Following Seas

I've been reading posts where folks encounter rough rides due to following seas causing broaching. My question (maybe silly) is " how fast are following seas? I ask this because we are considering a single screw 40 ft, 30k pound semi displacement boat. If we get a big enough engine where I could (when needed) run at 12 to 14 knots would this be enough speed to make the ride safe in typical following seas? If not, I'll save $$ and get the smaller engine and just try to avoid these situations.

Running ahead of the seas isn't always the answer. In fact I find that slowing down tends to give a better ride in many cases.

You bring up a good point. Certain boats are able to sit on the back of a swell and ride it, but that’s highly variable and requires constant adjusting. 10-15kts is probably a good rule of thumb, beyond many traditional trawlers. I admit my boat really struggles in following seas, and I’m jealous of those that have the option of accelerating. But that’s rare and not sure it’s worthwhile on its own.

Commercial fishing, I once made good 22 knots in following seas while making turns for 7 knots over many hours. I had to hand steer to avoid broaching. That boat could do 14 knots max, but wouldn't have made a difference and might have made control worse as the swell passed underneath. As it was, props sucked air as the wave top passed. I don't know the height because it was at night. I guess 20-30 feet. I could see white water going down the sides from the glow of the side lights as the swell passed. That was a 55', twin screw boat. The conditions weren't unique but the results of strong winds far away as I was traveling south along the Oregon and Northern Cal coasts about 50 miles out.

Keep in mind the speed of the waves increases with the height. So getting a good boat speed to ride them well depends on how high they are.

I've run a bunch of different boats offshore, and some were miserable in certain following seas. But between changing power setting and/or course, there was always a way to make it tolerable. Never did I wish I had lots more hp.

I suspect this may be a Downeast boat?.... Don't buy into the hype of some are bad in following seas... Some are but the reality is ,if your not going to the canyons, the times you'll spend dealing with this is minimal..Nice having a cockpit

It is not necessarily a speed issue. In open water there is going to be a comfortable speed where the boat is not wallowing or slamming. It then becomes a matter of anticipation. Turning the bow slightly just before the following wave wants to yaw the boat. It can be a long exhausting manual steering day but at some point the anticipation process becomes almost automatic. When the waves are beyond anticipation you will have to adopt sailing techniques and tack to your destination.

Coming into an inlet is a different story. A CC with twin 150's may be able to stay on the back of a wave. But waves change speed and it takes a nimble responsive boat to stay situated. Trawlers are slow and not as responsive so speed isn't going to help you. At some point the waves will start breaking and that's where broaching will happen. It requires anticipation and quick wheel response. A trawler simply doesn't have the speed to stay on the wave. Sit out and read the wave grouping before entering the inlet. You will know when it's go time. Then it's just stay on the wheel. And try to avoid coming in on ebb tides.

All good comments. SoWhat - on the ebb tide, why is it bad to come in on ebb tides? On my planing boat I rarely worry about tides even though I draft 42 inches other than to worry about grounding. Granted my current boat weigh 8k pounds and can reach see speeds of 40mph +.

Mark P said:

All good comments. SoWhat - on the ebb tide, why is it bad to come in on ebb tides? On my planing boat I rarely worry about tides even though I draft 42 inches other than to worry about grounding. Granted my current boat weigh 8k pounds and can reach see speeds of 40mph +.

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Mark many inlets, especially on the Florida East Coast, can get pretty nasty when there is an Easterly blow against an ebb tide. We have had a couple of interesting entrances at Fort Pierce and one going out of Mayport.

Mark P said:

40mph ?????.

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You won't have to worry about ebb tides. I'd be more worried about speed limits

It isn’t about speed or power. And waves come at many speeds.

But being able to deal w those seas gracefully requires a good hull shape whereas the stern very much resembles the bow. Having a good CG and weight distribution ... not too heavy at either end. And of course a big rudder that’s fast enough to swing back and forth as fast as the waves pass under the boat. But there’s only a few boats that fit the above. Full Displacement boats. Less than 10% on TF I feel quite sure.

There are issues involved in making a bigger rudder for SD boats so few do. However I feel a bigger rudder is an excellent choice and as long as it’s up to the much larger loads I’d feel comfortable it. Articulated rudders and other similar rudders can even be better.

