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Old 03-17-2019, 10:27 AM   #21
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Old Dan 1943.
To answer your question.
No it would not be cost effective to retro fit unless you could get the parts at trade prices and sell your old electrical thrusters.
However for anyone thinking of installing hydraulic thrusters you can buy a belt driven pump or g/box p.t.o.
If re-engining an engine gear driven pump would be the way to go.

As to the diesel fuel question, all truck manufacturers instruct you to add paraffin to diesel in a ratio of 50/50% if working temporarily in minus 15+ temperatures, for permanent work in those temperatures the suppliers sell a 'winter grade' diesel (its all about tax).
In Europe you can only use white/road diesel for pleasure cruisers.
its quite easy to remove the dye and use agri diesel which will pass a cursory test, as this is a public site + the US litigation laws I'm unable to post the method of removing the dye publicly.
A diesel engine will run quite happily on virgin olive, rapeseed or sunflower oil if you add 20% paraffin (to help the initial starting). Soft oils from burger/chicken outlets can be recycled and used but particular attention must be paid to cleanliness (use a centrifuge) and acidity, the recycled oil must have a neutral PH.
But keep it to yourself and DON'T TELL THE TAXMAN !

As proof I cruised my Birchwood 33 single Perkins engined boat down though Ireland and across the Irish sea and along the English channel using rapeseed oil/paraffin. Then the tax authorities got wind of everyone using it and doubled the price.
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Old 03-17-2019, 11:18 AM   #22
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RE Ballast Below Decks; Engine Swap

("If you reduce the engine weight by a significant amount, you may have to replace that weight with additional ballast to maintain stability, so you may want to run the idea by someone that can speak definitively before you assume you'll get a shallower draft.)

I had actually already taken that into account. I read somewhere that on a liveaboard you are limited to roughly 600 pounds of "personal stuff" weight per
person.
I have often wondered about some boats seeming top heavy, bouncing
around like a cork.
My thought is to keep as much weight as possible below the water line for stability. I have a bunch of tools and size constraints permitting, would feel comfortable with as many spares and supplies as might seem necessary.
Much like the ancient mariners putting ballast stones below decks.
Makes my statement about drawing less water kinda mute!
Regards, Gary
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Old 03-17-2019, 11:22 AM   #23
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Thanks so much, I was thinking of stowing tools and other weight below decks to offset the loss. Thanks
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Old 03-17-2019, 11:23 AM   #24
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Only if you use them. I have a 250 hp. Looking at my log I'm at under 1.5 gph over the last 600 hours. That's perhaps extreme, but there are lots of folks here running high hp motors at low throttle and getting acceptable economy. Not optimal but not worth the complexity and cost to downsize for most.
Another example:

Over the last 2,400 hours our 37 Nordic Tug (28,000 lb loaded, with a 330hp Cummins running at 1,300-1,400 RPM) averaged 3.8 nautical miles per gallon at 7-7.5 knots.

That's ~ 2 gph, and some of that fuel has been used by the generator. We seem to have no need to run up to higher power levels unless we want to go faster - the engine is in great shape. We can cruise at 12 knots if we want to, but hardly ever do more than 8.
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Old 03-17-2019, 12:00 PM   #25
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Originally Posted by gfr51 View Post
("If you reduce the engine weight by a significant amount, you may have to replace that weight with additional ballast to maintain stability, so you may want to run the idea by someone that can speak definitively before you assume you'll get a shallower draft.)

I had actually already taken that into account. I read somewhere that on a liveaboard you are limited to roughly 600 pounds of "personal stuff" weight per
person.
I have often wondered about some boats seeming top heavy, bouncing
around like a cork.
My thought is to keep as much weight as possible below the water line for stability. I have a bunch of tools and size constraints permitting, would feel comfortable with as many spares and supplies as might seem necessary.
Much like the ancient mariners putting ballast stones below decks.
Makes my statement about drawing less water kinda mute!
Regards, Gary
Top heavy boats don’t bounce like corks; boats with a light weight do that. Top heavy boats roll more than boats with a lower center of gravity, but they may also have a slower more comfortable motion in a sea. A rapid short roll due to a low CG can be extremely fatiguing. I would be careful about taking too much weight out of the engine room.

I’m not sure where you read about the 600lb figure, but it sounds bogus. What is a suitable weight allowance for a motor yacht would overwhelm a sailing catamaran. Heck, my motor scooter up on the fly bridge is nearly 1/2 of that!
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Old 03-17-2019, 12:06 PM   #26
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eat 3 to 13 gallons per hour.

