The Limits of Bulbous Bows
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- čas přidán 20. 05. 2017
- Bulbous bows are not miracle devices. Learn their limits and how to use them effectively.
Want to design a bulbous bow? Start with these two papers:
A. M. Kracht, "Design of Bulbous Bows," SNAME Transactions, vol. 86, pp. 197-217, 1978.
P. Blume and A. M. Kracht, "Prediction of the Behavior and Propulsive Performance of Ships with Bulbous Bow in Waves," SNAME Transactions, vol. 93, pp. 79-94, 1985.
And just to prove that there are exceptions to every rule, meet a firm that developed a simple bulbous bow. It looks like a dumb pipe, but they have model tests to show that it works.
www.brayyachtdesign.bc.ca/inde...
Get the full article here: wp.me/p3pMQV-1lP
View more tips and helpful articles at dmsonline.us/ - Věda a technologie
Good video mate. Brief and with animating the general concept, perfect for intro class. Perhaps a video about propeller characteristic next time ?
Good idea! I'll add that to my list of videos that I want to produce. I am also working on a video to diagnose why a ship might be listing to one side.
Thank you for referencing my "bad bulb", it produced a 12% reduction in powering. I found your video very informative but with a few myths. A bulb does work exactly as you have described, full points for that. The "good bulb" you reference is designed for one speed and as you have pointed out only produces maximum effect at one speed. The bulb form that we use is effective over a wide range of speed and draft. It is typically used on craft under 100 ft. and speeds to 20 knots with a 12% - 17% reducing in powering and over 30% reduction in pitching. We have retrofitted them to over 60 vessels and now have such a large data base that we can use simple formulas without need for model testing or CFD on every bulb. I am sure for an additional $100,000 in CFD you could probably squeeze another 1% but then maybe not. Oh yes, and we have done extensive model testing and CFD on our bulbs and hull forms. You can find many of our model test programs on CZcams.
My apologies. I have seen many simplified bulbous bows based on capped pipes, where the pipe length was not calibrated to produce the correct interference pattern. I'm especially impressed if your company has created effective bulbous bows with such a simplified construction. Nice job. And I'm glad to see you verified it with model test data. That is a true professional. For anyone interested, you find videos of model tests conducted by this firm here: czcams.com/video/vnJ-qGTOkO8/video.html
This should not be as funny as it is, but it is :D He also got the minimum amount of required CFD calculations, when used during the design phase, wrong... Though I guess his video series is aimed at non professionals so...
Edit for it not showing Nicholas' answer. Props for that!
Patrick Bray thats good news now rry usung that bulb for a 30 foot sailing catamaran wide hulls rhat still sail fast and are blue water capable would make a good livaboard.cruising yacht.
A hundred thousand for cfd calculations? Are you serious? We charge a fraction of that. And yes. Bulbs work great for one trim, one draft and one speed... So great for ferries.
Hahaha, what are the odds that this dude is watching CZcams and sees a picture of himself under ‘bad design’ !
@03:42 as a student of naval architecture I had the pleasure to get to know Dr. Alfred Kracht during my two years that I was working as a trainee student in the Berlin Ship Model Basin VWS where he was one of the senior ship hydrodynamicists, such a fine guy and endless source of wisdom and experience.
Hi bro
Great video, I came looking to see if the bulbous bow would've affected a historical merchant ship and your video was thorough enough to answer without directly talking about sailing vessels.
Excellent video. I now understand how they work and will be able to talk about bulbous bows in the pub without people looking at me strangely.
I have enjoyed your video, thoroughly amusing and informative. Thank you.
Most operators wpuld benefit more from properly coating their hulls to avoid growth of sea life. The parisitic drag of a healthy dose of barnacles is going to do more harm than bow design. I was also impressed at the suggestion of looking into screw design. Very few people seem to understand the benefits of an efficient propeller. I find this strange as many pleasure craft operators will put high efficiency screws on outboards yet multi billion dollar companies don't give a second thought.
Jets are the future propellers will soon be obsolete
@@joshlower1 Nope.
@@freefall0483 yup
@@joshlower1 Although there are some advantages to water jets, fuel efficiency is definitely not one of them.
