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Scuba Forum / General / November 2003Ferry from Miami to the Keys? Sounded good
http://www.wsvn.com/news/articles/local/C29410/ didn't it? :^) > http://www.wsvn.com/news/articles/local/C29410/ > > didn't it? :^) I wasn't even aware of the plan for a ferry ride. It'll be quite popular for special events, things like Fantasy Fest and the St. Patick's Day Bar Stroll. Any time there's a major event in the Keys, this will be a better way home than driving. One road, sometimes two lanes, for 100 miles is not the best idea ever for keeping traffic jams to a minimum. It seems obvious that the boat was not traveling at it's cruising speed when it hit. It's been a while since I've been out Port of Miami, which is where the picture was taken. If it's like Port Everglades, the port area is all slow speed zone. It used to be unrestricted, but post 9-11 actions by Homeland Security have changed things in major S. Florida ports. Good thing for them they weren't going at full speed. If they had been, they would be stopping traffic in both directions. The damage does not look serious. Something must have gone very wrong with the steering for them to hit. I presume this is one of the jet drive boats. Twin engine prop driven boats can be steered by the motors alone if necessary, with no rudder control at all. Since the drives are the rudders on jet powered boats, they can not be controlled this way as reliably. Lee >didn't it? :^) In 2000 I did the crossing from Newfoundland to Cape Breton on a larger cat that Marine Atlantic (the ferry service) had leased for the summer season from Norway (or maybe it was Finland) to supplement their fleet. It held about 250 cars, and did the crossing in 2.5 hours compared to 6 hours for the regular fleet. It did about 30 knots, while their larger ferries do about 15 knots. It quickly got the nickname of the "Vomit Comet". It was not renewed the following season. The day I was on it the seas were quite calm (1-2 foot), and we were still bounced around a lot. As well the whole thing (including the decks) vibrated all the time. It was not a pleasant trip. Given that 12-20 foot seas are not uncommon, this thing must have been miserable indeed at the worst of times. The one that ran aground in Miami looks to be a smaller version that travels even faster. Even on calm days the ride has to be pretty brutal. While avoiding traffic would be great, I'm not sure spending 4 hours feeling like you are in a blender is a big positive.  SignatureRemove preceding and trailing X from username for replies (Sorry, but I'm SICK of spam...) > >didn't it? :^) > [quoted text clipped - 12 lines] > 12-20 foot seas are not uncommon, this thing must have been miserable > indeed at the worst of times. with a 1-2 foot chop, a 26 foot cat should be smooth riding. riding the 126 foot Reef Prince out of Cairns to the outer reefs, we did about 30 knots, in perfect comfort, with several hundred passengers aboard. within a year, they were expecting to upgrade the engines with blowers for a faster ride. generally cats provide a pretty smooth ride. > The one that ran aground in Miami looks to be a smaller version that > travels even faster. Even on calm days the ride has to be pretty [quoted text clipped - 4 lines] > Remove preceding and trailing X from username for replies > (Sorry, but I'm SICK of spam...) > The one that ran aground in Miami looks to be a smaller version that > travels even faster. Even on calm days the ride has to be pretty > brutal. While avoiding traffic would be great, I'm not sure spending > 4 hours feeling like you are in a blender is a big positive. I'm reasonably sure you are mistaken about this particular boat. I took the Cat, out of Miami, to Nassau. It was quite a bit larger than the boat pictured, but otherwise very similar. It was very stable even in rough seas, even at more than 50 mph. It was most impressive. These are high speed catamarans, powered by some of the biggest water jet engines you've ever seen. They're all displacement hulls and handle rough seas better than more conventional boats. Lee >> The one that ran aground in Miami looks to be a smaller version that >> travels even faster. Even on calm days the ride has to be pretty [quoted text clipped - 8 lines] >ever seen. They're all displacement hulls and handle rough seas better than >more conventional boats. I wonder if the difference is related to payload? The ferry I was on held roughly 200 cars. When I was on it in 2000, it appeared to be pretty much brand new. It was twin jet powered too. Maybe it was just an good example of how poorly you can build a cat car ferry. Of course, it didn't run aground and the one in Miami did. Imagine the mess if a ferry with 200 cars in the hold hit the shore. In any case, I'd be damned sceptical if somebody offered me a 4 hour trip on another similar ferry. Maybe my first experience wasn't typical. SignatureRemove preceding and trailing X from username for replies (Sorry, but I'm SICK of spam...) Al Rudderham wrote in message ... >In any case, I'd be damned sceptical if somebody offered me