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Old 02-07-2008, 10:36 AM   #21
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Design

Ken---

Thanks for the clarification and the ability to decipher the writing (unless you have your own clearer copy of the chart). Everyone always seems to quote the 120 hp @ 2400 rpm figure for this engine so I just assumed it was so.

Do you know what they mean by "BS overload" and "BS rating?" British Standard? (That's a total guess.)

When we went down to California to inspect, sea trial, and survey the boat we now own*we took the head of the Northern Lights/Lugger (formerly Alaska Diesel Electric) engineering department with us as he's a personal friend who, after 30-plus years in the marine*diesel business,*knows WAY more about engines and engine systems than most people on the planet.* He told us a rule-of-thumb fuel consumption formula that he says can be*applied to any marine diesel, which is 1 gallon per hour per 20 horsepower used.* Using this formula, he said, and the fact that at the typical cruise rpm of our boat each of our FL120s would be putting out about 60 hp, our*fuel consumption would be about 3 gph per side or 6 gph total.*

We have measured the fuel consumption of our engines at our cruise rpm of 1700.* Our fuel consumption is 6 gph almost on the money, which if the formula is reasonably accurate, would indicate our engines are producing at least 50 percent power at 1700 rpm.


-- Edited by Marin at 12:05, 2008-02-07
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Old 02-07-2008, 03:11 PM   #22
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RE: Design

I'll say it again in a slightly different way. When you are 800 rpm down from full throttle your throttle is set far below wide open throttle and the hp that your engine is making is far far less than what it says it should be at 1700 rpm.The hp numbers given on any hp curve I've ever seen are achieved at full throttle and it represents the maximum power the engine can produce at that rpm or engine speed.

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Old 02-07-2008, 05:56 PM   #23
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Okay. Prompted by what FF said earlier, I just got off the phone with my friend at Northern Lights/Lugger and he explained the difference between what I'm seeing on the brake horsepower/rpm chart and what horsepower is actually being generated by the propeller. So as Eric has been pointing out, at 1700 rpm my prop is NOT generating 70 hp but is putting out considerably less. My friend explained that there is a formula to figure all this out, and it involves knowing the diameter and*pitch and surface area of the prop and*figuring out the cube of something, at which point I said, fine, I understand all that I need to understand.

When I asked him the bit about how the engine would generate 70 hp at 1700 rpm only if it was running at full throttle at that rpm setting, which would mean the boat would have to have way too coarse a prop on it so the engine would only turn 1700 rpm at full throttle, he said, "well.... sort of, kind of, yes and no,*it's not quite*that simple."

He offered to explain it all in detail over lunch sometime.

-- Edited by Marin at 19:16, 2008-02-07
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Old 02-07-2008, 07:13 PM   #24
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Marin wrote: "Thanks for the clarification and the ability to decipher the writing (unless you have your own clearer copy of the chart). Everyone always seems to quote the 120 hp @ 2400 rpm figure for this engine so I just assumed it was so.

Do you know what they mean by "BS overload" and "BS rating?" British Standard? (That's a total guess.)"

I do have a copy of the same chart you posted in my engine operators manual. With a magnifying glass one can read the chart a little better. The older I get the more I depend on the bifocals and the magnifying glass.

I have no idea what the BS stands for. I supposed it could be British Standard.

As for fuel consumption there are many ROT's for power available in a gallon of a given fuel. It's interesting to see what different people calculate their fuel use as. I've used FloScan meters for the past 16 years on two different boats now. I find the information they provide is useful for running a boat in an optimal range. My previous boat was accurate within a half gallon on a 120 gallon fill up. With this boat I haven't burned enough fuel to know exactly how close it is dialed in yet. It appears to be within a couple gallons on a 150 gallon fill, but until I get 10 or more fills in, I don't totally trust that I have it adjusted properly.

Between Xmas and New Years I ran a quick chart on my boat, a single 120 Lehman pushing a 40' Taiwan hull. At 1700 RPM I was using 2.1 GPH. At 1750 it was 2.3 GPH @ 7.4 Kts. That doesn't fit most ROT's for power unless one believes that the Taiwan hull is extremely efficient. As time goes by I'll have more data to support or renounce these initial numbers.

