Repower

Derating a large diesel

Having a large engine de-rated to give much less power does seem to be a good idea for a trawler displacement yacht. How to do this economically is the question which I would like to put forward.
Taking a TAMD60c Volvo, the first suggestion is to de-rate the injectors.
Can one take off the turbo and if this would done what benefits might that give as turbos don't usually come in until the engine revs go over around 2000.
Perhaps it is just easier to resize the prop limiting the revs to say 1500 at 8 knots?
Any thoughts are most welcome.

I would remove the aftercooler and the turbo. Timing can be advanced to the NA specs, this will help cold starts and reduce smoke. The injectors are a non issue but the IP will need to be recalibrated to the MD70 NA specifications. Scrap the Volvo preheater and install a Cummins 12 volt intake heater system, much simpler. You'll need to reprop or at least take out some pitch to match the lower rating.

hollywood8118 said:

We currently have a 225hp Volvo in our 40' Ocean Alexander.

It started life as a 275hp TAMD70C, have the injectors stepped down to the 225hp rating of the TAMD70 during a complete injector service.

We never used the upper 700 rpm of the range as it sucked fuel like a 66 Cadillac climbing a mountain pass.. we cruise the boat at 1600-1700 rpm making 8.3kts in flat water.. she would do 11kts fire walled.. no need to go that fast.

I have the opportunity to get a 10 year newer motor that is 110hp at a reasonable cost.. I would do all the re-power myself.. no big deal.

My TAMD70c has all new exchangers/coolers.. but has a lot of crap hung all over it in the form of pre heat start system etc.. the 70c motor is known as a bulletproof block.. hard to kill motor.. as in most marine diesels it is the stuff hung on the outside of the block that normally fails.. parts for the thing are very hard to get and wicked expensive.. the injection pump is almost the sive of the motor on my 7.5kw genset!

Its one really bad attribute is it smokes BAD when cold on start up.. but no smoke when warm.

So my long winded question is this...

Repower with the 110hp motor?

Strip off any unnecessary stuff ( aftercooler,cold start system that doesn't work anyway and simplify the tamd70 to a tmd70?

Is 110hp enough for the 40' hull to hit 8kts reasonably?

I am trying to keep this boat reasonable.. plan to take it to Mexico and possibly leave it for a few seasons and winter there..

The 70c motor is a monster.. a bit more room in the E.R. would be nice..

Personally I want to sell off everything and buy a Nordhavn and split .. but the Admiral isn't completely warmed up to full time cruising again just yet..But she loves the Mexico idea.

Thoughts and input from anyone ?

HOLLYWOOD

Click to expand...

Hi.
You asked "Is 110 hp enough for the 40' hull to hit 8 kts resonably?"
Yes, provided that you have a fair reduction on you gear, at least 3:1 ratio, that will multiply the given torque by 3 (i.e. 600 Nm x 3= 1800 Nm.)
so your OTTER can swing a big propeller, that will push hard tru the Water.
-and by no Means a egg beater. I think you,ll hit 8.8 @ 1900 rpm.
You said it yourself: The MTD.70 is a monster, but it a workhorse as well!

Full displ.boats alwayes need big slow turning propeller, has to have a big diameter,


in order to shovel a large a quantity of Water astern, so full bodied hull will go tru Water, but also be able to stop boat fast.
IF in doubt, please confirm fact. Experienced over many year.

mikecambrai said:

Having a large engine de-rated to give much less power does seem to be a good idea for a trawler displacement yacht. How to do this economically is the question which I would like to put forward.
Taking a TAMD60c Volvo, the first suggestion is to de-rate the injectors.
Can one take off the turbo and if this would done what benefits might that give as turbos don't usually come in until the engine revs go over around 2000.
Perhaps it is just easier to resize the prop limiting the revs to say 1500 at 8 knots?
Any thoughts are most welcome.

Click to expand...

Mike.

You dont have to remove turbo or intercooler at all, if derate to 1500/1700 rpm.-first get at bigger propeller, (prop.is turning slower,so a more slow srew tru water!) maybe some 2 inc./ or if same dia. 3 inc. more on pitc. NEVER a SMALLER prop.!

