Which one out of these small multi-hull designs will be the best for my needs?

Hi Vijay,

Yes, I have seen Oryx. Your post made me look more in depth into this particular design, to see if it can be adapted for my needs.
The result is a center cockpit Bi-Plane rigged KD860 stretched to 9 meters, based on KD860 open,
I will share the sketches I have made in the next post.

Thank you for your kind wishes.

Best regards,
Eli.

 

Hi all,

I thought I would give an update regarding the design selection process.

Since I began the search for a design that fits my needs, I have been corresponding with Ray, Rob, Bernd and Richard.
All have been very kind, and answered all my (multiple) questions in an informative way. I have also bought multiple study plans from them
and have been comparing those in depth. For the purpose of building the boat - I have obtained a permission to use a 9 meters long yard nearby,
which limits the length of the build to 9 meters, and unfortunately exempts the DUO1000 out of the possible build list.

Looking more in depth into the Bi-Plane extended KD860 Oryx and the "KD860 Open" designs, I thought a similar concept 9 meters long could suit my needs.
I began to make some sketches that I would like to share, together with my thoughts regarding this configuration.
The sketches are not completely to scale, and are based on a stretched to 9 meters "KD860 Open".

The helm is in the front of the saloon in a safe and protected from elements position, with good all-around visibility. All lines led to helm.
The access to the front deck is through a 60cm cockpit door making it safe and convenient to go to front, without the need to climb the hulls from outside.
The Bi-Plane rig clears the front of the boat, improves visibility and makes it a much better hanging out and working space during anchoring or docking.
Right of the helm is 2 meter "sofa", small NAV table and a table that converts to a bed.
There is enough space for a 120cm kitchen in the saloon, making cooking more sociable.

The Port side accommodates a twin bed positioned at a bridge deck level, and a full headroom shower with composting toilet.
The ship's only thru-hull and the water systems are on this side making it safe and easy to troubleshoot.
On the Starboard there is a twin bed, and storage/appliance room.

The stern has seating for 8 people and a platform for diving/dinghy. The Engine configuration is not final.
The composite lightweight Hard-Top spans all the living area and accommodates 3KW of solar panels and the mainsheets runners.
Because of the hard top, the Bi-Plane rig loses some sail area. I think I can live with the reduced performance.
I like the Bi-plane configuration, because it makes both building and sail handling easier, and lowers both the center of gravity and weight.
The hand-built carbon-fiberglass masts will be cheaper than a new aluminum mast, as well as the sails.








This picture is before the modification, to show the base design.



Any opinions or feedback are welcome.

Regards,
Eli.

 

Eli, you like the biplane rig, so what is your sailing experience?

 

I used to sail and compete in childhood on various types of monohulls. Did few short passages.
Later, life took over for 20 years.
Few years back I did official skippers training, inshore and offshore. That being said, my overall mileage is modest.

 

Hello everyone, this is a subject of great interest to me, as I'll be starting my 1st catamaran in September. And it will be a BK design.

The same thoughts as Eli led me to Striker/ Siren 8.4/ KD860Open.

Now that I'm living in France on the Mediterranean, I need to buy 4 or 5 catamarans that can be dismantled to start up a boating business again. The exorbitant price of berths means that catamarans have to be dismantled in September if they are to be profitable.

As the Striker and Siren are designed to be dismantled, I started by modifying the purchased plans for the Siren 8.4 into a 9m bi-plane on Freecad. In the end, I concluded that it would be wiser to modify the KD860open to a demountable version.

About the bulb shape of the Siren and the gain in volume. If you want to on the KD860, you can do that too. The KD860 Onix does it. BK's Pelican does it too. As BK explains so well, the volume gain must be done where it counts without touching the wet volume. It is possible to make it sexier (as in drawing 1) and to structure it as on the Siren with epoxy strips or on the DUO1000 in the underwater spine line with longitudinal plywood strips.

And the extra weight combined with working time will only be of interest to those who, like me, have a problem with the ratio of road transport length to habitable volume. Otherwise, it would be wiser to go for the KD1000/ DUO1000 / KD105, which will be lighter/more efficient/quicker to build/habitable.

