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Saturday, April 20, 2013

Construction is underway - Week 2

I haven't given any update on the actual construction of the boat.  So far they have been making great progress.  The "mold date" was back at the end of February.  The hull is constructed from the outside-in using a mold to form the outer surface.  Needless to say, the mold is quite large and consists of several sections that get prepped then bolted together.  The mold surface is highly polished since it will create the finished outer surface of the hull.

Below are the two forward halves of the mold, and you can see that they are not yet joined together.  The scaffolding hangs from the cross beams so none of it touches the inside surface.

Hull mold being prepped
 I only know a tiny bit about doing fiberglass work, but to get a mold like this to release from the boat, you need to wax the hell out of it.  Otherwise it will never separate from the fiberglass.  The guys in the hull are probably applying that release wax.

Here's a view from the stern of the boat.  You can see a blue area on the right inside the hull.  I think that's the seam for the extension to the mold that turns the N55 hull into an N60/63 hull.  Obviously the transom section has not yet been attached.

Hull mold viewed from the stern

The transom section gets prepped separately, probably to make access easier that trying to do it after attaching to the rest of the hull.  It appears to have already been gel coated, and the blue stuff I'm told is some sort of bonding agent.

Transom mold prepped and ready to attach

Below is the mold fully assembled

Fully assembled mold

Fully assembled mold
The outermost layer of a boat is gel coat, so that's the first thing that gets applied to the mold.  In the pictures below you can see the crew spraying it on.

Spraying on gel coat

Applying gel coat
After the gel coat is applied, the layers of fiberglass are laid down, slowly building up the thickness of the hull.  Once the hull skin is compete, a series of reinforcing ribs are glassed into place.  Otherwise you would just have a big floppy sheet of fiberglass.  Next, the lower bulkheads are glassed into place, further strengthening the hull, and ensuring it doesn't sag or distort once the mold is removed.

In the picture below, the foreground where the guys are working is the engine room.  Forward of that is the laundry/utility room. Next is tankage - a combination of the fresh water, grey water, and black water tanks.  And the forward most section is the "basement".

Fiberglass ribs and lower bulkheads installed

 And then the mold starts coming off.  The first to emerge is the transom.

Transom mold section removed

And the full hull emerges to see the light of day.  The picture below shows the aft-most bulkhead that separates the engine room from the lazarette

Hull emerges from the mold

 And the full hull viewed from the outside.

Hull out of the mold
On the surface there is no rhyme or reason to the manufacturing process.  I haven't been to the yard yet, but I'm told that one day the boat will be empty, and the next day there will be a person in every corner, closer, and crawl space.  We've dubbed it "swarm manufacturing".  You never know when it will happen, but when the swarm descends, lots gets done is a very short time.

Over the two weeks that ensued after the boat came out of the mold, the swarm appears to have been in full force.  In the picture below which is facing the bow, you can see what I mean.  The two people in the foreground on either side of the boat are crouched on the two main fuel tanks  The tanks (all of them) are fiberglass and get built right into the main structure.  The space between the tanks is the engine room.  The red thing a bit forward and on the right is the top of one of the forward fuel tanks.  Ahead of that you can see some blue and some black.  Those are the fresh water and black water tanks respectively.  Furthest forward where there is another worker is the bulkhead separating the master stateroom from the guest stateroom.

View forward
Below is a view aft with the blue (and a little black) fresh, grey, and black water tanks in the foreground.  Moving aft you can see the red top of the forward fuel tanks.  Beyond that is the engine room with the two main fuel tanks on either side with the workers on top of them.

View aft

And last, here is an overview of the whole thing.

All this represents about 6 weeks of work.  It seems good to me and PAE thinks it's moving very fast too, but there is no construction schedule to benchmark it against.  I guess that's the nature of swarm manufacturing.  My hope is that the swarm will continue, and there is reason to believe that it will.  The yard is just finishing the very first N120, and it has been consuming a lot of resources which hopefully can help move my boat along.

Saturday, April 13, 2013

A Plan for Fuel Management

A few posts ago I talked about fuel management, mostly focused on the need to have fuel gauges on all 4 tanks.  The other issue I was trying to sort out at the time was the best strategy around which tanks to draw down when, and when to move fuel around between tanks.  Now I have a plan, subject to change of course, and unverifiable until I actually have the boat.  But here it is anyway.  It should allow someone, somewhere to look back and say "I told you so"....

