Article - 'The bulbous bow - why some ships have it and others don't' (TheNavalArch)

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We are glad to publish a new article titled The bulbous bow - why some ships have it and others don’t

This article is a two-part article providing a complete introduction to Bulbous bows, their principle, characteristics and their effect on the vessel’s lifecycle.

An excerpt is presented below:

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The principle of the bulbous bow is that it is sized, shaped and positioned so as to create a wave system at the bow which partially cancels out the ship’s own bow wave system, so reducing wave-making resistance. This can only be done over a limited speed range and at the expense of resistance at other speeds. Many merchant ships operate at a steady speed for much of their lives so the bulb can be designed for that speed.

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The bulbous bow - why some ships have it and others don’t - TheNavalArch https://thenavalarch.com/the-bulbous-bow-a-primer/

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Team TheNavalArch

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So the lower speeds we see in most ATB units would be the main reason that we haven’t seen bulbous bows on the barges yet? I wonder about the math on building a bow on in a barge that is averaging 10kts. It would be easier for me to understand the formula provided if it had some units with it. I’m presuming the length at the water line is in meters.

The Froude number is dimensionless. As long as you use the same units for length and speed and gravitational acceleration** in the formula the number will be the same no matter which system of units you use.

** meters, meters per second, meters per second per second for example.

Here’s a whole article on the Froude number, much of which is way beyond me: https://en.wikipedia.org/wiki/Froude_number

I noticed on one of the Bouchard newbuilds a bulbous bow, does it make a difference? As tight as Morty is there must be a reason.

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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. http://www.brayyachtdesign.bc.ca/inde…

Get the full article here: https://wp.me/p3pMQV-1lP View more tips and helpful articles at https://dmsonline.us/

In general Wikipedia isn’t very helpful on a lot of technical subjects as they are not written with the layman in mind. I’ve had good luck looking for videos instead.

This one is interesting but having to do with stream beds ect, Froude shows up at just before 7:00.

Seems related to the Mach number? https://forums.x-plane.org/index.php?/forums/topic/73282-the-froude-number/

Laminar flow being the most common denominator. We were all drawn to the little square tabs on top of the wings when Bill Lear’s original model 23 and 24 came out in the mid 1960s. Up until then vortex generators had only been used on high performance military aircraft. By interrupting laminar flow over the top of the wing at both extremes of the spectrum, both low and high speed stall characteristics were improved.
Same reason fish scale patterns have been suggested as hull surfaces to reduce drag.

Hornbeck tried it on some of there boats. But had to take them off. All it did was beat the bow to death in heavy seas

The New Zealand Maori used a fish scale pattern on their large war canoes that were up to 115 feet long. The canoes called Waka Tau were paddled by up to 100 warriors and were capable of reaching about 12 knots. There is a fine example of the type at Waitangi which is launched on February 5th each y ear.

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