Fuel Line Installation Guide For Rc Boats

When it comes to RC boats, there are a few options for fuel lines. The type of fuel line you choose will depend on the size and specifications of your boat's engine.

For smaller boats, a 5/16 fuel line is often sufficient. This size is typically used for kicker motors and sailboat outboard engines. It's also worth noting that most smaller boats have fittings or quick-connects designed for this size of the hose.

However, if you have a larger boat with an engine above 115 HP, you'll need to use a 3/8 fuel line. This is because larger engines require more fuel to run at higher RPMs, and a smaller fuel line could starve the engine of fuel, leading to strain on the fuel pumps and potential damage to the powerhead.

Additionally, it's important to consider the type of fuel hose you use. There are different specifications for hoses that go above or below the deck of the boat, and these specifications are in place for safety reasons. Below-deck hoses, for example, have a fire-resistant covering, while above-deck hoses do not.

When choosing a fuel line for your RC boat, always refer to the manufacturer's recommendations and ensure that your connections are tight to avoid air leaks, which can cause problems with engine performance.

Choosing the right size for your RC boat fuel line

Engine Size and Performance:

The size of the fuel line is directly related to the engine size and horsepower of your RC boat. For smaller outboard engines, a 5/16" fuel line is typically suitable, while engines above 115 HP require a larger 3/8" fuel line. This is because larger engines demand more fuel to run at higher RPMs, and a smaller fuel line could starve the engine of fuel, leading to strain on the fuel pumps and potential damage.

Fittings and Connections:

Ensure that the fuel line size matches the hose barb on the engine connection. A loose connection can lead to air leaks, causing the engine to lose prime and run into performance issues. It's important to have tight and secure fittings to prevent fuel leaks, which can be dangerous on a boat.

Fuel Flow and Pressure:

The size of the fuel line affects fuel flow and pressure. A larger line reduces pressure drop, making it easier for the fuel pump to draw fuel from the tank to the engine. However, using an excessively large line may not be necessary for shorter runs.

Fuel Type and Compatibility:

Consider the type of fuel you will be using. For gasoline, it is important to use Tygon tubing or a similar material. Do not use silicone tubing for gasoline, as it is only suitable for water lines. Additionally, some fuel lines are designed specifically for two-stroke or small engines, so choose accordingly.

Ease of Installation:

When selecting a fuel line size, also consider the ease of installation. A larger line may be more difficult to feed through tight spaces or connect to specific fittings. In some cases, adapters or barbed fittings may be necessary to transition between different tube sizes.

Safety and Maintenance:

Always prioritize safety when choosing a fuel line size. A fuel leak on a boat can be hazardous and challenging to manage. Additionally, consider the long-term maintenance of your boat. Using the correct fuel line size can help prolong the life of your engine by ensuring proper fuel consumption and reducing the risk of premature failure of fuel system components.

When in doubt, it's best to consult a specialist or refer to the manufacturer's recommendations for your specific engine. Safety and performance go hand in hand, so choosing the right fuel line size for your RC boat is a critical aspect of your setup.

The pros and cons of collapsible bags as fuel tanks

Collapsible bags, also known as IV bags, saline bags, or bladders, are a great alternative to old-style hard tanks and newer "made for gas" tanks. They are used by both racers and recreational boaters. Here are some pros and cons of using collapsible bags as fuel tanks:

Pros:

• They create a closed fuel system with many advantages and fewer disadvantages than standard vented gas tanks.
• No vent is needed, eliminating the chance of water being drawn into the tank through the vent.
• They are less smelly, and there is no way for fumes to escape since no vent or external connections are present to leak gas or fumes.
• Bags keep the gas-oil mix from foaming, which can be a performance limiter with standard tanks.
• Bags are lighter in weight than most standard nitro fuel tanks adapted for gas.
• Center of Gravity (CG) adjustments can be made easily as the bag doesn't have to be permanently mounted and can be moved based on wind or water conditions.
• Bags can be easily removed from the boat and stored separately, eliminating the gas smell.
• It is cheap and easy to retrofit boats with bags, and new installations are even easier.
• IV gas bags allow the CG of the gas tank to be placed very low in the boat.
• Bags are temperature resistant between -50°C and +90°C and have a long service life.
• Bags are made from materials that are resistant to a broad range of fuels and other media.
• Bags are lightweight, sturdy, and crash-resistant.