a 4 hour >trip on another similar ferry. Maybe my first experience wasn't >typical. I dunno, our ferry runs at 22knots and takes 14 hours ( 72 hours once!) although I've never been seasick on it, I have been on it when I'd left it too late to get a cabin with 500 on board in a force 9 of which 450 appeared to have terminal sea-sickness...... shortening that would have been good, it wasn't what I'd call pleasant - restaurant was quiet, Winter is almost aways rough, but at least its not usually full, which is much better X from username for replies >(Sorry, but I'm SICK of spam...) > In any case, I'd be damned sceptical if somebody offered me a 4 hour > trip on another similar ferry. Maybe my first experience wasn't > typical. I suspect that's the case. The Cat is running from somewhere here in Florida to somewhere in the Bahamas again. If you get a chance to make a trip on her, take it. Stay away from the slot machines, but by all means try your hand at Roulette. Lee > Stay away from the slot machines, but by all means > try your hand at {RUSSIAN?} Roulette. > > Lee "Lee Bell" < > I'm reasonably sure you are mistaken about this particular boat. I took the > Cat, out of Miami, to Nassau. It was quite a bit larger than the boat [quoted text clipped - 5 lines] > > Lee Earlier this summer the PurrSeaverance passed by while I was out at a reef off Key West. Heres a cut from page below: Some interesting facts (about PurrSeaverance) reported by the owners of Fast Cat Ferries: l The hull of the boat is made of Dupont's Kevlar cloth, PVC foam core, and aircraft epoxy. l It will be powered with four Caterpillar, 1100 hp diesel engines, while the fan blowers will be powered by twin Caterpillar 315 hp, one each per hull. The air cushion will support 85% of the boat's weight. l Propulsion will be achieved by advance surface-piercing propeller design by Pulse Systems, Inc., since water jet propulsion is not compatible with the boat's air cushion design. l The boat is expected to have a shallow draft, reportedly requiring only 3.5 feet of water at rest and 14 inches at speed. The owner claims that it will have a wake of only 12-inches or less at normal operating speed of 50 to 60 knots. source (bottom) http://www.baycrossings.com/Archives/2001/07_August/breaking_the_speed_envelope_ for_passeger_ferries.htm > l It will be powered with four Caterpillar, 1100 hp diesel engines, > while the fan blowers will be powered by twin Caterpillar 315 hp, one > each per hull. The air cushion will support 85% of the boat's weight. Is there an 'apron' between the two hulls that contains the air to provide lift? like a hovercraft? (just wondering how the 85% weight lift of the hull is achievied.) > > l It will be powered with four Caterpillar, 1100 hp diesel engines, > > while the fan blowers will be powered by twin Caterpillar 315 hp, one [quoted text clipped - 4 lines] > > (just wondering how the 85% weight lift of the hull is achievied.) each hull has an 85000 cfm fan pressurising it, think of emptying 1000 80cubic foot scuba tanks in each hull every minute ! I remembered doing a search and then writing a coworker an email about the technology, snipped from my "sent" file from May of this year, "Interesting design and technology: kevlar/carbon fiber construction & two 85000CFM fans pressurizing a pocket in each of the hulls enabling fuel efficient operation at high speeds !" http://www.seacoaster.com/ I don't think that it is a displacement hulls. A displacement hull of the length described would not have a hull speed of more than 50 mph. From the descriptions given, it appears that the hull planes on a cushion of air. Then again, I could be wrong. > > The one that ran aground in Miami looks to be a smaller version that > > travels even faster. Even on calm days the ride has to be pretty [quoted text clipped - 10 lines] > > Lee > I don't think that it is a displacement hulls. A displacement hull of the > length described would not have a hull speed of more than 50 mph. From the > descriptions given, it appears that the hull planes on a cushion of air. > Then again, I could be wrong. Or right. I don't know for sure. I can say that some of the modern small catamarans are displacement hulls with a designed speed in the 40 mph range. I don't have any idea how they do that, only that they do. > I don't think that it is a displacement hulls. A displacement hull of the > length described would not have a hull speed of more than 50 mph. From the > descriptions given, it appears that the hull planes on a cushion of air. > Then again, I could be wrong. Not too far off though, fast cats actually plane on top of the water. http://powerboat.about.com/library/weekly/aa012403a.htm There's a formula to run the speed of -true- displacement hulls on that web page along with illustrations and descriptions of the other hull types. It would have to be the length of an Aircraft carrier to be able to have a -true- displacement hull capable of 50mph (which they are btw) The nice thing about a fast "power" cat is that it is really two extremely -sharp- angled deep vee'd planing hulls. So, they slice