Gas-powered Unmanned Vessel(GUV)

A manned motorized small vessel, of 20-60 ft in length, is often used as an observational platform in coastal waters and estuaries The survey boats are thus useful moving platforms but can be ineffective under certain conditions such as in shallow coastal bays of the Louisiana coastal waters given their vulnerability to running aground if they were used in shallow waters, such as near banks, particularly at low tides. In addition, the cost, logistic requirements, and labor needs can be limiting factors for continued observations through entire tidal cycles (at least 24 hours in Louisiana coast because of its dominant diurnal tidal nature) across tidal channels or where tidal and daily fluctuations are important. Another drawback of manned boats, including airboats which are often used for wetland studies, is that their gas motor(s) or fast speed usually produce a significant amount of disturbance to the water column and bottom sediment in very shallow waters. Therefore, when using these boats, extreme caution has to be practiced in shallow waters to avoid sampling waters affected by the turbulence from the boat’s propellers or fast motion (such as in the case of an airboat) if only the water column conditions under natural (undisturbed) situations is of interest.

Figure 1. GUV in action. This GUV is made of fiberglass.

 

 

 

 

 

 

 We have recently developed an automated unmanned boat, or GUV; (Figure 1) with some specific considerations of continuous operations. Three GUV have so far been made and rigorously tested. They are made of aluminum, plastic, and fiberglass, respectively. The newest GUV (made of fiberglass) is equipped with a 600 or 1200 kHz ADCP and/or a 3MHz mini-ADP (there are two wells on the GUV for either or both instruments), an optional side-scan sonar, an optional Seabird Electronics SBE 45 surface thermosalinograph (micro TSG), a high resolution GPS (~ 0.25 m accuracy), and up to two real time web cameras. The GUV has an onboard computer with a long-range (~ 10 km) wireless connection to another computer on land or on a mother ship.  A software package written in Visual Basic computer language is developed in-house by us. It can be programmed to run through a series of (unlimited number of) predefined waypoints continuously with high precision. The prototypes have been able to maintain the same data collection transect over many replications accurately (to resolve tidal variations), a task that manned vessel cannot accomplish with comparable precision and endurance. The boat can achieve 4.5 knots cruising speed with at least 24 hour endurance without refueling. The fuel consumption is very economic: about 2 gal per day. In comparison, a 26 ft catamaran with twin engines of 150 HP each that we have been using consumes about 40 gal of fuel per day. The cost of the GUV is less than $20,000 including the labor (excluding the cost of instruments). The GUV is light weighted and can be easily picked up by 1 person and it can be put on top of a racked truck for easy transportation.

 

Figure 2. Sample GUV Track at Bay Champagne, a shallow lake with a depth ranging mostly between 0 and 1.5 m with an average of about 0.75 m.

 

 

 

 

 

 

Figure 3. Test of Energy Requirement for the GUV. As the speed decreased from 3.1 knot to 2.4 knot, the power need dropped from 400 Watts to about 200 Watts! 

 

 

 

 

 

 Field tests have demonstrated that the average offline distance from the planned route was 0.97 m (with the plastic GUV) or smaller (with the latest fiberglass GUV) under swift flow conditions (flow velocity ~ 1 m/s).  In addition, multiple intensive test runs have been conducted in the LSU’s University Lake, a number of tidal channels at Port Fourchon, Belle Pass, Bay Champagne, and Vermillion Bay of Louisiana (Figures 2 and 4; and Table 1), with each test lasting between less than an hour to more than 24 hours (day and night continuously) for the hydrodynamics and hydrography and multiple days for the sidecan sonar (during the days only).  These tests demonstrate that the GUV are very reliable, endurable, efficient, and accurate. It can go to much shallower waters (almost any depth close to the bank) than a manned boat without getting stuck in the mud or bank. In all the tests and surveys where the water depth is less than 1 m, for e.g. Bay Champagne, the GUV has never got stuck, even at the muddy bank.  This makes it a useful tool in shallow deltaic or muddy coastal environments like the Chenier Plain. Most importantly, it can follow a programmed route accurately (and repeatedly if needed) for sustained automated operation to obtain a high resolution map of bathymetry, flow conditions, and fisheries data obtained from echo sounder sonar, with a quality and quantity that a manned boat can never achieve.

Figure 4. Sample GUV Track near Port Fourchon obtained on Jan 9, 2008. The black lines are the ship tracks (latitude and longitudes). The colored contours are the water depth (purple is deepest ~ 16 m, and red is shallowest ~ 0 m).

 

 

 

 

 

 

 

 

These(Figure5, 6 and 7) are survey route produced by SolidCAM for CNC machining. SolidCAM allows us to produce smooth, uniformly spaced survey routes for best data coverage.

                                                                                 Figure 5.

 

 

 

 

 

              Figure 6

 

           Figure 7