Single Screw Handling in Following Seas

Apollo32 · 10-23-2017, 12:00 PM

I was curious how everyone else's rig handles in following seas. I do my best to stay on the backside of a wave in following seas, matching the speed, etc., but I swear to King Neptune that my boat will swap ends in even a 2 foot wave in following seas, if I somehow screw up the speed and get on the front side of a wave. Obviously staying on the back side of the wave is the only way to cruise in following seas, but I was quite alarmed to lose control of a 32 foot boat on the front side of a 2 to 2.5 foot wave the other day. While on the front side of this wave, the bow went to port, and with rudder to full starboard, the bow kept going to port until the boat had turned 180 degrees. Of course the boat handled like a champ after swapping ends, so I just slowed down a little bit, turned on the wiper and went home to boat another day. It wasn't significant emotional event but not understanding what happened was of the most concern. I am assuming I may have handled the throttle improperly to get myself on the front side of the wave to begin with. The winds were also 15 knots up the stern at the time as well. Just looking for a little constructive criticism, please and thank you. We have had a great season aboard the Sean P, putting 300 hours on the hour meter, entertaining many a guest, and look forward to many more adventures.

O C Diver · 10-23-2017, 12:20 PM

Some boats handle following seas better than others. My 35' downeaster charter boat doesn't like them at all on plane going over the crest. An auto pilot can only react to change, it can't anticipate which way the bow will fall off, so it has to respond which is often to late. Better for me to hand steer that boat in bigger following seas.

Ted

Nomad Willy · 10-23-2017, 12:21 PM

Sounds like a boat design problem or ballast/trim.

If that’s the nature of the Apollo 32 you can confirm by talking to other owners.

If it’s a trim problem it gets more difficult .. but happily fixable. If your boat is a twin IO you may have too much weight aft. But for following seas a bit of extra weight aft would probably be better than fwd. if you can experiment by shifting moveable weights do that first.

If you have an inboard engine the problem may likely be rudder/s too small. That may be easy to fix w a bit of welding but if adding to your rudder consider the structural limits of the rudder components like the control horn.

sunchaser · 10-23-2017, 12:22 PM

You'll get a ton of suggestions. Too small a rudder, not enough RPM, poor design etc. Being a single engine vessel has nothing to do with it.

Until you get it figured out if ever, boat in the conditions that swapping ends is 100% avoided. Go to Chapman and look up the term broach.

Wxx3 · 10-23-2017, 12:23 PM

It's more a function of your hull shape and stern in particular.

You can see how the KK42 handles following seas is you check out the videos I've posted on Smugmug.

The link is posted on my last blog post and the gallery is
Dauntless crosses the Atlantic again
Or something like that.

Richard on Dauntless

Apollo32 · 10-23-2017, 12:29 PM

I've always felt that the rudder was too small. The boat handles fine in glassy waters, but its really hands on with a wave height of 2 feet or more. I had the boat hauled this spring and asked about a new rudder, to which the guy at the boat yard told me that the current sized rudder was optimal for the length and weight of the boat. If there are any other single screw Apollo 32 owners out there that can chime in, I'd appreciate it... There's not too many of these boats in North America. Thanks for the replies. I am starting to just think its a design limitation of the vessel and there's nothing I can do about it, but am hoping to find out otherwise.

Apollo32 · 10-23-2017, 12:33 PM

Quote:

Originally Posted by sunchaser

You'll get a ton of suggestions. Too small a rudder, not enough RPM, poor design etc. Being a single engine vessel has nothing to do with it.

Until you get it figured out if ever, boat in the conditions that swapping ends is 100% avoided. Go to Chapman and look up the term broach.

Avoidance is indeed key, I agree 100%. I don't push my luck on the Sean P, but pose the question to this wealth of experience to see if there's a solution to the problem. If that solution is boat related, great. If its due to my own mishandling of the vessel, I say even better! Learning is free. new rudders and other things of this nature aren't

thanks for the advice.

