[PUP] Emergency Power (The Dashew's trip planning)

[John Marshall]

The Nordhavn wing concept has a few elements to minimize common points  
of failure:

1) Mechanical diesels. The mains have to be electronically controlled  
turbo diesels for efficiency and emissions these days, but the wing  
engines use the older tried and true mechanical injection systems. A  
lightning hit or electrical fault that took out the main engine  
computer or controls might leave the wing in operating condition.

2) Separate batteries and electrical systems from main.

3) Separate fuel supply... as Scott indicates, you make sure its  
scrubbed and clean, but you have to refresh it periodically. The wing  
tank is easily drained and the only way to fill it is to use the  
transfer/polishing system which runs through a 2 micron Racor during  
the filling process.

4) Shaft/prop mounted off center, above and ahead of main. Prop is  
normally folded so it can't easily snag lines, which would likely get  
wound up on the main shaft anyway, and hopefully trail behind when  
underway.

5) Separate control system using cables, manual transmission, etc.  
Unlike the main, which are Mathers fly-by-wire control on the mid-size  
and up Nordhavns.

6) Quick engagement... in an emergency, total time from deciding you  
need the wing to getting it started and pushing the boat is maybe 15  
seconds. Not a big deal at sea, but if your main died coming into a  
marina...

Also, even when the main engine is sound, when going through very  
hairy narrows (narrow, swirling, salt water rapids) in the PNW or  
Alaska, or when docking in high winds or other hazardous conditions,  
some owners have the wing warmed up, running and ready to engage.  
Losing power for even a few seconds in those conditions can break your  
boat. In addition, being that the wing is mounted off center-line, you  
get some of the maneuvering benefit of twin engines at the dock,  
especially if thrusters are down or need help.

Drawback is speed (5 knots in flat water, a lot less when going  
uphill), minimal generator capacity (you'd have to drop back to using  
only essential navigational and communications electronics and minimum  
lighting), and lack of stabilization (no hydraulic pump -- except  
maybe on the largest of the single-engine boats, N62, N64). Between  
the lower power and lack of stabilization, you might not be able to  
make decent or comfortable headway on some headings in a big sea.

No redundancy is perfect, and I certainly wouldn't want to travel too  
many days on the wing engine, but a lot of thought went into making  
sure the wing doesn't share the same failure modes as the main engine/ 
shaft.

John Marshall
Serendipity - N5520

On Mar 2, 2008, at 5:04 AM, Scott E. Bulger wrote:

> Brian suggested:  Sorry, but isn't the 'wing' engine in most cases  
> linked to
> the main shaft
> rather than having a shaft of its own??
>
> Scott:  Not on a Nordhavn.  All the Nordhavn's I know of (except the  
> 35 and
> perhaps the twins) have a separate wing, shaft and folding prop.   
> The term
> "most" applying to all boats would need to include all fishing  
> trawlers and
> production cruising trawlers.  I'm not aware of any definitive  
> statistics to
> allow anyone to make the statement "most"...
>
>
> Brian added:  And if you leave this undisturbed 'emergency' fuel  
> suppy set
> for quite a
> while, the fuel turns sour, particularly these days??
>
> Scott:  Any competent skipper runs his wing to maintain its service  
> life.
> This includes periodically refreshing the supply of fuel in the wing  
> tank
> from a known good supply of fuel.  It isn't hard to insure it's full  
> of good
> clean fuel as you add fuel from your existing tanks after verifying  
> it's
> good.  Quite simple really.
>
> Scott Bulger, Alanui, N40II, Seattle Wa
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