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Old 25-05-2016, 21:52   #781
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Re: Bestevaer 49ST

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Thou ist stirring up fecal matter. Tsk. Tsk.
I tell you Mr A... it is so good that if I ever have an excess of folding, I would consider a dual hulled vessel in Aluminium.
Really impressed with every part of the process so far..
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Old 25-05-2016, 23:01   #782
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Re: Bestevaer 49ST

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Work is proceeding rapidly on the boat. Each day we visit there is something new to "ooh" and "ah" over . Yesterday it was the bow thruster tube.

We are heading back to our current boat on the weekend for a week of antifouling before splashing for the summer, so I will try and add a few more images before we leave. New photos will probably be arriving next week .

This is the day fuel tank (upside down). The plan for the fuel system is pretty much as was sketched back in post #359.

The capacity is around 60 litres. It has a large inspection port, sump, and can also be filled manually from the top:


Fuel system:

Thought all makes sense, and then.... "day tank"???

I'm trying to understand the logic behind that? Is there an issue with pressures? There is no fuel pump after the day tank, and gravity feed doesn't make sense on a diesel.
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Old 25-05-2016, 23:30   #783
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Re: Bestevaer 49ST

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Thought all makes sense, and then.... "day tank"???

I'm trying to understand the logic behind that? Is there an issue with pressures? There is no fuel pump after the day tank, and gravity feed doesn't make sense on a diesel.
Why doesn't gravity feed make sense? It eliminates a pump (less to go wrong) and means an easy fill of the engine fuel filter after changing it. It will also feed the Refleks heater without the need for a pump.

The day tank is usful for several reasons:
- The interior can easily be kept spotlessly clean.
- With fuel filters before and after it ensures pristine fuel (contaminated fuel is one of the biggest reason for engine problems).
- It can easily be filled manually if for some reason the tanks need to be bipassed.
- If there are engine problems troubleshooting is simpler, as the fuel supply is dead simple and therefore easy to check.

Edited to add: I forgot to add the simple fuel supply to the engine means not only is it easy to check, but there is clearly less to go wrong .

SWL
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Old 26-05-2016, 00:54   #784
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Re: Bestevaer 49ST

Re header tanks.. I found out the other day from fellow CFer 'Shakey Doug' (a very knowledgable engineer) on here that some injector pumps prefer a reasonble head of pressure to work at optimum efficiency, so even with the header tank, unless mounted about 6 foot above the engine, a boost pump might still be needed with some engines.

In any case there should probably still be the on engine lift pump to boost the pressure, so it shouldn't be an issue unless the engine doesnt have this and has the sensitive type of injector pump.

http://www.cruisersforum.com/forums/....php?p=2116058
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Old 26-05-2016, 01:26   #785
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Re: Bestevaer 49ST

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Originally Posted by Seaworthy Lass View Post
Why doesn't gravity feed make sense? It eliminates a pump (less to go wrong) and means an easy fill of the engine fuel filter after changing it. It will also feed the Refleks heater without the need for a pump.

The day tank is usful for several reasons:
- The interior can easily be kept spotlessly clean.
- With fuel filters before and after it ensures pristine fuel (contaminated fuel is one of the biggest reason for engine problems).
- It can easily be filled manually if for some reason the tanks need to be bipassed.
- If there are engine problems troubleshooting is simpler, as the fuel supply is dead simple and therefore easy to check.

Edited to add: I forgot to add the simple fuel supply to the engine means not only is it easy to check, but there is clearly less to go wrong .

SWL
Hmmm, I was under the impression that diesel injectors need a certain amount of pressure, and that gravity feed won't do it. I'd have to talk to my mechanic friends, so wouldn't swear on it, but I'm sure that has been a discussion item.

I know you guys have put a LOT of thought into this boat, so this is a learning opportunity.

EDIT:

I see Snowpetrel is making the same point.
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Old 26-05-2016, 03:57   #786
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Re: Bestevaer 49ST

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I think (from memory) stiffness goes up to the square of the plate thickness, so doubling the plate from 4mm to 8mm gives four times the stiffness for only twice the weight.
Opps my memory was wrong, sorry, hat tip to Uncivilised for jogging my memory on a different thread.

Stiffness is actually thickness^3 so doubling the thickness from 4mm to 8mm gives 8 times the stiffness.
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Old 26-05-2016, 05:12   #787
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Re: Bestevaer 49ST

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A few hull plates have now been bent into shape.

