Multihull Structure Thoughts

Glad you like it as I'm doing something similar on the tri that I'm building, though I'll have a much longer boom.
I wanted to keep the mast really light for getting it up and down at the launch ramp, so keeping it short is part of that.
I got lots of experience with screechers on the G-32 and really like them. The ability to easily roll it in or out and then be able to hoist and drop with it rolled up is good. I had a smaller screecher that was designed for upwind that was very versatile. It worked well in conjunction with the jib because I could move the tack to leeward a bit with the articulating bowsprit when sailing upwind, or move the tack all the way to weather when off the wind, which effectively moves the sheet lead outboard.
I did have small issues with lee helm on the G-32, which I hope to be able to avoid on the trimaran because the centerboard can go past vertical.
I know I've posted this photo before, but it does illustrate what we are talking about. The mast on the G-32 is about 18" shorter than the boat is long.

 

This is a short one for those who aspire to stand out when sailing. I know that Rob Denney and some of his clients have tried kite rigs but this Harryproa C50 concept is on another level. I suggest this is an idea generator to build interest. The underlying kite control technology is advanced but the practicality of 4 or 5 kites to control, even with computer automation, is interesting to say the least.

The designer of the Kite rig and associated computer controls is Seth Carlson from California. He is at an early stage of rig development and is still developing the hardware. I have shown a jpeg (last one) that describes some of the detail he is trying to develop. His web site is: Ripcord Kite.Boats – Kite Sailing Development https://kite.boats/

Some jpegs to give an idea.

 

There's some dissonance in my mind looking at the jpegs. The proa per se looks "Denneyish" but the accommodations are grouped at the longer hull which appears to be the windward hull. Maybe I'm missing something and it will all make sense in the morning after a nights sleep. It is interesting.

 

This looks reasonable. Unlike the normal, vertical sails, kites produce much smaller heeling moment, so the lee hull is not heavily loaded (nor the windward one unloaded). So, the heavier hull should be longer, and the lighter one can be shorter.

regards

krzys

 

The following is a collection of kite rig boats to give an idea of what has been suggested and tried. These developments have been tried for decades but have only become mainstream with single person boards with or without foils. There are several smaller (under about 30 foot) boats that have done one off kite sails across the Atlantic.

The first series of jpegs are of a Humphrey’s yacht design who did a tentative proposal for a 40M SkySail MotorYacht. They’ve termed it a SkySail-supplimented MotorYacht, “The use of the word ‘supplemental’ is chosen carefully. While we expect this family of boats to be able to ‘sail’ efficiently under SkySail, we foresee that fundamentally the boats have to be very efficient and seakindly motoryachts, and in this respect the common denominator for efficiently under both forms of motive power is low hull resistance. Thus our work on this generic set has evolved towards slender body hulls that derive stability from wavepiercing outriggers….they are in effect trimaran derivatives, which will have long rang capability under engine, not to mention the ‘free’ miles under SkySail."

The next item is Anne Quemere who single handed kite-sailed across the Atlantic in '06 in a monohull. I like the buoyancy bar aft to help stability. Next jpegs are the Noah 76 catamaran and also the TRAWLIVARUIS kite cat.

In all these cases they are real organisations trying to develop real solutions to kite control issues through some form of automation with minimal human input. I do not think the processes and controls have reached a viable point yet. Even sailing craft that are “successful” with kites, that are not computer controlled, require 100% human control when flying the kite. There is a future here but there is a lot to learn.

Large shipping companies are paying big money to develop kite auxiliary sails as there are substantial fuel savings that can be made if the kites operate even 30% of the time.

Most of the kite companies shown here have gone out of business which indicates the state of the kite market. The jpegs give the idea. The PDF is about the Humphreys boat

 

Kite Powered Boats
I was also very interested in this subject at one time,...and very enthralled with Humphrey's design

I started this subject thread on some ideas.
New Age Trawler/Motorsailer; Kite assisted PowerYacht https://www.boatdesign.net/threads/new-age-trawler-motorsailer-kite-assisted-poweryacht.20319/#post-171356

ie,...

