Thoughts on prop load for com-fish/tow boat

Interesting! It would be fun to hit the stick-shift into 4-low, as it were.

Though doing a cursory look. They only have them up to “light-duty” as far as I can tell. And the ratios offered are more geared towards high-speed boats, with up to incredible amounts of input horsepower. I’m rather stuck on the other side of the spectrum. Under-powered and over-loaded with my 3:1 transmission.

 

Ah so your rocking factory stern post. Wonder if you do a keel extension would the taper add room for a bigger wheel. The 44 Hansen's could swing a 30 inch wheel on a 4 foot extension, some of the delta leclerq boas could also swing wider depending on which of the two keels they had. Took a look at the fed boat in the slings passing through homer today, not a lot of room under there even with a 28 inch wheel in there.

Mid body is sure nice, but with the submarine tendencies of the big Ledfords the stern does make sense.

The duty rating is light and pleasure but they make a 550 version that even pleasure rating will out last a 6090 swinging a 28 inch wheel... the 325 would be a little light with a long 2.5 inch shaft.

 

I was wondering the same. Think I’ll try to have an inch or two of pitch taken out for this season. Which would be a good time to play with straight edges and squares to see what a keel/shaft extension might give.

I *feel* like my shaft angle is pretty flat. The one concern would be having to drop the rudder shoe to fit a bigger prop.

Agreed about submarine qualities of factory built Ledfords with added RSW. We played it safe with my mid-ship 6’ stretch on the last boat. Made the new Main hold the same length as before. Added a 4’ Sunday hold. Gave 2’ to the laz. It worked out pretty dreamy.

 

Be interesting to play with a laser and see if it line's up for a little bigger wheel. Looks like the keel shoe could be tweaked a little on that side without a step shoe.

Renaissance does swing a lot bigger wheel, as does rebel. Didn't realize they had such keel and tunnel variations.

 

Yeah,I think they were headed in a good direction when the market dropped out of com-fish. I believe the bigger ones were their last seiners, ending in 91.

 

Yeah seine evolution stopped in the winter of 91 and 92. New boats built after are just re hash of 1990 tech on an American diet.

Kinda a bummer, selfishly I'd like the price higher for personal finance. Equally it would be nice to see some tech grow, in the same 35 years fisheries in other places have evolved much more than ours.

For now we tweak boats older than us to try and wring out more efficient harvest.

What size shaft are you spinning?

 

About the propeller; in Scandinavia most vessels that tow fishing gear use CP propellers, even in this size. And you use the exhaust temp to get the right load on the engine. Now I wonder what your hull looks like aft. I did a rough calc on propeller dia and pitch from the numbers you provided, but the result is somewhat confusing, since the prop you use can't swallow the 300+ hp at the shaft speed of ~700 rpms. It is far too small, would need to spin at about 900 rpms, so what is out of the frame? Gear ratio wrong, tacho miscalibrated or what??

If you look at the engine power curve, it is completely flat over a wide range. The screw pitch should be selected to allow slightly higher rpms at light load, then you would have the full top power available at lower speeds for towing. With the present setup you are operating with too small torque margin when you need pushing with both shoulders, as I see it.

 

One boat like his has a variable pitch propeller, it was a hundestad unit. Very well built but performed very poorly, hub took up entirely to much of the usable diameter. Guessing the 3:1 was the selection based off of loaded weight. Boat probably curbs 55-70k and loads 2x that weight.

When they were developed they fished for terminal wild stocks. In the last 30 years the shallow aspect for much of area m, chignik, kodiak and pws has heavily adapted to deeper open water fisheries intercepting a mix of wild and hatchery fish. Sadly the tiny little egg beater props remain, so we shove rather heavy platforms around.


We tow hard on some sets, but it's a small percentage of what we do. Most boats are increasingly light in the torque department, having been built with 12-14 liter mains in the 400 hp range. Fuel prices and main cost means a lot of boats are trading out smaller, it works because 85% of what we do is low in the power need. Biggest change in the fishery tech wise is our nets, so we're dragging less through the water than 20 years ago.

Crawled under the only 6 foot stretched 50 I'm aware of, think a full flow nozzle would take up a lot of space. Between the prop hub and nozzle clearance would leave precious little room for flukes. Looks like a 2 inch shaft. Quick eye balling it, I'm guessing you could get a 30 inch under there if you followed the shaft line back to the new stern and keep the keel iron at the sams angle. Maybe do an intermediate bearing with a steel keel Ala the stretched leclerq boats. Think a 30 with a bit less pitch would absorb the 3:1 better and be cheaper, as it sounds like you have real diy skills.

 

very interesting about the controllable pitch props. I’d be a little concerned having such a finely tuned mechanism down there. We regularly grind sand/mud. And I have propped a rock before.

Concerning my calc numbers. I believe the tach is accurate, but I could check it with a photo tach. Truth be told I’m saying 3:1 gear based on what the previous owner reported on the survey. The data plate isnt readable, from corrosion. But I might be able to do a rubbing (or pop it off to see if I can read the backside.

2.5” shaft

 

Away from the boat for the weekend, but will report back, with photos

 

How about a 4L80-E. You'd have to add a thrust bearing on the shaft. Then overloaded engine becomes impossible. And everyone would talk about you. Hopefully in a good way.

 

The 2 speed zfs are a standard 325 or 550 with an inline gearbox that adds the the second speed capability. It's a very small ratio change in the .9s. Having only seen a 325 one in person, it's a hefty unit. A lot heavier than a mid size truck transmission, 9 liter John deere is still pretty powerful compared to passenger vehicles.

 

Wrapping my head around the effect of gear ratio change. For a fixed “load,” the percentage of ratio change would equal a direct percentage change of prop diameter?

E.G. assuming a starting point of 3:1 with 28x28 prop
2.5:1 = 23x28
2:1 = 19x28

Alternatively, retaining a fixed prop diameter and load, but changing pitch (assuming 1” diameter = 2” pitch)
3:1 = 28x28
2.5:1 = 28x18
2:1 = 28x10

Do I have that right?

 

Playing with the VicProp.com calculator. My baseline of 325hp, 3:1 gear, & 28x28 prop; adds up to me being grossly under-propped, and should a much higher diameter/pitch. As baeckmo said in their previous post.

Whereas, in reality, I’m limiting out ~200rpm shy of rated, at WOT.

When I change the ratio to 2.5:1, in the calculator, I get a prop recommendation closer to what I currently have. I’ll be looking harder at the transmission data plate when I get home this week.

 

Unless they sold the previous owner a gear they had sitting on a shelf. The boats were built with 2.5:1 and 2:1 gears behind 12 to 14 liter mains. On occasion you see a 3:1 as the drivetrain was oversized for the smaller torque higher reving 8 and 9 liter mains that guys replaced them with.

I'd be kinda surprised if it was a pre existing gear that it's 3:1 for a 28 inch wheel. Most those were built with big Volvo or luggers and a occasional Detroit, 28 inch wheel and your likely curb weight would have had closer to a 2 ratio.