Looks like a Mac capsized in RI

[DaveB]

I might add one other, the ballest was half filled why the boat wanted to lay on it's side.
Dave

Let's see..... what we seem to have here is a MacX, with the front hatch wide open while under way, no center board down, and no water ballast.

If any or all of this is the case, then...

Root cause: Failure to RTFM.

*sigh*

Well, I'm glad to hear everyone was OK. Let's hope that they were at least wearing personal floatation devices. And that they all learned something.

[John McDonough]

Another theory is that he may have been motoring with the sails up, the centerboard down and was gradually increasing speed, which could of caused the unballasted boat to capsize.

The first time I took my new 26X out (summer 2000) I was motoring full speed on plane riding with 3` swells and light wind. Suddenly the boat started to sway out of controll. I immediatly cut back the throttle. I would slowly build up speed and as the boat started to plane it would sway back and forth. I motored slowly into a safe anchorage and dropped anchor for the night. I noticed the boat was not swinging at anchor, and seemed like the centerboard was stuck. I checked the centerboard rope and it was locked in the up position. Then I heard something banging below the boat. . Anchored in only 3` of water I jumped into the water to check. I relized that the Centerboard was down, and as the boat drifted backwards I was stuck in the sand. The next morning when I could see, I discovered that the end of the centerboard rope had no holding knot. I put the rope thru the hole and tied a knot. I then started motoring at full speed with no problem.

IF you read your owners manual.. It warns us not to motor over 6 knots with the centerboard down, or you risk Capsize. There is also a warning not to Motor fast with the Sails up..

So I go on record as predicting that this Capsize was caused by motoring too fast with the Sails up and centerboard down. A lot of people so not read thier Manuals..

[Don T]

Hello,
Those 2 pics (UK and US) of the boats on their side IMHO shows the ballast was full. When the cabin takes on water and the ballast is empty the boat rolls further over because the tank is buoyant. The US capsize pic has the boat low in the water with the mast horizontal. Even with ballast in, the boat has very little righting moment with water in the cabin. Any water ballast mass is almost completely equalized by water in the cabin centering itself over the buoyancy. Lead on the other hand has a higher density so water centering itself in the cabin cannot equal the mass of lead off center. In other words, any volume of lead has much more weight than an equal volume of water hence it retains righting moment although reduced. Had the sails been released, hatches closed and cabin pumped, the boat would have righted itself. It may have righted, with a little help, with just the sails released because the buoyancy of the foam flotation is way off center but the effect would reduce greatly as it rolled upright. It's one of those things I'd like to test but I'm unwilling to get my boat wet on the inside and do damage to all my stuff. Wouldn't those numbers help you stay safe and push her to the limit?

Glad my feet are dry says I, the armchair hind-sighted diagnostician.

On edit: I braved another look at SA and there is a thread over there about a J120 that sank participating in the Baha ha ha. They sound very sympathetic, empathetic, civil. Still no activity on the latest Mac episode.

[MD Dunaway]

I think the tank was partially filled. Just enough air in the tank to keep the boat from being righted. . Image C shows a partially filled ballast tank and a swamped cabin. The tank should by its own buoyancy keep the boat on its side. Image A and B show a partially filled ballast tank in the upright and heeled positions. Image D shows a fully buoyant ballast tank. I think even a partially filled tank would prevent the boat from being righted once the cabin was flooded. Once I got to thinking about this it was quite interesting. While water ballasting is effective and allows a boat to be of a more reasonable weight for transport it is not without its drawbacks. The tank on the S is 150 gallon. That is a lot of buoyancy. Four 55 gallon air filled drums will float a small dock!

[Duane Dunn, Allegro]

I think this very clearly shows the ballast was full or partially full, and something else caused the roll that then flooded the cabin. Powering at higher speeds with the board down could very easily be the cause. The rolling this induces is very tricky. You can go for quite a distance with no ill effects and then all the sudden something in the flow of the water over the board becomes unbalanced and the boat snap rolls. Caught off guard with the forward hatch open you could have flooding. Throw in a partially filled tank and you could very well go over and not come back.

