Hull almost finished!

Hi all!

Sorry for not updating this blog more regularly. It is more time consuming than I thought and we have a lot of other things going on besides our building project. Julia is expecting again :-), due date is mid of September. And I am moving with my primary business ( also September :-() which is pretty stressful at the time.



Anyway. there are some new photos uploaded to the gallery, so have a look. It is incredible to see the real dimensions of the cat now. From time to time I thought the 1360 would have been better but now I am definitely convinced Рthis is the right boat! We changed our mind regarding the tiller steering. Though I like the idea to be linked to the boat in a direct way I could not see where to sit safely as a helmsman with good sight and in reach of the sheets. So we decided to close the left window of the main bulkhead and install a wheel at that place. See the gallery for more explanations.

The next steps will be installing the remaining interior (galley, salon seating), the daggerboard cases, the electric drives and the rudders. Exciting!!!!

One more thing ūüėČ …. We get a lot of requests of people wanting to visit us. We perfectly understand your desire but for us it is hard to make all the arrangements, especially in the next couple of months. What we might do is selecting a weekend lets say end of¬†October and do the sightseeing in a more compact way. Anyone who is interested, please let me know.

All the best and happy summer


Forward section

Here are two photos of the forward section.

forward section


The space where Roman is working is going to be the diesel tank. It can hold apx. 200 liter and will be laminated directly into the structure. The opposite side will take the water tank, it will hold about 400 liter. To prevent sloshing we need to install 2 or 3 baffels with openings at the bottom.

forward section

The frame shows the size of the hatch. It is fairly large but it makes all four compartments accessible with only one hatch. Stefan used to install these on his own designs and they work very well. The hinges are going to be on the side, so you open it from the middle.  A gasket makes it watertight. With the anchor, chain and ropes and stuff the compartments still need a drain.

cabin top

We¬īre not far from installing the cabin top :-))

The electric system on our Arrow 1200

There seems to be a lot of interest in our plans to power our catamaran with an electric propulsion system. And of course there are a lot of critics with proven points. If Lagoon had to replace all their hybrid systems in their charter fleet because of never ending problems why should we do better. Lagoon, probably the biggest catamaran shipyard, if they can¬īt do who else? Well, that was back in 2006, I don¬īt know the system of the Lagoon hybrids but I know that diesel-electric propulsion works. What is different to 2006? I think the key is the advance in battery technology, namely the Litium Iron Batteries. And of course the improvement in efficiency of all components, Generator, Inverter, Motor, shaft and prop makes the whole system work better than 9 years ago. So far in theory. We made our decision, for a practical review you¬īll have to wait ūüėČ

First of all, what are our needs. With twin diesels I would have decided for 2 X 15-20 hp, e.g. the Sole mini 17 or any other 2 cylinder diesel engine (Volvo, Nanni, Lombardini, Yanmar etc.) But what does that mean for electric motors. Why can we choose them smaller in terms of power and how small can they be?¬†Basically, we are able to turn a prop of same size with a less powerful electric motor because of immediate and evenly distributed torque in¬†the whole range of rpm. Diesel motors supply torque very unevenly, especially at low rpms there is a lack of it. That makes it hard to match the prop in terms of diameter and pitch perfectly to the motor.¬†To compensate that yacht diesels are usually a number to big for the prop (and the yacht). That makes them speed up fast but the load at higher rpms is actually to low. In addition¬†there is loss due to¬†friction of a saildrive or a gearbox. Because of the evenly distributed torque it is easier to match a prop to an electric motor. Greenstar uses a slow rotating disk motor without the need for a downshift. The motor axis is connected straight to the shaft. A low friction bearing is used for the shaft. All in all the system should be a lot more efficient than a diesel Motor. Is the chosen power enough? For now I have to rely on the calculations Greenstar did for our boat. The Greenstar 20D System nominally¬†has only one third of the desired diesel power but if you look at the facts mentioned above it should be enough. It¬†drives two 14×8 Flexofold props. Both motors weigh 28 kg (without shaft and props).

