Internet? And… engine load factors

(Entering Guatemala)

 

Sans Souci has two senior ship’s captains aboard, plus two engineers, but no computer geeks. I just spoke with Jeff, and they’ve been at sea long enough that they are starting to miss email.

 

Few boats are more “connected” than Sans Souci. We have six or seven different options for Internet, for usage in different circumstances. However, none are particularly easy – especially if your computer skills are not the greatest. In this particular situation, were I on the boat, I’d be running the Fleet 77, which has two internet modes; MPDS (about $60 a megabyte OR $6 a minute). I’d sign on for just a minute, letting Outlook download message headers, disconnect, look to see what messages I want, and reconnect for another minute, collect the messages, sign off again, and do some reading, then sign on AGAIN, and send my responses. Even with the “wealth” of email that I receive, I’d only have about three or four minutes of usage. Jeff is an AOL user. He’s a good friend and a terrific ship captain, but he’s an AOL user (which DOES not translate to computer literate in any modern language). I started trying to explain to him how to check his mail offline, to keep costs low, on a sat phone — which didn’t work. Ultimately, I think I told him how to connect the Fleet 77 (double-click the icon), and then sign in to the internet the same way he would at home .. but, Be Fast! I also explained carefully how to disconnect from the net. At $6 a minute you don’t want to forget to log out (as I have done a few times).

 

I had forgotten that I also have skymate on the boat, which I use to have the boat send me information about its location, and whether or not the shore power cord is plugged in. Skymate has limited, and inexpensive email capability, and a REALLY simple user interface. Jeff sent me a test message, and I sent him one. Skymate works “funny” in that it isn’t instantaneous. It stores emails, and waits for a satellite to pass overhead. Hopefully we’ll get each others emails sometime in the next hour. Skymate also has “ok” weather reports. I installed, and subscribed to, the OCENS weather product, which I use, but it requires an internet connection. Jeff is trying to connect to Fleet 77 as I’m typing this. I think part of the problem is that Jeff realizes how expensive the Fleet 77 is, and doesn’t want to hit me with big bills. I appreciate this, but want to make sure he is getting good weather info. After a bit of discussion I encouraged him to not worry about all the techie stuff and just call the weather router on the sat phone.

 

Jeff said the weather has been horrible. The seas are reasonably decent, and the boat is handling it fine. They have been in non-stop rain since their departure, with an endless stream of squalls. The squalls hurt visibility on the radar, and running in places like Nicaragua and Guatemala, it can be nerve wracking to have limited visibility with limited radar.

 

And to return to yesterday’s discussion on engine load… Here are excepts from yesterday’s email:

 

B Gram said: “… I believe the load rating display is the percent of power the engines are currently generating(how hard they are working) to move the boat at present. A load rating of 40% means you still have 60% in reserve at that point. If you were around 80% to go the same speed you may have put in the wrong engines or wrong pitch on the wheels. It might be worth noting this number from time to time. I imagine if the number slowly increases(so will the fuel rate) you might want to have the bottom cleaned. If it changes drastically, you should unhook those nets you snagged or maybe you forgot to untie that aft mooring line. Enjoying the reports- thanks!…”

 

Peter VC said: “… Ken, I read your blog today, and thought I would comment on your question about load percentage. Actually I want to connect your two comments below:

 

When we spoke he was making 9.5 knots, at 1,350 rpm, consuming just 14 gph (including the generator).

I must confess that I don’t at all understand the load percentage numbers. The engine murphy gauges show the load percentage, but I’ve never known how to interpret it. I asked Jeff what the engine load was, and he said 40%. Does this mean we are wasting 60% of the power being passed to the props? If someone reading the blog understands this topic… explain it to me below…

 First, load % is a measure of how hard the engine is working as a % of the maximum output it could provide. In the interests of (i) fuel economy, and (ii) long engine life, this load % is an important factor. Nordhavns seem to have a sweet spot at around 25% load factor. Above that, fuel economy worsens exponentially, and wear-and-tear increases proportionately. We ran our N57 at 25% load virtually all the time. That meant around 1100 RPM, 8 knots, and 5 GPH (yes, that’s 1.6nm per gallon, instead of the 0.68 nmpg your captain is getting!). I would bet that if you had your captain back off to a load factor of 25% (1100-1200 RPM on your boat) you would see a huge improvement in fuel economy, for maybe a 1 knot reduction in speed. And your engine would be incurring less wear.

 

Hope that’s helpful…”

 

David S (owner of the second N68) says: “…

 

A couple of things for you. The load is the percentage of power available from the engines being transferred to the props. If the prop pitch were greater, hence the load would increase at a given rpm. Look at it like a car going on level ground at 1000 rpm. the load would be less on the engine than if the car were going up a steep hill and maintaining the same 1000 rpm. You are not losing anything but fuel efficiency. Since the props are loaded based on pitch and rpm at a constant rpm the load only changes based on more or less pitch.

 

Since the engines are capable of obtaining 100% load at wide open throttle if the pitch is great enough to create the load it is advantageous to have enough pitch to load the engine. Since our pitch is to low we are not able to use the available load at a given rpm. The prop is basically a screw that is pushing the water out the back and the greater the degree of pitch the more water is pushed at a given rpm. Since your boat has more pitch than mine you theretically get more miles per revolution than I do. The fuel economy decreases with higher load, but the happy medium is at a load where the boat moves fastest with least engine rpm and fuel burn.

 

All of the prop programs tell me to be at about a 39″ pitch which means one revolution of the prop would move the boat 39″ forward if the water did not have any slip in efficiency. I now have 36″ pitch – you have 37″. The only differences would be the difference in torque and HP per rpm between the Lugger and Detroit, hence the reason for prop programs.

 

Regarding the stabilizers. The problem may be the little yellow lazer that reads the rpm off of the shafts. They need to be sure the little window is clean and can read the reflective tape on the shaft.

 

I would make sure the reflective tape is clean and not loose from the shaft and that the small window on the face that points towards the prop shaft does not have some debris on it. Use a Q tip with alcohol to clean it off. If the reflective tape is lost or trashed any reflective tape can be substituted. Worst case steal some off of a life jacket and tape it on the shaft to fix….”

 

Rod says: “…

Ken: A long and interesting article, fairly technical

 

http://www.proboat-digital.com/proboat/20070809/?pm=2&z=fw&pvieww=992&zin=169&u1=texterity&search=propellor%20load%20percentage&pg=84&fm=19&u1=texterity&search=propellor%20load%20percentage&pg=84&fm=1

…”

 

And on a different topic… here’s a REALLY COOL link that was sent to me by Jon. Spend some time with this one, and think about all the implications when this becomes more widely used…

 

“…ken you may know of this site http://www.marinetraffic.com/ais/ or others that show you boats coming in and out of several ports along the west coast, seattle being one, in real time using the boats ais. “

 

-Ken W

 

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Credits     |     Video produced by: Rock Steady Media     |     Teletype photo: Arnold Reinhold     |     PDP-11 photo: Trammell Hudson