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Old 09-16-2013, 06:44 PM   #1
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Cat 3208 - too much for the boat?

Hello

My wife and I are long time sailors with a fair amount of long distance cruising and live aboard experience. As I sneak thru my seventh decade of life I occasionally think that a nice big trawler would be less work and more comfortable. My wife has been convinced of that idea for years.

We are very interested in a DeFever 61 (80000#, 60’ LWL, 17’ beam) with a pair of Caterpillar 3208 (375 HP) engines. The engines have a little over 5700 hours on them. The previous 20+ year owners were meticulous in their maintenance.

I have a lot of experience with 35 – 120 HP diesels but no experience with larger and more manly diesels. I have done a LOT of reading about higher horsepower engines and have a couple questions about surveys, inspection, usage.

I have a computer program, based on Frank Beebe’s formulas, which calculates required horsepower delivered THROUGH the prop to the water to move the boat at a given speed.

My program results/predictions verify very well with data I collected in 1000 miles of operating a 60,000 pound 53’ trawler in the Sea of Cortez. That boat had a pair of Lehman 120s installed and carefully adjusted FloScans. The FloScan data was within about 5% of the calculated data based on refueling after a little over 1000 miles.

I have over 2000 engine hours of data for our sailboat with a Yanmar 4JH2E and the program data is within a few percent of that measured data.

I have used a chart produced by Caterpillar that shows prop HP –vs- Crank HP to determine 3208 engine speed –vs- Prop HP and calculated boat speed. The 375 HP engines are E-rated.

Three such data points for prop power and associated engine power are:

HP Delivered to water – Knots – RPM – Crank HP (375 HP engine)

51 HP – 7.9 Knots – 1325 RPM - 2.5 GPH - ~175 HP
73 HP – 8.7 Knots - 1500 RPM - 3.4 GPH - ~210 HP
111 HP – 9.4 Knots - 1750 RPM - 4.0 GPH - ~230 HP

QUESTIONS:

1) How does one operate a pair of overly powerful engines at economical cruise speed when a single engine can provide all the needed power at a low RPM? The DeFever 61 needs only 73 HP at the prop to move at 8.7 knots which can be delivered by ONE engine at 1500 RPM.

2) Assume I want to cruise at a S/L of 1.15 or 8.7 knots. My calculations show that the 3208s will be running at less than 1400 RPM which is way below the 2800 RPM max and 600 RPM below the torque peak of 2000 RPM. Will the engines survive long term running at such a low RPM and load? How much diesel longevity will such slow running lose?

3) Two different Caterpillar 3208 mechanics that work for Caterpillar Marine dealers have told me 5700 hours are not much in the 375 HP engine. They both will charge me about $400 per engine to do a pre-purchase inspection which includes cold and warm start analysis, sea trial, fuel, and engine oil analysis. How much confidence will I have in the engines once I receive the results of the inspection?

4) I don’t mind spending money on diesel, lord knows I could have purchased over 6,000 gallons of diesel for what I spent on sails and rigging over the last 15 years, but I would like to keep total fuel flow below 5 GPH while making an economical cruise speed. My program says the DeFever 61 can cruise at 8.4 – 8.9 knots for about 5 GPH (~2.7 GPH/engine). Does that sound reasonable?
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Old 09-16-2013, 07:13 PM   #2
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Well, I can't speak for the DeFever, but I have a turbo Cat 3208 in this boat.

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Old 09-16-2013, 08:17 PM   #3
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Quote:
Originally Posted by Tacomasailor View Post
QUESTIONS:

1) How does one operate a pair of overly powerful engines at economical cruise speed when a single engine can provide all the needed power at a low RPM? The DeFever 61 needs only 73 HP at the prop to move at 8.7 knots which can be delivered by ONE engine at 1500 RPM.

2) Assume I want to cruise at a S/L of 1.15 or 8.7 knots. My calculations show that the 3208s will be running at less than 1400 RPM which is way below the 2800 RPM max and 600 RPM below the torque peak of 2000 RPM. Will the engines survive long term running at such a low RPM and load? How much diesel longevity will such slow running lose?

3) Two different Caterpillar 3208 mechanics that work for Caterpillar Marine dealers have told me 5700 hours are not much in the 375 HP engine. They both will charge me about $400 per engine to do a pre-purchase inspection which includes cold and warm start analysis, sea trial, fuel, and engine oil analysis. How much confidence will I have in the engines once I receive the results of the inspection?

4) I don’t mind spending money on diesel, lord knows I could have purchased over 6,000 gallons of diesel for what I spent on sails and rigging over the last 15 years, but I would like to keep total fuel flow below 5 GPH while making an economical cruise speed. My program says the DeFever 61 can cruise at 8.4 – 8.9 knots for about 5 GPH (~2.7 GPH/engine). Does that sound reasonable?

