Ovni AVS?

[cco]

Originally Posted by Doodles

Me too !!!!

But I'm wondering ... does anyone (you Ovni owners ?) know "why" Ovni puts their ballast in the hull as opposed to the keel like say a Southerly? I'm sure they have their reasons and arguments for why its better in their eyes. Just wondering.

For the stability issue, more than 1500 boats made by Alubat since the beginning, none of them missed to recover in case of capesize.
But once again, I am surprised of how much you guys are focused on AVS.
AVS is something to be taken in account on a pure mathematical base, not on real conditions. We all know that the wind is never the main cause of a capsize, but the wave is.
And when you have such waves that you boat will capesize, AVS of 124° of 145° will not make the change.
This is the reason why having ballast in the hull is much, much safer than on the keel. When you are upside down, if the keel by its weight, goes down in the boat, this is this end...
And the Ovni's roof itself is designed to actively help the boat to return on its normal position, as the floatable mast.

[goboatingnow]

Originally Posted by cco

For the stability issue, more than 1500 boats made by Alubat since the beginning, none of them missed to recover in case of capesize.
But once again, I am surprised of how much you guys are focused on AVS.
AVS is something to be taken in account on a pure mathematical base, not on real conditions. We all know that the wind is never the main cause of a capsize, but the wave is.
And when you have such waves that you boat will capesize, AVS of 124° of 145° will not make the change.
This is the reason why having ballast in the hull is much, much safer than on the keel. When you are upside down, if the keel by its weight, goes down in the boat, this is this end...
And the Ovni's roof itself is designed to actively help the boat to return on its normal position, as the floatable mast.

AVS is also calculated by an incline test. It's incorrect to dismiss AVS. Yes it's not the only factor far from it. But it is a reliable number. The other factor that's important is the area of the stability curve below the line. In the Ovni this is a very large area.

The primarily reason that alubat put the weight in the hull is to save the weight and cost of engineering a substantial keel box to carry a ballasted keel. A simple substantial locking pin solves the inverted issue.

All coach roofs on all boats aid in returning the boat upright. In the case of the moody Ds 42 the cabin body contributes to the fact that the stability is all above the line an infinite AVS !!


Dave

[cco]

Originally Posted by goboatingnow

The primarily reason that alubat put the weight in the hull is to save the weight and cost of engineering a substantial keel box to carry a ballasted keel. A simple substantial locking pin solves the inverted issue.

All coach roofs on all boats aid in returning the boat upright. In the case of the moody Ds 42 the cabin body contributes to the fact that the stability is all above the line an infinite AVS !!

Dave

Sorry Dave, but I spent some time to work with Ovni manufacturer and architect and I can confirm that Alubat put the weight in the hull NOT to save any cost of engineering substantial keel box etc. but for a design purpose, design of a full centerboard ship, where the keel must NOT have any ballast.
The additionnal weight needed regarding a ballasted keel is as costly as a keel box due to the lead price. On Ovni 455, they have a keel box AND ballast in the hull.

[goboatingnow]

Then I stand corrected. In this thread my main point was why Ovni have always refused to publish official stability figures for the 385. Given the widespread user experience etc. I'd have thought they would marshal their arguments and take the issue head on. Now that STIX is mandatory they have to deal with it as 30 is low for a blue water cruiser ( what ever that means)

Dave

[noelex 77]

Originally Posted by cco

AVS is something to be taken in account on a pure mathematical base, not on real conditions. We all know that the wind is never the main cause of a capsize, but the wave is.
And when you have such waves that you boat will capesize, AVS of 124° of 145° will not make the change.
.

AVS is just as relevant and important for a capsize due to wave action.

A boat with an AVS of 145 will be a lot more resistant to capsize than a yacht with a 124 AVS. This is true no matter what the cause of capsize wave or wind.
The danger with a very low AVS combined with high inverted stability is that the yacht will remain inverted. This is the case for catamarans, but they do have the advantage over a yacht that they generally remain afloat when inverted.
The risk of conditions that will overcome, even low positive stability, is rare. Many people are willing to take the small risk of a rollover accident even if that means the boat sinking.
Life has risks. It is however important to recognize and understand those additional risks.

