The LPG Alternative

The LPG powed Rivercraft 4600

With the price of petrol increasing almost every day I looked into the LPG ( Liquefied Petroleum Gas) option. After doing a few sums and talking to people I started to acquire the parts needed for the conversion (some second hand). Due to LPG not being available at every service station the duel fuel option was the only way to go. There are still a lot of sites though, for example with the Rockgas brand, there are 300 locations New Zealand wide. There are none in the back of nowhere, but with 150L of petrol aswell you can go for hours and hours without ever seeing a jerry can!!

The Setup

Imco model L Regulator, VFF 30 lock off valve, 300A 1 & 2.0 Carburetor, 80 Litre (WC) Tank.

Engine: 383ci Chev V8, 600 Holley carburetor, HEI ignition.

LPG capacity varies depending on temperature, 74L has been put in but generally the amount should be a little less ( 80% of 80L).

When installing LPG, careful consideration needs to be taken where the tank, regulator and carburetor are placed. Since LPG is heavier than air the system must be vented outside the hull to prevent the build up of a potential explosive gases, should a serious leak occur. The regulator, vacuum lock off and two brushless DC fans are located in the " black box". The fans suck air from the rear of the boat, push it past the regulator and lock off, down to the tank, then past the filler hose connections and back rear of the boat where it exits. All hoses and cables entering the "black box" have tight seals. The lid is removable and also has an air tight seal. Water is prevented from entering the system by the high coils ( well above water height). All hoses are protected by a heavy duty nylon strengthened pipe in which the ventilation air is passed. The electric fuel pump is controlled by a micro-switch on the LPG carburetor. This ensures that the engine is not duel fueled at any stage ( with the exception of the remaining petrol in the carburetor during change over between petrol and LPG). Changing from LPG to petrol automatically starts the petrol pump and normally the engine does not have time to stop. Change over is easily controlled by a push pull cable mounted on the dash. Electric change over for the Impco carburetors are available but I opted for the manual cable type since it is less complicated and easy to fix should anything go wrong. The HEI ignition system provides a good spark which is essential for all LPG setups as poor spark can cause a motor to run very rough even though it maybe OK on petrol ( spark gap 45 th ). A LED type fuel gauge gives a approx. reading of the tank level ..... but from my experience not a very accurate one.

Fuel Saving

Since LPG cost is around $ 0.60 per litre and petrol around $ 1.27 ( 9/9/2000), even taking into account that you may use a little more LPG it still works out with a big saving. This saving is used to pay for the installation of the setup. In our case pay back time is about 60 hrs. Even less if fuel prices keep rising!!

Examples (old 350 motor).

LPG used @ 3000 RPM for 45min and 20 min @ average 2000 RPM was 29L which cost $18. This same trip on petrol would have cost an EST $ 35

LPG used @ 3000 RPM for 1hr 30min and 30 min @ average 2600 RPM was 54L which cost $34.

Example (new 383 motor).

Boating for 2 3/4 hrs at an average of 2800 rpm cost $43 which equates to $ 15 - $ 16 per hour. This was a full tank run until empty.

Update 8th July 2002. The new motor has been running on LPG for 180 hrs now. Fuel consumption has drop since installing new exhausts and can now get around 3hrs from the tank. Oil changes have been at 60hrs using Mobil 1 5w50 and when changed looks clean with only a small amount of darkening.

Update 11th October 2004. The boat is now up to 250hrs without a problem. The cost of installing has been well covered and savings are in the thousands. Best investment ever.

What about the power loss

If you setup LPG correctly it will produce the same or more HP. On petrol WOT 4090 RPM on LPG 4050 RPM that's only 40 RPM. It performs just as if you were on petrol, when you plant the boot it gets up and goes just the same except the accelerator pump is not putting heaps of petrol down the carburetor.

How much does it cost to convert

Most of the installation I did myself, i.e. installing the tank, regulator box, carburetor and hoses to hold the gas lines. The installation of the filler and HP and LP gas lines were done by a specialist LPG installer. Bruce from "The Jet Boat Base" built the purpose built box for the regulator and setup and tuned the unit. Bruce has a background in the use of LPG in the Shotover boats as well as other vehicles so was able to recommend which carburetor / regulator unit works well. Adding up the cost of parts and labor cost was approx. NZ $ 1100. This may seem a lot but the consumption of petrol for quiet year of say 60hrs will break even. With the savings I'm sure I will be doing a lot more hours in the years to come !!

Photographs   

     Click on the image to enlarge.
 

Regulator in black box    curls in ventilation hose
 

                               Tank under seat              Filler and vent holes