[Capt J]

[quote=K1W1]So you think the Blower displaces 8 x 71= 568 cu in?

of airflow? Yes, it is designed to displace the same amount of air that size engine would naturally ingest. It does not produce any additional airflow. They ARE considered naturally aspirated even though they have a gear driven rootes type positive displacement supercharger on them. The displacement of the 'blower' is exactly the same as the displacement of the engine, so consequently no boost pressure is developed. There is no provision for 'overdriving' the blower.

I would say yes, is not a definate yes and does not sound too convincing. What pleasure yachts have you run, where and how did you run them, and what did they have for power?

[Capt J]

Originally Posted by Marmot

"... have either of you operated ANY Detroit Diesel or other mechanical diesel in a yacht? Do you have any real world experience with these engines in operation in a yacht or sportfish?"

Rather a substantial amount in both yacht and commercial applications from 2-71s up through the largest EMDs over a long period of time.

If you are finished trying to smokescreen the issue with a bunch of rubbish about duty cycles and airflow, would you like to make another attempt at explaining how your magic engine gets close to 50 percent efficiency at idle? This is especially interesting now given the volumes you have written about how badly these things run at low rpms.

It has not much to do with which engines, most all diesels sip fuel under 1,000 rpms. Most diesels at no load, idle will burn less then 1/2 gph. It has to do with at which speed the particular hull is most efficient. Each hull is different but each one is most efficient closest to it's displacement speed and takes the least amount of hp for the speed. Once you pass that speed you're applying more power with very little gains in speed until you overcome the water and the hull climbs onto plane (given it's a planing hull).

You can also adjust displacement speed for each hull depending on where the weight is located in the vessel (ie. fuel). Generally in a total displacement hull, you will remove fuel from the stern tank(s) first and it works well in planing hulls until you get to the point where the bow starts digging in and plowing. Look at Broward's range figures in and of itself. It gets a heck of a lot better range at 10 knots which is only 2 knots slower then 12 knots.

Look at Searay's for example, they have a low displacement speed. It doesn't take much to move them to around 7.5 knots but once you get to that point, they won't go hardly any faster regardless of how much rpm's you give it until they get on plane.

Another example..... I worked on a long range 97' steel motoryacht. It drew 9' of water. It cruised at 8-10 knots depending on current. It had twin 250 HP Gardener diesels for power and used 1.5 GPm at cruise speed 1050rpm's (it maxed out at 1200 rpm's if I remember correctly.) and much less at slower speeds. Needless to say it only took about 400hp to move that massive and heavy boat 8-10knots........It came to the US from England on it's own bottom

Needless to say, in relatively calm seas, I believe the range figures published by Broward and have done a lot of deliveries at those speeds.......

[Marmot]

"Most diesels at no load, idle will burn less then 1/2 gph. It has to do with at which speed the particular hull is most efficient."

That is truly a bizarre statement. One last time before I give up a lost cause. Go find the propeller curve for that 16V2000 and get back to us would you.

[Capt J]

Originally Posted by Marmot

"Most diesels at no load, idle will burn less then 1/2 gph. It has to do with at which speed the particular hull is most efficient."

That is truly a bizarre statement. One last time before I give up a lost cause. Go find the propeller curve for that 16V2000 and get back to us would you.

Most diesels at no load, idle burn less than 1 gph. That is just running with NOTHING attached to it. No propellor, 0 load. You're joining 2 totally different statements together.

Each hull has a speed that it is most efficient and requires the least amount of power to push. On this particular Broward you lose 20% efficiency just by speeding up 2 knots to 12 knots. It's probably even more efficient at 8 knots but nobody would be interested in seeing that in their specs

[Marmot]

"Most diesels at no load, idle burn less than 1 gph. That is just running with NOTHING attached to it. No propellor, 0 load. You're joining 2 totally different statements together."

How can you possibly make such an absurd statement? What are you doing, averaging every diesel under about 500 hp, including the single cylinder units?

Your original suggestion that I still claim is BS, was that your 2000 hp engine burned 3 gph with the clutch engaged. I challenge you to look up the propeller curve for that engine and tell me what the horsepower load is at 600rpm. That isn't joining different statements, it is getting back to what we were talking about before you started blowing smoke and writing science fiction stories. And while the concept might be difficult for you, there is a difference between efficiency and fuel consumption.

By the way, the blower on a 71 series engine delivers just over 1.3 times the swept volume. In other words, it delivers more than 30 percent more air than the engine displaces.