 

Power & Aerodynamics (from that subject thread referenced above)

brian eiland said: ↑
I think there is some misunderstanding here. One of the reasons the kites are 'flown' in an exaggerated manner is too be able to extract more pulling energy from them per square foot area...more power from a smaller kite.

Remember the old theorem, the pressure goes up as the square of the velocity of the wind. So if you fly figure-eights the kites can develop substantially more power/sq ft.
From their website;

"By means of dynamic flight maneuvers , e.g. the figure of "8", SkySails easily generate five times more power per square meter sail area than conventional sails."

"Their double-wall profile gives the SkySails towing kites aerodynamic properties similar to the wing of an aircraft. Thus, the SkySails-System can operate not just downwind, but at courses of up to 50° to the wind as well.

"Unlike conventional wind propulsions the SkySails-System causes minimal heel."

 

Get Home Power (emergency power)

In a recent discussion on Passagemaking Under Power, the subject of "Get Home Power" came up



The response was interesting:

We had looked at using a traction kite several years back on Swan Song. I had several emails, calls and proposals from a couple of companies interested in the project but when push came to shove nothing developed that could be purchased then.

There have been many kite advances in the past few years and I think that a kite is a very viable aux power system for a passagemaker. Both as a "get home" and fuel saver on long passages. Significant power can be developed with a traction ( as opposed to a sport kite) kite in the off wind passages that most of us favor. I for one really don't like slogging into head seas/winds for days on end even tho our recent Mexico-Hawaii passage had two full days of this. Beam and aft wind/seas are much preferable. Most passagemaking, as opposed to delivery passage planning, should focus on making major runs with the wind/sea aft of beam. This blends into the strength of the kite.

Kites can offer power from 110 degrees off the wind. This translates into a usable arc of ~140 degrees. All but 500 miles of our recent 2700 km passage, for example, would fit in this wind angle.

A kite with a nominal pull of 20-25 HP would have given us a ~ 4 kt speed under kite alone or decreased our fuel consumption by about half. So we'd have a "range extender" and Swan Song would have an 8000 km range vs. the 4000 miles we have based on the MX-HI trip. A significant advantage, IMHO.

How big a kite to do generate this pull? That is very dependant on the design. Spinnaker type kites are large but inexpensive and have several disadvantages mostly becoming a drogue :-( Rigid wing kites are much easier to fly, can be water launched and recovered from the water easily. They are controlled from a single control point with two or three lines. There are designs range from self inflating (not good for us). to ones with battens to those that are inflated with pressure for shape (best for us, I think). All of the rigid wings develop more power than the early spinnaker designs for a given size. Size and design is important in launching from a deck as we don't want to intentionally launch from the water nor have an unruly web of fabric/lines looking for a place to self destruct.

Launching from a foredeck pylon, aka a small mast, could be easy and once launched the kite flies from just above deck level to what ever altitude you desire. The higher it is the more wind there is thereby the more available power. Parked over head they develop no power. As you pull the control lines they move forward of the boat and generate incredible power. Easing the trim and they depower instantly. Using the trim to move them from side to side increase the average power even more.

Sitting a kite surfer of the foredeck in a chair strapped down to the deck with a seatbelt should be a good seat of the pants test as how one of these work and could be adapted to a passagemaker.

This certainly would be far cheaper than a wing engine, I couldn't see more than $15K for the whole system, and it would not have the issues of space and additional fuel consumption of twins.

 

How about this crazy idea,..

 

I like the overall looks of the boat.

I'm not a fan of that swinging fore-stay attachment concept. First off it would be difficult to do,.. while maintaining decent fore-stay tension. Secondly I think would fine that it doesn't add anything aerodyamically to the upwind performance. You would have to go back and read somethings on the 'slot-effect' by Arvel Gentry to see how those two headsails should be most effective.

