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Old 07-04-2017, 16:33   #16
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Re: Ovni 365 now reclassified as Cat B

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Ben, I just now looked at the Ovni curve. Holy Roller, Batman! That is indeed scary, with an AVS of only 100 degrees, and greater stability upside down than rightside up. Shades of mulltihullls!

But, there are lots of these boats cruising, and I've not heard of a big fraction of them being rolled or inverted, so what gives? Is our sacred cow of AVS> 125 not really applicable ?

There must be more to it than the simple numbers indicate.

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Old 07-04-2017, 20:09   #17
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Re: Ovni 365 now reclassified as Cat B

Yes, AVS at 100 degs is not what one really likes to think of on a scary rough night, also the negative area looks quite 'deep', not just wide. This much said, I have never seen nor heard of an inverted OVNI. Have you?

What IS truly scary though is that EU politicians are going to tell us now that the same boat just built in different years is either A or B rated. This is in fact, plainly stupid. And not the first stupid thing we are supposed to swallow and smile that comes from Brussels.

Will be interesting to watch how the whole thing unveils now. I expect quite a number of designs to be affected.

Thanks for posting this here. Most interesting.

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Old 07-04-2017, 20:20   #18
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Re: Ovni 365 now reclassified as Cat B

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Ben, I just now looked at the Ovni curve. Holy Roller, Batman! That is indeed scary, with an AVS of only 100 degrees, and greater stability upside down than rightside up. Shades of mulltihullls!

But, there are lots of these boats cruising, and I've not heard of a big fraction of them being rolled or inverted, so what gives? Is our sacred cow of AVS> 125 not really applicable ?

There must be more to it than the simple numbers indicate.

Jim
Jim from what I see most high production cruisers have better STIX numbers that Ovni but most of them are very stable inverted as well. I think these boats are much harder to get inverted. Most boats require a good sized wave to self right after being inverted.
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Old 07-04-2017, 21:03   #19
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Re: Ovni 365 now reclassified as Cat B

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Jim from what I see most high production cruisers have better STIX numbers that Ovni but most of them are very stable inverted as well. I think these boats are much harder to get inverted. Most boats require a good sized wave to self right after being inverted.
I dunno... look at the curves for the Jeanneau 3600 that Snowy posted. Tiny area under the axis. huge above, great AVS. But, once inverted, the rig kinda acts like a keel and/or roll damper, and that can inhibit righting. But those numbers would give me some confidence in the boats stability.

Friends of ours were delivering a VAliant 40 from NZ to t he states, and were rolled whilst hove to in a bit of harsh weather. It stayed inverted long enough for them to be stuffing towels into the dorades to stem the inflow. Seemed a really long time to them! After a while, the rod rigging let go, the mast snapped and the boat quickly righted. Dunno what that proves, but interesting, factual experience.

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Old 07-04-2017, 21:03   #20
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Re: Ovni 365 now reclassified as Cat B

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... Most boats require a good sized wave to self right after being inverted.
Or a lot of water inside. Free surface effect is very useful when you are upside down! I suspect the open 60's that stayed inverted were actually A byproduct of watertight compartments and very watertight companionways. Without these flooding would have quickly righted them.

I also love the idea of a bit of foam inside the top of the mast, or bouyant sealed masts. A lot of righting moment there provided the stick doesn't collapse.



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Old 07-04-2017, 21:14   #21
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Re: Ovni 365 now reclassified as Cat B

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I dunno... look at the curves for the Jeanneau 3600 that Snowy posted. Tiny area under the axis. huge above, great AVS. But, once inverted, the rig kinda acts like a keel and/or roll damper, and that can inhibit righting. But those numbers would give me some confidence in the boats stability.

Friends of ours were delivering a VAliant 40 from NZ to t he states, and were rolled whilst hove to in a bit of harsh weather. It stayed inverted long enough for them to be stuffing towels into the dorades to stem the inflow. Seemed a really long time to them! After a while, the rod rigging let go, the mast snapped and the boat quickly righted. Dunno what that proves, but interesting, factual experience.

Jim
Interesting case Jim and it would have been hell of a scary place to be.

Some research at the AMC after the 98 sydney hobart seemed to show that without a rig some boats could be slower to right, as they could end up surfing down the waves upside down blowing downwind rather than lying broadside to the waves, where with the rig in the boat a decent wave would cause the boat to "trip" over the rig and start the righting process, kind of like the centreboard up vs dowm scenario., but who really knows. A huge number or varibles...

What this does show is that for all its flaws Stix actually seems to kind of work. At least its identified an issue that if you take a small Ovni offshore you should at least be aware of.
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Old 07-04-2017, 21:19   #22
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Re: Ovni 365 now reclassified as Cat B

There is also some interesting recent research that seems to link chances of a wave induced complete inversion as opposed to a much less nasty knockdown (mast well underwater but boat pops back quickly) being roughly proportional to the area under the curve between 90 and the AVS. Makes a lot of sense.