To max. engines performance and fuel burn: Lock the trottle at fuelpump,
set to max. 1600 rpm. (do this in idle rpm.) Make sure your new prop.are measured to new HP+/rpm!!
I have done this with good result, from 60 HP down to 40 HP. get better fuel, from 9 liter/h. to only 3.5 litre/hour. same speed, because my boat is a heavy disp.- so FAR too many HP. install. by former owner.
Removed the small 16"x11" prop" to a 18"x12"- all worked out very good.
Real many trawler/ tug type boats are often. far overpowered,
almost embarrassing,!-and for what use.??
What matters are engine slow rpm.1800-2000 rpm. and a deep red.ratio 3 or 3.5:1 for max. TORQE where the power+torque is to be transmittedd: Namely to the propeller.
Propeller move ship, engine only turn propeller. yes, for propulsion!
Its not the horsepower that moves ships or boats, no, its the important PROPELLER.! We all sometimes forget..
Seems like this: How many HP.to move my boat at a given size?
Its more rigth: How big a torque, to turn propeller, do I need to push my
boat? Said by f.eks. by mr.Dave Gerr, in his "Propeller Handbook."
Quote from GERR: Its all about TORQUE.! his book are worth reading.

The problem with having an aftercooler at very low power settings is that it cools the air WAY to much resulting in more smoke because of low cylinder temps. and inherent cylinder wall glazing that is the result of it. Its a vicious circle. And, the turbo is just not needed as it wont produce boost at the power output that you want.

Railroads have been known to down rate the locomotives (as in removing turbochargers) when downgraded to local/switching service when superseded by more modern locomotives. This reduced maintenance costs. Don't know if this would apply to small diesel engines and typical recreational use, however.

kulas44 said:

The problem with having an aftercooler at very low power settings is that it cools the air WAY to much resulting in more smoke because of low cylinder temps. and inherent cylinder wall glazing that is the result of it. Its a vicious circle. And, the turbo is just not needed as it wont produce boost at the power output that you want.

Click to expand...

KULAS44.

You are quite rigth,the way you describe the "vicious circle":
Not mush boost, low cyl temps.If at partly loaden engine.

But it seems that you have clean overlooked the bigger propeller.
It will fully load "OTTER"s engine at wanted ex. 1600 rpm.
A fuul boots will be present to Work the turbo blower at full speed,and temps,will be rigth, (engine exaust teperature at its normal.
Higth load more fuel more power, more boost to turbo.

But of importance: Engine MUST be Locked ( best if plumbed.)- so it will not exeed 1600 rpm. - otherwise exausst Black as Coal..!

All because of a Bigger Wheel,( or same prop. with more pitch adjusted for the new lower turning speed.(on prop.)
If you keep the old prop., engine will just be partly loaded at 1600 RPM. It as simple as that. And the vicous circle will occur!
KULLAS44 are fully rigth, - in this situation.

Its used and tried every day by commercial fishermen in the North Sea and by norwegians, where easy adjusting to more pitch on prop, when decreasing engine speed , from full ahead to half speed. By VP
props.)

Hi, guys:

FF has it right. Your fuel consumption will tell you what power the boat is using. If you can establish the fuel consumption reliably at the cruising speed you desire, then use the slightly inaccurate, but conservative for this purpose) rule of thumb that one GPH of diesel equals 20 horsepower, you'll have the power the boat is using.

As far as the rest of the conversion: I did convert an Isuzu industrial diesel for marine use. I mounted a surplus heat exchanger purchased off of E-Bay which incorporated the expansion tank, mounted a Yanmar sea water pump that a friend gave me, and made a wet elbow using stainless steel pipe with a seawater injection pipe inserted through the elbow, down into the discharge pipe, with the end plugged and slots milled in the pipe to direct the water flow against the sides of the pipe. It works well, the outside of the pipe is cold to the touch at full engine power. I used a new ZF gear with a Borg Warner adapter to the Isuzu's SAE standard bell housing, and a drive disc machined by a local machine shop to the flywheel. Works fine. It'll do nine-point-something knots at full tilt boogie, and cruises at 6.5 knots at a gentle 1850 rpm.

That engine replaced the Albin AD-21 diesel in my Albin-25. I do 6.5 knots on 0.4 - 0.5 GPH. I have about 400 hours on 'er now. Curiously, the replacement shaft, screw, dripless seal, drive saver, line cutter, cutlass bearing, etc. cost more than the engine.

Go figure...

