Re-powering

Boosting your Horses

Generally, re-powering is considered because the existing engine has reached the end of its economic life (and is either due for an overhaul or replacement), or the owner is tired of being overtaken by his cruising mates and wants increased performance.

Re-powering is straightforward if the replacement engine produces similar horsepower at the same revolutions as the original engine. Provided it has the same 'footprint' as the old engine, it can be a simple exercise, with only minor modifications to the exhausting required.

But re-powers as simple as this very rarely occur.

HULL SHAPE
Before embarking on a re-power exercise, consider the boat's hull shape. There are basically three types of hull shapes in power boats: displacement, planing and semi-displacement.

Displacement hulls are shaped so the bow cuts a wedge in the water, which the forebody then moves aside to the extent of the midsection. Aft of the midsection, the hull is shaped to allow the water to converge at the stern in a natural flow and reduce drag to a minimum.

The general characteristics of a displacement hull are:

The maximum speed of a displacement hull is determined by the formula:
Speed (knots) = 1.34 multiplied by the square root of the water length in feet.

Any additional horsepower applied to a displacement hull over and above what is required to achieve this maximum hull speed is wasted as the hull will just lift its bow high in the air and squat down at the stern, with no significant increase in speed being achieved.

Normally, when re-powering a displacement hull, the new propulsion unit should be of similar maximum rated horsepower, as increasing the existing power will give little or no increase in performance (unless the original engine was underpowered).

In a re-powering exercise on a displacement hull, if the maximum rated rpm of the old and new engines is different, then the gearbox ratios will probably have to be changed to give the original shaft rpm. In this scenario the original shafting and propeller can be retained, often along with the original exhaust system.

The planing hull is designed to ride on top of the water at higher speeds. These hulls tend to be relatively flat at the stern where the water breaks freely from the bottom of the hull at speed, creating a negligible amount of drag at high speed. The more power applied to a planing hull the faster it will move through the water, as speed is not limited by hull shape.

The semi-displacement hull is a cross between the displacement and planing hulls, possessing characteristics of both. The semi-displacement hull warps from a pronounced V-shape at the bow to a flattish stern, normally having a pronounced chine forward that forms a wide-sweeping bow wave, rather than one that rides up along the hull. As with a planing hull, the more power applied the faster the vessel will travel through the water.

For mathematically-inclined readers, a planing hull normally behaves according to the following formula:
Speed (knots) = K factor x by the square root of the total shaft horsepower divided by the vessel displacement (in long tons).

The K coefficient is dependent upon hull form and the vessel's speed/length ratio. From actual experience, K has been determined as follows:

Example:
Say the vessel receiving the transplant is a 36-foot Vindex or Mark One Corsair with a 180hp (174shp) Ford. Current performance is a cruising speed of 12 to 13kts and a maximum of 15kts. The weight of the vessel in cruising trim is seven tonnes.

If re-powered with a 350hp engine of similar physical size of six to seven litres (say a Caterpillar C7, a Cummins B Series, Fiat, Yanmar or a Volvo TAMD 63 series), the theoretical speed of the vessel can be calculated. The calculation can be done using sophisticated computer programmes - such as Volvo Penta's MACP2 - or the relatively simple K-factor formula.

Using the K-factor method, the formula is: Speed = K x by the square root of the shaft horsepower, divided by the weight (in long tons).
That is:

Using the original performance information of the vessel, we can ascertain the K factor of the hull is equal to three.

If re-powering with a 350hp engine (339shp), and the weight and K factor remain the same, the new engine will give a speed of 20.9kts.

It can be seen from this that by nearly doubling the horsepower in the launch, the speed can theoretically be increased from 15kts to almost 21kts, a 40 per cent increase in performance.

Once this is established, the next important consideration is to see if the increased horsepower can be transmitted into forward thrust via the propeller. It cannot be emphasised enough – the propeller is where it all happens. Get it wrong and all that is produced is expensive froth and little or no increase in speed.

PROPELLERS
There are three important factors in sizing a propeller:

Getting back to the 36-foot Vindex or Corsair in original trim: the 180hp Ford peaked at 2450rpm, the gearbox ratio was 2:1 reduction, the shaft size was 1.5-inch and the propeller was a three-blade design (25 inches x 16 inches). Propeller tip clearance was four inches from the bottom of the hull.

Let's say the new engine-selected hull produces 350bhp (339shp) at 2800rpm. If a 2:1 gearbox ratio is selected, then the propeller size needs to be approximately 26 inches by 19 inches. Stop right there! With this propeller the tip clearance is only 3.5 inches. This is less than the acceptable 15 per cent of the propeller diameter.

To achieve the required tip clearance requires a smaller diameter propeller, and this in turn means the gearbox ratio should be around 1.77:1. With this ratio, the propeller should have a diameter of 24 inches and the tip clearance will be a suitable 4.5 inches (it's in excess of 15 per cent of the propeller diameter).

