View Poll Results: I've used a backup on my single-engine boat
Because of a problem with the main engine 1 4.35%
Because of a shaft/prop problem 0 0%
Because of a fuel supply problem 1 4.35%
Never 5 21.74%
I don't have a backup, just the main engine 16 69.57%
Voters: 23. You may not vote on this poll

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Old 05-16-2016, 04:54 PM   #1
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Backup

I'm a single-engine kind of guy. Let's just take that as a given.

Many single-engine boats going offshore have a backup propulsion system. These backup systems have varying degrees of dependence on the primary systems.

How often are these backup systems used in anger? How often is a more-independent system more valuable than a less-independent one?

Ideally I'd love to see some numbers here: the main engine in such an environment fails every XX hours, the prop/shaft becomes disabled every YY hours, fuel problems that impact all boat systems occur.. That'd make it easy to quantify the value of not only backup propulsion systems in general, but the the relative value of specific types of backups.

Unfortunately I'd be real surprised if such numbers exist in a statistically significant form. And so I'll ask for anecdotal information:

If you do go out of towboat range, have you needed your backup system? What type of failure did you encounter, and what would have been the consequences of not having the backup?
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Old 05-16-2016, 06:10 PM   #2
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Our backup engine is entirely independent, except for drawing diesel from the same two tanks. We had to use it once, almost twice.

Failure type: ruptured oil filter (bolt backed thru it (kid you not)) caused low oil alarm on main. Shut down main started backup and tied to the first dock we saw. We were in the ICW, it was 30 minutes till dark and we had no way to quickly anchor (windlass was being rebuilt). So it was very useful to have it.

Btw, the windlass had been due back aboard almost two months prior...although it was stupid of me to leave without reconnecting the anchors to their chains. I could have at least dropped them quickly if I needed it.

So what would you have done in the ICW with 30 minutes of light left, no engine, no backup, no anchors. (For the record, without having the backup we wouldn't have left in the first place without the windlass)

Second time was in the middle of the Gulf of Mexico, the water pump started leaking and we considered shutting down the main and running on the backup while we fixed it. In the end we didn't and chose to continue as it was and fix it at the dock two days later. But had it gotten worse we would have.
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Old 05-18-2016, 02:15 PM   #3
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This is why I'm lusting after a twin screw, although the economics are a lot worse.....

Previous boat was single screw and had a backup propulsion system....... 400 square feet of dacron.....
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Old 05-18-2016, 02:33 PM   #4
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I'm not answering your question about usage of a back-up system, but if I had a single screw as I used to, I'd be tempted to look into a diesel outboard. Apparently Yanmar makes a 50 hp model. not sure if legal in U.S., and storage & rapid deployment would take some thought and engineering, but I like the idea of completely separate system. Has anyone tried this?
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Old 05-18-2016, 03:04 PM   #5
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Why not two small twins?

My engines come to 348hp total.
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Old 05-18-2016, 04:50 PM   #6
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Menzies,
I'm with you in preferring two small twins. I was thinking danderer had a single and was contemplating adding a back-up propulsion system....
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Old 05-18-2016, 05:06 PM   #7
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Quote:
Originally Posted by menzies View Post
Why not two small twins?

My engines come to 348hp total.

I think OP means he's already got a single-screw boat, and if so that "twin" ship has already sailed, so to speak...

I could imagine an electric motor driven off a genset. Don't know as an actual implementation like that would be best with another shaft/prop, or whether it could be clutched into driving the main shaft/prop.

Which in turn suggests a clutching mechanism, probably no small problem, would have to also be able to disconnect the main shaft from the main engine.

Relying on the main shaft/prop would be building in a dependency. OTOH, it may be practically easier/better/cheaper -- and good enough -- for very occasional circumstances.

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Old 05-18-2016, 05:31 PM   #8
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I see.

Well, what about setting your genset up to connect to the shaft. That is another popular method.
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Old 05-18-2016, 05:34 PM   #9
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Quote:
Originally Posted by ranger42c View Post
I could imagine an electric motor driven off a genset. Don't know as an actual implementation like that would be best with another shaft/prop, or whether it could be clutched into driving the main shaft/prop.

Which in turn suggests a clutching mechanism, probably no small problem, would have to also be able to disconnect the main shaft from the main engine.

Relying on the main shaft/prop would be building in a dependency. OTOH, it may be practically easier/better/cheaper -- and good enough -- for very occasional circumstances.

