how do cats handle big waves?

One of the most respected yacht research organisations in the world is the Wolfson Unit at Southampton University

Some years ago they were commissioned to do comparative tests between a model monohull power boat and a catamaran. The test were carried out in a test tank with a variety of wave heights and directions.

Try as they could they were not able to capsize the powercat. Whereas the monohull capsized easily.

I have seen the video they made and it all looked very realistic to me. (I have been in real waves of the size tested in the tank)

An old Hobie video showed Hobies sailing in big breaking waves without capsizing.

Did the monohull in this video "survive" what is actually a relatively small wave. (Check the wave height to the boats freeboard)

http://www.youtube.com/watch?v=5vK074Ymlqw&feature=related

I think this was a bigger wave

http://www.youtube.com/watch?v=9frzM-8hEe8&feature=related


So I think you must be accurate with your "a multihull would not survive" statements if you want to be believed

Richard Woods of Woods Designs

www.sailingcatamarans.com

 

Here's what I've never been able to understand: monohull sailors who feel that cats are unable to cope with horrific conditions, but who carry a life raft, just in case the monohull goes down in those horrific conditions.

Do they not realize that a cat is a raft? Except, of course, that it's a raft with vastly greater stability than any life raft.

It should be obvious to anyone who thinks about it that a cat is much less likely to be rolled over than a monohull of similar size, and not just because of its vastly greater stability. A well-designed cat does not have a deep keel, and many monohulls are rolled because they trip over their keels. A good cat is much lighter than a good keelboat, and this and its shallow draft allow it to surf sideways when hit with a breaker. About 30 years ago, I singlehanded a Wharram Tane through the fringes of a hurricane, and I feel certain that this phenomena contributed mightily to my survival. It's a weird sensation-- the G forces are large, but it's a lot better than flipping.

I'm not sure that any boat can survive a really massive rogue wave, be it cat or mono, but if I had to take my chances, I'd rather be in a cat.

 

Sailing cats are fun. I did that when I was a kid at Ocean Shores, WA. We played in surf like what capsized that mono in your video. However, the pic of the Hobie jumping does not have the same class of wave as the one knocking down the in-the-surf mono and the jumping video is set up specifically for the video. I know, everybody's a multi-hull designer these days and I've offended by saying anything less than " It handled heavy seas wonderfuly" but, in this instance, NO little sailboat wud do well and I was addressing power cats specifically. No lubberly types, even respected tank testing kids at a university can comprehend what I am talking about.
I have far more experience in this than any of you, seriously, and if you do not care to believe, that is fine, too. You have never, nor will ever, see anything like the conditions I described. The people at the university have not got a wavemaker that can duplicate it, even at scale. The violence and power is unfathomable to someone that sits in an office. Even in the example of boats getting in trouble down by Australia, there was pointed out a couple with a lot of experience, 18,000 miles, I think it said. I put in that in many single years. We will never agree, you will always think I am exaggerating or that your two hulls are better than the other guy's. So be it. I take a stab at educating, or to put it a different way, "to make aware" but it is certainly not of much value to me to discourse on multi vs. mono, watch a vid of a mono dead in the surf, and such. My boat, well found but no secret, special design, might have capsized had I let it ride quarter-to a breaking eight footer in surf. That has nothing to do with the scenario I put forth.
All of this being said, a prudent mariner does not put himself in the spot I was in Sunday and a little planning and PATIENCE wud avoid the weather altogether, no matter what the vessel. All I am saying is that, IMO, a forty foot cat wud not have made it thru. It is from my experience being in and watching multis in severe conditions.
Certainly a "(under 10 tons), light, high volume boat will rise quite fast, and so not notice as much" up until the point that it is crushed and flailing parts at the once-occupants trying to clamber back aboard. I am truly sorry that the acedemic discussion does not play out the way you want in real life - I wish it did.

 

I carry a life raft because I am required to or for the unlikely event of fire (Twice I have pulled people from their burning boats. Believe me when I tell you that fire is worse than weather.). My vessel and skills are my raft, as well. Pay special attention to my comment about clambering aboard a vessel that is trying to beat you with its parts. Yacht people seem to think that the sea is going to sit there benignly while you follow your plan. Have fun out there!

 

I for one, would be interested to know what boat you have and where you use it. (I know WHO Homer is/was, but not WHERE it is)

Richard Woods

 

No story, but here are some data collected by the Wolfson Unit on catamaran capsize by waves.

