Category Archives: Building

What´s going on?

Hi all!

No news for a long time, so you might be wondering what is going on? Well, the building is taking a break at the moment. Not for long, but currently I am very occupied with my work at home. From Easter on we want to continue with the building and that will be the time when the next updates and photos will be available. Meanwhile, we decided to go for the E propulsion. End of January we had the boot exhibition here in Dusseldorf. We talked to a lot of people, got quotes for various solutions (Inboard Diesel, saildrive, shaft drive, outboards …) but finally got stuck with the greenstar electric propulsion. Despite all the concerns and comments (thank you Tom for your detailed and profound analysis) we want to give it a try – though try is not the right word. Greenstar Marine has already 500 systems installed in Scandinavia over the past 7 years. I am quite optimistic that it all works out the way we wanted it. The only thing undecided is the battery choice. That must wait until the whole system is ready installed.

Another thing we decided at the boot fair was the choice of mast and boom. Though we liked the idea of the demountable carbon mast by CCR ( ) we opted for a conventional alloy mast by VMG ( ). I am still waiting for a quote for a full carbon mast but I guess this will be out of our budget – even though it would fit the boat quite well!

Meanwhile in my little spare time I am working on the two daggerboards. Schionnings original design has a wooden spine, foam core and a carbon/glass laminate. Paul and Jolanda from the Netherlands are currently working on the daggerboards for their Gforce 1500C                             ( ), they have some pretty nice pictures. I decided for a hollow construction, made of two halves vacuum bagged in a mould. There will be a separate post on this in the near future.



Currently we are rethinking our choice of propulsion. Jeff Schionnings original idea was rather simple: one central 30 hp outboard would keep the boat light and the cost down. In the beginning I liked the idea a lot but there are downsides: a lack of maneuverability with the central motor and the rudders far away from the flow, petrol instead of diesel, noise, you need a lifting device for the heavy motor … all in all not perfect. Of course we could have just gone for twin diesels but recently I stumbled upon an interesting alternative.

By accident I found the website of electric propulsion specialist greenstar marine of Sweden. They offer a system that seems ideal for our catamaran. Greenstar20D1Unlike other providers it consist not only of motor and controller but is more or less plug and play with charger, shore power connection, power recuperation and even comes with a matching folding propeller and a specially designed shaft. The main question was how to generate and store the electric energy.  And how much would be needed?

The greenstar 20D system has two 24 V DC motors with continuous power of 3.6 kW each. The recommendation for yachts is to have 1 to 1.5 kW power per ton ship weight. The weight of our Arrow 1200 is calculated with 5000 kg. Of course we want to keep the boat light but if we assume at least another 1000 kg for equipment the 7.2 kW continuous power is definitely on the low side. With this setup motoring into strong wind against current an waves for hours is not possible. Maneuvering in and out of a berth and accessing anchorages should be just fine. So how much energy storage do we need? And what if we want to motor away from calm areas. How can we extend our range?

If we assume that 7.2 kW is full throttle we need a current of 7200 kW / 24 V = 300 Amp. Wow, that is quite a lot. And definitely to much to draw out of a lead/acid battery, even the `good ones´. The max discharge rate of a good AGM battery should not exceed 1/2 C (capacity), so for 300 Amp you need a 600 Ah battery bank weighing approximately 300 kg – rubbish! The only alternative is Lithium Ion batteries which are able to provide up to 3 C of current. Theoretically a battery of 100 Ah would be enough but for how long? Wit a maximum DOD (depth of discharge) of 70% for LiIon batteries we would have 15 min of full throttle – hardly enough to get out of the berth, so 300 Ah at 24 V should be the minimum.

Straight out of the box you can buy for example the Mastervolt MLI Ultra 24/5000. It is a 360 Ah Lithium Ferrit batteryMLI 245000 with intergrated BMS (battery management system). The Lithium Ferrit (LiFePO4) batteries have not as much capacity in relation to their weight as the Lithium Ion or Lithium Polymer types but are a lot safer when short circuited. The battery weighs 58 kg which is related to the AGMs pretty good. But – this battery costs 5100,- EUR, quite a lot for 45 min of motoring. The alternative is configuring a system by yourself. This is of course a lot more complex but manageable.

For our 24 V 300Ah we need 8 single LiFePO4 cells and a balancing/BMS system. The best known cells are probably the Winston (Thundersky) LiFeYPo4 cells. You can get them from 40 Ah up to 1000 Ah. Each cell has a nominal voltage of 3.2 V which is kept even at high discharge rates. The operational Voltage range is 3.8 – 2.8 V which equals a DOD of 80%. The producer claims a cycle life of 5000 charge/discharge cycles (Mastervolt – 2000). Constant discharge current should be <= 3C with an optimum for charging and discharging at 150 A.

