Hydrodynamics and Hull Design: Linking Hull Shape to Powering 

Hi hope you doing well. I would like to build a 48' loa steel boat and haul is a subject can you advise. Thank you.

I wish I could say more effort went into the aerodynamics, but it is more of an afterthought (excluding sailboats). Aerodynamic drag makes up around 2% - 5% of the total drag on a ship. For high speed ships (35+ knots), that can be more significant. And high speed ships do see more aerodynamic design. One area where aerodynamics play a part: the sideforce on a ship. Large ships have a lot of wind area when viewed from the side. A sideways wind generates significant force. This becomes a large factor in designing mooring systems for the ships and rudders to control maneuvering at slow speeds in port.

Basically yes. The relationship between compression and pressure change is the bulk modulus. (This can also relate to density with a few conversion formulas.) However, for water, that bulk modulus is so ridiculously high that we see no effective change in density for any normal change in pressure. Technically, the water is compressing when we see a pressure change. But not enough compression to ever effect the density.

What you imagine as a collapsing zone of turbulent water does not happen when we carefully design the hull with a streamlined shape. The key is careful design, with a very gradual reduction in the hull area. Imagine it more like a wide river slowly expanding. The water velocity gently slows down. As water speed decreases, the water pressure increases (the energy shifts from velocity into pressure). Because the increased pressure is pushing on the aft side of the hull, we see a slight forward push, known as pressure recovery. This is still a very small change. You can only detect it with precise experiments, or with Computational Fluid Dynamics. But clever designers know about it and design to intentionally create the effect for maximum hull efficiency.

Probably not. But I like the way you are thinking. The teardrop shape is a great beginning. And at 600 ft long and 60 ft wide, you have a length to beam ratio of 10:1, which is considered very fine. You would typically see that ratio on very fast ships. But moderns ships already use variations on the teardrop shape, plus some additional tricks. Try to also incorporate parallel sections into your ship design, as these come almost completely free from resistance. You don't need to taper to a perfect point for the teardrop shape. A flat transom stern can help. You are definitely on the right track. Every naval architect started out experimenting and with different hull designs and trying to make it better. And we pretty much keep doing that for the rest of our career.

@@DatawaveMarineSolutions Thank you for the tips!

That sounds like the hull profile of some higher-performance sailing hulls. I think it would perform quite well, that is the most aerodynamic/hydrodynamic shape, hence a lot of protrusions like rudders are that shape. To build such a ship probably wouldn't be very practical though, considering reduced internal space and the lack of a parallel section. The main benefit of a parallel section, or section of constant cross section, is that it's easy and cheap to build - a series of identical frames that can be mass-produced on the same jig to the same design, the same segment of hull repeated over and over again. All covered by flat plates which are cheaper to make. With your design the cross-section would be constantly changing, most surfaces curved, no two frames alike. This is seen on smaller vessels, like sailing yachts, where this cost is seen as acceptable (not huge as the vessel is much smaller) for the performance gain, but for a large ship I think it would be difficult to justify. Would be low-drag, and very beautiful, but when designing such large ships all anyone wants is for it to cost less and carry more.

Absolutely. Ice breaking hulls often require wide flat bows, which is a terrible shape for open water travel. Some icebreakers get around this by designing the ship to operate in reverse when breaking ice. They have a normal shaped bow for open waters, and their stern is shaped for ice breaking.

For solar power, you need a catamaran hull, intended for a sailboat. Preferably one of the high performance catamarans intended for higher speeds. They achieve higher speeds with really low hull resistance. Unfortunately, with current solar technology, you need a solar panel area larger than the boat deck area. Technically possible, but not easy. Unfortunately, it takes a lot of power to move through the water, even at slow speeds.

@@DatawaveMarineSolutionsthanks for the quick reply. Honestly i thought that was a lazy answer. Solar energy turning a propeller should do “something” so i wonder just how inefficient would it be. Continuing, i found a regular guy with a 1981 bayliner 245, with 2 minn-kota electric motors, 5000 lb power boat (monohull), added two solar panel and, two electric motors and now gets 4-5 k unlimited range (max speed is higher) without lowering the capacity of the 8 marine batteries. This is without your level of expertise. I’m not a “boater” although i still hope to be despite me being 75 (code for too old to build a solar boat). So i wonder, if that garage mechanic could do that with $500, what could a naval architect do if he put his mind to it?

They do that for different reasons. Racing boats use the flat wide stern because they sail fast enough to plane on the water, and want a planing stern. Cruising boats do because it creates more internal space, and because the boat sails more upright, making for a more comfortable ride.

First of all don't use superlative forms of adjectives if you can't prove it. This is the worst practice of criticism. (yes sometimes superlative forms are funny) Another thing is I have no experience in designing a ship. I'm just a technical interested Person and I think I did understand the explanation. So it might be not that bad.