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Old 07-04-2017, 21:20   #23
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Re: Ovni 365 now reclassified as Cat B

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Originally Posted by Jim Cate View Post
Ben, I just now looked at the Ovni curve. Holy Roller, Batman! That is indeed scary, with an AVS of only 100 degrees, and greater stability upside down than rightside up. Shades of mulltihullls!

But, there are lots of these boats cruising, and I've not heard of a big fraction of them being rolled or inverted, so what gives? Is our sacred cow of AVS> 125 not really applicable ?

There must be more to it than the simple numbers indicate.

Jim

As Snowy said, It's the ability to raise the board and slide that dissuades a rollover. If you get pushed out of the way instead of digging in, you're less likely to spend time upside down. Thought, for it to really work well, I'd want the sheer line- deck to hull joint- to be rounded too.

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Old 08-04-2017, 01:52   #24
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Re: Ovni 365 now reclassified as Cat B

It's all speculation on my side because I can remember when these boats first came out and looking at the AVS I was not convinced that they would make a good offshore boat. Then I met Jimmy Cornell when we were both tied up in Hawaii and he was sailing one, this is a lot of years ago. Anyways he had just come from the Antarctic and explained to me how the boat would slide on the face of waves as it had not keel to trip over when the center board was up. He also said it was very easy to fly spinakers in most winds again with the board up, he said it would just sort of skid and could never broach because it had nothing to trip over.
I rethought my ideas and decided that there probably was something to what he was telling me and their record seems to bear that out, although that was a 40 footer and not a 36.
Jim, I'll believe your Valiant story, most cruising boats are over loaded and often way too much weight. high up that reduces it's resistance to rolling and helps it stay inverted. Valiant yachts do have a pretty good track record though. I think some of the newer designs that are super beamy would be very stable upside down, fortunately it takes a very substantial wave to make that happen.
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Old 08-04-2017, 18:20   #25
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Re: Ovni 365 now reclassified as Cat B

My understanding was that when proposed the directive made some sense but almost no production boats then built got anywhere near cat A. This horrified the producers so the lobbied the EU to change the reg on the grounds that they would loose a tone of money. Reg where duly changed so that most production boats where then cat A which also made the regs meaningless! Typical example of regulatory capture. Maybe they are going back to some more sensible regs but basically if you, as skipper, cannot determine whether the boat you are on is suitable to undertake your proposed voyage should you be doing it?
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Old 08-04-2017, 19:27   #26
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Re: Ovni 365 now reclassified as Cat B

The graphs AVS etc. assume no mast, huh?

I would rather carry some sort of auto-inflatable bag on top of the trunk. Much more volume than a sealed mast. Masts, mostly, snap in rollovers.

I always consider our dinghy stored on the foredeck to be that little extra much as I know it is silly to assume it would not be punctured or something.

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Old 09-04-2017, 13:14   #27
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Re: Ovni 365 now reclassified as Cat B

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Originally Posted by barnakiel View Post

What IS truly scary though is that EU politicians are going to tell us now that the same boat just built in different years is either A or B rated. This is in fact, plainly stupid. And not the first stupid thing we are supposed to swallow and smile that comes from Brussels.

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Does one really need to ask why Britain left the EU?

They should just kick out Brussels...
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Old 10-04-2017, 05:54   #28
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Re: Ovni 365 now reclassified as Cat B

The regulations serves a purpose, not just to let the EU bureaucrats have fun imposing regulations upon us.

The boating industry have been part of the work updating the the new directive. The Norwegian/Swedish lobby worked to get the new rule that you should be able to enter the yacht unaided, e.g. a ladder reachable from the water.

This document tries to explain the new regulations,
http://www.boatdataservices.com/uplo...df_version.pdf

See 2.1 about classification. The words Ocean, Offshore etc are left out. Exactly how the testing is to be done is not set in neither of the documents. It does say: "However, design category A now defines abnormal conditions as storm, violent storm, hurricane, tornado and extreme sea conditions or rogue waves. "

I started this thread since I was unsure exactly why the 365 was reclassified. It must most probably be due to the the above quote.

The document above make interesting reading.


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Old 10-04-2017, 06:09   #29
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Re: Ovni 365 now reclassified as Cat B

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The regulations serves a purpose, not just to let the EU bureaucrats have fun imposing regulations upon us.
Ole
OK, some EU rules are sensible, like having a way to board a boat from the water.

However, clearly some of the EU and RCD regulations are made by people who have no idea what they are doing.

Example: Some European boat builders were using BRASS valves for seacocks. These are for house use only. When these brass valves are exposed to stray electric current, they can dezincify in a few days and become very fragile if not failing all together.

So what to does Brussels do? State that one has to change his boat's seacocks every five years.

Right!!! All Skylark's seacocks are 40+ year old Wilcox-Crittenden silicone bronze and are in perfect condition and well maintained. Am I going to change them in 5 years? Don't think so.

I put my 1973 Pearson 36-1 through Post-Construction Assessment survey and had to make five minor "corrections". A couple made sense. A couple didn't.

I think many regulations are for people that need to be told how to maintain or build a boat. If everyone did things correctly, we would need the regs.
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