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Old 09-09-2016, 07:56 PM   #1
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Onan Genset and our Trawler Search

I think (hope) our summer long trawler search is coming to an end. We just returned from a 2000 mile goose chase from Albany NY to Savannah GA and Patsy has been asking me, "Why do all these boats we are looking at have so many problems?" Answer: Because we are not in the $200 K market.

We spent the day looking at a Gulfstar 43 which, although a 1975 boat, is very much what I had in mind when thinking about $200 K boats. It has always been in freshwater, stored in a heated shed, and was restored by a professional captain with evidently a touch of OCD. Not a hint of water stain or water intrusion anywhere inside except a little wrinkle in the veneer next to the door. Neat as a pin. Decks solid.

One engine was out of commission as the FW water pump was sent out for rebuild, not because of failure but just slightly elevated coolant temps. So we haven't gotten to sea trials yet. The yard didn't want to move the boat to the lift on one engine and the workboat was unavailable for some unknown reason. So, we are waiting on haulout as well.

The only flaw in the ointment was when I got to the Onan 7.5MDJE generator. It started right up and ran well but, when I went into inspect it, water was dripping steadily from the RW pump through a plug fitting. I expect that will be easy to fix. However, the drip pan was full to overflowing with oil and there was oil and well soaked oil pads in the bilge.

I've ordered a full machinery survey but, for planning purposes since we have to return to Albany pending arrival of the engine pump next week, I would appreciate any Onan owner's opinions about what we might be facing with this generator. Is there a common source of oil leaks on this model? It is a startling flaw on what otherwise seems like a perfect boat for us at a very good price.
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Old 09-09-2016, 08:17 PM   #2
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Onan

Hi Roger,

I have 78 Defever with a 4.0 Onan. I was told by a local parts supplier that Onan used Kobata's for the gensets for those years, which are generally good diesel engines.

Mine had a small oil leak from the pan, so replaced the gasket and it has been fine since. Depending on the age, it could be something as simple as gaskets or a messy oil change.
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Old 09-09-2016, 08:26 PM   #3
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The 7.5 MDJ series can be made reliable, it is not known as a chronic leaker.....BUT... It is a very rough and loud machine. Two large cylinders and about the worst dynamic balance you can get out of diesel except for a single cylinder, and it ain't much better than that.

If you want to put money and effort into fixing the gennie up, it can be done. Due to age there may be some parts finding challenges, but most can be overcome with diligence and creativity.

My recommendation would be to replace it with a modern 3 cylinder 1800rpm unit. Many good brands out there in the 8kW range. Smooth, quiet, reliable.

Nothing like being on a trip with a dead gennie and no parts to be found.

How to negotiate that into a purchase contract, tough nut if old one is at least somewhat functional. Hard to get seller to discount enough for a new machine. But trust me, a new one would be worth it if boat intends to travel.
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Old 09-09-2016, 08:29 PM   #4
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Sorry to burst your bubble, but I think you should pass on this boat. FW pump sent out for rebuild? Usually just the impeller needs to be replaced, which is a simple job that can be done in the boat. Perhaps the pump was just an excuse so you wouldn't notice major engine problems.

And serious oil and water leaks from the generator? Plan on removing the generator from the boat and sending it away for repair. Assuming that the generator is the same age as the boat, 41 years old, it is not surprising that seals and gaskets would have dried out and cracked. Probably true of the main engines too.

I guess what I am saying is that it will be much cheaper in the long run to pay a little extra for a much newer boat, and hopefully avoid these problems. Good luck in your search.
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Old 09-09-2016, 08:45 PM   #5
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There are plenty of things I`d be checking before rebuilding the FW circulation pump because of "just slightly elevated coolant temps". Maybe it had other signs of issues. What engines are these?
The MDJE is probably original. My boat began life with one, replaced with an MDKD 6.5 by the time I bought. 3cyl, smooth and quiet, presumably a Kubota, (touch-wood) gives little trouble. All that oil in the drip tray overflowing to the bilge, and absorbers in the bilge suggests, especially in an otherwise OCD maintained boat, something difficult needs fixing. I`m with Ski, budget on replacing it.
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Old 09-09-2016, 09:03 PM   #6
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Sorry to burst your bubble, but I think you should pass on this boat. FW pump sent out for rebuild? Usually just the impeller needs to be replaced, which is a simple job that can be done in the boat. Perhaps the pump was just an excuse so you wouldn't notice major engine problems.

