Visit our Popular Forums

svrodeorm · 01-08-2010, 23:22

Why consider 20' too small for safety?

It's been made and proven IMHO.

Welcome to Sven Yrvind- the official website
Introduction to the junk-rigged Corribee Mingming

just to mention the first two, that comes to my mind...

barnakiel · 02-08-2010, 19:08

After Sailboat Design and Stability

"... If a boat is positioned into a breaking wave, most boats (wide and narrow beamed) can survive a 55% LOA (overall boat length) breaking wave. However, a 35% LOA breaking wave hitting a wide-beamed boat beam-on can easily capsize the boat. All yachts tested rolled to 130 degrees. No yacht, no matter how stable, could consistently resist capsizing when hit, beam-on, with a 55% LOA breaking wave. (K. Adlard Coles' and Peter Bruce's (editors) Adlard Coles' Heavy Weather Sailing (30th edition) Stability of Yachts in large breaking waves. Chapter 2 pp11-23 International marine, Camden, Maine)

Putting this in perspective in a 40 foot (LOA) sailboat: In a highly stable boat wave survivability would increase by 8 feet, if hit beam-on by a breaking wave. A 40 foot sailboat no matter how stable will not consistently survive a 22 foot breaking wave. Thus, in a strong gale with 22 foot seas and breaking waves, a 40 foot sailboat is at risk of capsizing no matter how stable ... "

A 20 footer must be beamy, otherwise it is called a kayak.

For a beamy 20 footer the 35% is 7ft.

How common are 7ft waves?

Cheers,
barnie

svrodeorm · 02-08-2010, 23:38

Yes, if the height of the breaking wave is at least the equivalent of 35% of the LOA of the boat, that same boat can theoretically capzize.

In 'optimal' circumstances for capzizing, which obviously are far from optimal circumstances for sailing.

The key word here is breaking, which is another story than crest, foam etcetera.

In normal cruising waters and normal cruising conditions breaking waves like that are very uncommon unless one is taking one's chances on shallow water.

Off the Portuguese west coast, there is at least one yacht each year that's capzized and or lost due to the fact that the crew do not recognize the risque involved in approaching a lee coast when there is a swell. Doesn't take more than a couple meters swell to create high and breaking surfs when the depth decrease close to shore. Hard to see when you're going downwind too.

The old adage - 'the most dangerous thing at sea is the shore' is valid.

I know of at least one boat, a 7 m Viggen (smaller sister to the Albin Vega) sho capzized off the swedish west coast by going to close to the shore in an attempt for a shortcut. This was many years ago and during an off-shore race...

At the end of a day, waterline length does make a huge difference, not only in this way but gives a more comfortable motion at sea too.

barnakiel · 04-08-2010, 10:27

Quote:

Originally Posted by svrodeorm

1) ...The key word here is breaking, which is another story than crest, foam etcetera...

2) ... In normal cruising waters and normal cruising conditions breaking waves like that are very uncommon unless one is taking one's chances on shallow water.

ad 1) I am not certain they talk the white water. It may be they talk about a X ft tall wave that is breaking, in general terms. Read the whole source text then go on to Marchaj - he also seems to be meaning an X ft tall wave, breaking, not a X ft worth of white water. (But I am ready to change my mind on this should anybody make a clear reference to a well made and clearly written piece of research on the subject). And yet, continue reading ...

ad 2) To me, the normal cruising waters and normal cruising conditions are the deep sea and whatever the ocean throws at you. My boat (26' LOA) was capsized in a place with thousands of fathoms of water depth and in nothing but average gale conditions (say like maybe sustained F8, gusting 9, average wave height not looking more than 12-15 ft.

So, much as I am willing to accept the idea of white water vs. total wave height (if good data be provided), from the practical point of view I can tell you that proper breakers happen everywhere, not only in the shallows, and a 20 footer is a suicidal boat for any extended ocean passage. And 26 footer too, but that's just what I have, so I stick to my guns and try not to repeat the same mistakes twice!

Exercise 1: Name 3 sub-30' boats that have circumnavigated and had no wipe-out or capsize experience.

Exercise 2: Name 3 over-40' boats that have circumnavigated and had no wipe-out or capsize experience.

Which of the exercises turned out easier?

