Bulbous bows

[John Arton]

These come in all shapes and sizes, I sailed on a container ship that had a mairform? Bulbous bow which was very angular and designed to be ice breaker.
In 77 I joined a new build burmeister and wain panamax in Copenhagen as 2nd mate. It was a yard standard design and was a good ship, hydraulic side rolling hatches, dump valves for emptying the top side wing tanks plus really good accommodation. The hull design was unusual, forward she had a large rounded straight stem with very little flare to the slightly raised forecastle whilst aft was very angular construction to get good water flow into the propeller and onto the rudder. The anchor arrangements standard design had individual windlasses port and starboard with the gypsy leading directly to the chain stopper and the hawse pipe all in line but C.P. wanted the cheaper arrangement of a single drive motor to power both windlass using dog clutches. This meant that the windlasses had to be turned so as they were parallel to each other. This meant that after the chain stopper the cable made a sharp turn to lead down into the based pipe. We were doing initial surveys which included windlass testing. On heaving back up the anchor there was no way the yard could get the flukes to trip and stow tight up against the hull. The only way they could get it to stow was to have a barge alongside that would lassoe the flukes and trip them so as they would stow. Because the windlass set up had been changed by the company, the yard reckoned that should how it would be done in the future. Class obviously did not accept this so the yard had to come up with a construction that could be welded to the hull around the hawse pipe that would trip the flukes and thus allow t!he anchor to be stowed safely.
After sailing from the yard on her maiden voyage to Brazil to load iron ore, the hull form seemed to be working as designed with fuel consumption and appreciate as per designed criteria. Only a few years later there was much talk about retrofitting bulbous bows claiming that by doing so fuel consumption would really dramatically lowered.
I never saw any new build with such a bow design but recently have seen new build chemical tankers with a very similar? Rounded stem design, could not see if they had bulbous bows though.
The bulbous bow is designed to be most effective at ballast draught as a vessel in ballast is generally not earning money.
Rgds
J.A.

[vic mcclymont]

In 1964 Lithgow's built two ships for Trident Tankers, on with and one without a bulbous bow. The Ida was to compare any fuel savings (if any) between both bows.
No idea of outcome.
Vic

[Tony Taylor]

These come in all shapes and sizes, I sailed on a container ship that had a mairform? Bulbous bow which was very angular and designed to be ice breaker.


The bulbous bow is designed to be most effective at ballast draught as a vessel in ballast is generally not earning money.
Rgds
J.A.

John.
I have seen one in the tyne a few times recently, cant recall the name but definitely as you describe, I dont think I have seen another anywhere

[happy daze john in oz]

All cruise ships now have a bulbous bow of some description or other.
Passengers are informed this is to prevent the ship from pitching in high seas.
But I was informed it was to improve fuel consumption as a ship with such has better forward thrust with it.
Not sure which is correct, maybe someone on site with knowledge can assist.

[j.sabourn]

Apart from statements by various people who say it increases speed and assume it proves less rsistant to water, it also will increase the reserve buoyancy of the vessel and thus. Increase stability . As regards the dynamics of the forces of propulsion a ships architect would be better to explain all the reasons , which I have no doubt were originally proved in a ship model tank. It looks to the casual observer rather a weak point on a vessel but have no doubt behind the facade, the ship construction regarding frames both horizontal and vertical will be quite substantial. JS..

[John Arton]

The principal behind the bulbous bow is that it creates a low pressure area just ahead of the bow of the vessel reducing the force required to push the vessel ahead through the water whilst at the same time improving the flow of water down the sides of the ship's hull. Well that's was what I was taught in nav art for masters and who am I to disbelieve it. Again it is said to be most effective at the ballast draught for many vessels but as regards passenger vessels and many container vessels they rarely sail in ballast so their bulbous bow will be most effective at the loaded draught. Doing fore peak tank internal inspections where the bulb is situated, you need to be a slim Jim in order to crawl around the stringers and frames making up the bulb.
Rgds
J.A.

[Barry M]

The Maierform bow is the exact opposite of a bulbous bow as it is a cut-away design similar to an icebreaker's that designed to ride up over ice sheets. It is claimed to aid propulsive (and thus fuel) efficiency by straightening out the forward portion of the curve of cross sectional areas.

Bulbous bows are the exact opposite and project forward from the stem while having an effect in both laden and light conditions. The theory is that it creates a pressure system that tends to supress or cancel out the normal bow pressure system and thereby the wave-making resistance in vessels travelling at higher speeds. Slower vessels may also benefit because the bulb redistributes the velocity of the bow waves and thereby reduces the overall frictional resistance of the hull. The longer the bulb, the more pronounced the effect appears to be and this has led to some very long bulbs.

It really has very little to do with reserve buoyancy and/or stability.

Alternatively, it might just be the shipyard pixies looking for some overtime from the additional construction.

BM

[John T Morgan]

I was taught and understand like you the reasons for the bulbous bow, but theT2 tanker hull design indicates a slight bulb at the base of the stem which was there for no apparent reason.
I wonder if it was the start of the modern bow. Strange if so, the T2's were wartime mass produced vessels built in the United States, but perhaps they knew something no one else did.