I admire the 3 architects and study their ideas and designs carefully. But with each study I end up coming back to BK's concepts. The bi-plane is fantastic! His anti-vortex drifts are fantastic! Every time I think about improving one of his designs, I end up breaking my nose. And if I work on other designs, it's to make them look like BKs. So I'll be making modified BK boats to suit my needs, giving him all the credit and promoting his designs as much as possible.

About your modifications ELI :

1st point: Passage on the front through the beam is not possible. BK designs light! VERY LIGHT! All its structures form an integral whole. Apart from the DUO800/900/KD105, since the early days with the Zeeman or P95, he seems to have remained faithful to his concept of an X-beam that cannot be touched. And even if the X structure is less obvious in his latest designs, it's still there. What makes his Open designs so resistant is the large cross-section of his central and rear beams, which he only makes lighter when he makes a roof. In these cases, the roof and floor form a complex 3-dimensional X-cell with the outer faces of the hulls. On the other hand, you can have a passage in the roof of the square adjoining the beam with a simple porthole. However, with a bi-plane you have no need to go forward in bad weather. Even a floating anchor on the bow can be dropped from the stern if you have prepared lines under the saloon beforehand.

2nd point: The integral hard top would be like making a KD860. With the disadvantage of making it heavier on an open boat and the risk of doing it badly. Possibly, consider a canvas hard top that would close the hulls and be removable. In the low position (in black on drawing 1) your sails will work as on the original plan and at anchor you will have headroom (in grey in the high position). The advantage of the shelter in bad weather and the advantage of ventilation and panoramic views in good weather. You can also create a head passage in this hard top for a central helm station, which will be more comfortable and closer to your winches, as shown in drawing 2.

Drawing 2 is a delusion of a KD860 pushed to 9.2m x 6 wide. Is it realistic to spend a weekend with 10 people on it? Absolutely not! The extra weight generated by the modifications and 10 people on board would make it unsafe to sail. That was to give me some ideas.

Thinking in all directions, and as others have written, I've come to the conclusion that there's no point in trying to radically transform Striker/Siren/BK. They can all withstand minor modifications, but the work of these 3 exceptional architects is so accomplished that you can't do much more than that. We have to bear in mind that this is their work and that our skills only allow for minor modifications. Above all, I think we should be grateful to them for making these boats available to us. Thinking in extremes allows us to find and retain a few small improvements. So I would never advise against looking. Quite the contrary. You only have to look at the way BK continually tweaks its designs to see that improvements are always possible. But it's a perilous exercise and I'm happy to find a forum where I can discuss it with you.

 

Hi lolo,
Thank you for your remarks and the insights. They are correct, and very in place.
It gives some place for thought.

I think, what might make the difference is the intended purpose:
You need 4-5 yachts for boating business - They have to be very safe and with a great stability margin, to accommodate
large random crews for weekends and/or chartering. The open cockpit makes a great socialization place, while fabric roof enclosure
gives a lightweight sun and rain protection. Light weight construction makes it fast and safe, provisioned lightly -
you might even manage carrying up to 10 people onboard in good weather. You have also added single bunks in front of Bi-Rig.
Overall, your pictured concept above looks very nice for the intended purpose.

My concept is slightly different - this is a family boat for weekend sailing, that is all climate/weather cruising capable with 3-4 PAX.
Solar is important for water production, propulsion, lighting, Navionics, climate control etc.., as well as a proper insulation and bridge deck pilothouse
hosting the helm and the saloon for inclement weather protection. Hence for me the roof is an essential core part of the design. Carbon and light
weight construction elements will be used in the roof and saloon to save weight. The remark regarding the center beam is correct. some issues might be remedied by adding carbon for strength,
maybe adding stairs in saloon before the beam together with an opening in the roof will preserve center beam integrity and will allow for center passage to bow - the center passage adds safety
and ease of bow access in all sea states.