Of course keel coolers work well also. Hamilton marine sells the bronze through hull fittings for mounting a copper tube outside the hull to make a homemade keel cooler. There are many lobster boats in Maine running around with truck engines using these setups.

I repowered a friend's Marine Trader 40 from Lehman 120 to an Isuzu 4BG1T, 4 cylinder turbo. WHAT AN IMPROVEMENT! Starts instantly, almost inaudible in the main salon and in the 6 years it's been in, has never leaked a drop of anything. Uses 1.5 - 2.0 gph at six-point-something knots. That was also an industrial engine, and I made the stainless wet elbow for it. We reused the heat exchanger from the Lehman (it had just been renewed) and an expansion tank from a 3208 Cat generator set. Sadly, it is no longer available, a victim of advancing emissions regulations. We adapted the Paragon transmission from the Lehman to the SAE standard bell housing on the back of the Isuzu using a Twin Disc adapter. The conversion, including the engine and all the parts cost about $6,000.

With respect to the discussion of Cummins engines (Note the spelling: there is no "G" in Cummins). The "B" series engines (the six cylinder is 5.9 liters, the four is 3.9) absolutely are magnificent machines. Old Dodge pickups rot away to nothing and the engines are still good. They are great for all applications, except (in my sincerely humble opinion) boats.

The reason is the older ones (the ones with two valves per cylinder) are NOISY! (What did you say? I can't hear you.)

They never break down, parts are readily available and inexpensive and they're very economical. All of which makes them great for lobstermen, but if I had one in a long distance cruising boat, it would drive me round the bend.

I'm a huge fan of John Deere engines. I just got a quote on a new 4045 marine one, and the pleasure boat rating of it is 220 HP! Yikes! That's way more power than I thought they were good for, but if John Deere says it's true, then I'll believe them. I forget the continuous rating, it was probably 160 or so.

That was in connection with a daydream I had about a 32' Lobster-Cruiser. Have you seen a contemporary lobster boat out of the water? All I can say is WOW!. The keels are huge and, well beefy doesn't do them justice. These are boats you can run aground on a granite ledge and wait for the tide to float them off. Built double strong and reinforced. Check out Young Brother's boats as one example. But, they're definitely semi-displacement and built for speed. Eight hundred horsepower engines are no longer uncommon.

Not my cup of tea.

Glad you allowed me my two cents worth. As always, YMMV. Contrasting opinions welcome.

Stay strong and cruise on!

Cheers

JS

Knowledgable

John,
You seem to really have your ducks in a row (just as FF) on marine power. Call me crazy but I just bet when you prop your repowered boats you do it according to tried and true reccomendations from the engine manufacturers. Cummins (the no g verison) for instance specified 2800 neutral and 2600 rpm WOT. No reccomendations to "overprop" to save fuel. There is a reason the manufacture does the research, the test, use highly educated engineers, sensors and goes to the trouble to make these highly informed reccomendations. Are we on the same page here?

Close reading of over propping threads I think pretty well explains why you don't overpropped a boat that has a much smaller engine repower and needs most of its hp to reach cruising speed....except in a few cases of out of the ordinary diesels.

Replies that discuss over propping engines being used to propel neat their upper limits only confuse the issue.

Over propping is usually only done to properly extract hp from an engine that has good torque lower in its rpm range and is being run way low in those ranges. Whether there is true success with a particular boat, engine, and cruising style is pretty specific and needs to be discussed with those in mind.

I, for me do not subscribe to over propping, been there, ain't going there again. The proper gear, the proper prop all to put the engine at the most efficient rpm in its power curve while achieving factory reccomended RPM at wot is for me. Few if any armchair engineers can out do the professionals.

Yes, Mule I do have the screw on Driftless set so the engine can reach full rated RPM.

I do understand, however that some folks prefer to "Overprop" so they can reach the necessary horsepower to cruise at a lower RPM than would be necessary if "correctly" propped.

The important thing to understand is that the power the propeller absorbs is proportional to the rpm SQUARED whereas the power developed by the engine is (roughly speaking) directly proportional to the rpm. This means that as we go down in rpm from rated speed, we reach the point where the propeller is using only a small fraction of the power the engine can produce. "Overpropping" means the power needed is delivered at lower rpm.

I suppose this might allow me to cruise at, say, 1300 or 1400 rpm than at 1850 as-now.

