Multihull Structure Thoughts

[oldmulti]

AdrianN. I can only work off the Schoinning Web site that said it was aimed to be a production boat but is now available in a Kit Form boat with plans and kits available to any buyer. Two issues. A cat this large has a lot of competitors especially in Europe like the Balance and HH series etc. They are light fast cats of a similar nature. The heavy cats this size from Lagoon, Bali etc are directed to a different market segment of charter or luxury cruiser aimed at comfort not speed. Also the capitol required to establish a production facility for large cats is not small, many have plans but when a business find out the real costs of producing 55 foot cats they reconsider there plans.

Second issue. The money the Schoinning group make from kit and plan design fees would probably be higher per boat than the fees they would receive from a production boat. The Schoinning group know how to make money.

 

[oldmulti]

The Prowler 40 Open is a power cat designed for commercial purposes from being a charter cat to being a work vessel for EG a Dive cat. This boat could also be used as a private family cat in open format or as the base for a cruiser with a deck cabin. The pictured version is set up as a charter vessel for up to 32 guests and 3 crew. The aim is to provide an affordable vessel that is economical.

The Prowler 40 Open is 39.4 x 15.1 foot with a weight of 8500 lbs and a displacement of about 16,000 lbs (including about 6,300 lbs of passengers and crew). The draft is 1.6 foot. The engines are 2 x 70 HP 4 stroke outboards. The Prowler with these engines can cruise at 16-18 knots and have peaks of 20 to 22 knots.

The build looks like a production build with the Prowler 10.40 moulds extended. Therefore I will assume it is a foam glass vinylester build but I do not know further details.

The real reason for the item is its stern treatment. This is a variation of Malcolm Tennant Canoe Stern body that he developed for his power catamarans. The advantage of the shape is there is a good flow of water onto the propeller aft, but pure canoe sterns are not good at dampening pitching. Tennant’s genius was to put a flat plate above the propeller that had 2 advantages. The flat stern section helped dampen pitching a lot, the second advantage was the propeller very rarely “sucked” air when motoring improving the efficiency of the propeller.

Now 2 big qualifications The above about propeller efficiency applies to inboard instillations with the propeller under the flat stern plate. Second we are not talking about surface piercing propellers used in high speed boat installation.

Now we get to the next point. Outboard installations don’t have the advantage of improved propeller efficiency but still gain from the canoe shape underwater and the flat stern shape to dampen pitching. Overall the stern shape shown in the jpegs are often a net gain but they are not the only solution. Tomorrow we will discuss another 40 foot power cat with a different stern shape.

The jpegs give the idea.

 

[oldmulti]

The following power cat is a real distance cruiser with a range of 1200 miles with onboard tanks. The power cruising cat was designed by Shawn Arber and 1 of the 2 was built at Shawns yard in Queensland around 2013. Iron Maiden and Kinkuna are sister ships. The cruising power cats are 40 x 23.3 foot with a displacement of 18,000 lbs. The draft is 2.8 foot over the props and rudders. The engines vary. Iron Maiden is claimed to have 2 x 40 HP diesels, Kinkuna has 2 x 62 HP diesels with shaft drive and 4 blade propellers. The performance of Kinkuna is a cruising speed of 8 knots using 8 litres/hour up to 10 knots using 12.5 litres/hour. Peak speeds are 15 – 16 knots. There is also an onboard Generator.

The accommodation has 3 wide double berths in the hulls with a separate toilet shower area. In one hull is a large galley and in the other hull is a navigation storage area. There is a 150 ltrs of refrigeration and 85 ltrs of freezer space for those long trips. The main cabin area has a very large seating area with table and a wide opening door to the cockpit which extends the entertainment area. There is 6 foot plus headroom throughout. The helming position is in one corner of the cockpit under the roof with the steering position looking through the main cabin windows. This arrangement can work well on a long trip but in close quarter work it can be difficult, especially if you are depending on crew to warn you of any other boats etc.

The structure is for the hull, underwing and decks material is a composite of strip plank cedar in epoxy. The cabin and cabin top are foam sandwich with vinylester resin. Shawn normally has plywood bulkheads for ease of building.

Shawn Arber is a very experienced designer who works from his past history. His hull shapes are good and his sailing and power designs often perform very well due to good shapes and light weight. With this design the cat has high freeboard, low windage cabin and thin waterline hull with a large flair above the waterline for internal space and reduction of spray and any wave action coming over the gunnels.

The stern treatment is square flat with a minimum bustle used to fair in the keel/propeller support fin. Again this shape provides pitch dampening while limiting any air getting to the propellers. To do 1 litre/mile of fuel indicates a very efficient hull.

