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Old 05-05-2015, 13:45   #211
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Re: Characteristics of Offshore Yachts

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Originally Posted by stevensuf View Post
Size counts, plain and simple, I'd rather be in a 40ft bendy than a 30ft tank when it comes to survival situations (...)
You can't argue like this. It is not quite fair.

Take either different styles or different sizes. When you cross over size with design style it is becoming oranges and apples.

I think it is fairer to go along a line like this:

'... I'd rather be in a 40' tank than in a 30' tank when ...'

or

'...I'd rather be in a 40' bendy than in a 30' bendy ...'

I can be wrong too. But that how I compare boats.

b.
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Old 05-05-2015, 13:53   #212
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Re: Characteristics of Offshore Yachts

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Originally Posted by barnakiel View Post
You can't argue like this. It is not quite fair.

Take either different styles or different sizes. When you cross over size with design style it is becoming oranges and apples.

I think it is fairer to go along a line like this:

'... I'd rather be in a 40' tank than in a 30' tank when ...'

or

'...I'd rather be in a 40' bendy than in a 30' bendy ...'

I can be wrong too. But that how I compare boats.

b.
Barnakiel beat me to it!

I was thinking the same thing!

Compare two boats on ONE changeable feature or characteristic.

For example:

40 foot Bendy vs. 40 foot Tank

12 foot beam Bendy vs 12 foot beam Tank

30 foot LOA Bendy vs 40 foot LOA Bendy.

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Old 05-05-2015, 13:57   #213
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Re: Characteristics of Offshore Yachts

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Originally Posted by stevensuf View Post
If anyone cares to dig, there are some interesting videos on youtube, by some English university on Wave tank trials, they made models of various boats , various keel ballast ratios, and they found that they made very little difference.

A breaking wave equal to your beam will roll you, plain n simple! IE if you have 14ft beam then 14ft of breaking wave will roll you, The AVS or ballast ratio made no difference to this fact! Yes if you make the ballast ratio too small then a wave less than the beam could roll the boat, but we are talking extremely small ballast ratios here.

Most boats with a high AVS tend to be skinny beamed and thus are more likely to be rolled in the first place than a boat of simmilar length but with a wider beam. The Higher AVS boat will probably self right pretty quickly, while the lower valued AVS boat may will take longer to right.
So don't lie ahull or go beam on to the seas.


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Originally Posted by stevensuf View Post
So again i retiterate, In a storm you are better off in 40ft of bendy toy than 30ft old skool tank, by a huge margin!
Have to go along with Barnakiel on this one. Your trying to compare apples and oranges with very little common ground.

So again I'll reiterate. If the 40' toy boat breaks up in the storm I think I'll go with the 30' boat that's still floating, even if it rolls a couple of times and leaves the mast behind.

By the way, just for clarification, my boat is a modified fin keel with a skeg hung rudder, not an old skool tank although I do like to think it is reasonably sturdy.
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Old 05-05-2015, 14:01   #214
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Re: Characteristics of Offshore Yachts

I have to apologize--by roll I meant 360 degree recovered capsize, not oscillation due to heavy seas.


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Old 05-05-2015, 14:05   #215
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Re: Characteristics of Offshore Yachts

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So in a rollover certainly there is a risk of serious injuries or death but you do have a chance to survive. Sinking in a survival level storm your odds of survival are zero.
Considering the boat of mstrebe a rollover would be as risky as sinking in a storm and it wouldn't matter at all if the boat is damaged or not.

Sorry mstrebe, I couldn't stop myself but all those sharp corners and all the room to be ballistic..
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Old 05-05-2015, 14:27   #216
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Re: Characteristics of Offshore Yachts

Well now you know why I'm worried :-)


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Old 05-05-2015, 15:14   #217
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Re: Characteristics of Offshore Yachts

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Originally Posted by stevensuf View Post
If anyone cares to dig, there are some interesting videos on youtube, by some English university on Wave tank trials, they made models of various boats , various keel ballast ratios, and they found that they made very little difference.

A breaking wave equal to your beam will roll you, plain n simple! IE if you have 14ft beam then 14ft of breaking wave will roll you, The AVS or ballast ratio made no difference to this fact! Yes if you make the ballast ratio too small then a wave less than the beam could roll the boat, but we are talking extremely small ballast ratios here.

Most boats with a high AVS tend to be skinny beamed and thus are more likely to be rolled in the first place than a boat of simmilar length but with a wider beam. The Higher AVS boat will probably self right pretty quickly, while the lower valued AVS boat may will take longer to right.

How long would i take to fill a 40 footer with water compaired to a 30 footer?

So again i retiterate, In a storm you are better off in 40ft of bendy toy than 30ft old skool tank, by a huge margin!