That central board of his (be it centerboard or dagger board) really needs a lot more 'anchoring' than he gives it. I would suggest a look thru some of these discussions,..
Central Nacelle on Crusing Catamaran (lots of pluses) https://www.boatdesign.net/threads/central-nacelle-on-crusing-catamaran-lots-of-pluses.69063/
I had lots of experiences trying to tame those central boards on the Stiletto catamarans.

I would also suggest the possibility of a wishbone boom of the rear sail.

 

Marko in Madagascar wanted a boat, he started with a dugout canoe which was pretty unstable so he decided to add some stabilisers. The tri ended up about 12 x 9.2 foot overall. The floats are a 19.6 foot length of 90 mm PVC water pipe and cut in half to form the floats. Each PVC tube end was plugged with a timber insert and bent into a banana shape. The cross beams were thin “stakes” (trees) that were screwed onto the wood canoe and bolted by brackets and ply to the PVC floats. The mast is a 11 foot “stake” (small tree) supported by ropes to the crossbeams. The sail is a flat piece of heavy cotton with reinforced edges.

The oar rudder was mounted to a cross beam. Initially the tri did not sail to windward as the small keel on the main hull did not permit the tri to tack. Marko upgraded the tri by taking of the keel and added 2 leeboards to the main hull. This allowed the tri to tack a little, but the addition of a small jib which could be back winded improved its tacking and upwind capability.

The tri could now be sailed in stronger winds, but Marko found the tri in waves tended to get him wet. Marko had real fun and had an offer from a local person to buy the tri.

No performance numbers are available, but a guess would be 5 to 6 knots at peak speed.

A very cheap simple boat for day sailing fun.

 

A quick update on the world sailing speed record attempt. Paul Larsen in 2012 aboard Vestas Sailrocket II set the world sailing record of speed record of 65.45 knots (75.3 mph). The Swiss SP80 team plans to reach 80 knots using a kite sailing technology. The SP 80 is 34.4 x 24.6 foot with a 215 to 538 square foot kite depending on the wind conditions.

The design of the SP80 was based on the need to exceed the mythical 54-knot (62.1 mph, 100 kmh) speed barrier, considered the supersonic barrier on the water, on an unpowered sailboat. At that speed, cavitation beneath the water begins to slow down any hull and foil requiring special hull and foil design is critical for moving beyond 54 knots.

The SP80 is designed as a trimaran with its main focus is to keep all three hulls in contact with the water, minimizing the risk of capsizing due to high-speed airflow. The SP80 accommodates two crew members seated in tandem. The rear seat occupant is responsible for managing the kite via a control arm located behind the cabin, while the front seat occupant handles the steering. During the design phase, sensors are used to improve and control the robustness of the high-performance materials (carbon, titan, stainless steel) of the boat’s structure. Thanks to the design of the super-ventilated foil, stability is optimized and the impact of cavitation – a phenomenon in which water starts boiling around foils at extreme velocities, slowing the boat down – is avoided. During the speed run, data are collected from the various electronic modules and control sensors directly integrated into the boat, and from the monitoring sensor communications between the pilot and the technical crew on shore, including biometric data transferred through sensors worn on the pilot’s body such as vital and security parameters.

After years of development and testing, with speeds peaking around 50 knots, the team analyzed on-water data and returned to the shipyard in early May 2025 for a round of optimizations. The improvements paid off as soon as sailing resumed on May 20: in just two outings, the boat shattered its previous personal best of 52 knots, reaching 58.261 knots (108 km/h, 67 mph) in France. "We know the boat has the potential—now it's up to us to become more precise in our handling" explained Benoît Gaudiot, kite pilot. "We're discovering how the boat behaves beyond 100 km/h and learning to control it. This week, we came close several times to averaging 50 knots over 500 meters. It's naturally a bit frustrating to end the week at 48.6 knots, but we know it's only a matter of time. Every run helps us improve.”

