Rusty the Junk - Engine

Rusty's engine is a 4 cylinder Ford New Holland Diesel (NHD450L) developing 80BHP. It drives a 2:1 reduction The engine goes round twice as fast as the propeller. PRM gearbox. On the back of the gearbox is a flexible coupling attached to a 1.75inch stainless steel prop shaft, on the end of which is a 25*17 bronze propeller.

The complete power train was supplied by Lancing Marine in Brighton. They had been recommended to us by Ken Howells, the Harbour master at Southwold when we arrived, who is an extremely experienced and competent boatman.

We considered several types of engine, however when at the boat show we discovered that Lancing had a special Boat Show offer on the NHD450L, the decision was largely made. Lancing calculated gearbox reduction and prop size based on the boat's characteristics. Initially there was some uncertainty about the size of propeller because we didn't have the drawings with us, and it depended how much space there was for it.

We have to especially thank Paul Toland and Rosie Kitchiner who largely sponsored Rusty's engine.

The engine beds are 10m thick 100*100 steel I beams mounted between steel bulkheads at the fore and aft of the engine room. The engine is mounted on flexible feet that are bolted directly to the beds. The gearbox is bolted directly to the engine. The flexible coupling is bolted to the gearbox and has a clamp for the prop shaft.

The prop shaft goes through the aft bulkhead with a watertight seal, and then into a packing gland under the bedroom floor. The prop shaft exits the boat through a cutless bearing mounted in a tube under the bedroom floor. Just forward of the prop the prop shaft is supported on an A bracket and another cutless bearing. Both cutless bearings are water lubricated.

The exhaust is raw water cooled, it runs to a water trap and then via a swan-neck to the hull on the starboard side, just below the water line. Coming out below the water makes it quieter. It does mean, however, that we can’t check that the exhaust cooling water is running by looking for water from the exhaust. There is a tell tale from the water feed out through the hull, provide this check. Back pressure is not a great problem because it is such a short exhaust run, but it is eased further by a cowl at the front of the exhaust outlet, which creates a suction effect. Our surveyor suggested that we strengthen this to avoid the possibility of it being bent over the exhaust.

The engine room is below the wheelhouse floor, which can be opened to allow the engine to be lifted in and out. The engine has been arranged with most maintenance parts on the starboard side, because that is far easier to access in the engine room.

Having a low, sealed, roof to the engine room created a few problems in getting the valves, swan-necks and water filter high enough above the water line. Fortunately we had built the roof up over the wheelhouse seats. We’d done this to provide a passageway in, but it proved invaluable as a high point.

There are dual controls for the engine. The lower set is in the wheelhouse, by the inside steering position. The other is on top of the wheelhouse by the outside steering position. The engine instruments are mounted by the inside steering position.

The engine is significantly larger than specified by Bruce Roberts, however with appropriate gearing and propeller there doesn't seem to be a problem, and it is really nice to have plenty of stopping power. Our previous boat (Duet) had only a 10BHP engine and was seriously underpowered. This caused us some problems, so we feel that it is best to err on the overpowered side.

The initial uncertainty about the propeller size caused us a problem when we came to the sea trials. Lancing had supplied us with instructions and log sheets for the trials. We found that the boat was very eager at low revs, but wouldn't pull all the way to 2000rpm as expected. We reported this to Lancing, who after a brief pause for thought, called us back, having realised the problem. Initially they had specified a 1.5:1 reduction gearbox and a smaller prop. However when the prop was made larger they had not corrected the gearbox to 2:1 reduction. Thus the engine was trying to spin this huge prop only half way through it's power range. Lancing were extremely apologetic and accepted all responsibility. They shipped a replacement gearbox and paid for the gearbox to be swapped at the local boatyard. After that the sea trials were excellent and the engine exceeded our expectations.