@@christianeriksson4733 like anything else they will eventually be made more efficient
sorry that it took some thumbnail click bait to get me to notice you. What a huge collection of videos, wow! I will see them all in the coming weeks. Love this stuff.
Great video, Sir. Thanks to you, I am no longer seeking to install a bulbous bow on my sailboat.
Awesome vid, with great info. One little sticking point, a theory is an idea that has been proven in practical application, is well documented, and is repeatable for the purpose of peer review. Let’s not diminish the word, regarding its science and engineering value, to cater to the widespread misuse in everyday parlance. The everyday “theory” people speak of is more closely represented by the word hypothesis, or even speculation.
Outside of the strict linguistics of the physical sciences, meaning everywhere else the language is used, the meaning is much closer to hypothesis. The word was not formed for the express use of scientific literature.
now onto some low energy aplications: cargo sailing.
would it be possible to tune the bulbous bow against the pentatonics of hull resistance that it stays on: stronger winds ~ higher speed?
Any opinion on the bulbous bow used on some of the Nordhaven yachts?
The queen Mary 2’s engineers are great
on the other hand... I worked on a ship with a very round, barge like bow once. When in ballast (being a tanker on a time charter, that was 1/2 the time) she had VERY poor directional stability. Not sure how much a bulb itself supports directional stability, but that was the only ship I ever worked on with a bow like the HMS VICTORY, and it was the only one I ever encountered that kind of directional instability.
Also, speaking of BAD bulbs, look up the DOUBLE EAGLE class tankers made by Newport News Shipbuilding in the late 1990's... oye!
thanks for explaination mr.nich i am student in marine engineering and i'm trying to understand for this problem
Any bulbous bow that doesn't have a glass viewing dome is useless.
How else can you get your Captain Nemo on?
Thanks for the video. I've always found large freight carriers interesting.
High Ship Coefficient being one of their main characteristics.
Could one design a telescoping bulb, to optimize at different speeds?
In theory - yes. And perhaps in practice it is possible to design such variable flow profile or "speed" bulb design. There were some studies done. But it is not practical for few reasons. As it was pointed out in this video, bulbs are added to increase efficiency of slow moving large ships, and benefits are felt over a longer period of time (i.e. imagine oil tanker on 1,000 miles route, even a 0.5% increase in efficiency will be practical). For those ships it make sense to design a bulb for cruising speed and slap the steel and leave it be. Where one may think variable bulb may make difference is ships with dynamic "performance" - think of faster moving ships (military vessels), yachts and so on. Their overall performance is largely improved and affected by special hull shape, propulsion systems and so on. They are not economical ships for the most part and having the "fast hull" or multi-hull or different propulsion (variable) will have far greater effect than any BB added. Let's say, a BB will increase efficiency 2% efficiency over 5% of time (low velocity/speed scenario i.e. in ports). That is not much - given that the design will be very complex, added weight and require maintenance. So, it would be a cool feature - but with minimal economics (in fact, mostly negative).
Fast moving vessels, or vessels that are maneuvering a lot at various speeds - require either smaller wetted surface to reduce drag (friction) or hull shape of low "box coefficient"...
strelnikoff7 it’s about harmonics, as I understand it. I read that motorcycle companies toyed with telescoping exhaust manifolds to adjust back pressure at different RPMs.
Nick, it occurred to me that if you could make the bulbous bow variable in length it could then be adjusted to suit any change in the optimum speed range for the vessel. It would not be easy to make but as with anything it could be achievable.
What are you thoughts on the matter?
Interesting thought. Possible, but I'm not sure the benefits would be worth the extra hassle. Generally, any situation where the ship frequently changes speed will be when the crew are maneuvering the ship in a busy area. In those cases, I doubt they would take the extra time to adjust the bulb. But I could be wrong. I'm sure there is a niche application where this could work.
There are other examples of tackling the problem of multiple speeds. I believe MARIN offers a service to optimize the bulbous bow to work at two or three different speed (but not the whole range between them). I'm a little skeptical about those.