Soooo run it at 3 gph and save the 13 gph for when you really need it.
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Old 03-17-2019, 12:53 PM   #27
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From my shabby memory and notes
Background..........
AT34
Displacement 18,700
Main engine: Cummins QSB 5.9 Model 380 HO
Transmission: Twin Disk Model: 5061SC Ratio: 2.43:1
Generator: 6kw Northern Lights

NOW I have a factory speed vs gph
Conditions: Fuel Tanks 1/2 full 200 gal
Water tank 1/2 full 75 gal

In Theory
7 knots 1400RPM 2.1gph
10 knots 2000RPM 5.1gph
12 knots 2400RPM 10.9gph
17 knots 3000RPM 18.1gph
There are some "bumps and bruises" on the factory fuel graph but, you get the idea.

I doubt if the generator was running and loaded for sea trials.
Best guess for the generator, something less than 1gph

Conclusion: If I run it at 8knots nice economy. If I run it at 10knots the fuel economy begins a downward slide.
If I run it at 17knots.... I might consider loosening the fuel fill caps to keep from drawing a vacuum in the fuel tanks (just a joke)
From experience: If I keep it between 8 (2.1+gph) and 10 knots (5.1+gph) I am satisfied with the fuel economy. With all my crap on board it is still pretty close to the factory chart.
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Old 03-17-2019, 05:09 PM   #28
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So, given all the advice posted so far, are you still set on re-powering?

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Old 03-17-2019, 06:30 PM   #29
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It’s clear to me the problem isn’t that you’ve got the wrong engine ... it’s that you’ve got the wrong boat.

If you had the right boat it probably would have the 77hp engine you speak of. Either a SD boat at the low speed range for SD or a FD boat. Like a 36’ Willard. A lot more boat than a Mainship and suprisingly there usually one available. Not many made and the’re a 60’s boat though.

Didn’t notice where you are from but there’s 40’ Willards too. You can look up the 40 in the book Voyaging Under Power. There’s a 40 PH for 130K in the Seattle area.
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Old 03-17-2019, 09:20 PM   #30
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Some have noted the high cost of repowering and have given some data. Let me provide manufacturer data for fuel consumption for two different engines: the high output 6LY 400 hp Yanmar and the low output 80 hp John Deere NA 4045 engine.


Both produce about 17 hp per gph of diesel at 60 hp output.


How can a 400 hp engine be as efficient as an 80 hp one? Two reasons. The first is that they both make that 60 hp at about the same rpm which means that parasitic rpm related losses will be similar. But the JD has 23% less displacement which should mean a parasitic loss advantage. Well the second reason is that the slight turbo boost of the Yanmar at low rpm compensates for that displacement disadvantage.


The engines discussed above are both modern Tier 3 compliant engines. With older NA engines such as the Continental and Mercedes diesels discussed above, the modern Yanmar will actually have a fuel consumption advantage at similar power outputs.


So don't think you are saving fuel by repowering. You are just spending a lot of money and destroying your boat's resale value.


David
Not always.
While in general, if it takes 50 HP to push a boat the fuel burn will be similar between a 400 HP and the 80 HP you described. However if the larger HP engine is a tier 0 (before they had tier ratings), mechanically fuel injected, and run at a very low RPM and essentially off the torque curve, it can be quite inefficient in that situation.

My boat came with a Cummins 6CTA 450 HP engine. At 7 knots is was running at 1,200 RPM and got just under 2 NMPG. I ran it about 1,800 miles before the repower, so the fuel consumption numbers are pretty solid. Repowered with the John Deere 4045TFM75 135 HP tier 2. At 7 knots it gets 3.5 NMPG. That is 2 GPH (About 19 HP per gallon). Tier 2 through 4 engines do far better at low RPM when producing a very small percentage or the engine's rated HP. In my experience, the older engines don't do as well.

Here is a link to the initial analysis after my repower from my refit thread.

Repower Consumption Numbers

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Old 03-18-2019, 06:39 AM   #31
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"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!!!!
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Old 03-18-2019, 07:05 AM   #32
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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
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Old 03-18-2019, 08:01 AM   #33
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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.
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Old 03-18-2019, 08:42 AM   #34
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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.
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Old 03-18-2019, 07:25 PM   #35
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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.)
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Old 03-18-2019, 09:00 PM   #36
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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.
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Old 03-18-2019, 10:29 PM   #37
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...
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.
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Old 03-18-2019, 11:55 PM   #38
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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.
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Old 03-19-2019, 02:24 PM   #39
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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
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Old 03-19-2019, 02:48 PM   #40
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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.


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