Multihull Structure Thoughts

[kdifzero]

Prout did some very interesting early developmental designs before producing its range of rather boring cruising catamarans. One of experimental boat was Phantom Wake, an 80% bridge deck catamaran of 40 x 19 foot that weighed 5000 lbs and displaced 6000 lbs carrying 610 square foot of sail. The hulls were asymmetric. The hulls were 4 mm ply on 19 x 38 mm stringers at 150 mm centre lines. There was a 6 mm ply shelf across the hulls at wingdeck level. The hull gunnels 600 mm higher were 19 x 70 mm. The keel was 150 x 19 mm with a T section cap of 120 x 19 mm. Frames were 6 mm ply a minimum of 110 mm wide at any point. The main cross beam box was 580 x 36 mm with fore and aft faces of 7 mm ply. The top flange was 22 x 22 mm with a 22 x 22 mm doubler over the mid 3.4 meters. the bottom flange is 22 x 45 mm for the full width. Vertical/diagonal trusses of 22 x 38 mm separate the top and bottom flanges with a 22 x 50 mm mast post in the centre. The rear beam is a 580 x 28 mm open "box" beam with 6 mm ply on the aft face. The bottom flange was 22 x 38 mm, the top flange 22 x 38 mm doubled over the centre 3.3 meter. The decks were 6 mm with 19 x 38 mm stringers at 150 mm centre lines. Cabin roof were 6 mm with 19 x 38 mm stringers at 300 mm centre lines. Underwing stringers were 19 x 38 mm at 150 mm centrelines on 6 mm ply. There was a vertical 6 mm ply panel from wingdeck gunnel to deck running the full length of the wing deck. The details were in Multihull International magazine 148. The boat raced successfully for a few years around Britain. The boat was very well built and shows it is possible to have very light skins if you have a lot of framing to support it. In the Philippines were framing timber is cheap but ply expensive they build 60 foot offshore fishing boats with 6 mm ply with stringers at 300 mm centre lines.

Any images of Phantom Wake?

 

[oldmulti]

Phantom Wake jpegs. Also page 36 (15 nov 2019) of this thread. Sorry jpegs are not larger.

 

[oldmulti]

This is about a monohull but with an unusual rig. The rig is the story not so much the boat. Dave Zeiger (originally from France) now living in Alaska, who likes to cruise in comfort with simple and easy to build boats. He thinks a month is all you need to build a 32 x 12 foot boat ready to sail. Smaller boats can have their hulls assembled in hours. It helps the designs are flat bottom scows with extremely simple box hull shapes and minimal or no taper fore or aft.

The design which runs this rig is 15.5 x 4 foot and weighs 425 lbs empty with a displacement of 1,400 lbs. The sail is a Crab Claw of 84 square foot. Yes, a controllable from the cockpit crab claw sail. The lateral resistance is a leeboard and a rudder. The draft ranges from 120 mm to 3 foot when the leeboard is down. A small outboard can be fitted, but it can be rowed at around 3 knots. The designer says the Trilobyte 16 will reach 4.5 knots under sail.

Warning about the hull shape, the jpegs below will show 2 developmental “construction” plans which have a tapered bow scow with a tapered stern. The protype Trilobyte 16 had straight sides from bow to stern with flat panels from the keel line to the deck line for and aft. This shape is easier to build but has some limitations when going upwind. For a true mini camp cruiser the limitations will not cause much problem as speed to windward is not the primary design consideration. Time cruising is more valuable than time building.

The cabin length is 7.9 foot and 4 foot wide with a 3.4 foot headroom in a “Bird Watcher” type cabin top. There is enough room for 2 people to survive for a week or so.

Now to the rig. Clab Claws are difficult to setup, tack and reef especially in a proa format. In a monohull a single mast supporting the crab claw, means when tacking, either lowing the sail move to the other side of the mast or having an inefficient sail on one tack. After looking at Marchaz work on various rig types Dave found crab claws are meant to be 40% more efficient than jib-headed sails. Dave looked at the control problems and decided to try an idea out. He installed a pivoting short mast with a lateral boom that connected to the 2 yards of the crab claw sail. The base of the crab claw sail connected to a rope that connected to the short mast. Sheets connected to half way up each yards. Ropes also connected to the short mast. Now everything was controllable by the ropes allowing the mast and foot of the crab claw to be positioned to adjust the height of the rig and the sheets connected to the yards to adjust to the tack angle on either tack. Avery good solution. The only thing it did not directly address was reefing. But the crab claw sail could be laid horizontally if required for adjustment (reefing) if required.