The catamaran is the most seaworthy hull form with regard to wave-induced capsize.

 

Mark: I like the story/experience you are relating. It's one we often don't imagine when thinking about cats and monos in rough weather. It's something like a bar crossing or the Gulf Stream in the States, where there is a very similar phenomenon and a lot of boats get beat up badly.

Now, I think you would want to compare apples to apples here though.

When you are talking about these short, steep, frequent waves, what LOA is your boat? We would want to compare the same LOA catamaran to the same LOA mono in this case, because you are heading directly into these waves in your account, right? In that case, only LOA matters.

Another interesting bit about the kind of waves you describe is that they also occur in the Great Lakes in the States. There are hundreds and hundreds of lost vessels in the 100-200ft range littering the floor of the Great Lakes. Why is this? The seas there whip up really steep waves in shallow water. Many of the ships lost (all monohulls due to the time period) were steel boats that were simply cracked in half from the steep waves, as the entire vessel would come to rest on a wave amidships in a fore and aft sense.

If you took a well found 30ft monohull and stuck it into those same seas, it mostly likely would not have been affected, as it would have rose up and rode over those steep waves, while the large, heavy boat with the long LOA was broken in half and sank.

The same principles apply to your waves. If you are motoring straight into these things, a catamaran would behave identically to a monohull of the same LOA. Why? There is little to no force through the cross beams if you are going straight into seas. The catamaran, in your case, behaves just like a monohull.

As for not liking the motion, that's just a personal preference. It has nothing to do with seaworthiness or safety at all. Just personal taste.

 

i wasn't thinking about capsize, just the SLAM,

the HIT


of a single wave.

i've read accounts from guys who have had all the superstructure washed off large yachts from pure green water single waves that come from out of nowhere,

so the thing i was thinking was the hull reserve volume to weight ratio of a catamaran should surely make them lift a lot faster than a lead bum vessel.

and since waves have slope, all is well as the cat has time to rise, but i was looking for peeps who have actually been there to say yes "all is good" or no, "you still cop the smack"


still interested.

come on richard, you've done more than a few miles, how is the SMACK! compared to yachts?


m

 

The lighter weight (with high ultimate displacement) does really pop a cat up over the wave much faster.

However, your bridgedeck... KA-BOOM!

Bottom line is they're just different. They still need to be up to task and built well.

You still cop that smack.

 

Dung beetle

I assume you watched the video I linked to in my previous post

A catamaran won't behave like that in that size wave. It will be thrown sideways but will stay upright.

I was hit by a wave from nowhere when sailing my Eclipse off the Canaries. The wave broke completely over the boom (8ft above the sea). Before the crest broke I'd estimate it as a 15ft wave.

We were OK, although we were both soaked through as we went completely under water. Some water got below, and my shaving mirror broke (don't worry as Eclipse was a live aboard cruiser I carried a spare). But the boat stayed upright and didn't roll.

If you have only sailed monohulls it is hard to imagine a boat that doesn't roll to the waves when lying a hull, but catamarans don't

Well designed catamarans don't slam their bridgedecks. I have felt more slamming loads coming from the underside of trimaran mainhulls when going to windward than on my Eclipse catamaran. And definitely more slamming loads from waves hitting the hull sides than from underneath or from above. And those waves hit all boats of course, irregardless of number of hulls.

Richard Woods of Woods Designs (who will be risking his life on Saturday by sailing a monohull)

www.sailingcatamarans.com

 

