Why Are Bows That Shape?

logic says that for a ship to move as fast as possible you should have a bow that is as sharp as possible yet when you look at different ship designs you'll notice that all of their bowels are different some are fine and sharp while others are what can only be described as dumpy so why are there so many different bowel shapes and what possible advantages can each really have a few months ago i released a video about the rms empress of island where the observant among you will have noticed the shapes of the bowels of the two vessels the empress as a classic ocean liner had a straight bow which when viewed from above tapers in from approximately the bridge position the idea is that it's sharp enough to cut through the water yet it still gives sufficient width to the hull at a reasonable distance partly for space for passengers but mainly for buoyancy and stability you see if the hull was really long and thin it would need to sit so much deeper in the water to be able to support the weight of the passengers and cargo not only that but you would lose the ability to rely on form stability to keep the ship upright meaning that you would need a massive great weight low down to keep the ship stable this is what the old sailing ships had to do their rounded hulls couldn't provide the same degree of form stability so they were supplemented with ballast in their keels anyway we've now established that the bow of a ship has to be a compromise between sharpness to reduce drag and width to increase capacity and stability but what about its side profile again in the empress of island video we saw two examples of different profiles the empress with her straight bow which makes sense from a logical perspective and the store start with a tumble home bow which proves so devastating in the collision a tumble home bow is one that slopes inward the higher up you get it creates this protrusion underwater and results in a shape that is much easier to cut through heavy seas as waves ride up over the bow there's minimal increased displacement meaning that it's less likely for a ship to pitch up and down as these ships move along they just look solid and they appear to cut through the waves rather than ride them unfortunately however as we saw with the empress of ireland when one of these tumble home bows is involved in a collision they inflict an immense amount of damage under the water line of the other vessel drastically reducing his chances of survival so much so in fact that this very incident was the catalyst for the next evolution in the design of ship's bowels the flare a flared bow is one that sticks out much further as you get higher up the idea with these is that they're much better at riding waves because as the wave approaches the water encounters more hull increasing the buoyancy and lifting the bow up with the wave where the tumble home was prone to punching straight through a wave the flare increases the ship's ability to ride the wave and unlike in the empress of island incident a flared bow is going to do a greater amount of damage above the water line in the event of a collision but the vessel that gets hit is at least more likely to maintain sufficient watertight integrity to remain afloat the amount of flare does vary between ships of course a modern ocean liner designed for the north atlantic has quite a prominent flare while a huge crude oil tanker has far less of course these two vessel types had some considerable differences which came into play when their bowels were designed the ocean liner needs speed and comfort for passengers while the crude oil tanker primarily needs as much cargo space as possible and it needs to be able to operate at a much wider range of drafts fully laden a cape size crude tanker might have a draft of over 25 meters yet in ballast you would expect less than half that any flaring of the bow could only occur on the part above the fully and water line which given the density of the cargo it's not going to leave much hull available compare that to say this car carrier and you can see what's possible when the cargo is much lighter there is so much hull above the water that you have space to not only create the flare but also to build multiple decks of superstructure high above the water line to protect the cargo in this particular case the flare of the bow is necessary to maximize the cargo carrying capacity without it you'd be limited to the footprint of the underwater hull it's the same story with military vessels such as aircraft carriers for them deck space is the most important thing obviously you can always use the space straight above the submerged hull but for a bigger runway you really want it to overhang and you don't want water sloshing over the deck in heavy seas the flare at the bow accomplishes both protecting the larger deck space by allowing the ship itself to ride up and over large waves when it comes to destroyers however the priority can shift they don't need lots of space above the waterline in fact they benefit from less superstructure because it reduces their radar cross-sectional area reducing how visible they are on other vessels radar screens size is only one element of course because the tumble home hull also has the advantage of angles all those sharp lines and upward facing sections mean that any radar pulses that strike the hull are going to be deflected up into the sky so they won't bounce back to the radar they came from a flared bow on the other hand would tend to bounce the pulse back towards the surface of the water increasing the chance of it propagating back to the enemy radar moving back to the commercial world the next bowels to consider are those on vessels such as this osv while you do get some that have a flared bell the most modern ones are tending towards this sort of inverted bowel design instead there are a little like tumble home in that they slope inwards as you get higher up but the key difference is that inverted bowels do not necessarily reduce their beam as you get higher on this ship when you reach the top accommodation deck and the bridge deck it will still be the full width of the ship the idea is that the superstructure is still sufficient to provide a good amount of buoyancy at the bow so it won't dive through the waves in the same way that a full tumble home would of course it's not going to ride the waves in the same way that a flared bow would either but given the area of operation of these sort of vessels that's probably a good thing the seas are often high and steep so having a hull that can cut through while still riding a little will make the movement much more tolerable moving from commercial to pleasure we can see all the same principles at work i've seen small yachts with straight or plumb bows and i've also seen them with raked or a bit like flared bows just with less curves the rake allows more space in the hull and better sailing in some conditions while the plum bow is better at reducing pitching which is the up and down movement of a vessel when we get smaller still into the realm of ribs and speed boats the shape of the bow itself is less important as you're more interested in the overall shape of the hull you need the bow to work with the hull to allow the boat to reach such a speed that it can start to plane it lifts up out of the water and starts skidding along the surface rather than needing to cut through the same story applies to hydrofoils where the bow is only there to get the hull up to a sufficient speed for the foils to lift it out of the water going the other way under the water we get a completely different design again unlike all other vessels submarines are designed for a combination of reduced drag and pressure protection that's why their hull is more cylindrical with a bow designed to feed the water smoothly across the entire surface area of the cylinder with all the vessels that we've looked at today you'll notice all their bowels have one thing in common they're all designed to minimize drag from moving through the water yet still provide specific benefits for the vessel's design purpose whether it's the flare of an aircraft carrier to protect the flight decor the nose of a submarine to protect against external pressure the bow is always designed for so much more than simply speed

Channel: Casual Navigation

Views: 2,944,243

Keywords: casual navigator, marine, shipping, casual navigation, maritime explaination, merchant navy, sailing, marine animation

Id: sLII1NAvYog

Length: 7min 22sec (442 seconds)

Published: Fri Jul 08 2022