through the waves much more easily, while at they same time providing a higher level of stability, than is possible from getting out of a single, much wider and -dull- vee'd planning monohull. Extremely popular in Pacific areas (Hawii, Oz, ect) where the waves can get really big and bad. Haven't caught on here in Fla because people think they "look funny", some models can be wetter riding (called "sneezing") and, they're quite a bit more expensive than a similiarly sized monohull. -- SJM > The nice thing about a fast "power" cat is that it is really two > extremely -sharp- angled deep vee'd planing hulls. So, they slice > through the waves much more easily, while at they same time providing > a higher level of stability, than is possible from getting out of a > single, much wider and -dull- vee'd planning monohull. Perhaps that's what these things are, but I thought Glacier Bay advertised displacement hulls. Hobie cats sail faster than they should be capable of too, at least by beliefs before Hobie proved otherwise. Lee Some multihulls are displacement hulls but they are not terribly fast. As noted in my previous message, hull speed depends on length and beam so a multihull and a monohull of the same length will have different hull speeds -- the multihull quite a bit faster. A displacement multihull is usually called a trawler cat. Chris > > The nice thing about a fast "power" cat is that it is really two > > extremely -sharp- angled deep vee'd planing hulls. So, they slice [quoted text clipped - 9 lines] > > Lee I think that the formula on the web site is an approximation of what is called the prismic (sp?) coefficient of the hull which in its long form takes into consideration both the hull length and beam, the fineness of the bow and deadrise. One of the reasons that warships are so fast is that they have pretty narrow beams at the waterline and extremely fine bows. It is really a remarkable sight to look at an aircraft carrier and how sharply it narrows from the flight deck to the waterline. Many of these ships also have a bulbous bow. Though multihulls are more expensive than monohulls per foot of length, they are much beamier and have far more interior space for the dollar. Also, their operating costs are far lower because of the fineness of the bow and the relative narrowness of each hull compared to its beam. Multihulls at trawling speed (hull speed) routinely get over twice the mpg as similarly sized monohulls. On the downside, they do not have as much buoyancy so you can't carry as much stuff and they don't look "yachty." I have been researching multihull trawlers for years. Hoping to get a Maryland 37 when I retire (hopefully sooner than later). Chris > > I don't think that it is a displacement hulls. A displacement hull of the > > length described would not have a hull speed of more than 50 mph. From the [quoted text clipped - 25 lines] > -- > SJM > prismic (sp?) coefficient Close; prismatic coefficient. Sure brings back memories of long hours with a planimeter (a marvel of engineering) measuring the area of the 10 hull half sections trying to get the PC to something like .48-.49 if I remember correctly. The limiting factor of displacement hulls is that they build up a bow wave which thay have to try to climb while at the same time having to dig out of the hole they leave behind. The faster they go the bigger the hill and hole. In practice that limits most displacement hulls to 1.3 * the square root of the LWL in ft. For finer hulls (like those found on cats) the number goes up from 1.3 up to 2 or even more (cosider a Toronado with about 1-2 ft beam at the LWL with a LWL of almost 20 feet). As pointed out in some of the classic boat design books, the rules are rules of thumb for practical boats. If you took _any_ displacement boat of say 30 or 50 feet and hooked it up behind the Queen Mary, it would go as fast as the Queen Mary, no longer limited by it's own personal hull speed ... it just isn't very practical to use that much power to overcome hull speed limitations :-) All of the above is moot once you are on a plane and the displacement is carried by riding/skimming on top of the surface rather than by just displacing an equal mass of water. The idea of converting a Stiletto to a power cat for diving sure has a lot of appeal ! -Sven >While avoiding traffic would be great, I'm not sure spending > 4 hours feeling like you are in a blender is a big positive.> I'm sorry, for some reason your description of the "vomit comet" reminded me of my days traveling on the Bombacharger from St. Thomas to Tortolla (and yes, back too). It was completely enclosed, smelled to high heaven bounced like a bronc and you'd get on it at 7:30a.m. and they'd offer you some kind of rum and a banana liquor. I don't remember it being a cat - I can't remember what kind of boat it was but it was damned amusing watching the people who thought free booze at that hour in those conditions was a "good idea." Until the first few wave sets. Wonder if the thing still runs? Thanks for the memory and the laugh! Dive safe, Kim |
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