The rolling process:




A completed plate with capping added:

That looks tricky. What method do they use to get the profiles right? Rack of the eye or CNC templates?
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Old 26-05-2016, 06:18   #788
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Re: Bestevaer 49ST

Is the day tank actually welded into the hull or is it mobile? Where will the day tank be?
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Old 26-05-2016, 07:10   #789
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Re: Bestevaer 49ST

When looking at the fuel system diagram, and not being an expert on these matters, I'm wondering how the connection from the three way valve to the engine works. If you switch the three way valve so that it directs the flow towards the engine, would you then close the latter on/off valve (not the first one because of the Refleks heater) in the pipe coming from the day tank to the engine? That is, to avoid taking fuel from both sources, or to avoid reverse flow to the day tank (or Refleks heater) when the closest Walbro pump is on.

There could be also another three way valve in the other three way junction right next to the engine. Wondering if that would be a good approach.

Let's then assume that you are taking fuel from the port tank, and the flow bypasses the day tank as described above. Is is possible that the overflow from the engine will first fill the day tank, and then fill the starboard tank, and then overflow to some unknown place? If so, there could be an overflow pipe from the starboard tank to the port tank.

Just wondering and trying to understand .
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Old 26-05-2016, 07:22   #790
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Re: Bestevaer 49ST

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Hmmm, I was under the impression that diesel injectors need a certain amount of pressure, and that gravity feed won't do it. I'd have to talk to my mechanic friends, so wouldn't swear on it, but I'm sure that has been a discussion item.

I know you guys have put a LOT of thought into this boat, so this is a learning opportunity.

EDIT:

I see Snowpetrel is making the same point.
I am not sure I am understanding you correctly. Do you mean you think there will be problems with normal operation or only if the engine lift pump fails?

I thought you meant with normal operation.

With engine lift pump failure, I could be wrong, but my understanding is that the engine will continue to run. Obviously if the high pressure pump fails the engine will stop, but high pressure pump failures are rare.
That is not the reason day tanks are fitted though.

SWL
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Old 26-05-2016, 11:14   #791
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Re: Bestevaer 49ST

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Originally Posted by Seaworthy Lass View Post
I am not sure I am understanding you correctly. Do you mean you think there will be problems with normal operation or only if the engine lift pump fails?

I thought you meant with normal operation.

With engine lift pump failure, I could be wrong, but my understanding is that the engine will continue to run. Obviously if the high pressure pump fails the engine will stop, but high pressure pump failures are rare.
That is not the reason day tanks are fitted though.

SWL
Not sure if this answers the issue of gravity feed. IF the day tank relies on gravity feed, I see it as an issue. I would suspect that another pump would be required between the day tank and the injectors. I don't see how the day tank will be pressurized if you are having problems with the main tanks.

I now understand the logic of you having the day tank, I just think (again, I am by no means a mechanic or engineer) that you will need another fuel pump between the day tank and the engine to provide the pressure most diesel engine designs today require. I'm assuming it uses a common rail.
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Old 26-05-2016, 11:31   #792
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Re: Bestevaer 49ST

The engine's lift pump will provide the proper flow and pressure to the injector pump.

In some boats the lift pump draws from a tank below the engine. And must lift fuel against this head distance. This is common and the reason for a lift pump.

With a day tank gravity feed above the engine's lift pump there is no head distance. Which makes the lift pump's job all that much easier.

I don't see a problem here.



Edit to add....... maybe "no head" is incorrect. Maybe better to say with a day tank will have positive head pressure instead of negative head pressure. At any rate the lift pump's job becomes a cake walk.
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Old 26-05-2016, 14:19   #793
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Re: Bestevaer 49ST

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That looks tricky. What method do they use to get the profiles right? Rack of the eye or CNC templates?
I watched little of the bend process as the noise was absolutely deafening. It seemed that every now and again the curve was checked by eye using blocks of wood as templates.

SWL
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Old 26-05-2016, 14:22   #794
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Re: Bestevaer 49ST

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Is the day tank actually welded into the hull or is it mobile? Where will the day tank be?
The day tank will sit just behind and above the engine, but out of the watertight engine bay. It will sit sit bolted to a "shelf" (the sump protrudes below).

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Old 26-05-2016, 14:28   #795
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Re: Bestevaer 49ST

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Edit to add....... maybe "no head" is incorrect. Maybe better to say with a day tank will have positive head pressure instead of negative head pressure. At any rate the lift pump's job becomes a cake walk.
I take it that this positive pressure is another advantage of having a day tank. Leaks are more obvious and air is less likely to enter the system.
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