CAT 3208 T's and running bigger twin diesels

Folks .. I am looking to purchase a '86 Hatteras Sedan with twin 320 turbo diesels with 1200 hours, equipped with Raycors and Walker Seps. Its priced right and in exceptional condition, and has always been a freshwater boat (so far!). My plans are to do the loop. I don't need speed but like to have some in reserve. The Hatteras weighs in around 26,000 lbs. Does anyone have any experience running large twin diesels at displacement speeds on a planing hull to gain fuel economy. I can't find fuel curves below 1,500 rpms so I would be interested in what my fuel economy might be. I suspect some of you are also running on one engine to conserve fuel and then alternating to the other. Could you please share your thoughts with me?

Many thanks !

forgot to mention .. they are 320 hp

Piper, if they are 320 hp they are E rated, which theoretically may not be ideal for a trawler.* Here is what CAT says about the E rating:

High Performance - For vessels operating at rated load and rated speed up to 8 percent of the time, or one half hour out of 6, (up to 30 percent load factor). Typical applications could include but are not limited to vessels such as pleasure craft, harbor patrol boats, harbor master boats, some fishing or patrol boats. Typical operation ranges from 250 to 1000 hours per year.*

I'd talk with CAT about the application in a trawler for these engines, and whether they would have any concerns.* Fuel consumption down to 1200 rpm you can get from them as well.

"320 turbo diesels with 1200 hours, I can't find fuel curves below 1,500 rpms "

Turbos have better results with positive pressure, even 1lb works to keep the engine +exhaust + turbo from plugging .And the compression pressures high enough to not slobber , and burnish the cylinder bores.

My guess would be 1500 is the bottom of the graph for a REASON.

The best you can do is blow her out every chance you can , and find out about single engine operation , weather the OFF engine will be damaging the tranny by spinning.

Prop brakes can be found on the sailboat side of the parts bin , and could be a usefull addition.

Might even be of use to the next owner if he is doing the loop.

Piper,I'll bet it's "priced right" for a reason, that probably being low demand for boats like that.
The price of fuel isn't ever going back down.
Just go find a more suitable boat.


Eric Henning

"I'll bet it's "priced right" for a reason, that probably being low demand for boats like that."

Perhaps , but on a cheap boat "What Me Worry" lets just go cruising ,would be a very simple concept to live with.

While these 3208 Cats might get to 5000 hours with great PM , maint and proper loading ,

SO WHAT! WHO CARES?

If the engines are low time , there will still be 2 or 3 , 1000hour Loops in them before they need to be replaced (throw away blocks).

Good maint and an occasional power run might save most of compression too.

At Slobber time the trannys could just be moved to a different engine.

AS the fully electric engines from cars get more common ,it wont only be Yanmar that drops BMW engines into marinization kits.

The fully electric injection engines have loads of tricks like running on fewer cylinders to increase the load per firing event. In 5 years they could be common and cheap as dirt, as bent cars are scrapped..

Also my fuel price is down to about HALF of what it was at the peak,(as is the "value" of my house , and motor home.

Thinking fuel prices will "always" be going up has been a bad trade for a long time.
Weather it will continue depends on weather the current DEFLATION continues.

No Fred. It has little to do w the economy and all to do w supply and demand * * *..for oil.More and more people will be needing oil. Lots of undeveloped countries are developing fast and there will be huge increases in the numbers of people even w no development. People can't stop having babies (they lack control) and all those new people are going to want oil just like we want oil. But the supply will not mach or exceed demand unless there is an extraordinary technology breakthrough in energy. Not likely. If gas this time next year is less than today I'll buy you dinner Fred.


Eric

Nomad, prices could well go up if we keep electing folks who want to reduce carbon based fuel consumption by throttling production and demonizing oil companies for the sake of playing to the lumpenproletariat.* If we don't and develop the prodigious petroleum resources we have in this country that are within easy reach, prices will go down.* Every year consumption goes up, as well as known reserves.* There's a reason for that - there is a heck of a lot of oil out there, and the more we look, the more we find.* True,"Jed Clampit" oil is mostly gone - the kind you get when shooting a rabbit and the bullet unleases a gusher.* But start drilling in shallow water off Alex Baldwin's house in Malibu and gas will be still be cheaper than milk.

85% of the US energy supply is off the market , which could change with the next lever pull.

Nuke has been dead for almost 40 years , at least in the USA.

Brazil has a huge reserve , and there are many Brazils yet to be discovered , and used.

Genuine research (no not gov throw away bucks) has been going on for 50 years for Fusion, better energy storage , 100x cheaper solar cells and low loss distant transmission.

