, the rudder will go dead and you will feel the resistance slack.
As the stern lifts more the swell is moving faster than the boat.
Quickly push the rudder to starboard (this is the opposite of what you feel is right).
The bow should correctly turn with the swell.
When the stern is halfway up the swell and boat is surfing, straighten the rudder.
When the boat is at the top of the swell quickly push the tiller to starboard.
The bow should correctly turn across the swell.
Then get ready to do it all again.
Turning with the swell then across the swell will average out your heading to where you want to be.

When I say turn quickly, I don't mean push hard and all the way.
The bigger the swell the harder and wider you have to turn.
There is a lot more tiller movement than you think.
In 2 foot swells, there will be a lot of quick but short movement.

I'd like to hear what others have to say.

By the way, I can only use my outboard inside the marina.
If someone is at the mast raising the main, my outboard will cavitate at the slightest wake.
I usually sit on the starboard side and raise on a port tack.
Once the main is up, I cut the outboard.

Russ (C250WB #793)

Edited by - Russ.Johnson on 06/27/2006 01:14:43

Arlyn Stewart
Master Marine Consultant

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2980 Posts

Response Posted - 06/27/2006 : 07:33:57

Kevin,

Most sailboats are tougher to helm to a quartering sea (a sea off one of the stern quarters). There are two dynamics that added together, cause the difficulty. 1. There is side impact of the sea upon the rudder as it rolls under the boat. 2. As the sea rolls forward, it cancels out the aft flow over the rudder and thereby momentarily stalls it (kills the lift that gives the rudder control).

With the rudder stalling at the same time as the side impact, the boat is yawed to windward several degrees then requiring a turn back on course once the rudder regains lift. Each yaw can be the precurser of a broach... all it takes is a little extra momentum to yaw the boat enough to bring her beam on the wind with sails full for an offwind course.

Boats like the c250 with a large rudder are more suceptable, the impact is greater and the need for control is greater.

Fortunately, there is a solution as the other answers point out. I personally call it anticipatory helming because if one waits to give a rudder movment to correct the course after the boat starts yawing... its too late... the yaw force has had its way, the rudder is stalled and the helm movement produces no immediate response but must wait until lift is regained.

The challenge is to time a helm adjustment prior to any yaw for the reason of vaning the rudder to the sea at the moment of impact. Doing that places the aft rudder edge to the sea rather than the flat surface and thereby eliminates the yaw force at the moment of stall. This helm adjustment timing is critical, because given too early before the rudder stalls, it will of course cause a course change to leeward and if given to late will have allowed the side impact.

While one could watch each sea roll under and throw the helm leeward (vane it to the sea) as the sea rolls under, a good helmsperson gains a feel and timing of when to throw and when to bring back to course. When done well, the boat remains on course and suffers no yaw.

For me, timing offers the best method of when to throw, and feel offers the best method of when to return the helm to course. As John points out the timing has to do with the boat pitch as it tells where the boat is with the seas. The feel comes from knowing that the rudder when thrown is stalled and that if left there, it will alter the course of the boat when lift is regained... so it is eased back as lift is felt in the rudder to avoid heading off to leeward.

If the boat is allowed to yaw, then the sails come into play. The main then contributes to the yaw effect and a potential broach. The headsail has a steadying effect and if conditions warrant only one sail, the headsail is preferred, albeit boat speed should be kept below hull speed to avoid overloading the forestay.

The challenge over a long day on such a course is that the sheer number of anticipatory helm movements will result in some failures because of lack of attention or strangeness of wave action.

For this reason, some cruisers like to steady the yaw effect of a quartering sea by running warps (lines trailed off of stern cleats) as a way of gaining helming forgivness or allowing the autopilot to helm these difficult courses.

Edited by - Arlyn Stewart on 06/27/2006 07:41:00

kevinmac
Admiral

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USA
732 Posts

Response Posted - 06/27/2006 : 09:39:34

Tom,

How far is Coupeville from Everett? If it is a half day's sail, we will likely come up on Monday, the 10th, weather permitting. That is the only day my friend and crew has the entire day free, on the other days I will be sailing with him in the mid-afternoon, and sometimes sailing in morning with other friends and family who live in Seattle.

Russ and Arlyn,

Thanks very much for the explanation, that makes it very clear to me. A follow up question about broaching: What is the risk to a broach for our boats, i.e. if I blow it and end up beam to the wind, I can see getting heeled over pretty good. In our boat, is there risk of getting the boom in the water, and if so, what happens then? I know, I'm not very smart about this stuff, that is why I am asking. All my sailing experience is in dinghies, and I KNOW what happens when you broach a dinghy - the water start rushing into the boat because of low freeboard, and you get dunked. What happens in a C250?

Thanks in advance for you help.

Edited by - on

Arlyn Stewart
Master Marine Consultant

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2980 Posts

Response Posted - 06/27/2006 : 12:22:17

A broach on a 250 isn't a big deal, it will round on up rather than lay beam on the wind and the weight issue is not severe.

A heavily ballasted boat when broaching will inflict very serious loads on the rigging when broached. On those boats, a broach can quickly blow out a weak sail and turn a good sail into a baggy sail that won't sail fast in a good breese. The 250 will forgive a broach as long as nothing untoward happens when it rounds up [ie] one doesn't run over the windward boat in a race.

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kevinmac
Admiral

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USA
732 Posts

Response Posted - 06/27/2006 : 23:06:38

Thanks! -Kevin

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Russ.Johnson
Commodore

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USA
855 Posts

Response Posted - 06/28/2006 : 11:44:33

Arlyn,
Thank you for the clarification.
I knew that when the rudder stalls to throw the helm to leeward.
I had not considered the side impact on the rudder was one of the causes for the yaw.
I understand the forces better and maybe I won't have to zig-zag so much.
Thanks, Russ (#793)

Edited by - on

crystal_blue
1st Mate

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USA
71 Posts

Response Posted - 07/19/2006 : 14:02:59

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by Arlyn Stewart
 On those boats, a broach can quickly blow out a weak sail and turn a good sail into a baggy sail that won't sail fast in a good breese. The 250 will forgive a broach as long as nothing untoward happens when it rounds up [ie] one doesn't run over the windward boat in a race.
<hr height="1" noshade id="quote"></blockquote id="quote">

As a newbie here, I'd like to ask what I'm sure is a rather elementary question:

What, exactly, does it mean to "blow out" a sail? Does it involve the sail completely coming apart, or just being stretched out of shape?

Thanks.

--Jim

Edited by - on

Bay Tripper
1st Mate

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USA
56 Posts

Response Posted - 07/19/2006 : 19:26:10

The sail completely comes apart.

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crystal_blue
1st Mate

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Response Posted - 07/20/2006 : 09:50:57

Thanks, Dick.

--Jim

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