T&T: Cape Horn Trawlers

[Mike Maurice]

It's only a coincidence that you posted about this topic today, as I was 
going to post some thoughts about efficiency of azimuth drives verses 
regular drives.

The PUP forum has been debating the criteria for the "ultimate passage 
maker". The Cape Horn Trawlers were a spirited effort at actually 
implementing such a concept boat. Most of the early boats had the 
azimuth Z drives. The smaller boats did not have room for the rotating 
platform that allowed 360 degree of thrust position.

I have about 8000 miles of experience with one of the 55' boats with the 
Z drive, which did not rotate. I had difficulty getting more than 1 mile 
per gallon. For instance: from Ft. Lauderdale to Golfito Costa Rica we 
used about 2100 gallons, which included running the gen set. The 
distance is about 1800 miles.

The Flo Scan was so erratic that I could not use it to determine actual 
flow, only relative flow. I experimented with various speeds through the 
water, rpm and engine speeds. As I recall, I settled on about 8 knots 
through the water, about 1400 rpm on the engine and I can't recall the 
prop speed, but there was a rpm gauge for that as well. There was a 
exhaust gas temp gauge and it generally ran about 600 F. The John Deere 
people were concerned about low rpm at the engine for fear that the 
engine might be overloaded, but I never saw exhaust temps that indicated 
  the engine under stress. On the other hand I was inclined to baby the 
engine as it was the only source of motive power and I did not want any 
trouble from it.

I just ran a 60' steel commercial fish boat 1200 miles from LA to 
Seattle. It had a similar sized engine, about a 4:1 reduction and it was 
run at about 1400 rpm, 700 F. exhaust temperature, water speed of about 
8 knots, it used about 500 gallons. The gen set ran all the time. Both 
boats carried about 3000 gallons of fuel. The range on this latest boat 
is about 6000 miles, the Cape Horn about 3000 miles, maybe. Depending on 
the price of fuel, the cost differential is substantial.

I am under the impression that these fuel consumption figures were the 
primary reason that almost none of the Cape Horn boats after about hull 
#5 were built with Z drives. I think the total number of Cape Horn boats 
was about 18, before the builder quite production.

I really like steel boats for long passage making. I thought the Cape 
Horn boats were exceptionally safe in that regard. But, that's another 
story.

One more thing, the Z drive system leaked hydraulic fluid into the bilge 
sump at about the rate of 1 gallon every 100 miles, or about 2 gallons 
per day while the boat was in warm water from Cuba to about Turtle Bay 
Mexico. I never found the source of the leak and it slowed to about 1/10 
of that, as soon as we got into colder water approaching San Diego. I 
can't prove it but I was suspicious that the leak was at the Z drive, 
down in the sump.

The fish boat likely had a bigger, slower turning prop and the evidence 
suggests that such a setup is enough more economical with improved 
cruising range to make the Z drives a poor choice.

Regards,
Mike


_____________________________________
Capt. Mike Maurice
Tigard Oregon(Near Portland)