Multihull Structure Thoughts

[brian eiland]

Very early on I sought to employ a central rib/nacelle to gain longitudinal strength down the wing area. And employed thick sandwich cored bulkheads athwartships,...LINK

here is a reference I made back in 2003,...

Post in thread 'Center nacelles and wave pounding in cats.'

Jul 29, 2011

ReOpen this Subject

I am looking to reopen this subject, and examine the largest number of existing designs out there that have made an attempt to provide a modified surface area in the wingdeck area to combat the wave slamming that can occur on many catamarans.

I searched the forum for "bridgedeck slamming" and came up with primarily 3 subject threads with that wording in their titles, but this one's title seems to embrace concept most closely.

Here is another subject thread with some good postings on the subject...

• brian eiland

ReOpen this Subject

I am looking to reopen this subject, and examine the largest number of existing designs out there that have made an attempt to provide a modified surface area in the wingdeck area to combat the wave slamming that can occur on many catamarans.

I searched the forum for "bridgedeck slamming" and came up with primarily 3 subject threads with that wording in their titles, but this one's title seems to embrace concept most closely.

Here is another subject thread with some good postings on the subject:
Slamming waves and open bridgedeck crossbeams. http://www.boatdesign.net/forums/multihulls/slamming-waves-open-bridgedeck-crossbeams-22833.html
....and a more recent one here:
Bridgedeck Clearance http://www.boatdesign.net/forums/multihulls/bridgedeck-clearance-37666.html


I recall bring this subject up back in 2003, not long after joining the forum:
Big Cat, alt CB's & sail rigs http://www.boatdesign.net/forums/boat-design/big-cat-alt-cbs-sail-rigs-2225.html
First, imagine a flat plate, on edge, mounted down the centerline on the underside of the bridge deck. This flat plate will act as a rib to strengthen the fore-to-aft rigidity of the vessel, a somewhat weaker characteristic in a catamaran structure vs. a keeled monohull. If a tow bundle (rope, etc) of carbon fiber (kevlar, PBO, etc) was laid along the bottom edge of this flat plate, the rigidity could be even greater (sort of akin to a bottom truss structure, or a flange of an 'I' beam).
The front of this nacelle/plate could be configured to act as a wave splitter to actually attack, up front, the formation of those peaky waves under the tramp areas that eventually slap at our bridge deck underside. We kind of slice those waves down a bit. A lightweight fairing might also be added to this 'flat plate nacelle' so it appears outwardly much more esthetically pleasing, as well as more curvature to shed those peaky waves.

My 'nacelle plate' actually extended out to the front of the bridgedeck quite a bit to "attack" the water formation that might slap at the wing.

Hopefully we will get a number of participants supplying photos of good and poor examples, that can be analyzed as to why or why-not they worked.





RunningTideYachts.com
Distinctive Expedition Yachts

Here are a number of interesting discussions about the leading shapes of those central nacelles,...

X

Thread 'Center nacelles and wave pounding in cats.'

Sep 1, 2007

«The idea is that the force of the wave collisions will be dampened by the cushioning effect of the V section (of the nacelle)". ( Chris White, The Cruising Multihull)
On the other hand, the wave collisions are more frequent on a catamaran bridgedeck with a center nacelle, aren’t t they?

• xarax
• Replies: 79
• Forum: Multihulls

 

[montero]

Harryproa in Brisbane.

We are using the same rig on the cargo proa

anyone else ?

 

[rob denney]

anyone else ?

It's a long story. Click on the YouTube link to see it.

 

[oldmulti]

LOYD Shipyard is a shipbuilding company located in Istanbul Tuzla, Turkey. It builds mainly work boats in aluminium, steel and HDPE. The following is a sample of there HDPE built fire and rescue catamaran designed for open water.

The HDPE fire and rescue catamaran is 52.8 x 17.7 foot with a build weight of 29,000 lbs. The length to beam on the V hulls is 8.3 to 1. The draft is 2 foot with waterjet or outboard power. The underwing clearance is 2.8 foot. A sample of engine option could be 4 x 300 HP OXE outboards (total 1200 HP) giving a peak speed of 32 knots OR 2 x Cummins QSC6.7 525 HP (total 1050 HP) driving EG 2 x DOEN WaterJets. This gives a peak speed of 24 knots. Many other engine and propulsion systems are available to suit a customer’s needs.