I chose not to, mainly because it would eliminate the possibility that I now have to increase speed to 8.5 - 9.0 knots if circumstances require, such as outrunning weather. There might be a small increase in fuel economy, but who cares? (I once came from Portland, Maine to Dighton, Massachusetts, including transiting the Cape Cod Canal and Buzzard's Bay, a distance of 195 miles on sixteen gallons of fuel.) It might reduce the sound somewhat also.

Overall, I'm quite pleased with the engine installation. The Isuzu engine has been quite up to it's reputation. Oddly, this one was manufactured by Yanmar, and private labeled by Isuzu. Go figure...

Carry on, keep calm and Cruise on.

JS

Driftless said:

Yes, Mule I do have the screw on Driftless set so the engine can reach full rated RPM.

I do understand, however that some folks prefer to "Overprop" so they can reach the necessary horsepower to cruise at a lower RPM than would be necessary if "correctly" propped.

The important thing to understand is that the power the propeller absorbs is proportional to the rpm SQUARED whereas the power developed by the engine is (roughly speaking) directly proportional to the rpm. This means that as we go down in rpm from rated speed, we reach the point where the propeller is using only a small fraction of the power the engine can produce. "Overpropping" means the power needed is delivered at lower rpm.

I suppose this might allow me to cruise at, say, 1300 or 1400 rpm than at 1850 as-now.

I chose not to, mainly because it would eliminate the possibility that I now have to increase speed to 8.5 - 9.0 knots if circumstances require, such as outrunning weather. There might be a small increase in fuel economy, but who cares? (I once came from Portland, Maine to Dighton, Massachusetts, including transiting the Cape Cod Canal and Buzzard's Bay, a distance of 195 miles on sixteen gallons of fuel.) It might reduce the sound somewhat also.

Overall, I'm quite pleased with the engine installation. The Isuzu engine has been quite up to it's reputation. Oddly, this one was manufactured by Yanmar, and private labeled by Isuzu. Go figure...

Carry on, keep calm and Cruise on.

JS

Click to expand...

I totally get the idea regarding conversion of a industrial rated motor to a
marinized unit the expansion tank/heat exchanger and required oil coolers and raw rater pump is a no brainer.. you mentioned making up a water injection unit for the exhaust but there is no mention of a water cooled exhaust manifold?. What did you do regarding this?
HOLLYWOOD

Mule said:

I, for me do not subscribe to over propping, been there, ain't going there again. The proper gear, the proper prop all to put the engine at the most efficient rpm in its power curve while achieving factory reccomended RPM at wot is for me. Few if any armchair engineers can out do the professionals.

Click to expand...

Just remember many great advances in history were done by armchair engineers....

Orville and Wibur were bicycle guys before inventing controlled flight.

IF the engine with a stock prop actually was anywhere near the most efficient RPM in the power curve for cruising there would never be a discussion of fitting a cruising prop.

As long as the engine is over sized for the boat (as most are) the use of a prop for WOT PM will have little in common with a prop for efficient cruising.

Oveproping (not my term, I prefer cruise prop)) and overloading are 2 different concepts.

Running at a proper load at lower RPM will extend the vessels range , lower the engine wear and the noise aboard.

Sadly most new boats are budget builds so a better compromise a CPP is never contemplated .

$$$ 10K to $ 15K to save 10% or even 25% on a 200 hour a year boat will never pay.

psneeld said:

Just remember many great advances in history were done by armchair engineers....

Orville and Wibur were bicycle guys before inventing controlled flight.

Click to expand...

Yep, but propping has kindda been done just about every way possible, and documented. Flying by the Wright Brothers was an unplowed field.

FF said:

IF the engine with a stock prop actually was anywhere near the most efficient RPM in the power curve for cruising there would never be a discussion of fitting a cruising prop.

As long as the engine is over sized for the boat (as most are) the use of a prop for WOT PM will have little in common with a prop for efficient cruising.

Oveproping (not my term, I prefer cruise prop)) and overloading are 2 different concepts.

Running at a proper load at lower RPM will extend the vessels range , lower the engine wear and the noise aboard.

Sadly most new boats are budget builds so a better compromise a CPP is never contemplated .

$$$ 10K to $ 15K to save 10% or even 25% on a 200 hour a year boat will never pay.

