Multihull Structure Thoughts

Interesting hull shapes on Dazcats, hard to see on this one but in the past I have seen quite the rounded V shape which is a departure from the usual rounded dory to carry weight.
They have also dabbled in Delta keels, before Covid I was going to visit the south of England and was going to try and get a look at Dazcat.
Interesting designs that don't always follow the herd.

 

They are very nice cats indeed - Darren Newton certainly is a genius with his designs.
https://www.multihullcentre.com/dazcat-catamaran-range/

 

Oldmulti, I'd like an e-mail address for you. You could send it to our business e-mail: info@ptwatercraft.com
Thanks

 

There will be two items related to this 39 foot power sailor trimaran. The first item will describe the concept and initial performance, the second will describe the vessel development. The power sailor trimaran “Beaujest” is 39 x 19 foot with the swing wing floats able to be folded to 10 foot beam. The boat can be disassembled to fit in a 40 foot container. The envisaged displacement fully loaded was 7,840 lbs. The length to beam for the main hull is 5.2 to 1. The draft is 1 foot. The tri is powered by two 30 HP outboards. The performance aim was a 10 knot cruising speed using 2.2 litres of fuel per hour with a 20 knot maximum speed. The fuel tankage totals 1000 litres over 2 tanks, 1 forward, 1 aft to allow the tri to be trimed. There is a crab claw rig to provide additional sail assistance in down wind and broad reaching situations.

The concept was developed from five 15 foot prototype plywood models. The hull lines were flat with no or minimal curves. The idea was the tri was a displacement non planning vessel that is ocean capable but can be shipped in a container to any global location. The “owner” hired a naval architect to do the structural design. The architect wanted to have curves in the hull lines (both fore aft and laterally) but the owner insisted on flat shapes based on wedges due to his prototype experience. The jpegs give the shape.

The fun starts. 15 foot models only give a guide to a 39 foot trimaran performance and sea keeping characteristics. AC monohulls used half sized models in tank tests and discovered up to 5% variations in drag between the prediction of very good tank tests and full size AC yachts. In mono AC racing 1 % was enough to win or lose. The AC models had small bumps in the bow region to turbulate the water to reflect the real water characteristics at larger sizes and speeds. There are 2 main problems. There is a scaling effect, what works in a smaller boat does not always work in larger boats. And what works in a smooth inland water testing in low wind speeds that does not reflect real waves in open water. EG a 19 foot sailing mono can sail faster for its length than a 40 foot monohull of the same concept. Computer performance prediction programs are very complex and only work for a specific set of conditions EG 10 knot winds in seawater of a certain density with an assumed hull surface treatment etc. In short don’t assume what you see work in a 40% prototype will be accurate for a 39 foot tri. A guide, yes not an accurate representation.

Next the naval architect provided CNC files and the “thick” aluminium panels were cut by a company and delivered to a professional builder who built the basic aluminium shell structure in 14 days. Flat shapes have one very big advantage, a fast shell build. The “thick” aluminium has less internal framing than normal but the tri still has a support structure. The main keel line is 100 mm wide running the full length of the boat to provide an item for beaching etc. The folding cross arms follow the Dragonfly trimaran approach. The fit out was meant to be rapid (under 6 months), and done by the owner and his girlfriend. Now let’s sort something out. The guy who conceived the idea, built the prototypes, project managed and did the fit out is not the “owner” of the tri. The girlfriend paid for the tri which was initially estimated to cost $80,000 in aussie dollars in 2007.

The power tri was launched in 2008 and did some initial trials before the owners finalised the fit out and systems before they shifted aboard full time. Tomorrow we will discuss the modifications and the tris overseas travels. The jpegs give some of the idea.

 

Russell. e-mail forwarded to you. For everyone else I found this jpeg of a home built trimaran that was moored at Airlie Beach in Australia. Its someone's floating accommodation dream with sails. I hope it does not travel to far from a shoreline.

 

Oh dear, was she dragging her anchor / mooring?
She looks perilously close to the breaking waves (on the shore?) in the foreground.

As for a houseboat, one would be hard pressed to get more living space than that for the given overall dimensions.

 

Bajansailor. She was deliberatly moored close to shore for "easy" access. The wind then built up and your seeing the outcome. I am guessing the builder and or owner was not that knowledgeable about trimarans and seamanship. Tiny housing crossed with trimaran hulls possibly?

 

That is an interesting idea (for me).
Tri-based "houseboat", that has amas that open (Dragonfly-style), to make it possible to cross more adventures waters (say, from Uk to the canals of France, or this side of the Atlantic, Florida to Bahamas).
Plus, the "house" has decks on the nets when the amas are open.
Is there an example you guys have seen?

 

The "ideal cruiser" based on some not that rational expectations:
- accommodations for 2 adults+2 kids (my current situation) or 2 couples
- under 30 ft LOA, 10 ft beam amas folded (on the trailer or on the water), both for the marinas, trailering to more destinations and winter storage
- economical propulsion (displacement trimaran, one diesel on the smaller side)

 

Accommodation;
Just buy an old Horstman.