As a recap, the N60 has 4 storage tanks and 1 "day tank".  The two main storage tanks are 1000 gal each, with two forward tanks of 150 gal each.  The day tank is about 30 gal.  All operating fuel is drawn from the day tank, and excess is returned to the day tank.  Fuel can get from the storage tanks to the day tank in one of two ways; via a filtered fuel transfer pump, or via gravity flow.

As I understand the concept of a day tank, it is supposed to be an isolated tank filled with enough filtered and clean "known-good" fuel to run the boat for a day, hence the name "day tank".  You fill up the day tank once a day, and do it through a filtered transfer pump, thereby ensuring that only clean fuel is ever in there.  It's a great concept, and a good way to ensure that stirred up crap in the bottom of a storage tank doesn't find its way to your engine.  I think every book that I've read about a power boat disaster involves heavy seas that stir up crap in an old fuel tank, plugs filters, and kills the engine.  Once the engine is lost, bad turns to worse, and there is something to write a book about.

The trouble with the N60 (and a bunch of other models) is that the day tank only holds enough fuel for roughly 2-5 hrs depending on how fast you are going.  Rather than filling daily, you need to fill it multiple times per day.  And, despite its many benefits, day tanks have a down side to them.  If you let them run dry, the engine will stop, and restarting a diesel that has run dry is a royal pain in the butt because all the air needs to be bled out of the system.  This can easily be a 30-60 minute process.  I love the concept of a day tank, but it's just too small on the Nordhavn to accomplish its goal.

There is another issue with the small day tank on the Nordhavn.  Heat.  And the problem is worse with the transition to modern, high pressure diesel engines.  Diesels draw fuel from the tank, pump it up to some pressure, inject what's needed into the cylinders to power the load, and return the excess back to the tank.  This circular flow is not only a technique to maintain a predictable injection pressure, but serves to cool the pump and injection system by carrying heat away in the excess fuel flow.  Common rail engines (high pressure fuel systems) generate a lot of heat when the they pump the fuel up to that high pressure.  The return fuel can be well over 150 deg.  All that hot fuel goes into the day tank and circulates back to the engine, reheating it over and over again, and radiating heat into the engine room.  A larger body of fuel would heat more slowly, and a larger body of fuel has more surface area to dissipate the heat, preferably through the hull to the surrounding sea water.  The small day tank accomplishes neither of these things.

I've talked to a number of owners, and the most common approach to fuel management seems to be:

- Keep the small forward tanks empty unless you are planning a passage.

- Draw fuel from the large tanks via gravity feed, alternating port and starboard at some interval to keep the boat trim.

- Fill the forward tanks in advance of a planned passage, and once you are certain the main tanks are down enough, pump the entire contents of the forward tanks into the main tanks.

This works, but in my opinion completely defeats the goals of a day tank, and leaves the boat exposed to stirring up of crap in the main tanks.

So what's a boater to do?  This is what left me puzzling after my last post on the topic of fuel management, but I think I've found a solution.

- Rather than use the small forward tanks only for extra storage for long passages, I'm planning to use them constantly as a big day tank.  Instead of a 30 gal day tank, I'll have 300 gal, and there will be a gauge on it so I know when I'm getting low.

- The forward tanks will flow via gravity to the real day tank, and be drawn off from there for the engine and generator.

- The forward tanks will ONLY be filled via the filtered transfer pump.  They will never be filled via the deck fillers.  Prior to fueling, I'll transfer fuel from the main tanks to top up the forward tanks.  Then I'll fill the main tanks from dockside.  If I happen to be down so low that I can't pre-fill the forward tanks, I'll just transfer fuel while I'm filling.

- While underway, I'll always move fuel from the main tanks into the forward tanks for use, running through the transfer filter on the way.  That will ensure isolation of any crud that develops in the main tanks.

- To mitigate the heat build up issue, I can return the excess fuel to the forward tanks rather than the day tank, slowing the heat build up, and providing better dissipation through the bigger forward tanks.

- Right now I'm thinking that I will just open the valves for both forward tanks in parallel, allowing fuel draw from both.  This could lead to some listing, but I figure that I'll just compensate for trim by controlling fuel in the main tanks.

I think this will work, and restore many of the virtues of a day tank, and eliminate the problems associated with a day tank that's just too small.  Time will either confirm or contradict this theory, and hopefully the unknowns won't bite me in the ass.  For example, I'm assuming that keeping the forward tanks full won't negatively impact the fore-aft trim of the boat, or it's ride in various seas, but I won't know until I actually try it.

Water Makers

Having a good water maker is an import component of a cruising boat.  In various parts of the world, shore-side water is of questionable quality, very expensive, or not available at all.

Poor quality water is probably the worst scenario.  Top up you tank with it, and not only have you taken on bad water, but you have contaminated all the rest of the water you had before.  Now you are really stuck.