Originally Posted by cco

And the Ovni's roof itself is designed to actively help the boat to return on its normal position, as the floatable mast.

AVS is a reliable number it does take into account the buoyancy of the coach roof and flotation in the mast.

All yachts are compromises Ovni has a lot of excellent qualities. The un-ballasted lifting keel is a bonus in many cruising situations, but recognize it does have drawbacks as well as benefits and sail accordingly.

[SaltyMonkey]

The problem with AVS and all these figures is that it is assuming you are getting linear responses from the waves and environment etc. Unfortunately, the sea is not so linear and controlled in a storm situation. There are too many variables in the conditions that surround, and it quickly becomes non-deterministic.

As much as I have used AVS and in some cases STIX calculations in the past in my comparison spreadsheets (STIX being extremely hard to calculate since manufacturers don't release all the necessary variables in the spec sheets), I don't think its really serving that much in the end.

If you want to do measurements, at least linearly, your best bet is to do a tank test and watch what happens. In fact, thats what most ocean racing contests require.

[noelex 77]

Originally Posted by SaltyMonkey

The problem with AVS and all these figures is that it is assuming you are getting linear responses from the waves and environment etc. Unfortunately, the sea is not so linear and controlled in a storm situation.

The stability graph does not make any assumptions about a linear sea state or wind force. It doesn’t need to. It just tells you the amount of force trying to bring the boat back to upright or keeping it inverted
The AVS is one point on the graph. It is a useful single number to use when comparing boats, but does not provide a complete picture like the stability graph I provided for the Ovni 385.

[Doodles]

AVS and STIX aside, we know Ovni has made over 1,500 boats over the last 25 or so years and most of those are out cruising the oceans. So, where are the all the capsizes? If this were a problem won't we have some track record or case history by now? There is theory and there is reality, and there seems to be a big gap to me.

[SaltyMonkey]

agree doodles..lets at least see one or two articles? Any evidence? anything???

[stevewrye]

OK help me out here, I'm a bit confused from some of the posts. From all I know when running on a broad reach in a center board boat your keel is up. Reason the less keel in the water the less chance of wanting to round up. Also not sure how one could bury the leeward rail running at 150 degrees unless you had way too much sail up. One of the advantages of a fin keel in big seas is that if you do slide down a wave sideways you have less keel in the the water to trip your slide than a full or modified keel. Why wouldn't a centerboard which would be running like most boats in storm conditions be even better as it has no keel down to trip the boat on the slide. From most of the accounts I have read or accounts from sailors who have been knocked down is that their knock down came about from rounding up while going down a wave with a breaking face. The boat slid sideways down the face till the keel caught in the lower section of the wave where the steepness is not as great, then over they went. Granted that if a wave is so steep that a boat does a free fall such as what happened to many boats in the Sydney to Hobart race no boat is going to survive that. But a boat with little or no keel deeper in most storm wave faces should be able to slide sideways till breaking wave stops breaking and the wave moves under them. I must admit I have only been in a couple of storms with serious breaking waves in open ocean and in a full keeled boat, "none like the Sydney to Hobart race" and what I observed was that the breaking top part of the wave only lasted for a few seconds at most before reforming without the white water. Those were waves of about 6 or 7 meters and where the white water ran down the entire face or close to it on occasions. On fifty foot waves I think all bets are off for any boat and that's why most boats in the Sydney to Hobart race stopped running and turned into it with motor running hoping to steer around monster waves. Does anyone know what book the info on the Ovni in Sydney to Hobart race came from?
I'm not trying to justify centerboard modern designed boats because I am having one built I trust no boat including my own till it proves its self.

[noelex 77]

Originally Posted by stevewrye

Does anyone know what book the info on the Ovni in Sydney to Hobart race came from?

Fatal Storm is a good book on the Sydney to Hobart. I do not think there has ever been an Ovni in the race, unless it was in the early days before the safety laws. There are now minimum stability requirments required to participate and an Ovni would not meet these.

[fblc]

I don't know the Avs of my Ovni 345 boat but what i like is that when running on a broad reach with the keel up I really feel in safety, there is no crooked leg effect in the bottom of the waves.