This is a true cruising power cat that will satisfy many. The jpegs give the idea.

 

[oldmulti]

Thor is a motor trimaran that was originally built as a prototype for future production. The original shell was built by a Danish shipyard in 2003. The next owner completed a complete conversion between 2004 and 2008 into a cruising power trimaran. This implies the base hull structure may have been an EG Dragonfly tri then it was modified to be a power tri. I am just guessing here.

Thor is 47 x 19.5 foot of 15,500 lbs displacement. The draft is 1.6 foot over the hull and 3 foot over the rudder and propeller. The engine is a Yanmar 6- Cylinder, 370 hp inboard diesel with a Volvo Penta Z drive. There is a 1000 litre fuel tank. There is no performance data but with this much power, 10 knot cruise speed and over 15 knot peak speed should be very possible.

The accommodation is in the main hull with a double berth aft with a toilet. The external cockpit is next, followed by the internal wheel house featuring a helming position and seating. Next is the main saloon downstairs with the galley on one side and a seating and table arrangement on the other side. Forward is a toilet shower area and further forward is a double berth. Floats are used for storage.

The construction is “GRP, outer skin reinforced with Kevlar in the underwater area and glued in multiple layers with epoxy.” I do not know if it is foam glass or solid GRP. The displacement would suggest the structure is a foam glass structure.

The real skill with power tri’s is the positioning and size of the floats. Sailing trimarans need floats to be long, have buoyancy forward and the floats well separated from the main hull for stability. Power trimarans need float buoyancy aft to help prevent squatting aft. The float bow positioning needs to be optimised to not add EG extra wave drag at the designed cruising speed. If the float bow is incorrectly positioned the mainhull bow wave will hit the float bow adding to the total drag. If the mainhull bow wave interacts with the gap between the mainhull and float the total drag can increase at semi displacement speeds especially if the mainhull is fairly fat etc. Please choose a good naval architect or do some basic modelling or tank testing before you spend real money. And finally float size and volume ranges from a small percentage to a large percentage of the total displacement of the boat. Small floats are cheap to build and act as stabilisers but ocean going power tris need to be able to resist wave action and tend to have larger floats. As I said float size and position is an important design consideration to match the intended purpose of the power tri.

The jpegs give the idea.

 

[SolGato]

I found the post about the Prowler 40 power Cat above interesting, specifically the idea behind the hull extensions over the props.

I experimented with the same idea for the same reasons, but on a much smaller scale with my Solar Electric Beach Cat conversion, and the benefits were noticeable.

On my boat I added oversized flat “anti-cavitation” plates that sit at water level and allow the props to run as close to the surface as possible without sucking air.

The plates are made from Ipe wood and help to lift the low volume sterns and combat pitching in ocean swell.

And being an electric boat, they also help to improve overall efficiency.

 

[oldmulti]

The Prowler 1500 is again a Schionning design, and is a semi displacement power cruising catamaran. This is intended to be a true long term and distance cruising catamaran for a family. The Prowler is 50.5 x 23 foot with a weight of 30,250 lbs capable of carrying 6,600 lbs for a total displacement of 38,250 lbs. The hull draft is 2.15 foot. No engine power is specified but similar designs have about 2 x 200 to 300 HP for this type of cat which will give about 10 to 15 knots cruise with peaks of 20 knots. This is a cruiser not a performance power cat.

The accommodation is aimed at 4 to 6 people with 2 large double berths (partially on the bridge deck) cabins forward with toilets and showers in the hulls. Single or double berths can be done aft. The main saloon has a large galley and seating/table with an opening door to the “integrated” cockpit. The flybridge/pilot house is fully enclosed for helming, navigation and general entertaining with great views of the world going by. The flybridge/pilot house can also be used as a temporary double berth cabin if required at an anchorage. There is plenty of storage space for toys etc.

Now the reason for featuring this design. The x rays of the structure will help people understand the layout and number of components to form the structure of the design. Schionning is very good at integrating furniture, partitions and bulkheads into the overall structure to reduce weight and gain stiffness across the cat. Construction is the Schionning build system that has been produced catamarans for over 20 years. The high tech composite materials, including pre-laminated panels, with some strip planking (to achieve the soft curves of the design) combined with West System epoxy and S-Glass (lighter yet with the same strength and stiffness of standard fibreglass) cloth is used for the shell construction. Carbon options are available to suit the owner chosen budget. If you don’t like taping seams, sanding and fairing, a design like this may not be to your liking. Even with a lot of well done and nearly finished flat panels being used in the structure there is still a lot of fairing to do over the seam tapes etc.

An interesting design and build. The jpegs detail give a lot of detail.

