Simple Steam Launch - Boat Construction

After the hull design had been drawn out, the boat was constructed using a traditional method of planking over a frame.

Completed Launch ready for float testing

To start - the plans were printed out full size.
The four keel pieces were then stuck to a piece of 12mm thick plywood and the profile cut out using the bandsaw.

The same process was used to create a deck profile from 6mm plywood. The deck part had a large centre cut-out to provide access to the steam plant. It also had a smaller cut-out towards the stern to house radio control gear.

Keel outline ready to be cut.
The full sized rib prints were stuck to some plywood and the band saw used to trace the profiles.

6mm plywood was used for the majority of ribs, but 12mm was used for rib 7 which would form the transition between the Vee part of the hull and the flatter section over the propeller and rudder.

A thicker wood was used for the stern plate too (rib 10).

Rib parts
Each rib had a chine notch cut into it. The chosen chine material was 9mm square section pine.

The cut-outs in each rib were made lightly shallower than 9mm so that after sanding the chine would form a smooth transition between the bottom and sides of the hull.

Each rib also had a cut out made at the bottom to suit the chosen keel width.

Test fitting the chine on a rib
The rear stern plate, rib 7 and rib 1 were glued and nailed to the keel first.

Then the keel was place upside down on the deck panel and all the remaining ribs were glued in place.

Note how the keel was left proud of the ribs so that after sanding it would provide a flush fit.

Deck, Keel and Ribs glued together.
Once the glue on the basic frame was dry, the chines were added.

These parts were pinned and clamped in place to help them hold their correct position whilst the glue set.

Chine glued and pinned

Marking out the propeller shaft position.
Before the hull was planked the steam plant was positioned in the hull and the propeller shaft was offered up to mark the location of the required hole.
The chosen propeller shaft was 7" long.

The angle of the shaft was minimised whilst still providing clearance for the propeller under the hull.

The hole was drilled oversize so that final alignment could be set later and the shaft held in place with epoxy glue.
The whole hull was sanded using sand paper on a block; so that the keel and chines formed a smooth transition to the ribs.

A straight edge was used to check for the correct angle along each rib.

Checking chine and keel angles
After sanding; each area of the hull was planked in turn. Each planking strip was glued clamped and pinned as necessary to get the plank to follow the profile given by the frame.

The planking material was 1.5mm modeling plywood.

Due to the nature of the hull profile it was possible to plank it using 5 pieces of ply.

First plank section in place
Each planking panel was cut oversize and then trimmed once the glue had set. Trimming was done with a craft knife and then sanding was used before fitting the next panel to ensure a flush fit.
Planking complete (click to enlarge).

Boat floor in place
After applying some coats of gloss paint to the inside and outside of the hull, an engine room floor was cut from 9mm plywood. This floor was shaped to sit between the ribs and was long enough to support the burner tray when extracted from the firebox.
The final position of the propeller shaft and engine was dictated by finding the locations that offered the lowest friction when turned by hand.

With the engine output being so low, reducing friction would be important to successful sailing.
The chosen linkage was a commercial universal joint, drilled to suit the axle diameters. 

Setting coupling alignment
At the back of the boat a servo set up and linkage was devised to control the rudder.

The rudder was a brass plate soldered to a shaft which could turn in a brass tube.

The servo was mounted in a cut-out in the rear deck and linked to the rudder with a wire connecting rod.

Servo and Rudder linkage on rear deck
In the electronics compartment were the radio receiver, batteries and an on/off switch.
Also a water alarm made from a Velleman kit which would sound an audible warning if water started getting into the hull.

Underside image showing final propeller location and brass rudder plate

The deck and superstructure were created by tracing the hull profile onto a piece of 6mm plywood. This was cut on the bandsaw and a rectangular hole was created to clear the steam plant as shown.

The top deck part was secured to the main hull with three pieces of threaded rod glued into the hull and tightened down with some brass mooring bollards.

The deck section was long enough to also cover the electronics area, but short enough to leave the rudder mechanism uncovered.

Top deck outline
The superstructure was made from plywood offcuts, sanded and shaped to resemble a sporty looking fast launch.

A mixture of gloss blue and black paint was used to waterproof the wood, combined with some sticky trimlines for detailing.
The roof of the cabin had a cut out for the smoke stack and for the regulator control.

Metal plates were added to the bow and stern to allow the electric rescue boat to connect with the steam launch if needed.

Side view. Click for larger image


Float test to check for stability and trim
A float test in the bath proved that the hull was buoyant and sat level without the need for any ballast. The hull remained water tight throughout the test and a stability check showed that the hull would self right from quite extreme angles.

However a steam test showed that the friction in the drive train was too much for the model engine. Allowing the propeller shaft some end float helped the situation.
Another issue was that the roof of the cabin got too warm and presented a possible fire risk.

So a curved aluminium heat shield was glued into place inside the cabin as shown on the right.

Aluminium heat shield


Bow view showing mooring bollard

Engine room in action

Front 3/4 View

Rear 3/4 view