Capsize Ratio

[MicHughV]

technically speaking, the definition of a "yawl" is that the mizzen is located aft of a perpendicular line where the stern exists the water....some folks have a slightly different definition, but the above is the correct one. Most "yawl" mizzen masts are quite short, not to be confused with a mizzen mast on a ketch, which will be quite a bit taller.

38', in my opinion, is a tad small for a successful center cockpit design....my Landfall 43 was 43' with a center cockpit, bigger of course, but not big enough. I think 46' is about minimum to have a successful center cockpit design. smaller ketches are also to be found.

a ketch does split the sail area up into smaller sails, my Roberts was a snap to singlehand...some people simply don't like ketches, but I'm quite enamored by them.

[Adelie]

Originally Posted by MicHughV

technically speaking, the definition of a "yawl" is that the mizzen is located aft of a perpendicular line where the stern exists the water....some folks have a slightly different definition, but the above is the correct one. Most "yawl" mizzen masts are quite short, not to be confused with a mizzen mast on a ketch, which will be quite a bit taller.
......

Attached are photos of Atalanta, formerly one of the Ondines.
Is that a ketch or a yawl?
According to the rudder post definition it’s a Ketch since the rudder is transom mounted.
Better definition is relative size compared to main, but there’s a gray area where one could say it’s either/or and people don’t like fuzzy definitions.

Photos by:
Dustin Smith
&
Pacific Fog Photography.

[DMF Sailing]

Originally Posted by Adelie

Attached are photos of Atalanta, formerly one of the Ondines. Attachment 231737Attachment 231738
Is that a ketch or a yawl?
According to the rudder post definition it’s a Ketch since the rudder is transom mounted.
Better definition is relative size compared to main, but there’s a gray area where one could say it’s either/or and people don’t like fuzzy definitions.

Photos by:
Dustin Smith
&
Pacific Fog Photography.

Fuzzy definitions make the world go around.

Just looking at it, I imagine that the easiest way to sail a ketch singlehanded is with the genoa and the mizzen, at least on a reach in the conditions we get around here, 15-25 knots most days when there's a prevailing SW. You'd never have to reef. And then when you get into the 30s go with the mizzen and staysail.

Put that in your capsize ratio!

I should start a ketch thread.

[MicHughV]

Atalanta looks to be a Ketchy'awl...

sure falls under that " grey" area category to my eye...the mizzen boom hangs way back over the transom...I'l take a pass on this one...

[MicHughV]

I don't know that reaching with mizzen and genny is optimum....I have only occasionally done this, typically only in heavy weather, when the genny wasn't used at all......my Roberts sailed quite well under main and genny only...
The mizzen was handy for setting a mizzen staysail...I did often sail under spinnaker and mizzen staysail only....with the main down, the spinnaker was better behaved...and I didn't have to worry about backwinding the main...and having a boom flying over my head and spilling my beer..
lots of people don't like a spinnaker, but mine was always in use...

[DMF Sailing]

Originally Posted by MicHughV

I don't know that reaching with mizzen and genny is optimum....I have only occasionally done this, typically only in heavy weather, when the genny wasn't used at all......my Roberts sailed quite well under main and genny only...
The mizzen was handy for setting a mizzen staysail...I did often sail under spinnaker and mizzen staysail only....with the main down, the spinnaker was better behaved...and I didn't have to worry about backwinding the main...and having a boom flying over my head and spilling my beer..
lots of people don't like a spinnaker, but mine was always in use...

In other threads (and in this one) the way you describe your Roberts I imagine it being a heavy, stable boat in most sailable conditions, with a very low capsize ratio in real terms, if not numbers

[MicHughV]

Yep, I could explain it, but it would require some diagrams and some math mumbo jumbo...I don't think my boat was particularly heavy....fully loaded with gear, food, etc, it weighed about 20,000 lbs...this according to the strain gauge on the travel lift..later verified by the 3rd owner.....there are 38' boats that are heavier...and off course, lighter.

My boat was slightly stretched out, but I don't think this meant much one way or another, as during the build, I did a few things differently, giving a LOA of 39'3" if my memory holds. I believe the fiberglass versions of the R38 came in around 17,000 lbs,

Balanced against this is sail area.....again....middle of the road...my main mast was 40' above the deckhouse, the mizzen 30', I can't remember the sail area, but it was a bit more than the plans called for as my masts were taller and my booms a tad longer. I bought these used and that's how they came.

My boat floated with the upper chine showing above the water, but I've seen other Roberts 38, where this chine was several inches below the water.

