THE LONG THIN HULL

vert.jpgKey to the Trybrid design is a hull form of very efficient shape. There is little point in developing a fuel efficiency model based simply on motors and hybrid power unless there is a composite push to develop a hull that requires very little energy to drive it, in the same way you would hesitate in deploying the hybrid drive of the Toyota Prius in a 2000 kilo Cadillac.

The planning hulls that get most small boats up to speeds over 15knots have very limited passage making capacity; both from drawbacks of the fuel burning cost, but also the relentless slamming that will reduce any crew to stress after a long, pounding run. The planing hull pioneered with the US Navy’s Pacific torpedo boats of the Second World War, designed with lightweight, high performance petrol engines, and not much else, have over the years, seen the once light planing hull, now weighed down with heavy of diesel engines, luxury interiors and heavy fuel and water loads. And at sea, these 2008 planning hulls are just not sustainable, both from a comfort point of view, and their dreadful fuel consumption.

The displacement hull, such as yacht, has a ‘glass ceiling’ on performance, when the laws of physics simply pull the displacement hull under when excessive power is applied. A hull so thin that it would capsize without lateral support, and where the beam to length ration is less than 6-7%, has a whole new fuel use and speed curve, when compared to a conventional displacement hull. Unlike a regular displacement hull, a super thin hull increases speed in relatively direct proportion to the power applied…the Trybrid has no sudden ‘glass ceiling’ on performance, and some graphs of fuel use compared to speed, detail this characteristic of the super long thin hull form.

The Trybrid has no need to jump up and plane across the water, nor is it ‘sucked under’ like conventional displacement hulls. The main drag that the Trybrid has to overcome is skin friction. Accordingly, design speeds up to and above 30knots are possible with a 33.5m hull. However, unlike Earthrace, the Trybrid is not about world speed records, but rather world speed records as a product of fuel minimization. And, hypothetically, an around the world race by Trybrid would, for example, be and exercise in speed vs. the fuel burnt. One day, it’s hoped, there will be a motorized around the world race, but not in 80 days, but on 80 barrels. Accordingly, and with the simple realities of lumpy sea conditions, the design top speed of Trybrid has been reduced, with purposeful practicality to around 20knots. When the current around the world, Cable and Wireless Adventurer recorded an average speed of 17 knots, it’s clear that the ocean itself dictates practical passage making speeds, and this, when added to fuel minimization objectives, urges a restraint on top speed capacity. Trybrid’s 15-20 knot cruising speed in most long distance sea conditions is no slouch.

Nigel Irens, the extraordinary naval designer to who expertise in designing the ILAN, ( Incredibly Long and Narrow extreme trimaran) has made some interesting comparisons of 3 differing types of hull, in terms of fuel consumption. In Nigel’s comparison, all 3 motor boats weigh around 5 tonnes, and this is what the Nigel Irens has to say of the comparisons. Nigel qualify’s his comparison to say, ( With full copright respects to Nigel Irens )
“Some comparative data follows that is intended to complement and corroborate the qualitative information. It should be used with great caution because numerical information does not tell the whole story.

The powering curves are shown below for three contrasting generic vessel types.

The first test vessel – the BAVARIA BMB 32DC built by Bavaria Yachtbau GmbH – represents a typical mainstream planing-hulled power yacht. BAVARIA BMB 32 DC, Designed by J&J Design
LOA: 10.20 trybrid-the-boat_html_m4d0284e5.png
BOA: 3.20m
Displacement: 5000 kgs
Power: 2 x 260 HP

The second is the RANGEBOAT built by Seatech SARL which represents a fairly moderate departure towards the ‘slender-hull’ semi-displacement philosophy.trybrid-the-boat_html_m4c8b74e5.jpg
RANGEBOAT
Designed by Nigel Irens Design
LOA: 12.00m
BOA: 3.30m
Displacement 5500 kgs
Power: 1 x 130 HP

A third vessel, iLAN VOYAGER,trybrid-the-boat_html_36e9ef37.jpg is a proof-of-concept vessel that has been included for the purposes of illustration only. This very extreme trimaran (which happens to share a displacement the other two vessels) was built to explore the possibilities offered by carrying the slender hull philosophy to its logical conclusion.
iLAN VOYAGER
Designed by Nigel Irens Design
LOA: 21.30m
BOA: 10.00m
Displacement 5500 kgs
Power: 1 x 237 HP

The graph below compares the power requirement for each of the three vessels concerned. As the arguments are largely economic ones, applied power has been expressed in terms of fuel consumption for convenience. The ‘Y’ axis is therefore graduated in litres per nautical mile.”
If you look at the 15-22 knot range on the lower axis of the graph, you will notice at 20 knots, for example, the ILAN is burning 0.9 litres per nautical mile, compared to 1.4 litres for the planing hull, and 1.6 litres for the narrow displacement hull. At a typical and comfy 15knots, the ILAN’s fuel efficiency is half its competitors use.picture-4.png
These fuel use comparisons are of course made on vessels without diesel-electric power packs, where diesel electric engine maker OSSA Powerlite, for example, might argue, you can reduce fuel use by a further 30-50%, if optimised. The Trybrid Project seeks to explore the seemingly appealing possibility that hull shape can almost halve fuel use at swift but not break neck speeds, atop which diesel-electric could possibly halve fuel use once again, and these aspirations are made before the addition of photovoltaic and battery energy is added to the equation. As you can see, these, ‘off the shelf’ ideas, when combined, have powerful draw of promise when it comes to improving marine transport’s potential fuel efficiency.

