balast ratio....

laffinskip said:
. . . but in anything of a sea give me a medium to heavy displacement boat anytime.
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Well once you have the stability and seaworthiness basics covered, you then enter the world of personal preference and not science.

Lots of sailors are happy with their 'saucers' whilst scooting round Cape Horn, whereas the Smeetons, thought that after two attempts in their long keel, heavy displacement yacht had failed, that perhaps in hindsight, once being rolled and pitchpoled would have been enough.
 
I have no intention of making this into a 'heavy vrs light displacement argument. The internet is full of them and are as fractious as any other religious debate.

My simple point is this in a thread about Ballast Ratios: there is only very, very limited insights to be gained from considered one or two characteristics of a boat in isolation, be it ballast ratio, displacement or the shape of its keel. The behaviour of boats is much more complex than that and even when combinations of a boat's characteristics have been used, as with SSSN, STIX, RCD categories they still have their limitations. As LW395 pointed out, a Fisher 25 might be CAT A, but does it really have all the qualities needed of an ocean going boat?

Further to that, once you have short listed a full list of 'seaworthy vessels', then people are free to choose the one for them through personal preference. But personal preference isn't the same as 'provable science'. Personal preference simply means that when the '3M's 5200 hits the propellor' you are confident and happy you chose the right boat - which is really important if you are to enjoy your sailing.

The Smeeton's boat may well not have been a 'very seaworthy boat', but that's my exact point; just because it was full keeled and heavy displacement means nothing if its seaworthiness was undermined by other shortcomings. Everything must be considered in the round.

Finally the point about boats capsizing in harbours is utterly fatuous. There is no real comparison in the dynamic between the fully developed waves found in the deep ocean and a dumping surf wave in shallow water. YouTube can provide masses of evidence of breaking waves being negotiated in harbour entrances in Australia and the Pacific Northwest USA. Whether the boat in each capsizes or not seems to be down to luck, engine power, helmsman's skill, etc (or a combination there of) rather than any relationship to displacement or keel configuration.
 
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TimBennet said:
Whether the boat in each capsizes or not seems to be down to luck, engine power, helmsman's skill, etc (or a combination there of) rather than any relationship to .
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Naturally luck plays a great role, as one may be caught in dangerous situation or not. Helmsman's skill is also of great importance. So a bathtub may make cross Atlantic, why not? Or a man I knew once made it in open boat below 20'
But this is luck. Or skill. Nothing wrong with taking chances :)

Boat design is not about taking chances, but designing the boat for purpose. One may be for speed, other for sunbathing on holidays, another for safe cruising at sea.
For safety boat should be designed so it can ride a storm safely without the need for expert handling by the crew - since it makes a difference whether the boat saves her crew, or the crew has to save a boat. For naval engineers or designers "displacement or keel configuration" seems to have a relationship to seaworthiness, for which a lot of experimental, as well as theoretical work has been done.
This is knowledge, rather than "luck".
 
My comments about 'luck' was solely in regards to negotiating breaking waves in shallow water such as harbour bars and entrances.

There's no design in the world that can safely run through a breaking wave with a height greater than the boat's beam and just be left to look after itself. Every boat in that situation would need high levels of crew skill and a degree of luck.
 
TimBennet said:
My comments about 'luck' was solely in regards to negotiating breaking waves in shallow water such as harbour bars and entrances.

There's no design in the world that can safely run through a breaking wave with a height greater than the boat's beam and just be left to look after itself. Every boat in that situation would need high levels of crew skill and a degree of luck.
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I agree.
There is a saying that the biggest component of seaworthiness is the nut on the end of the tiller.
If the crew we are discussing had been clipped on, they would probably have survived.
Or if they'd worn LJ's etc.
Or if they had the knowledge to avoid the issue in the first place.
The design of the boat is only part of it.
 
So, Americas Cup Class (IACC) had a ballast ratio of 85%, does this mean that they were the safest boats ever?

Also, I just found out that many multi hullers have been cruising their boats, often for years, without ever being informed that they have a ballast ratio of 0%, it's irresponsible of manufacturers, I recon. The RNLI should run an awareness campaign or something.

Agree there should be an optional RYA stability course, aimed at day skipper level of prior knowledge, and boat manufacturers should have more controlled methodology for producing numbers like AVS and Ballast, and displacement as built, and polars. More like car makers MPG numbers. At the moment, they seem to just print whatever **** they like.

Also, if I went into a dealership, and specced up a shoal draft Sun Odyssey 32, ticked the box for In Mast Furling, Roller Furling, Radar, Bimini, TV antenna, AIS antenna, radar reflector, etc, would the salesman take the time to mention that the boat would now not self right with 5 crew clinging to the deck?
 
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Got it right, he wouldn't :D How would he know, anyway? :confused:
I still think that old way of establishing stability, an inclining experiment - with "inclining until she finally topples" is the only way. Not so difficult to do. I guess they still do it for Volvo Race.

BTW, bit earlier I was informed that under UE recreational craft directive (or whatever) boats obligatorily have AVS over 120 degrees.
Well, just recently tried to find those requirements and searched through some hundreds pages of directives, finding emission rules, sanitary rules, engines rules, and a lot of various paperworks required, but nothing of stability or safety.
Can anybody help me, some link or whatever, please? :o
 
Rossynant said:
Got it right, he wouldn't :D How would he know, anyway? :confused:
I still think that old way of establishing stability, an inclining experiment - with "inclining until she finally topples" is the only way. Not so difficult to do. I guess they still do it for Volvo Race.

BTW, bit earlier I was informed that under UE recreational craft directive (or whatever) boats obligatorily have AVS over 120 degrees.
Well, just recently tried to find those requirements and searched through some hundreds pages of directives, finding emission rules, sanitary rules, engines rules, and a lot of various paperworks required, but nothing of stability or safety.
Can anybody help me, some link or whatever, please? :o
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Try
ISO 12217-2
Small craft -- Stability and buoyancy assessment and categorization -- Part 2: Sailing boats of hull length greater than or equal to 6 m

Found the reference here http://www.rya.org.uk/SiteCollectio...nts/RCD Documents/1 RCD Compliance Guide.pdf:)
 
ProMariner said:
So, Americas Cup Class (IACC) had a ballast ratio of 85%, does this mean that they were the safest boats ever?
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This reminds me that when reading some of the old sailing books from the thirties, fifties and before, they mentioned it was possible for a yacht to "sail under" and sink.

This was because if driven too hard, they created waves big enough to lap over the gunwhale and pour into the cockpit, which were often not self-draining. Glug Glug Glug and down they went.

Reserve buoyancy was meant to help against this. Reserve buoyancy is a term hardly heard nowadays because modern lightweight yachts have so much of it, it is taken for granted.
 
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