The constraints of available building space that allow me to build long but only narrow hulls, unfortunately dictate much of the changes. Otherwise, I would build the DUO 1000.
The intention is not to "force" KD860 OPEN into 9M but rather pay Bernd to design a custom boat that will fit my needs.

I did the basic calculations of the expected loaded weight vs design displacement, and on paper it might work. That being said, I did not talk to Bernd yet since I was finishing the design,
and he might provide some valuable input and insights.

The transverse rear bunks is something I did not think about and is a nice way to add space inside hulls.

Thanks again for your input,
Eli.

 

Good evening, Eli.
Sorry about my writing.
Like all bad Frenchmen, I'm going by the computer translation, which reflects my thoughts badly.
My previous plan was just to illustrate the fact that it's possible to design an 8 or 9 metre boat with 8 or 10 berths, but that it's ridiculous to think that it's usable.
On the contrary, the catamarans I'm going to make are exactly in the spirit of the tient.
In my experience, under 44'' and with a minimum of 2 WCs, it's unrealistic to plan for more than 6 berths. In the Seychelles where I worked, we had 4 couples + skipper + coock for a week's cruising on 44'' with 4xSDB. By spending the days ashore cruising in an enchanting setting, the week went well. If the rain got in the way of the cruise, it could turn into a nightmare. Same scenario on 47'' with 10 customers + 2 crews.
For the 14-day fishing trips to remote islands, we went out with 10 people on 47'', which was often very hot on a human level. For 12 people, you need a minimum of 16.5m, as BK had prescribed in a charter boat plan he had designed. Around 4 people between 7 and 8m and 6 people from 9m. So your wish of 4pax on 9m is, as I think, very realistic.

Personally, I'm going to start with an ECO750 that I'm pushing to 8.1m, ideal for 2 adults and 2 children. Same bi-plane sail as on the DUO800 and AntiVortex. BK advises against using them on multi-spine hulls, but he designed it for a customer and the performance was there, much to his surprise. It can be dismantled into two sections less than 2.5m wide for transport over a few kilometres. This will be a trial run to master amateur construction and validate the mechanical strength of my ideas for dismantling in heavy weather. The Mediterranean is generous in terms of extreme violence, so it will be very easy for me to test my ideas. Then I'll be making a KD860 open in 3 dismountable sections for 4 people and DUO1000s for 6, also in 3 sections.
The only point where we differ is the galley. On these sizes of catamaran I'm in favour of positioning them in the hulls. More space, more stable and the fridge can be integrated into the hull.

Your concept for dealing with any situation is no different from those designed for ocean cruising or circumnavigation. Especially if you're talking about solar power to manage water production.
I'm working with the same ideas, because who can do more can do less. I wanted to stay under 400kg of equipment all told.
Electricity/electronics/hot water/solar/oven/fridge/freezer/pilot/electric WC with black water tank/water heater/motors... are the items that required the most thought and work for me.
I thought it was doomed to failure but in the end it's largely possible by opting for counter-intuitive/forgotten/anti-commercial solutions.
What are your thoughts on the subject?

Laurent

 

My unprofessional thoughts on the matter:
Charter or commercial boats use engines a lot. Electrical propulsion is not realistic in this scenario,
since even with very big battery bank, you will get not more than 1-2 hours of full power. Random crews
rarely plan in advance and not having power when needed can be not safe, said the least.
Petrol outboard will be lighter, simper, safer and by far cheaper.

Family boat is a different concept, and there is a trend of moving to Solar in last years since the pros are more than the cons.

SOLAR
The roughly estimated numbers I got when researching Solar:
1kw power = 5m2 of solar panels. (ex. 3kw = 15m2 of panels)
weight of flexible solar panels = 2.5kg for every 100watt. (ex. 1kw=25kg)
weight of batteries = 10kg per kwh. (ex. 15kw = 150kg)

You can build your own batteries much cheaper than commercial options if building yourself from prismatic cells
bought from a proven supplier from China, coupled with proper BMS. Victron seems to be the standard for
solar converters/electrical system components. I would not go cheap on core components.
Thought should be given for battery placement - weight distribution wise and safety wise. Lithium fire cannot be extinguished with
water. Proper fire extinguishing and fire alert system should be used. The batteries cannot be placed in hulls or human occupied areas
due to fumes, leaving the front or rear lockers as the only suitable location.

