Multihull Structure Thoughts

The following is not just about the 33 foot power boat but more importantly about its structure and build. HDPE is the high density plastic used in some kitchen cutting boards and can be used in boat building. It is waterproof, scratch resistant, does not need to be painted and can be plastic welded together. There are already 2 multihull designs (a 28 foot and 43 foot catamaran) that have been built using this material. The material is relatively heavier for its “strength” than aluminium, plywood or foam glass but lighter than solid glass. The following is the first more detailed plan of the materials use. PS there are several firms in Holland that produce production power boats for industry using this material.

The 10 meter high speed power boat is 33.5 x 12 foot with a weight of 6700 lbs and a displacement of 22,400 lbs. The draft is 1 foot for the hull and 2 foot with the outboards down. The outboard engines can range from 2 x 150 HP to 2 x 300 HP. The peak speed with 2 x 150 HP is 65 Kph and with 2 x 300 HP is 87 Kph.

The structure is mainly 15 mm HDPE plate and HDPE tubes. The boat is designed for HDPE sheet material (low-pressure polyethylene). With the availability of cutting parts on CNC machines and the manufacturability of welding HDPE material, an amateur self-builder is quite capable of building a 10-meter boat on his own. HDPE welding methods are developed and there is no shortage of HDPE welding machines. Basically, the design of the boat uses sheets of HDPE with a thickness of 15 mm. All structural parts are made of HDPE sheet plastic (designed for sheet widths up to 1200mm), fender bars and keel reinforcement made of HDPE pipe. The assembly of the boat hull is carried out using the standard classic method. Welding of the HDPE boat structure is carried out with a thermal welding machine. Work with it is within the power of non-professionals. The boat can also be built from 12mm FSF plywood or from metal - aluminum or steel.

From what I have investigated so far HDPE boats have been built using 10 to 18 mm sheets depending on the size and supporting frames stringers etc. An interesting topic needing further investigation.

 

The second HDPE power boat is an outboard designed for rivers, lakes or coastal areas. The boat could be used for fishing, water taxi, pleasure boat, water skier towboat, work boat, patrol speed boat for border, customs rescue or police service. Again, it’s the structure that is important here.

The planning monohull has an 18 degree V bottom and is 21 x 7.35 foot with a weight of 1,570 lbs and a full displacement of 6,700 lbs. The hull draft is 1.5 foot. The power is a single outboard from 180 to 420 HP. The peak speeds when fully load is with a 180 HP outboard gives 45 km/h, 230 HP gives 60 km/h, 300 HP gives 74 km/h and 420 HP gives 90 km/h.

The boat can be built from HDPE sheet material (low-pressure polyethylene, HDPE), which is gaining great popularity in small shipbuilding. With the availability of cutting parts on CNC machines and the manufacturability of welding HDPE material, an amateur self-builder is quite capable of building a 6.5 meter boat on his own - reliable in operation, unpretentious and maintainable, durable, and not requiring much maintenance. HDPE welding methods are thoroughly developed and there is a large offer of HDPE welding machines. Basically, in the design of the boat, sheet HDPE with a thickness of 10 mm is used. All parts of the structure are made of HDPE sheet plastic (designed for sheet widths up to 1200mm), fender bars are made of HDPE pipe 250mm. After the exhibition of frames, a longitudinal set is cut into the slipway - keel, stringers, fenders, and welded. Then the hulls are sheathed with 10 mm HDPE sheet on the bottom and 8 mm on the sides. Then the hull is turned over and the deck and pressurized compartments are arranged. Welding of the HDPE boat structure is carried out with a thermal welding machine. The boat can also be built from 12mm FSF plywood or 4mm aluminum.

This boat is in the displacement range and speed ranges of below 26 foot multihulls showing the material may be able to be used for EG shell and internal frame work for hulls. Cross beams and load points would require some alternate materials EG Aluminium cross beams bolted on etc. but the majority of the boat could use HDPE. An effective low maintenance cruiser could be developed. Spirt Catamarans did a 28 foot cat using HDPE as the shell building material.

The jpegs will give the idea.