Tanker Behemoth.

An organization; Wecansolveit.com, have been sposoring TV and Magazine ads of late. The organization demands that we "free ourselves from our addiction to oil". A recent ad in, Scientific American, shows a visual impact picture of a collossal tanker. It is moving slowly through the water.

The tanker, if viewed in plan has a perfectly rounded bow. The bow at the waterline also seems to be rounded. That detail grabbed my attention and prompted questions: Is that the standard layout for vessels designed for that purpose? It is clear that rounded ends as opposed to pointy ones can provide more interior volume. How does that planform square with propulsion efficiency? Comments ?.

I reckon that the ship cruises at S/L ratios of considerably less than one. Nonetheless that bow is going to throw up one helluva bow wave. I would not want to be within 5 miles of that thing when I am playing around in my dinghy. (fortuneately there are precious few tankers plying the inland lakes of Florida where I am most likely to sail. That picture will surely keep me from sailing in Tampa Bay near Port of Tampa gas docks)

 

You mean this...?

 

Guillermo; Not the same picture that I referred to but your pic has the same layout. Egad! that thing is scary... ....and big. Your picture has the ship throwing up a lot of froth but does not seem to be creating the gigantic wake that I would have expected.

 

It's only small in scale. If we take hull speed to be 1.34*sqRt LWL, then if the vessel is 850' long or thereabouts, the Vx will be travelling somewhere in the neighborhood of 39 MPH. At 22 knots or so, what these things travel at, the wake they would throw is not nearly as big as it could be.

Regardless, though, in absolute terms, the wake is still what happens after something displaces several tens of thousands of tons in the space of seconds....

 

The bow shape, and the entire hull form, works because the vessel is moving at what is a very slow speed relative to her length.

VLCC or ULCC's are well over 1000' long these days, average might be 1200' with the largest being 1500'. Average cruising speed for these ships is between 12 and 16 knots. This works out to a speed/length ratio of approximately 0.34-0.46.

 

The water pressure that build up in front rebuilds in the astern giving back the power lost in the front.

I think I heard once a perfectly shaped bullet would have 0% loss if it was painted in a frictionless paint.

Hydrodynamics is not my strongest subject.

 

Tad; I defer to your knowledge. No doubt some very astute dsigners have done the requisite assesments of efficiency versus capacity. That is to say that bluff ends will allow extra volume which constitutes an economy. That economy might well outweigh the propulsion energy disadvantage and be valid within a particular velocity envelope. Relative to length these things move more slowly than I imagined. That's good enough for me.

StianM; The subject vessel does not work as simplisticly as that. Would that it were true. Water does converge at the stern and probably imparts some force in the forward direction but much is lost in the energy transfer process. Davey Jones does not allow zero sum games.

 

If you look at the photo closely, you see that there is considerable flare in the bow. Projected to the waterline and below, this gives the monster a much more pointy than circular bow in plan view. There is probably a bulb down under the water when loaded as in the photo.