Greenstar 20D

Greenstar 20D


So we got the motors, what electrical power do we need? The Motors run on 24 V DC which is nice, because I don¬īt have to change the voltage for the boats DC grid. At full throttle each motor draws about 150 Amps, makes a maximum of 300 Amps which need to be delivered at least for a short period of time. Half throttle, which is supposed to be cruising speed (flat water, no wind, 6 knots, the Arrow with low resistance hulls maybe¬†a little faster) draws about 50 Amps each Motor. We want to be autonomous, so we need a source that delivers the apx. 100 Amps for cruising speed continuously, even when the battery is getting low. At first sight the Whisperpower M-GV 4 Piccolo marine system we chose seems complicated but actually it is pretty smart.

First of all there is the Motor/Generator. A 306 ccm one cylinder 5.8 hp diesel motor is turning a permanent magnet alternator at 2800 – 3600 rpm. The Motor/Alternator is fully capsulated (quiet 65 dBA at 1 m distance), fuel consumption is 0.8 – 1.2 l / hour, weight is 69 kg, it has electric start (need for an additional 12 V 55 Ah lead battery, 18 kg) and remote control. It has a unique exhaust system where fumes and cooling water are separated with the outlets for fumes above and for the cooling water below the waterline to reduce exhaust noises. All in all it should be a very quiet system. The alternator produces electricity with 94 % efficiency (using the torque of the motor ideally) but in voltage and frequency not suitable for our needs (up to 400 V at 500 Hz).

Whisperpower Piccolo Genverter

Whisperpower M-GV4 Piccolo with PMG module

To change that the WP PMG module (7 kg) is connected next in line to get pure sine wave 230 V / 20.5 Amp AC (3.5 kw continuous/4.0 kw max/8.0 kw for 5 sec. max power 95 % efficiency). It also has a 12 V/7 Amp output to recharge the starter battery.

Next in line is the WPC 24/3500-90 sinewave inverter/charger (28 kg). The numbers say it charges at 24 V/90 Amp max and inverts from 24 VDC to 230 VAC with 3.5 kw max. The efficiency is 94 %. You can not tell where is in or out. On the one side you  can connect a) the Generators 230 VAC and b) 230 VAC shore power, on the other side you connect the 24 V battery bank. The basic idea is that the WPC delivers the power where it is needed automatically. It is fully programmable with loads of parameters and does for example

  • start the Generator automatically when the battery¬†drops below a certain programmed voltage (manual start possible as well)
  • charges the battery with up to 90 Amp according to programmed parameters
  • automatically inverts from 24 VDC to 230 VAC when shore power or generator power or both together are insufficient for whatever you need it for.
  • simply delivers 24 VAC when it is needed here or 230 VAC when it is needed there, provided the battery is not low.
WPC 24/3500-90

Whisperpower WPS


This system alone should be able to power our Arrow 1200 up to almost cruising speed (90 Amp output). The Generator is then loaded with 2.3 kW. There is still 1.2 kW power left to install another 30-40 Amp with an additional charger if needed. But of course we need a buffer, a battery suitable for our system. It must a) be able to deliver up to 300 Amp DC at 24 V and b) be able to supply power to go full throttle for some time, let¬īs say at least half an hour. When you see the figures it is pretty clear, that even deep cycle AGM lead acid batteries are not suitable. To go 30 min at full throttle you need 150 Ah. Considered not to discharge a lead battery more than 50 % you need a battery bank 300 Ah/24 V – which weighs 180 kg – nonwithstanding that a current of 300 Amp will destroy the battery within a few cycles. The answer is Lithium, in our case Lithium Iron because of the minimal fire hazard. Unlike Lithium Ion (Tesla) the Lithium Iron batteries contain to little Lithium for a severe fire or explosion. Nonetheless you have to be careful and never ever short circuit these batteries. The nominal voltage of the batteries is 13.6 VDC, not dropping even at high discharge rates. Greenstar sell their own range of Lithium Iron batteries which are basically relabeled Super B¬īs.

