Capsize Ratio

[GordMay]

Here’s an older (longish) discussion CF ➥ https://www.cruisersforum.com/forums...ios-78528.html
And a shorter CF discussion ➥ https://www.cruisersforum.com/forums...atio-5964.html

Capsize screening formula
➥ https://www.tedbrewer.com/yachtdesign.html
➥ https://goodoldboat.com/brewer-by-the-numbers/

[LittleWing77]

Originally Posted by thomm225

Unfortunately, these days big boat factories are pouring out sailing cruisers that are neither directionally stable nor have balanced hulls. Still they are being sold as ocean cruisers since their static swimming-pool stability has been found (or calculated) to be good enough.

You’ll easily recognise these boats by their sharp, vertical bows, wide sterns and huge steering wheels to cope with the weather helm.

In a pinch, these floating caravans could be used for marina-hopping, mostly in sheltered waters - and always with an eye on the weather forecast.

You have been warned.

+1 Thanks, Thomm!

Plus, they're bloody ugly.

When I was racing in Aus, they used to call them "sleds", because they're best pointed downhill to run before-the-wind only.

Cheers, Thomm and Happy New Year!
Warmly,
LittleWing77

[DMF Sailing]

Originally Posted by LittleWing77

We really are an incredibly pathetic lot, aren't we? When we all get so excited about righting moments and capsize ratios?

The untold secret about sailors: This is how deep our love of boats goes.

Warmly,
LittleWing77

P.S. Loved that Hugo Boss vid when it came out, Tenchiki. Fascinating to watch. Fortunately, it wasn't tested for Hugo Boss this Vendee...

Motion/comfort ratio is another one, Little Wing. Did you know that while the capsize ratio of the Hanse 375 (1.96) is not that far off from that of the Island Packet 379 (1.82), though the motion/comfort ratio of the sleek blade keel cruiser-racer with the ginormous main sail bows to the heavy displacement full-foil-keel cutter by 25.11 to 35.88?

I'm so glad I know that now

(The vessel in the picture in my signature is a Hanse 375, and in my experience, Thomm's description is pretty accurate

"these floating caravans could be used for marina-hopping, mostly in sheltered waters - and always with an eye on the weather forecast."

though somewhere there's a YouTube video of two guys sailing one in a Force 10)

[HeinSdL]

Originally Posted by thomm225

Unfortunately, these days big boat factories are pouring out sailing cruisers that are neither
directionally stable nor have balanced hulls. Still they are being sold as ocean cruisers since
their static swimming-pool stability has been found (or calculated) to be good enough. You’ll
easily recognise these boats by their sharp, vertical bows, wide sterns and huge steering
wheels to cope with the weather helm. In a pinch these floating caravans could be used for
marina-hopping, mostly in sheltered waters - and always with an eye on the weather
forecast. You have been warned.

Another Capsize Ratio Article:

https://theboatdb.com/blog/what-is-s...to-measure-it/

I am not sure I agree with this sweeping generalisation. My boat fits that description pretty well, except for the bow which is not vertical, but only because the design dates from the late 80's when my boat's design was more or less current. The stern is wide and the wheel is large, the question though is why.

The basis of the design is closer aligned with the planing dinghy and much less with the traditional ocean cruiser (whatever that is, but let's say continuous keel, protected rudder, etc) but this does not make the boat fundamentally inferior. So the stern is wide, not to be able to fit in a huge cabin in the back, but mainly with performance in mind. And therefore it also has a large steering wheel. Absolutely not because of excess weather helm but because of a need to sit on the rail while steering (a racing helmsman would never sit mid-ships). It's an old fashioned solution, today you would have two steering wheels to overcome the same problem (wider stern yet the need to sit in the rail). Just look at some of the Wally yachts...

About weather helm - it's inevitable, a mathematical certainty, the moment the boat heels over. The forward force produced by the sails is not directly over the force produced by the water on the hull so the boat will indeed luff up if you let go of the tiller/wheel. And that is how it should be, without weather helm there is a sail trim issue. Nevertheless, my boat, when sailing close hauled in a breeze can be sailed with the wheel between thumb and index finger, no force required. So again, no relation between size of wheel and weather helm. But when you let go of the wheel it will indeed luff up.

