CATAMARAN DESIGN: Why Are Some Catamarans Safer Than Others? Ep. 4.
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- Опубліковано 26 чер 2024
- Welcome to part 4 of our catamaran design series, where we discuss righting moment and structural strength.
Righting Moment and structural strength of Catamarans is important to understand the possibility of a catamaran capsizing and whether it is suitable for offshore sailing. This episode we talk to Antoine Richer, one of Corsair marines Naval Architects to learn how the construction methods affect strength. We also discuss righting moment and how that is affected by the type of catamaran you are sailing.
We have learned so much by getting facts from a designer rather than a broker and we hope that you find this a valuable tool if you are considering buying a catamaran, whether new or used.
We have more episodes in this series to come, so please give us a like, a 👍 and subscribe to the channel if you like what we do.
Much love,
Nick & Terysa xo
Another strong presentation. This series should be required viewing for all potential cat owners. Even if you're buying used, buying "off the shelf", or buying a full custom rocket, this series helps educate them and function as a guide for better sailing. Examples such as "weight kills", how a "cruising bow" may respond to wave action, etc. should help people reevaluate how they sail, where they sail, what they bring, etc.
Well Done
Best of luck with the series & the purchase
@@zzzxxzzz3248 will you elaborate?
i hope you can prove that cheapmaran is fast because you never mention the speed when you test seawind 1260 in thailand.. 😉
More weight makes a catamaran less likely to turn over from a wind gust. It's right there in the equation for stability. I have no idea what a "cruising bow" might be, and I know a lot about the subject.
Wonderful information, thank you both very much for this education.
one point. The narrower hull doesn't dissipate the wave energy, it takes less energy out of the wave
That’s what I thought I was going to use the word ‘absorb?
@@JG-iz8ko -- The hull shape could deflect the wave energy ... it will absorb some too.
When the waves break, we fix them!
Yer it’s how it cuts thou the waves to instade of riding on top of the waves
agreed
How about the narrower hulk slices through the wave.
This is exactly what I want to know about multihulls and their designs. Excellent!!
Thank YOU guys. Connecting with the professionals and publishing the interviews; rated the whole cat-manufacturing... Your view become a new and the best class for HOW TO ________CATAMARANS!... Very much appreciated
Always a pleasure
I'm really enjoying, and learning, from these Technical Mondays ;)
The next one looks to be very interesting.
Great discussion.
I'm a full time skipper a FP 47 Saona, and in heavy weather the Saona has very little under hull slap, it's very well designed, I've been very surprised how good it is.
your timing is perfect! Thank you.
Always a pleasure
This is why i am the very happy owner of a SMG50. The best built and safest blue water Cat I’ve ever sailed. The architect managed the magic of mixing and reducing all the compromises to perfection.
What is an SMG?
So glad you included summary statements/question. This made it easier to understand after the technical discussion. I am really enjoying following this series even though I am a confirmed monohull sailor! Thank you for this series.
Very informative video.. I’m learning a lot through this series. Thanks.
I feel that Nick somewhat misconstrued what the naval architect was saying on the strength of performance versus cruisers. Weight for weight, then the performance cat is indeed going to be stronger. But if you are not so concerned with weight, as cruisers aren't, the structure can always be beefed up at the cost of more weight. The safety from that point of view is a result of 'how safe and strong do you want it to be?' versus 'how fast and inexpensive do you want it to be?' It is not that performance cats are inherently safer as Nick took it to be on that point, although of course they are weight for weight. And the shape of the lighter cat may cut through the waves more, which reduces stress, but the lighter cat will bounce around more, which increases it somewhat. Similarly on bridge deck clearance, the naval architect can choose that, and admittedly the designers of charter cruising cats often make them too low. But the worst of all world's in that respect would be an overloaded performance cat, sitting a lot lower in the water than it was designed to do.
The ability to carry a lot of weight is a good thing, not a bad thing, and there are all sorts of valid trade offs which can be made between that and speed.
If you want to get out of the way of storms by running fast reliably, there is a lot to be said for a big engine and plenty of diesel.
It is what you fancy far more than safety for performance versus carrying a lot of stuff.
👍🏻
yea this nick guy is quite ignorant and full of himself. big yikes problematic.
Nick, this is incredible, all my nerdy questions answered in this series. Thanks mate.
Always a pleasure mate. The next one will blow your socks off!
Thanks for this learned a lot about my catamaran with a detailed explanation and logic, good stuff.
Thanks for sharing, great video and very informative.
Loving the Technical vids!
Thank you, Nick. Very informative. Cheers..!
