The modern modular system allows a lot of different solutions for our customers: The length of the boats can differ from 5m to 15m due to 20 variable construction possibilities.
Construction in the greatest variety
The construction of Lehmar-boats – be they multi-purpose or rescue boats - follows universal principles. It is always possible to accommodate and implement the wishes and suggestions of our customers. These so-called customized boats are of superior quality and durability. Even after purchasing one of our boats, you can rely on Lehmar’s excellent customer service.
MODERN MODULAR SYSTEM
Our boats constructed with the GRP-AIREX-sandwich technology have the following advantages:
- The foam used is AIREX 63.80 – a highly viscous, almost solid foam – which does not draw any water in the case of an accident. Due to the use of this foam in the sandwich of the hull the boat gains in buoyancy to the order of 880 lbs to 4000 lbs
- The AIREX 63.80 foam permits a certain degree of visco-elastic deformation of the material without cracks or structural damage to the boat skin appearing while the boat is subjected to stress situations i.e. as occurring in waves, during landing, or loading and unloading from trailers, when pulling oil-booms, etc.
- The complete outer skin of approx. 29 mm (heavy duty) has about the 6-7 fold rigidity than 4 mm volume density of aluminium.
- The AIREX material has an own weight of ca. 80kg/m³, as opposed to aluminium with ca. 1,900 kg/m³.
- Vibratory or dynamic cracks, as they may occur when pulling heavy loads, when landing, in waves, or when being transported by helicopter, are almost impossible.
- The GRP sandwich construction can be repaired easily and quickly in almost every situation, even in areas with an underdeveloped infrastructure, in emergency situations.
- Especially when handling damages caused by oil, onboard accidents are common with slippery aluminium surfaces. Further, aluminium also cools down quickly and freezes over in winter; in summer it becomes very hot. Sandwich constructions provide a more counterbalanced temperature.
- Great power transmissions, e.g. in connection with a helicopter transport or through the bow ramps cylinders are possible.
The bow-ramp developed and patented by LEHMAR differs from the classic hinged drop-down ramp as it has been used for years in landing crafts, because these ramps can only be opened once the boat is on shore. Today similar systems for use on water are installed higher from the freeboard, which may lead to obstructed visibility and problems in rescue situations, or when working on the water surface.
The LEHMAR bow-ramp is suspended on both sides by two-point bearings with double-action lifting and pressure cylinders. This way, the bow-ramp uncovers a gap between the boat-deck and the ramp itself after opening. Due to the curvature on the bottom and the even surface of the upper side of the ramp, a negative pressure is created by the water streaming at the lowered bow-ramp (similar to air streaming against an airplane-wing). Although the water streams over the ramp partly, the Venturi-effect prevents the water from entering the boat with a bailing capacity of up to 26 gals/sec (100 L/sec). The bow ramp's volume contains air and creates buoyancy when immerging into the water or onto the water surface. This way the longitudinal stability of the boat is increased considerably. With this additional buoyancy the boat can lift itself in a wave much earlier, so that much less water enters the open bow ramp. The special shape of the upper front edge of the ramp helps to break any possible remnant of a wave.
When landing, working near the water surface (i.e. with oil booms), or when rescuing people, the bow ramp may be lowered to the waterline, which considerably improves the captain’s view. Further, a person needing to be rescued cannot disappear under the boat. The strength of the hydraulic cylinders allows the boat to be raised easily when it is being "beached"; thus, the boat becomes unable to float without needing to tie it up. The stern can be stabilized by engine power, depending on the direction and speed of the water flow.
Should the hydraulics ever fail, the bow ramp can be fixed easily by removing the cylinder and using the entangling rope – the operation can be completed.
The stern ramp developed by Lehmar can be lowered hydraulically to a depth of up to 40-50 cm /18 in. below the waterline. This enables the crew to carry out works from the stern directly on the water surface, to take persons and material on board and it also provides easy exit for divers with equipment.
The hull is built in a hard chine construction with stabilizers in the front third and as a glider with a round bilge in the back area. The stabilizers are arranged in such a way that the boat has the following features:
- When gliding the boat does not produce a bow-wave-system, since the developing wave is broken immediately by the stabilizers and pressed onto the water’s surface as a flat spray. This way the total wave appearance is reduced with the stern-wave-system due to the lacking overlay (advantage in flowing waters)
- Due to the distinct form of the stabilizers the boat can be driven in a curve with a possible lateral slope of up to 45°. The stabilizers undertake the function of the keel whilst at the same time providing the raised propeller with water by creating an upper wave in the stern area and in this way considerably reducing the chance of cavitations.
- After the curve the boat regains its upright and stable position without rolling instantly.
- When reducing the speed, the boat stops evenly thanks to its stabilizers, thus avoiding the bow dropping.
- The swim-position of the boat (with a slight stern-trim) allows a higher load capacity. This increased load is further enhanced by the stabilizers, since the load in the bow-area results in a larger volume to immerse in the water and consequently in a higher water displacement.
Due to the distinct form of the stabilizers the boat can be driven in a curve with a possible lateral slope of up to 45°.
Hull and the bow ramp from LEHMAR multi-purpose boats have been patented.
The patent numbers
Australia: No. 643739
United States: No. 5,191,854