Twin vs single

Nomad Willy said:

I have a gas Onan in my motor home.
It has priming problems.
Why do you call yours “old school”?

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Mine is old school because it's an MCCK. It's built in the 80s, but the engine design on it dates to about the 1940s with very little change except a newer carb design and electric fuel pump. It's a flathead with points ignition. It's got its quirks. It usually takes a few cranks to prime the carb and start if it's been sitting for more than a couple of days. And it seems like the fuel mixture adjustments don't hold perfectly on the carb, as they periodically need to be tweaked to keep it from surging and misbehaving.

But when it's running well, it's a great unit. Barely a hiccup when you kick on a 16k BTU A/C unit.

Our 1977 Tolly's orig Kohler 7.5 is a beast! Runs well and powers all we want.

Seldom does she need anything. No idea of the hours on her. Never uses a drop of oil. Has capability to be set up with switches as an instant start for when an "on" breaker suddenly experiences a load [fridge, 120V need or AC]. For several reasons I never leave switches setup in that pattern. I always do a hands on start or stop sequence and never leave the boat with genset running

TwoToTango said:

Also just how often really end up using the twin in a back up situation ? I’ve been told if one goes down the other is likely because it’s usually fuel issues that cause a diesel to stop .

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Not often.

Have separate fuel supply if twin engine.

Twins are nice for maneuverability, except less so without counter rotation - smaller boats with V-drives usually.

But, my particular point: A twin engine boat with one down is out of practical service until fixed and the odds of that are twice as high, as is the cost of maintenance.

EngNate said:

Not often.

Have separate fuel supply if twin engine.

Twins are nice for maneuverability, except less so without counter rotation - smaller boats with V-drives usually.

But, my particular point: A twin engine boat with one down is out of practical service until fixed and the odds of that are twice as high, as is the cost of maintenance.

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I wish you would have told me that before I used my boat on port engine alone for approx 32 hours. I could have stayed home instead.

EngNate said:

Not often.

Have separate fuel supply if twin engine.

Twins are nice for maneuverability, except less so without counter rotation - smaller boats with V-drives usually.

But, my particular point: A twin engine boat with one down is out of practical service until fixed and the odds of that are twice as high, as is the cost of maintenance.

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The odds of engine failure can easily and simply be reduced to zero, just by having no engine(s) at all.

Let's keep this going.

With today's most popular and trendy motor vessels being outboard powered, the twins Vs single argument for very old boats seems a bit dated. Kinda like Ford Vs Chevy, yesterday's news.

Nordhavn you say? Humm, all of those have a spare engine too. Point to Dauntless as proof of something. OK, I'll do that. Her journeys are less about the the boat and more about the owner. Few of us are as extraordinary and driven as Richard.

The best cruising passage makers remain, ta da, sailboats. Proof positive, of what I'm not sure. Just like single Vs twins arguments, proof positive of ongoing

EngNate said:

Not often.

Have separate fuel supply if twin engine.

Twins are nice for maneuverability, except less so without counter rotation - smaller boats with V-drives usually.

But, my particular point: A twin engine boat with one down is out of practical service until fixed and the odds of that are twice as high, as is the cost of maintenance.

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EN - This thread, and especially seeing your 31' Uniflite in Avatar, make me want to reveal the following:

Bout a decade ago... My son and I had been cruising in SF Bay for the day. During the last jaunt from Golden Gate Bridge I'd been cruising on plane; 18 knots with bow slightly raised. All went well till we came into the 5 mph canal leading toward marina where I docked the boat. Took a couple minutes puddling along on idle before starboard engine quit. I tried to start it with no luck. Then the port engine quit. Luckily it was calm day with little current. We dropped anchor. Motor sailer with a boating class soon came along and side tied us for the last 3/4 mile. Skilled skipper plopped us straight into the slip and would not take a dime! 1973, 31' Uniflite had one big gas tank that fed both engines. While bow was raised a bit... enough fuel to feed both engines had then been to tank's rear. When I'd throttled back to idle, and bow dropped down - well it's obvious what happened. Yup!!! I felt pretty dumb!!!

Anyway, it may interest you to see a double to your boat! Uni's are really nice boats to play with... if we keep enough fuel aboard!! LOL

Wow, how did we get pulled into another "single vs twins" debate???

EngNate said:

Not often.

Have separate fuel supply if twin engine.

Twins are nice for maneuverability, except less so without counter rotation - smaller boats with V-drives usually.

