Introduction
“Are you sitting comfortably?” It was quite important when watching children’s TV, but it is also a vital aspect of driving a RIB. If you are not sitting comfortably and securely in a RIB, then you will not only find it difficult to use the controls effectively, but you will also be in danger of injuring yourself when the boat is bouncing about. For the professional RIB, secure and safe seating is vital under the requirement of an employer to have a “duty of care” towards his employees. For the leisure RIB, good seating can add consider ably to the pleasure of driving or crewing in a RIB.
When we first started developing RIBs over 30years ago we needed to find seating which kept the crew low in the boat, but which also offered security. The saddle seat was the preferred option and much of the initial success of the RIB came from using this type of seating. Not only did the seating allow you to grip the seat with your knees as you would when riding a horse, but it also allowed the use of toe straps to give extra security.
The result of using this type of seating was that it left the helmsman with two hands free to drive the boat. With one hand on the wheel and one on the throttle you are in full control and I am sure that much of the success of the RIB and its excellent seaworthiness came from the fact that the helmsman was able to have much better control than on compet ing craft.
One of the alternatives to saddle seating is to stand up at the console. It works well when you can brace your legs against the movement of the boat, but you still need to hold on. Holding on and controlling the boat are not compatible, as the steering wheel tends to become a handhold rather than a control. Today, we have things like shaped bolsters and even bolsters which convert to seats at the flick of a switch so that standing at the helm is a more viable option on larger RIBs.
Saddle and more conventional seating has also come a long way as RIBs have developed over the years. From the wide range of choices available you can find something to suit every scenario, but there are three essential criteria for all seating and bolsters on RIBs: strength, security and shock absorption. These three S’s should govern all seat design.
The human body is a heavy weight when bouncing around in a RIB. It can effectively be several times its own weight under heavy G-forces, hence, the need for strength in the seat design. The need for security is obvious and if the seat can locate you securely then there is less need for white knuckles whilst you hang on! Finally, shock absorption can help to take some of the pain out of the situation when the boat is being driven enthusiastically.
Seating is the key to RIB safety and security. The articles in this section will give some idea as to what is available and what can be done. Seating will also be fully explored in the ‘Safety in RIBS Conference’ being held in Weymouth on the 21st May in conjunction with RIBex’99. Come along and make your contribution to the seating debate.
Dag Pike
The Doctor’s prescription saves lives…and backs.
By using your legs, arms, natural reflexes and a complete new helmsman’s workstation, you can handle fast rescue boats during speed and weather conditions that normally are very dangerous.
Dr. Johan Ullman MD served in the Royal Swedish Navy Reserve when he realised that the majority of drafted men that served as helmsman on the torpedo boats suffered back and neck problems caused by pounding through rough seas at high speeds. The medical problems began to occur within one years service in the Swedish military.
Dr. Ullman, being a professional inventor as well as specialist in ‘Anaesthesiology and Intensive Care in Occupational Medicine’ set out to solve this problem in his normal manner. Assuming that natural behaviour is sound, he claims that `if it feels good, it probably is’. “In actual fact, we find solutions to most ergonomic problems in mans’ own natural behaviour,” he says. “We just have to create machines which let us do what comes naturally. This is where the reflex reactions are adequate and protect you from injury”.
Dr. Ullman has taken a scientific approach to the problem and will soon present his PhD thesis on the subject at the Occupational Orthopaedics, University of Gothenburg, Sweden.
The back and neck injuries are caused by a number of factors. The most obvious are the compression forces that act on your body as the vessel hits or pounds on the surface of the water. A new method of measuring impact on the back was designed by fixing accelerometers to a special kind of kidney belt. We measured up to 7g of compression force on drivers’ backs in the new military vessels.
In normal sitting, the spine forms a `C’ as the back slouches. This shape of the spine causes uneven distribution of weight and impact on the discs and vertebra. The `C-shape’ then becomes more accentuated under the force of impact. However, when standing, the shape of the spine is `S-shaped’ with a natural lordoses (backward bend) in the lumbar region. The same natural S‑shape as that of a rider of a horse.