And serious oil and water leaks from the generator? Plan on removing the generator from the boat and sending it away for repair. Assuming that the generator is the same age as the boat, 41 years old, it is not surprising that seals and gaskets would have dried out and cracked. Probably true of the main engines too.

I guess what I am saying is that it will be much cheaper in the long run to pay a little extra for a much newer boat, and hopefully avoid these problems. Good luck in your search.
Think you're mistaken.

The impeller that normally needs to be replaced is on the raw water pump not the fresh water pump. An engine running a little warm usually isn't a big deal to repair. Could be one of the pumps, the heat exchanger needing to be cleaned, the thermostat needing to be replaced, or a fouled raw water strainer.

Replacing the raw water pump is certainly no reason for removing the generator. Buying a newer boat doesn't mean that the water pump won't leak. When I bought my boat it was 12 years old and both the generator and the propulsion engine raw water pumps were leaking (900 hours on the engine 500 on the generator).

While I agree with Ski that a new generator would be a good investment, it sounds like you might be able to square this one away enough to postpone a replacement for a couple of years.

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Old 09-09-2016, 09:35 PM   #7
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Think you're mistaken.

The impeller that normally needs to be replaced is on the raw water pump not the fresh water pump. An engine running a little warm usually isn't a big deal to repair. Could be one of the pumps, the heat exchanger needing to be cleaned, the thermostat needing to be replaced, or a fouled raw water strainer.


Ted
You are correct. I should have read the post more carefully. Fresh water pumps do sometimes need to be rebuilt.
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Old 09-10-2016, 05:47 AM   #8
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The boat has a "professional" captain.

Not unusual for some captains to send as much work to the boat yard as they can get away with, just as they get a percentage of the fuel bill.

Gaskets may "dry out" on unused for years machinery but seldom on an operating vessel.

The old OHNO still have almost every part available for repair , and most operate with less fuel at light loads than more "modern" engines.

The old Gulftubs were mostly solid glass and do not go downhill as fast as many other boats of that vintage = cheap to keep.
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Old 09-10-2016, 06:00 AM   #9
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Presuming we decide on generator replacement, what does this group think the best choice of generator make would be?

Now, here is a strange question from a naval architect? How many KW do we really need for this boat? I've done electrical load analysis and generator selection many times but it was a quarter century ago (after that I had "people" to do those things). Besides, I trust real world experience more than calculations on this kind of thing.

I'll be in a car for the next couple of days and need to get an approximate handle on this while negotiations may be going on. The boat is 43 feet long with two reverse cycle AC units, electric stove, separate refrigerator and freezer, and the usual stuff. We got by with an inverter on our last trawler, even with an AC only household fridge, so we are not big electrical consumers.
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Old 09-10-2016, 06:30 AM   #10
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Presuming we decide on generator replacement, what does this group think the best choice of generator make would be?

Now, here is a strange question from a naval architect? How many KW do we really need for this boat? I've done electrical load analysis and generator selection many times but it was a quarter century ago (after that I had "people" to do those things). Besides, I trust real world experience more than calculations on this kind of thing.

I'll be in a car for the next couple of days and need to get an approximate handle on this while negotiations may be going on. The boat is 43 feet long with two reverse cycle AC units, electric stove, separate refrigerator and freezer, and the usual stuff. We got by with an inverter on our last trawler, even with an AC only household fridge, so we are not big electrical consumers.
Lots of good choices in generators. Real happy with my Onan. Things I would look for are low speed (1,800 RPM) for less noise, which engine (like the 3 cylinder Kabotas), and a good sound shield.