"Namibia has been a mecca for speed sailing ever since the first kite records were set there in 2008, so the idea was always in the back of our minds", explains Benoît Gaudiot, SP80 co-founder and kite pilot. Between now (June 2025) and summer 2026, the streamlined core team will focus exclusively on preparing every detail of the Namibian campaign, with the goal of being fully operational in Walvis Bay by September 2026. That means SP80 still has 16 knots to gain, but the team is confident it can continue progressing.

The jpegs give the idea of the SP80.

 

This is for those who have a spouse who will not leave their garden to go boating. The Sphinx 40 is a powered electric cruising catamaran that features 97 square foot of garden area. Not only are you getting cheap electric travel but you can also grow your own food as you travel. Sovereign Ships from Pensacola, Florida USA are the builders of this fine cat.

The Sphinx 40 catamaran is 40 x 22 foot displacing 22,050 lbs. The hull length to beam at the waterline is 8 to 1. The draft is 3.7 foot over small fixed keels, rudders and propellers. The Sphinx 4.0 will run on electric motors powered by batteries fed by the sun or by connecting to a dock power point prior to travel. There 728 square feet of solar panels (equals about 40 x 500 watt panels) on the roof and partially on the hull sides with an auxiliary kite for wind power. The solar panels feed into a 20 KW battery pack that provides a range of 26 miles and a max speed of 7.8 mph. If range is an issue either a bigger battery pack or travel slower for longer range. The optional Kite rig is available for additional distance under the right wind conditions.

The accommodation is interesting. There is a master double berth cabin with ensuite in the port hull and in the starboard hull is 2 x double berth cabins with a toilet shower area. The main saloon forward has a helming navigation position followed by a large seating table are which can be converted in a lounging area then a large galley aft. Surrounding the main cabin area internally is a 97 square foot gardening area to grow fruit and vegetables or flowers if you want. Aft of the main cabin area is the cockpit.

The build is mainly foam glass but little detail is known.

This is an interesting design intended for those who want to take a EG 3 months cruise around Florida or Great Barrier Reef in Australia. You could live cheaply in your $500,000 boat overlooking those who have spent $1 million for the fixed land based house. When the view gets boring you can move to another location.

The jpegs give the idea.

 

Do you know many asymetrical things in real world ? What if the wind change suddenly ?

 

Sovereign Ships is producing the Sphinx 40 cat but did a few other conceptual designs prior to gauge interest. The first was a 40 foot monohull which was to be electric powered and again had a garden, this design then was modified to become a swath (small waterplane area twin hulled) vessel. Lets look at the evolution of the conceptual designs.

The Sovereign Spirit 40 is 40.5 x 14 foot with a displacement of 18,739 lbs. The draft is 2.5 foot. There is no details of the power beyond it being electric with a 266 square foot solar array (about 15 x 500 watt solar panels). The garden area in this boat is 126 square foot. So less solar power and more garden space. There is an optional kite sail for auxiliary power.

The next evolution came in the form of a SWATH version of the Sovereign Spirit 40. The standard monohull was lifted onto stilts with 2 swath hulls placed underneath. The overall beam increased to about 28 foot with the swath hulls being about 45 foot long. The length to beam on the swath hulls about 15 to 1. The swath hulls forward have a “control” foil to minimise nose diving. I suspect the overall displacement would have increased to about 22,000 lbs. As the design was never detailed, I am doing educated guesses from the existing jpegs of any numbers on the swath version.

The accommodation in the monohull or swath version is the same. A fore and aft double cabin separated by a galley area and a head shower unit. There is a small cockpit aft and in the bow cabin a helming position. The 126 square foot garden bed surrounds the outside edge of the interior cabins. I can understand why Sovereign Ships decided to put the 40 foot Sphinx catamaran into production first as for a similar cost it has more accommodation and solar area to achieve the cruise able home.

The jpegs give the idea.