Other factors to consider include `bending’ and ‘shear’ forces. These may cause discs to rupture as well as fractures of the vertebrae. Shearand bending forces are involved in the so called whiplash trauma, where the weight of the head acts uncontrolled on the cervical spine or neck. People have actually died from this kind of trauma on board RIBS at sea. The more oblique or lateral the direction of the impact, the more dangerous. Added to this, a side impact tends to be harder as the hull hits the wave with a flat surface instead of with the apex of the hull.
By studying the natural behaviour of horseback and motocross riders, it became obvious that both seating positions offered different advantages that could be applied onboard. The horseman has a great advantage by working with fairly outstretched legs, whereas the motocross biker has a great advantage by using his arms for stability and control – both lengthways and sideways.
However, no one would dream of driving a motorbike sitting on a chair, steering with one hand on a steering wheel, and using the other hand for a throttle lever.
In his scientific work, Dr. Ullman has shown that his new system reduces impact on the back from levels well over 3g to below 1g. He has also shown that modern navy boats with regular spring loaded seats can expose drivers to over 7g when the boat is exposed to just 3g.
These results made it absolutely necessary to develop a completely new springing and damping mecha nism. The demands were obvious: lower the weight and volume, double the spring travel, triple the payload capability, no wear, no maintenance, no corrosion and no movable parts.
The end result is now being produced and has found applications in many other areas.
Many people laugh at the steering bar concept, but this is because they haven’t tried it. Once you have experienced the opportunity to control both the steering and the boat speed while holding on to the optimised grips of the handlebar, you will never want to use anything else. Coastguard helmsmen who have tested the steering bar have commented on the feeling of security it provides. “No one should have to be afraid while performing their daily duties,” states Ullman.
Dr. Ullman managed to convince Captain Ake Dagnevik, technical director of the Swedish Coast Guard, into supporting a research and development project that, to date, has generated four generations of prototype boats. “The concept, which originally was a very hard sell in my organisation, has now got 100% acceptance and no one wishes to go back to the old style,” states Capt. Dagnevik.
The concept consists basically of three components:
(1) a saddle like seat with a high backrest;
(2) a newly developed springing and damping mechanism with double composite leaf springs;
(3) a steering bar with twist throttle and gear control. This concept has been tested on outboard and inboard motors, diesel and petrol, drive and water‑jet, single and dual outboard installations.
A total of five 8m RIBs where built by Swedish Coastguard at Nimbus Boats in Gothenburg and donated by the Swedish government to the Estonian and Latvian Coastguards. They were equipped with Volvo Penta KAD42 motors of 230hp and water-jets.
A recent telegram from the Estonian Prime Minister to the Swedish Coastguard relates the account of a rescue mission where three rescue vessels set out to assist a sinking fishing boat. Due to extreme weather conditions, two of the rescue craft were forced to return to shore – one being a new 15m boat. The only boat that could operate in such adverse conditions was the 8m RIB with the Ullman designed workstations! Four fishermen were plucked from the water hours after their boat had gone down.
The latest Ullman design is a 8.5m RIB with foam filled fender collar Fitted with a Penta KAD42 and DPX drive capable of 47kts. The boat takes 6 sitting passengers on the motor box, which also serves as a workbench for resuscitation, and up to 3 laying in the cabin.
The rescue boat is designed to be able to transport casualties quickly, whilst being protected from the wind and spray and the risk of hypothermia. Sadly, people have died on the way home, after having been rescued, on board open rescue boats. Hypothermia at sea claims more lives than drowning. A casualty suffering from hypothermia will continue to lose body heat so long as he is wet and in air cooler than 30°C.
Other special features of the craft relate to the design of the stern which in a following sea gives the aft sections added lift. The boat also incorporates a special raised landing surface which has been designed to make the process of boarding from a larger craft easier.
Continual development and experimentation has resulted in a number of new solutions. Tradition is good, common sense is better, but, paired with medical science, tradition and common sense will give some surprising results.
Johan Ullman
John Ullman MD
Ullman Human Design Group
Johannebergsgaten 30
S-412 55 Gotenburg
Sweden
Tel +46 31 201500
Fax +46 31 205056
Email: johan.ullman@ullmans.com
Website: http://www.ullman.org