Just because you have lots of horsepower doesn't mean you always have to use it all. Operate the engines at appropriate temps... which is relatively easy to do once you've got 'em warmed up and are underway. Occasional short bursts of RPMs at about 80% of WOT. Even fewer occasional bursts of WOT.

You could in fact operate on only one engine sometimes, but steering is goofy... and it's probably easier on the autopilot when both engines are running anyway.

-Chris
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Old 09-16-2013, 08:19 PM   #4
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Cats 3208s are cheap and 10,000 hours is reasonable to expect...maybe more if they were run well and well maintained.

They are a dime a dozen rebuilt even if you have an issue...they won't be around forever...but parts and working on them should be a given into the next decade without any doubts on my part.

Those engines will run 10,000 hrs at 80% WOT...don't be afraid to use them. Busses and garbage trucks all over the US have beat the crap out of them with great fleet records of reliability.
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Old 09-16-2013, 08:32 PM   #5
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Cat use to guarantee to have parts available, or the tools to make the parts, for all of their engines and equipment for fifty years. I don't know for sure if they still do.
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Old 09-16-2013, 08:41 PM   #6
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Quote:
Originally Posted by Tacomasailor View Post
Hello

My wife and I are long time sailors with a fair amount of long distance cruising and live aboard experience. As I sneak thru my seventh decade of life I occasionally think that a nice big trawler would be less work and more comfortable. My wife has been convinced of that idea for years. Smart lady


QUESTIONS:

1) How does one operate a pair of overly powerful engines at economical cruise speed when a single engine can provide all the needed power at a low RPM? The DeFever 61 needs only 73 HP at the prop to move at 8.7 knots which can be delivered by ONE engine at 1500 RPM. You could trail shaft 1 engine (as long as the transmissions are equipped to do so). We cruise at about 1400 RPM at 8 kts.

2) Assume I want to cruise at a S/L of 1.15 or 8.7 knots. My calculations show that the 3208s will be running at less than 1400 RPM which is way below the 2800 RPM max and 600 RPM below the torque peak of 2000 RPM. Will the engines survive long term running at such a low RPM and load? How much diesel longevity will such slow running lose? The engines will be just fine. We cruise at 1200-1300RPM and have had zero issues with our Cat 3208TAs.

3) Two different Caterpillar 3208 mechanics that work for Caterpillar Marine dealers have told me 5700 hours are not much in the 375 HP engine. They both will charge me about $400 per engine to do a pre-purchase inspection which includes cold and warm start analysis, sea trial, fuel, and engine oil analysis. How much confidence will I have in the engines once I receive the results of the inspection?

4) I don’t mind spending money on diesel, lord knows I could have purchased over 6,000 gallons of diesel for what I spent on sails and rigging over the last 15 years, but I would like to keep total fuel flow below 5 GPH while making an economical cruise speed. My program says the DeFever 61 can cruise at 8.4 – 8.9 knots for about 5 GPH (~2.7 GPH/engine). Does that sound reasonable?
Sounds about right.
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Old 09-16-2013, 11:49 PM   #7
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Well, I can't speak for the DeFever, but I have a turbo Cat 3208 in this boat.

Did you shrink it?
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Old 09-16-2013, 11:56 PM   #8
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I am not sure about the 3208 engine, but the boats with diesel cats I have been on have manufacturer's instructions to run the engines at 80% throttle for the last 15 minutes of your cruise to clear carbon buildup out of the engine (exhaust manifold I assume) to ensure long life of the engine.

I would also imagine that that extra HP will help you safely get out of some hairy situation you might find yourself in, especially with the type cruising you have under your belt. Maybe only once a year, but it is still there if you need it.
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Old 09-17-2013, 12:06 AM   #9
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Cat use to guarantee to have parts available, or the tools to make the parts, for all of their engines and equipment for fifty years. I don't know for sure if they still do.
Not sure about the word "guarantee", however I talked to a CAT field mechanic with 20 years with the local dealer today and he said "he hasn't been told no by the parts department yet". If it ain't in stock somewhere in their network they'll dust off the drawings and make it was his answer to me. And he works on some "really" old Cat equipment from time to time. Apparently a farmer around here somewhere still operates a couple original Holt(pre-Caterpillar) crawlers.
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Old 09-17-2013, 01:08 AM   #10
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We run our Cat 3406 at 1250 rpm (about 90hp)
most of the time with no ill effects. The engine is rated at 540hp at 2100 rpm. As long as it reaches operating temp, shouldn't be a problem.
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Old 09-17-2013, 06:25 AM   #11
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The Cat 3208 started as a 210 hp engine at 2600 for skool buses.