But, my particular point: A twin engine boat with one down is out of practical service until fixed and the odds of that are twice as high, as is the cost of maintenance.

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This is just WRONG.

I have seen twin outboards that were not counter rotation, but they are rare. Inboards, including v drives, are always counter rotating. Besides, who of us are in small twin outboards?

Twin with one down is just as usable as any boat with just a single, as that is exactly what you have.
If you have twins with a total hp the same as the single your identical boat mate has, the cost of maintenance is going to be very close.

Most engine failures are not fuel related any more. That may have been the case in the days before EPA rules forced clean fuel upon us. Nowadays, you can alter your fuel filter change schedule to "when necessary" instead of annually or more frequently than that. I know this. My last filter change, according to my log, was 12 years for secondaries, 4 years for primaries. Even then, only one of the 4 I changed really needed changing.

sunchaser said:

Let's keep this going.

With today's most popular and trendy motor vessels being outboard powered, the twins Vs single argument for very old boats seems a bit dated. Kinda like Ford Vs Chevy, yesterday's news.

Nordhavn you say? Humm, all of those have a spare engine too. Point to Dauntless as proof of something. OK, I'll do that. Her journeys are less about the the boat and more about the owner. Few of us are as extraordinary and driven as Richard.

The best cruising passage makers remain, ta da, sailboats. Proof positive, of what I'm not sure. Just like single Vs twins arguments, proof positive of ongoing

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No kidding Chev trampled Ford back in the 70's.

Soo-Valley said:

No kidding Chev trampled Ford back in the 70's.

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The real battles were in the 50s and 60s when the V8s were being beefed up and fins, distinctive style and great colors added. By the EPA throttled mid 70s the battle was pretty much over until a decade ago with Mustang vs Camaro being re- energized. Cars are sure great fun with many hours spent tinkering in the garage when winter boating has slowed down boat time.

Classic car tinkering... New radiator, water pump, clutch fan... etc.......

Hope photos came out straight! Been having problems getting them straight when posted on any forum; from newer phone. Other place I send photos they come out straight and correct.

Edit: Well, that didn't work to straighten photos!

What fun and nice work Art.

Art, yes I do love the boat, esp with the single Cat. I did have a bit similar issue, hauled out with low fuel, bow down a bit & lost the prime to the diesel heat.

Koliver, there are definitely inboards with V drives that are not counter rotating, I have a customer with one, sea trialed another when I was buying.

Soo Valley, and others check your transmission manual with regard to lube and cooling requirements for a freewheeling shaft.

rslifkin said:

Mine is old school because it's an MCCK. It's built in the 80s, but the engine design on it dates to about the 1940s with very little change except a newer carb design and electric fuel pump. It's a flathead with points ignition. It's got its quirks. It usually takes a few cranks to prime the carb and start if it's been sitting for more than a couple of days. And it seems like the fuel mixture adjustments don't hold perfectly on the carb, as they periodically need to be tweaked to keep it from surging and misbehaving.

But when it's running well, it's a great unit. Barely a hiccup when you kick on a 16k BTU A/C unit.

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rslifkin,
You said the magic words ... electric fuel pump.
But the carb will need to be designed for the right amount of fuel pressure.
Put a new carb on it recently. I thought of an OB squeeze “bulb” for priming but I don’t know where to put it. Thanks for the electrifying idea.

Nomad Willy said:

rslifkin,
You said the magic words ... electric fuel pump.
But the carb will need to be designed for the right amount of fuel pressure.
Put a new carb on it recently. I thought of an OB squeeze “bulb” for priming but I don’t know where to put it. Thanks for the electrifying idea.

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In my case, the electric fuel pump isn't an add on, it was done by Onan on the later production units.

What model is the unit in your motorhome?

EngNate said:

..............

Soo Valley, and others check your transmission manual with regard to lube and cooling requirements for a freewheeling shaft.

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Thanks, for Borg Warner 71C. From the owners manual


There is no other warning or caution in the 88 page service manual.

Soo-Valley said:

Thanks, for Borg Warner 71C. From the owners manual
View attachment 95686

There is no other warning or caution in the 88 page service manual.

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Importance is to not go above trolling speed... 4 to 5 knots. When we run on one with the other in freewheel... if duration of more than an hour is to be expected, on the hour I start the freewheeler and shut down the previous power supply. That way not too much freewheel burdon is experienced by either trany!