But there are other examples of adjusting for speed. Propellers face the same problem that they are design to be most efficient at one ship speed. So we created controllable pitch propellers where the crew can actively change the angle of the blades to get best efficiency at their current speed.
Right just rub as needed lol
My thoughts exactly you beat me to the comment
@@DatawaveMarineSolutions It is all automatic. A variable geometry bulbous bow would also be.
hey Grest video, i see that a lot of cruise ships are now putting in inverted bows and vertical bows with no bulb or a tiny bulb. can you tell me why? i know the bulb is to reduce the friction of bow so i don't understand why cruise ships are getting rid of them. is it because the inverted bow has a longer waveline resulting in a higher max efficency hull speed? or is it because the new bows reduce pitching? They say the new bows are more efficent but i don't understand how. could you help me out? Thanks
The hydro-dynamic effects and the additional bouyancy?
Thanks for sharing knowledge, you success explain it easily. Why i just found this account now. It should be 8 years ago when i studied in university
Awesome video, thanks!
So what if your driving a 75 to 90 foot trawler yacht at 7 to 8 knots. They are a long haul vessel with a more constant speed. Would a bulbous bow be worth while in this application? You see a lot of yachts with them now.
I have been looking for a video like this for ages!!!
Also - this is an idea I have been thinking about for a while now - would a retractable bulbus bow be a decant concept? Let's say your ship's engines can operate at a maximum speed of 25 knots; but your ship usually operates at 18 knots. Why not make a bulb that can move forewords and backwards to match the speed of the ship and operate at maximum efficiency at all times.
BTW: I'm still only a kid so I think it's an accomplishment on my part to even know about complex subjects like the operation of ships.
@@woxof46 brilliant son!!!
Can a bulbous bow be tuned on a small ship to affect the stern wave in a positive way?
Not really.
Any waves that the ship generates get dispersed away from the ship. This is what we call the Kelvin Wake (www.wikiwaves.org/Ship_Kelvin_Wake). So by the time the wave from the bulbous bow reaches the stern of the ship, it has already dispersed too much to be effective. However, I have seen some limited studies into creating bulbous sterns. (www.sname.org/pubs/viewtechnicalpaper?DocumentKey=a50b80a4-463e-426f-bfb8-fe9a9432951d) Same idea as a bulbous bow, but with the flow direction reversed. The problem with bulbous sterns is that any bulb also reduces the efficiency of the propeller, which still hurts you.
The other part of your question: application to small ships. In theory, a bulbous bow might work for the stern on a very small ship. Unfortunately, with a ship that small, your Froude numbers (en.wikipedia.org/wiki/Froude_number) get high enough that bulbs of any type are no longer recommended. With a small ship, your best bet is to make the hull as skinny and streamlined as possible.
All that being said, you are definitely thinking along the right track. Bulbous bows are not the only trick we do to improve efficiency. There are other things like guide vanes for the propeller, designing for pressure recovery on the stern, optimized propeller inlets. I have even seen a stern lifting foil on some yachts. I think there are still plenty of opportunities for creative innovations.
I learned something today! Question, have they ever made a ship with an "extendable bulb"?
never show your extendable bulb in public
I wonder why many Navy vessels have bulbous bows, other than for the sonar that is. The Arleigh Burke class destroyers have it, and those are relatively small vessels that change speeds all the time depending on whether they're navigating alone, engaged in combat or sailing as part of a Carrier Group. At least on a surface level they sound like bad candidates but I'm pretty sure that every naval engineer at Bath Iron Works knows a wee bit more than I do about the subject.
Gibbs & Cox was the Nav Arch / Marine Engineer for the Burke Class.
Great video. I'd love to see one on x bows next! Thanks
So what stops you from having bows of several lengths and changing once the fuel price has increased enough?
Nice to see this vid. Good job.
very nice. would you comment on bow angle? I have seen modern fast coast guard vessels with vertical bows.
The bow rake (vertical angle of the stem) is more concerned with seakeeping capability. I will release a video next month that discusses this in more detail. But the short version for now:
The original forward raked bow mostly evolved from tradition. Ships always had pointy bows, period. But with modern design techniques like CFD, we are able to look at the flow patterns of the bow in more detail and explore alternatives. Those vertical bows and reverse raked bows are designed around new flow patterns that benefit the ship.