This propeller and gearbox combination will give a maximum tip speed of 157kph (98mph), which fits within the acceptable criteria. Assuming that the clearance in front of the new propeller is not closer than 7.2 inches to the strut or keel, this new engine/gearbox/propeller combination should be successful.

However, if you think this is the end of the planning exercise, think again. You need to ask: "Will the existing shaft be capable of absorbing the extra horsepower or will it twist, bend or fracture on the first day out?"

If the existing propeller shaft is 316-grade stainless steel, it will either need to be replaced with a new shaft made from higher-grade material that is capable of transmitting the increased horsepower, or a new 316-grade shaft of greater diameter, along with a larger stern gland, strut and bearings.

If, after all this, it is found that an efficient propeller at an appropriate gearbox ratio cannot be fitted into the propeller aperture without major surgery to the vessel, then it must be accepted that a smaller engine has to be fitted with a corresponding decrease in performance.

INSTALLATION
You have now cleared a major hurdle, and found that your desired engine and gearbox combination will deliver its power efficiently at the propeller.

Now - will the new engine/gearbox physically fit where the old engine was mounted? If not, major surgery will be required to the engine bearers, flooring and sound insulation.

If the new engine will fit in the engine space, the next step is to consider the ancillary engineering (exhaust, water supply, fuel supply and air supply) required to ensure the installation achieves maximum efficiency.

If the old Ford had a 4-inch water-lock muffler and exhaust, this will have to be replaced with at least a 6-inch or larger water-lock muffler and exhaust system to meet the maximum exhaust back-pressure as specified by the engine supplier. Excessive exhaust back-pressure gives the engine constipation, resulting in a dramatic drop in performance, burnt valves and a shortened engine life.

The water intake system, including the water filter, will more than likely have to be increased in size to provide increased water flow to cool the more powerful engine. Too small a diameter inlet and piping causes suction vacuum in excess of the manufacturer's specifications, reduced water flow, which will lead to premature wear on the rubber impeller, and engine overheating.

Modern engines rely on the flow of salt water not only to cool the engine via the heat exchanger, but also the combustion air through the inter-cooler. Excessively high inlet air temperature in the combustion chamber crack heads, break rings and leads to early engine failure.

Higher horsepower engines consume substantially more air than lesser horsepower engines. The air intake vents that supply fresh air to the engine room may need to be increased in size to allow for the extra air used by the new engine, as well as the air required to dissipate engine heat.

The basic rule of thumb is: one square inch of air intake vent is required for each horsepower. In our vessel, the vent size will need to be increased from around 180 square inches to 350 square inches.

A tell-tale sign of an engine suffering from air-starvation is the black soot lines that appear in the saloon carpet which covers the engine room hatches. This shows that the engine is desperately trying to suck air from anywhere it can, including through cracks, clearances and carpet. Air starvation also causes excessive black exhaust smoke as well as premature engine failure.

Fuel line sizing and primary fuel filter/water separator size must be checked to ensure they meet the new engine specifications, or fuel starvation will occur resulting in lack of power.

Starting battery voltage, cable sizing and capacity must be checked to see if the new engine supplier's recommendations are met. It may take more electrical draw to crank over a higher compression engine and this may overheat undersized cables.

Other considerations are whether the old throttle and gearbox controls are compatible. Do they require upgrading to the new mechanical or electronic controls that are now available? This also applies to the engine monitoring instrumentation.

STERNDRIVES
In addition to conventional drive trains, many planing hulls are powered by single or multiple sterndrive units. These have proven very popular in vessels up to around 12m, particularly in production boats such as Mark 11 Corsairs, Genesis and Formula 4000s.

The engine of choice 12 to 20 or more years ago was the 200hp Volvo DuoProp. Hundreds of these engines are still providing reliable performance, but some are at a point where rebuilding or re-powering options are being considered. Volvo Penta has a very interesting website (www.volvo.com/volvopenta) where you can go to the 'Out of Production' pleasure vessel engines and then to 'Configurator'.

Enter your vessel's parameters (speed required, weight and length). The programme then lists the suitable current model engines that would take the place of your old model. As an example, I used a Formula 4000 at 12 metres, twin engines, 8000kg and a speed of 30kts.

The configurator offered three options:

It is important to take professional advice in advance of any re-powering exercise, and that accurate costings are carried out - it is very easy for an expensive mistake to be made.

Choose a marine engineer who is competent in engine and driveline installations (ask to see installations he's done) and ensure that all aspects of the installation as required by the engine/transmission supplier are done as per their specifications. Do not cut any corners as you will more than likely be disappointed by the finished product.

Done properly, the transplant should live up to your expectations and give many happy and safe years of boating pleasure.