Very well planned and informative series. Keep it up👍👍👍👍
Much appreciation for this video.
A Wonderfully Brilliant set of videos, An Absolute must watch for anyone interested in sailing and even for those of us that just like watching .... Well Done ... We should call you Prof Nick !!! Stay Safe & Fair Winds !!
Excellent episode with very informative content. Thank mate!
Always a pleasure mate
Where there is talk of “stringers”, and where the furniture is integrated into the mould & the design of the bridgedeck making it non-flat, is all about making the structure stronger by adding “compound curves” - they impart incredible strength, with minimal additional weight.
I've heard from other sources as well that computational fluid dynamics (CFD) modeling is not done as much as you'd suppose. Computer-aided design is used mainly for manufacturing - planning the fit and cutting materials. Modern designs rely mainly on empirical data of what works and what hasn't in the past. Use of CFD is growing, but generally just used to spot-check specific components.
I love this series you've put together! Thanks for sharing this with us!
Nice info. Thank you.
Righting moment brought tears, either it was funny or memorable, priceless tho. Its counterintuitive like the term Light crew. In interlake racing that means being the last nth degree crew weight allowed. Needed in big windy days and out on the rails. Little youth in other words.
Skipper screaming. Holding on, hoping and praying. Mostly that if it tips it doesn't turn turtle. Fun times.
THAT mar apply for a heavy mono but not so much on a cat need to have experience in Cat sailing fast (learn on a beach cat-hobie cat), tip over for fun and LEARN THE ROPES... then gradually go bigger and bigger until you have a 40 ft LOA, by then you may know what is "fit for your purpose"...
Excellent...👍
Very interesting, thank you
Amazing presentation. Thank you! Looking into a leopard 46 for our first cat!
This was a cool one!
Excellent thank you
You know, I am an old old subscriber of your UA-cam channel, from the time when you was sailing a monohull and me I was owning a sailing catamaran, I see you make the step of choosing to sail a sailing catamaran, you will see in long run is much safe, much faster and much more live aboard friendly that a monohull ( I am a big fan of catamarans, I can't see myself owning for many years a monohull 😁😁😁)
Thanks for showing us what idea store looks like LOL and a piece of stand alone furniture just in case I had trouble visualising it. You really make your edit a lot more work than you nedd too some times.
Rules of thumb:
For an offshore cat with a beam approximately half the length:
For an offshore cat with a beam wider than half the length, additional bridgedeck clearance is usually needed. The further apart the hulls are, the lower the hulls will ride on the shoulders of waves and the higher the crest will be between them.
20% of the distance between the hulls = minimum bridgedeck clearance.
Inadequate bridgedeck clearance would give a hellish ride in choppy conditions, with horrifying pounding.
I would call the 7-8% of length bridgedeck clearance a "rule of thumb" rather than a formula, but all in all a good attempt. Thanks for your effort!
If you ever do a follow-up to this...I think it would be interesting to explore what it actually would take to flip one, picking a real world example or say a particular seawind model... what combination of wind speed and sail area...and then that coupled with tilt from a beaming sea?
A Conser overturned off of Lanai from a wind gust off of a cliff. It is a very light boat, (12,000 lbs at 47 ft. loa,) with not much stuff on board since it was a day trip boat. It had a tall rig. It did have a lot of people on board, 44, perhaps about 8,000 pound of people.)
Great series on cat design Nick! Interesting that performance cats are lighter, yet stronger, but for live-aboards, are they as comfortable as a heavier production cat? Terysa has said that you spend about 90% of your time at anchor, so does having a lighter performance cat, that might be more sensitive to the flux and pounding of the seas, matter if you're only sailing 10% of the time?
Looking at the photo of the caterman. The first thing you see is the dagger board down. The question is are both down. My understanding is that the Lee dagger board should be up. Should the windward hull lift then the Lee should slide to prevent it overturning.of both dagger boards are down then it will flip.
2nd there is no sail s visible
3rd very little of the hull is in the water to me it on a reef or sand bar or something.
4th dagger board s increase the risk of this happening as more inexperienced people are buying sail boats and heading out to sea
These tech videos are very good . appreciate.
A pleasure mate
Super cool dude. Way #OfTheEpic infogig for sure. Thank you thank you thank you dude.......
I'm an engineer. When I'm trying to imagine how some things work on often take them to extremes as a mental exercise. A model boat hull could be made of epoxied cardboard and it will last for a while. The same shape hull that's 100x larger even though it's the same shape, there's almost nothing the same about how it will behave or react in water. Do the same mental exercise now with weights being close to zero and over weight. Etc. Some are useless, some aren't.
