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Old 13-05-2021, 20:22   #1
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The reason lighter cats are safer?

Hi folks,

Iím trying to absorb as much as I can from this forum to avoid asking stupid questions in my first post. Iím very grateful to everybody on this forum for contributing their knowledge.

I keep reading the point of view that lighter cats are safer but I havenít been able to find information that spells out why?

Iíve come up with my own rationale but I donít know if itís correct. I could be wrong in lots of my thinking so please correct me.

Main assertion, the greatest risk to a sensibly skippered cruising cat is pitchpoling, not capsizing.

If this is the case will not heavier cats with fatter hulls only start surfing down waves in stronger winds and bigger seas? So does that mean that the lighter cats would be expected to deploy drogues to maintain control earlier than a comparable length heavier, fatter cat? If so it seems the lighter cat is at more risk?

Or is the above way of thinking wrong? A light cat carries less momentum and therefore its bows are less likely to dig in and pitchpole before the buoyancy overcomes the momentum and lifts them up?

Or is it because even though the light cats have the potential to go faster their lower momentum makes them more easily controllable with reduced loads when deploying drogues?

There surely is the point that lighter cats sail faster and potentially can avoid the worst of the weather but is this the only thing that makes lighter cats safer?

Or none of the aboveÖ maybe thereís no consensus?

So you can gauge your level of responses to my experience, Iím a middle aged guy trying to build up my abilities but its currently limited to a few years dinghy sailing. Go easy please!
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Old 13-05-2021, 23:28   #2
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Re: The reason lighter cats are safer?

i'm not aware of any research that shows lighter cats are safer. in fact i'd say just the opposite - some owners of light weight boats might argue this, but the 2 or 3 cats that have capsized in the last few years in our part of the world have all been what i would call 'light displacement'

however the short answer is 'it all depends'

how light is light ? too light is imho dangerous...probably more dangerous than too heavy. but it's a gradient...there is no magic cut off point or ideal weight / length relationship

our boat is on the heavy side - 7.5mt for 12m LOA / 6m BM. a tonne lighter - without losing strength - would not make this boat any more or less dangerous...but say 4mt lighter definitely would.

anyway, i suspect your thinking is correct...a light weight boat will react more quickly to waves / gusts. this may be too quick for crew to respond. the boat will (almost certainly) also be going faster so eg runs the risk of running into the wave in front

a light weight boat will also be much harder / tiring on the crew, which has it's own dangers. on the other hand may put less stress on gear & rig...so...

it is also more expensive to build a strong light boat than a strong heavy boat, so many (not all) light cats will not be as strong or likely last as long, as a heavier boat. of course this is a generalisation and there are exceptions to every rule, but that's the idea.

hope this helps

cheers,
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Old 14-05-2021, 01:20   #3
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Re: The reason lighter cats are safer?

I'd agree that there is no definitive answer to light or heavy as "safer".

One aspect to consider is that light boat's do have the advantage that you can put a smaller rig with lighter loads for the same or better performance. On the other hand, lots of lighter boats are oriented towards racing so have a big very powerful rig.
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Old 14-05-2021, 01:21   #4
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Re: The reason lighter cats are safer?

In heavy weather a light cat is not a good idea.
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Old 14-05-2021, 02:52   #5
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Re: The reason lighter cats are safer?

If you only look at the weight to gauge the safety, you will probably not end up with a correct result. There are a lot of other factors (and ratios) that influence the safety.

However I am pretty sure, that for a given design, the overloaded boat is unsafer than a sistership that is floating on it's design waterline.

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Old 14-05-2021, 04:21   #6
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Re: The reason lighter cats are safer?

Greetings and welcome aboard the CF, siggy.

You've certainly posed an interesting question.
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Old 14-05-2021, 04:33   #7
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Re: The reason lighter cats are safer?

Can you share some of the sources? I've never heard suggested that light weight by itself causes them to be safer.

Like any time you look at one variable in isolation, you often lose the context and can come to incorrect solutions.
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Old 14-05-2021, 06:35   #8
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Re: The reason lighter cats are safer?

Quote:
Originally Posted by valhalla360 View Post
Can you share some of the sources? I've never heard suggested that light weight by itself causes them to be safer.

Like any time you look at one variable in isolation, you often lose the context and can come to incorrect solutions.

I don't have any research but I have seen several posts here commenting that lighter weight is safer. I don't believe it was in the context that payloads above the design weight increase risks as that is just too obvious. The reduced loads on lighter cats are understandable as a safety factor but I didn't think that alone would be enough to make a blanket statement overriding all other factors.