THE RIGHT PROP
Do not cut costs by installing an inferior propeller. A few years back a client of mine spent a few hundred thousand dollars re-powering his 58-foot charter launch. The original 800hp V8 diesels were due for replacement.

After due consideration, a pair of new Caterpillar C12's were installed and to save some money, a cheaper pair of propellers were ordered. The first sea trials resulted in an 8-knot drop in top speed. The original propellers were refitted and even though they overloaded the new engines, top speed went back to around 30kts.

The propeller slip for the new propellers was in excess of 40 per cent (20 to 22 per cent is acceptable). A new set of propellers were manufactured by a reputable supplier and the vessel's top speed climbed to new heights.

AHOY! JOHN DEERE
John Deere entered the marine market with factory-built engines in 1994 and this range has expanded considerably over the years.

Marine engines are manufactured at three factories in Mexico (4.5 and 6.8lt), France (4.5 and 6.8lt) and the USA (8.1 and 12.5lt).

The range is based on the same wet sleeve liner, long stroke, high torque, low speed, fuel efficient design used in all John Deere products. The engines range from 85hp (63.4kW) to 610hp (455kW).

The 4.5lt range features two, four-cylinder modes: the 4045D naturally-aspirated engine (max 85hp at 2500rpm); and, the 4045T turbo (max 150hp at 2600rpm). Both have full length, gear-driven, counter-rotating balancer shafts for vibration-free running.

The 6.8lt engines have three six-cylinder models: the naturally-aspirated 6068D (max 120hp at 2500rpm); the 6068T turbo (max 225hp at 2600rpm); and, the 6068S turbo with sea water after-cooling and electronic Bosch VP44 mechanical fuel injection.

An additional engine (the 6068SFM75) will be added to the 6.8lt platform later this year, with turbocharging, sea water after-cooling and a full authority High Pressure Common Rail (HPCR) fuel system with electronically controlled injectors.

Typical full load HPCR operating pressures are around 23,000psi. The HPCR system controls the amount of fuel injected into each cylinder, along with injection point timing, and all these enhancements will extend the 6.8lt power outputs to 400hp at 2800rpm.

The 6081A 8.1lt model is a turbocharged six-cylinder freshwater after-cooled engine for a max 375hp at 2400rpm, using HPCR technology.

The flagship of the range is the 6125A. It is a 12.5lt six-cylinder, turbocharged and after-cooled engine featuring a full authority EUI fuel system. There are two variants of the turbo 6125A engine: the freshwater after-cooled 6125AFM75 (max 525hp at 2100rpm); and, the 6125SFM75 seawater after-cooled variant (max 610hp at 2100rpm).

All models are generally carried in stock in the John Deere Limited (JDL) distribution centre and workshop in Brisbane.

JDL also offers a range of engine accessories, control systems and transmission options, allowing each engine order to be custom-built to meet end-user requirements. Sea trials are carried out as part of the supply process to ensure that all installations meet the installation and maintenance requirements.

For more info, phone 0800 111 505, email: 23SYDDC@JohnDeere.com, or visit www.deere.com.au

STEYR MARINE DIESEL ENGINES
Steyr Marine Diesel Engines are manufactured by Steyr Motors GMBH and first introduced into the Australian market by Distributor McIntyre Equipment Pty Ltd in 1997.

Founded more than 130 years ago, the Austrian manufacturer has always produced a variety of products including trucks, tractors and military vehicles, as well as automotive and marine diesel engines. Steyr's engineering expertise has also seen it provide the technology behind some of the world's most recognised automotive brands including Mercedes, BMW, Chrysler and Audi.

In the marine business today, Steyr Motors manufactures a range of four and six-cylinder marine diesel engines with unique design features.

The first of these is the 'monoblock' system where the engine block and cylinder head are manufactured into one piece. The cast iron alloy 'monoblock' ensures even temperature and cooling. The advantage is that the usual problems identified with diesel engines such as blown head gaskets are eliminated.

Another design feature is the patented two-stage camshaft actuated direct injection which eliminates black smoke and diesel knock, and ensures a smooth and quiet ride.

Lastly is the electronic engine management system which monitors and controls the engine's vital functions. In keeping with the latest boat building technology, Steyr engines de-rate in cases of overheating, or low oil pressure.

Further to this, Steyr Motors has recently introduced the Steyr Control Centre which uses state-of-the-art display panels to provide technical engine information in a modern and stylish format. With comprehensive alarm and error messages, this self-diagnostic system allows monitoring of engine data, speed, fuel management, cooling water temperature, voltage, power trim and GPS data. The Steyr Control Centre is available as an optional extra throughout the Steyr engine range.