The accommodation is designed 10 sitting crew of fire fighters/rescuers and a helmsperson. Down in the hulls is aa galley, storage and toilet facilities. This vessel could be converted to a cruiser with minimal effort.

The construction is mainly HDPE. I am surprised at how large a vessel you can construct using the material as this is one of several firms using HDPE to construct work boats for its durability and low maintenance. The design has to be done to allow for slightly more weight and more frames, stringers etc as HDPE is not as stiff as EG plywood for a given weight, but if done well its structurally as good as a steel or plywood build with a lot less maintenance.

A few jpegs gives the idea of the concept.

 

[brian eiland]

The construction is mainly HDPE. I am surprised at how large a vessel you can construct using the material as this is one of several firms using HDPE to construct work boats for its durability and low maintenance.

How does someone build a vessel with HDPE ? It is very difficult (almost impossible) to get any other materials to adhere to it,...and even to bond it to itself??

High-Density Polyethylene (HDPE) has a very low surface energy, meaning standard glues, epoxies, and super glues cannot stick to it. To bond HDPE, you must use specialized structural adhesives with a surface primer, melt the plastic via thermal welding, or use mechanical fasteners

 

[montero]

0:05-0:09

 

[brian eiland]

I saw this video by a US builder,..

but no idea how they are doing it ??

 

[oldmulti]

For Brian. HDPE should bee welded just like an aluminium structure. It also can be glued if you have the correct glues but gluing with the correct glues is weaker than welding. The following is a cut down version of the following web page: https://whatiswelding.com/how-to-weld-hdpe/

1. Prepare the Surface

Clean the surfaces you’ll weld. Dust, oil, or moisture can ruin the bond. Use a cloth soaked in isopropyl alcohol. Ensure the surfaces are dry before applying heat.

1. Choose the Right Welding Technique

Select a suitable welding method for your project. Options include extrusion welding, hot air welding, or butt fusion. These methods operate at different temperatures—commonly between 220°C and 300°C (428°F to 572°F) depending on the HDPE type. Each technique has different setups, so choose wisely!

1. Set Up the Equipment

Gather your welding tools, like a welding gun, HDPE rod, and temperature gauge. Set your welding heat gun to the correct temperature, usually between 200°C and 300°C (392°F to 572°F) for HDPE. Keeping the temperature steady is crucial; fluctuations can ruin your weld!

1. Heat the HDPE Ends

Heat both edges of the HDPE pieces until they become glossy—this means they’re ready to bond. A good rule of thumb is to apply heat for about 30 to 60 seconds. Keep moving the gun to avoid overheating. Once they’re hot enough, you’ll notice a slight sag in the material—this is your cue to proceed.

1. Join the Pieces Together

Press the heated edges together with firm, even pressure. Ensure proper alignment; misalignment can weaken the joint. Hold the pieces together for about 10 to 15 seconds as they cool slightly and bond. Monitor the joint for any gaps or separation as it cools

1. Proper Cooling

Let the weld cool fully—at least 10 to 15 minutes—before handling. Faster cooling can leave a weak joint. Avoid moving or stressing the weld during this time. Patience is key for a reliable finish! Additionally, understanding the importance of a suitable table height can significantly enhance your welding efficiency and safety.

Common Welding Methods for HDPE

Welding Method	Best Use	Temperature Range (°C / °F)	Advantages
Hot Air Welding	Sheet and pipe welding	200-300 °C / 392-572 °F	Good for large areas and joints
Butt Fusion	Pipes and fittings	210-260 °C / 410-500 °F	Strong seams with minimal equipment
Electrofusion	Pipes and connections	Varies with fittings	No open flame; great for tight connections
Extrusion Welding	Large fabrications and repairs	220-240 °C / 428-464 °F	Fast and creates thick seams
Laser Welding	Thin sheets and intricate designs	Varies significantly	Precise, minimal thermal impact

When it comes to welding HDPE, different methods suit different applications. Understanding these methods is essential for a successful weld. Here are the main ones:

Each method has its context. For instance, if you’re working on a large pipe project, butt fusion might be your best bet. Think about your specific needs before getting started!

