Shannon Class Lifeboat Models and How to Fit Waterjet Drives

The Shannon class at a glance

The Shannon is the newest all-weather lifeboat in the RNLI fleet. It entered service in the mid-2010s, and new boats have continued to join the fleet since, gradually replacing the older Mersey class. For a modeller, a few things set it apart:

• Size. It’s about 13.6 m long and displaces around 18 tonnes, much smaller than the Severn or Tamar.
• Waterjets. It’s the first RNLI all-weather lifeboat driven by waterjets rather than propellers. Twin jets give it a top speed of about 25 knots and let it turn very tightly.
• Flexible launching. It can be launched from a carriage across a beach, down a slipway, or kept afloat. Carriage-launched boats use a dedicated tractor launch and recovery system.
• Operational numbers for the class start with 13.

The jets are what make the Shannon interesting to build as a working model. There are no exposed propellers or rudders to fit, but you do need to install and seal jet units properly, which is what most of this article covers.

Shannon model kits

Kit ranges change over time, so check what’s currently available before you plan a build.

The Airfix 1:72 starter kit

Airfix makes a plastic RNLI Shannon Class Lifeboat at 1:72 (kit number A55015). It’s sold as a starter set, with 54 parts, a sheet of decals, six Humbrol acrylic paints, two brushes and glue. Airfix rates it skill level 1, its easiest category.

The finished model is roughly 190 mm long. Buyers’ reviews mention good fit, an interior for the cockpit, and that it’s simple enough for a beginner. If you’d like to make a small plastic hull run, see converting a plastic model boat to RC. It’s a static display model, and it also makes a useful reference for studying the shape before you start a big working model.

Larger RC Shannons

For a working model you’ll usually be looking at a GRP (glassfibre) hull kit or a semi-kit from a specialist model boat maker, or plans for scratch-building. Because the Shannon is relatively new, the choice is smaller than for older classes, and availability changes. Model boat clubs, forums and model shows are the best places to find out who currently makes a hull and at what scale.

When comparing kits, check:

• Whether the hull has the recesses for the jet intakes and nozzles moulded in, or whether you’ll need to cut them
• Which parts are included (superstructure, fittings, glazing, decals)
• Whether jet units are supplied or recommended
• What size the finished model is, and whether you can carry it

Choosing a scale

Approximate figures, based on a full-size length of 13.6 m and a displacement of about 18 tonnes:

Scale weight is the real boat’s displacement divided by the scale cubed. Real models rarely match it exactly, but it’s a good guide to what the boat will need to weigh to sit on its waterline.

A Shannon is a good size for a working lifeboat. At 1:12 it’s still smaller than a 1:16 Severn, and at 1:16 there’s comfortably enough room inside for two jet units, batteries and radio. Smaller scales are possible, but the jets and electronics take up proportionally more of the hull.

Why the waterjets matter for a model

On a propeller-driven lifeboat, the running gear is mostly outside the hull: shafts, propellers, A-frames and rudders. On a Shannon, the drive is inside. Water is drawn in through an intake in the bottom of the hull, pumped by an impeller, and pushed out of a nozzle at the transom.

For a model, that means:

• No rudders. You steer by turning the jet nozzles.
• Reverse comes from a bucket. A deflector, often called a reversing bucket, swings down over the nozzle to send the jet forward.
• Holes below the waterline. The intakes need cutting and sealing carefully.
• Different handling. Jets usually give little steering effect when there’s no thrust, so the model is steered with the throttle as much as the sticks.

Some builders choose propellers hidden inside the hull or under dummy nozzles to keep things simple. That works, but you lose the Shannon’s jet-boat handling, which is a big part of its appeal.

How to fit waterjet drives

These steps describe a typical twin-jet installation. Always follow the instructions supplied with your jet units, as designs differ.

Choosing jet units and motors

Commercially made model waterjet units are available in various sizes, usually as a combined intake, impeller housing and nozzle that bolts or bonds into the hull.

• Size the jets to the hull. Check the unit’s length and the depth it needs below the hull bottom against your hull before you buy.
• Match the motor to the jet. Jets work best with higher-revving motors than you’d use with a large scale propeller. Use the motor size and type the jet maker recommends. Many builders use brushless motors with suitable speed controllers (see choosing a brushed or brushless ESC).
• Use two. Twin jets match the real boat and allow steering by varying the thrust on each side.

