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Old 21-06-2008, 20:34   #46
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The main reason why I made the comment has nothing to do with stability. It is just pure comfort. The multi's I have been on and we are talking powered here, are just to uncomfortable when it is riff. Stable as a work platform, but it is the extra bouyancy of two hulls being pushed around by the sea state that make them uncomfortable IMO.
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Old 21-06-2008, 21:14   #47
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It wasn't worth spending the extra dollars to take the so called faster ride.
I also think another reason for the Incat being dropped was that they cost so much to operate given their high fuel consumption.

I did a crossing on one of the Incat's during the rough days (in the late 90's), I noticed passengers weren't use to the speed of the quick start/stop & flicking motion when going through waves, seem to make quite a few ill.

Not really surprised about the Mono wave piercer damage that MidLandOne refer's to (I think she was the first fast ferry & used to berth on the other side of Lambton Quay (close to us)). These things are built in alloy to be light[1] (now in sealium to be even lighter), although alloy has the same strength as steel for less weight, it does not have the same elastic principles (steel will dent where alloy will rip at the same pressure). Having said that, I can't see that these Incat's can take these types of waves head on without trying to slow right down & ride over them (instead of going through them). Taking a 20m (65') wave on the side, I dunno. I don't think an Incat would capsize (except in 100' maybe?) but I do wonder how it would handle that amount of stress when the wave travels b/w & slams into the windward hull, the superstructure & leeward hull. Note that there's a lot of water in a 20m wave & that each m3 of it is approx 1,025kg. IMHO: a longer & stronger steel mono is going to handle these types of waves better (although it will roll, the wave only has to pass one hull).

Would a very large & wide steel cat such as a swath hull (2 submerged hull's with bulbous bow's) work? Dunno, but in big sea's it would also have to slow down & would have the same issue with taking big sea's head on (due to its superstructure b/w the hull's).

[1] Have seen her have major trouble berthing (damaged against the wharf) during a blow due her design of being light (i.e. lack of draft), this is despite the fact that she also had bow & stern thrusters.
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Old 21-06-2008, 23:05   #48
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Originally Posted by 44'cruisingcat View Post
IIRC the cat service from Melbourne to Tasmania was limited to 3m SWH.

Our crossing was delayed by one day due to this. I was actually able to speak to the captain of that boat and he said the 3m was an arbitrary figure someone had pulled out of thin air.

As he pointed out, the day before the waves were just over 3m, and we weren't allowed to sail, but that day they were just under 3m and there we were, doing 40-45 knots, in complete safety and comfort.
2.5m significant wave height (so of order of 3m for some waves) is pretty common limit for both high speed cats AND high speed monos imposed by regulators in the country of operation mainly for structural reasons and passenger safety (and, I assume, vehicle deck safety as well).

When originally design appraised by the classification society into which they were entering they will also have had a structurally constrained operating profile "approved" which would have included more than the 2.5m significant wave height but at low speeds (I am not familiar enough with these very large cats to know what that profile might be).

I don't know if you are aware but some (not sure how many now) of these big cats from Incat have been in service with the US Navy. I have seen one in service and looked very impressive and ominous in grey.
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Old 21-06-2008, 23:51   #49
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I don't know if you are aware but some (not sure how many now) of these big cats from Incat have been in service with the US Navy. I have seen one in service and looked very impressive and ominous in grey.
Yep. There's 2 (originally done as a joint venture b/w US Navy & Incat). PS. Haven't seen any pic's of 'em in really big sea's though.



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I just wanted to add to my previous post (re: large swath cat stability). I seriously think that if these were viable then they'd already be in service (or under construction) for the Cook Strait line. I state that point - because I'm sure those lines would really like to be able to conduct more crossings with less risk of cargo damage (& human seasickness or any injury).
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Old 22-06-2008, 00:34   #50
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I just knew it, someone had to didn't they. LOOK!!! I HAVE NO BLOODY BIAS!!! Full stop, end of point, I don't want to hear it again. And I am not going to debate this anymore.
Now back to our regular discussion.
Sorry about that. Fair enough, you have no bias. Neither do I.