 

[oldmulti]

The Nautitech 41 Type S takes the same place in the lineup as the Nautitech 40 Open, it actually bears very little resemblance to it. This new model is the third joint project between Nautitech and Marc Lombard Yacht Design Group. “I believe this is the most successful project we’ve ever completed in terms of the concept and specifications: in terms of performance, elegance, design details, and finish, we’ve nailed it…” Eric Levet, co-manager of MLYD says. The 41 Type S is a performance cruiser that is lighter and more efficient in design than previous Nautitech designs.

The Nautitech 41 Type S is 41.3 x 23.3 foot with a weight of 21,560 lbs. The 60 foot mast carries a 780 square foot square top mainsail, a 508 square foot genoa and a 1260 square foot gennaker. The hull length to beam is approximately 8.8 to 1. The draft is 4.75 foot over fixed keels. The motive power is 2 x 3ym30 Yanmar inboard diesel engines.

The cat’s accommodation is in one hull a double cabin aft and a master cabin with head and shower forward, In the other hull a double cabin aft central shower head then a choice of another double forward or a storage room. The main saloon is a large galley with seating, table etc and a navigation area. The cockpit is an extension of the main saloon with seating etc. The helming is on either side of the cockpit aft with sheet ropes etc lead to either helming position. Comfortable for 4 for extended cruising.

Initial test sails suggest the 41 Type S is faster than the Nautitech 40 it replaces although it is about 2000 lbs heavier. MLYD has done some excellent work on the hull shape to provide better performance.

The build is a foam composite that has reinforced structure, multi-material composites with carbon fiber/vinylester zones to absorb loads. No details beyond that statement.

An interesting update of what is virtually a completely new cat. The jpegs give the idea.

 

[oldmulti]

There is a Canadian who wanted to travel the inland waterways of Canada. A great part of the world. He started out with a narrow monohull about 18 foot long that could seat 6 people. The monohull had a solar panel roof to power an electric motor and travelled at about 4 knots max. He was frustrated by the slow speed, rolling and the lack of internal accommodation/private toilet area. He reasoned that a catamaran may provide more speed, less rolling and may be able to set up some accommodation. The vessel he developed is a combination of a Kdesign Echo 5.5 catamaran for the hulls and a custom design above the bridge deck level to suit his needs.

The catamaran overall is 18 x 8.2 foot with a shell weight of 600 bs and a displacement of 1350 lbs. The draft is .75 foot. The initial power was a Torqeedo Cruise 2.0 electric outboard set in a well and powered by a bank of batteries housed beneath the forward bench. The sixteen 3.5-volt lithium-ion phosphate batteries are configured to provide 24 volts with a capacity of 10kW. The boat is capable of a top speed of 11 mph but cruises at an average speed of 5.3 mph. The batteries are charged by eight flexible solar panels in two arrays on the canopy. They have a rated output of 660 watts for the first string of three and 900 watts for the second string of five, giving a total theoretical capacity of 1,560 watts, which is rarely, if ever, achieved because of adverse conditions: the angle of the sun, the hour of the day, cloud cover, etc. The canopy is supported by four motorized struts that can lower the canopy 30″ to rest on the bulwarks for trailering and control the port-to-starboard tilt of the canopy to maximize solar performance. There is also a 200 watt solar array aft that feeds 2 x lead acid batteries that are used for ancillary lighting and emergency use if there is a problem with the primary battery circuits. The batteries weight a total of 260 lbs. The batteries were upgraded to 16 KW a few years later along with an upgrade to the outboard to a Torqeedo 6 cruise long shaft which is a 4.3 KW max power motor (equal to 10 HP).

The performance was intended to be about 10 knots with the 1.5 KW electric outboard. Reality intervened. Peak speed averaged about 4.9 knots, or about 20% faster than the monohull. There was additional work required due to uneven trim (batteries needed to be moved forward), drag around the electric outboard leg (a pod put in from to minimise wave action and a reangling of the leg itself to get a better prop angle) and small wedges on the aft chines to direct water flow to lift the sterns a little. These modifications improved the performance to about 6 knots (a 50% increase over the monohull) but the more power was going to be required to go faster. At 6 knots and good light the cat could run, under solar, for many hours. EG At 10 KM P/H (about 5.5 knots) the cat draws about 1500 to 1700 watts per hour. On an average day the solar panels charge at about 850 to 900 watts/hr.

