Broward sudden stern swing?

What happened to make it go "almost out of control" in dead calm conditions? Were there any UFOs or strange fog banks nearby? Was the bow still in control when this happened?

Is it possible for you to share your obvious wealth of knowledge without the incessant derision of others?

In that case, why not just ask the guy who was driving? If the boat was "almost out of control" in dead calm conditions surely the bridge team would be a good place to start asking questions.

Very little information was "covered" in your post. Now that you have provided some information, it appears that the seller or his crew said nothing about unusual handling characteristics, none were observed during the sea trial, (if one was performed pre-purchase) and you guys drove it a fair ways across the hemisphere with no problems until entering a channel. At that point the boat went "almost out of control" in "dead calm" conditions for no descernible reason.

At the risk of being accused of being contentious or (heaven forbid) even derisory, has your resident Son of Magellan considered doing a handling trial to find out if his new charge has suddenly developed dangerous characteristics or to see if that little quirk can be duplicated with a following sea? Did anyone notice if the steering system might have contributed to this peculiar behavior? Or if maybe some bright spark pushed a button or twisted a knob to see what it would do? Was it on autopilot, followup or non-followup steering? Lots of possibilities here besides a sudden and rather late onset of poor design.

The simple answer is "Yes", in following, especially quartering sea conditions, they get pushed around quite a bit, and I have been nearly broached in them in relatively small conditions, 6'-8' when making the turn into Marina Del Rey. As you have surmised, it takes a healthy handful of throttle along with the rudder to bail you out due to the small rudders and lack of leverage.

Back in the early 90's there were quite a few boats extended and , although this is 2nd hand, I remember several people telling me that their handling characteristics were ruined as well as other problems such as bad welds and supporting structure. I don't think it takes a genius to figure out that adding 10' to a 100 footer, in effect moving the running gear 10% forward is going to affect handling. From personal experience I can say that the weight of a hydraulic swim platform changes the handling and speed on a 51' Bertram or a 46' Sea Ray for the worse.

I've run quite a few Motoryachts with extensions, including a 103' Broward that had not 1, but 3 stern extensions.

The trick is, you have to keep the stern heavy always. They almost always add another fuel tank in the extension and a water tank also, this is to balance out the extra bouyancy the extension created and trying to keep from moving the center of gravity foward. If the stern is light, the bow will dig in and the stern will swing 90 degrees or more in a following sea. It doesn't help to have your running gear 10' foward of where it should be either. Drain the fuel from the bow first and the stern tank last, this will help immensly by keeping more weight on the stern. even still they don't handle as well as without the extension, but this makes it livable.

If you had any real world experience running a motoryacht with an extension, you'd know that it is the nature of the beast in a following sea or following current and has to do of where the rudders are located and the vessel's pivot point being too far foward, nothing to do with who was at the helm. Although having someone experienced at the helm helps maintain control.

The simple problem is having the weight in the wrong place with a yacht with an extension causing the bow to dig in and the stern to surf in whichever direction it wants.

A swim platform would help add a little more weight back there and probably help the situation (as long as it's out of the water) and as long as it has adequate drainage (slats or such) it shouldn't act like a trim tab.

Having driven tugs, yachts, and my own boats up and down the inside passage between Seattle and SE Alaska I do know how following seas and the strongest currents in the world can effect a boat, extended or otherwise.

Having read the original post, which seems to be ignored by most contributors to this thread, the conditions in which this boat "went almost out of control" were stated to be "dead calm." That says there was no following sea, no strong current. The boat was proceeding along normally as, evidently, it had for the previous few thousand miles without incident.

There is more to this story than the poster has contributed. Either the conditions were not "dead calm" or something else happened. Maybe if he gave the name of the boat a reader with experience driving that boat could ask the right questions. If this boat has a tendency to go "almost out of control" in "dead calm" sea conditions surely someone else has had the pleasure of that experience and would share the story. In the meantime, color me skeptical.

I normally only connect "dead calm" to wind and sea state and not to current, that would be "still water". What all actually happened there is up for bid, but good tidal rips are known for the area.

So, there is more to the story. You never said there was a "nasty cross-current" and the Sons of Magellan, according to you, only said "*6$#@ if I know" which indicates that if there was a current, they were unaware of it. Which brings us to the next statement.

Yes indeed prevention is better than cure. Planning the arrival means knowing the speed and direction of the current. So, if there was a strong current that the SoM did not know about, wouldn't yoou agree that proper planning might have prevented a potentially dangerous situation? That is the prevention side of the equation.

Now you say you are going to see what "remedial action" might be taken when the boat is out of water. Does this mean you are going to shorten the boat aft or lengthen the shafts and relocate the rudders? Why look for a technical solution to an operational failing? If there was a strong current across the inlet then you already know where the problem was located, it was in the wheelhouse.

Do you want to know why I sound so "impolite" about this? Because here is another poster-boat for why owners get out of yachting. Poor planning and perhaps even incompetence is cloaked with the possibility of poor design or some other item that might be fixed with enough of the owner's money.

If there was no current and conditions were indeed calm then as engineer maybe you need to find out if there is a problem with the steering system or the bridge crew's knowledge of how to operate it. Like I keep saying, there is more to this than has been posted.

So if there is more why are you so defensive about sharing the information? You might have had some good leads already if you had provided all the information upfront. Not to mention that your experience might save some other operator a lot of problems in the future.

I have seen on some yachts that I've run with extensions on them, where the builder of the extension put a small keel on the extension part that stuck down about a foot for the length of the extension. This may or may not help and you would need to talk to a naval architect about that. I have also seen where the main keel was lengthened. But keeping the most amount of weight in the stern (ie. fuel and/or water) helps greatly in a following sea or current. I've seen on boat with extensions that a following current exudes a lot more side to side swinging of the stern of the vessel over a following sea. (within reason.)

One also has to know be very familiar of the proper running angle of the vessel they're running with an extension. If you drain too much fuel off the bow, and the fuel in the stern is too heavy it will start slowing you down too. It doesn't take much of an off balance. On that 75' Hatteras 50 gallons too much fuel off the bow once you pass the sweet spot and she really starts slowing down.

In the original post libertyac mentioned "entering Ixtapa inlet". As we all know inlets tend to build swells and generate strong currents except at slack tide even "in dead-calm weather", and even a slight opposing breeze can exacerbate the situation. Not being on the helm he would only see the result and possibly hear the skipper cursing as he fought for control. So from what he said of the handling it was a pretty safe bet they were coming through on the inbound tide with a following current.
BTW libertyac, do NOT mention the name of that boat. It could be a bad career move.

There were quite a few 58 Bertram Motoryachts extended to 68 feet with unchanged running gear. For the few that actually got into conditions (big quartering aft seas, for example) that warranted some extra helsmanship, the recommendation from the NA was to extend the chord of the rudders 6"+ for more lift, i.e., bite during slow speed ops.