As to size, my 45' boat has 3 air conditioners, electric stove, electric water heater (and engine heat exchanger), 125 amp battery charger, clothes washer dryer, and microwave for the primary power consumers. Not sure I could run it all at the same time off my 8 KW Onan, but most of the time I'm hovering at 50% or less which is were I want to be. In my cruising, the stove, electric water heating, and washer dryer rarely get used (more likely when tied to the dock). So for me, 8 KW is a good fit. You may be able to go smaller, but not much.

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Old 09-10-2016, 07:14 AM   #11
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I think I would calculate it in two different ways based on how I see generators getting used.

1) When air con is in use, you will need the gen on all the time. In this case your load will be the AC units plus what ever other loads you will want at teh same time, or that you can't conveniently control. I would probably figure in the two AC units, plus the stove or the hw heater. The stove and HWH are probably similar loads, and you could control use to only one at a time without too much hassle. I''d size that for maybe 75% of the gen capacity to allow for misc stuff.

2) When you don't need AC, I think the gen will get used a couple of times a day to recharge batteries, make hot water, etc. In this case the loads will be the HWH plus your batter chargers. Some people like lots of charging capacity to load the generator and speed up recharge. You also might want to be cooking at the same time, so you might want to figure in the stove at the same time. Once again I'd size this for about 75% of gen capacity.

1 and 2 may come out about the same number, or they might be very different. But I think you will start to triangulate on the right size.

You might also want to look at your min load which is probably in case (1) above when you are asleep with AC running and it's cycling on and off, so maybe figure one AC unit running. Long lightly loaded gen runs are not great, but in my experience unavoidable if you want to use the AC, and there are times when AC is a must for whimps like me.

On bigger boats, I know a lot of people with two gen sets, one big and one small. These are typically boats that run a gen all the time, or most of the time, and the little gen runs at night, if not most of the time when operating in case (1). Then the big gen gets run when at anchor with battery charging, laundry, water making, hot water heating, etc. all happening at the same time. But I bring this up only to illustrate that there are lots of operating strategies for gens and you'll need to pick what works for you. Two gens would be silly on a 40' boat.
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Old 09-10-2016, 07:34 AM   #12
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When contemplating the size of the noise maker consider weather the inverter is a pass thru style.

These allow loads that would be problematic for the noise maler to be handled easily.

The usual hassle is starting #2 or #3 air cond with a modest unit or at a summer overloaded dock system.

If you like the hook a double belt pulley on the front and large alt will beat most batt charger easily , and free that batt charger juice for other uses.
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Old 09-10-2016, 08:01 AM   #13
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I have a 1980 Onan MDJE, 7.5 KW. Also has some oil in the tray after running for a while, although I haven't pinpointed the source yet. It isn't enough to worry about yet, but I know the day will come when I'll face the choice you're facing.

I can heartily agree with the comment about these things being serious rattlers. With the sound shield and an AquaLift muffler, it's whisper-quiet outside the boat. But the genset is mounted directly on the stringers, so the vibration inside is pretty bad.

As for sizing, I think the builder just added up all the potential loads and sized as if they'd all be used at once. I have two, 30A shore power circuits. I'd have to max out both (60A x 125VAC = 7,500W) to max out my generator. I've never done it.

I like TwistedTee's approach better.

I have two, 15,000BTU air conditioners, a 100A charger, 1,500W water heater and electric range/oven. I never use more than one 30A shore power cable, split to power both sides.

I can get by with 20A, or even 15A shore power, but it requires some load management.

My typical genset use would be after 12-24 hours on the hook, with the batteries down to 70%-75% SOC. The charger starts pulling 10A (1,250W) for a while when first powered up. The water heater will pull 12A (1,500W) for a half-hour to 45 minutes. By then the batteries are in "accept" mode and the charger draw is negligible. Even if I add in 1,500W for cooking, I can't come up with the need for anything larger than a 5KW genset.

The wildcard here is your air conditioner use. With a 5KW generator, I'd be worried about starting the air conditioners with too many of the other loads going. I don't do this now, mostly because running the genset that long would rattle all my fillings out. But if I had a quieter unit, I'd just manage my loads. Maybe shut down one air conditioner while running one of the other big loads. Some would find this inconvenient. I don't.
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Old 09-10-2016, 08:24 AM   #14
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Without doing a load study, most boats in the 43' class have something about 8kW. That should run just about everything at the same time. If you don't mind a little load management, you could go down to a six.