Actually scale models are an excellent way of designing a hull to predict its behaviour. This is done by many large companies, simulating waves and water speed and wind. Weather is unpredictable though, which is the hardest aspect to predict.
good talk for the general cruising fraternity some of the cats i have seen and worked on beggars belief some of the construction and layups of laminate are not good long term for dealing with high loads
Great Q&A. Thank you. There is confusion around bridgedeck clearance, that is important, but was not answered by the architect. If you're going downwind with waves then the bridgedeck clearance is largly irrelevant , this is 80% of circumnavigation cruising. When you're going upwind, the classic way to look at slamming, waves will hit the bridgedeck causing slamming. That is an issue of course but...a more real issue is bow waves. On a monohull when you go over a wave it splits the water and a wave will fly to either side. On a catamaran one side will be between the hulls and that wave will fly across smashing the hull on the opposite side between the two hulls. This is the most alarming and creates the most noise and discomfort while sailing for the crew. If that wave can be broken with a nacelle type structure in the middle it can be redirected downwards before hitting the other hull. This I believe to be the main reason for the nacelle's in many catamaran designs. Stray Kitty
You get more head room in the bridgedeck cabin with a nacelle, if the cabin sole is in it.
I really appreciate This searies because I have been desigigning my ideal catamaran in my head for 60 years and this helps me know wheter I have the design princeples correct. My goal is to hve submersible hulls so that waves can pass between the hulls and bridge deck in any direction. The weight of a wave pushes down as well as up against buoyancy
huh? 🙄
Winglets on both ends except the front need to pivot to keep the depth of the Hull steady under water and floats up when you stop moving
Love your graphic analogies that you employ to convey your lamen terms Nick. Haha....
Just a clarification from my understanding of the equation for Righting (or Restoring) Moment on a catamaran does not have anything to do with the sail area (or the height of the mast). I thought the formula was "weight * righting arm length" where "righting arm length" is the distance from the fall line of center of mass to the heeling pivot point. It is a torque vector measured in N * m. The sail area plays into the Heeling Moment which needs to be offset by the Righting Moment.
That’s correct. Righting moment is all about the hull and doesn’t have anything to do with sail area.
More sail area or increased mast height simply raises the centre of effort, which means there will be a lower static stability based on a given righting moment for the boat.
But it doesn’t follow that a performance cruising catamaran will have more sail area than a more accomodation-based catamaran. In fact, it may be the opposite, as a performance cruising catamaran can use less sail area to keep sailing as it isn’t as heavy and is more easily driven. Our 55 foot catamaran (a 2003 Outremer 55L) has nearly the same sail area (115 square metres) as the 10 foot smaller Seawind 1370 with a sail area of 116 square metres. For cruising, a smaller rig is safer.
@@tomjarecki Good remark guys! I was intending to flag out that sail area has nothing to do with righting moment, but being a bit lazy, I wasn't looking forward to writing a long explanation note.
Thanks for taking care of that.
I felt like you had to pull answers from the "Navel Architect" and often he answered "yes or no ". You had some VERY GOOD POINTS to make . Interesting to me. 🤔⛵🤠🌵
Thanks Stephen, glad you found it interesting
Very interesting topics and issues covered here. But not sure that Nick understood all that Antoine was saying about righting moment: sail area does not affect righting moment; it affects heeling moment.
I'm really enjoying this series Nick, very good information and insights to cats, thanks.
Are you going to get into the stability specifics for viewers to understand how stability works and how it is calculated ie TCG, LCG and VCG, KG, the righting arm, metacenter etc and the hydrostatic tables that should be supplied with each vessel in the owners manual (many don't supply these) and the full light ship stability details? Just wondering as these details would be very helpful to many to understand how these factors affect the stability and safety of all vessels. As a retired captain, daily stability calculations were part of the job.
@Flamingo lover
I love your gentle honest
comments, you don't have to prove anything, but wishing the best for everyone's greatness and safeties !
👍👏☮️💟
it would be interesting to discuss about bali catamaran design
So from what was said if I have got this right ? If you have a fast light cruising catamaran you are more likely to capsize if you get it wrong (fail to reef in time etc )than if you were on a heavier charter type catamaran which is more likely to de mast and have rigging failure if you get it wrong ( fail to reef in time etc )
?? Ps great Chanel and informative and entertaining episode as always Thank You
The amusing moment when Antoine reiterates that a heavier production cat generally has less chance of lifting a hull and inverting, but that it is totally irrelevant anyway because the standing rigging and mast will break first. So really what it comes down to assuming the price is the same, is load carrying capacity, space and comfort vs a circumstantial speed increase. I say circumstantial because power to weight of some charter cats are faster on motor. Build quality has nothing to do with anything but price, a slow palatial catamaran can still be built to the highest standard using the best materials but not be considered performance oriented. Great and honest video, I love that your videos are based in facts rather than blindly pushing a particular cat like an Outremer. ;)
It's not really about speed, rather more about the ability to sail well in all conditions. Sailing well means being more comfortable and rested during passages. Most performance catamarans have perfectly good accomodations.