Another advantage of the super thin hull is the very small wash. Low wash needs are growing around the world, as more governments move to protect shorelines and small boat traffic from man made boat wash. Given the extremely small 1m draft, and the protected skeg and rudder, the Trybrid has intentional river and estuarine application, where low wash will be more important than just a boating courtesy. A boat with a hull profile of a rowing 8 makes very little wash. Huge horsepower is wasted making most fast boat wash, and the bigger the wash, the bigger the energy wasted.

91520nj11m1.jpgThe issue of a hull’s skin friction is important. A mathematical rule says a semi circle as a simple shape has the minimum surface area when compared to say a deep V or box shaped hull, and accordingly, the Trybrid hull is a simple semi circle in its underwater shape, to minimize skin friction.

The wave piecing hull used for example on the242-id1472-flyer1-20pc.jpg larger pioneering Quicksilver ferries give superior sea ‘slicing’ ability. The Earthrace design took wave piecing ability to new levels, where the Earthrace vessel is designed to be fully submersed, as it cuts through waves.

There is no rocket science here, it is a simple a question of boat vs. wave, and a boat can either ride over a wave, slam through a wave, or more happily, slice through it.

The Trybrid hull is not as determined as Earthrace’s submersible hull, graciously conceding its need to both slice through, and ride over big swells, as can be seen in the hulls buoyant hull flare under the main cabin and aft deck. Albeit there in no hesitation in pointing out that the long thin bow sections of Trybrid are all about wave piecing efficiency.earthrace-afloat.jpg Given sea conditions have a self leveling effect on speed, even on Earthrace’s powerful 2 x 350kW (540 hp) Cummins Mercruiser grunt, the design philosophy of Trybrid says keep the hull as narrow at the waterline as possible, and flare the hulls out, once they are high enough away from most wave slam. But once the sea conditions become so violent as to create heavy slamming on the bridge decking, then it is time to simply slow down.
The trimaran hull, or 3 hulled vessel, has seen its most common manifestation in the sailing trimaran. The sailing tri has the somewhat stressful need to counter the overturning motion of the sails and masts, such that many European racing trimarans have outer hulls almost as buoyant as the centre hull. The design decision to not have tall sailing masts on Trybrid purposefully reduces the size and buoyancy of the outer hulls, and this brings with it the ability to have those outer hulls produce minimal drag. There will, nonetheless, be an ancillary, down wind sailing capacity on Trybrid, but with short, lift up, twin ‘A’ frame configured masts, only 8-9m high, for down wind sailing, or in lay terms, sailing where the wind is coming from behind the vessel, such that the wind in not trying to overturn the hull.

Many big, fast sailing multihulls face the possibility of being overturned at sea. Whilst without tall masts encouraging the boat to roll, it is still necessary to design the Trybrid to remain afloat if it was ever rolled in a huge sea. A common safety feature of these boats sees underbody escape hatches, and watertight compartments that keep an overturned boat safe and habitable even when capsized, and Trybrid will use these usual safety design features.

Maneuverability of 33.5m light and long hull is a challenge. The rowing eight certainly cannot easily turn in its own hull length, for example. So bow and stern thrusters, that are basically through hull pipes with an internal propeller, are one way of maneuvering a long thin hull alongside a dock.
But when using small electric motors, and not diesel engines direct coupled to the propeller, new opportunities for locating engines in the thin outer hulls arise. A 25hp electric motor is not much bigger than a waste paper basket. Whilst the engineering solutions are not yet final, the Trybrid plans to have small ancillary electric motors in the two outer hulls. Capable of low speed propulsion, docking the Trybrid using the outer hull’s motors alone, creates some of the maneuverability of the multihulled ferry. So a conventional bow thruster may not be essential.

If the ocean was permanently flat, traversing it in small, high speed boats would be simple. But the ocean is a lumpy place. Swells boom across oceans at speeds of over 15 knots. And when a swell or a wind ‘chop’ slam into a hull heading in the opposite direction, the wave energy can impede a boat’s progress with a slam. But if the slam can be reduced, by sharpening the hull into a pencil thin shape, then the energy needed to maintain momentum is not lost. This, in simple terms, is the main reason for the Trybrid’s long thin hull form.

So in summary, the unique hull form of the Trybrid is fundamental to the boats fuel efficiency. And as fuel efficiency becomes more and more pressing, it is beholden on designers, whether in regular architecture, or automotive design, or wherever, to look more closely at the shape and form, not just the function of all energy efficient initiatives. There would be little point in developing a fuel minimalist engine and propulsion system for Trybrid if it did not go hand in hand with a light swift body. There is no point in developing super fuel efficient engines, just to have them installed in a Cadillac body. There are some examples of the solar hybrids being used in marine application such as the DSe Hybrid, but as you can see if you click onto their web site, whilst their solar hybrid systems are state of the art, the hull form is far form super efficient. We applaud the DSe production nonetheless; it’s a great step forward.

dse_islandad02.jpg

In conclusion, there is more to this project than machinery and solar cells, and fundamental to the design philosophy is that the hull itself be at the leading edge of energy minimization. The approach to the drive chain is also innovative, as follows.