-Chris
I like this idea. If I was going to go to the trouble, I'd want a separate shaft and prop, I think.
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Old 05-18-2016, 05:55 PM   #10
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back to outboards--if you like the generator for energy idea--what about using an electric outboard? Torqeedo makes a 40 and 80 hp model. provides not only redundancy in shaft/prop, but also potentially steering.
Any thoughts? Actually, just read that the electric outboard uses high voltage, so it's probably not practical. back to diesel.....
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Old 05-18-2016, 06:57 PM   #11
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Aren't two engines twice the problem and twice the expense?
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Old 05-18-2016, 07:05 PM   #12
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Greetings,
"Aren't two engines twice the problem and twice the expense?" NOT if you have the right anchor...

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Old 05-18-2016, 07:10 PM   #13
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Backup

Sweet!!! Another singles vs twins thread!

Edit: I believe that huge thread was started with MarkP as the op as the result of a thread split??? Hmmmm, Mark always seems to be an early poster in this subject
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Old 05-18-2016, 07:21 PM   #14
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Old 05-19-2016, 06:27 AM   #15
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Quote:
Originally Posted by Dawdler View Post
back to outboards--if you like the generator for energy idea--what about using an electric outboard? Torqeedo makes a 40 and 80 hp model. provides not only redundancy in shaft/prop, but also potentially steering.
Any thoughts? Actually, just read that the electric outboard uses high voltage, so it's probably not practical. back to diesel.....

Maybe there's a way? Even a separate genset, if necessary?

An electric outboard would weigh much less than a diesel outboard, I think.... so maybe storage, mounting, etc. issues would be more easily managed.

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Old 05-19-2016, 06:44 AM   #16
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what about using an electric outboard?

A hp in a boat engine will make about 20 lbs of push.

At say 2 GPH perhaps 30-35HP is sent down the shaft for about 600-700 lbs of push.

An outboard with 20-40 lbs of push is not going to get much boat movement.

Unless fitted with a special lower unit and big prop even a 20-25 hp dink motor will have a very hard time at 3k or 4K towing or on the hip.
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Old 05-19-2016, 06:57 AM   #17
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Actually, that "dink towing on the hip" thing is another possibility for OP's question.


Maybe suggests a larger rather than smaller outboard, plenty of gas, and a connection (towing, pushing, hip) set-up... but maybe that's sufficient to move a 2006 Mainship 34T (see OP's avatar) in an emergency?


-Chris
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Old 05-19-2016, 07:31 AM   #18
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You can look at failure rates and probabilities all you want, but any statistician will tell you that a failure can still happen anytime. And any boat owner can confirm this.

So I think the real question is what are you going to do when any given failure occurs. You have three choices:

1) Work around the problem. This is where redundant/backup systems come into play.

2) Fix the problem. This is where carrying spares, tool, and knowledge come into play.

3) Call for help.

Where you are cruising is a major factor in how you approach all of the above, and will typically result in very different decisions between different boats. If you cruise the ICW or other populated areas, many boaters will skip right to step 3 and call for help. No need to carry spares or know how to fix anything. But the further away you get form civilization, #3 ceases to be an option and you must be able to handle the problem in steps 1 and 2, i.e. work around the problem or fix it. This is where you see boats with critical systems that are redundant, and with spares tucked in every corner of the boat.
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Old 05-19-2016, 07:33 AM   #19
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Quote:
Originally Posted by ranger42c View Post
Actually, that "dink towing on the hip" thing is another possibility for OP's question.

Maybe suggests a larger rather than smaller outboard, plenty of gas, and a connection (towing, pushing, hip) set-up... but maybe that's sufficient to move a 2006 Mainship 34T (see OP's avatar) in an emergency?
-Chris
I was able to get my old 34 Mainship to move with an 8 hp outboard/dink setup. But if there was any wind or current I don't think it would move very well.

I've been single engine boating for 25 years without a backup. Have I had shut downs? Yes a few times but they were all (but one) fuel related and I was able to get the engines running again, sometimes in harry situations, sometimes not.
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Old 05-19-2016, 08:30 AM   #20
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On our boat the backup is exact duplicate of the main engine.
Same spares carried for the both of them.
We've never had a motor or trans failure however we have had ropes,nets etc stop a shaft.
The sound of silence is not a song I like to sing when underway.
It's nice to have redundancy when Murphy pays a visit.
Although the guy who owns this seems to have taken that argument a bit further along than me.
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