Click to expand...

Now FF, I defer to your superior knowledge on boats, not politics but boats. Why worry about the specific boat but instead about neutral WOT and WOT underway? My last boat had a 5.9 Cummins. Neutral WOT was 2800 RPM. In gear recommended was. 2600. With various props I went between 2250 and 2550, she was happiest at 2550.

Mule said:

Yep, but propping has kindda been done just about every way possible, and documented. Flying by the Wright Brothers was an unplowed field.

Click to expand...

I've done a fair few hours ploughing in my time, having grown up on a tillage farm. My favourite tractor was a Ford 6600 with 80hp and a 4 furrow plough.

How did we work out what gear to plough in given that each field had different type soil? Easy! Select the gear that gave you the fastest speed, but would still let you increase revs so that the engine wasn't overloaded. We poughed at about 2100 revs all day long , with wot at 2200.

Surely if you can increase revs on your boat engine to Wot, then by definition you are NOT over-propped? Conversely if you put on more throttle and nothing happens then you ARE definitely over-propped.

Us rednecks ain't as stupid as we look.

re-power

hollywood8118 said:

We currently have a 225hp Volvo in our 40' Ocean Alexander.

It started life as a 275hp TAMD70C, have the injectors stepped down to the 225hp rating of the TAMD70 during a complete injector service.

We never used the upper 700 rpm of the range as it sucked fuel like a 66 Cadillac climbing a mountain pass.. we cruise the boat at 1600-1700 rpm making 8.3kts in flat water.. she would do 11kts fire walled.. no need to go that fast.

I have the opportunity to get a 10 year newer motor that is 110hp at a reasonable cost.. I would do all the re-power myself.. no big deal.

My TAMD70c has all new exchangers/coolers.. but has a lot of crap hung all over it in the form of pre heat start system etc.. the 70c motor is known as a bulletproof block.. hard to kill motor.. as in most marine diesels it is the stuff hung on the outside of the block that normally fails.. parts for the thing are very hard to get and wicked expensive.. the injection pump is almost the sive of the motor on my 7.5kw genset!

Its one really bad attribute is it smokes BAD when cold on start up.. but no smoke when warm.

So my long winded question is this...

Repower with the 110hp motor?

Strip off any unnecessary stuff ( aftercooler,cold start system that doesn't work anyway and simplify the tamd70 to a tmd70?

Is 110hp enough for the 40' hull to hit 8kts reasonably?

I am trying to keep this boat reasonable.. plan to take it to Mexico and possibly leave it for a few seasons and winter there..

The 70c motor is a monster.. a bit more room in the E.R. would be nice..

Personally I want to sell off everything and buy a Nordhavn and split .. but the Admiral isn't completely warmed up to full time cruising again just yet..But she loves the Mexico idea.

Thoughts and input from anyone ?

HOLLYWOOD

Click to expand...

Hollywood.

Your straigth questings were: Shoud I go for derating my TAMD 70 engine.
OR buy a newer straith MD.70 110 Hp.?

I would take the newer engine 110 hp. have a red.ratio 3.1 Tvin Disc or ZF. marine gear, maybe already on the MD.70 now.?

Recommed the 3:1 reduction, - 600 800 rpm. on prop. for max. trust, OTTER is heavy to get tru Water.

Your engine smoke at start up, so do mine, at idle, 650/700 rpm. rev her up to a 1000/1200 rpm. or where she runs smooth, for better compression
and lesser smoke if any.
After a while when tept.start raising, let her run where she spins well, without smoke, - this unburned gasoil is a nuisance for all aboard.

I fully agree with you about all the exstra hang/up on a TAMD.
since "whats not there will not break" Simple and accessible.

Good luck.

Hollywood:

On both of those repowers (with the Isuzu industrial diesels) we used the original "dry" exhaust manifolds, wrapping them with the insulation tape from Hamilton Marine. Works fine. They don't get particluarly hot, even at full power.

I wish the Isuzu 4BG1T were still available - I bet it would do a terrific job for you. When Isuzu first came to the states, a lot of them were sold to fishermen in Maine because they were (at that time) cheap. What they found was that they were also incredibly well made and durable.

My friend's Marine Trader 40 with that engine in it is incredibly quiet - it's as though we're being propelled by an electric motor.

Good Luck! Be calm and cruise on!

JS