Engine Swap help needed

[FF]

"Our 1972 220D Mercedes owners manual, for instance, stated that if you cannot find diesel fuel, you can fill up the tank with regular gas and pour a quart of motor oil in the tank with it. Whoulda thunk?"

I have heard of using kerosene with a quart of oil per every 5 gal to run as emergency diesel, and adding 10% gasoline to make a diesel easier to start below zero,

But operate on gasoline , NEVER! Totally unique!!!!

 

[Mako]

It sounds like the OP is new to powerboats so he should definitely do it.

Pretty much every one of us boating meatballs has blown tens or hundreds of thousands of dollars on the lifestyle. He might as well get his feet wet

 

[sunchaser]

There may be some deals out there that due to wrong or bad engine, make an otherwise very nice Mainship boat conomically suitable for a repower. This assumes though that an engine swap is performed in a top notch fashion using a popular and correct engine.

My bet would be on Cummins 6bt without an after cooler. Reman most likely with a warranty. A faster cruise speed of 10 to 12 knots would be preserved when needed.

The owner would have to put lots of sweat equity into the install with a spot on professional install being the end result. The wrong engine in the right boat seems counter productive, as well noted by other posters.

The whole deal could be revenue neutral and preserve the resale value. The key ingredients are desire, time, right initial boat purchase and ability. Have at it, the first step and a very big one has been taken - the notion.

 

[denverd0n]

I'm going to echo the comments about resale value. I think you would absolutely KILL the resale value by putting that small of an engine in the Mainship. Yes, that's all you need to run at hull speed, but most buyers looking at a boat like the Mainship are doing so specifically because they want to run at MORE than hull speed some times. If you do manage to make back the cost of the engine swap through lower operating costs (which I think is very doubtful) then you will just lose it all again when you go to sell the boat.

I would either look for a boat that was originally sold with a smaller engine in it to begin with, or I would buy the Mainship and run it at lower speeds to save fuel.


Good luck, whatever you do.

 

[OldDan1943]

I'm going to echo the comments about resale value. I think you would absolutely KILL the resale value by putting that small of an engine in the Mainship. Yes, that's all you need to run at hull speed, but most buyers looking at a boat like the Mainship are doing so specifically because they want to run at MORE than hull speed some times. If you do manage to make back the cost of the engine swap through lower operating costs (which I think is very doubtful) then you will just lose it all again when you go to sell the boat.

I would either look for a boat that was originally sold with a smaller engine in it to begin with, or I would buy the Mainship and run it at lower speeds to save fuel.


Good luck, whatever you do.

We know that lending institutions have turned down loans because of an engine rebuild.... Not sure how they would react to the installation of a used and smaller engine. SHRUG (if they found out.)

 

[dhays]

Greetings,
Welcome aboard. Well, you can pretty well put almost anything in anything given enough time, patience and $$. My first and gut reaction is buy the Mainship and go easy on the throttle. I suspect it would take many, many years to save the amount of $$ it would take to swap to a smaller diesel engine.

Most definitely NOT ridiculously stupid, just a bit IMO.

This!


If the current engine is running fine, you will save a lot more money by keeping it in place and just controlling the throttle than would would swapping the engine.

 

[BruceK]

...
Our 1972 220D Mercedes owners manual, for instance, stated that if you cannot find diesel fuel, you can fill up the tank with regular gas and pour a quart of motor oil in the tank with it. Whoulda thunk?Gary

Not me! Distracted, I put a litre of gas in my diesel Peugeot before switching to the correct diesel pump nozzle,filling it to the max to dilute the gas. I waited for Armageddon,nothing happened. Trying to run a diesel on a tank of gas with a slug of oil is asking/begging for trouble.

 

[Mako]

So seriously, I think that an overpowered full-displacement boat would better benefit by a re-power down to a more appropriate size. But not a semi-D boat like a Mainship which is designed to run at faster speeds.

 

[gfr51]

OK so maybe repowering is not a viable option but what about de turboing

OK so maybe repowering is not a viable option, at least down to 77hp.
But what about de-turbo'ing ?

With 4 diesel cars under my belt, the non turbo's got roughly the same fuel economy regardless of the constant rpm's.