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Old 02-08-2008, 04:01 PM   #25
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RE: Design

Ken and Marin,
I like your numbers Ken and it tallys with knoledge/experience. I had a Sabre 120 ( same engine as the Lehman engine ( 380 cu in Ford )) and the manual called for 5.6 gph at WOT and 2500 rpm.
Marin, I've heard the 20hp per gallon rule and it seems to always work. My boat takes 20 hp to cruise and it burns 1gph. I wonder if your boat is a CHB Ken. One of my favorite boats except for the structural problems and they are much more of a displacement hull. I don't think the CHB will step out at over 10 knots like the GB though. Marin, perhaps you're burning less fuel than you think. Can't be all that bad Eh? I am supprised you can figure out the engine loading at less than WOT with charts and numbers ... count me out too. I was thinking your Lugger man would be a good source of information. Keep him handy. Have you guys read Voyaging Under Power? Very good reading for Trawler guys and even better for Passagemakers. I'll throw out some stats of boats written about in the book to get more scope on how efficent a good displacement hull can be.
Krogen 42 42' - 39k - 130hp - 7.5knots - 2.5gph
Willard 40 40' - 33k - 130hp - 7.2knots - 2gph
Sinbad 45 45' - 65k - 150hp - 7.7knots - 3.75gph
Mona Mona 50' - 66k - ? - 7.5knots - 3gph
Nevelle 39 39' - 40k - 105hp - 7.2knots - 2.3gph
Mona Mona, despite having a 16' beam some submerged transom, Plus huge cabin space as she is flush decked w large cabin space above and below the main deck. If one would compute the ratio of cabin space to the fuel burn this boat it would be an extreem number...extreemly good. This boat is not a river boat or a house boat either ... it crosses oceans.
Eric Henning
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Old 02-08-2008, 04:46 PM   #26
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Eric---

I believe the CHB uses an underwater hull configuration very similar to the GB. At least the ones I've seen on stands in the boatyard in our marina look pretty much like the GBs sitting near them. But there may be significant differences that have not been obvious to me.

The time we measured our fuel burn using the car method of topping off the tanks, taking a cruise, then topping the tanks off again and dividing the gallons used by the hours run, we got six gallons an hour. This tallies with what our friend at Northern Lights told us the fuel consumption would be when we bought the boat, and what we see on the fuel gauge, although we don't trust the fuel gauge for anything more than an approximation.
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Old 02-08-2008, 05:48 PM   #27
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RE: Design

Marin,

The CHB can be decieving. The run at the chine is close to horizontal but the aft section is warped so the inboard run of the bottom ramps up at a rather steep angle ... like a displacement hull. Most of what we've talked about suggests your'e making about 40 hp per engine and should result in a burn rate of about 2gph ... as your Lugger man's rule suggests .. 20hp per gal. I'm stumped. Most yachtsmen screw up thier gph numbers by useing the hour meter and thus including lots of leaving the dock time ect ect. But that would lower your burn rate instead of increasing it. Could your hour meter be fast? Shoot'in in the dark .. time to go empty the garbage.

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Old 02-08-2008, 06:51 PM   #28
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RE: Design

Thought it might be interesting to take a look at the configuration of the CHB hull. These are photos from the CHB website and show their current model. However they claim this model is based on the same hull that "made CHB famous."

-- Edited by Marin at 19:58, 2008-02-08
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Old 02-09-2008, 04:03 AM   #29
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RE: Design

Krogen 42 42' - 39k - 130hp - 7.5knots - 2.5gph
Willard 40 40' - 33k - 130hp - 7.2knots - 2gph
Sinbad 45 45' - 65k - 150hp - 7.7knots - 3.75gph
Mona Mona 50' - 66k - ? - 7.5knots - 3gph
Nevelle 39 39' - 40k - 105hp - 7.2knots - 2.3gph


On an old Detroit Diesel (1936 design) you might get 16hp from a gallon an hour fuel flow.

On a tractor or truck engine designed in the 60's maybe 18 gp/gal, (Ford , Perkins)

With a new computer injected , with turbo and intercooler , and variable cam timing perhaps 23 or 24 , in the right load range.( BMW )

So if we use 20 as a simple to work with number that 130hp RATED engine that is slurping 2 gph is running , at best at 40hp.

Thats severe enough underloading to be of concern.

And surely way outside the lowest fuel flow per hp range .