 

The second part of the “Beaujest” 39 x 19 foot, 7,840 lbs fully loaded aluminum power tri. The boat was launched and initially tested with an 8 knot top speed using more fuel than expected. The boat was then parked at a marina for final internal fit out and installation of systems. The real owner (girlfriend) wanted to live in a comfortable space and ensured that she got what was initially promised. Airconditioning, reasonably sized fridge freezer, small washing machine, electronic toys etc that could be run as required. This required a 13 HP Chinese copy of a Honda generator, AGM battery bank etc.

The result, an estimated 11,200 displacement with the tri sitting stern down. Further trials were done with upgraded propellers and the tri achieved 10 knots “cruising” speed but its peak speed and fuel consumption was not good. The owners had finished the internals of the power tri and moved aboard for full time living.

To solve the performance fuel problems, two 90 HP 2 stroke outboards were purchased to replace the two 30 HP outboards. Next the stern down problem was solved by 2 modifications. The first was to add a 3 foot detachable extension on the stern to provide additional buoyancy and the floats folding cross arms were adjusted to a semi fixed arrangement that reangled the floats so there was less drag. In the later jpegs you will notice the flaots have less freeboard and a bow modification to give the impression of more freeboard. Also the owners sold all there land based assets and shifted things like bikes etc aboard. Result, the estimated weight of the power tri is now 15,000 lbs.

The power tri performance with the 90 HP engines was: “Under the 2 x 30hp Hondas cruising speed was 6.5 knots at 4,000 rpm. With the new 2 X 90hp I get 11 knots at 3,000rpm. The new motors are still being run in, so I can't push the rev's beyond 3,000 rpm to a maximum of 5,500 rpm for full throttle, yet. I now have 2 X 90 hp outboards, I can motor on one outboard at 9 knots. With two motors I have seen 12 knots but I am still running in the motors and I need to change the props for a finer pitch (to increase the rev's)” After initial trials with the 90 HP engines, he found the tri did not pound in 5 foot seas and no water came over the bows in those conditions.

The power tri then went up the east coast of Australia and then to Papua New Guinea. “At 5,250 rpm (max) I recorded a speed of 15 knots, I had to pump 100 liters of salt water into the anchor well to keep the nose down.” The stern trim problem was still there. In cruise mode: “I run the Tohatsu outboards at 2,000-3,000 rpm cruise at 7-8 knots and use 10-15 liters and hour for both motors. I normally run them at 2,000 rev's each for a speed of 7 knots at 3 litres (per motor) a nautical mile.”

By the time the power tri had reached Indonesia the tri had: “My latest addition is a 10 HP four stroke outboard which use's a max of 2.5 litres an hour and pushes the boat at 4.5 knots for long distance travel. With the fine bow entry the boat handles 25 knot conditions very well. The boat is very stable particularly at anchor, with no rolling, but we do try and get in close where ever possible.”

Due to medical issues and new Australian financial rules the owner had to pack the power tri into a container and return to Australia where it was being sold in 2016. The owners are now land bound but have a lot of fun over 4 years of travel. They also found frustrations of trying to get spare parts in remote locations but fuel was often cheap. The fast 14 day shell build then was followed by a year long initial fit out with a 3 year evolution development. Please understand that full time liveaboards load a lot of weight on to a boat, that weight translates into reduced performance which in this case resulted in larger engines which added more weight. Finally, the fuel consumption got too high which resulted in a smaller engine and slower speed to reduce fuel consumption. Realistic initial design weight estimates and performance criteria help enormously. Speed in flat water and no winds does not reflect the reality of wind, waves and tide/current effects in long distance cruising.

The jpegs show the loaded and modified boat. An interesting development curve which educates us all.

 

Oldmulti what are the new financial rules you mentioned in the last post?

 

Scuff. The guy was receiving a pension (= USA 401K I think) from the government. The government used to pay it to any valid Australian citizen where ever they lived. Many people lived in Australia for 20 years then moved to eg Italy or Indonesia for 20 years once they started to received the pension at 65. Australia then changed the rules saying you must live permanently in Australia with only limited overseas holidays, as the pension is a privilege not a right. Australia's pension costs fell significantly as a lot of people choose to stay overseas and lose their pension

 

Swedish naval architect Stefan Törnblom is proposing a new all-carbon trimaran. Stephen Tornblom first came to my attention in the early 90’s with a tri call T35 Nexus (renamed Seagull later), a 35 x 27 foot, weight 2,900 lbs fully rigged and loaded excluding crew. Sail area is 775 square foot. The T35 was followed by Gazelle, Gepard, Seaon96, KISS T30, T29 and assisted in the Seacart 30 design. Translation Stefan has designed light fast, to very fast, tris for 30 years and knows how to make them work.