It was Southampton University Institute of Oceanic Research I believe that did the Wave tank trials after the 1979 Fastnet Race and yes the conclusion was that ALL boats regardless of design or type would roll IF/when they met the wrong wave as in one that matched 'their' critical criteria. One of the critical factors in that ill fated Fastnet storm was the meeting of two wavetrains after a wind shift creating a seastate that was punching way above it's weight for the actual surface windspeeds, high as those windspeeds were. Some boats by luck were in locations that were less bad, some boats got unlucky. you could argue speed was a factor because some faster boats were round fastnet rock and on the way home whereas others were still trying to get to it. some boatslike the OOD 34s class were in the wrong place at the wrong time whereas others like the Co32 class got to the bad bits after the bad bits had moved or maybe abated, but it allowed the legends of the 'superior co32' with it's long encapsulated lead keel to gain credibility and the converse of the OoD34s and similar boats reputations to be rubbished . Ironically the OOd 34, designed by Doug Peterson was also sold as the Contessa 34 in cruising form, built by the self same company as the Contessa 32s so presumably no bean-counter engineering had yet taken place ( that is intended sarcasm BTW) to be blamed by the armchair cognoscenti

One of the other conclusions made after the Fastnet Race storm enquiry was that those boats which were kept actively sailing by their crews rather than those who adopted the 'close it all up and pray' tactics were the ones that actually fared the best. Also the bigger boats did better ( 'size matters' as the actress said to the Bishop) ,presumably faster too, came out generally better although one or two had damage like Morning Cloud ( the then Prime minister's boat) lost her rudder ( carbon fibre ruddershaft broke I believe) I think the same rudder loss happened to the Ron Holland designed golden Apple.

So no real culprit emerged and bean-counter engineering in a race fleet doesn't really fly. Are Formula one race cars bean counter engineered?? rather the contrary I would suggest.

We are back to the Sh!t happens, so deal with it, philosophy. Build a sailboat Titanic by all means but it still ain't going to be invincible Otherwise do what you can with the human input, be well prepared, be or have an experienced/ knowledgeable and efficient crew and treat 'em well with a dry bunk to rest in and well fueled with warm food and drink. We once had 15 hours in a 33 footer running before a rogue storm and huge breaking seas and that produced windspeeds over the deck of 50kts plus, despite our average SOG dead downwind of around 10 kts. (boatspeed plus tidal current speed My lovely Lady wife kept me supplied with regular hot soups and coffees and even jumbo hot dogs as I recall throughout the 13 hours that I hand steered because the autopilot had got tired of it all and gone on strike.
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Old 05-05-2015, 16:45   #218
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Re: Characteristics of Offshore Yachts

Im sorry with the apples and oranges thing, but some pepole were advocating that small older boats were safer in a storm than newer bigger lightweight boats or were under the misconception that a high AVS number made the boat more difficult to roll, or that a bigger ballast ratio made it less likely to roll etc all fallacies.

I would imagine there are many people just learning reading these threads and giving them misleading info could one day put their lives in danger.

Now I wonder if a boat with a lower AVS would be more likely to right keeping its rig than one with a high AVS, the process is certainly going to happen slower in the boat with a lower AVS.


Offshore yacht?

Plenty of stays, baby stay or tinwheadsail rig, twin backstays, shrouds 3 a side with seperate chainplates (too many boats have a single forestay /backstay with shrouds all mounted on the same chainplate) redundancy should a stay/chainplate/link fail, fair chance youd keep the mast.

Keel, im not against bolt on keels as long as they have plenty of bolts and the hull has good strength.

Rudder, well twin rudder boats look good for redundancy, but only few new ones have em , skeg hung certainly is more favourable than spade, especially in older boats. Lots of spade rudders have detached themselves. LOTS..

Curved coachroof, good for drainage and better if rolled, flat roofs are harder to right.

we really need a cat mono , 2 rudders , 2 engines, but self righting.

Water tight bulkheads would be nice and an airtight companionway hatch.

Some kick ass bilge pumps, And the ability to keep em going for a good amount of time!

Probably centre cockpit for comfort.
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Old 05-05-2015, 19:55   #219
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Re: Characteristics of Offshore Yachts

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Well now you know why I'm worried :-)
Well maybe I can help. Here's some suggestions that will reduce your chances of a rollover or pitchpole in any boat to almost zero.

1. Don't make passages in any tropical area during hurricane season.

2. Don't make passages outside the tropics in the winter (maybe even late fall depending on where you are and how far north).

3. Don't sail north or south of 40 degrees latitude in any season.

This should cover at least 95% of all survival level storms and 95% of all cruisers. Doesn't mean you will never see a storm at sea. It does mean that if you follow the above the odds of encountering a large, breaking, boat rolling, rig smashing wave are teeny-tiny.