About rigs breaking before flipping, I'm not sure that's true for any boat. Can you imagine the risk of purposely designing for a rig to break, then it causing damage and/or injury on the way down?
@@tomjarecki 10:12 Antoine states it in the video that the mast should break before a production cat will flip....the rig and mast is designed to break....Seawind is a production cat, go phone a manufacturer like Leopard or whoever and ask them. "Performance" cats don't "sail well" or comfortably in all conditions, less weight and more speed usually translates to a rougher ride unless you purposely slow it down like most do. If you want to talk about what this "debate" is really about all over UA-cam, it is about manufacturers like Outremer pushing a particular product based on very selective facts, fabricated controversy and pseudoscience through certain UA-cam channels. Seawind/Antoine have actually said some very wise and insightful things in this series. He is not engaging in the hype of "performance cats vs..." but is designing a well rounded catamaran that keeps in mind what the market wants. The Seawind 1370 or 1600 was in my final two catamarans but they need to work on their sales end. If they sold directly to the public like Leopard without the BS of trying to get information out of a salesman, I might have bought the 1600.
@@trentspencer7991 He says the mast “will” break but says nothing to back that up nor to point to a Seawind statement. I believe it is an English as a second language problem that he didn’t say “would” or “could”, which is I’m sure what he meant.
No catamaran manufacturer anywhere says that they design their rigs as a fuse to prevent capsizes. If they did, they would be sued every time a mast fails, regardless of the conditions. The difficulty for systems like UpSideUp is to set the force high enough so that it doesn’t release when pumping through a wave but does release before the point of no return, is that it is nearly impossible to establish that force level. And good luck getting insurance if the manufacturer says that the rig is designed to fail.
@@tomjarecki So you didn't bother to call a production manufacturer and actually ask them did you? You do realise that he works for Seawind/Cosair and as such is representative. You would prefer to think that you are right rather than actually obtain an answer. You speculating is pointless, go and ask a manufacturer or engineer. Why would they put it in writing for you or anyone else? Have you read an insurance contract? If you knowingly sail into a storm using a full sail plan you will most likely void your insurance regardless of a rigging failure or capsize, that is how they cover themselves. The mast and standing rigging should fail BEFORE it lifts 10+ tons of boat out of the water, not under normal conditions, not because it is designed to fail but because of its physical limitations.
@@tomjarecki Sorry again Tom, but cruising catamarans are truly designed and built so that the rig fails before the craft reaches the heel angle of vanishing stability.
Mmm that must have been excruciating Nick!!
You should have uses strong instead of safe when talking about different cats. When the furniture or options are molded in at the factory, they all become somewhat load bearing in some situations thusly making it stronger than one with added on features. All boats are only as safe as the captain and the decisions made under way. Great video! Love to need out with ya. Oh, the upside down ITEC book did kind of make me crazy. Gotta love OCD. Thanks
Soooo keep in mind that I don't sail and I live vicariously through y'all as far as sailing life goes, haha, but I'm relieved to hear this discussion about righting. Have been so excited about your upcoming cat endeavor, but silently worried about y'all being in a righting scenario. It's daunting to think of cat sailors having an inverted boat. I just can barely stand the thought of people in that awful position. I pray you'll never ever have that problem and I appreciate this video's explanation.
Also excited that your cat may not have the water slamming issue. I watched a Distant Shores episode a long while ago, when they were on a cat, and the slamming was horrid, and poor Paul was quite disenchanted. Lol.
Anyway, I honestly don't "worry" about you guys, as you always research so diligently and you willingly take in advice from other sailors, and you are stellar in your own experiences. So I have no two cents.
But I'm thankful that you'll have the best cat and it will serve you well.
This is why I want a outremer catamaran
Thank you for the great information. Is there a specific year or two where the production boats made significant step changes in design improvement? For example, are pre-2015 production boats to be avoided, since post-2015 boats have better hull shape, bridge deck clearance or mast position?
Low volume sterns like those of Wharram cats tend to pitch more, which is unpleasant and slow. A full width stern, (one in which the transom is the same width as the maximum hull beam,) however, tends to have too much drag.