I wasn't speculating about why the cat service doesn't run where you are. I have no idea about that. I was actually talking about the bass strait cat service. The fact was, that cat wasn't allowed to run in conditions it could handle with ease. (This was certainly the opinion of her skipper.) The day I was on her, the conditions were supposedly "just good enough" and the passage was smooth and fast.
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Old 22-06-2008, 00:36   #51
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Originally Posted by MidLandOne View Post
2.5m significant wave height (so of order of 3m for some waves) is pretty common limit for both high speed cats AND high speed monos imposed by regulators in the country of operation mainly for structural reasons and passenger safety (and, I assume, vehicle deck safety as well).

When originally design appraised by the classification society into which they were entering they will also have had a structurally constrained operating profile "approved" which would have included more than the 2.5m significant wave height but at low speeds (I am not familiar enough with these very large cats to know what that profile might be).

I don't know if you are aware but some (not sure how many now) of these big cats from Incat have been in service with the US Navy. I have seen one in service and looked very impressive and ominous in grey.
I wonder if the US Navy is prevented from using these boats in seas over 3m?
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Old 22-06-2008, 00:41   #52
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When I was fishing in Bass Strait, there was a cat fishing boat that was fishing in extra 5-10 knots of weather due to its stability and comfort. It had extended bow bulbs- over a meter and had a horizontal plate between the hulls. I don't know if this was to keep the bows together or for damping motion. Even though it was a pretty ugly looking boat, we were pretty jealous to see its stability while we were rocking and rolling. Most of the abalone boats and more and more cray boats are cats in this area. The only real problems I have seen is seeing one not being able to bring its bows up into the wind. It was blowing about 45-50 knots off shore and we were very sensibly sheltering in a small bay, when we noticed this boat doing some strange antics, until they loaded the ab bins on the front deck to give the bows some bite
Building of composites rather than alloy should reduce fatigue problems, one of the reasons for aeroplanes going this way

Thee have been a few roll on , roll off monohull ferries ending up in uncomfortable situations in Europe when there form stability was compromised by water sloshing in the lower deck
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Old 22-06-2008, 00:57   #53
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Not really surprised about the Mono wave piercer damage that MidLandOne refer's to (I think she was the first fast ferry & used to berth on the other side of Lambton Quay (close to us)). These things are built in alloy to be light[1] (now in sealium to be even lighter), although alloy has the same strength as steel for less weight, it does not have the same elastic principles (steel will dent where alloy will rip at the same pressure). It is not elastic properties you are talking about but toughness and malleability. It depends very much for both of them on the type of steel or aluminium and the quality of welding
Steel will also rip and alloy will also dent. There are a lot of tinnies around getting an absolute hiding, with lots of dents in them, but very few steel ones. I was on a tuna boat whose brine tanks eventually split from rocking and rolling too much and tipping out too much water allowing a severe free surface, and heavy hydraulic ramming into the upper edges of the tanks.

Better to build in thicker aluminium alloy than go to steel , if it wasn't for the price
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Old 22-06-2008, 01:30   #54
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When I was fishing in Bass Strait, there was a cat fishing boat that was fishing in extra 5-10 knots of weather due to its stability and comfort. It had extended bow bulbs- over a meter
Am aware of these (I think they're out of business now?)

They make sense for craying (have crayed myself in NZ) & paua because they don't have to carry large loads (like trawlers) & their deck space (beam) is great for stacking a lot of pots. Not sure of the lwl of the fishing vessel you refer to, but bulbous bows are only useful for larger vessels (as they become a pain when steering, almost like having an extended nose).

http://members.datafast.net.au/comcat/Star-Cat/album.html





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Steel will also rip and alloy will also dent.
Sure, but for the same rated strength (pressure), steel will bend before ripping.

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I was on a tuna boat whose brine tanks eventually split from rocking and rolling too much and tipping out too much water allowing a severe free surface, and heavy hydraulic ramming into the upper edges of the tanks.
I can visualize what your saying. but If you note the previous posts, the high speed alloy wave piercer damaged its bow going into a large wave.