Vertical bows typically try to maximize the waterline length. That allows you to stretch out the bow and make a sharper bow angle. Reverse raked bows usually happen for seakeeping reasons. Reversing the bow often reduces the violent pitch motions that many complain about.
The more raked a bow is the less efficient the bow will be due to increased surface area of material in the water.
Very informative thank you for shareing
Even a simple pipe welded on to the front has benefits. The water flowing past the bulb is flowing in laminar state, by the time it hits the main hull it's transitioned to a turbulent state. The turbulent state offers less resistance.
Let me know what you think.
Hi Tom, great comment, w h at you stated males a lot of sense in regards to the laminar flow at the bow of the vessel.
Is there such a thing as a telescoping bulbous bow? Perhaps if the length of the bulb could be changed with speed and see State they might be more efficient more often.
Are there any studies on the possible use of variable length bulbous bows? Would that be a possible solution to increase the performance envelope of a bulbous bow at different speeds?
Most of the studies I came across focused on new shapes of bulbous bows that deliver improvements across all speeds. The idea is to sacrifice perfect performance at one speed to get generally better performance over a larger range. But still a single bulb length.
You should look into getting an on camera teleprompter, that way you can look perfectly into the lenses when you read notes. There are lots available on b&h.
So, these are best suited for cargo ships engineered for a specific load, speed, and power setting. On a warship that has to adjust speed depending on the strategic and tactical situation, not so much.
What do you guys know about submarine design. I have been working on a prototype that so far has tested to out perform everything else on the water. Just curious what you might think about a more organic flow design.
Submarine design is so specialized that I have not worked on any projects designing a sub. But I do know the underlying principles. As for more organic shape, it could be beneficial. But think carefully about directional control. A streamlined sub can also act as a giant wing on a turn, pulling you in the wrong direction. Worst case scenario:. The sub goes for a turn and gets pulled down below crush depth. ☹️
@@DatawaveMarineSolutions yeah i thaught about that. My sub has two forms of propulsion. A swimmer mode and a new hydroget design. We have three sizes of sub we are working on. A one seater a two seater and a twelve person sub. I designed them to follow the forms of dolfins sharks and whales. Strearing controls are designed along the lines of fins. I am using an anamorphos fin design that allows me to reshape the fin depending on speed. Programing the controls was complex but we got it to work. I was curious as to if anything like this has been considered in ship design and if you think the actual phisics of organic design would be benificial to other areas of ship building. What about the bulb designs on super freighters. What if it was designed to change its shape through out the speed curve of acceleration would such a design actually help those ships perform better.
Small boats in sea lanes are very common in some parts of the world such as southeast Asia. If a small boat happens in the path of the ship, the bulbous bow lifts the boat up and throws it to one side, saving the boat and its captain. Without the bulb a small boat is more likely to be crushed. A bulbous bow is worth it for this reason alone.The bulb also works for debris.
Good point about debris dispersion, for example semi-submerged containers floating aimlessly.
Also the small boat captain may not necessarily survive the accident after being flipped out of his boat , ca use he then has to face the prop. next on the stern of the ship....
@@kenlee-97 Going thru Singapore I saw an old lady oaring a sampan, successfully cross the path of a container ship. It was something to see.
@@kenlee-97 I know how to build REAL sailing boats.
I wonder if a bulbous bow would be worth considering on a Nordhavn 92 feet exploring yacht or similar,they seem to have a low cruise speed and a range of 3000 miles or so. My guess is over the life of the vessel it might work but from a professional perspective I don’t know.
Very informative.
I thought that bad bulbs on trawlers could still save fuel by reducing the amount of pitching. The bulb was not sealed but allowed to fill with sea water.
from this education video..i'd assume that FDHF lifts the hull when the hull is above the design bulbous bow hull speed..yes..?
Could one put adjustable fins in front of a ship to cancel out waves at different speeds?
Theoretically, yes. Fins would work. But adjustable fins is a different story. To cancel the waves would require some property to adjust the length of the cancelling wave. I don't know of any fins theories that could achieve this. (But I also admit that I can't keep up with every paper on ship science.)