Cons:

• A fuel pump is needed to fill the bags.
• Bags may be more prone to rupture and harder to keep away from sharp or hot objects like pipes or engines. However, this can be mitigated with thoughtful installation.
• It is challenging to know how much reserve fuel is left in the bag, as there is no advanced warning before running out of gas, unlike conventional gas tanks.
• Bags must be made from plastic that is compatible with gasoline.
• Bags need to be stored with a small amount of gas inside to keep them soft and pliable. If drained, they must be stored flat and not folded or creased to avoid cracks or tears.

How to attach the tubing to the bag

To attach the tubing to the bag, you will need a length of Tygon tubing, a bag of suitable size, a short length of brass or aluminium tube, and a zip tie or similar tubing clamp.

Firstly, cut the brass or aluminium tubing to around 1 inch in length. Insert this tube into the end of the Tygon tubing, pushing it about 1/2 to 1 inch inside. Then, insert the other end of the Tygon tubing (with the brass/aluminium tube inside it) into the open outlet of the bag. It should be a very tight fit, so you may need to soak the outlet in warm water or carefully stretch it with needle-nose pliers before insertion. Be very careful not to tear the outlet tube.

Once the tubing is inserted into the bag, secure it with a zip tie, making sure it is as tight as possible to prevent leaks.

Mounting the bag

When mounting the bag, it's important to plan for success. The mounting methods for the bag fall into two categories: laying it flat in the hull or hanging the bag from a hook mounted under the deck or side of the boat.

If you choose to lay the bag flat in the bottom of the hull, you may need to remove all the air from the bag, or "burp" the bag. This can be done by filling the bag to the proper level, tipping the bow of the boat forward so that the air rises to the outlet, and then running your fuel pump backward to evacuate all the air. This will allow you to position the bag under the motor, closer to the centre of gravity (CG) of the boat.

If you hang the bag at an angle or vertically, with the outlet facing down, there is little risk of air being ingested into the fuel line, and you won't need to burp the bag. However, this might mean positioning the bag in a traditional location, similar to a hard tank. A good combination is to place the bag under the engine, with the outlet facing the transom, and elevate the bow end of the bag. A 1000ml bag works well for this setup.

For a flat mount, you can use a zip tie with a lock on each end between the stringers and through the hanger hole in the top of the bag. If you need to epoxy a piece of plywood to the underside of the deck to screw the hanging hook into, be sure to screw in the hook and cut off any excess threads sticking out of the backside of the plywood before applying the epoxy.

You can also be creative with your mounting method. For example, you can use a rubber band to keep the bag from swinging around while the boat is underway. The barbed tubing coupler can be used to hook up the filler line from your gas pump when filling the tank.

No securing of the bag is necessary if the bag is held in place by the hook it is hanging on and the stringers inside the hull.

Filling the bag

There are many different ways to fill a bag fuel system, depending on the method used to fill the bag. It is important to install a fuel filter between the filling point and the bag to ensure that the fuel is filtered before it enters the bag, and any contaminants in the bag are trapped before they enter the carburettor.

Air in the bag is a factor that must be dealt with when using bag tanks. If the bag is hung at an angle or vertically, with the outlet facing down, there is very little risk of air being ingested into the fuel line. This eliminates the need to "burp" the bag and simplifies filling. However, it may mean positioning the bag in a traditional location, similar to a hard tank.

If the bag is laid flat in the bottom of the hull, it may be necessary to remove all the air from the bag by "burping" it. This can be done by filling the bag to the proper level, tipping the bow of the boat forward so that all the air rises to the outlet, and running the fuel pump backwards to evacuate all the air.

Another method for filling the bag is to plumb directly from the filter to the carburettor. To refuel using this method, remove the fuel line from the carburettor, connect the fuel pump, and fill the bag. Once the bag is filled, "burp" the air out, clamp off the end to keep air from entering the line, and reinstall the fuel line on the carburettor.

It is important to note that bags may be more prone to rupture and should be kept away from sharp or hot objects like pipes or engines. This can be mitigated by thoughtful installation, such as using a 1-liter soda bottle split lengthwise to cradle or cover the bag.

Frequently asked questions