As posted above the boat floats very high when rolled with an empty, sealed, air filled tank. In effect there is a giant life preserver attached to the bottom of the boat when you have an empty tank.

The simple truth about our water ballast is it has no righting movement at all until it is lifted above the surface of the water. A container of water submerged weighs nothing, it is neutrally buoyant (excluding the weight of the container itself). This is why our boats are tender at first even with ballast full. Until you heel far enough to lift the tank of water above the surface of the surrounding water you have no extra weight producing any righting movement.

Yes, some will argue the water in the tank does have weight as evidenced by the lower waterline height when the tank is full, but that is a false argument. The boat sinks lower with a full tank because the effective outside of the hull has shifted from the exterior hull skin to the inside wall of the tank which has less surface area and can't support the raw weight of the boat itself as high in the water.

[MD Dunaway]

Yea. It would appear that even a fully filled tank would have little effect to right the boat when the cabin is flooded. Only that little tip at the top on figure C that would be above the surface of the water. Hopefully some component of this and the foam floatation together would partially right it, but I wouldn't count on it. Macs need some permanent ballast even 400-500lb would help.

[Don T]

Duane,
The water ballast does not have to be above the water line to be effective. What's the reason water ballast is more tender on an X boat than the S? The reason is the shape of the ballast tank. Righting moment is all about the center of gravity and it's relation to the center of buoyancy. X boats have high, wide tanks at the fore and aft. It takes a good amount of heel to get sufficient mass off center of buoyancy to oppose the force on the sails. The S boat has a long, skinny tank low in the hull where more mass gets off center at less angle of heel (why there's less headroom in the cabin). Lead has a greater density than water and a great deal more mass (C of G) moves off center with less angle of heel. When water is in the cabin of an X boat the leveling of water can completely off set the mass of the ballast because they have the same density and occupy the same volume. The ballast swings off center but water in the cabin can counteract it keeping the center of gravity directly over the center of buoyancy. AT least until the foam flotation is under water and indeed the ballast tank moves above the waterline, then the center of buoyancy & gravity move off center in opposite directions.

Theoretically, one could fill the capsized X cabin with more water, pushing the foam deeper and the boat would right itself. OR, pump the cabin out and the boat would again right itself (full ballast). Both of those options move the center of forces to opposite sides of the boat when laying on it's side. One irony is, if the boat turtles with no ballast, it doesn't take on water (until wave action anyway) but there is insufficient righting moment and if the ballast was full then water does get in the cabin and once again there is insufficient righting moment. So it seems to me the only logical choice is to try to right it using human ballast (in either scenario) with the sails released and failing that, tow it to a shore facility (on it's side) and pump it out. The second option is how every capsized Mac has been handled to date. I can understand rescuers frustration when everything they try out on the water fails and the boat just lays there on it's side. Frustrating physics no doubt.

Finally, it's the reason the boats need to have some weather helm, when knocked over they turn to weather and that helps keep water out of the cabin.

[opie]

I think John's guess is probably right. If you follow that logic about motoring with the board down, would it also make sense, if caught in a blow offshore, to raise the CB or DB when (and if) deciding to "hove-to"? (so as to prevent trippng?)

[Russ]

If I remember correctly, the boat on the Solent was without ballast and it's inflatable got caught in the rigging during a gust of wind and pulled it over.


I would have to believe that if the ballast tank were full, the portion that is above sea level would have a lot of righting power. I feel very confident that with ballast totally full, the boat will eventually come back barring something holding it over.

[opie]

Let's go the whole way then..... add John's guess about motoring without ballast with board down, and add the comment from the lady at the beginning of the video saying that she saw the mainsail luffing and then add the guess that two crew members were on topside of the unballasted Mac taking down the luffing sail, and you have the recipe for disaster that is warned about on the side of my helm by the factory sticker.......
Russ, your comment is probably right on.