So, what was the real world experience? The designer said: “We constructed and rigged her in three days of spring break, with time left over for sea-trials. The modified crab claw rig rotates around three axises. To tack, roll it over the top or around the front of the short mast. No reefing; rolling toward horizontal directs force upward, converting heeling moment to lift. When fully horizontal (neutral), it’s a bimini (collecting and shedding rain aft). Backward sailing is easy! All ‘remote control’ via running lines from shelter! After about 25 knots in bimini mode it gets loud, but is easy to strike. ‘Clears away’ in 5 minutes, tops. The sea trial sail had 75 days underway with a round average of 45 miles made good per day. Let’s say we put in 12 hours per day, with 9 of those rowing in shifts at 3 knots (we row at 4 knots, together, and sail at 4.5 knots in a fair, brisk wind, so hope that surpluses offset set-backs from moderate headwinds).” On good days they averaged 64 miles per day.

So, if you have 3 days some plywood and timber you will be able to build the basic boat. The polytarp or Tyvek sail and associated spars will be fast (some old Windsurfer masts will probably do for yards). The most expensive bits will be oars, ropes, blocks and the ply (several 6 mm and 1 sheet each of 9 mm and 12 mm).

An interesting rig idea that could be applied too EG a cat or a tri. Some nice experimental fun for someone. The last 2 jpegs are the developmental construction drawings of a tapered bow and stern.

 

[oldmulti]

A student of naval architecture, Vijay Krishna, did the following conceptual drawings of a junk rig biplane cat with a few unusual features. He said he was inspired by "Oryx" built by Pete hill. Oryx is a modified Bernd Kohler KD860 catamaran a beautiful and simple cat.

I do not know any dimensions of this cat or any other details but the cat looks about 40 foot long. An unusual feature is the kickup leeboards based on the outside of the hulls. Great for avoiding damage to the hull if you hit bottom and avoiding the drag of the daggerboard or centreboard slot although the external leeboard holder would weigh a bit.

Interesting concept. The jpegs give the idea.

 

[Robert Biegler]

Dave looked at the control problems and decided to try an idea out. He installed a pivoting short mast with a lateral boom that connected to the 2 yards of the crab claw sail. The base of the crab claw sail connected to a rope that connected to the short mast. Sheets connected to half way up each yards. Ropes also connected to the short mast. Now everything was controllable by the ropes allowing the mast and foot of the crab claw to be positioned to adjust the height of the rig and the sheets connected to the yards to adjust to the tack angle on either tack.

From the pictures, it seems the rotation axis between the yard and that rope is a symmetry axis of the sail. The centre of pressure will be forward of that, so I expect that you can't take wind out of the sail by just letting go of a sheet, you have to pull in the brace to windward. Is that how it works?

 

[oldmulti]

Robert. I am no expert on this but I think like you releasing a sheet will reduce the pressure on the sail but as you suggest the brace sheets will need to be adjusted as well to in effect reef.

 

[oldmulti]

So, you want to go fast and have some accommodation for that weekend away. All you need is 1200 HP out the back, a stepped planning hull and foil assistance to make the cat a little more fuel efficient. Good so far, it would also help if you had a million dollars to pay for the boat. The Architecture & Design is done by Andrei Rochian who works from Bordeaux France and has done design work for many companies globally including Prout catamarans.

The 14 metre foil assisted power sports catamaran is 46 x 16 foot with a 2,0200 lbs weight. The hull beam is 5.56 foot at the waterline which gives a hull length to beam of 7 to1. The draft is 2 foot. The deadrise at the transom of the stepped hull is 37 degrees. Power is 4 × 300 hp outboard engines (total 1200 hp). Foil-Assisted: Two foil systems (one forward and one aft) Stepped Hull: Two steps in a hull.

The accommodation is 2 double berth cabins forward with the doubles on the forward wing deck (don’t attempt to sleep in them at speed). A toilet shower in each hull. Then on the bridgedeck is a galley/bar forward with an inside helming position. Fore and aft on deck are some very comfortable lounge seating areas. Also in the exterior cockpit is 4 seats for helming at high speed so you don’t break ankles etc.

Now in theory the catamaran hull shape and foils should provide a softer ride at speed and probably will, but do not think you will have a jolt free ride. High speed craft hitting waves still bounce around if they do not plow through waves.