With The 3 different makes of turbo diesels, they do great economy wise up around 2,000 rpm's but drop below 1900 and the economy drops off dramatically.
The boat I am looking at is 1 1997 39 footer mainship with a 3116 turbo diesel 325hp.
What if you removed the turbo and all associated components returning the motor back to a naturally aspirated motor. Yea you would likely have to tune the pump. it seems to me like it is a doable option and might increase the fuel economy at lower rpm's ...Might have to change props too.
Any knowledgeable thoughts appreciated here.
Gary

 

[RT Firefly]

Greetings,
Mr. g. NOT trying to pee in your cornflakes but why not find a boat with the engine you REALLY want rather than fiddling around? Unless you like fiddling around. In that case, go for it but as many have mentioned, be prepared to spend $$$ and not do any boating while doing so. There are a plethora of boats out there and yes, ONE with YOUR name in it.

 

[Comodave]

I still think that you will spend more on changing the engines around to make them more fuel efficient than you will ever recover in fuel cost savins. And you may make the boats value decline.

 

[JohnP]

OK so maybe repowering is not a viable option, at least down to 77hp.
But what about de-turbo'ing ?

With 4 diesel cars under my belt, the non turbo's got roughly the same fuel economy regardless of the constant rpm's.

With The 3 different makes of turbo diesels, they do great economy wise up around 2,000 rpm's but drop below 1900 and the economy drops off dramatically.
The boat I am looking at is 1 1997 39 footer mainship with a 3116 turbo diesel 325hp.
What if you removed the turbo and all associated components returning the motor back to a naturally aspirated motor. Yea you would likely have to tune the pump. it seems to me like it is a doable option and might increase the fuel economy at lower rpm's ...Might have to change props too.
Any knowledgeable thoughts appreciated here.
Gary

Good Question--My Cummins 6bts @ 210hp can speed me along at 13knots. I usually cruise between 7 and 8 knots. A pair if 6b,s non turbo @ < than 140hp is all I need. The question is how much does the conversion cost? If it would ever save enough fuel to break even. Of course I would have no turbos to service or repair. Hmm?

 

[ranger58sb]

What if you removed the turbo and all associated components returning the motor back to a naturally aspirated motor. Yea you would likely have to tune the pump. it seems to me like it is a doable option and might increase the fuel economy at lower rpm's ...Might have to change props too.

Without factoids "proving" (nearly) in advance that fuel economy WOULD (not "might") improve... and without factoids proving such a conversion wouldn't come with a whole 'nother raft of secondary requirements (like props, which aren't cheap)...

It wouldn't ring my chimes.

Even if there's "proof" fuel economy would improve, saviings would have to outweigh the costs of conversion quickly enough to happen in my lifetime...

And -- note avatar -- fuel is not my "most major-est" expense.

-Chris

 

[Woodland Hills]

Man, you really want to spend some money on your boat! Please keep us informed about your work program as there is nothing better than watching someone else get involved in a complicated project.

I hope you can find a project boat in excellent condition so you won’t have to spend a second bank on the hull and systems as those are also typically big cost items too.

 

[gfr51]

Good Question--My Cummins 6bts @ 210hp can speed me along at 13knots. I usually cruise between 7 and 8 knots. A pair if 6b,s non turbo @ < than 140hp is all I need. The question is how much does the conversion cost? If it would ever save enough fuel to break even. Of course I would have no turbos to service or repair. Hmm?

Well being a backyard mechanic I called around the block and a guy with supposedly 38 years experience with cat diesels, in my instance, said that basically you are just removing all of the turbo and afterburner stuff and plugging some holes left by the removal. I am sure you would have to re-tune the injector pump. As for resale you still will have all of the factory parts to put back on. Yes you may want to get a different prop for low end torque.
I am planning on travelling around on this boat not sitting so I can appreciate 1/2 half gallon or more per hour!
In researching online I came to the conclusion that they are taking a standard non turbo engine and pumping it up to way more horsepower causing longevity issues.
I also called Caterpillar Technical Line and they said Oh No we don't recommend changing the factory motors because they are specially built with stronger pistons, connecting rods, cylinder heads to accept the extreme pressures.... Me being an old time Drag Racer I am thinking Oh Boy I would have a much stronger....more well built motor....with suddenly much less strain put to it....In my thinking that makes for a much longer lasting rig.
Correct me if I am wrong.
regards, Gary

 

[O C Diver]

Good Question--My Cummins 6bts @ 210hp can speed me along at 13knots. I usually cruise between 7 and 8 knots. A pair if 6b,s non turbo @ < than 140hp is all I need. The question is how much does the conversion cost? If it would ever save enough fuel to break even. Of course I would have no turbos to service or repair. Hmm?

On the Cummins it's not as simple as removing the turbo. If memory serves me correctly, the pistons are different and maybe the heads between the turbo and the naturally aspirated.