Positioning and sealing the intakes

1. Mark the centreline and the jet positions on the inside and outside of the hull, matching photos or drawings of the real boat. The nozzles should exit the transom at the correct height and spacing.
2. Check the intakes sit fully submerged at the boat’s normal waterline, so the jets pick up water from a standstill.
3. Cut the openings undersize first, then file to fit. It’s much easier to enlarge a hole than to fill one.
4. Bed the units in with a marine-suitable adhesive or sealant, as the jet maker recommends. Make sure there are no gaps around the intake flange.
5. Fair the outside so the intake sits flush with the hull. A step or lip disturbs the flow into the jet.
6. Fit the intake grilles if your units have them. They help keep weed and debris out of the impellers.

Leave the sealant to cure fully before any water test.

Steering nozzles and reversing buckets

• Steering. Link both nozzles to one servo with a pushrod or a bellcrank so they move together. Check that they reach the same angle each side and don’t bind at full lock. The linkage principles are the same as in setting up rudder servos and linkages.
• Reversing buckets. These need a separate servo, or one per jet if you want to control each side independently. Set the linkage so the bucket clears the jet fully when raised and covers it fully when lowered.
• Neutral position. Many jet units let you set the bucket part-way down so forward and reverse thrust roughly cancel. This lets you hold the boat steady and steer gently, much like the full-size boat.

Reversing the motor isn’t a good substitute for a bucket. Most model jets produce very little thrust when the impeller runs backwards.

Radio set-up and mixing

A twin-jet Shannon needs more channels than a simple twin-screw boat:

• Throttle (or one per motor)
• Steering nozzles
• Reversing bucket or buckets

A transmitter with programmable mixing makes life much easier. Our radio control setup guide explains channels and mixing. A common set-up mixes the steering stick into the motor speeds as well as the nozzles, so the boat turns more tightly at low speed. Start with small mix amounts and increase them once you’re used to how the boat handles.

Testing before you close the hull

• Run the motors briefly in a tank or bath with the intakes submerged, never dry for long, as the jets rely on water flow.
• Check for leaks around the intakes after each test.
• Watch that the nozzles and buckets move freely with the jet running.
• Make sure the wiring and servos stay clear of any water that collects in the hull, and fit them on raised mounts where possible.

Ballast, trim and handling

Ballast a jet-driven model in the same way as any lifeboat: fit everything heavy first, then add weight low and central until the boat sits on its waterline and floats level. Then check two things in particular:

• The intakes stay underwater as the boat accelerates and when it turns. If a jet draws in air, it loses thrust suddenly.
• The stern doesn’t squat too deep. Moving batteries forward can help. See how to ballast an RC model boat down to its waterline.

On the water, expect a short learning period. Jet boats can spin almost on the spot, and they respond to throttle more than to steering at low speed. Practise in open water before you try close-quarters moves near the bank.

After a session, flush the jets with clean water if you’ve been sailing in weedy or dirty water, and let the hull dry with the hatches open.

Detailing and painting

The Shannon has a compact, enclosed wheelhouse, a lot of grab rails and a busy roof with radar, aerials and lights. Useful priorities:

• Glazing. Fit the windows after painting, with clean frames.
• Rails. Build them on a jig so they’re straight and evenly spaced.
• Fendering. Fit it last so it doesn’t get painted over.
• Lights. LED navigation, search and blue lights are easy to add and look very effective.

The paint scheme follows the modern RNLI pattern of a dark blue hull and orange superstructure. See our guide to painting a model in accurate RNLI livery for shades, masking and markings.

The launch tractor and carriage

At many stations the Shannon is launched across the beach from a carriage, pushed by a tracked tractor. A model of the tractor and carriage makes an impressive display piece, and a few builders make working versions. A beach section, built with the techniques in model ship dioramas, sets it off well. It’s a big project in its own right, so many people build the boat first and add the launch rig later.

If you’d like a larger RNLI subject with conventional propellers, see the Tamar class lifeboat model kits or the Severn class lifeboat models. Our guide to radio controlled lifeboat models compares all the main classes.