Cost is another issue.  A water maker isn't cheap to install, and isn't cheap to operate, but it's cheaper than buying water in some areas.

And then of course there is the luxury of having plenty of water and not having to worry about it.  I like that.  It's great not having to ration water when you are on a long voyage, be able to shower as much as you want, and do laundry as much as needed.  The trap, however, is that you also need to have a plan if the water maker fails.  The trick is to keep the tank topped up, or at least know what minimum amount you need to reach an external source on rationed consumption.  For example, if you can get by on 15 gal per day and have a 20 day voyage, you don't want to let your tank get below 300 gal.

I thought the water maker selection for N6062 would be easy, but not so.  The N60 includes a standard "option" for a 600 gal per day Village Marine water maker, and most Nordhavns are equipped with that or a similar model.  That sounds like a well worn, well proven path, so I just checked off the box next to the option.

Our current boat has a Spectra water maker.  I selected that one for two primary reasons.

First it's DC powered which means we can run it while the boat is underway without the generator.  Water makers like clear, clean salt water to work on.  That's abundant out in open water, and scarce in harbors and anchorages.  As a result, the best time to make water is while you are out in open water and have the engine running providing a source of power.

Second, the Spectra comes with a automatic control and flushing system.  The control system operates all the pumps and valves, monitors the salinity level of the produced water, dumps it overboard until the salinity drops below a certain level, then produces clean fresh water for as long as you tell it to.  When it's done, it automatically flushes the system with fresh water from your tank.  This is an important step to prevent the growth of biologic matter in the sea water still in the system, and extend the life of the expensive filter membrane.

In fact, the fresh water flushing is so important that you are supposed to do it once a week if the maker is not used, and the spectra does this automatically as well.  After you make water, it kicks into this maintenance mode where it counts down the days, does a flush for a few minutes, then starts counting down all over again.  It really takes the hassle of of owning and operating a water maker, and is particularly useful if you are away from the boat for more than a few days, which we typically are.  Last summer, we were up in the New York and Canadian rivers for nearly 2 months and the water maker just took care of itself until we returned to salt water and were ready to put it back to work.

All this background is a log way of saying that this auto flush feature was the full extend of my due diligence on the Village Marine unit supplied in the Nordhavn, and sure enough, it has such a feature.  Well, sort of, it turns out.

As I searched around on the net reading about people's experiences, and talking to Village Marine owners, I came across a few serious gotchas.

The biggest is that the Village Marine is an AC powered system.  At first I didn't think this mattered.  It's a much higher capacity system that the Spectra that I currently have, so I figured I'd just run the generator, make water, do laundry, etc.  Because the maker can crank out a bunch of water is a short time, the generator run time would be limited.  And I figured that if we are leaving the boat for an extended time in a marina, it would be on shore power so the flush process would continue to work.

But the part I overlooked is that the whole control system is AC powered, and when AC power is interrupted, the control system forgets what it's doing and needs to be restarted.  That means that while cruising, when AC power is coming and going all the time, the system will keep resetting to zero, completely defeating the countdown and auto flush feature.  So even though it has an auto flush feature, in practice I'd have to count down the days myself and manually start a flush when needed.  That sucks.  And the same problem exists while on shore power.  Anytime the power blinks, which is regularly in a marina, the auto flush feature would stop.  In essence, the Village Marine does not have auto flush, even though it's listed as a feature.  It simply doesn't work in any useful way.  The only way to make it work would be on a boat that has 24x7 generator power (not me), or to install a dedicated inverter just to power the water maker.

So, back to the drawing board on water makers.  I know the Spectra product and know it works in a sensible way.  One of the great misconceptions about water makers is the mistaken belief that DC water makers are very low output, and that you need an AC unit to make water in any reasonable quantity.  It is true that many DC units are very low power and very low production rate, designed for use on sail boats where power is scarce.  And it is also true that very large water makers for mega yachts and cruise liners require so much power that AC makes the most sense.  But in the range required for anything is the 40' to 100' range, there are DC models that match the performance of the AC models in every way.  And in many cases, their overall efficiency in terms of kwh consumed per gallon of water produced is much better.  For example, the standard issue Village Marine used by Nordhaven is either 600 or 800 gallons per day output.  Spectra offers a DC model in three flavors of 360, 720, and 1000 gal per day.  Seems the same to me.

So, after some haggling over price, I've deleted the Village Marine and replaced it with a Spectra Newport Mk II 1000 gallon per day DC powered water maker.  That will meet our needs much better than the Village Marine.