The R38 is a very fine ended boat, with a beam of only 11'3", I believe the design LWL was around 27'6"....but obviously mine was a bit longer, I seem to recall 29'. You could not fit davits on this boat as the transom width is quite narrow, I carried the dink on deck.

I've been in some seriously bad weather, 65 knots, with seas to match, but was never concerned about the boat rolling, capsizing or otherwise misbehaving.

You seem to be fixated on the R38. I was very happy with the boat, it sailed extremely well, was easily handed, tracked straight and true...and for a 20-something lad at the time, I couldn't ask for more. It was my home for about 12 years.

If I were to do anything different today, I would opt to have an aft cockpit.

[Idlegreg]

Originally Posted by Mike OReilly

That's cool. I wonder how they do it. It looked, and stayed, perfectly stable upside down. And then it finally started to go over. The keel didn't seem to move to my eye. Was there some other mechanism being used?

Standard monohulls with capsize ratios below 2.0 are inherently unstable when upside down, so they can't remain in that position. At least that's the theory.

You must have missed it, they cant the keel to right the boat, as Alex says at one point. The keel moves slowly but it is way over before the boat starts to turn back. Most boats do not have the ability to do this trick so cannot be sensibly compared with an IMOCA.

I imagine the IMOCAs have a poor ratio because they are VERY wide - if you don't cant the keel they will likley stay upside down.

I think very few boats have a 180 degree AVS and so in theory, on flat water and undisturbed, the majority of boats would stay inverted. But as I understand it, in any kind of seaway (and especially the kind of sea that would lead to capsize in the first place) the boat will be likley to right itself if it has an acceptable AVS - the trick is to decide what is acceptable.

I think there are many other factors which effect both the liability to capsisze and the likelyhood that the boat will right herself promptly, so there is not one single minimum AVS that makes a boat suitable for offshore use. I have a vauge idea that (at least for slightly larger yachts) having an AVS of 125 degrees might be considered acceptable - someone with more knowledge of this than me can chip in now with better info :-)


nb: Not the 'New' Hugo Boss any more - that is the 2016 version!

[MicHughV]

there is a video of Hugo Boss testing it's righting capability on Youtube, The boat is flipped upside down by crane in the water, sans mast and sails, Alex crawls inside thru' the stern escape hatch, cants the keel over....and voila....back around she goes...presumably with the mast and sails on, it will still do this, but it wasn't tested that way....so I'm unclear on that aspect....
Those Vendee hulls are relatively flat from front to rear...several documented cases of these boats losing their keel, going over and staying over...

[laila23]

I don't think capsize ratio means anything by itself. It's a valuable parameter when the other ratios are taking into consideration and the over all quality of the design.
Oceanis 30.1 and Contessa 35 have very similar capsize ratios, but then.......
https://sailboatdata.com/sailboat/contessa-35
https://sailboatdata.com/sailboat/oceanis-301-beneteau

[Don C L]

It would be interesting to see a comparison of capsized hulls at a 30 or 40 degree angle, as in on the face of a wave, (with and without jibsheets and mainsheet cut to free the sails, if the mast is still up.) But all this is moot if water is allowed to get in making a "free surface" to mess up all the calculations.

[kazo]

Originally Posted by tenchiki

On the other hand, there aren't too many boats that have to prove that they can right themselves from inverted before acceptance: the new Hugo Boss:

but that was after dismasting

[kazo]

Originally Posted by tenchiki

On the other hand, there aren't too many boats that have to prove that they can right themselves from inverted before acceptance: the new Hugo Boss:

but that was after dismasting
and to my eye the keel moved.

[JBsurfin]

Originally Posted by Mike OReilly

That's cool. I wonder how they do it. It looked, and stayed, perfectly stable upside down. And then it finally started to go over. The keel didn't seem to move to my eye. Was there some other mechanism being used?

Standard monohulls with capsize ratios below 2.0 are inherently unstable when upside down, so they can't remain in that position. At least that's the theory.

With a completely watertight cabin, the weight offset flips it over. Looks to work great in flat, calm waters.. Do they do this test in a raging ocean?

[Mike OReilly]

Originally Posted by JBsurfin

With a completely watertight cabin, the weight offset flips it over. Looks to work great in flat, calm waters.. Do they do this test in a raging ocean?

I just watched it again. Yes, the canting keel moves over, but it's amazing how stable the hull remains even with the keel well over. It takes approximately 15 sec. before it starts to roll over. And this is without any rig attached.

I realize a wave will likely knock the boat off its inverted position rather quickly, but I really wouldn't want to be the one to test this in real life. With the rig in place (at least partially, one assumes), and with a rolling sea, it would not be a fun place to be.