Fast Boat – No Power


I grew up around boats and have had several of my own – power and sail.  I also did the surfing scene in my youth but that was back when the boards were 12 feet long and weighted 65 pounds or more.  When I had a sailing sloop, I was fascinated by being able to travel without an engine.  I began experimenting with what other kinds of thrust or moving force I could use to move me over water.  I eventually came up with something that is pretty neat.


My first attempt was to put an electric trolling motor on my 12-foot fiberglass surfboard and a small lawn mower battery.  Later, I added a solar panel to charge the battery.  A newer one that I tried about two years ago was much larger and made enough power that I could use the motor at low speed for several hours.  I put a contoured lounge chair and two tiny outriggers on it and traveled from Mobile AL to Pensacola, FL, non-stop in one day.  I liked it but not fast enough.


Surfing always surprised me at how fast you can go.  Even normal ocean and Gulf waves move faster than most boats – averaging about 25 MPH.  I wanted to make a boat that could use that power.  A boat that was featured in an article in Popular Science especially motivated me.  The Suntory Mermaid II, an aluminum catamaran was built by Yutaka Terao in 2007 and has been tested.  It will sustain a speed of 5 knots using an articulated fin (foil) that is activated by the up and down motion of the boat in the waves.  This obviously works but it is slow and obviously depends on bobbing up and down.  I wanted a smoother ride and to go faster.  Much faster.  It took a few years but I did.


At first I took the purely scientific approach and tried to computer model the Boussinesq equations along with the hull formula and other math calculations to help design a method for keeping the boat in the optimum point on the wave.  I even got Plato to help and this gave me some background but the leap from model to design was too difficult to design and I was confident I could figure it out. 


What I learned is that ocean waves vary by wavelength and that varies their speed.  The USS Ramapo calculated that waves they encountered were moving at 23 meters per second and had energy of 17,000 kilowatts in one-meter length of those waves.  That is 51 miles per hour and enough energy to move a super freighter.  That is about twice as fast as the average wave.  Waves with a wavelength of about 8 meters in deep water will have a speed of about 10 m/s or about 22 miles per hour – a very respectable speed for a boat.  The energy in a wave is equal to the square of its height – so a 3m wave is 9 times more powerful than a 1m wave but even a 1 meter wave has more than enough energy to move a boat hull through the water.


I started with a small 21-foot motorsailer with a squared off stern and a deep draft keel.    I selected this because it had a narrow hull and had a deep draft for a boat this size.  It also had an unusual keel design – instead of a deep narrow keel, it extended from just aft of the bow, down to a draft of nearly 5 feet all the way back to the stern and then rose vertically straight up to the transom – giving an area of almost 85 square feet of keel to reduce the lateral forces of wave and wind action.


I installed electric motor thrusters below the waterline on the port and starboard of the stern with an intake facing down on the stern.  These were water jet thrusters I salvaged from some old outboards with bad engines.  I put in electric starter motors from cars to run the jet thrusters.  This gave me near instant yaw control so I could keep the stern of the boat facing the wave. 


After I got the yaw thrusters working and tested, I replaced the inefficient starter motors with brushless DC motors.  My new water jet thrusters are mounted on fore and aft look like a shrunk down version of the Azimuth Stern Drives (ASD) or “Z” drives used in ASD tugs.  The gimbaled thruster housing extends outside the hull while the BLDC motors are safely inside.


I then experimented with the transom/stern design and found that having a weather deck (one that could take on and empty a wave of water without sinking the boat) was essential but it could also simply be a sealed deck so that water could not get onto the deck.  I started with the former and ended with the latter.  The obvious intent is to optimize the design so as to minimize the problem of broaching – when a wave overtakes a boat and can pushes it sideways and capsizes the boat.


I also wanted to make sure that the pressure from the wave on the stern was strong and focused on creating thrust for the boat.  I called this addition the pushtram.  To do this I tested several shapes for a concave design of a fold-out transom (pushtram) that extended down to the bottom of the keel.  This ended up taking the shape of a tall clam-shell that could fold together to form a rudder but when opened, it presented a 4 foot wide by 5 foot deep parabolic pushing surface to for the wave. 


The innovation on this pushtram design came when I realized that facing the concave portion of the design toward the bow instead of aft, gave it a natural stability to keep the boat pointed in the direction of the wave travel.  As the boat points further away from being perpendicular to the wave, the pushtram exerts more and more rotational torque to direct the boat back to pointing perpendicular to the wave.  This design essentially all but eliminates the danger of broaching.


The lifting of the stern and plowing of the bow is also a problem so I also installed a set of louvers that closed with upward travel and opened with downward travel of the stern in the water.  This controls the pitch fore and aft of the boat as it moves in and out of the waves.  This “pitch suppressor” stuck out aft from the lower most point of the hull for about 4 feet and was reinforced with braces to the top of the transom. 