The build of this cat is aluminum. An interesting point is the framing required in this cat is about 15% of the entire aluminum to build the cat. The stepped hull would be an interesting build issue as would the semi lifting foil attachments to the hulls.

An interesting idea but I do not know if the design was finalized and built. Only 1 jpeg.

 

[Robert Biegler]

Robert. I am no expert on this but I think like you releasing a sheet will reduce the pressure on the sail but as you suggest the brace sheets will need to be adjusted as well to in effect reef.

I think my mistake was to assume rotation around only one axis, between the tack and the middle of the yard, and that only three lines controlled the sail.

But the sail also rotates around an axis parallel to the yard, and that rotation is controlled by the two sheets. Releasing those lets the sail rotate around the mast. Then there are braces from the foot of the mast to the ends of the yard, which control rotation around the symmetry axis of the sail.

 

[oldmulti]

This is about HDPE catamarans. HDPE is a form of plastic that can be purchased in sheet form. Think of plastic cutting boards used in kitchens. The characteristics of HDPE versus Aluminium is HDPE is lighter (about 35% of aluminium weight), weaker but using thicker HDPE means it can be about equal “strength” with slightly more weight. Most multihulls need stiffness (thicker materials generally are stiffer, the reason for foam glass sandwich structures) more than outright “strength”. I am using “strength” as a structural coverall, not EG tensile strength, modulus of elasticity etc. The very big advantage of HDPE is it is waterproof, does not need to be painted and can be home built by either using appropriate glues or preferably “welding” (requires skill and appropriate equipment) the panels together. The HDPE panels can be obtained in several colors and many sizes EG 8 x 4 foot.

The first is a 9 and 9.7 meter HDPE catamaran by Andrei Rochian who works from Bordeaux France. The 9 meter cat is powered by two 200 HP outboards, the 9.7 is powered by 2 x 45 HP inboard diesels. The 9.7 is an extended 9 meter.

The second HDPE cat is done by Damien Smith Design Pty Ltd and is an 8.5 m catamaran landing craft in class 2C survey capable of carrying 8 people or a small 4 wheel drive. This vessel is constructed in HDPE and is registered with the local Department of Transport in USA.

Both these cats can travel at 15 to 20 knots.

The structure is frame of bulkheads, stringers, partial frames and external shell panels all of HDPE that when done by professionals is welded together. The welding is not hard but needs to be done at the correct angle, speed, temperature etc. This is easier than aluminum construction because you are dealing with thicker panels that do not distort to any degree. Thin aluminum panel welders real skill is minimising distortion in the aluminum panels.

The jpegs are of Andrei design first then Damien landing craft next. The hull framing shoots are of Damiens landing craft.

 

[oldmulti]

Damien Smith (Naval architect and designer based in Australia) has designed an open plan aluminum charter catamaran in 1D & 1C Survey Classes, which means she is permitted to operate in Harbours and also Offshore for Whale Watching. The cat could be converted to a cruising design if wanted. The cat was built by Alumarine Victoria in 2016 and now charters around Sydney harbor.

The Harbour cat 41 is 41 x 19 foot with a guesstimate displacement of about 30,000 lbs including the maximum of 44 guests. The 50 foot fixed aluminum mast carries about 900 square foot of sail in the main and self tacking jib. The draft is listed at 1.5 foot but I suspect this is the draft over the hull not the rudders and engines when they are down. No mention of keels or boards. The engines are Twin Yamaha 4 Stroke High Thrust 60 hp running on unleaded fuel feed by two 150 litre tanks. There are 3 engine batteries and 3 electric house batteries of 275 A/H.

Accommodation comprises of a shower and toilet area, a galley bar area on the bridge deck and seating for up to 44 people. There are 6 person seating modules for and aft to provide a variety of seating for the guests. There are clear roller blinds that provide protection if required but otherwise all roll up to provide total enjoyment of the surrounds. Refrigeration is provided in under cabinet fridges and 2 extra large eskies under some seats. The partially opening roofs provide flexibility at the client's whim. There is a forward helming position in front of the galley bar unit.

The structure is mainly aluminum. The construction proceeded rapidly using a suite of custom extrusions and 3-D printed aluminum components. This vessel is also the first use of our innovative fendering system which incorporates an HDPE section and new aluminum extrusions.

