NavyRecognition reports on Hull Vane’s presentation at the MAST-Asia 2017 Conference.
The new NSCs and FRCs are costing more to fuel than the ships they replace. The OPCs will almost certainly cost more in fuel than the 210s and 270s, they will be replacing. This should not be surprising. These ships are larger and have much greater installed horsepower. Since our operating budget has not been growing, the greater fuel used, as more of these ships come on line, is going to become a problem. Surely we will try to get increased operating funding, but in the mean time we need to work on operating more economically.
If we have not already evaluated this design modification, we probably should.
In addition to fuel savings, addtional side benefits are claimed.
While reducing the energy consumption is usually the main goal, the Hull Vane® has additional effects which are very desirable for naval ships. When a ship sails in waves, the Hull Vane® dampens the pitching and yawing motions, making helicopter landings safer and improving the performance of onboard systems and personnel. As the Hull Vane® reduces the stern wave, the propeller loading and the engine power for a given speed, the ship will also have a reduced acoustic (and visual) signature. On newbuild naval ships, the cost savings on engine power to reach a given speed are generally much higher than the cost of the Hull Vane. Retrofitting a Hull Vane® on existing naval ships typically has a payback period of one to three years.
We did discuss this innovation earlier. I am going reproduce comments from my previous post on this topic.
First a disclaimer: I am from the Hull Vane sales team and I have presented the paper at the FAST conference. You can download a copy of this paper on our website (www.hullvane.com) from the news section. That will clarify a lot.
Then to answer some of the comments here (and the email quoted, which is not from our team as far as I know):
1. The Hull Vane is very different from a trim tab, because it’s a hydrofoil. Actually the design is not so much speed-dependent, but hull-shape dependent. When it works, it works on quite a wide speed range, as long as the speed is high enough (Froude number in general above 0.2). On the Holland-Class, we achieve a positive result over the entire speed range (from 5 knots to 22 knots), but that’s in part because the Hull Vane allowed (and actually required) a reduction of the depth of the trim wedge which is currently installed.
2. The Hull Vane is a new and patented fuel saving device. Of course hydrofoils have been used before, but never on displacement vessels with the purpose of generating forward thrust and reducing the wavemaking resistance.
3. The angle of attack is more a function of the buttock angle of the bottom plating than it is of the speed. That’s why having an adjustable Hull Vane (we looked at it) gives you a very marginal performance increase, while adding a lot of complexity (hydraulics, control mechanism, maintenance, etc.). The fixed Hull Vane works really well and is not more complex than bilge keels or a bulbous bow. The design is indeed complex and requires both know-how and accurate CFD simulations, taking into account both frictional and pressure drag. From our 12+ years of experience, we know how to get it right, but we also know that it’s very easy to get it wrong. There are ship types where we can’t achieve a positive result, but on patrol vessels and naval vessels, we have consistently achieved very good results.
4. Just like the rudders, and propellers, you indeed want to avoid marine growth, which has a more detrimental effect on appendages than on the main hull. There are solutions to this (coatings), and furthermore the Hull Vane is easily accessible for cleaning without drydocking. On the vessels sailing with the Hull Vane, marine growth has not been an issue.
5. Regarding our “limited abilities to accurately predict the flow field below and aft of a bluff transom vessel”, I completely disagree on that. Our parent company Van Oossanen Naval Architects has used CFD (Fine/Marine) for many years with excellent results, confirmed both by model tests and sea trial results. This includes the results we have obtained for the Hull Vane performance. For stuff like the Hull Vane, where viscous effects (and the thickness of the boundary layer) are important, we believe CFD to be more accurate than model tests.
6. The Hull Vane is not limited to “short fat frigate territory”. We have achieved good results also on the DTMB 5415, a slender destroyer hull shape released for research purposes. The performance is better however on the fuller-bodied and wider-transomed hull shapes like the typical US Coast Guard cutters, which we would very much like to do some work on.
To sum it up briefly, the Hull Vane is very comparable with the bulbous bow, although it looks totally different. If the bulbous bow hadn’t been applied as widely as it is, people would also find it hard to believe that it can reduce the resistance. The bulbous bow also requires careful design to work well and has a speed range in which it works well. One of the main advantages of the Hull Vane is that it also improves the seakeeping (reduced pitching, heaving, yawing and rolling). There’s a video on our website explaining the working principles very clearly. If you have any questions, don’t hesitate to contact me.