 

[oldmulti]

The Growler 1500 GTR is an unusual Schionning that a repeat client wanted as he shifted from sail to power. This power cat is a performance cruiser, more performance and reasonable but not expansive accommodation. This Growler has high HP outboard power limiting this cat’s range due to its fuel consumption. The design is a refined version of the smaller Growler range of power cats.

The Growler 1500 GTR is 49.2 x 24 foot with a weight of 13,450 lbs. As the 2,000 litres of fuel weighs 3,300 lbs and 1,000 litres of water 2,240 lbs plus maybe 1,500lbs of crew and extra’s the total displacement may be close to 21,000 lbs. The length to beam of the hulls is 10.5 to 1. Draft over the hull is 1.4 foot with 2 foot over the propellers. The underwing clearance is 3.2 foot. The outboard power is either 2 or 4 outboards. The recommended power is 4 x 250 HP 4 stroke outboards which will give speeds up to 40 plus knots. The cruise is 30 to 35 knots using about 6 litres/mile (about 320 miles) in fun mode but if you would like to go 500 miles a speed of around 20 knots is required.

Now this leads to an important question. The structure of the cat, as 20,000 lbs of boat doing up to 40 knots requires a very good design, structure and most importantly a very good builder. Choose a builder who understands “light”. She uses light composites as per the majority of Schionning designs but more finely tuned, much like the G‐Force cats. Glass is “S” glass for lighter and yet stronger results with carbon caps and carbon reinforcing in the high load areas. Balsa cores will be used for their higher impact strength in high impact areas with honeycomb and balsa Duflex panels for furniture, bulkheads and all flat areas. All coupled with WEST or ATL’s epoxy resin systems. The impact loading of this cat will be substantial and any weakness in the build will be discovered fairly quickly. This is not a home build unless you are very experienced and have the equipment to do EG vacuum bagging or resin infusion.

The accommodation has 2 double berths in the hulls with associated cabin space and toilet shower rooms. The bridge deck has a large forward cockpit with access from the main cabin. The main cabin has seating table and a large galley. The helming position is shown as internal beside the entrance to the forward cockpit. There is an integrated cockpit aft that provides additional seating. At 40 knots the ride in the forward cockpit could be a little exciting and the sleeping berths forward I suggest would be a slow speed or moored option only.

I hope the cat will be built soon so we can all find out the Growler 1500 GTR can live up to or exceed expectations. The jpegs give the idea.

 

[oldmulti]

We have seen this tri before under the name of “Stinger” (page 64 this thread), a Len Surtees design initially prototyped in Australia and then exported to England for a fore runner to a “production” version of the tri. The Stinger or Sting 600 started as a home build trimaran design that can be converted into a foiling tri. The tri is 19.6 x 15 foot able to be folder to 8.2 foot for trailering. The boat weighs between 924 to 1,067 lbs depending on its configuration. The crew can be 2 to 3 people with a maximum payload of 500 lbs. The draft is 1 foot over the hulls and 3.6 foot with foils down.. The 31 foot high mast carries a 183 square foot main plus 18 square foot wing mast, 93 square foot jib, 230 square foot screacher and 387 square foot spinnaker. The boat folded on a trailer is 25 foot long (excluding the mast). The outboard suggested is 3.5 HP.

The Stinger has now being promoted in England in 2 models. The Adventure 600 Sport trimaran and the Fast Foiler model that can foil under sail in very low winds. The front foils and rear inverted T foil still generate lift allowing the Fast Foil tri to sail very fast in many wind conditions. The initial trialling of the foiling trimaran was done in Australia and Len found that having 3 “fixed” foils did not allow for variations of wind speed and sea conditions. He redisgned the rudder T foil rudder box to allow some adjustment of the aft foil a few degrees which allowed the rear foil to produce more angle of attack on the front foils when required (by lowering the lift on the aft foil). Once the adjusts were done the Adventure 600 could foil as was originally intended. This tr is a cheap alternative to a Pulse 600 or production day sailing foiling cats. It can be built for you or you can buy plans. The foils will have to be brought as they are built in production moulds which would take a home builder a lot of time to replicate.

The boat can be built in plywood with foam glass cross beams or timber plywood cross beams. The folding cross beams are the same as the Seaclipper 20 approach but are much lighter. The boat was designed and intended to be a foiler from the outset and has been progressively developed over a couple of years. The foils were designed by a structural engineer who tested them with a static load of 440 lbs at the end tip of the foils to ensure structural integrity and rigidity.

There is discussion of a cabin version of the Adventure 600 CC with a small cabin and galley up front “to enable easy, and comfortable overnight accommodation”. Don’t expect any more than a single bunk and a camp galley. There is a hint you can have foils on this model but I would suggest the additional weight of the cabin and camp gear may impact the foiling capability.