There is no indications of performance but the designer claims it can sail well, and the cat was sailed from Victoria to Sydney offshore over 500 miles without and issues. The cat has done many miles offshore doing whale watching etc as well as normal harbor sailing.

The jpegs give an idea of its concept etc. The cat was recently sold for under $400,000 Australian (including the charter company and a liquor license) and is still in the charter business.

 

[oldmulti]

Damien Smith (Naval architect and designer based in Australia) has designed an aluminum charter power catamaran in 1C Survey Class for 50 passengers, to do tours of Wilson Promontory in Bass Straight Australia. This can be a very rough bit of water and requires a seaworthy vessel to do charter work. The cat was built by Alumarine Victoria.

The “Game Changer” design is a 39.6 x 17.7 foot catamaran with a loaded displacement of 40,000 lbs. The cat can carry 50 charter passengers. The hull draft is 1.9 foot. The hull design is an asymmetric V shape with a Z bow. Z bows were conceived to provide extra waterline length and a semi wave piercing bow. If designed well they help but if not designed well they do not help much. The power is 4 x 300 HP Suzuki outboards fitted with duo props. The peak speed that can be reached is 38 knots. The cat carries 1800 litres of fuel. The fuel consuption of these cats is from 100 to 150 litres per hour depending on the speed you are travelling at.

The accommodation is pure charter. 50 guest seats, a small galley/bar, a toilet/shower area and an inside lower helming position and an internal upper flybridge helming position. The bow area has a fold down ramp to allow passengers to walk on and off the cat as required. Game Changer is equipped to cater for all of her passengers’ needs, with a 240V drinks refrigerator and Zip hot water service powered by 2 x 5VA inverters. Also fitted is an aft swim platform with steps which fold down to the water level allowing snorkelers to enter and exit the water.

The construction of the hulls and deck are aluminum with some internal areas fitted with composite GRP panels.

The jpegs give an idea of Game Changer, the last jpeg is not blank, its line drawings of Game Changer.

 

[oldmulti]

HDPE is becoming interesting as shown by the following charter power monohull with a Z bow. Built almost entirely from HDPE plastic sheeting, the charter vessel can service it guests in relative comfort, speed and in a sea kindly fashion. It is rated to go offshore with 40 passengers. In Australia a under 39.5 foot vessel can be used as a charter boat and be crewed by a coxswain (one step below a Captain) which requires less pay and qualifications.

The craft is 39.5 x 13.8 foot with a weight of 13,440 lbs and a displacement of 23,750 lbs (with fuel and 40 people onboard). The draft is 1.8 foot. The power is 2 x 325 HP outboards with 1200 litres of fuel. The wave-piercing Z-Bow is meant to reduce vertical accelerations, enhancing passenger comfort and stability by gliding through waves instead of crashing into them. Coupled with a two-stepped hull, this design provides good handling, even in challenging conditions (in theory, it depends on how good the designer is. I suspect this is another Damien Smith design and he knows what he is doing).

The accommodation is basically an open deck with seating for 30 plus people and little else. This boat is for short trips for EG Whale watching or to see specific sites etc. The line plan is below.

The constructed is entirely from HDPE which offers strength and longevity without the problems of traditional materials. HDPE is highly resistant to corrosion, punctures, and marine growth, with a lifespan of up to 50 years with minimal maintenance. Its smooth hull resists algae and other growth, eliminating the need for antifouling, while its flexibility absorbs impacts, providing safety for passengers and the hull alike. Unlike GRP, HDPE is free from delamination risks, osmosis, and complex repairs. Plus, HDPE’s environmental footprint is five times lower than that of aluminium, making it a sustainable choice for eco-conscious operators. A positive summary of the reason I am interested in HDPE. There is a NZ guy who has designed a 42 foot sailing cat in HDPE and Spirit Design who did a 28 foot motor sailor cat in HDPE.

The jpegs give the idea of an interesting material build approach.

 

[kdifzero]

Phantom Wake jpegs. Also page 36 (15 nov 2019) of this thread. Sorry jpegs are not larger.

Thankyou

This is about HDPE catamarans. HDPE is a form of plastic that can be purchased in sheet form. Think of plastic cutting boards used in kitchens. The characteristics of HDPE versus Aluminium is HDPE is lighter (about 35% of aluminium weight), weaker but using thicker HDPE means it can be about equal “strength” with slightly more weight. Most multihulls need stiffness (thicker materials generally are stiffer, the reason for foam glass sandwich structures) more than outright “strength”. I am using “strength” as a structural coverall, not EG tensile strength, modulus of elasticity etc. The very big advantage of HDPE is it is waterproof, does not need to be painted and can be home built by either using appropriate glues or preferably “welding” (requires skill and appropriate equipment) the panels together. The HDPE panels can be obtained in several colors and many sizes
.........snip.........

