Get Home Installations

The owners of most single screw Trawler Yachts intent on ocean cruising rightly insist on some means of auxiliary propulsion. Despite the high reliability of modern diesel engines it is always wise to be prepared for the unexpected.

There are two ways to arrange an aux. propulsion system:

• Auxiliary drive to the main propeller shaft
• Independent wing propeller

In both cases motive power comes from a generator set power take off or auxiliary engine.

An auxiliary drive to the main propeller shaft is arranged by connecting a hydraulic motor to the shaft by sprockets and detachable roller chains. The hydraulic motor is driven from a pump mounted on a generator set. This hydraulic circuit is usually integrated into the vessels other hydraulic systems.

While quite simple in principal it has the drawback of not being instantly usable because chains have to be fitted and it is useless in the case of propeller shaft fracture or failure in some other part of the drive train. Another limitation in larger vessels is that the generator set does not usually have enough power output to drive the vessel at a reasonable speed.

What we have found after intensive study over many years is that an independent wing propeller is the best solution to the “get home” problem. And for this arrangement we always incorporate a self feathering propeller to minimize resistance when not in use.

For vessels up to about 40 feet a wing propeller shaft may be driven hydraulically from a pump mounted on a generator set. For larger vessels we find once again the generator set typically has insufficient power to drive the vessel. The size required would nominally be twice as much as the maximum electrical load required; resulting in a massively oversized and under utilized generator set. It can be done with less power but the result is usually in the 2.5 - 3 knot range. This is not safe enough as it leaves no margin for adverse weather conditions.

Short of fitting a larger than necessary generator set the best solution we have found is to fit a dedicated diesel engine complete with reduction gearbox direct connected to the wing propeller shaft in the normal way. An alternator of the necessary rating for ship services is connected to the front end of this engine. This is the Gen-Gethome™.

Gen-get-home(tm)

The Gen-GetHome™ is primarily a generator set, with a reduction gear and independent shaft with folding propeller. It is a completely self contained installation. Trial speeds for this arrangement in our W48 model, shown above, were 6.5 knots.

wing propeller


Of other options for a get home arrangement, and clearly a waste of an engine and consumer of valuable engine room space is the “dedicated” engine specifically for get home service.

This only leaves sail; we need to be serious here; a jerry rigged sail will probably take you somewhere in the end.

GET HOME POWER REQUIREMENT

To be of any use we always design “get home” systems to achieve a trials speed of v/?L = 0.95 -1.0. Any less power than this will result in poor performance in any kind of seaway.

The following are the “get home” horsepower for our range of single screw vessels:
                                               Service speed
WATSON 48   -   38 BHP    6 knots
WATSON 54   -   64 BHP    6 knots
WATSON 72   -   180 BHP  7 knots

Last Updated (Wednesday, 08 September 2010 03:54)