Do Bulbous Bows Really Work?

Bulbous bows are not miracle devices. Learn their limits and how to use them effectively.
Want to design a bulbous bow? Start with this paper:
A. M. Kracht, "Design of Bulbous Bows," SNAME Transactions, vol. 86, pp. 197-217, 1978.
View the article on the website: wp.me/p3pMQV-1lP
View more tips and helpful articles at dmsonline.us/

[@eduardodaquiljr9637]

Bulbous bow is not for wave streamlining,but to add bouyancy on the fore to prevent pitching during strong waves.

[@DatawaveMarineSolutions]

@@eduardodaquiljr9637 Incorrect. The bulbous bow is almost fully submerged. Meaning it can not contribute additional buoyancy to mitigate pitching. There is no additional structure to submerge. The bulbous bow does provide additional buoyancy forward, but there are easier ways to achieve that. For example, modern bows with vertical stems provide additional buoyancy forward.

[@marc0523]

A quick question: is there any reason why there isn't a movable bulbous bow so that it can work at different speeds?

[@DatawaveMarineSolutions]

Nothing comes to mind immediately. Simple reason: no one tried it yet, and no one cares enough to optimize the bulb that much. Most ships fall into two modes of operation: those that change their speed constantly (like a tug or workboat), and those that set one speed and hold it for days. I don't know if a constantly changing bulb would offer significant fuel savings on a tug or workboat. You may have the next big idea.

[@marc0523]

Thanks for the reply.

[@akoponen]

The expanding and shrinking bulbous bow would get a lot of dirty jokes made about it. But yeah, an automatically speed controlled bulbous bow extension seems a no brainer improvement for the large slow ships that would save fuel by having them.

[@bertcox4484]

Would a 60-70 foot vessel with a 10:1 ratio, ax bow(with out the sinking keel), and a planned speed of 7-10 knots benefit from a bulbous bow. And not be a risk to life and limb in a storm state.

[@DatawaveMarineSolutions]

Not really. Planing boats rely on different wave physics than conventional boats with bulbous bows. Similar to the difference between subsonic and supersonic jets. A bulbous bow on planing boat just gets in the way. But at a 10:1 ratio, the hull was already so thin that you really would not need a bulbous bow.

[@wilkinsonyachtbrokerUK]

I worked on a 185 foot Feadship displacement hull and it didn't have a bulbous bow. It cruised at 12 kts

[@HardWoodHauler]

But why? Why do the waves cancel out?

[@DatawaveMarineSolutions]

When we say "cancel", the waves aren't eliminated. They don't disappear. But at the single region near the bow, the two waves act in opposite directions. You have a wave trough, with low pressure, and another wave peak with high pressure. The ship hull only sees the net pressure difference between those two. If we do our job right, that net pressure will be very small. But those two wave systems still travel down the hull once they pass the bow. So "cancel" is probably better to think of moving the regions of high pressure away from the bow. If that high pressure happens along the parallel section of the hull, in the middle, then it doesn't contribute to ship resistance. (Nearly. There are a few tiny details to the process that I'm ignoring at this level.)

[@jackpez]

They do...