FF

-- Edited by FF at 05:05, 2008-02-09
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Old 02-09-2008, 07:45 AM   #30
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RE: Design

Purchase survey- 1983 42' Chubbie

Steve<a>[img]download.spark?ID=150750&forumID=115492&abKey=05fb b804b049c105fd3087b589766706&type=tn[/img]</a>
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Old 02-09-2008, 11:50 AM   #31
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RE: Design

My boat is a 1980 Puget Trawler. Of course the difference between a CHB/Puget Trawler/Ocean Alexander/etc. is who imported it and what name did they screw onto the bulkhead. Mine came in thru Edmonds Yacht Sales which used the Puget Trawler name as well as a couple others. The documentation and registration use "EYS" as the manufacturers ID. (first three of the hull id number)

I've attached a picture of the corner of the bottom of my boat which I believe is very similar to GB just as Marin states. My boat won't come up out of the water with the single 120, but I would imagine that with twins/more HP*it will rise and try to climb out of the hole. My top is 8.7 kts @ 7.3 GPH, 2560 RPM.
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Old 02-09-2008, 01:53 PM   #32
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RE: Design

FF,
I'm puzzeled by your last sentence. Most seem to be running at about 40hp and 2+ gph. That matches nicely with the 20/gal rule. I completly agree about the under loading. Most of these guys are running at less than 40% load. If the 75/75 rule for loading is true these guys would seem to be in need of engine overhauls very frequently.
Marin,
The first picture looks different than the CHBs I've seen. It looks like a GB ..like you say. I think I'm not stumped about your fuel burn today ... who knows about tomorrow. You said you thought your engine was rated at 2400rpm. Some trawlers were over proped from the factory. My Willard was OP 250rpm. It gave the propeller more bite at cruising speed. This is the only thing I can think of that will explain your 3gph fuel burn at 1700. You should repitch your prop such that you get almost exactly 2500rpm. Then your burn rate should go down about 3 quarts an hour BUT you will no longer be makeing 8 knots. You'll need to bump your rpm up to 1900 or so to regain your favored speed ...and fuel consumption.
Steve
Is a " Chubbie " a CHB?
Ken,
Youv'e got plenty of submerged transom. Even a bit more than a GB I think. Just judgeing from the picture. I'll bet the bottom looks juts about exactly like a GB.
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Old 02-09-2008, 02:55 PM   #33
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RE: Design

The operational evidence from boats like GBs, CHBs, etc. that use 120hp engines at relatively low power settings does not support the notion that frequent engine overhauls are necessary aS a result of the low power loading. An FL120 operated conservatively and maintained properly is a 12,000 to 14,000 hour engine in recreational boat service according to the company that knows them best, American Diesel. Obviously the ancillary equipment won't last that long--- pumps, coolers, injectors, alternators, etc.

I know a couple of boaters whose FL120s have in excess of 9,000 hours on them right now and other than routine servicing and the occasional replacement of a pump, belt, etc. have yet to need any major work. And one of these guys never takes his engine above 1,500 rpm. This is just enough to maintain proper cylinder head temperature to ensure complete combustion, which is more important to the engine than the actual rpm. I don't believe that's the best way to run this engine, but it obviously has not affected its service life. I won't argue Eric's point that if that's all the power this fellow needs he doesn't need that large of an engine. But that's the engine the boat was built with so he's working with what he's got.

The configuration of Ken's transom appears to be virtually identical to our GB, including the amount of draft at the transom judging by the actual waterline of Ken's boat which, like our boat, is below the exhaust outlet. The wetted part of our transom is about the same depth as the end of a "license plate" zinc, two of which we have bolted to the transom, so about 6-8 inches.

We will be putting new props on the boat next month as the ones on the boat now are worn out.* We will probably be switching from four blade to three blade as three blades are more efficient.* However I'm more concerned about maximizing engine life than I am about minimizing fuel consumption.* We're working with a company I'm told is the best prop shop in Seattle so we'll see what we come up with.

-- Edited by Marin at 16:03, 2008-02-09
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Old 02-09-2008, 05:32 PM   #34
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RE: Design