They work fine long term at about 150hp ( 9-10GPH) .

Your boat has probably spent .01% of its life at full bore so plenty of life is still left.
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Old 09-17-2013, 06:35 AM   #12
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Did you shrink it?
Nope, fits right under the console.
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Old 09-17-2013, 09:45 AM   #13
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I have 3208's on my Defever 48. I rarely run them up 2700rpm to plan the boat any more. When I bought this boat in 1997, I was paying $0.87 per gal and would run the boat fast at little more often. Now I am typically running at 1400rpm around 7.5kts at a total engine burn of about 3 gal each per hr. I can do a little better running slower or on one engine.

The Cats are generally easy to work on, with parts available all over at reasonable prices. For example, I just bought a new spare fresh water pump for $85 (compare that to the $350 fresh water pump I bought for a Westerbeke Genset).

I have considered repowering with smaller engines, but I'm not sure I would ever recover the cost in fuel savings.
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Old 09-17-2013, 09:55 AM   #14
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A 40 something foot Sabre pulled into the marina this summer with a fuel leak on one of the 3000 hour Cat 3208 375 TA's. A Cat service truck was subsequently parked in front of the boat for two days as two service techs pulled the intercoolers on both engines to get at a leaking shaft seal under the intercooler (located in the "V" of the engine). I'm not familiar with the engine, so don't know what device is located in that area, but it was leaking. They pulled the aftercooler on the second engine and replaced the same seal as a precaution (along with flushing both aftercoolers). The tech said this particular seal is a common replacement item on that model and further stated that the intercoolers need to be removed and flushed every so often. The cooling tubes on these particular engines were nasty. I've also read about intercoolers having a corrosion issue on older engines. I'm not suggesting the 3208 isn't a great engine....just passing along observations for your engine surveyor to look for and to consider over the long term. The Boat Diesel site likely has a thorough discussion of that engine's service history.
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Old 09-17-2013, 10:00 AM   #15
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That is a lot of HP for displacement speeds, out of curiosity what would that vessel cruise at 200 rpm off the top?

Came to the right place, a lot people here have great experience and engineering data to back it up.
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Old 09-17-2013, 11:18 AM   #16
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Skid Gear wrote, " A Cat service truck was subsequently parked in front of the boat for two days as two service techs pulled the intercoolers on both engines to get at a leaking shaft seal under the intercooler (located in the "V" of the engine). I'm not familiar with the engine, so don't know what device is located in that area, but it was leaking."


It was probably the injection pump. It sits between the cylinder heads, and is the shape of a miniature V-8 engine.
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Old 09-17-2013, 11:41 AM   #17
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The tech said this particular seal is a common replacement item on that model and further stated that the intercoolers need to be removed and flushed every so often. The cooling tubes on these particular engines were nasty. I've also read about intercoolers having a corrosion issue on older engines.

Periodic flushing and cleaning aftercoolers is part of a normal maintenance regime.

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Old 09-17-2013, 12:48 PM   #18
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Tacomasailor, unfortunately I can't add anything as we only recently purchased our boat but I also have the 3208TA's and wondered about the burn rate and effect of extended periods at low rpm. Why they would put so much unneeded horsepower in vessels that were clearly designed / intended for slow cruising simply mystifies me.

Incidentally, that was a well crafted post, great points, concise and wonderfully articulated! I note your comment about sneaking through your seventies and while I'm not far behind you, I have trouble remembering if I unplugged the shore power cord while pulling away from the dock much less the neurons left to navigate complex tables and formulas. I'm envious.
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Old 09-17-2013, 03:11 PM   #19
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Why they would put so much unneeded horsepower in vessels that were clearly designed / intended for slow cruising simply mystifies me.
This was just discussed (briefly) in the current "hull type" string. Most of these older trawler style boats had semi-displacement hulls with a semi-planning capability. Pre-fuel price crunch...the speed wars were raging amongst some manufacturers in this segment. Grand Banks were one of the worst offenders. Huge engines in hulls that could be pushed into the twenties...but were not well suited to do so. Sadly there are many grossly overpowered (and even more underpowered) semi-displacement hulls out there that have engines which are not matched to the range of capabilities of the semi-displacement hull design....hull speed to trans hump plus a little.
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Old 09-17-2013, 03:18 PM   #20
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Periodic flushing and cleaning aftercoolers is part of a normal maintenance regime.

-Chris
Right. While I'm a fan of turbocharging diesels, I'm not so enthusiastic about intercooling both for the maintenance headache and the fact that intercooling on these older engines normally meant the engine guys were trying to squeeze 10 pounds into a 5 pound bag.
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