The Steyr range includes 14 models from 85hp to 250hp.
The four-cylinder engines are 85hp, 110hp, 144hp, 163hp and 176hp, and weigh between 243 to 258kg.
The six-cylinder range are 122hp, 163hp, 190hp, 230hp and 250hp, and weigh between 305 to 322kg.

Steyr marine engines are available with a range of optional accessories including electronic hand controls and flywheel generator.

Steyr also offers the homologation SOLAS (Safety of Life at Sea) for all its engines. This is a world recognised certification for marine engines for use in life and rescue boats.

Throughout Australia today, Steyr marine diesel engines can be seen in a wide variety of vessels from military and commercial, to rescue craft and pleasure boats.

In fact Steyr marine diesels are now being used by many well-known boat manufacturers and already have extensive experience in re-powering older vessels such as Mustangs, Riviera, Mariner, Markline and Bertrams.

For more information, phone Steyr Motors Australia on (07) 3356 9808,
email: enquiries@mcintyre-equipment.com.au, or visit www.steyr-motors.com.au

DH PORTER
DH Porter and Co Pty Ltd is an Australian owned and operated company that has been serving the boating industry since 1912.

The company specializes in the manufacture, supply and repair of marine propulsion equipment including fixed, folding and Propulse adjustable pitch propellers, shafting, stern gear assemblies, rudders, skegs etc., for all types of boats and yachts.

Other marine fittings are available or can be made to order. As well as stocking a wide range of marine bearing material, DH Porter is the NSW stocking distributor for PSS shaft seals.

The company is located in North Parramatta and its experienced staff can assist you with any queries you may have - phone (02) 9890 1766.

AUSTRALIA'S FIRST YANMAR BY ENGINE BACKED UP
Following much international fanfare surrounding the launch of the new Yanmar BY series of engines, Adelaide boatbuilder Jim Theodore was the first to order and install a 6BY...and then following sea trials, immediately ordered a second, said Yanmar importer Power Equipment.

Based on the same condition rail diesel engine fitted to select BMW models, the Yanmar BY engines have quickly won acclaim throughout Australia as more and more are now being fitted into the engine bays of Aussie built boats, said the importer.

The Theodore Coastal 720 is a relatively new boat, a rig that caught the eye of the AMIF Boat of the Year judges who bestowed 'runner up' on this boat in two categories. And just as the AMIF judges were impressed with the boat, Jim Theodore was impressed with his Yanmar 6BY that he installed, said Power Equipment.

"The Yanmar impressed me with its light weight and frugal fuel consumption", said Theodore.

"We had previously been installing a variety of makes of diesel sterndrives and the 6BY came in at 200kg lighter than the most common diesel sterndrive that we had been installing," he said.

The light weight not only translates to a superior power to weight ratio for enhanced on-water performance, but the benefit caqn also be measured in the towing weight of this trailerable rig, said Power Equipment.

When a kerbside package gets towards the top end of a legal towing weight, a saving of 200kg can often make the difference between legal and illegal.

"After we installed and ran the first of the Yanmar 6BY engines to the Theodore 720, we decided to order and install a second, we were so impressed. Both installations have featured a MerCruiser Bravo III duo prop drive", said Theodore.

The 6BY dry weight with the Bravo III drive is 408kg; without the sterndrive it weighs in at 310kg and develops 260hp at 4000rpm.

On the water the Yanmar punches the big two-tonne 7.2m hull onto the plan quickly, said Power Equipment adding, and equally rapid is the acceleration as the turbo kicks in and a light turbo whistle can be heard as the power builds.

At full throttle, the Coastal 720 is good for an even 40kts running 28-inch pitch props, and an ideal cruise speed is achieved at 3000rpm where the GPS shows a speed of 25.5kts with fuel consumption of 22.9lt/h.

The owner of the first Theodore Coastal 720 powered by the 6BY reports that over the first 100 hours of general boating, fuel consumption worked out at less than 8lt/h, said Power Equipment.

The 6BY has plenty going for it", said Theodore.

"The fuel saving is just unbelievable. The Yanmar uses only about one-third of the fuel consumed by a big four-stroke outboard when the fuel flow is compared at for both engines at say 22kts", he said.

Other attributes of the Yanmar, as identified by Theodore, include an easy installation, true drive by wire throttle control, great instrumentation, low noise and no diesel odour or smoke from the exhaust.

"But overall on-water performance is what will win customers over", said Theodore.

"This diesel engine delivers petrol-like nimble performance with diesel torque and economy. And even down low it is impressive trolling at 4.3kts with the engine ticking over at 600rpm", he said.

As a genuine bluewater fishing machine, the Coastal 720 targets fishing devotees, with some spillover interest received from divers. The dockpit is huge and, moreover, the rig is trailerable being one of the largest boats about that can be legally towed, said Power Equipment.

For more information, phone (03) 9764 0711, fax (03) 9764 0678; or email:  power.equipment@yanmar.com.au