Super B 12V160Ah

Super B 12V160Ah

Now what is important about Lithium Iron batteries. Unlike lead acid batteries they do not need to be fully charged and discharged every time but it is crucial to never overcharge or discharge them. Once deep discharged and they are dead! This is valid for the single cell of the battery, e.g. a nominal 12 VDC Super B is made of 4 single cells and their voltage must not get out of a range of 2.5 V to 3.65 V. Lithium Iron batteries out of the box like the Super B¬īs have an integrated BMS (battery management system) which monitors these parameters, balances the individual cells and cuts off either the charging current or the discharging load to prevent the battery from damage. The parameters that influence the cycle life (No of cycles of discharging/charging) are a) the DOD, depth of discharge in percent and b) the charging/discharging current. To get as much as possible out of your expensive batteries the DOD should not exceed 80 % of the nominal capacity. The charging current should not exceed 1C ¬†(means 1 x capacity, e.g. 100 Ah battery, max charging current 100 Amp) and discharging current should not go further than 3 C. Less is always better. The maximum size for a Super B LiFePO4 battery is 12 V/160 Ah. We need at least 2 of them connected in line for 24 VDC. Charging them with 90 Amps equals 0.56 C which is OK. Discharging them with 300 Amps (Full throttle, no Generator running) equals 1.87 C- not perfect but acceptable. 80 % DOD are roughly 130 Ah. For that we get 25 min full throttle only on battery or 75 min at cruising speed. These numbers increase when the generator is running. All in all it is not perfect! The biggest¬†advantage is that I buy from one dealer/distributor which is of course better in case of a failure and guarantee. Still, for the same amount of money I can buy an individually configured battery system with BMS made of Winston LiFeYPO4 single cells with 400 Ah capacity.

Winston 300 Ah LiFeYPo4 cell

Winston 300 Ah LiFeYPo4 cell

The advantages are obvious. Lower charging/discharging rates, lower DOD, resulting in higher cycle life. The range without the help of the generator is extended (about 3 times as long). In addition they work at a slightly higher voltage. The weight: 2 Super B 12V160Ah 60 kg, individual bank of 8 Winston LYP400 with BMS 110 kg. If I reduce to 300 Ah it is 80 kg.

Bottom line:

We want to keep our catamaran light which is crucial for a good sailing performance. If we sum up all the weights (regardless the shafts and props since they are the same) we have for diesels

  • 2 diesel engines with gearbox and motor mount – 220 kg
  • 2 55 Ah starter batteries – 36 kg
  • cabling, wiring, exhaust etc. 20 kg
  • about 280 kg in total

Electric installation

  • 2 electric motors with motor mount – 35 kg
  • Generator M-GV4 pcc. with PMG – 76 kg
  • 55 Ah starter battery – 18 kg
  • WPC Charger/Inverter – 28 kg
  • cabling, wiring, exhaust 15 kg
  • roundbout 180 kg

The weight for the battery is about the same, e.g. 300 Ah Winston indiv. batt. bank 80 kg, 300 Ah 12 V AGM 90 kg. The diesel tank remains the same but we might not always fill it up to the top with the small consumption of the generator. If electric cooking works we spare the weight and the hazard of a gas installation. A total saving of about 100 kg should be possible.

The initial costs for the installation are higher than with twin diesels but the follow up costs should be a lot lower. We can produce electricity ourselves by wind, sun and – recuperation. From 5 knots boatspeed upwards the motors can produce electrical energy. With this it even might be possible not to run the generator at all.

Again, so far in theory. We are happy with our decision but only time will tell if it works out … The delivery of the parts start beginning of May, it¬īs going to be an interesting summer ūüėČ


Update coming soon ….

Hey everyone,

I am really sorry for not keeping you updated, but at the moment I am lying in bed here in a hospital, recovering from my tonsillectomy just 2 days ago. I actually thought it would be worse but still, I sure need a couple of days to get back on my feet again. So I guess from Easter on I will be able to post on a more regular basis with more details on the building and the fitting out of our Arrow 1200-

So long Chris

What¬īs 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 Рeven 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¬ī. 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 Рthis 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 Р2.8 V which equals a DOD of 80%. The producer claims a cycle life of 5000 charge/discharge cycles (Mastervolt Р2000). 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¬īt do only with the battery – we need a range extender in form of a Diesel Generator.

To keep the advantages of the system Рsmall and light РI 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¬īll 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¬īt 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.