Just wondering where you got your degree from? I was thinking of majoring in Naval Architecture many years ago, but few schools offer it.
I went to University of Southampton, UK for my undergrad and graduate degrees. Very true that we have few options in the USA. Your choices are basically: University of Michigan, Webb Institute, University of New Orleans, or Texas A&M University. We also have the naval academies, but those are more focused on operating the ships rather than designing.
Nicholas Naval Architect I was thinking of going to SUNY Maritime in New York for a while. But after some time in the Navy, I decided to go home and chase girls at Temple University in Philadelphia. A wise move at the time. Anyway, well done lecture on the topic. Now in the 19th century, the ram bow became a design fad in warships. While intended as weapons, did Ram's provide any of the same effect as the bullbous bow? Or would it have been needed to calculate the wave cancelation?
Hmmmm....Can we make a computer-trimmed dynamic bulb? Changes distance between bow & bulb based on speed etc.?
Appreciated the video, BS NAME, U of M, 1972.
what about ships like arleigh burke. It has a weird bulbous bow or is it just a sonar cover?
The first priority is a sonar cover. But as the design evolves, the shape of that sonar cover can also provide some wave cancelation. I can't say if the Arleigh Burke class specifically meant their sonar cover to also provide wave cancelation. I would need to analyze their hull form for any definitive conclusion.
Can you do (or have you already done) a video on the pros and cons of bows like the axe bow or xbow? What even more outlandish bows are there out there?
That one is in the works right now. I plan to release it next month.
Cool and thanks in advance!
I would think with technology there should be ways to automate bulbous bows to retract or change shape, maybe by rotating in conjunction with retracting. to be more efficient in varying conditions. Is this being studied?
So, in other words, we need a bulb with a variable erection size for different speeds of operation?
Wavepiercing bows/hulls next?
So... no bulbous bow for my RC boat?
Only if your RC boat is a bearing sea icebreaking RC boat.😁
if you want an rc container ship, then get a bulbous bow
Upvoted for the use of doobelleedupe.
Will it work on my patio pontoon boat. I got a welding machine
Perhaps an obvious question, is their 'adjustable bulbous bow' that adjusts longitudinally forward or rearwards as the speed changes? The design does not have to be incredibly streamlined given the drag inefficiencies for the set bulbous nose design that has apparently exponential drag increases + or - 2 knots of the bulbous nose design efficient design speed. I understand the engineering aspects of a hydraulically powered bulbous bow that dynamically alters as the speed alters, but it is not impossible given the advances in aerodynamics in adjustable swept wings, flaps, leading edge slats and falps, blown flaps, boundary layer controls, high speed torpedoes, etc. Its not impossible, so I am interested why this is not an apparent consideration?
Imagine a bulbous bow that expand and contracts depending on speed and wave conditions 🤔
Could be do-able on a tugboat:)
I was thinking about that too. I guess it would be quite a hard to get it working and be reliable for years under water. Rubber that is inflated with water is one thought but it would lack rigidity and change form on it's own.
What if you reinforced it with leaf springs and a pistion,creating a wisk shap that can change sizes and shap
Via compressing the leaf spings with the piston?
@@skunkjobb What about using one of those expandable rhombicosidodecahedrons, or whatever they're called?
Of course, why did nobody think of putting our magical expandy-thing on ships that accomodates the waves, yet is strong enough to be placed on the most stressed part of any ship? Also, it cannot have moving parts, but its magical, so thats fine, isnt it?
Looking at simplified bulb construction, length, diameter, and vertical position are major parameters. Length could be varied with a telescoping bulb. Diameter strikes me as the most difficult major parameter to change in operation.
Always wondered what that nose-like protrusion on large ships was for.
SHIP BONER
Good video! Thank you for not using a robot voice.
I would think that a reduction of surface area should be your design starting point. Then look at other factors depending on the service she will fulfill.
Surface area is only part of the problem. Ship resistance comes from two major sources: friction and waves. On a good hull, the friction is only about 20-35% of the total resistance. Wave making is normally the dominant part. Hence why we often go for bulbous bows.