Thanks for another great vid! Any thoughts on Aluminium construction versus composites?
Have you checked out Sailing Jupiter.?
@@wyattfamily8997 Indeed! I am very interested in the Mumby48 that Jamie and Princess are sailing. It would be great if someone did a thorough deep dive into the pros and cons of composite versus aluminum. There are other great performing boats out of Australia similar to the Mumby48 but in composite...
Should they have aluminium tubing as strengthener going from hole to hole to and to make the mask stronger to hold up to ?
Cats are faster due to less wetted area. Performance cats are lighter, to reduce wetted area. Hull shape contributes here too. Righting moment on heavy cruiser cats is so huge, the rig will fail first. This is by design to save the boat when in the hands of inexperienced sailors. I feel safer sailing a big performance cat in high winds than I would a cruiser or a tri. One has rudder authority for longer on a cat than a tri, meaning you can correct upwind at high angles of heal. Cruiser cats, you should never risk sailing in high wind, you'll likely loose the rig before you have any indication of overload. I would say that lack of rudder authority is the biggest contributor to Tri capsizes. Once you fly your centre hull, no rudder, you need to de-power or you'll get into lee helm and over you go. The amas with high volume will drag you down wind and you just can't dump enough main or jib to counter. Cruiser tris have less ama volume to give you time and then to pitchpole rather than capsize.. the design here is to submerge the bow but not pitchpole, but it not a controlled event and if trapped running this way, cut the back stay and let the rig go to lee. You can recover it afterwards, usually pretty buoyant.
As a multihull sailor for years I can tell you once you get used to them you can tell when your overpowered and reefing is required. It’s hard to describe but it’s there. I would say that if your quick you tend to be safer. Slow can be hit by gusts that put high loads on your rig but turning all that power into forwards motion can bring you undone very very fast
I'm thoroughly enjoying these technical talks so thanks Nick for that. What I don't understand with this video is the actual righting movement, no cat either performance or cruising is going to right itself if flipped, indeed the mast and rigging would probably give way long before that happened. With that in mind what are we actually referring to or concerned about when saying righting in this instance ?? As you quite rightly point out when sailing a cat you REALLY need to know your numbers and your rig to sail the boat safely and I would have thought that was more important that the righting movement. I may well be looking at this totally wrong (not being an experienced sailor like yourself) but I feel a little confused at this point. Having furniture built into the hull has many benefits and you would only have to look at catamaran IMPI and all the changes that Brett has made to his Lagoon 440 to make it the world cruiser it is.
Thanks again Nick, hopefully you can set me straight on the righting question. Stay safe and keep having fun.
It's not about how easily it rights itself as much as how much force is required to lift a leg outta the water.
What he's saying is that a performance cat has huge sail volume so you need to be wider and or lower to the waterline and heavier to stay upright but the last thing you want on a performance cat is to be low and heavy. So it's all a balancing act, quite literally. Don't know why they don't just call it the moment of inertia tbh. Maybe it's more complicated than that, < engineer not a sailor 🤣🙈
Edit. I should have added its about how FAR you can lift that leg outta the water, stay safe, be at an efficient angle of attack and reduce drag BEFORE you end up popping the lid on the epirb and pulling the cord of the raft 😁
As Andy C has said righting moment is a function of how heavy the vessel is + how wide the vessel is. The wider & heavier you are the less likely the vessel is to heel (like a monohull) & the more likely it is to return to the stable position. remember righting moment is given as an angle that the vessel can heel to before it wont right anymore.
What isnt being talked about is that some monohulls can be at 120deg (almost fully upside down) and they will return to their upright position (if they maintain water integrity). A catamaran will only return to its upright position if it hasnt gone past around 60deg.
Another thing that I believe is important to talk about when discussing righting moments, is to talk about "tripping". In a monohull in big beam seas the waves will roll the boat in a way that may get the vessel close to a 90deg angle, when this happens the keel is on an angle that allows the force of the wave to dissipate and thus the monohull will easily return to the upright position easily.
In a catamaran, while in big beam seas the vessel can approach the 60deg angle very easily (imagine the boat on a big wave, and the angles it could see), but the difference is that the Mini keels or dagger boards can trip the catamaran and force it over the that maximum heal angle, where the vessel will never return to an upright position. This is why some ocean catamaran sailors prefer dagger boards because in these conditions they can lift the downwind daggerboard totally out of the water (both dagger boards if it is really bad) and remove the risk of the catamaran having a tripping event. eg: the Catamaran will slide sideways against the force of the waves(or down the wave), instead of tripping over the keels and ending up upside down. In a monohull you slide sideways, and only if the wave is big enough will it roll you over the 120deg point.
