Hello from Berlin, Germany

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Heimfried
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Joined: Sat Nov 23, 2019 4:49 pm

Hello from Berlin, Germany

Post by Heimfried »

Hello everyone,

my name is Günter and I live in Berlin, Germany. Since 2017 I’m building a boat: Cabin-Katamaran 6.3 m (LOA), ply on frame, Bernd Kohler design “ECO62”. She will be driven by electric (outboard) motors, as far solar assisted as possible. I’m interested in measurements of some values like drag, power efficiency of propelling systems.

After I learned about boat hydrostatics I did a website to calculate some values of an example boat and visualize a bit of her behavior if loaded or loads are shifted.

Gruß, Günter

John Perry
AYRS Chairman
Posts: 81
Joined: Tue Nov 08, 2016 6:39 pm

Re: Hello from Berlin, Germany

Post by John Perry »

Welcome Günter, - look forward to hearing more about your boat building project and perhaps seeing some pictures. I have not been to Berlin but I understand that there are many navigable rivers, canals and lakes in the area and I imagine that these would be ideal for leasurely exploration with a mobile houseboat such as you are building. Your website sounds interesting, do you have a URL to share?

I guess that the 'ECO62', if powered by low powered electric outboard(s) will operate as a 'displacement hull' with most of the drag being skin friction which does make the drag relatively easy to calculate by traditional methods - as you probably know the Michlet software is one way to do this using the 'ITCC line' as the basis for determining a skin friction coefficient. Electric propulsion with solar panels, and presumably a battery (mabe LiFePO4 ?) for when the sun is not shining seems to make sense for your kind of project and I see that the design has a large rectangular flat roof which looks to be ideal for mounting an array of solar pannels. I recall that some years ago I saw a similar plywood houseboat design at the Beale Park boat show and this actually used pedal power with two sets of pedals, another possiblity, at least for auxiliary propulsion.

Heimfried
Quiet member
Posts: 12
Joined: Sat Nov 23, 2019 4:49 pm

Re: Hello from Berlin, Germany

Post by Heimfried »

Hello John,
thank you for your welcome. Regarding my boat building project: I was starting in a former garage which was just large enough to allow the build of one semi hull at a time. So I had to erect a tent (4 m by 8 m) in my garden to accomodate the further assembling of the boat. I'm reporting about progress, experiences and thoughts in this thread https://www.boote-forum.de/showthread.p ... ost4995890. Sorry, it's in German and very long, but you will find a lot of pictures, which could cause questions that I would appreciate. Last autumn we (many helpers and me) were flipping the brigde deck unit with the semi hulls and now I'm building the cabin.

Regarding my hydrostatics website the URL is http://www.bootsphysik.de/. Top right you will find a button "English". A lot of buttons marked "i" can be clickes to display information. The displayed graphs are simple but the math is not. Unfortunately there is at moment only one hull to play with. It is because a description of a hull consitsts of about 90,000 numbers (array).

The pedal drivben plywood house boat you have seen could have been a design of the late Phil Thiel (Seattle). His plans (Escargot, FriendShip, Ark) are in my desk also.

ImageImageImage

John Perry
AYRS Chairman
Posts: 81
Joined: Tue Nov 08, 2016 6:39 pm

Re: Hello from Berlin, Germany

Post by John Perry »

Good project - nice to have it documented on-line. Looking at your pictures at boote-forum.de I was interested to see the way you are making the roof of the cabin. Good to have the airspace between the upperside of the expanded polystyrene and the innerside of the outer deck skin and I guess that you are planning to have this space ventilated to avoid a build up of humidity in that space, which could cause condensation against the inside of the outer skin. But if the boat is not going to be lived in for long periods perhaps this is less critical.

Heimfried
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Joined: Sat Nov 23, 2019 4:49 pm

Re: Hello from Berlin, Germany

Post by Heimfried »

Until now I don't think a ventilation of the space between the plywood panels is necessary. For sure there will be some condensation in cold nights. But it will evaporate once the sun shines on that deck. As I work on boat building in a tent and watch temperature and humidity and log their values automatically, I know that even a cloudy sky heats up the roof of the tent quickly and remarkably.
A problem would be any enrichment of humidity in that closed space. In theory the thin (4 mm) panels of okumé marine ply coated on both sides with epoxy resin should not allow water vapour to go thrue. We will see.
This is another field I prepared a webpage for calculations and showing Mollier h,x diagrams. http://www.hygrothermik.de/ .
(Sorry, in German only.)

John Perry
AYRS Chairman
Posts: 81
Joined: Tue Nov 08, 2016 6:39 pm

Re: Hello from Berlin, Germany

Post by John Perry »

I just thought it might be a problem if the boat is inhabited for long periods in colder weather, which perhaps is unlikely. As you say, the epoxy coating on the panels should be pretty well impermeable to the transmission of moisture. However, I remember being briefly involved in some study, I think at the Building Research Establishment in the UK, in which they were measuring the transmission of moisture through various actual building structures by adding a slightly radioactive gas to building spaces and measuring the decay of radiation inside the buildings. It was quite surprising how much the air inside the building exchanged with the air outside even though all windows and ventilators were closed - a typical building construction may look hermetically sealed but often it is not. In your case you may have an epoxy coated panel on the inside but maybe you will be piercing that panel with holes for light fittings, cables etc. Generally, if you have insulation inside any kind of cavity wall I think it is good practice to minimise the transmission of moisture through the inside skin and also leave a small space between any insulation material and the outside panel, that space being ventilated to the outside atmosphere. That way you still get most of the thermal benefit of an insulated cavity wall while avoiding the possibility of moisture condensing on the inside of the outer panel where it may cause all kinds of problems and may eventually saturate the insulation.

Sorry, all this is digressing from boat building! Although it may be relevant to those building steel or aluminium boats with insulation inside.

Heimfried
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Posts: 12
Joined: Sat Nov 23, 2019 4:49 pm

Re: Hello from Berlin, Germany

Post by Heimfried »

For sure I will be piercing the roof at a number of points. Knowing the dangers I will look closely after this points and sealing them. Having studied physics many years ago I'm a little obsessed with measuring and I own some equipment to measure temperature and humidity and use it regularly. So there will be e.g. the values of temperature, humidity and CO2 content of the inside air of the cabin logged and evaluated.
The attached curves coming from my "boat yard", a former garage the peaks are from CO2 concentration and checking the slope to the right of the peak I would be able to calculate the air excange (inside - outside).
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