After some experimenting, I also added a horizontal fin (foil) under the bow that was motorized to increase its lift when the rear louvers closed tightly as controlled from a computer.  This bow-foil lift was created by a design I had developed for the US Navy that uses oil pumped into heavy rubber bladders to selectively reform the lifting (airfoil) effect of the blade.  The all-electric control could change the upper and lower cambers of the foil in less than a second.  Combined with a small change in the angle of attack (to prevent cavitation), I could go from a lift coefficient of zero to more than 10.5 (using Kutta-Joukowski’s theorem).  I also used my computer modeling to optimize laminar flow and minimize the Kutta condition, keeping the drag coefficient below 0.15.


The effect of this weird underwater configuration was to allow me to control the stern to keep it perpendicular to the wave front with the yaw jets and long keel.  I then used the louvers and front foil to keep the stern down and the bow up as waves pushed the boat.  The computer controller for all this was the real innovation.


I used eight simple ultrasonic range finders that I took from parking sensors for cars and placed them on the four sides of the ship.  Four were pointing horizontal and 4 were pointing down.  The horizontal ones gave me distance to the wave, if it was visible to that sensor and the ones pointing down gave me the freeboard or height of the deck above the water line.  I also installed a wind vane and aeronometer for wind speed and relative direction. I fed all this into a computer that then used servos and relays to control the yaw jets, foil and rudder.


I had modeled the management software in a simulated ocean wave environment using a Monte Carlo analysis of the variable parameters and it took four days of running but the modeling found the optimum settings and response times for various combinations of input values. I also developed settings to allow for angles other than 90 degrees to the following waves so I could put the boat on a reach to the winds.  This placed a heavy and constant load on the yaw thrusters but I found that my boat was lightweight enough to go as much as 35 to 40 degrees left and right of perpendicular to the wave front.


At first, I kept the sail mast and kept the inboard motor of the motorsailer but after getting more confidence in the boat’s handling, I took both off.  I do keep a drop-down outboard motor for getting in and out of the harbor. 


In operation, I would use the drop down outboard to get out of the harbor and into the Gulf and facing in the direction of the wave travel.  While the outboard is still running, I open up the pushtram and lower the bow-foil and aft pitch-suppressor and bring the computer online.  The software is preprogrammed to run a quick test of the thrusters and bow-foil and gives the boat a little wiggle to let me know it is all working.  I then run the outboard up to what’s needed to get me on a wave crest and then shut it down.  Within a few waves, the boat settles into the perfect location on the wave to receive the optimum benefit of the gravity, wave motion and system settings.  The end result was a boat that travels +/- 40 degrees to the direction the wind is blowing at sustained speed up to 35 knots or more all day long without using any gas.


Waves being as inconsistent as they are, the thrusters and bow-foil and pitch-suppressors kick in every few minutes to try to correct for a change in wave or wind direction or when I drop a wave and have to pick up another.  Between the pitch-suppressor and the pushtram, it usually only takes about 2 or 3 waves to get back up to speed again.  This happens slightly more often as I deviate from the pure perpendicular direction using the thrusters but it still keeps me moving at almost the speed of the waves for about 80 to 90% of the time.


I recently tested an improvement that will get me to +/- 60 degrees to the wind’s direction so I can use the boat under a wider range of wind and wave conditions.  I found that using some redesigned shapes on the pushtram, I can achieve a stable heading that is nearly 60 degrees off the wind.  The innovation came when I mixed the use of the hydraulic reshapeable bow-foil idea on the pushtram.  By using the computer to dynamically reshape the pushtram using pumped up oil bladders controlled by the computer, I can create an asymmetric parabolic shape that also creates a stable righting force at a specific angle away from the wind.


I also recently incorporated a program that will take GPS waypoint headings and find a compromise heading between optimum wave riding and the direction I want to go.  This was not as hard as it seems since I need only get within 60 degrees either side of the wind direction.  Using the computer, I calculate an optimum tack relative to the present wind that will achieve a specific destination.  Because it is constantly taking in new data, it is also constantly updating the tack to accommodate changes in wind and wave direction.  It gives me almost complete auto-pilot control of the boat.  I even set it up with automatic geofencing so that if the system gets too far off track or the winds are not cooperating, it sounds an alarm so I can use other power sources.


I began using a 120-watt solar panel that charges the batteries with a small generator for backup.  I keep a few hours of fuel in the on-board tank for the outboard in case the waves and wind die or I need to cruise the inland waterways or intercoastal.


Once I’m in the sweet spot of the wave and traveling at a constant speed, the ride is smooth and steady. 