The buried million volt DC will solve a bunch of grid loss problems, batteries still suck ,and printed solar cells or roof shingles are just starting to be made.

In any one year the economy/fiscal policy* is more important to fuel price than what is coming down the pike.

But I would wager a decade from now energy prices (constant dollars) will be lower.

Tho if the world Govs cant inflate away their insanities , in constant dollars the price could be Higher though it might* show* 99c on the pump.

-- Edited by FF on Monday 28th of June 2010 04:34:03 AM

Well, back to the boat/engine question. I just bought a Carver with twin Cummins 330 HP turbo charged, and intend to use it like Piper, running at hull speed. I have been told it is important to run the engine at higher speed and have the turbo kick in at least once a day for about 20 minutes. Running on one engine is an option, but* like as been mentioned, make sure the tranny can free wheel, mine can. I have been told to expect 1 mpg at planning speed (23kts) and performance curves on boatdiesel.com have confirmed this. Hopefully slightly better than twice that at hull speed of about 7 to 9 kts.

Fresh water is a plus an worth some extra money. Just confirm this. Disassembling the aftercoolers will probably tell you. I just installed a fresh water flush in my boat and can't understand why it doesn't come installed from the factory. It's easy to do and cost next to nothing.

High preformance diesels like you're considering have many more issues than the normally aspirated Perkins and Lemans. I am no expert, but if your plan is to conserve fuel, I would stay away from the high performance engines. I would have except I couldn't find a boat that my wife liked. But then again, if you want to go fast, even just once in a while, then there is no other choice.

The experts on these engines reside on boatdiesel.com and I would encourage you to join.

Generally a boat that has been maintained cosmetically has also been maintained mechanically. Just a general rule, but have a survey.

Lastly, prices on used boats fluctuate wildly. I thought I got a good price on my boat and I may very well have, but the market for used boats is so far in the buyers field, that if you are patient you will get a good deal. Then again 2 months after you buy you'll probably realize it wasn't the deal you thought.



-- Edited by timjet on Monday 28th of June 2010 05:10:50 AM

-- Edited by timjet on Monday 28th of June 2010 05:19:27 AM

timjet wrote:

Running on one engine is an option, but* like as been mentioned, make sure the tranny can free wheel, mine can.

Click to expand...

The transmission's ability to freewheel is only one part of the "run on one" equation.* If your boat has a raw water feed to the shaft log to ensure proper cooling and lubrication you can ruin the shaft and log in short order if you shut off the cooling feed (by shutting off the engine)*but the prop and shaft can still rotate.

Not all boats have this feed*(ours does) and a cooling feed to the shaft log is not automatically an indicator that the boat has drippless seals (ours doesn't).* But it's something to be aware of if one is thinking that because they have a transmission that the manufacturer says can be freewheeled at the speeds the boater wants to go.

*

Good point Marin. I don't have a dripless or water cooled shaft log so I hadn't considered the cooling issue.
Interestingly my Carver manual does not recommend single engine operation, but does not explain why.

Carver manual does not recommend single engine operation, but does not explain why.


Check the tranny mfg for trailing a shaft.

FF,

By trailing a shaft I assume you mean single engine ops. My ZF Hurst manual specifically states free wheeling the tranny is OK and does no harm. It also states that though not recommended the tranny can be shifted up to full engine rpm.


For those whose tranny can not free wheel without damage or the shaft log requires raw water engine cooling, my guess is if you lost an engine you would continue with the failed engine in gear.

my guess is if you lost an engine you would continue with the failed engine in gear.



Maybe , if the tranny simply shifts like a mechanical, but uses hyd to do it, it will probably be in gear and not allow the prop to spin. Less drag with a locked prop.

Some hyd trannies use fluid pressure to hold the clutch pack together. No pressure , no being in gear, so the prop could windmill.

Hi folks, thanks for taking the time to share all this information and perspective. I really appreciate it. I now have a purchase offer pending on the Hatteras subject to the usual survey and inspection/ sea trial by a Cat. certified mechanic. I did ask the the Cat guy about freewheeling and he said not a good idea on the transmissions Cat uses. Seem the best course of action is install shaft brakes, like they often have on sailboats. Hey ... that was quite a discourse of fuel consumption and prices. I know* this boat will use a lot more fuel than a single lehman trawler even if* I'm running at trawler speeds. During my boat shopping I found that good trawlers up here in the Great Lakes are at $30 to $50 thousand more for a vessel in similar condition to the Hatt I found. So I figure that price differential is going to buy me a lot of diesel fuel ! And I like the fact the boat and engines are made in the USA and parts and service are easy to come by. Thanks everyone !