Winston 300 Ah LiFeYPo4 cell

Winston 300 Ah LiFeYPo4 cell

There are various balancing/BMS systems on the market. Basically the BMS is needed to level the voltages of the individual cells and protect them from low or high voltage. I might do a separate post on that topic some time. A system mentioned above should be around 4000,- EUR with the advantage of higher cycle life. Still, one couldn’t´t do only with the battery – we need a range extender in form of a Diesel Generator.

To keep the advantages of the system – small and light – I chose a generator supplying 150 Amp constant current at 24 V. That would

  • charge the battery within 2 hours
  • give me 1.5 hours at full throttle (150 Amp from the battery, 150 Amp from the Generator) when battery is full
  • let me cruise at half throttle until I run out of Diesel when battery is down
  • let me do without propane gas using electric cooking instead

The smallest and lightest Generator I found is the Whisper Power M-GV 4 Piccolo Marine. It is a very small and light (70 kg) 3.5 kW permanent power AC Generator.

Whisperpower Piccolo Genverter

Whisperpower Piccolo Genverter

It has to be run in combination with the 24V 150 Amp DC power cube, transforming the AC power to 24 V DC with an efficiency of 94 %. The decision is not made yet. I still have to do some research because it might be better to install a DC Generator with more power in combination with more powerful motors to have a real diesel-electric prop system.

Some web links, tbc

Marine electric propulsion

Distributor of Winston LiFeYPo4 cells (Europe)

BMS Systems

Marine generators

A first retrospective

Hi all!

Vsitors of our blog

Visitors of our blog

When we started our blog, it was just for the purpose of letting our friends know what is happening. Now, barely four months in, we are overwhelmed by the fact that we are getting so much attention and encouragement from all over the world. So thank you all for your interest! If you have any ideas on how to improve our site or special interests, please comment. We would love to have a lively debate on our project!



As promised in an older post, here is a first summary of our catamaran building project.

I guess everyone was impressed about how quickly the catamaran took shape. Up to this stage we spent about 850 hours working on the boat. These are made up of the following:

  • joining the panels and cutting the tabs – 170 hours
  • preparing the building site – 20 hours
  • building the starboard hull – 270 hours
  • cabin top assembly – 60 hours
  • building the port hull – 200 hours
  • inserting the main bulkheads and the bridgedeck – 130 hours

This fast pace was based on several things: as the boat is being built at a professional boatyard, all the tools and facilities necessary for the building process are available. For example, the setup of the strongback only took minutes because there was one there already.  The help of Stephan, our friend and professional boatbuilder with building experience of over 25 catamarans cannot be rated highly enough. He sure saves us a lot of time and his crew helps us whenever they can. And as you can see, with the gained experience it was easily possible to increase the building speed from 270 hours for the first hull down to only 200 hours for the second hull. Despite the fact that something was slightly wrong with the measures of the hull length, all Duflex parts fitted quite well and did not need extensive readjustments. Between the long hull panels there were few gaps of up to 2 mm but we thought this was tolerable. The chines need to be filled ad taped over anyway. So all in all we are quite pleased and confident that we will be able to finish construction of the catamaran within the estimated 3000 hours. We´ll see!

The upcoming work will not show a lot of progress. The hull structure will be fortified by shelves, floorboards, steps, furniture etc. Everything is again precut from Duflex, for the furniture a lightweight foam core is used. Next all the open edges need to be decored and backfilled and after all, the surfaces have to be filled and sanded. This will take us quite a while. Besides we are working on the daggerboards. The original construction is made of foam/wood core, glassed over, filled and sanded. I wanted to try a more lightweight construction. My idea: make a mould out of 2 mm Perspex according to the desired profile. Then make 2 sandwich parts and glue them together with a carbon pole as leading edge and a sail batten as trailing edge. My first try looks quite promising.

50 cm trial of daggerboard

50 cm trial of daggerboard

I need to improve the profile, the surface didn´t come out of the mould as brilliant as desired and the final boards need a spine for what I intend to use some scrap Duflex.Dagger02

The sandwich layup from outside to inside: 260 g carbon fabric, 3 layers carbon uni tape along the deepest part of the profile, 400 g carbon biax, 4 mm Foam with bleeder holes, 400 g glass biax, vacuum bagged.