[Capt J]

The propellor curve that is published starts at 1200rpm's, not 600. I can tell you what the engine computers were saying was 3 and 3-4gph. Go find a vessel with 16v2000's and take it away from the dock and tell me what it tells you. I don't know what more to tell you. I know what the boat burns, I know what the engine displays read, why do I need to go find a propellor curve and this and that? It's irregardless to me. I also ran a 45' Cabo with c-18's and it burned 3-4gph total at idle with c18 cats 1015hp each, and did 8 knots at that speed.

According to Broward's website the vessel in this post holds 9,000 gallons and at 10 knots it has a range of 7,800 NM. Obviously the engines are not at 600 rpm's to attain that speed. So they're showing a fuel burn of less then 12 gph at that speed 9,000/780 hours= 11.54 gph. and at 12 knots 6,000NM= 18 GPH. Why would it be so hard to imagine that at dead idle the motors wouldn't burn less then 12GPH? Do you think that Broward Marine would risk a lawsuit from a buyer because they published range figures that are totally offbase? Why don't you e-mail Broward Marine and ask them what their burn rates are and what RPM they are seeing that consumption if it's so unbelievable. Also you're looking at the M93 propellor curve chart for fuel consumption and that is the 2400HP version. Detroit Diesel also makes an 1800 and 2000hp version of the 16v2000. I would think consumption would be considerably less on the 1800hp version at 1200 rpm's

[K1W1]

Hi,

I am glad there is such a mix of types posting here, it makes life interesting in a warped sort of way sometimes.

There has been some good reasoned technical data provided in response to some absolute drivel and falsehood being posted as fact.

I will not waste any more keystrokes or any more of YF's bandwidth by continuing to reply to ridiculous statements still pouring forth after several attempts to explain errors or gain further info as to how and where this info is sourced are simply ignored and more junk is posted.

[Marmot]

"Also you're looking at the M93 propellor curve chart for fuel consumption and that is the 2400HP version."

You seem to be backpedalling so fast you've lost track. The original poster asked about a boat with those engines. I responded to that post. You chimed in with some nonsense about the 2000 hp version burning 3 gph. If you go back and read you will see that I replied to your post with: "Using the figures supplied by DD for the 16V200-91 (2000 hp @ 2350 rpm)..." I don't think there is much room for confusion on that issue.

So far your 2 -3 gph has increased to 3 -4 gph, the 71 series engines don't blow exactly the same volume as they displace, no engine made by DD can obtain 49 percent efficiency and lowest BSFC at idle, and load factor is a ratio. You don't seem to understand how propellers are loaded and think that if a boat goes fast enough it will use less power ... Instead of supplying data you keep responding with anecdotes about how fast a particular model of fishing boat goes.

I give up. K1W1 pretty much nailed it.

[Capt J]

Originally Posted by Marmot

"Also you're looking at the M93 propellor curve chart for fuel consumption and that is the 2400HP version."

You seem to be backpedalling so fast you've lost track. The original poster asked about a boat with those engines. I responded to that post. You chimed in with some nonsense about the 2000 hp version burning 3 gph. If you go back and read you will see that I replied to your post with: "Using the figures supplied by DD for the 16V200-91 (2000 hp @ 2350 rpm)..." I don't think there is much room for confusion on that issue.

So far your 2 -3 gph has increased to 3 -4 gph, the 71 series engines don't blow exactly the same volume as they displace, no engine made by DD can obtain 49 percent efficiency and lowest BSFC at idle, and load factor is a ratio. You don't seem to understand how propellers are loaded and think that if a boat goes fast enough it will use less power ... Instead of supplying data you keep responding with anecdotes about how fast a particular model of fishing boat goes.

I give up. K1W1 pretty much nailed it.

I understand how propellors are loaded as well as vessel speed is not directly related to RPM either. An Engine/vessel is propped for a 100% load factor at rated RPM in this case 2350 rpms. Some vessels from the factory may turn 2380rpm's, some 2330 rpm's and that is still within DD specs. Anyways, a propellors load is not linear throughout the RPM range. There is slippage and some propellors are more efficient at certain speeds then others. For example a 4 blade prop will almost always make more speed on the top end then a 5 blade prop. Less drag. 5 blade props are usually more efficient at slower speeds. If you look at 10 different vessels with 16v2000's, each one will show a different load factor at idle in gear. Heavier or less efficient vessels will show more load, lighter more efficient hulls will show less load. The Broward hull is obviously lighter and has more of a flat bottom (as they always have) to achieve the top end speeds they are. Load factor is directly related to fuel burn. a 16v2000 at 1800rpm's is not going to burn nearly the same fuel in neutral with no load attached to it, as it is going to burn turning 1800rpm's and pushing a 60ton vessel. The higher the load at a given rpm, the more fuel needed to maintain that rpm. ALSO each propellor has a certain amount of slippage which is usually around 20%, but that is also not linear through the rpm range and some props will slip more at different rpm's and be more efficient at others.