TOILET
Composting toilets like Air Head or SunMar weight 25kg, don't need black water tanks and smell better.
Not sure chartering crews would like to deal with it though....

KITCHEN
Is bigger, simpler to build and more comfortable below / Safer for small crews and more sociable above. Really a matter of preference here.


Here is an estimated very rough weight calculation I did for myself:

The estimated typical payload
1) 3 Pax + Provisions + 100L water: 350KG.
2) 10m2 Hard-Top + 2KW Solar panels: 100KG.
3) Rig, Sails and winches: 50KG-100KG.
4) Anchor, chain and windlass: 50KG.
5) Electric Outboard + Battery: 75KG.
6) Composting toilet: 25KG.
7) Life raft & Fire Extinguishers (per regulations), Radio and other unmentioned gear, add about 100KG.

Total: 800KG.

Hope it helps.
Regards,
Eli.

 

A production 10m polyester boat of the designs discussed would weigh at least twice as much. Loaded with the electric comfort offered by the boat builders, the boat would quickly weigh between 7 and 10,000lbs. For this reason, motors and a windlass are important. Electricity needs to be generated too, and to get everything moving you need to add sail area and therefore weight to the structures to support it all. A never-ending climb! And as you say, if you want to add an electric motor, the equation becomes insoluble.
Outboard petrol is also the option I've chosen. The 7.5hp to 15hp air-cooled motors used by Asian fishermen weigh 10 to 15kg and cost nothing (when they break, buying a new one is the equivalent of 2 hours' mechanic's labour). I've seen a lot of Wharrams using them without any problems. It's easy to centre the weight wherever you want. What's more, with the shaft lines disengaged and dragged through the water, (with 2-blade propellers) you can have 2 very capable hydro-generators. (No alternators but 7010 brushless motors from 100 to 170KV).

SOLAR
Dangerous batteries are those used in computers/tablets/smartphones/drones/cars/electric bikes, etc. They are LiIon & LiPol. LifePo4 and LTO are OK.
We tested a lot of flexible panels and ended up giving up. Apart from the expensive Solbian, I won't risk it again. That's why I'm integrating 3 rigid 35x 120cm panels in the fin/bossoir + 2 on the roof, which will give 2kw/day.
Victron is a reference in the boating industry. But I prefer hybrid domestic equipment. Inverter 1200w + Battery lifepo4 24v 200AH + 6*panels at 7kg I stand at 90kg with 220v and 24v cables throughout the boat.

(My first job was as a refrigeration engineer. Today I install and import photovoltaic equipment from China while I refinance my boating project).
I prefer to have 2 voltage circuits. 220v and 24v. The electrical efficiency of 24V consumers is on average 8% higher than 12V. And in 220v you only have to compare the Danfoss BD50F refrigerant compressor in 12v with the Danfoss TLES4.8KK.3 in 220V. Same consumption but 2x more powerful in equivalent working conditions. Add a hydraulic exchanger for cooling with seawater, top insulation and a chest opening so you don't lose the cold when you open the fridge, and you've reduced the boat's biggest consumer by a factor of 4. And just so you know, its R600a refrigerant is simply butane gas. So you won't have to worry about finding any if you need servicing.

TOILET
Composting toilets are the right solution. However, I prefer electric toilets, having found that the pumps are reliable and that the electricity consumption over the day does not exceed 2A for 4 people. The flush is very fast. What's more, you use less water, which is important if you have to use the black water tank. With a marine toilet and not a compost toilet, the black water tank is just there for the absurd legislation. It is in fact always open. The black water tray should be made in the same mould as the hand wash basin / sink / fridge-freezer and water tanks so as not to add weight. If it's closed at certain anchorages, it will be open when you sail again. So I'm only considering the weight of the ceramic toilet and pump (12kg), while holding out hope of finding a lighter all-plastic camper van toilet to fit.