Another good upgrade for better following sea conditions is to insure the boat is balanced both fore and aft .. port and stbd. If too heavy at one end IMO it’s better to have the heavy end aft. Judging from viewing past TF pictures of members boats underway it appears that being bow heavy and bow down isn’t all that uncommon. Not surprising as that’s the pointy end that provides far less floatation but many boats have engines further fwd than the center of the boat. Heavy equipment and tanks for fluids should be placed to counteract the weight of engines in an undesirable place.

Many other elements to consider such as windage and vertical CG.

When a substantial tidal flow in a relatively shallow inlet opposes a significant wind, water flow, breaking waves, and waves with no back side can get really hairy. Then throw in some sand bars for good measure. Spent several weeks each summer for 30+ years running out of Hatteras inlet. Every year the inlet changed. Visualize coming in with 2 to 3' waves and going through the inlet blind on the back of 10 to 12' waves, using a loran for navigation. Imagine channel markers being pull through the waves. Then there were the days you waited in the Ocean for the tide to change because the waves were coming at you.

Unfortunately, inlets of this description tend to be unique. Often it's best to follow a local you trust or wait out the tide.

If you're going to ride the backsides of waves, 15 to 20 knots of speed would be my recommendation. My boat does reasonably well at 7 knots with the waves going under the stern. A BIG rudder helps a lot. Autopilot gets a workout in those conditions. Fun to watch a round stern or a wine glass like a KK42 have the waves go underneath the stern. Almost looks effortless to keep the boat on course.

Ted

Problem with the wine glass sterns is that my aft cabin would be so small that it would be unusable...

Where we keep our boat (The Merrimack River in Massachusetts) is one of the worst inlets on the US east coast. It's fine unless there is a strong easterly swell against a strong outgoing tide. You learn how to deal with it, but lots of speed is never the answer. At most, you need enough speed to ride the back of a wave in. That is about 12-14 knots. Going out against the waves the best speed is usually even slower.

Ken

Just try transiting, in the protected inland waters of the San Francisco estuary, eastern Suisun Bay opposing a strong ebb tide opposing an opposite wind creating steep five-foot waves. Had to cut boat speed, but water spray was higher than pilothouse and also broke the mirror in the forward cabin.

kchace said:

Where we keep our boat (The Merrimack River in Massachusetts) is one of the worst inlets on the US east coast. It's fine unless there is a strong easterly swell against a strong outgoing tide. You learn how to deal with it, but lots of speed is never the answer. At most, you need enough speed to ride the back of a wave in. That is about 12-14 knots. Going out against the waves the best speed is usually even slower.

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Lived in Newburyport for many years. Learned to navigate the Merrimack by trial and error. Seas look flat coming in against a setting sun that has you squinting as hard as you can. Then all of a sudden you are in a maelstrom of breaking waves. USCG frequently stations a boat just inside the inlet.

In those days I had enough power to get up on the wave. Now have a trawler (aka water plow) and there is no power so it's either wheel work or stay out until slack tide. Often the better choice.

Note that by wheel work I don't mean steering a steady course within the inlet channel. Following seas aren't usually directly perpendicular to your stern. If the waves are predominantly hitting your port stern and pushing your bow over then a correction to stbd ahead of time and correcting as the wave passes to stay centered will prevent a broach. A rule of thumb is a wave height half the length of your boat will broach it so wait until slack.

When crossing a bar the more depth you can have the better. If the depth is 15' and the swell is 10' the bottom of the trough is just 5' if your boat is horizontal. I had a commercial fishing friend that pitchpoled on the Eureka Bar coming in. The bow slightly contacted the bottom and the incoming swell lifted the stern over the bow. The swells pushed him into the harbor and the boat didn't sink, but the mast and most of the topside gear was gone. The boat was pointing in the opposite direction when it righted itself. Boat was a heavy 40' wood troller, with a Detroit, about a 6' draft. The entrance channel is dredged to 30-35' and I don't remember the tide details.
Worst crossing I ever had was SF where there really isn't a bar. 55' boat. I went at exactly the wrong time and tide and hit a series of big, close together waves, probably 20'+. Wheelhouse was about 20' back from the bow and I buried the bow 3 times with solid sea over the flying bridge. Outside the windows was just solid green water. Scared the s... out of my then wife. Ocean outside was 5-15', calm for there.