Yes, but her use in service should be the 1st consideration. From what I understand, the bulbous hull was 1st used on the Japanese Battleship Yamamoto due to her wide hull. Ships in the early 20th century reduced surface area with sharp straight bows, narrow hulls and rounded transoms, but this is very limiting on overall design and comfort. The sea is a world of compromises. I like planing hulls for the speed :-) Thanks for your reply and I enjoy your channel.
hydrodynamics is more of a or just as much a challenge than aerodynamics
how to calculate the sonar dome ?
If someone gave you 100 thousand dollars to design a 200 foot motor yacht (jets vs propellers) that can travel at 60 knots; - what software would you use to design the ships aluminum hull. What software would you use to check performance at different speeds and at different wave heights. IMO i believe Computer/softwares fluid dynamics is less expensive and provides a very quick turnaround ( ie ... a different design each day for 45 days until its perfected) of data before actually building a 10 foot scale model and test it in a water tank.
3:02 Huzzah! the fun been doubled! XD
Bulbous bows seem to conflict between reduced residual and increased frictional resistances. What about bulbous bows in naval ships? Even DDG-51 almost got a small bulbous bow on top of a large one. Several operating naval ships with large speed ranges use bows, some of then very fat bulbs probably to accommodate sonars and several with small and thin bulbs (i.e. Meko A-200). Too many future naval concepts incorporate bulbs. And what is the effect of inverted bows on the seakeeping of naval vessels?
Can you design the combination of the shape of a bulbous bow/ship to optimize at a predefined speed.
Yes. That is the ideal scenario for a bulbous bow. They work best when we have a single predefined speed to optimize for.
@@DatawaveMarineSolutions Can you accurately simulate water flow around a ship bow to determine how to minimize water eddies? Eddies cause drag.
@@richrepublican3493 Yes. But it isn't automatic. CFD tells you where the eddies happened and can even measure the impact of each eddy. But it can't use that to back calculate a fix to the hull shape. That is why a CFD engineer must be a fluid expert first. They use their knowledge and experience to manually try refinements to the hull shape. CFD let's them quickly test those refinements and tells them exactly where to apply the changes.
Very informative! I was wonding why you cant just slap one on say - your Yacht, if it really saves fuel. In hindsight it seems obvious.
Hello. That was really fascinating. I wonder if you can help me? I"ve been looking at bulbous bows on large vessels for decades. I think I've seen every possibility on bulkers. tanners and container ships. Lately all the new bunkers seem too have the same kind of bow-rather bluff with a not highly developed bulb? I just wonder was there ever a time when they got bulbous bows right for different classes and proportions of ships? Or does fashion play a part? Hoping you can give me some guidance or suitable references. best wishes. :-)
Hi. Fashion is definitely a part. But in this case, the biggest factor was better science. I don't have the exact dates, but from around 1960 to 2010, the prevailing science said that a properly designed bulbous bow would always reduce resistance. (Provided that the ship operator used that bulb at the correct speed.) But that science all assumed perfectly calm water, with no ocean waves.
Around 2010 - 2014, some new research came out that added waves back into the mix. That showed that in many cases, the bulb increased average resistance, because of the wave interactions.
So that is the current state: bulbous bows can still help some vessels. But it takes more effort to make sure they are beneficial. Now, we need to look at calm water performance and wave interactions. Given all that, many owners decide to avoid the hassle of a bulbous bow.
@@DatawaveMarineSolutions Thanks. It was just she sheer variations of size and proportions that has fascinated and puzzled me. But that's a greta expiration,T hanks for taking the time f to explain to a layman. :-)
what about added flotation forward? doesn't that help too?
Maybe? Do you mean the extra buoyancy we get from the bulbous bow? That extra buoyancy helps a little, but it isn't a major hurdle. If we don't have the bulbous bow, we normally just design the ship with more weight in the aft end. That bow of the ship is so narrow that we normally only use it as a tank for ballast water, so we don't normally need to worry about getting extra buoyancy forward. Did that answer your question?
Nicholas Naval Architect your video suck
What about Ulstein bows? Good, bad or ugly?