KITCHEN
Yes, his position is a vast debate. What matters to me is an oven (15kg from WOL and 3x cheaper than an ENO) for desserts and fish and seawater so as not to consume fresh water. To wash the dishes for the big tables, I prefer to be on a back deck with a large basin (fitted with a drain plug) and a bucket. It takes just 2 minutes. A piece of epoxy-coated furniture and a water drain for tidying up and wringing out all at once. And washing up is no longer a chore. A cloth to wipe salt from glasses and dessert plates is better than rinsing with fresh water.

BATHROOM
Same battle, all epoxy integrated into the structure. When it's empty, it doesn't add weight and in all cases it contributes to rigidity. What's more, it makes better use of tortured volumes, which saves usable volume.
People have been washing with seawater for centuries. All you need to do is find the right soap (generally acidic) or moisturise the skin and hair with a greasy substance after drying to remove the hardness of the seawater. However, women demand soft water. Some groups who followed our advice consumed only 100 or 200 litres over the week. Others emptied their 1000 litres in 24 hours and accused us of not having filled up before leaving. We had to get out the calculator and explain to them that 20 minutes of showering at 6l/min (given by the electric pump) at 8 gives 960L. But also in electricity 3A x 0.66 x 8 =6 amps so 15 minutes of nauseating engine and diesel to recharge. Hot water is more complicated. The gas boiler with a home-made heat exchanger for hot water from the sea is my personal solution.

GUINDEAU
LiPo4 batteries do not withstand high discharge currents.So no electric windlass.For windlass aficionados, there are some inexpensive options. I've seen 4x4 winches modified for chains, 2-speed winches also modified and hardwood capstans.However, my 1st personal boat was a Sélection37.It weighed 9000lbs when cruising and had a larger wetted surface than the catamarans we're talking about.Without a windlass, of course.I never had any difficulty leaving an anchorage, even in strong winds.And most of the time without an engine.

ELECTRONICS
No electronic pilot. A simple DIY regulator like Wharram offers is sufficient and easy to make.The depth sounder on a boat the length of a shin under water is ridiculous in my opinion.Even on a big boat at night in the lagoons, a torch to shine in front of the hulls is more useful.You have to be able to read the surface of the water, be vigilant, not trust the charts and only in these conditions do you have a chance of never tearing a hull.For anchoring, a depth sounder can be useful, but it depends on your anchoring area and habits.The only thing I find useful is a speedo windvane bi-data system, while I'm getting to grips with the boat and finding the best sail trim or establishing polar performance.The AIS, GPS, SSB for weather and other functions are all done via PC.I've just installed a Chinese INTEL N200 mini PC on a friend's boat, which consumes 6w without heating up except when his young children play on it, when it goes up to 40w. The screen consumes more.
I'm not counting what I consider to be incompressible, such as sails, winches and deck fittings.2 masts rather than a big one without shrouds must be equivalent, but I don't care who wins on that score.I'll wait until I'm sailing on it before cutting weight if I have to.
I think that if you build with care and seriousness you gain more.

I hope this helps too.

Best regards Laurent.

PS For all of you who agree with the philosophy on this forum, please enjoy this
The Joy of Small Boat Sailing https://thegrandarchive.wordpress.com/the-joy-of-small-boat-sailing/
Jack London gives us an insight into his yachting experience.And that white-collar Sunday sailors have always existed.

 

What about a Kurt Hughes 27?




Bigger than the Eagle, still demountable. I don't know that any have been built (which is one of many attractive features of Richard Woods's boats - so many successful builds).

 

Since we've strayed into designs without the bridge deck cabin that the OP requested, I'll mention again Brine Shrimp and Dandy II (links in headers below) by the late Thomas Firth Jones. They represent affordable ocean-crossing capability with Brine Shrimp being smaller but hinged for relatively easy seasonal trailering and Dandy II offering at lot more cabin space. Despite the Spartan accomodations, I think Brine Shrimp would make an excellent affordable cruiser for a couple with small kids.