A well designed boat, a I feel mine is, actually makes use of the rudder foil to produce additional lift. So yes there is some weather helm but the force produces by the rudder on the hull will also counteract sideways drift. In practice the keel can be placed slightly further forward but because the weight needs to be directly below the center of effort of the sails the keel is designed swept back, as mine is.

And so it goes on. Many different variables to consider but I don't think having a wide stern, a big wheel and a vertical bow is evidence of poor design. The engineering behind the design is important though. Hence I very much like having a galvanized grid on which the mast stands, to which the keel is bolted and in which the shrouds are anchored, visibly fixed to the inside of the hull (and hence the only role left for the hull is to keep the water out and provide stiffness for the fore and aft stays) as opposed to the more common matrices.

[AiniA]

Originally Posted by thomm225

Definition Capsize Ratio:

Avoiding capsizing an offshore cruiser
Capsize ratio

With offshore cruisers in mind, I have tried to find some formula which cover the resistance
against capsizing. Now I found this text on the web:
CAPSIZE RATIO: Some years ago the technical committee of the
Cruising Club of America came up with a simple formula to
determine if a boat had blue water capability. The CR compares
beam with displacement since excess beam contributes to capsize
and heavy displacement reduces capsize vulnerability. The
formula is the maximum beam divided by the cube root of the
displacement in cubic feet:
Capsize Ratio = Beam/Displacement.333.
The displacement in cubic feet can be found by dividing the
displacement in pounds by 64.
The boat is acceptable if the result of the calculation is 2.0
or less but, of course, the lower the better. For example, a 12
meter yacht of 60,000 lbs displacement and 12 foot beam will
have a CR Number of 1.23, so would be considered very safe from
capsize. A contemporary light displacement yacht, such as a
Beneteau 311 (7716 lbs, 10'7" beam) has a CR number of 2.14.
Based on the formula, while a fine coastal cruiser, such a
yacht may not be the best choice for ocean passages.
The formula works both when you use imperial or metric numbers.


Unfortunately, these days big boat factories are pouring out sailing cruisers that are neither
directionally stable nor have balanced hulls. Still they are being sold as ocean cruisers since
their static swimming-pool stability has been found (or calculated) to be good enough. You’ll
easily recognise these boats by their sharp, vertical bows, wide sterns and huge steering
wheels to cope with the weather helm. In a pinch these floating caravans could be used for
marina-hopping, mostly in sheltered waters - and always with an eye on the weather
forecast. You have been warned.

Another Capsize Ratio Article:

https://theboatdb.com/blog/what-is-s...to-measure-it/

You read something that sounds quite authoritative until you hit something that is just nonsense, e.g. what is in red above. They put big wheels on for a couple of reasons - they look sexy at the boat show and, more importantly, they allow one to steer from further out so you can see Genoa trim. I say this as someone who did my serious cruising on a narrow-assed Bristol 45.5 that had a moderate size wheel. Now have a Catalina 36 MK II which has a bigger wheel than the Bristol but has no weather heels to speak of. Bigger wheel allows you sit comfortably and see the penny.

[Mike OReilly]

Originally Posted by DMF Sailing

Oooh!

Thanks for providing this cool toy!

I've sailed dozens of cruisers, none of which I want to buy, so it'll be fun to compare and shop and just plain nerd out in the years to come!

Yes, hours of fun .

I always take these raw-number comparisons with a grain of salt. As we all know, a boat is more than just the sum of its basic stats. But I do think this is a useful tool for comparing similar types of boats. And if you can ground the results by comparing it to real boat that you know well, it can be a good way to get a sense of unknown boats.

[Greg K]

The topic of capsize screening is covered in detail in this article In Ocean Navigator. https://www.oceannavigator.com/assessing-stablity/


All boats will capsize. The important question is whether they will come back up before the helmsman, who is presumably clipped in, drowns. 2 minutes is about the longest most people can hold their breath. According to the formula, boats with a screen below 2 will return upright under the two minute period.