Obviously this is a simplification and not all inclusive but does cover the great majority of sailing.
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Old 05-05-2015, 20:54   #220
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Re: Characteristics of Offshore Yachts

Hard to argue with any of that.
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Old 05-05-2015, 21:32   #221
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Re: Characteristics of Offshore Yachts

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Well maybe I can help. Here's some suggestions that will reduce your chances of a rollover or pitchpole in any boat to almost zero.

1. Don't make passages in any tropical area during hurricane season.

2. Don't make passages outside the tropics in the winter (maybe even late fall depending on where you are and how far north).

3. Don't sail north or south of 40 degrees latitude in any season.

This should cover at least 95% of all survival level storms and 95% of all cruisers. Doesn't mean you will never see a storm at sea. It does mean that if you follow the above the odds of encountering a large, breaking, boat rolling, rig smashing wave are teeny-tiny.

Obviously this is a simplification and not all inclusive but does cover the great majority of sailing.
I found Dudley Dix discussion of how water ballast affects a roll over in PBB very interesting. I also think it lends him credibility that he has rolled a boat, his own boat, and kept on sailing.

In my dreams I'm always designing the ultimate boat and it seems to go without saying one would have to include water ballast. For the typical 'money is no object, maybe someday' owners of today I would think it would be at the top of their list.

I'd make it fresh water of course so it would have a varying utility as ballast. That's just the compromise that would have to be made since I have no intention of putting fussy and delicate technology like a water maker into my dream boat.

Why not do the same with fuel and run it through filters going from side to side to polish it.

The thought of what I could do with 800 lbs up on the windward rail is intriguing. That means more sail, more speed, more directional stability and a smoother ride.

BTW I love built in tanks for water. I made one on Korrigan and lined it with Brewcoat epoxy. It's so waterproof that it doesn't even get wet and the built in tank is huge. When I get over the trauma of building that first one I'm going to turn the other settee into another and have boat loads of water, we're talking 'down on her lines' amounts of water baby.

100 gals both of fuel and water seems mandatory for a dream boat. Just hit that 'survival' storm when your tanks are half full.
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Old 05-05-2015, 21:41   #222
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Re: Characteristics of Offshore Yachts

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...Why not?...
Because we need the interior space for stowage, equipment and machinery, provisions, living quarters, etc. And because we can do it more simply and with less effort.
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Old 05-05-2015, 21:55   #223
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Re: Characteristics of Offshore Yachts

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Displacement (as a proxy for size) is what the nun said.

I think a size bigger than whatever gets toppled over in a regular ocean gale is desirable.

The problem is I can't say exactly what we are talking about in numerical figures. I have see only one author talking about this factor.

How much displacement (or size/displacement) is desirable so that the craft does not get overpowered by regular ocean gale conditions?

NWS JetStream - Wind, Swell and Rouge Waves

Because if we were to assume that even regular gale conditions can overpower a relatively big ocean going craft (say 40+ ft LOA, 12k+ pounds displ) then we can drop the case and stick to our "build it as if you were sure she will get overpowered once and likely more than once"!

Which I believe is the case.

b.
This sounds like wisdom to me. These kinds of arguments are always hypothetical to my experience but just based on my limited exposure to waves I would say that a gale at the West Entrance to the Straits of Juan could easily roll a 40 foot sailboat, and roll it again, and again.

But then I haven't been in a full westerly gale at the West Entrance so maybe I'm mistaken. It is north of 40 degrees though and the current does always go out, sometimes at several knots....

Even in the Straits I'm always prepared for at least a 90 degree knock down. Beam reaching across a steep chop in gusty winds it doesn't take much.

I honestly wouldn't see myself as truly ocean ready until everything inside is secure for a full inversion. That seems like common sense to me. The boat itself sure is and I even put access ports over the dorade inlet so I can screw plates in to keep the water out.

But then whadoIknow? I haven't even had my three nights offshore for years now.
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Old 05-05-2015, 21:57   #224
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Re: Characteristics of Offshore Yachts

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3. Don't sail north or south of 40 degrees latitude in any season.


Obviously this is a simplification.......
No kidding! 40 North is only a short way north of San Francisco. That means do not sail anywhere in Oregon, Washington, or Canada.

Your wording is not correct either. The entire world is either north or south of 40 degrees latitude.
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Old 05-05-2015, 22:24   #225
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Re: Characteristics of Offshore Yachts

I think that, generally, people spend waaaay to much time worrying about knock-downs / roll-overs / angles of vanishing stability, etc.
If you choose your passages to suit your boat and your ability, and keep your boat in reasonable condition, and pay reasonable attention to the seasonal weather patterns and local weather forecasts, chances are you will never have to experience conditions where a knock-down, rollover, do the hokey pokey is likely.
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