This tri will satisfy a lot of sailor wanting a fast practical tri that can sart os a normal tri then with foils added turn into a very high performance tri and in its older years turn into a camp cruiser. If you want you can home build the design and buy the foils as required. The foil cases are structurally sound from the initial build of the tri. The folding cross arms make the tri easily trailable. An interesting design. The jpegs give the idea.

 

[oldmulti]

Rapido trimarans build a variety of tri from 40 to 60 foot. Most have a folding option and as a result have a slightly limited main hull accommodation compared to a EG NEEL trimaran. Rapido was asked by an Italian client, Aldo Fumagalli, to do a trimaran that did not fold but had more accommodation at a bridge deck level. The result was the Rapido 53 XS (was also temporary named 50 XS and 52 XS). The XS stands for additional space but the Italian owner still wanted to maintain the Rapido performance characteristics. Rapido went to work and created the new design with more accommodation and changed the rig, daggerboards and rudder foils to improve the performance. The Rapido 53XS takes the Morrelli & Melvin hull design of the “classic” 50, using a fixed structure (i.e. not foldable) with an added 1,760 lbs of extra superstructure.

The Rapido 53XS is 53 x 34 foot with a weight of 20,613 lbs. The 75 foot carbon fibre mast carries a 1260 sq ft mainsail, a Solent of 786 sq ft, a stay-sail of 268 sq ft, a Gennaker of 1,615 sq ft and a spinnaker of 2,476 sq ft. The tri has moved to having fixed pre-preg carbon rudders on the floats only and instead of one straight daggerboard in the central hull, has a prepreg carbon C foil dagger board in each float. The draft as a result ranges from 2.3 foot to 11.5 foot. That should keep the XS sailing well even with the extra weight and windage.

The purpose of this design is to improve the accommodation and as a result the Rapido 53 XS has a larger flare above the waterline of the centre hull, which accommodates a salon that is not exceptionally large but has a 360-degree view of the surrounding waters. There are double berth cabins with a bathroom in the bow and stern of the main hull. The main saloon cabin has a large galley, seating and table, a double berth and a single berth with a navigation computing area. The accommodation is more like a catamaran main saloon with expansive 360 degree views. The advantages of the sailing characteristics of a tri with the views of a cat.

The build is Foam glass with a lot of carbon fibre reinforcement. The fixed crossbeams are mainly carbon fibre as are the C foils, rudders, mast and boom.

The tri is due to be launched by March 2024 with initial sailing from Vietnam through the Red Sea to the Mediterranean. I hope all goes well. There are no performance figures beyond estimates of over 20 knots in good conditions. My simple calculator says 10 to 12 knot averages are possible.

This is an interesting development and the limited jpegs give the idea.

 

[oldmulti]

Folks, I am having serious computer problems and this coming from a borrowed machine. Should be back in a few days.

 

[oldmulti]

Hi, I should be back tomorrow. Computers are a pain sometimes especially having to rebuild them.

 

[Russell Brown]

I liked the last couple of trimaran postings. I have such a hard time with the condo-cats. Not totally sure why, but I've got some kind of bug up my butt about them.

 

[redreuben]

I liked the last couple of trimaran postings. I have such a hard time with the condo-cats. Not totally sure why, but I've got some kind of bug up my butt about them.

It’s because they are so wrong on so many levels except popularity.

 

[tane]

It’s because they are so wrong on ALL levels except popularity.

...fixed it for you...

 

[oldmulti]

This is a small one as I am testing some new software. The following power tri was a well considered but a simple design that was started in 1970 by a man who wanted a deep V but was concerned about the power required to drive a full bodied deep V. So Easyrider was conceived to have a narrow deep V in a simple to build concept with smaller float hulls for stability. Therefore a lower power should drive Easy rider at a reasonable speed.

The Easyrider is 28 x 9.2 foot and is built “lightly”. The outboard power was 55 HP and provided 11 to 14 knots of cruising speed depending on the propeller. The boat has 220 litre fuel tank.

The power tri hulls were built from 9 mm plywood with timber framing and stringers. The cabin is from 6.4 mm plywood and framing. The windows are Lexan.

Quotes from the designer builder. “Ride was very soft. Directional stability very high (occasionally to a fault). Attitude was very level and she turned very well considering her hull shape.” and also a small warning “I jumped the wake of large vessels flying through the air mostly and almost went over backwards in 50+ mph winds. The Rider was a fun and capable boat, but light”. This power tri travelled from Alaska down south so the light weight appears not to have been much of a problem.

The simple jpeg drawing is not accurate but gives the idea. An interesting design.