Stefan latest is the T28. A 28.25 x 21.65 foot with a weight of 2,425 lbs. The carbon fibre rotating mast carries a 355 square foot mainsail, a 237 square foot self tacking jib and a 732 square foot gennaker/asymmetric kite. Stefan says “The sail plan is, compared to the T29, designed with the mast further back for larger head sails, a little lower main sail and mast. T28 is light enough to do ok with a self tacking jib but for racing I see an overlapping max jib with a reef. The thought is also that the boat is sailed without screecher/code 0 and with a high aspect masthead kite.” The floats are designed with a lot of volume in the ends for good diagonal sailing stability and with a lot of reserve displacement when pushing hard. The maximum draft of the T28 is 5 foot with a kick up rudder on the main hull and a kick up centre board in each float. We will get back to the float centre boards later.

The accommodation is 4 berths including a “double” berth, a basic galley and a portapotti. The tri has full length carbon cross beams which can be disassembled to allow the tri to be transported as required.

To keep the cost low, compared to the T29, Stefan chose a little smaller and lighter format needing smaller rig, sails and equipment and also less carbon fibre. The hull structures are foam carbon fibre construction. The fixed carbon fibre beams and waterstays which eliminates the need of structure to handle compression loads on the main hull. An easily demountable trimaran can be built much lighter, stronger and to a lower cost than a foldable one. For trailer transport and hard stand storage the floats can be easily handled by two persons.

The original T35 Nexus was 450 gsm triax 12 mm airex foam 450 gsm triax. The main hull below the waterline had an additional layer of 193 gsm Kevlar inside and out. Carbon may reduce weight a little but you can still build a very light boat with good e-glass fabrics.

Back to the boards. The T35 and several other of Stefan designs have daggerboards in the floats to get good upwind performance. But for the T28 design Stefan made the following statements: “Also a light boat like this should be raced with the centre hull skimming the water which will make a central center-/daggerboard less efficient.” With: “I’ve chosen to design the T28 with pivoting centre boards in the floats line operated from the cockpit. Apart from better space in the cabin this also give them higher efficiency through increased righting moment working metres to leeward of the mast and they can be placed optimally lengthwise and made as deep as needed.” And “A common problem in the design of a trimaran of this type is the longitudinal placement of a daggerboard. A vertical dagger board just aft of the mast can be designed with an efficient planform but its depth is restricted by the height of the ceiling. If you want a deeper dagger board it has to exit in front of the mast and with a backwards sweep to align with the Ce of the sailplane, that is not so efficient due to the not ideal relation between sweep and planform” The final reason for the kick up boards in the float is the shallow water in Sweden. If a dagger board hits bottom at speed normally a broken board. Also the boards could be angled to provide some lift when sailing fast. An interesting discussion is at:
Asymmetric daggerboards are they more efficient? https://forums.sailinganarchy.com/index.php?/topic/220133-asymmetric-daggerboards-are-they-more-efficient/

The initial jpegs give the idea of the T28. The last 3 jpegs are of the T35 Nexus and the renamed rerigged T35 Seagull.

 

Enough of reality. Produced by VPLP Design under the design direction of Patrick le Quément. If VPLP want more money to develop some of their ideas such as the Oceanwings reefable wing mast rig etc. The best idea is to produce a good concept design and hope someone will be interested. The design featured here would need 30,000 plus hours of design effort alone. The hull is relatively easy but the systems design, continuing design development project management as the build evolves and regulatory compliance would be the hard parts.

Seaffinity is a super streamlined trimaran which illustrates VPLP Design's vision of the future of yachting. Equipped with 2 Oceanwings wing sails and hybrid engines, powered by electricity produced by a fuel cell and hydrogen. The Seaffinity was to be launched in 2021 and is a 148 x 55 foot with two 116 foot carbon masts carrying a 2700 square foot of reefable wing sail on each mast. The Oceanwings sails can be computer controlled and reefed etc by using your mobile phone etc. The length to beam of the main hull is about 7 to 1. This implies a displacement of about 250 tons (560,000 lbs). The draft of the tri is 6.5 foot in its basic form. No mention of centre boards etc.

Accommodation is anything you want, the Seaffinty is a “living space” according to VPLP that should be more than enough for about ten people to live lavishly, including crew members. With 9000 square foot plus of living space over 2 levels plus an engine systems level you need a lot of money to fit this tri out.

The basic shell structure is aluminium. Large 300 foot aluminium catamaran and trimaran ferries have educated a lot of companies of what works in the construction of large aluminium multihulls. The Oceanwings rig have been developed by VPLP over the last 20 years and it has been used on some 50 foot plus boats. The largest proposed build is a freighter that will transport Arianne rockets from France to its launch facility.

The jpegs give the idea. The ‘launch” was meant to be in 2021 but I suspect Covid may have interrupted the schedule as there is no reports of the actual tri in the water. Interesting concept but the rig is the most interesting part.