I have not heard of a modern 6kW marine unit having any trouble starting a marine air.

Regarding brands, just use the following criteria: Three cylinder, 1800rpm, direct drive, electronic volt regulator. No two cylinders, no belt drive, no capacitor exciter.
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Old 09-10-2016, 11:43 AM   #15
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Here is another way of calculating.

Assuming that you agree that there is no point in having generating capacity greater than your shore power hookup, so if you have one 30A cord:

30A X 120V =3600. You should never operate a generator continuously at greater than 70% load, so 3600 divide by .7 = 5kw (rounded off).

The same calculations for a 50A cord = 8.5kw.

Note that this number is nearly the same as a couple of other recommendations .

We have a 5kw Onan generator connected to a Victron Multiplus inverter/charger, and a single 30A shore power cord. There is a control panel which allows us to dial the max amps drawn from the generator or shore power. (usually set at 30, but sometimes less). If the electrical load exceeds this number, the inverter makes up the difference from the batteries, then recharges the batteries when the load drops.

A comparative test of small marine generators is here:
https://www.victronenergy.com/upload...7-jan-2008.pdf
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Old 09-10-2016, 02:00 PM   #16
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[QUOTE=Rossland;You should never operate a generator continuously at greater than 70% [/QUOTE]


I don't think Northern Lights would agree with that. They claim full power continuous duty. Not sure about Onan, but I would expect the same.
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Old 09-10-2016, 03:22 PM   #17
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I would like to bring the subject of the FW pump back up. When they do fail, it rarely has anything to do with circulation unless the bearing seizes up. The impeller is non-interference so they aren't worn and they aren't exposed to salt so they don't corrode away. They either leak at the seal which wouldn't cause any "slight raise in temp", it would have no impact as long as fluids are topped off and would have a dramatic rise in temp if they aren't topped off. If the bearings wear out (frequently due to a leaking seal) and the pump continues to circulate at the same rate until it is fixed or fails catastrophically, neither would be slight.
I am not implying any funny business, maybe he is doing a few maintenance things at the moment but the FW pump would not be my first suspect for this symptom.
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Old 09-10-2016, 03:57 PM   #18
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As stated by others, the coolant pump issue would slow me down, even more than the genset. Tell the owner to get down engine up and you'll be back.

BTW, in the PNW 12.5 KW is not too big. We are an all electric boat and microwave and hair dryers have to be watched when reverse cycle heat, chargers and clothes dryer are on.
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Old 09-10-2016, 04:04 PM   #19
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I don't think Northern Lights would agree with that. They claim full power continuous duty. Not sure about Onan, but I would expect the same.
Agree completely. My genset engine is rated for double the HP when installed as a primary mover in a sailboat, at around 3000 RPM. 1800 RPM at a full 12.5 KW is just loafing vs design. Design cooling capacity is of course different at lower HP.
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Old 09-10-2016, 06:56 PM   #20
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I would like to bring the subject of the FW pump back up. When they do fail, it rarely has anything to do with circulation unless the bearing seizes up. The impeller is non-interference so they aren't worn and they aren't exposed to salt so they don't corrode away. They either leak at the seal which wouldn't cause any "slight raise in temp", it would have no impact as long as fluids are topped off and would have a dramatic rise in temp if they aren't topped off. If the bearings wear out (frequently due to a leaking seal) and the pump continues to circulate at the same rate until it is fixed or fails catastrophically, neither would be slight.
I am not implying any funny business, maybe he is doing a few maintenance things at the moment but the FW pump would not be my first suspect for this symptom.
I tend to agree. Leakage is the usual problem when a pump goes bad, and bearing failure if it's left for too long. Seldom, if every do they cause overheating.

But I think the most likely explanation is a repair tech who is doing what too many do best - guessing and replacing parts in hopes of fixing the problem. I wouldn't worry too much about the pump, and focus on pushing the engine at sea trial to see if it over heats. Then take it from there.
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