One long thread covered a debate over the pros and cons in heavy weather of just running under bare poles or deploying a series drogue.


https://www.cruisersforum.com/forums...g-60057-2.html


So I was thinking if there were still no consensus on drogues amongst people far more knowledgable than myself, what choice of hull could I make to lessen the chance of needing to make the decision to deploy a series drogue in the first place. Seemingly a fatter and likely heavier displacement hull would be the better choice in this respect but I was trying to square that thought with the "lighter is safer" comments.
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Old 14-05-2021, 08:17   #9
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Re: The reason lighter cats are safer?

If by light you mean also with easily driven hulls, i.e. a more performance focused boat rather than just a 'normal' boat built lightly, then I'd agree. What I mean is light weight on it's own doesn't make the boat safer.

If however you build a boat that has easily driven hulls AND is light then I'd argue that for most situations it's safer, a few reasons:

- for a given speed you will use a smaller sail area. This also gives a lower CofE which is fundamentally safer as it creates less heeling moment, less stress on all components etc.

- if a narrow bow is driven into a wave it will more likely drive through easily, slowing the boat much less, whereas a wider hull will struggle. The heavier less easily driven boat will thus have a higher pitch-pole moment of inertia which when combined with the higher CoE and more power in the rig is fundamentally less safe. Wave-piercing hulls are a thing in high performance cat design.

- if you are in a big wind and seaway and are running just for safety, maybe under bare poles, the lighter narrower hulls are again safer as they will much more easily drive through waves rather than tripping on them and slowing the boat causing either a pitchpole and/or broaching risk.

To those who say heavier is better in big wind, I would say that if you are in a big enough wind to literally pick up a boat then what's a couple of tons going to change? You have bigger problems at that point, but the faster boat would have had more chance of getting out of the dangerous situation in the first place. If you can average 200nm rather that 150nm per 24 hrs, that extra 50nm could mean the difference between safety and disaster. With modern forecasting that extra safety window could easily stretch to 3/4 days, 150/200nm distance. When you look at it that way speed suddenly does become your friend.
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Old 14-05-2021, 08:50   #10
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Re: The reason lighter cats are safer?

I haven't any offshore experience in cats, but I once took an ultra light mono to New
Zealand from the US. We were going downwind in 45-55 knots for a day. I was a little concerned about pitchpoling until I saw that the light boat never got on the steep part of the waves, which were 4-6 meters. We were doing 14-18 knots with just a reefed main and the autopilot couldn't keep up, so the biggest problem was doublehanded driver fatigue.

OTOH, a lighter cat has a lower capsize resistance. I also remember being blown over backwards on a Hobie when I tacked on the top of a steep wave and the wind got under the trampoline.
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Old 14-05-2021, 08:56   #11
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Re: The reason lighter cats are safer?

A lighter cat tends to sail on top of the water and waves. A heavier cat tends to plow through which induces more stress on the structure.
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Old 14-05-2021, 09:00   #12
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Re: The reason lighter cats are safer?

In the first post, it seems that there's an impression that surfing is automatically unsafe and if it happens, you must deploy a drogue to slow the boat. Personally, I'd disagree with that idea. Yes, there's a point where you're surfing too fast for the boat in question and risk stuffing the bow into the next wave and broaching. But up to that point, if the boat is handling well and not showing any bad behaviors due to too much speed, I see no reason to slow the boat down.
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Old 14-05-2021, 10:30   #13
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Re: The reason lighter cats are safer?

Ask Riley, on Sailing La Vagabonde!

He made a video about that question:
https://youtu.be/LGD5pmANdgA
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Old 14-05-2021, 11:01   #14
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Re: The reason lighter cats are safer?

You need a boat for your purpose.
If main purpose is sailing, and not cruising, an empty lightweight performance cat is for you.

If you pack it with all your creature comfort stuff for liveaboard, you will make it a lame duck and will sacrifice safety. A lightweight design is built for weight reduction and not stability.

On the other hand a heavy production catamaran is built to carry a lot of cargo. A 400S2 Lagoon weights 10t and can carry another 4t easily. A heawy hull is better st anchor, better for living on board. It is slower than an empty performance cat with narrow hulls, and doesn't point that high, but is much more liveable. If you add all the stuff you have on a Lagoon into a performance cat like a Outremar of the same size with the narrow hulls, you will make it slow and sink the waterline.

A formula 1 racing car is light and fast, but you cannot use it as an RV. A RV is not made for the racing track either.
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Old 14-05-2021, 11:20   #15
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Re: The reason lighter cats are safer?

Quote:
Originally Posted by siggy View Post
Main assertion, the greatest risk to a sensibly skippered cruising cat is pitchpoling, not capsizing.
A bit pedantic, perhaps, but I'd like to very strongly proclaim that a sensibly skippered cat will not have any great risks at all, whether lighter or heavier displacement. Conversely, a cat (or half-boat), that is at risk of pitchpoling, is not sensibly skippered.

Once you accept this, it makes no difference which category your potential boat is in, and you select it using other criteria.
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