Cheers,
barnie

barnakiel · 04-08-2010, 10:28

Thread drifters. That's what we are ;-)

Apologies,
barnie

lokas0506 · 04-08-2010, 11:16

still its interesting neverthless is it an offence ? maybe unless someone reports u that u are off topic but i dont mind in talking in capsaizing its quite interesting

svrodeorm · 04-08-2010, 12:13

@barnakiel-
agree on the thread drift and pretty serious too, but since it's already apparent, why not go on and let a moderator move in...

if they wish, or maybe rename the thread...

re 1. and here I've got to admit that it is quite a few years since I read those reports, but, my firm belief is that foam doesn't contain any force or momentum to cause a capsizing alas green water do. Then my memory could be wrong, or my interpretation of the text we are referring to, but the way I did interpret it is that it's the height of the breaking wave (think surfing movie) that has to be higher than 1/3 the LOD of the boat in question... this is all quite theoretical, but let's not forget the last and maybe most important factor:namely that the boat in our experiment has to be positioned beam-to the breaking wave to make a capsize happen.

Last of the important criteria in this matter might be to define what is a capsize and what is not. Again, unless my memory fails, a capsize per definition is when a boat heals more than 90 degrees or when the rigging is completely submerged in other words. Less heel than that would be defined as a knock-down. A serious knock-down can no doubt be a very unpleasant experience but still not a capsize per definition.

The general consensus on heavy weather tactics are that they all do whatever they can NOT to allow the boat to be beam-to breaking waves. heaving to, running downwind, trailing drogues or lying to a sea-anchor all deals with keeping the boat from broaching to end up in the vulnerable position 'beam-to' and furthermore to reduce boat speed to reduce momentum (simple laws of physics here) to prevent capsize and pitch-poling.

re2. I would think that this field of scientific experiments still is there for anyone who voluntarily would like to go out and perform experiments in a F 9-10

...guess it's done in tanks like Mr Jordan and his series drogue.

Then to the disclaimer.... I have not yet in 30+ years of sailing either experienced a knock-down, or a capsize so no personal experience.

My heavy weather experiences have mostly been hove-to (which incidentally heavy deplacement long keeled boats generally do very well) or running downwind(if wind direction coincides with the preferred course) under a storm jib and a few times trailing a cord of garden hose to reduce speed and momentum) Never in more than a F9 (short duration only) and definitely not with breaking seas or even against current.

As an aside, the only times I've been worried, or downright scared, has been where the seas are confused due to the bottom , windshifts, capes, or straits and the likes. Then 95% of my miles until now have been coastal or passages shorter than a week.

fair winds- is what we all want

svrodeorm · 04-08-2010, 12:16

BTW, In real life, I would think that wave length is a vital factor too for 'optimizing capsize probability'.

A 4 meter high short/steep wave is more likely to cause a capzise than a long and smoother wave.

If I still remember the physics from college

barnakiel · 04-08-2010, 19:44

Yep. The steepness of the wave decides if it breaks. But the size of the roller in relationship to your length decides if you capsize.

1) avoid steep waves (shallows, but also e.g. gale against an ocean current ...)

2) get the bigger boat you can afford.

;-)
b.

lokas0506 · 05-08-2010, 09:49

35ft Ferrous Yauht. Needs TLC for sale - TradeMe.co.nz - New Zealand

a bigger boat i just gave it a second thought put lets say 3-5k$ in to that one bring her over and try to sell her ... wild guess

rtbates · 05-08-2010, 12:12

I'm about to start a book called "The Cork Boat".. Yup, this fellow built and sailed a boat built out of corks, 160,000 of them Cork Boat...

He didn't listen to the naysayers either..

Have fun and happy sailing

svrodeorm · 05-08-2010, 12:29

Quote:

Originally Posted by rtbates

I'm about to start a book called "The Cork Boat".. Yup, this fellow built and sailed a boat built out of corks, 160,000 of them Cork Boat...

He didn't listen to the naysayers either..

Have fun and happy sailing

It definetely ticks box #1.

It will float.

barnakiel · 05-08-2010, 17:18

Quote:

Originally Posted by rtbates

I'm about to start a book called "The Cork Boat".. Yup, this fellow built and sailed a boat built out of corks, 160,000 of them Cork Boat...

He didn't listen to the naysayers either..

Have fun and happy sailing

Had a similar idea - use empty PET bottles and use netting to form a raft. Boat, it is NOT. But will go downwind like a bat. If your cruise is Gibraltar to the reefs of the West Indies - do you really need a better boat?

b.