Great question! I am still doing my research on Ulstein bows. I hope to eventually release a video on them.
How about a SWATH ( small water area twin hall) design to gain better stability and fuel savings. I haven’t seen any of your videos speaking about the benefits of SWATH. It would be a great video.
I have that one coming out within the next few months. Looking forward to it!
Saw a diy one on a small sail boat on the great lakes once had to do a double take
For ships smaller than destroyers A Streched Capital _S_ shape may be the ticket. Instead of equal knife axe wedge or V we strech out an _S_ so 1 side of wedge has cut out for way & then the other side of the _S_ has another cut out scoop for wave to chill out a bit b4 traveling free down the side of ship. The bottom of _S_ gets flatened out& a equilateral triangle shape pnt facing down lowest prt front of V hull only it is angling back under the front of ship. The bal right & left scoop out we lost top side is back underneath the water small scale. How much does the equilateral triangle angle back underneath guess depends on tonage, but I would guess about 39 or 40 degs rake.
I have seen French trawlers with dual "bulbous" bows....ie, they have the normal bow shape on top to ride over the waves BUT under the waterline it the xbow or pointer" to cut thru the waves and allowing for smoother ride!!
The Wider yachts have a bulbous bow and they are small vessels in comparison to your examples, From 135 to 165 ft.
A speed controlled extendable bulbous bow could adjust its length and optimize its length for a range of speeds.
I never thought they would increase fuel economy I thought they were more for stability guess I was wrong. Thanks this changes everything I was interested in doing a refit of a older commercial ship and turn it into a yacht
I hate them to but it changed the regular ship into a waveless passer bye. If you see the ship leaving less wake and less waves? Then the medicine is working. Even at the docks you are the hero.
Thanks Nick.
They seem to work on modern subs, the whole sub is a bulb. And porpoises have a bulb in front (joking- I think). Do we need a shape like a sub with a conventional ship form on top?
I love this question! Great thoughts of looking to other examples and applications. And this shows one of the key elements of surface ships: the water surface. That water surface drastically alters the flow patterns around a surface ship. But designers optimize the submarine for travel far beneath the surface, and we don't get the same benefits any more than 5-10 meters deep. So the subs are still best as their current shape, unless someone designs something better.
I was thinking of gluing a sub on the bottom of the ship rather, to make the ship go faster. My original (barely educated) view was that the protuberance moved the bow wave forward, so the ship didn’t have to climb up it, and it made the ocean think the ship was longer and had a more narrow length to width ratio. But what do they do with aircraft carriers? The one on the JAG intro had a waterfall in front and no wake, just a ship-wide line of white water back to the horizon it seemed.
BTW, the best bow wave I ever saw was on the Tugboat Annie TV show, during one of her races with Capt. Bullwinkle the water must have gone down over 20 feet and a bit under the hull. This comes from the early-ish B&W days of TV so my recollection may be cloudy.
For many years sailing on a chemical tanker with a bulb bow, after 10 years this one was taken off the bow, I experienced a lot of problems during bad weather, specially in the Bay of Biscay, bow came out of the wave followed by the bulb, by plunging back into the waves first the bulb smashed into the waves and the ships bow, we lost all the speed
Bulbous make the waterplane-area smaller. The bigger bulbous the smaller waterplane-area. What if the ship had a huge bulbous? I think it reduces the pitch motion.
Those bulbous bows remind me of battering rams on those ancient Greek and Roman warships.
I wish he had mentioned how a smaller, narrower, sharper, wave piercing type of bow addition may come into play, if they could work instead of the larger type bulbous bows, or if that could be an option for smaller, but somewhat faster vessels. Such as commercial fishing vessels like lobster boats.
You want my other video where I compare different bow types. That includes wave piercing bows: czcams.com/video/5eepu_owFHI/video.html
They were a good way to change old ships into more energy efficient.
I’ve seen a 14feet dinghy fitted with a bulbous bow 😂
bulbs arent only for fuel savings. a lot of guys want a little more floatation up front or a crumple zone for hittin rocks. also an extra water tank or fuel tank are options.
