Long time at low loads = dead diesel?

Discussion in 'Diesel Engines' started by Gashmore, Oct 5, 2017.

  1. gonzo
    Joined: Aug 2002
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    Location: Milwaukee, WI

    gonzo Senior Member

    What kind of 80 horsepower 28 liter V12 are you referring to? Yes, you recommended to use airplane propellers, so probably losing the license as a prop selection guide would be appropriate.
    Nobody made a claim that decreasing RPM would create cavitation. Joakim correctly pointed out that following your advice of installing an airplane propeller would create cavitation.
     
  2. chinaseapirate

    chinaseapirate Previous Member

    The only one described on this thread - the OP's. I derated it to 80 hsp. It helped significantly when I took 8 of its cylinders out. His other engine was not given a prop for yet. It still has 8 of its 12 cylinders in it. The USE of airplane propellers in trawlers has only been referred to three times. Twice by your majesty. Joakim implied that decreasing RPM would create cavitation inadvertently when he, as your majesty has done so often, also failed to read what I wrote - unless he was responding to you (good for him). For the life of me, I have no clue how you could even construe that anyone advised using an airplane propeller in this thread. If one were to use some form of schizophrenic logic and relate that because I clearly recommended propellers that I've selected to be in fixed position when not in use=my preference of transport type specific propeller being of the wrong type, then they also would have committed the same common error of not reading posts before they comment on them because Joakim did not exclude narrow props used in marine propulsion, only failed to mention them. I did not read his link because I have never used anything less than 30% blade area except one time. On the 1500 knot trip I made to CNMI a bought a spare prop. In addition to the 30x33 two blade I bought a 24"x30" three bladed outboard type prop. It was faster (boat speed and RPM) in 5th, 4th even in 3rd but slower in 2nd because both props redlined the engine, no use to compare it in reverse. If there were 20% blade area sail drive props i would use those.

    To bring the project to reality, the Americas Cup 88 design and building team was recruited to build the boat. Under Shidler's philosophy of "Maximize Movement and Minimize Energy" the team set out to build a powerboat that would break traditions in efficiency. The design of choice was a 40 ft trimaran constructed of DuraKore Balsa strip plank, with carbon fiber and epoxy resins. The ultra lightweight craft was powered by twin outboard 27 hp Yanmar diesels. Launched under the name "ENDEAVOUR" preparations to begin the journey started immediately. Testing the craft entailed changing rudders and fins 5 times, working through a selection of 22 propellers, and 4 engines.

    It seems I'm not the only one to have difficulty finding props. That's a Gino Morelli project we are talking about there. His boat got 5.3 mpg with both engines and 9.9 with one engine. My 70 footer got 4knots/gallon with one engine. I did not pick my prop out of a hat. Go find your own references if you doubt in any way what I post pictures of or write. I'm not selling anything but the truth. If the OP ever shows up I intend to ask him what speed would he travel at and what he wants to pay in fuel. Also check his displacement. I understand that not every boat in the world gets to have its own tow test and that Americans like to drive pointy bathtubs around with gas V8's and big bad outboards with bold print mercury/yamaha/suzuki stamped all over them. What does that have to do with me? Is it insulting to other bloggers if I choose to discriminate and use only what is applicable to my proven design? Well tough turkey.
     
  3. gonzo
    Joined: Aug 2002
    Posts: 13,564
    Likes: 374, Points: 93, Legacy Rep: 2031
    Location: Milwaukee, WI

    gonzo Senior Member

    So you claim to have made a four cylinder out of a 12 cylinder engine, which is rather bizarre. You did advise to use airplane propellers and later edited the post.
     
  4. chinaseapirate

    chinaseapirate Previous Member

    I'm aware strange things happen in blog threads, I really don't worry about it. So if you insist on shamming me ...even if for no other reason than an attempt to mask your goal of moving into first place for the highest post/like on this site go for it. I may have been contemplating the use of some pvc pipes as a mold for a low blade area ratio prop and then cast part of one of the old props into it but decided against it. You can read my posts as I'm writing them then? I know I didn't edit the post in the manner you suspect so don't bother posting any "proof"
    Sort of. I claim the belief that knocking a 700hsp/750hsp whatever it really is without knowing the power curve or "researching it" that a diesel drops in power rather quicky the closer to idle speed it gets and it stalls out just below idle... so 750Hp at 1800 rpm does NOT become 375 at 900rpm. i know from my cat 3406 the beginning of torque curve is 1200so i gave it 320hsp at at 900 and took 1/3 of that and got 80. Which was also my estimate of BHP it would take to move the trawler at 8 knots (how convenient...huh) at 300 rpm with the 60 x 30 prop.....hold on i have to redo. wrong prop chart...used 3 blade 50DAR instead of 30DAR 2 blade for calc... I post new prop size when i get it. yeah its not even 80 hsp...more like 80 hsp at 1050 RPM.
    assuming you get back with a better prop size, post it, and I check it out as approved... ill give you a "like" lol
     
  5. chinaseapirate

    chinaseapirate Previous Member

    we are "assuming" 50 long tons disp.
     
  6. gonzo
    Joined: Aug 2002
    Posts: 13,564
    Likes: 374, Points: 93, Legacy Rep: 2031
    Location: Milwaukee, WI

    gonzo Senior Member

    The torque curve starts at the lowest idle speed. I accept you claim a belief, however that is not proof of a fact. For example, you believe that taking out 8 cylinders from a 12 cylinder makes it more economic than a 4 cylinder. Any engine, whether it is diesel, gas, electric or steam, drops in power the lower the RPMs.
     
    chinaseapirate likes this.

  7. chinaseapirate

    chinaseapirate Previous Member

    yeah. I realized that, thats how i got 80. 320/4 not 375... it wasn't enough. so i re -rated it 80 at 1050. there we other problems also. I scraped it hours ago. I may just design the the Op a free descrption of a prop (with boat attached) that might work better or not. i don't think so. No, its certainly less economical than a 4 cyl 80hsp running at peak torque or thereabouts. Just the cost was the idea. Post whaterver you want. I'm letting this get buried as fast possibe...
     
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