Capsize Ratio's

[stevensuf]

Adelie , I beg to differ, From all the research I've seen and read, size counts,full stop.

The tests done on various hull shapes, forms, ballast ratios etc, all made very little difference, Boats with almost nothing negative in the g/z curve were only minimally better to resist capsize than boats with larger areas. yes there may be some boats where a 35ft is more likely to resist capsize than a 37 ft, but few and show me a 30ft boat that will resist capsize better than a 40ft boat.

Again very stable boats will resist capsize a little more than less stable boats, and we are only talking a foot or two in wave size difference, the main difference is very stable boats will right far quicker, or may not fully roll from being knocked over and under and bounce back up immediately, but both will be rolled under, regardless.

Look at fatsnet, not one boat over 40ft was lost and as size went down likelyhood of loss went up.

[s/v Jedi]

It's the waves that kill boats, not the wind. Breaking waves unleash their power upon anything they encounter while non-breaking waves can pass without harm.

Rule of thumb is that a yacht can survive a breaking wave 2/3rd it's size when taken head-on. A 30 foot boat survives a 20' wave. A 60' boat a 40' wave. Big difference as I have seen 20' breaking waves but never a 40' breaking wave while my boat is 64'.

For breaking waves on the beam there are many factors involved, like freeboard, height of superstructure (more of both is better), keels, centerboards etc. (less of those is better), length and beam of the boat (more is better). But I don't think there are easy formulas. There are people on CF that will argue a small boat is better than a big one... but only if they happen to have a small boat

cheers,
Nick.

[barnakiel]

Well, I do not seem to have any issues with the formula: I look at it, see what goes in, how things combine and get a pretty clear picture of what comes out, why, and how to interpret it. The gigo (a.k.a cico) limitation applies.

To those who think CR is too difficult to interpret I suggest the following shortcut:
- take the CR of any boat,
- deduct one,
- read the result as the probability that the boat WILL capsize one day.

Cheers,
b.

[TeddyDiver]

It's not difficult... It's useless.. IMHO
BR Teddy

[Paul L]

Originally Posted by Adelie

The formula is intended to be used to evaluate the boat as designed, not as it is being used or misused.

Not exactly sure how you meant this, but on the face of it it doesn't make sense. The boats were designed onshore. How a boat is used and loaded is important to its stability. There's a lot of cruising boats that people bought because they were heavy, safe and had good CSF numbers, only to put 16 jerry jugs on deck, two kayaks, a 25hp outboard... that does, in practice, make them more vulnerable to the sea. A furniture 40 with a high VCG is not likely to be more stable than a lighter weight design with a low VCG. Either way, a big enough wave taken beam on will do them both in.

Originally Posted by barnakiel

.....
To those who think CR is too difficult to interpret I suggest the following shortcut:
- take the CR of any boat,
- deduct one,
- read the result as the probability that the boat WILL capsize one day.

Cheers,
b.

You are just making things up here. There is nothing in the CSF that even states that less is better. It just says greater than 2 is worth more investigation.

[capn_billl]

I heven't seen a boat that has a capsize ratio less than 1 so that leaves any boat with a 1-2% chance of capsize?

I prefer NOT to be in a sea of 20-30ft breaking waves. I am also not likely to own a 90ft boat.

That leaves me with a choice between buying an old full deep keel sailer, or one of the new wing, or fin keels that sail faster... And watching the satelite weather forcasts very carefully.

[s/v Jedi]

Originally Posted by capn_billl

I prefer NOT to be in a sea of 20-30ft breaking waves. I am also not likely to own a 90ft boat.

It is 2/3 of boat length, not 1/3. So with a 30' boat you can handle those 20' breaking waves if head on and Neptune is happy

ciao!
Nick.

[Hud3]

Let's see, capsizing is rolling over on the long axis of the boat, pitch-polling is flipping stern over bow, so what do they call flipping the bow back over the stern?

[Paul L]

Half gainer

[barnakiel]

Originally Posted by Paul L

(...) You are just making things up here. There is nothing in the CSF that even states that less is better. It just says greater than 2 is worth more investigation.

No, I am not. You are simply reading from different sources!

Quote: "The boat is acceptable if the result of the calculation is 2.0 or less but, of course, the lower the better." End of quote.

Cheers,
b.

[Paul L]

Originally Posted by barnakiel

No, I am not. You are simply reading from different sources!

Quote: "The boat is acceptable if the result of the calculation is 2.0 or less but, of course, the lower the better." End of quote.

Cheers,
b.

read the result as the probability that the boat WILL capsize one day.

Not. Using the various screening formulas for rough comparisons is fine, but trying to interpret them without some rational thought of the actual boats is not productive. A boat with 1.9 CSF vs one with a 1.75 CSF tells you nothing about whether one of these specific boats is a safer boat than the other in the dynamics of offshore conditions. It is just one small factor of dozens. If you take the CSF to extremes then no Cat would ever survive.

[childofgodus]

i;ve been reading post for a while and learned alot. knowing that a sailboat can roll over and rite its self is great news,depending on type i gather.
i;ll retire soon and my back yard project will float, don;t stack top heavy and fat is not healthy. full keel is safeist and face the wind RITE?

[Bash]

Originally Posted by topfish

I have a general Question regarding the importance of Capsize Ratios? Are they really important and have any real meaning?

No. It's total horsefeathers. Brewster came up with the formula "tongue in cheek," by his own admission. An attempt to sell narrow boats.

People selling narrow boats will sometimes use the ratio to attempt to convince the uninitiated that their boats are superior to boats with greater beam. Another reason to ignore yacht brokers when they get into their spiel. These are people who spend their lives either poisoning the well or fouling the nest.

Check your BS meter for proper calibration. If someone starts telling you that Vessel A is superior to Vessel B because of its capsize ratio, your meter should be pegged to the brown end of the spectrum.

[David_Old_Jersey]

Originally Posted by Hud3

Let's see, capsizing is rolling over on the long axis of the boat, pitch-polling is flipping stern over bow, so what do they call flipping the bow back over the stern?

A cracking good thread on CF? ......by somebody who was watching from a helicopter .

[mitiempo]

Originally Posted by Bash

No. It's total horsefeathers. Brewer came up with the formula "tongue in cheek," by his own admission. An attempt to sell narrow boats.

Not just narrow boats but narrow heavy boats.

All Santa Cruz designs (27,37,40, and 52) are over 2.

Most J designs are over 2 with a few squeaking in just under and a couple in the 1.8-1.85 range.

Whatever anyone thinks of the above designs most would not consider them dangerous.

It is interesting to look at the results shown here Sail Calculator Pro v3.53 - 2500+ boats
for different designs but it doesn't mean all that much.

The displacement /length ratio is another that has little meaning unless looking at similar boats.

The comfort ratio as well.