The structure is frame of bulkheads, stringers, partial frames and external shell panels all of HDPE that when done by professionals is welded together. The welding is not hard but needs to be done at the correct angle, speed, temperature etc. This is easier than aluminum construction because you are dealing with thicker panels that do not distort to any degree. Thin aluminum panel welders real skill is minimising distortion in the aluminum panels.
.

The above post reminded me I was following this topic on diy hdpe/dyneema/gf/carbon composites over at the HarryProa group but not had an update in a few years.
https://groups.io/g/HarryProa/topic/93707081

 

[oldmulti]

The following Z bow cat is a product of was built by Alumarine Victoria, Australia designed by Damien Smith. The 8.5 mtr (28 foot) Z Bow cat was designed and built for Parks Victoria for use in the large swells of Bass Straight. Often working in large swells this vessel is cable of a comfortable cruising speeds and ride in 4m swells with speeds between 28 and 30 knots. The Z Bow features very sharp bow entry, with full topsides above the chine. This allows the vessel to get up to plane easier and cut through waves in rough conditions.

The 8.5 Z Bow cat is 26.6 foot length on deck, 30.5 x 10 foot overall (including engines etc) with a displacement of 6,700 lbs. The draft is 1.2. foot over the hull. The power is 2 x 225 HP outboards which provides peak speeds of 50 knots but cruising speeds are about 30 knots. The total fuel onboard is 500 litres.

The basic design is a patrol/charter catamaran with a cuddy cabin providing protection for the crew. The cat can carry 2 crew and 12 guests some in the forward cabin in rougher conditions.

The build is aluminium with skin, frame and stringer construction. These boats are designed to handle tough conditions and meet government regulations. They are stronger than a privately owned cat would need but if you want a tough fast cruiser these cats will be a good option.

Important! Damien Smith design gave a very interesting warning about anchoring equipment and high strength shackles. “Alloy chain, normally sold as grade T or grade 800 is typically 2 to 3 times stronger than the chain normally used in moorings. Occasionally, you see this chain and more often the associated fittings making its way onto moorings when parts get substituted as mooring components wear. Unfortunately, this high-strength chain undergoes chemical changes when immersed in “aqueous chloride solutions” aka seawater. The process is known as hydrogen embrittlement makes the chain susceptible to failure under shock loadings which is generally considered to be a bad thing for moorings. Suspiciously small shackles, hammer locks and oblong lifting links are all usually grade T and should be avoided in moorings.”

The jpegs give the idea. The appearing to be blank jpeg is a line drawing or click on the PDF.

 

[rob denney]

Thankyou



The above post reminded me I was following this topic on diy hdpe/dyneema/gf/carbon composites over at the HarryProa group but not had an update in a few years.
https://groups.io/g/HarryProa/topic/93707081

Not sure who is doing what from that thread, but we are now upcycling waste plastic: all types, including hard, soft and 'unrecyclable' such as nylon, etc. Cleaning and sorting are not required.

We are producing products, some of which (frisbees, cricket stumps, dog bowls we are exporting to Australia. My focus has been on getting the pilot plant up and running, but now that it is I have moved on to0 developing thick slabs (200mm/8") for house building and thin blocks (10mm/0.6") for fishing canoe hulls. Both are made from polyethylene wrap, which is the most common plastic waste in Fiji, being used to wrap every pallet that arrives. Polyethylene is low density, dyneema is ultra high. LDPE vs UHMWPE.

The boat panels are a little over twice as heavy as the recycled PET foam/glass/epoxy we used in the Sustainable Boat Building course but many times tougher and almost free, helped by importers paying us to upcycle their wrap.

At present, we can produce a 400 x 400 panel in an hour or so. It would take ~the same time in a 3m long press, which is on the wish list when funding permits. Joining the panels is an ongoing experiment. Easy to do, tricky to do neatly and quickly.

For more on the process, visit www.mocebenu.com and Cargo Proa - Fiji — Harryproa https://www.harryproa.com/buildingblogs/cargo-proa-building-blog