GL: Hyper Mileing - Twin Engines

[John Foltz]

Improving fuel economy with twins is a great goal!  I thought I'd try  
it.

So, I checked the transmission manual. A "trailing on prop" is OK with  
my velvet drive.

In the Erie Canal, I slowed one engine gradually,  then stopped it.  
The Autpilot was on but it couldn't handle the change in power and  
steered off-course dramatically.  I went to manual steering. and  
didn't think much of it at the time.

In the lock, I used both engines. When exiting, I re-engaged the  
autopilot as I often do. Again, it steered very erratically!!!

Then I figured it out.

The autopilot is set up for my rudder size, boat type and is based on  
using twin engines. It also has an "auto-learning" function. When  
motoring on two engines it knows what to expect. When switching to one  
engine, it doesn't. But when the autopilot is started when only one  
engine is already on, it is smart enough to learn the sea-state and  
steer adequately. Then, when the second engine is started and the  
autopilot is turned back on, the autopilot computer has learned a  
single engine set up and steering is compromised again with twins.

So, the caveat is --- be careful using the autopilot for steering when  
you transition from single to twin engines or visa versa.  It may not  
be safe (depending on your autopilot and boat handling  
characteristics.)   I gave me a thrill exiting the lock!!

John Foltz
M/V Freedom
PT38
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2520 Vestal Parkway East # 309
Vestal, NY 13850
607-754-4774
john at boathousejournal.com