@@daveatticus1018 The righting moment curve on most catamarans is positive up to 90 degrees of heel, which means that at any angle of heel up to 90 degrees the catamaran will come back down upright. It will be less than 90 degrees due to windage on the underside of the windward hull and bridge deck, but not as low as 60 degrees. Relax.
On big waves, the angle of the boat on the wave does not affect the righting moment 1 for 1 as both hulls are still in the water. So a cat heeled to 60 degrees on the side of a wave will still have the righting moment equivalent to less than half of that angle. If this wasn't the case, we would have a heap more catamarans upside down, but we don't!
You are correct about daggerboards - raising the leeward board allows the catamaran to slide sideways when hit by a breaking wave. Keeping the windward board down increases the downward force on the windward hull, hence that board is left down.
@@HandyC Thanks Andy, I still think the amount of stress on the rigging to raise a leg on a cruising cat would be monumental, if you actually got to that point when cruising as opposed to being in a storm you would be a very poor sailor indeed. Thanks for the help.
@@daveatticus1018 Plus in a mono as the yacht heels over air spills out of the rigging thus reducing the affect, this is not possible in a cat as there is no heeling over which goes back to what Nick was saying about the stress on a cats rigging being so hard to feel. This is the first time I have heard about the 60 degree rule and it surprises me that it is that high, just imagine the stress on the rigging and structure at anywhere near that point. I knew that daggerboards help prevent "slippage" but I didn't know they would help prevent tripping - very interesting. Thanks for the information.
GREAT as usual ..... Now... What happened after the 10 meter belly flop? Visually and Mentally I was stuck in the loop. I keep wondering when you will right the ITEC book on your shelf. Just kidding. Great Content and Explainations.....First Class info and presentation...Thank You for your considerable time.
My impression of UA-cam videos debating the mono-multi-hull arguments is that at best a multi-hull is an engineering compromise of weight and balance. Offshore passaging is an absolute. At a minimum, an endeavor not to be taken lightly. It would be interesting to see what the impact forces vessels sustain on average in high sea conditions. Fiberglass, Steel, multi hull. Maybe those experienced in heavy sea passaging can chime in and share their point of view.
The hull clearance formula can also be estimated by Hull Length (ft) x 19 = clearance (mm)
I think going back to first principles is a good approach to this subject. (I just figured this out, so...check it out yourself).
Reefing a cat versus reefing a monohull. I think what Antoine Richer is saying might be better expressed with a graph or animation. A cat may not have to reef as soon as a monohull, in winds that heel the monohull, the cat doesn't lean much, as the winds increase the monohull heels more and more, while the cat doesn't lean much at all - until perhaps it is too late - hence the need to do it by numbers. In race videos once a cat starts lifting an ama, sometimes it can't be stopped. Also as a cat ama is lifted higher and higher it begins loosing it's downward force (trigonometry) (imagine a cat on it side amas vertical, it can go either way? Between flat on the water and vertical the weight of a hull loses leverage.)
Though seeing a lot of post-hurricane videos where we see lots of flipped and wrecked cats - smashed in hulls, etc (as well as the same to monohulls) I don't ever remember seeing a broken-cat, where the hulls are pointing in different directions, or one is ripped off. That seems to indicate one basic problem, overall integrity is solved.
Another concern I have about multihulls with the open stairs into the amas (floats, hulls) is if in a huge storm if a wave busts into the saloon that water is going down those stairs, it's easier then to wash back out where it came in. Flood one cat ama even to a small degree and you have a huge problem. As a sea kayaker I know from experience water always finds a way, and a little bit of water on board sloshing around can be a huge problem. I think one hull with a foot or two of water sloshing around is more an issue in pitching than rolling.
Hull slapping and pounding. This has to do with the likely shape of the wave that hits the underside. Ideally a nacelle is designed so whatever the typical wave shape is, it doesn't hit the bridge all at once. A perfect high dive quietly ripping into the pool, instead of a belly smacker.
Great video. Thanks for doing this.
I was waiting to hear which was the safest righting moment, perhaps depending on the skipper, or the crews collective karma.
This was one session where I had a better understanding. It would be interesting to hear what are some of the safer cruising catamarans and why?
I went through this, Look at how they are constructed. Lagoons for example are all "glued" together, glued bulkheads, cheap materials, glued bridge deck etc. Once the glue reaches its shelf life what happens? Well a UA-cam search will show you. The more structural fibreglass/carbon fibre etc and metal there is holding it all together, generally the stronger it is. Also call insurance companies ask them what brands have had the most structural failures, they can tell you, the last guy I called was very informative and told me all about certain manufacturers. This question needs to be asked with a budget as well, it is too broad.