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Better to build in thicker aluminium alloy than go to steel , if it wasn't for the price
But then we have extra weight, which negates the purpose of a high speed light cat. (btw: I wish the alloy price was cheaper too )
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Old 22-06-2008, 01:37   #55
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I wonder if the US Navy is prevented from using these boats in seas over 3m?
My understanding is that the Navy Incat is currently being used in the Arabian Sea of the Indian Ocean as a high speed “roll on roll off” & personnel transport vessel, I doubt she's likely to experience 3m+ sea's there.
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Old 22-06-2008, 01:44   #56
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Early 90's I went on the NZ fast ferry accross the Cook Straight - nice weather though ......we still have these locally, in a couple of sizes and they go accross to France and up to England.



They don't seem to lose too many days to bad weather, albeit in the Winter a reduced schedule and their is a convential passenger / freight vessel that runs to England through pretty much anything.

But although of course weather in this part of the world can get very unpleasant, not quite the same dynamics as the North / South Island crossing.
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Old 22-06-2008, 02:32   #57
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Sure, but for the same rated strength (pressure), steel will bend before ripping.
Am going to correct myself here It should read same thickness (not rated pressure).
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Old 22-06-2008, 03:42   #58
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I wonder if the US Navy is prevented from using these boats in seas over 3m?
I have no idea what the US Navy operating profile is for them but I would imagine it would be within that from the classification society's design appraisal (originally the US Navy vessels were leased and may still be, in which case would be a reasonable expectation for them to be operated within that profile as a requirement of the lease).

I hope it was clear in my post that similar maximum operating conditions applied by the country they are operating in if they are carrying passengers apply to high speed monos too - in both cases due to their speed potential and their light construction. A problem is the possibility of an unexpected event at speed such as ploughing into a larger than usual wave with a boat load full of passengers (as happened to the mono wave piercer I mentioned that bent its bows up).

My experience is mainly with power cats up to around 140 foot and one comment I would make is that the fast ones are very uncomfortable if they are not fully up out of displacement speed, and even worse if stopped, in more than lightish seas due to their firm jerky motion from their very high GM and light weight.

On sea trials I have seen even professional crews looking uncomfortable and others on board walking around with buckets during slower speed and anchoring trials. Even at speed after a day standing in the wheelhouse and about the boat ones legs get tired from the very stiff roll in seas.

I said before that I don't know what the operating limitations were for the big cats arising for structural reasons (ie from the classification society design appraisal) but as an example I have pulled out of my files those for a 80 foot power cat - decreasing limits in speed as wave height increases until at 2m wave height the vessel has to be operated at slowest speed and taken to shelter (pretty obviously the sea state limit on a big 300 foot cat is going to be considerably greater). I would expect this to be much the same as for a mono of similar speed and power to weight performance but obviously far less than a heavy slower mono, especially a displacement one. And no one in their right mind builds a slow heavy cat unless for some quite special workboat service where high stability is wanted.

That is not knocking cats, in my (and I think most operators) opinion they are the high speed vessel of choice out of them and high speed monos for the moderate conditions and short routes they are both suited to.
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Old 22-06-2008, 05:31   #59
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The high speed ferry service between Victoria (port welsh pool) and Tassie was scrapped. (craft made by incat,which are made in Tassie) The roughness of bass straight meant that it was not able to maintain its services to an acceptable level of reliability. There was also the difficulty of it having to leave from this port which is a fair distance from Melbourne. It is not to say that the boat was not safe, it was just that due to its ride motion, it had a limited sea state window to keep its passengers happy. If it was the same size as the large mono roro ferries that ply the straight it may have been just as comfortable
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Old 22-06-2008, 06:17   #60
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you macho mono guys are quite welcome to it
I grew up in these waters, doesn't have much to do with macho. Have been caught out in them many times.

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Deep keelers cant go where I CAN go, such as here:
Are you 100% sure? If you look closely, I think there's a couple of monohull sail boats across the other side of sand bank



Here's the alloy cat design from Canada I was referring to.
http://www.custom-aluminum-boats.com/L42.html



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This is the swath type hulls I was referring to. Don't know what this ones original purpose was but I noticed it about a year ago being marketed for a mega yacht hull with a service speed of about 12kts. Electric diesel propulsion is already installed. Also, swath hull's were originally patented in 1880.
http://www.yachtworld.com/core/listing/boatFullDetails.jsp?boat_id=1798780
http://www.swath.com/index.html


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Oh... ummm... btw... I've yet to see a multi one of these (with exception to one that's gone turtle )


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