[MARK PASSMORE]

1150 lbs of water is the same weight as 1150 lbs of lead. Weight is weight, no matter if it is in the ballast under water or above water. Just because it is water in the ballest doesn’t mean that it is neutrally buoyant. It would still have righted the vessel if the ballast was full. It had to be empty or partially full. There, Now I’m in on the record also.

[Currie]

1150 lbs of water is the same weight as 1150 lbs of lead. Weight is weight, no matter if it is in the ballast under water or above water. Just because it is water in the ballest doesn’t mean that it is neutrally buoyant. It would still have righted the vessel if the ballast was full. It had to be empty or partially full. There, Now I’m in on the record also.

I know what you mean - and in this case it doesn't matter. But in general they're not the same. The difference is in how much space (displacement) 1150lbs of lead takes up vs. how much space 1150 lbs of water takes up. Like I say, it doesn't matter too much here because it would all be inside the boat anyway, so you're right. But in general 1150 lbs of water must displace 1150 lbs of water and is therefore neutral if submerged - it's only useful if it can be raised from the water, like with a Mac. 1150 lbs of lead, on the other hand, only displaces about 100 lbs of water, so it's perfect for keels and such because it provides righting even when it's submerged.

Cheers,

~Bob

[MD Dunaway]

It's all about density, not weight. You can have 1200lb of water or 12,000lb of water and it doesn't matter it will not sink (so long as the temperature and salinity are the same). It is obvious that a flooded boat will behave differently from a buoyant one. What is more interesting is that the characteristics of the (water) ballast change depending on if and how much of the boat is flooded. This is not true for the lead ballast. Sometimes it is easier to understand with extreme examples. If a water ballasted boat were completely submerged the water ballast would have no effect at all. Or, if there were even a little trapped air in there it would flip the boat upside down.

[Don T]

Hello,
Don't forget, the drawings above do not reflect foam flotation.
I posted my drawing of the righting moment in the mod section.
http://www.macgregorsailors.com/modt/in ... ewimg=2228
CB = center of buoyancy
CG = center of gravity

On Edit: My drawing now accounts for form stability of the hull.

My analysis:
1. Very tender upright and low angles of heel because CB and CG are so close to each other.
2 The boat hardens up at 25* heel because the CG is rotating up and the CB moves away to the leeward side. The under water shape is asymmetrical with more buoyancy leeward because of the flat bottom and chine.
3. Righting moment only increases a little as the boat heels to 45* where the under water shape is symmetrical again (chine straight down) moving the CB back to center as the CG rotates around.
4. Beyond 45* the boat begins to loose righting moment as the CG begins to rotate above the CB and the underwater shape becomes asymmetrical again moving CB back to windward. When the wind is pushing it down, it will seem to just roll easier past this point.

Lead ballasted boats tend to get harder (more righting moment) as they heel more and more especially when the ballast is real low like in the keel. But then again, they also tend to sink like a stone when they take on water.

I have never done this analysis before and find it most interesting. I had not considered that our boats may have a "tipping point" at which it will seem to want to just roll over. In my experience, only once did I have the boat over past 45*. We were close hauled on the Columbia river and suddenly found ourselves bearing down on the Washougal shoal. Depth went from 30 ft to 3 ft in short order and the only thing I could think of, to save the centerboard and rudders from the rocks, was to raise them in a hurry. I only managed to get the CB up when the wind turned us around (cuz' It wouldn't steer anymore..... DUH) and knocked us down. We slid over the rocks with only one little ding on a rudder the mast dang near horizontal. I knocked the sheets loose as we cleared it and we righted back up. Fortunately we took on no water and survived to learn the lesson. Since then I have never had it past 30* and have not felt uncomfortable but maybe from now on I will be more wary.

[MD Dunaway]

Agreed, and nice pictures BTW. It is more complicated than it sounds when one starts trying to calculate for foam floatation, the position of the foam, the leverage asserted by the foam, air that may be trapped in the boat in various locations, the ballast tank (and if it is empty, full or partly full), other things in the boat like floatation cushions, PFDs, styrofoam coolers, and so on. I wish someone would just say what happened.