Catamaran building latest fotos

It´s amazing how with every step it looks more and more like a boat!


port side


last outer hull part


bridgedeck glued


Upper part of the hull side attached …






… and partly glued.





The two parts of the bridgedeck bonded with microfibres and taped, peelply on top. The bridgedeck is glued to the hulls with microfibres and microshere cove, not taped yet.



detail of sole/web assembly

detail of sole/web assembly

The small Boards made of scrap Duflex are taped with film from below. A cove is created from underneath with microspheres and after curing the boards can be easyly removed. The floorboard can now be glued on to these “dummy coves” and taped to the hull sides and bulkheads. This creates watertight buoyancy compartments.


Main bulkheads and bridgedeck installed

Next steps after aligning the two hulls was joining them with the four large bulkheads and install the bridgedeck. The question was – would they fit properly? We were a little doubtful since we found out that the two hulls are 8 cm short. How could this be? The only reason we could imagine was, that at the very beginning when joining the panels something must have gone wrong. Still don´t know what but I´ll keep you posted on that. So we were rather happy that the bulkheads fitted in by the millimeter.

Forward webs

Forward webs

Before we went for the bridgedeck – the largest and heaviest panel of all – we glued in the forward webs, so that the curved part of the bridgedeck would evenly pick up the bend. The spaces, formed by the webs are going to enclose things like fuel- and watertanks, Anchor, chain and windlass, Gas Bottles etc.

The bridgedeck also fitted in perfectly and after cutting saw kerfs crossways every 7 – 10 cm into the panel it was fairly easy to attach and glue the part to the existing structure.  The kerfs were filled with microspheres before the bending and after removing the excess this part was glassed over wet in wet.



Front view

Now it looks pretty much like a catamaran! I love it! The next steps will not show a lot of progress. There is lots of glueing and taping to do, webs and soles and other fortifications have to be installed, open panels need to be decored and filled an finally there is lots of filling and sanding to do.

At this point it might be time for a first resume. In the next couple of days I will share some thoughts about the building method, give you some figures on the time we worked on the catamaran and how we organized ourselves.

Cheers Chris042


Second hull turned

Hi all, no news for a long time. Partly because there didn´t happen anything, partly because the work on the second hull was not any different to the first one. Anyway, last week we were able to turn the second hull an do the alignment to join both and install the main bulkheads.



I must admit, when I first saw the two hulls in their final position I was quite impressed. 5.5 Meter from bow to bow is quite a distance for a 12 Meter Cat. Looking a little bit from above showed how narrow and sleek the hulls are.

The positioning of the two hulls is quite a complicated job to do. The waterline has to be level, the hulls must stand perfectly upright without twisting in the longitudinal axis, the two hulls must be absolutely parallel in the correct distance and have to line up lengthwise.

20141101_141715Sounds easy, problem is, if you make a correction here you will produce an error there. So what we did was placing and securing the starboard hull first and then did all the alignment on the port hull. Took some time but finally everything looked good. The next steps will be installing the four large bulkheads and the bridgedeck. I´ll keep you posted.

Captain to be

Captain to be

First hull turned!

As promised here the update of what we did before we went on our sailing trip. The cabin top chines  have been glued and taped so we were able to take away most of the templates.


Cabin top glued an taped






Bow, glued, glassed, filled and sanded

Bow, glued, glassed, filled and sanded

We turned hull No. 1 after the underwater section was ready filled an sanded. The plans did not give us precise instructions how to finish the bow. We made a microsphere cove from the inside, filled the outside and glassed it over with two layers 450 Biax.


laser leveling the bulkheads

laser leveling the bulkheads


After turning hull No. 1 we set up the bulkheads of the second hull on the strongback. Please excuse the bad quality of he picture but I wanted to show, how we aligned the parts with a laser level. This works quite well and efficient. Be aware, that on hull No. 2 Bhd 6a has an angulated position.

Cabin top assembled

cabin top

cabin top

cabin top assembly

cabin top assembly

After setting up the templates it was an easy job to assemble the cabin top. The chines are glued and now need to be taped over. The cutouts for the side windows will be made after the part has been connected to the hull.




Everything fits quite properly, no need for extensive adjustments!

Templates for the cabin Top


Starboard hull ready sanded

Here are 2 Pics of what we did last week. The glassed part of the hull is now ready filled and sanded, so we are able to turn the hull in the next couple of days.





Cabin top templantes


The other thing we did was setting up the MDF templates for the cabin top. These have also been CAD cut by VdL Composites. Our cat is taking shape ….