By the way ... anyone else have experience with running bigger diesels at low RPM's?

timjet wrote:

*


For those whose tranny can not free wheel without damage or the shaft log requires raw water engine cooling, my guess is if you lost an engine you would continue with the failed engine in gear.

Click to expand...

If it was a car you'd be right.* But some marine gears do not lock up with the shifter in forward (or reverse).* The ubiquitous Borg Warner Velvet Drive series is one of these.* I know--- we tried it once.* Put the shifter of the shut-down engine in forward, then put the working engine in forward and it didn't take much forward speed to start the non-powered, in-gear shaft to start turning, just like it did in neutral.

This is why we fitted our boat with heavy duty brackets and shackles on the underside of the floor beams directly above the shaft coupler on each shaft.* When we have had to shut an engine down, I hopped down into the engine room and tied off the shaft to the shackle--- it's the only way to prevent the shaft from rotating.

Or one could install purpose-built shaft brakes on the shafts but the rope and shackle method is way cheaper and just as effective. I'm also not a fan of the idea of using a pipe wrench or chain lock on the shafts as this can score them up pretty bad.* The rope doesn't damage anything.

*


-- Edited by Marin on Wednesday 30th of June 2010 07:54:50 PM

I've never had to think about this running one engine on a twin screw boat * *.. only as get me home. I can't understand why anyone would think about it except to imagine how much drag the stopped propeller would cause. I would think any advantage running single would be many many times over lost because of the drag of the stopped propeller. For sure if it were my boat I'd never run single. But somebody must think one would burn less fuel that way or this conversation would not be taking place.*

Eric henning

Eric,

It's not such a simple discussion. High*performance*diesels like Piper the original author is considering burn a considerable amount of fuel just*idling*due to the many*accessory's*on the engine as well as spinning that heavy fly wheel. There is a point when running single engine, *that the extra fuel necessary to overcome the drag created by the rudders to compensate for the assymetrical thrust and the free wheeling or stopped propeller will equal the fuel necessary to run the second engine. This point will be different for every boat/engine combination and may be so slow as to be impractical.
When I was considering a 38' Bayliner, several folks mentioned that they routinely operate single engine to conserve fuel.

nomadwilly wrote:I can't understand why anyone would think about it except to imagine how much drag the stopped propeller would cause. I would think any advantage running single would be many many times over lost because of the drag of the stopped propeller.

Click to expand...

Tests designed to record fuel use data between running on one engine with the shaft locked off and the shaft freewheeling show that you are 100 percent, absolutely, correct.

*

The only time we would ever (and have ever) run on one engine with the shaft locked off is because we had to shut the one engine down.* As I've said in other pasts, we've had to do this four times in the twelve years we've owned the boat, three times for cooling problems and the last time because I let an engine get a big slug of air during a fuel transfer (my mistake) and we didn't want to take the time to stop and bleed that engine's fuel system.

*

Because our transmissions (BW Velvet Drives) can only be freewheeled at very slow speeds according to the operators manual, and because our shaft logs require a cooling water feed from their respective engines, letting a shaft freewheel is not an option for us.* We have to lock it off.* As you say, it would be a foolish thing to do with regards to trying to simply save fuel.

"But somebody must think one would burn less fuel that way or this conversation would not be taking place. "


NO

The point of the exercise is to INCREASE the loading on the single engine to save IT , not the fuel it burns. Extra fuel is cheap, compression fix on a throw away engine would be costly!

Unfortuniatly the simple offshore expediant of removing one prop would not help in a loop run as the numerous locks , and perhaps marina nights require fair manuverability.

Here's a twin engine configuration on a Sumnercraft from the 60s you all may find interesting. No counter rotating engine required. I had a 29' Sumnercraft but it had SS. Not conventional though. The cross section was wine glass but w a fat stem and the engine was 90% inside the keel w a horizontal (nearly) P shaft. The trailing edge of the keel was faired to one side above the p shaft and to the other side below the p shaft. The result was that the water passing the TE of the keel was thrust sideways into the advancing propeller blade. The keel acted like the stator blades on a jet engine. Great boat but I gave it up and kept the Willard.Couldn't post the drawing and picture.
It was "not a valid image file".
The twin engine concept:
Engines in tandem but the fwd engine is turned around 180 deg so the timing ends are together. One p shaft runs alongside the engines and both are belt driven (probably the reason we don't see this configuration now).


Eric



-- Edited by nomadwilly on Thursday 1st of July 2010 09:42:33 PM