To me some year ago a huge lifting hull moment at 21 knot with my 9 meter sport cat ...instant lost 3 year of life and sweat shower .....never again!!
What about ballast to displacement ratio for catamarans? I'm designing a 5m stitch and glue catamaran and thought I would use deep narrow hulls with iron and epoxy at the lowest point and a layer of reinforced concrete above that for ballast. Like each hull having an encapsulated full keel. The idea is a trailerable pocket cruiser that I can pitch a tent on the deck of at anchor or beached, but that isn't as shy of weather as a Hobie.
I would be interested in your take on the VAAN R4/R5. Aluminum hull is tempting.
i worked in the construction of 96 metre+ high speed passenger, aluminium catamarans, even the 112m boats with a 30 metre beam only had a 2m draft, their hull plating was up to 12mm and 8mm above the water line, 6mm on the passenger decks and wheel house, frames were 1200mm apart with 'stringers' between 200mm to 400mm apart. I reckon a ~46ft version with the same wave piercing capabilities would be great.
I’ve a Seawind 1160
Bridge deck slamming is not an issue at. All it is a rare event
Hulls do lift when the wind is around 20 from abeam it’s hard to know when to reef
There. Are reefing instructions in the manual but it’s easy to luff up or bear away .
so, construct a narrow 60/70 ft. Cat. with a over-hang decking equal sqr.footage area Port and Starboard for Xwide comfort. ontop of the narrow hulls having good cabin berths but xtra longer, and it will do as you report about friction and energy dissipation?? the superstructure ie. salon/gallery/Nav center area being wider. ??
after careful reviews and practical use (you will pay twice as much when in a marina) cruising catamaran sped and ability to go up wind, maximum load, having to reef earlier than a monohull if you don t want to damage your rigging, extra maintenance on the rigging, the pleasure of sailing, even tho the cat offers space and no heeling I think of them as a power boat motoring more than on a monohull, it does depend your usage of the vessel it a personal decision that I respect
"Not suggesting any catamaran is inherently unsafe when leaving the factory" *Lagoon bulkheads designer laughs nervously*
Why don’t you two publish on “Rumble”? Could be another revenue source. Been following you two for years and will continue to. Wish you All the best with Ruby Rose II .
ahh He works at Seawind now i get it !!
Using furniture moldings is a low man hours way of making a boat, and an easy way to make a finished looking interior, but it is the weakest way of making an interior. If every piece of furniture is laminated to the hull, that is the strongest way to make a boat, because every piece of furniture is a stiffener. Molded furniture parts would prevent getting at the hull from the inside, which would be a huge problem if the boat has a hole in the hull from grounding on rocks or coral, or hitting an awash cargo container.
Is it safer to pitch pole in a mono hull or a cat?
Hi Nick, I really enjoyed the video today as I do with all your videos, it was most interesting. However....... I did get agitated having to watch you in your parents office where you have a set of five ITEC books, but.... the middle one is upside down. I think I must have a touch of OCD 😂🤪
I noticed those ITEC books. But I don't have OCD, I have CDO. Its the same mental derangement, but with CDO, all the letters are in the correct order!
Its the secret lever to the room behind the bookcase...
I’m sure you’ve said it in previous videos but when in the new catamaran coming?
In autumn 2021 mate
@@sailingrubyrose is that releasing autumn in England or Australia? Lol!
At the moment I’m more concerned about the upturned ITEC binder, than a flipped catamaran.
To learn how to push a catamaran HARD, buy a 16ft or 18ft "hobie cat" and sail in 20knots + winds and see how fast you go with a little lift on the windward hull... and how quickly you "loose it" when you heel too far... (DO NOT let the mast head go under !!! - put a large foam float on the mast head...)
Is there an English version available?
I'm surprised your neuroses haven't made you turn that centre ITEC book on the shelf to match the others. Mine sure would have.
Haha - too make them more noticeable?
One thing I think you’re missing is slapping, which is different than slamming. All those low bump outs and nacelles, and hard chines on both sides of the hulls, catch waves and make noise. The noise may be less than slamming but it’s very constant. It can even occur at anchor with very small waves. I owned a smaller cat that had near constant slapping and found the constant noise very annoying. I have rarely read about this but I am very focused on it in looking at catamarans. I would not buy a catamaran that has any hull bump outs or chines within a foot of the waterline. I want to see how a cat lies at anchor in a windy exposed anchorage and check the slapping.