First, I took a peek at the Chesapeake Yacht thing and it seems that there are some things to be learned there but towing to induce a pitchpole? Come on! That will only simulate towing a real boat to induce tripping a hull and (they call it pitchpole) and flipping. (In my book, tripping over a hull and tipping over diagonally is not a pitchpole which is likely to be a much more violent event.)
Catbuilder, I concur, except that because of the trampoline (can I shorten to tramp? No offense), There is more frontal area to get whacked on a cat (the tramp), therefore it cannot as easily maintain headway. I would further suggest that a narrow boat can take seas much better than a relatively wide one, such as mine. A small, well found, heavy, narrow wooden boat with sufficient windows could have cut into this stuff no problem - a bit like a submarine but no problem. My boat is light and that makes for violent reaction to every wave.
I hate to keep talking about last Sunday but it well expresses a scenario. At Pt Adams, lower Cook Inlet on Sunday, there was a Minus 5.1 foot tide flooding to 24.something. There was weather predicted from the W and I didn't want to stay and wait for it (passengers on board). All we had was a gentle swell from the W and the wind was building from the SW to maybe 18 knts. On this big of a tide, every wave is amplified, every shoal causes intense upwelling. Because of a 55 foot shoal below the point, I was hugging the shoreline perhaps a little more than I should have to avoid the associated breaking waves. I could see nothing but coamers on the horizon to the SW and W but from what I could see, not the NW. So, I thought "It'll be sloppy but as soon as I get out of the severe current at the point, maybe two hundred meters, it'll be not much but swell and chop again". At the same time that I was almost commited, the Timoneer rounded the corner at full snort, 40 meters of "fence" pinching me into the worst part of the rip, closest to shore. Rocks on one side, yacht full of people wondering what the hell I was doing there on the other, helicopter directly overhead. At the worst of it, some of the S chop combined with the Timoneer wake and I had to bolt pretty hard to avoid it to prevent being slapped on the side while compromised in manueverability and burying my bow on successive waves. I felt pretty lucky to have had enuf of a short break to power over and out of the worst of it but at one point, I fell so hard nose down that everything loose in the boat was thrown forward, coolers, fishing rods, cokes, lunches, people. I have never had this boat so bow down that items fell forward but I did then and at that time, full stop, the next wave threatened to knock the bow out from under me - a reverse pitchpole, if you will. Never seen it, nor even heard of it, but my hands are shaking as I type. I do not believe that a cat wud be able to get thru that and very well may have performed the dreaded "reverse pitchpole" maneuver. I do wish to suffix this by reitterating that it was my fault that I was there. I was trying to not keep the passengers out there and wait for the tide as more severe weather was coming. As it turned out, that was the final surge of the tide (about two thirds of the way thru the flood on a big tide at that point) and the fleet that I called back to and told to wait had a much easier go of it only twenty minutes later. Prudence, local knowledge and not being in a hurry wud have kept any of the boats in this discussion safe'

Google Maps http://maps.google.com/maps?f=q&source=s_q&hl=en&geocode=&q=Cook+Inlet,+AK&sll=37.0625,-95.677068&sspn=50.956929,78.662109&ie=UTF8&hq=&hnear=Cook+Inlet&t=h&ll=59.254825,-151.972504&spn=0.064852,0.153637&z=13
The water coming along the coast and that along the flat area (the flat area between Koyuktulik, "Dogfish Bay", and Point Adams to the NW we call "the bear slide", always home to goats and black bears) combine to not only send the current stream further westerly but also in a confused way. The five knots "further Westerly" is what got me. It looks pretty dang nice there in the Google shot!



A boat like so many others,..but mine
capable to tell of an E-ride

Rogue waves? To me, a rogue is combining waves to make a fifteen in ten foot seas, or combining twenties to make a thirty. You just deal with it - it is one wave. One wave is a walk in the park. Ninety footer in calm sailing? Fiction.

 

I just learned... going back to my Hobie days, what I was calling a tramp is the "bridgedeck".

 

I assume your boat is Northern Lights??

Richard Woods

 

Yes, the FRP one. Listen, I don't want to turn this into a cat vs. mono thing. To each their own. I just told a story as a means of relating an opinion about what I thought would happen with a small cat. I will not go out of the bay on one. Some cat guys would not own a mono. It's more interesting that way.

 

Design helps too

There are some design features that should be considered to help improve cat seaworthiness in waves.

Height of bridgedeck should be reduced - get CG lower
Ends of hulls should be balanced - a cat pitchpoled on a bar in Queensland which had very full sterns and fine bows
Wide stance
Good bridgedeck clearance

Worrying about cats capsizing is something that people who haven't sailed them tend to do far more of. I remember as a teenager sitting out on the windward hull of my mums Crowther 10 cruiser to help keep it flat. It didn't feel right to my dinghy and mono trained senses. A sistership sailed the world fine. As I learned about multis I got to understand them and recognise their capabilities. In the 80s and early 90s I lost count of people who would tell me that they had seen waves that would smash, capsize, or ruin my boat. After 25 years I have still to get close to popping any of my multis over and multis have continued to expand their horizons.

Don't worry about rogue waves. Worry about fire, falling overboard, hitting a reef, sleeping well, setting an anchor, using a drogue and parachute and getting to windward in a blow. Worry about the most likely events.


cheers

Phil