Another indicator is an 8 hour trip which went 68 KM averaging 8.5 km/hr using 1.2 KW/hr of energy whilst the panels generated 8.1 KW over the day

The build is standard Kohler Echo 5.5 hulls and bridge deck. Then the deck and topsides are Western Red Cedar, glass and epoxy. The quality of workmanship in the topsides is very good. The insignia on the foredeck should indicate what the man is capable of. The lifting roof top carries the solar panels and is basically on 4 post that allows it to be brought down for towing etc. There are canvas plastic sides for protection and privacy for the toilet or an overnight stop. This is a well thought out solution as a camp cruiser for river, lakes and smaller bays.

The jpegs give the idea.

 

[oldmulti]

This is a specialist item that is 25 years old but is very educational. The F27 beam laminate schedules. Modern Farrier beams are a different structure and configuration. The jpegs below will give you an idea what is involved in the construction and laminates used in a trimaran beam for a 27 foot tri. The F27’s beams were reliable but like all trimarans have issues when they are 25 years old. The first Farrier f 27’s were built in 1986 and had different laminate schedules which was upgraded in 1991 to the version you’re seeing here. Remember this is only a 25 year old guide, there are better solutions now available from various designers including the later Farrier designs.

The jpegs give the idea.

 

[brian eiland]

63' Catbird Suite, A Frame Rig
I wonder if she is still afloat, and I wonder if the original owner/builder is still alive?? He and his website stopped working in 2016.

Just wondered if your excellent tracking capabilities could help,....regards, Brian

Here is one of his original postings,...and a search method for his other postings

Post in thread 'WishBone Sailing Rig'

Wednesday at 10:33 AM

More info from High Tacker on his A frame rig.

*****Maybe much addition info can be gained by reviewing many of his postings on the forums

Search results

www.boatdesign.net

I'm looking forward to this as I had forgotten this possibility !!

High Tacker (www.damsl.com)

Hello to all, especially Brian Eiland and philSweet,

I'm a newcomer to the Boat Design Forum and first of all want to thank Brian for his references here to my A-frame rigged boat Catbird Suite and her website www.damsl.com. And it's good to see...

• brian eiland

 

[Eurosnob]

Catbird Suite was under sail in the Bay of Islands, NZ on 16/08/2026.

MarineTraffic: Global Ship Tracking Intelligence | AIS Marine Traffic

MarineTraffic Live Ships Map. Discover information and vessel positions for vessels around the world. Search the MarineTraffic ships database of more than 550000 active and decommissioned vessels. Search for popular ships globally. Find locations of ports and ships using the near Real Time ships...

www.marinetraffic.com

 

[brian eiland]

Catbird Suite was under sail in the Bay of Islands, NZ on 16/08/2026.

MarineTraffic: Global Ship Tracking Intelligence | AIS Marine Traffic

MarineTraffic Live Ships Map. Discover information and vessel positions for vessels around the world. Search the MarineTraffic ships database of more than 550000 active and decommissioned vessels. Search for popular ships globally. Find locations of ports and ships using the near Real Time ships...

www.marinetraffic.com

WOW, thank you sir.
sent you a private message

 

[oldmulti]

French company SeaBubbles has a fully-enclosed Bubble battery-electric hydrofoil water taxi. The initial taxi’s ran on the Siene and were 4 passengers plus one pilot, and measures 16.4 x 8.2 ft. The Bubble reaches a speed of 6 knots (7 mph or 11 km/h), its composite fiber hull is raised out of the water on three automatically deployed carbon fiber foils – one in the front, and two in the back. It then cruises at a speed of 12 knots (14 mph or 22 km/h), utilizing gyroscopic and altitude sensors to constantly measure pitch and roll angles, automatically stabilizing itself accordingly.

SeaBubble now has introduced the SmartBubble which is a larger version of the Bubble. This model is 26.2 x 11.5 ft foot. It seats 7 passengers plus a pilot, and cruises at 16 knots (18 mph or 30 km/h). Because it's heavier than the Bubble, it "takes off" at a slightly higher speed of 10 knots (12 mph or 19 km/h). The motive power is a 90-kWh battery pack that is good for about 1.25 hours of cruising. A longer-range 130-kWh battery model is in the works. The 2 x electric motors are at the base of the rear foils.

The boat incorporates four new patented technologies, including retractable foils. It's also worth noting that SeaBubbles recently acquired maritime mobility company Neocean, with an eye towards further developing that firm's unique foiling technology.

The jpegs of the SmartBubble give the idea.