Not a hint of a ballasted keel; the primary difference between a monohull and a catamaran. This, alone, makes a radical difference in righting moments. Also, the necessity of a polar diagram, for a particular boat, that shows righting moments. My understanding, that an active righting moment greater than 5⁰ one should begin to consider reducing sail.
Good thank you but what causes the cat to flip over you didnt discuss this in a the video Im very interested in this as a safety precautions thank you Nick I really want to find out more on catamarans but I eant it to be safe so lightist is the best right
The specialist told us in this video you wouldn't lift the hull, your mast would brake first.. I was rather surprised that Nick wouldn't ask more about that.. big issue.
intro music by flock of seagulls?
What brand of catamaran is the one that flipped over?
Cats are for flat-water - lakes, rivers.
the don't heel over well, and dangerous in rough weather blue-water.
I have never understood why is the engine room + fuel capacity is the least important aspect in a catamaran. It is so disregarded that many reviews ignore them. Why accomodations are more important than engines in cats? Engines are going to save your live if you loose your sails or if wind is zero or will help arrive on time to destination or escape a hurricane. Wind cannot be trusted. Motorsailing has being so important for me in the 80s from the Caribbean to Florida. I would prefer less living area in the hulls and bigger comfortable engine space (engines have to be inspected once per hour), fuel capacity (2k miles range under one engine) plus 2 generator, 2 water makers, high capacity drain pumps and inmediate access to all seacocks .... For me .... engineroom is the first thing that most be inspected in a vessel and easy access to all wiring, cables, electronics hidden behind walls and floors. Luxury never saves lives. Engine room in cats look awful compared to a motorsailer like the Shannon 53 HPS, the Nordhanv 56 MS, the Cheoy Lee 52 MS or the Diesel Duck 47 MS.
Very few cats have ever flipped. The always have been extremely strong winds been the cause
IE a micro burst to blame. These cannot be seen or predicted.
Thank you for this session. Bridge-deck slamming WAS an issue for me. My thinking was the higher the bridge deck, the less slamming. I now know that it is more a function of construction.
A strongly built Cat will still pitchpole, broach and capsize like any other Cat that's mishandled in very heavy weather (10+), but it might just survive these events relatively more intact.
Pitchpoling - too much speed in large waves, not likely when cruising. That's why bare poles and drogues are used in storm conditions.
Broaching - very difficult to do in a catamaran, they track like they're on rails and have two rudders set very far apart.
Capsize - that would be a bummer, but wouldn't break apart.
One of the biggest benefits of performance catamarans is that you can use much less sail area in any given conditions and still maintain reasonable speed. Heavier catamarans require more power to keep moving so are more at risk with larger sail area.
The fact is cruising cat very seldom capsize . The problem is that when they do they cannot self right . When considering stability it is often worth loking at the amount of energy required rather than just the force needed to case a capsize.
Re material choices: in reality they seem to go the opposite way to the way indicated here. The performance cat's usually use the superior materials. Very few (if any) charter oriented boats are made using epoxy for instance. Many fast cruising cats are.
How do you hold fiberglass together if they don't use epoxy?
Great series....even if I prefere monohulls 👍
@Tony Tiramasu Ferg I have a mono hull and I live aboard. Currently looking for a catamaran for the living space, inside and outside. Oh and the ability to take her into the shallower waters of the Bahamas.
Can you carbon fiber older catamarans to improve strength
Mr. MONK asked me to see if you can fix something? There are 5 ITEC books to your right. The middle one is not aligned with the other 4. Can you turn it around so they match? Have a Magical Day! I was also thinking: with one nacelle never in sync with the other because of the ocean moving. Can a Catamaran break in the middle?
Can a Catamaran break in the middle?
Short answer: Yes.
Long answer: Stress concentrations occur as a function of hull design. Material selection provides Young's Modulus of Elasticity. When the force applied exceeds ultimate tensile strength, bending to failure occurs.
Longer answer: Get an engineering degree! :)
Did they get to on keel sails? Isn't keeled sails safer and faster? Cat staying on top of the wave and strong while wide enough to gain 3 to 1 force vector ratio is two mast wide. What about these features in terms of power and rudder control. Wider is greater righting moment twice as wide as tall is three times greater righting moment. Stability and keeling of sails is most important.
All cats are designed to meet the same standard.
It's Just how you arrive at that strength
It all resolves on the weight of the vessel. Lighter the vessel less wave impact.
More pictures of bad verses good. Don't need to show names of manufactures. Great video overall! Thanks so much!