I have found that the power of the wave is sufficient that I could have considerable additional drag and still not change my speed or stability.  I jury-rigged a paddle-wheel generator and easily produced about 300 watts of power with no changes in my computer controller or control surface settings.  This plus the solar panels now can keep up with the usage rates for the electric thrusters on most days without depleting any of the battery reserve.


I am now working in a drop-down APU – auxiliary power unit – which will produce all the power; I need on board with enough left over to charge some large batteries.  My plan is to then use the battery bank to eliminate the need for the outboard motor and gas.   I figure I can get about 800 watts out of the APU and can feed into a bank of 12 deep cycle batteries.  When the winds are not right, I just turn the yaw thrusters to act as main propulsion and take off.  


I recently took my boat on a trip from Jacksonville Fla. (Mayport), up the coast to Nags Head and then on to Cape May, NJ.   There was an Atlantic high pressure off South Carolina that was slowly moving north so I got out in it and caught the northerly winds and waves.  The total distance was about 1,100 miles.  Being retired from the US Navy, I used the launching facilities at the Mayport Naval Station to put to sea about 8AM on a Monday morning.  I pulled into the Cape May Inlet about 7:30PM on Tues.  That was just under 30 hours of wave powered travel at an average speed of about 27 knots.  Not bad for an amateur.  The best part is that I used just over two gallons of gas and most of the trip I just let the boat steer itself.


All the modeling in the world does not hold a candle to an hour in the real world.  I observed firsthand how frequently that the waves are always parallel to the last one and how often that they don’t all go in the same direction.  I also observed groups of waves – called the long wavelength – of waves.  The effect of all that is that the boat did not ride just one wave but lost and gained waves constantly but at irregular intervals.  Sometimes I would ride a wave for as much as 20 minutes and sometimes it was 3 or 4 minutes.  A few times, I got caught in a mix-master of waves that had no focus and had to power out with the outboard.  This prompted me to speed up my plans for installing the APU and the bank of aux batteries so I can make more use of the electric powered thrusters for main propulsion so that I could add that into the computer controller to help maintain and steady the speed.


I powered around to a friend’s place off Sunset Lake in Wildwood Crest.  He had a boat barn with a lift that allowed me to pull my boat out of the water and change the inboard propeller shaft.  Earlier, I had taken the inboard engine out and the prop off last year but left the shaft.  This gave me tons of room because I also took out the oversize fuel tank. 


I salvaged one of the electric motor/generators from a crashed Prius and connected it to the existing inboard propeller shaft.  I then mounted a 21″ Solas Alcup high thrust, elephant ear propeller.  This prop is not meant for speed but it is highly efficient at medium and slow speeds.  The primary advantage of this prop is that it produces a large amount of thrust when driven at relatively slow speeds by the motor.  It also can be easily driven by water flowing past it to drive the generator.


I used a hybrid transmission that allows me to connect a high torque 14.7 HP motor-generators and converter to the propeller shaft and to a bank of 12 deep cycle batteries in a parallel-serial arrangement to give a high current 72 volt source.  This combination gives me a powerful thrust but also produces as much as a 50 amp current at RPMs that can readily be achieved while under wave power.


Now I have a powerful electric motor on the shaft and a bank of deep cycle batteries in the keel.   The motor-generator plus the solar panels and the APU easily create enough charging current to keep the batteries topped off while still giving me about 5 hours of continuous maximum speed electric power with no other energy inputs.  However, in the daytime, with the solar panels and APU working, I can extend running time to about 9 hours.  If I have wave powered travel for more 6 hours out of every 24, I can run nearly non-stop.


 I am now working on a refined controller for all these changes.  The plan is to have the motor kick on if the speed drops below a preset limit.  The computer will also compute things like how fast and how far I can travel under electric power using only the batteries, solar panels, APU and motor-generator in various combinations.  I’ll also be adding a vertical axis wind turbine that I just bought.  It produces nearly 1 kW and is only 9 feet tall and 30″ in diameter.  For under $5,000, it will be mounted where the sail mast use to be but it will be on a dampened gimbal that will maintain it in an upright vertical position while the boat goes up and down the waves.  By my calculations, on a sunny day with a 10 knot wind, I should be able to power the electric drive all day long without tapping the batteries at all.


These changes will be made by mid-July 2010 and then I am reasonably confident that I can travel most any direction, day or night, for a virtually unlimited distance.


My next trip was planned for hugging the coastline from Cape May south to Key West – then around the Gulf down to the Panama Canal – thru to the Pacific and up the coast to San Francisco.  An investor there has challenged me that if can make that trip; he will buy my boat for $1.5M and will build me a much larger version – a Moorings 4600 using a catamaran GRP hull.  Using a catamaran hull should boost the efficient of the wave drive to almost perfection. 


This trip was all set and then BP has to go a screw it up.  I figure I’ll make the trip in 2011.

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