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Tuesday, December 4, 2018

Nordhavn 68 Build Underway

It's hard to believe that it's been a full year since we signed the contract to build Nordhavn 6837.  And a full year and a half since we decided to move forward with the project.  In that time we moved off our Nordhavn 60, sold it, refined the specifications for the 68, did some travel to celebrate our 30th anniversary, and caught up on a number of other projects.  Oh yes, and our 68 build started....

I never tire of seeing these boats transform from barrels of resin and bales of fiberglass into amazing boats.  So let's get started.  In late June 2018, the mold freed up and our boat started.

You probably thought I was kidding about barrels of resin and bales of fiberglass, but I wasn't.  Here they are, ready for mixing.

In the beginning, there was resin.

And there were bales of fiberglass

The next step is the setup and preparation of the mold.  The hull gets built from the outside in, with the outermost surface of the boat (the gel coat) laid up against the red surface of the mold that you can see below.

Hull mold, currently separated to access the keel.

Once the mold has been prepped and all the plugs are in place, the gel coat gets sprayed on forming the outermost layer of the boat.  Colors always look funny in florescent light, but the hull is the standard Nordhavn light gray.  All the scaffolding is suspended from above so nothing is in contact with the mold surface.

First on is the gel coat.

Next, the first layers of fiberglass go on.  These are done with the mold halves initially separated so there is access to the deeper parts of the keel for building the finished surface.  Then the halves are joined, and all the structural elements are laminated and built up.
First finished layers of fiberglass laid in.

 Meanwhile, tanks are being built in other parts of the yard.  I think these are the two water tanks.

Water tanks, I think.

For similar access reasons, the transom is laid up separately, then this section is joined with the rest of the mold.

Transom

Here is the hull with ever increasing lamination to build strength.   Nordhavns weigh anywhere from 50% to 100% more than other similar size boats, and this is why.  Strong, strong, strong.

Progressive laminations

Once the lamination is complete, a whole grid of ribbing and stringers are laminated in to add stiffness and further strength to the whole structure.  In the picture below you can see forms in place, and in the next picture you can see the full structure.

Ribbing forms

Ribbing complete

Once all the ribbing is in place, all the hull bulkheads are fit and laminated into place.  These add additional structural support, and help lock in the form of the hull before it is released from the mold and has to support itself.

Bulkheads laminated in place

A cradle is fabricated for every boat, and will stay with the boat all the way through shipping to the US
Cradle

Finally, it's time to release the hull from the mold.  Below is the fully assembled mold.

Fully assembled mold

First, the transom mold comes off exposing the hull's derriere.

Transom section of mold removed
 The hull is then supported by overhead gantries from temporary attachment points inside the hull.  Then the hull halves are separated and peeled back.

One half separated

And now both halves are separated.

Released hull

Finally the released hull is placed in its cradle where it will live until final unloading in the US.

Hull released and in cradle
For some real fun, check out this video that Ta Shing made of the hull release.


Saturday, December 1, 2018

Testing BMS Voltage Sensing

In this article on building a BMS, one comment I received cautioned about "phantom" voltage reasons if one of the battery cell voltage sense wires broke, or a fuse blew.  His experience was that the phantom voltage was essentially the average of the two adjacent cells, and could appear to be a healthy battery when it's not.  That would be a problem, so I wanted to test it out.

Thankfully, my BMS doesn't exhibit that problem.  The three pictures below show the cell voltage readings, first with the sensor wires for cell #4 connected correctly, and then with each of the sense wires disconnected.

All sensor wires connected, voltage read correctly

Positive sense wire disconnected from cell #4.  Cell alarms and shows "phantom voltage of 17mv.

Negative Sense wire disconnected from cell #4.  Cell alarms and shows phantom voltage of 17mv
There is a small phantom voltage, but no where near enough to not realize there is a problem.

I think this all comes down to the internal circuitry of the sensing device, and in particular how much impedance there is between channels.