The FACT of the matter is that none of you so-called engineers have provided ANY published technical data that has refuted Browards range quotes. All I have seen is 1 propellor load/fuel consumption curve that starts at 1200 rpm's and only shows 2 other RPM points not even in 100 rpm increments. Why don't you guys come up with a real RPMvs fuel burn curve that starts at idle and goes through the scale in 100 or 200rpm increments or ANY published technical data besides a fuel chart from a dyno and not even installed in a yacht application. You're the ones smoke screening, I haven't seen one factual published article to back up your claims. Just guestimations based on 3 reference points on a very limited propellor curve.

[Marmot]

Second post of this thread dated 07-16-2008 at 01:16PM Refute it if you are capable.

And at the risk of being repetitious, load factor is a ratio.

[K1W1]

Hi,

CaptJ-Breaking my own decision to say no more on this subject I cannot watch more drivel and garbage be posted without responding.

I understand how propellors are loaded as well as vessel speed is not directly related to RPM either

If this were a true statement then surely you would understand that if a vessel does say 10 knots at 1000 rpm ( I am using engine rpm here) that this is a direct relationship between engine rpm and vessel speed?

I haven't seen one factual published article to back up your claims.

Have you seen anything FACTUAL to back up Browards claims?

You are the one behind the smoke screen in this thread.

[Capt J]

Originally Posted by K1W1

Hi,

CaptJ-Breaking my own decision to say no more on this subject I cannot watch more drivel and garbage be posted without responding.

I understand how propellors are loaded as well as vessel speed is not directly related to RPM either

If this were a true statement then surely you would understand that if a vessel does say 10 knots at 1000 rpm ( I am using engine rpm here) that this is a direct relationship between engine rpm and vessel speed?

I haven't seen one factual published article to back up your claims.

Have you seen anything FACTUAL to back up Browards claims?

You are the one behind the smoke screen in this thread.

What I meant is, Engine RPM and vessel speed are not linear and they are not always the same. If there is current, wind, or waves the same vessel may do 8.5 knots or 12 knots at 1,000rpm's when it does 10 knots in calm water with no current. Not always 10 knots. Just like a boat may do 16 knots at 1950rpm's or the same boat could do 21 knots if the trim tabs are properly adjusted. It's variable within reason as is load and fuel consumption. A yacht can be 10% heavier or ligher simply depending on the amount of fuel, water, and blackwater that's on board. There are A LOT of variables that determine how much a diesel engine will consume per hour in a yacht application. In rough seas when the yacht is climbing up a wave, fuel consumption and load will go up even at the same rpm's.

I believe Browards claims and it should be considered factual unless there is published evidence that anyone can provide to prove otherwise. Not formula's. They're a reputable company and I don't think they would publish lies with no research to back it up.

[Marmot]

"I believe Browards claims and it should be considered factual unless there is published evidence that anyone can provide to prove otherwise."

Well Cap, let's look at the published figures again. That Broward holds 9800 gallons with long range tanks. The generators are 65kW Kohlers. Kohler publishes a fuel consumption figure of about 3 gph at 75 percent output. So, for the time it takes to travel 7800 miles at 10 knots one generator will burn 2340 gallons of fuel. That leaves 9800 minus 2340 or 7460 gallons for the engines. To keep running for the 780 hours it takes to go 7800 miles at 10 knots those engines will have sip fuel at a rate of 4.78 gallons per hour each. Those are good engines but they aren't THAT good.

Are those published enough for you?

[CaptEvan]

Not even pretending to hang with the 3 "heads" represented here, I have some smaller recreational data for your consideration.

Having logged over 9,000 miles on Tiara's 5800 Sovran, powered by 3 Volvo D6's at a rated 435 chp each, I have witnessed at idle of 600 rpm, in gear moving at 4.9 knots, the combined consumption ranging from .9 to 1.2 gph. This is for a 50,000 lb. wet planing hull.

Further, the single 17kw Onan genset drinks about 1.2 gph with minimal load.

Don't expect an engineer's reply if you challenge me. All I can say is that I am within 2-4 gallons of expected fuel when taking on 500+ gallons, so the burn meters would seem quite accurate.

Evan

Ps: This thread is better than taking a class and serving 180 days plus in the ER. Thank you.

[Ken Bracewell]

Evan,
Your signature makes me ashamed of myself. I only own one set of clothes which require me to move when the weather changes.