Wer'e almost snowed in ..3' and it's still comming down. Props! Great. I agree with your choice of 3 blade too. I don't like 4 blades as 2 blades are in the shadow of the keel at one time so 50% of the prop is shadowed and 50% is not. With the 3 blade only one blade is affected at any given time. One thing that troubles me about props is that all I've found so far is Michigan. I like to choose products from several sources. I think the one I've got on the boat is Michigan and it runs fine but it's a bit thin and some pink is in evident. I like the looks of thier sailboat prop and it could be appropirate due to my low prop loading. I'm still in bit of a stew about engine loading. I'm not worried about myself as I'm sure I'm at at least 65% load but it's obvious to anyone around trawlers that few are powered above 45% and very few are repowering. If we hadn't moved to Alaska I would have just ran the old Perkins .. it diddn't even smoke. As to the 75/75 rule John Baker, with his turbo, is probably at at 75% power when he backs off 100 rpm! How could all these trawler guys be doing just fine and violate the he!! out of the rule. FF sugested ring design and someone else talked about turbos but Steve deAntonio has (as far as I know ) made no adjustments or amendments to the rule. Personnally I think the rule should be changed to 50/85. Everyone agrees that a diesel needs to be " worked " but only Steve bellies up to the bar and presents a rule. I'd sugest talking to your Northern Lights guy but in PMM in an article featuring them they said " run'em like you hate'um ". I can translate that to " Flog your engine ". I argued for the rule mostly to draw out a good argument against but very few participated.
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Old 02-09-2008, 06:18 PM   #35
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Here's a bold statement for you. Steve deAntonio is full of himself, as is Parlatore. They both believe that if they see it in writing, especially if they wrote it, it is gospel. Read the letters to the editor when people write contrasting opinions and you'll see they always are right with whatever they said. Even if the letter writer has them pinned to the wall with another equal solution to the problem, theirs is always better.

I only subscribe to the ragazine when I can get it on a good bargain. I think they had a special for $15. last year at the boat show so I bought in again to see if things changed. They haven't and I haven't seen a decent price yet so I'll be dropping out of the line of BS shortly.

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Old 02-09-2008, 09:04 PM   #36
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RE: Design

Eric,
A Chubbie is a Chung Hwa- mine is a Present 42
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Old 02-10-2008, 06:31 AM   #37
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"I'm puzzeled by your last sentence. Most seem to be running at about 40hp and 2+ gph. That matches nicely with the 20/gal rule."

"And surely way outside the lowest fuel flow per hp range ."

Actually there is no way to know on any particular vessel if that 2gph is creating 40hp or 28hp , unless perhaps the prop was removed and a drag test done.

On the posted graph the closer the actual load is to the max avilaible at ant particular rpm usually the more efficient the engine is operating.

The hassle is the prop loading drops so severely (its a square function) that any engine set up to pull mfg max published rpm is way inefficient at 500 to 800rpm less.

This is why I am always deploring the Mfg refusal to release the fuel map of their engines.

It makes it impossible to set up the engine for max efficiency at cruise.

Most tractor , taxi or lorry engines are never expected to EVER be run near their rated HP for very long , most are built internally to stand hours of ideling and light loads.As are some "prime"gen sets.

On a DD a "prime"{ (almost always on power supply ) will use 1200 a standby ,
used for emergency's is 1800rpm.

Larger , more heavy duty diesels are designed for cont service at 100% , they can take it.

However much longer service life is expected when the engine is used at 80% rated HP and 90% rated RPM.

This is how primes are set up at a remote hospital or to run a small town.

Getting down to the 50% rated power area with a heavy nduty engine is where stack slobber and all the hassles may happen.

Usually a fishing trawler problem where 550 rated hp is run at 35hp for hours on end to produce net retrival hydraulic power.

The question then remains weather its better to overpitch the prop to increase the cruising loads and lower the cruising rpm and noise , and be in a more efficient fuel burn operating area,,

VS the chance of an overload from an inexperienced operator .

My second choice would always be the overpitch,

My first choice of course would be to use the old engines speed and fuel burn log , and install a far smaller and better matched engine at overhaul time.

A big diesel eats big bucks at rebuild time , a truck take out , marineized may cost 1/2 the rebuild and have LONGER service life and lower fuel burn cruising. And be 30 years better tech.

Most times Bigger Aint Better! Unless your a GO FAST

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Old 02-10-2008, 12:00 PM   #38
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RE: Design

FF, well done!* If the reader can't understand that, there's a REAL problem.

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Old 02-10-2008, 12:25 PM   #39
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RE: Design

Eric---

All I can say regarding the "run 'em like you hate 'em" statement is that apart from break-in, I don't know any engine expert who actually follows that advice with their own engines. My friend at Northern Lights certainly doesn't. Of course, if one sells or repairs engines for a living, you need to drum up business somehow
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Old 02-10-2008, 01:22 PM   #40
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RE: Design

Marin,
Steve D (whatever you think of him) had a good piece of advice at PMU: have your new props scanned after they are fully tuned. Since your shop is top-rated they should have the capability. That way, if you ever need them repaired or replaced, they can be returned *exactly* to like-new condition.

Regarding whether Steve is bull-headed, my feeling is that he's been in the boat repair/building business his whole life, accumulationg first-hand experience with hundreds of vessels. It doesn't surprise me that he isn't swayed by the occasional responder who likely has far less knowledge.
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