[DMF Sailing]

Originally Posted by Mike OReilly

Yes, hours of fun .

I always take these raw-number comparisons with a grain of salt. As we all know, a boat is more than just the sum of its basic stats. But I do think this is a useful tool for comparing similar types of boats. And if you can ground the results by comparing it to real boat that you know well, it can be a good way to get a sense of unknown boats.

A football-sized rock of salt...

But yes, exactly, what I've been doing is running the numbers on the boats I know against the numbers of the mythical ideal unicorn "bluewater cruisers" out there

Think I'll run that Hanse 375 against a Rafiki 37

(or is sail stat stalking considered creepy on this forum?)

[Mike OReilly]

Originally Posted by DMF Sailing

A football-sized rock of salt...

But yes, exactly, what I've been doing is running the numbers on the boats I know against the numbers of the mythical ideal unicorn "bluewater cruisers" out there

Think I'll run that Hanse 375 against a Rafiki 37

(or is sail stat stalking considered creepy on this forum?)

Go right ahead. I'd be curious to see the graph.

[Don C L]

Keep in mind that it is a wave, not the wind, that will likely motivate a boat to lean too far over. As I am sure you have found, the distance of the ballast from the waterline does not figure into the capsize formula for some strange reason. This article may be of interest:
Offshore Sailor: Boat stability
It seems intuitively obvious to me that keeping the center of gravity far from the center of buoyancy as possible is a good idea and should figure into any evaluation of a boat's capsize resistance. Now there is also the matter of beam. A broader beam is good for initial stability, initial resistance to heeling, but once capsized, or close to it, that beam starts to work against the desire to right itself, compared to a narrower beamed boat. (My own boat has a very small area of inverted stability in the GZ curve, it really does not want to be upside down, but it is also a bit tender due to its narrow beam. If you are concerned about how the boat will behave once inverted, look to the area in the inverted stability portion of the curve.) And then there is the issue of the mast and sails below the boat, if they haven't snapped off. They will slow down any recovery too. But remember too that these things do not happen on a flat sea. The same mountainous waves that rolled a boat will in turn bring it up on its side again exposing the righting power of the ballast in the keel.
But, fear not. Joshua Slocum sailed around the world in a boat that probably had the worst capsize ratio possible.

btw, the last sentence of that article; I often think of that when I see little boats outfitted with every bell and whistle above the waterline, or on an arch, or up on the mast.

[DMF Sailing]

Originally Posted by Mike OReilly

Go right ahead. I'd be curious to see the graph.

It's real close! Two completely different boats, two completely different philosophies

(until you get to comfort)

[Jim Cate]

what is not discussed in those figures is how often and in how much minimum wind will the two boats reach their similar hull speeds? And by how much will they exceed those theoretical limis?

I think we all know the answer to that one!

Jim

[JPA Cate]

Well, there you go.

Have some nice racing, fellows.

Ann

[Lexi22]

These calculations are my new obsession.

[thomm225]

Originally Posted by AiniA

You read something that sounds quite authoritative until you hit something that is just nonsense, e.g. what is in red above. They put big wheels on for a couple of reasons - they look sexy at the boat show and, more importantly, they allow one to steer from further out so you can see Genoa trim. I say this as someone who did my serious cruising on a narrow-assed Bristol 45.5 that had a moderate size wheel. Now have a Catalina 36 MK II which has a bigger wheel than the Bristol but has no weather heels to speak of. Bigger wheel allows you sit comfortably and see the penny.

Since so many seemed to have differing opinions on the capsize ratio, I just decided to do search.

The guy that wrote it was a lifelong sailor from Norway but you can find similar thoughts by others.

Today though many boats with Capsize ratio's way above two are sailing far and wide because they have such good electronics they can avoid the worst weather

Some of Vendee boats had CR's close to 3.0!

Hall of Fame - Arne Kverneland - PDF Free Download

https://www.junkrigassociation.org/R...%20cruiser.pdf