Ted

 

[Ski in NC]

Nothing to be gained by taking a turbo off a trawler 3116. Running at trawler speed the turbo basically does nothing. A tiny bit of flow loss, but that is sooo minimal. The 3116 is actually quite efficient at low power. It does not have an injection pump, but cam operated unit injectors. Very crisp injection compared to an old CAV pump.

Also, getting the exhaust set up with no turbo would be quite a plumbing challenge. Not a simple job.

 

[Keysdisease]

Religion is an interesting thing

 

[OldDan1943]

Am I correct when I say, the Cummins and no doubt other diesels can be re-tuned to reduce the horse power?
How does this effect the gph?

 

[dhays]

Am I correct when I say, the Cummins and no doubt other diesels can be re-tuned to reduce the horse power?
How does this effect the gph?

I would be interested to see if Ski answers, but in some cases, I think you may be right. My understanding is that my Cummins 380hp 5.9L QSB is essentially the same engine as say a 230hp 5.9L QSB with a few upsized peripherals and a higher HP tune. For some boats, the added hp would be helpful. For my boat, not so much. I run it at a slow speed. The extra hp goes mostly unused at at my 1450 cruise rpm, I think I’m running the turbo at only 2.5 psi if I recall correctly.

 

[Gmarr]

I’m waiting for the anchor and head conversation ;-)

 

[Nomad Willy]

So seriously, I think that an overpowered full-displacement boat would better benefit by a re-power down to a more appropriate size. But not a semi-D boat like a Mainship which is designed to run at faster speeds.

Mako,
It would depend on several variables.
A FD hull needs X amout of power and if you want or need to run at 50 - 55% of max load your engine choice is very limited. But most don’t take the trouble to get the right amount of power and error up. So you get a high percentage of overpowered boats. Some insist on their favorite brand that only offeres engines above and below the ideal amount. I had to change brands to get to 5hp per ton. I would have been 15hp overpowered and would need to run about 30 to 35 /% of ideal power instead of 50% load if I had choosen my favorite brand of engine. The Isuzu I wanted to use was 54hp. And I went with a Mitsubishi 37hp. Interestingly the builder installing a 36hp engine in all the Willard 30’ boats means the builder got it right. But I think they called the Perkins engine 50hp for marketing reasons. The engine did make 50hp at 4000rpm in British taxi cabs. But as installed in the Willard boat the engine made only 33hp because they all were overpropped. Propped correctly they made 36hp.

Something not related to the above but related to re-powering is that one element of engine choice (cu. in. displacement) can significantly effect efficiency. If you have a bigger engine running at low power output you’re a victim of your engine being too big of a heat sink. A diesel engine is a heat engine and any heat lost that does not directly produce power is lost. These losses take a huge bite out of efficiency. There’s primarily the combustion chamber, the piston crown, the heat exchanger and all the heat lost in the pluming of the exchanger and exhaust system. Lots of heat lost and the quickest way to increase that loss is to have a bigger engine.

Engine size is more or less critical for FD boats but SD boats can legitimately fudge one way or the other .... usually up as errors can be much more justified. The designer or builder can just say the speed range is a knot or two higher. And a boat will sell much much better w too much power than w too little.
Then there’s the FL factor. Many more twin engine boats are sold than singles and these boats sorta naturally get overpowered. Several to many variables lead to overpowering.

But if your repowering you the skipper have the opportunity to correct the overpowered boat. But one should protect their investment and power w an engine that will not be viewed as undesirable buy future buyers.

 

[Ski in NC]

Am I correct when I say, the Cummins and no doubt other diesels can be re-tuned to reduce the horse power?
How does this effect the gph?

Yes, many basic engines come in numerous hp ratings. But lets say you need 50hp to cruise: No matter what the peak hp the engine is capable of, all versions of that block will burn nearly identical fuel rate at 50hp.

Basically means no advantage to de-rating.

 

[Nomad Willy]

OK I get it ...
At different engine speeds.
No I don’t get it.
Something to chew on tomorrow.
Looks like a good bone to chew.

 

[guy with a boat]

Gary,

Not sure if you are just looking for a fun project or really want to go boating. If its the latter, I highly recommend you buy a good quality, well maintained boat and use it. You will find that not everything you know from the car world directly translates to the boat world. Things that seem clearly wrong or at least sub-optimal, will make much more sense after you have some experience in boats.

There have been other smart guys enter the boating world before you. The things you are suggesting are not original concepts. The reason you don’t see many boats set up that way is that they are bad ideas. You are proposing doing work and spending money to make the boat less capable and reduce its resale value. Boats aren’t cars and the requirements are different. Spend some time in boats and your perspective will change. If you then still want to undertake a project to reduce your boat’s capabilities, then knock yourself out.