Ski in NC · 10-23-2017, 01:31 PM

My single can be a handful in following seas at low speed. Usually adding some power improves it greatly, even though the speed might not be the most efficient. You might try a little more power. Makes the rudder much more effective.

boathealer · 10-23-2017, 01:36 PM

Quote:

Originally Posted by Ski in NC

My single can be a handful in following seas at low speed. Usually adding some power improves it greatly, even though the speed might not be the most efficient. You might try a little more power. Makes the rudder much more effective.

+1

If there is no forward flow of water over the rudder, then it will have no effect no matter which way you turn it. If the following sea's water flow is moving faster than your boat from abaft, then IT will have control of the boat based on your rudder position, not you.

As matter of fact, if you envision your rudder hard over as you describe above, trying to counter the broach, and the following sea flow hitting it from aft, it could actually speed up your broach/180. Powering up would create flow past the rudder in the other (desired) direction and give you back control of the boat.

JMHO.

Nomad Willy · 10-23-2017, 02:38 PM

I doubt if adding 2” or so to the trailing edge of the rudder would effect drag noticably. The rudders on boat capable of 15 to 20 are kept small to keep drag low at those higher speeds but at low speeds bigger rudders are golden.
Prop walk could be causing more trouble depending on how you lay to the following seas. In other words it could aggravate the situation w the sea to port and help you go straight w the sea to stbd.

Lepke · 10-23-2017, 03:01 PM

I've handled many boats and ships, twins, singles some twins with single rudder. The longer the boat, the better it handles in a following sea. But longer boats don't pivot as well as short boats. Boats built for above hull speed usually have small rudders for the boat size to reduce drag. Every boat is a compromise.
My boat was built for double hull speed and has small rudders. It doesn't hold a course as well in some conditions. In a following sea the autopilot struggles. Next haulout I plan on measuring the rudders for replacement. I run below hull speed and the drag won't effect cruising speed in any meaningful way.

**Shrew** · 10-23-2017, 03:19 PM

How fast were you actually going when this occurred? In following and quartering seas my stern gets pushed around a lot. I posted on it earlier this year asking a similar question.

I've found a lot has to done with anticipation. start turning earlier when the stern starts coming around. you'll find you may need to start straightening back out earlier as well or oversteering starts to make the issue worse.

In some cases I need to give it a little throttle if I end up hitting the steering locks.

AusCan · 10-23-2017, 03:20 PM

There is a lot of variation in a boat's ability in following seas. Hull shape is the key, and it's tough to change that. A rounded shallow stern and a long pronounced keel may be the best design for good handling in following seas.
With a full displacement boat, `I don't have the option of keeping up with passing waves but the canoe stern design handles following seas fairly well up to about 8 feet even on autopilot. If the waves get steep and start breaking, then it time to get out of there..

With a semi displacement boat and a flat transom, you don't have the best hull shape to allow waves to pass under the boat. I'd suggest using a bit more speed. With a 2 or 3 or 4 foot wave, traveling a bit faster than the the wave set shouldn't be a problem, and you would stay in control with water flowing nicely over your rudder.

Al · 10-23-2017, 07:12 PM

Quote:

Originally Posted by Shrew

How fast were you actually going when this occurred? In following and quartering seas my stern gets pushed around a lot. I posted on it earlier this year asking a similar question.

I've found a lot has to done with anticipation. start turning earlier when the stern starts coming around. you'll find you may need to start straightening back out earlier as well or oversteering starts to make the issue worse.

In some cases I need to give it a little throttle if I end up hitting the steering locks.

To this point, Shrew has provided the more sensible study. "Anticipation", or commonly called, "flying by the seat of your pants". Human reactions SHOULD be giving you an anticipated motion early enough that you are counter moving to that motion reversing the action prior to the reversal of what you set up for.
Erik's mention of ballast shifting holds merit.One of the tricks I used when placing my movable ballast (50# ingots) was to place two of these in a 5 gallon bucket and move them about in a 2 foot following sea to determine the more comfortable location for placing the ingots below deck under the area determined with the bucket location.