Sandpiper is 40' LOA , 37' LWL, 13 beam, full displacement, 120 Lehman, cruise 8 knot

We prefer following seas to beam or head on. We maintain 8 knots and the autopilot keeps us on a relative straight course. The hull is wineglass shaped with minimal transom under water. The rudder is airfoil shaped which is more effective than a flat plate rudder on a single.

I'm talking about inland waters, not the open ocean or river inlets.

I have observed a large wake may cause a following sea to break.

menzies said:

Running ahead of the seas isn't always the answer. In fact I find that slowing down tends to give a better ride in many cases.

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My experience is just the opposite! Sometimes, putting a little more coal on the fire (speed) results in a much more comfortable and manageable ride. As the seas get higher, I prefer riding the back of the wave. I prefer larger engines that give me the option to adjust to the seaway. On calm days, I travel at trawler speeds to save fuel and enjoy the sea.

menzies said:

Running ahead of the seas isn't always the answer. In fact I find that slowing down tends to give a better ride in many cases.

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This is true. You are being pushed by energy and water flow. This is not a constant. It can speed up and slow down. If you push your boat in an attempt to stay on the backside of a sea, it is almost impossible to stay there. Now you have on your hands a fast moving boat with lots of momentum. When the bow gets pushed and the forefoot digs in , broaching is very possible.
If you slow down so that every wave goes under you, yes your boat will yaw but broaching is less likely. In addition avoid correcting the steering on every heading change. Just let the boat do it’s thing with small rudder input

We were coming down the west coast about 3 AM heading into Monterrey and had a following sea that would push us up to over 14 knots. When it passed us by we would slow down to under 6 knots. This went on for about 4 hours. We just bought the boat and were delivering it from Tulalip, WA to LA so we had not installed an auto pilot yet. It took lots and lots of steering to keep us on any semblance of our course. That boat would top out at about 12.5 knots under calm conditions yet we constantly hit over 14 knots with the following seas.

Every boat and sea is different in my 40+ years of experience I have found the slower you are moving the better. As long as you keep enough speed to keep from taking water over the stern. There is a BIG difference on waves and swells also.

I read somewhere, and it seems to be true, that in open ocean the speed at which swell waves propagate is equal to 1.5 times the swell period, in seconds. I don't think it is true that bigger waves go faster (it is just a matter of period), and for any given wave size, a shorter period requires more energy. So, if anything, bigger waves travel more slowly.

I remember reading in the forum I think not too long ago..... where someone posted that wave steepness is usually the key and when you should worry about wave height compared to boat freeboard.

At what point would you use a sea anchor or dredge?

Sea anchors are generally used off the bow and are not used to prevent broaching, they are meant to "hold" your position and bow to the waves or nearly so....often to avoid a lee shore.


Drogues are used mostly astern to slow you and control direction.


I would use a drogue when things are getting bad and expected to get worse....but not so bad that running with the waves is preferable to having them break on the bow....just too many variables to say when is appropriate.

Taras said:

At what point would you use a sea anchor or dredge?

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When I have lost my engines in running seas. Never when I have power.

Taras said:

At what point would you use a sea anchor or dredge?

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When its late in the day and I am on good fishing 30nm from an anchorage and want to fish it again at grey light, but don't want to run in circles or bob around like a cork all night.

I have one of the slower boats. Riding a wave back is not an option. I slow down so the wave passes under me causing minimal boat acceleration.

If the boat speed is still to close to the wave speed you may get pushed sliding down the wave front which you want to avoid. That may result in the bow digging in to the back of the wave in front causing a broach.

A quick hand on the wheel sometimes still isn't enough so a hand on the throttle may be needed. If the boat is heading for a serious yaw to broach then a fast, sharp throttle blip can often get the boat to pay attention and get to where I want it, in line with wave front or at least where I want it to go.

You are not trying to gain speed, just regain control by stopping the yaw, by shooting a whole lot of prop driven water past the rudder. Just get off the throttle as the boat gets back under control.