In the meantime, you will find that there is no shortage of ways to apply your time and mechanical abilities when you are a boat owner.

Good luck.

 

[Mako]

Mako... If you have a bigger engine running at low power output you’re a victim of your engine being too big of a heat sink... These losses take a huge bite out of efficiency... Lots of heat lost and the quickest way to increase that loss is to have a bigger engine.

That's an interesting thought and I hadn't considered that before. For example I've been studying a large, medium speed diesel. Turbo'd it's available from about 220hp to 500hp. In natural it's available down to 120hp. At 3-1/2 tons of weight, that's a lot of metal to heat up.

The higher hp turbo models are about 7% more fuel efficient than the lower hp turbo. The non-turbo are even less fuel efficient.

But I always assumed this was a characteristic of the turbo, not the high engine mass.

However, as I look at the specific fuel consumption curves, the maximum fuel efficiency of these engines is at 100% load, whereas your typical light weight, high speed engine (eg. Cummins, Doosan, etc.) would likely be down at 50%.

So perhaps you're right. Interesting stuff to consider.

 

[OldDan1943]

That's an interesting thought and I hadn't considered that before. For example I've been studying a large, medium speed diesel. Turbo'd it's available from about 220hp to 500hp. In natural it's available down to 120hp. At 3-1/2 tons of weight, that's a lot of metal to heat up.

The higher hp turbo models are about 7% more fuel efficient than the lower hp turbo. The non-turbo are even less fuel efficient.

But I always assumed this was a characteristic of the turbo, not the high engine mass.

However, as I look at the specific fuel consumption curves, the maximum fuel efficiency of these engines is at 100% load, whereas your typical light weight, high speed engine (eg. Cummins, Doosan, etc.) would likely be down at 50%.

So perhaps you're right. Interesting stuff to consider.

LOL, remember any fuel consumption curves are 'suggestions'. A lot depends on your transmission and prop and hull design, how clean your hull is and how much crap you put on your boat. Then sea conditions including current.

 

[Tom.B]

Well being a backyard mechanic I called around the block and a guy with supposedly 38 years experience with cat diesels, in my instance, said that basically you are just removing all of the turbo and afterburner stuff and plugging some holes left by the removal. I am sure you would have to re-tune the injector pump. As for resale you still will have all of the factory parts to put back on. Yes you may want to get a different prop for low end torque.
I am planning on travelling around on this boat not sitting so I can appreciate 1/2 half gallon or more per hour!
In researching online I came to the conclusion that they are taking a standard non turbo engine and pumping it up to way more horsepower causing longevity issues.
I also called Caterpillar Technical Line and they said Oh No we don't recommend changing the factory motors because they are specially built with stronger pistons, connecting rods, cylinder heads to accept the extreme pressures.... Me being an old time Drag Racer I am thinking Oh Boy I would have a much stronger....more well built motor....with suddenly much less strain put to it....In my thinking that makes for a much longer lasting rig.
Correct me if I am wrong.
regards, Gary

I think most of us feel like you are obsessing over the wrong aspect of boating. And as most of the members has proven, there is nearly zero advantage to trying to force yourself into better fuel burn numbers. Certainly not considering the 10's of thousands of dollars this project will cost you. By nearly any measure, fuel is not the expensive part of boating (I say that, but our boat burns a minimum of 10gph and a max of between 30 and 35). You will REALLY need to use your backyard mechanical experience in so many other ways that spending all that time to save a few hundred buck a year in fuel is going to find you behind the 8-ball with so many other things that you will almost certainly regret the move.

 

[OldDan1943]

I think most of us feel like you are obsessing over the wrong aspect of boating. And as most of the members has proven, there is nearly zero advantage to trying to force yourself into better fuel burn numbers. Certainly not considering the 10's of thousands of dollars this project will cost you. By nearly any measure, fuel is not the expensive part of boating (I say that, but our boat burns a minimum of 10gph and a max of between 30 and 35). You will REALLY need to use your backyard mechanical experience in so many other ways that spending all that time to save a few hundred buck a year in fuel is going to find you behind the 8-ball with so many other things that you will almost certainly regret the move.

IF you owned 2019 Corvette, yes you know it would get better gas mileage if you drive it slow. You would not swap the Corvette engine to get better gas mileage. Same way with the boat. Just enjoy what you have, drive it slow.....

 

[seighlor]

My boat has an older 375hp Cat engine. Cruising at seven knots, I average a burn rate of 2 gph.