When this operation was completed, I retained two ingots (3"X 6"X 12") with farm gate handles bolted on allowing easy lift and moving. These are in mode to adjust for people weight underway. Heavy person to the Port, shift one or both to the Starboard or vise versa. At anchor or slow moving, they are most likely centerboard aft in the cockpit. No, they are not really underfoot, as there are locations under area of the salon that do not interfere. With a 28 foot boat, human weight location can be uncomfortable. These movable ingots serve well. As to the following sea issue, our boat now rides following seas in a very controllable way. I agree, the auto pilot is off to utilize the 'anticipated' rudder action.

Al-Ketchikan

CDreamer · 10-23-2017, 09:30 PM

I can attest to Richard's comment above - the KK42 is a single and handles following seas very well. Soft chines, heavy full displacement, rounded transom/underbody, significant keel. But it was designed for long passages and ocean conditions, much different boat.

I believe your max speed is around 12 knots.? Short of simply staying home, you may keep control in 2-3 ft following seas by slowing down to 6...let the waves pass under more quickly. Or you could try "zig zagging" somewhat in those conditions and see how things go. Trial and error.

By the way, 7 knots is about hull speed on the Kadey.

CDreamer · 10-23-2017, 09:35 PM

Just to add: Ski maybe correct about speeding up. Hulls have such different characteristics, it's hard to tell.

Lou_tribal · 10-23-2017, 09:48 PM

I am far from an expert but I find surprising to see such an effect with 2 feet waves.
I cannot testimony for following seas per say as I am in fresh water inland waterways and lakes but in following +2 feet waves it was not such a drama. I really wonder what caused this.

L

C lectric · 10-24-2017, 12:29 AM

I too have a 32' vessel.

I'll add , use the throttle. I try to stay below the wave speed so they pass under me. If you get on a wave top you can lose control. If you get pushed from behind you can lose control.

My boat won't plane, has a squared off transom, so it gets pushed. I do have a fairly large rudder so that helps.
But I've learned to let the waves pass under and not travel at to close to the passing waves speed. If the wave and boat speed are to close there is more chance of getting pushed.
In larger stuff where cranking the wheel is becoming less effective too often I use the throttle. A sharp burst of power will shove a big shot of water past the rudder and will smarten the boat right up gaining control.

It's a sharp, short burst of power. You do not want to pick up any appreciable speed.
Then get off the power and back to the previous speed.
Try different speeds in varying conditions as the boat may react better with different speeds.

SoWhat · 10-24-2017, 12:54 AM

Difficult to stay exactly on the back side of a wave with a semi-displacement hull unless you have a lot of spare hp. SHape of the stern isn't ideal but should be able to handle 2 footers on the stern without a broach.

Check steering turns to turns. Maybe yours is slow to react.
Check slop or responsiveness in wheel. On a calm day move the wheel an inch at a time. Should see a consistent number of degrees in the compass.

GFC · 10-24-2017, 01:04 AM

Every had one of those AHA moments? I did today after reading through this thread. It got me thinking about a trip we were on in June, 2016 where we ran into some big waves on the Columbia. I had a thread about our experiences here: http://www.trawlerforum.com/forums/s...lor-26868.html

What I wondered about was why, after we had turned around and had the big waves on our stern, the boat did not display any of the characteristic "wave pushing on the stern causing the bow to swing to one side or another" that can lead to a broach.

So I looked at some of the pics I had taken when we were getting the boat ready for shipping out west. I found this picture and enlarged it. It shows how the stern is not flat but rather slopes downward. There isn't a flat surface for a wave to push against until it gets below the water level (shown on the picture with the arrow) and at that it's only a few inches tall. Not much there to push against so nothing to cause the boat to broach.

So there's my AHA moment. Thanks guys!