If have often wondered if a bulb is effective on small displacement yachts. It sounds like it was more of a marketing gimmick than an actual fuel saving benefit from reducing bow wave. Also bulbous bows prevent a vessel from being ice classed don’t they?
I don't remember anything in ABS rules for ice class that specifically excludes a bulbous bow (but I also don't memorize class society rules). However, ice class rules size the bow plating based on the angle between the hull plate and the ice. The more your bow looks like a knife edge, the less plate you need. A bulbous bow would generate so much pressure for ice breaking that it would require extremely heavy plate. So I suspect this is more an issue of economics for ice class, rather than anything preventing it in the rules.
So what your saying is the Hillstrands wasted their money adding a bulbous bow to F/V Timebandit?
Probably. But you never know. I have been surprised before by some of those seemingly simple bulbous bows.
Bulbous learnt from the Submarine during surfaces - best research ,
What about a bulbous bouffant?
3:03 the ship on the left is the ocean liner Queen Mary 2. What I don’t understand is why it needs such a prominent one, while the SS United States was flat as a board below the waterline, but was the fastest ocean liner _ever_ built. Obviously there must be something more efficient in a flat, sharp bow.
Not necessarily. With ships at this scale, we don't just build the hull to achieve the fastest speed possible. The speed is a target selected at the beginning of the design stage. The SS United States may have just been designed to go faster. If you want to compare the two, you need to examine the resistance curve for the two vessels. That shows power required at each speed. The lower curve is the more efficient vessel.
It would just make more sense for the designer of the United States to give it a bulbous bow then, to achieve his goal of fastest ever liner. Wonder why he didn’t.
Nice subbed
Tell that to the Crabbers boat “Time Bandit “
What is CFD?
Computational Fluid Dynamics (CFD). We use the computer to simulate water flow around the ship. CFD lets you examine the flow patterns in great detail. It has become a major asset for optimizing complex shapes like bulbous bows.
Computational Fluid Dynamics: using a computer and software to model gas or fluid flow around a shape such as a ship's hull or an aircraft. This helps engineers and designers to see what works better and to spot potential issues in much the same way as the construction and testing of physical models in a test tank or wind tunnel would. I believe CFD is a faster process than model testing, and results in more thorough analysis of a design's characteristics.
CFD is akin to FEA- Finite Element Analysis .... imo, very useful in terms of visualizing in theory to that of what you can investigate or witness in reality, computers and such modern tech are so useful to a point of perfection
Has nobody made an adjustable bulbous bow? Tune the length to your current desired speed.
So the old ocean liners with the knife like bow if they survived till today would still be fine without the bulbous bow? Like If we rebuilt the original queen mary we wouldnt need to add a bulb since she did about 30 knots on her own. The SS united states did 35 knots.
Yes, but speed isn't the reason to install a bulbous bow. We can almost always find a big enough engine to make whatever speed you want (within reason, no rocket ocean liners). But bigger engines burn more fuel, costing hundreds of thousands of dollars. The intent of the bulb was to reduce the required engine size while still doing the same speed.
the united states did 43 knots lol and i am responding to myself from 9 months ago...
Someone should figure out an adjustable bulbous bow that alters based on speed and sea conditions.
You basically have to re-create the hull lines plan and and get the baseline of the original hull, and then make the bulbous bow. Don't you need to figure out the buoyancy of the ship? And then have it applied? Also wouldn't the bulbous bow make the ship slower? Honestly I like older ships then modern, for example like the classic ocean liners and for example Titanic's hull!!!!
Yes. We do need to adjust the buoyancy typically. So the entire lines plan does get remade to incorporate the bulbous bow. Glad you like the the classic hull shapes. They are making a comeback.
So why don't they create an active bulb that changes shape and position for different conditions?
Some designers are working towards that effect. But instead of a shape changing bow, they are trying to adjust the shape so the bulb still works at a range of speeds. Sacrifice performance boost at one speed to improve overall performance across a range of speeds.
Seems like it would be relatively easy to find an "overall performance" shape as you say, but then put the bulb on a ram that adjusts its projection from the bow as needed. I would think fuel savings would pay for development costs.