Brine Shrimp

Brine Shrimp Catamaran https://www.boatdesign.net/threads/brine-shrimp-catamaran.58948/
Proa File | Trailerable Brine Shrimp in California https://proafile.com/multihull-boats/article/trailerable-brine-shrimp-in-california

Dandy II

Note that the original Dandy was well-proven but had a biplane rig which Jones eventually soured on. Dandy II returned to a straightforward stayed sloop rig.

 

@Eli I noticed a KD860 for sale today and was impressed by the quality of the fitout. It is hard to assess spaces when photographs are taking for marketing purposes, but it looks to have a lot of room for the size. Bernd Kohler Kd860: Sailing Catamaran for Sale | Timber Sail Boats | Boats Online | - Auckland NORTH ISLAND, North Island https://www.boatsonline.co.nz/boats-for-sale/used/sailing-boats/bernd-kohler-kd860/312201

 

Yes, it's Orix, a boat extrapolated from the KD860 plans.
But so modified that I would personally be reluctant to use it as an example to discuss the original plan.
Another one is for sale here: fr.boats.com/bateaux-a-vendre/?make=custom&model=kd-860
Same year. Same price. It too has been modified.
Both are larger than the original plans.
The two have been sailing for a long time.
Both are therefore reliable and prove that Bernd Kohler's designs are so well designed that they accept even heavy modifications with some risks.
But as with all amateur builds, we look at the successes and don't see the failures. How many amateur builders have modified architects' plans and failed?
Without a lot of work with Solidwork or Freecad or equivalent software that allows calculations to be repeated, I personally would not risk modifying the plans.

 

The volumes on Bernd Kohler's concepts are all excellent in relation to the programmes on offer. If we were to compare extremes, we could say that the p95 is the ultimate racing beast and the KD 860 a high-performance cruiser offering the same comfort that an industrial cruiser of equivalent size could offer, but with the performance advantage of the kd860 in epoxy wood rather than poly... Widen the p95's floats and increase its deck height, and you get an intermediate boat. Now take a KD 860, modify its hulls to make them asymmetrical while reducing their volume and deck height, and you end up with the same boat. But all this at the risk of failing in your venture.
The advantage over industrial boats is the use of wood/epoxy, which saves weight and increases durability and perfs.

 

The Catnano are a fine example of this. CATNANO Catamarans » Home https://www.catnano.com/en/
Although the directors of this company originally set out to produce the KD860 in professional quality, they ended up losing their way in attempts to produce industrial extrapolations of the KD860 that were far removed from the original concept.

Turn the problem on its head and you'll always get the same result. If you want volume, you lose speed and safety. If you want sleek lines and performance, design a boat with little volume. The best you can do when you choose a boat like the KD860 as a base, would be to make it a little longer to gain speed. But don't expect to gain in volume. Orix is a Junk biplane. A great success! Nouveau gréement Split Junk Rig de Peter Hill avec wishbones : Évolutions http://www.voiles-alternatives.com/viewtopic.php?f=7&t=454 Visit it! Please, you will take it and you will certainly be happy.

The Kurt Hugh 27, which has often inspired me, and the Brine Shrimp and Dandy II, with which I was unfamiliar, are fine examples of the choices that architects, and therefore the buyers. The KU 27 is beautiful, powerful, can be dismantled and towed behind a car. So it's radically different from the KD860, which is the same size but has to stay in the water. Bernd Kohler's KD650 / Duo 800 / KD105 offer the same dilemma if you compare them with their equivalent decked concepts, the ECO 6 / ECO750 / KD1000. Although they can't be dismantled and are 50cm shorter, these 3 boats offer more volume for performance that's just a notch below. A fine example, since they all come from the same brain and the same drawing board.
Choosing a boat is a never-ending discussion. You have to make a few sacrifices, because you can't have everything. And even if by magic a 28-foot boat offered 2 x the volume of those discussed, the volume filled by superfluous cargo would turn a racing beast into a turtle.