Single vs Twin: It's Baaaaack!

[Underway]

But then you would need a propeller capable of absorbing the full power and that prop would be way too lightly loaded in normal operation to produce much thrust.

Such a setup would require a pair of CPP wheels to be of much use and that setup would negate any cost savings plus add another layer of complexity and maintenance demands.

What's the point?

There is a good reason that the opposite of that scheme is the only method with a history of successful marine application, that is two engines (or more) driving a single shaft.

The chain(s) would be oversized solely for the purpose of insuring that the second (remaining) chain would not break following instantaneous failure of the opposite chain/shaft in a high power scenario...a safety consideration...that's all. Thinking in terms of a retrofit of something like a 46 GB with twin 375's or more. (I keep forgetting this is a mostly Lehman web site). Anyway, a 400 HP single would probably get 13-14 knots at max output for occasional use, but run comfortably at 8-9 kts ...where "fast trawlers" operate these days anyway. In fact one of those 375's could be pulled out and the remaining engine might do the job of getting the hull "on plane" for the occasional burst of speed. Objective would be to stay with existing gearboxes...maybe props...or possibly upsize props very slightly. The chain drive arrangement allows a great deal of flexibility in overall ratio. Of course changes would depend on capabilities of existing structure, loads, shafts, transmissions and clearances. Should be an overall weight reduction, the engine runs higher on the power curve at slow speed....possible fuel savings especially if the props were optimized.

 

[Chuck Gould]

Of all the goofy arguments ever advanced, the one presently peddled here has to take the cake. "You single engine guys are all scared s***tless of the water! If you were really manly men, you'd be proud to have your running gear exposed to damage from a log strike or grounding! You'd simply laugh at the risk, and consider boating more enjoyable as a result! Heck, I know of a guy who motored right past a number of suitable boatyards with a 9 square foot hole in his hull! That of course proves it's a smart practice for everybody else and that ripping off a stabilizer is no big deal- at least not for a really manly man. If you had any cajones at all, you'd be well advised drag them through the water, fully exposed, like us real mariners do." Of course, that's both exaggerated and misstated beyond what was posted- furnishing me with an example with which to make my point.

Ever notice that people who lack any convincing argument thrive on misstating or distorting an alternative point of view? That they then attack not the originally expressed idea, but their own distorted misstatement of same? It is more often the guy who is entirely unsure of himself who cannot tolerate an opposing opinion.

 

[Giggitoni]

Can we talk about "anchors" now...?

 

[psneeld]

Can we talk about "anchors" now...?

Why??...sounds like we are venturing into psychology now...

Ought to be a blast!!!!

 

[Chuck Gould]

Mahal: Anything protruding from the hull, including a stabilizer, increases the risk of damage to the hull from striking debris (like one of those wonderful, barely submerged cargo containers people hit from time to time) or grounding. The risk is substantial enough that, for example, many of the new "pod" drive systems are specifically designed to break away from the hull in the event of a catastrophic impact. Better to buy a new drive leg than a new boat.

When considering the advantages and disadvantages of both twin and single engine design, everybody will need to evaluate and assess the risk of unprotected running gear. Individual perspectives will apply. To me, if the other 10 reasons I prefer a single engine didn't exist, I would still be reluctant to own a twin screw boat because of the risk to the exposed shafts, more exposed props, and the possibility of holing the hull by tearing out a strut. That doesn't mean that my considerations make the purchase of a twin screw boat ill-advised for others, and it doesn't make me less of a boater or more "fearful of the water" as some twin screw boaters here want to insist.

 

[RT Firefly]

Greetings,
Mr. Giggitoni. Since I am storing several of my NUMEROUS anchors of various profiles in the spare spaces in my ER as well as under my foam topped coil mattress, would I be best to stack them or lay them flat? Would my rode (rope or chain?-Which is best?) be more or less likely to get caught up in the flywheel(s) of a single or a twin engine installation? Which anchor style AND weight would be best to minimize a "lethal" opening below the water line when the anchor gets flung about at high speed in the ER following rode entanglement with above mentioned flywheel(s)? YOU seem to have the most level head in this thread currently.
Mr. psneeld. Isn't the whole internet about psychology? "MY centipede is FASTER than your pathetic millipede....Here, hold my beer and watch this!"

 

[THD]

Chcuk-or you could have a twin with fully protected shafts, props and rudders, no struts at all, and then you are left with the primal decision-one engine or two?

Maybe we need to add dinghies to the discussion-one oar or two?

 

[RT Firefly]

Greetings,
Mr. THD. "Them's not oars. Them's me wife and daughters....

 

[psneeld]

Greetings,
Mr. Giggitoni. Since I am storing several of my NUMEROUS anchors of various profiles in the spare spaces in my ER as well as under my foam topped coil mattress, would I be best to stack them or lay them flat? Would my rode (rope or chain?-Which is best?) be more or less likely to get caught up in the flywheel(s) of a single or a twin engine installation? Which anchor style AND weight would be best to minimize a "lethal" opening below the water line when the anchor gets flung about at high speed in the ER following rode entanglement with above mentioned flywheel(s)? YOU seem to have the most level head in this thread currently.
Mr. psneeld. Isn't the whole internet about psychology? "MY centipede is FASTER than your pathetic millipede....Here, hold my beer and watch this!"

Yes but it's so much more fun when someone specifically wants to introduce it into a thread.

The only thing more fun is when two puff up their chests and call each other out (and neither could whip a wet noodle) or when someone is so far off base you start to wonder IF THEY ARE toying with the rest of us....

 

[RT Firefly]

Greetings,
Mr. psneeld. Toying? Moi?...

er....

 

[bfloyd4445]

Definitely. More wetted surface creates more drag.

A keel-less boat will have less wetted surface.

A keel can provide protection to shaft, propeller, and rudder.

A two engined/propellered boat will need at least two keels to provide protection. Expect two keels to have more wetted surface then one keel.

If two smaller engines were more efficient than one larger engine of the same total horsepower, wouldn't there be more dual-engined automobiles?

last night thinking about the single vs. twin question that same thought came to mind. Guess that answers the question once and for all. Single engine wins.................wait a minute............the current trend has gone to dual engines in autos. Seems the electric primary motor with a gas engine generator system like the volt is about to take over from the hybrids.
Maybe ten years from now we will see electric powered vessels with a diesel generator powering the motors

so that brings us full circle back to the original question dosent it/

 

[psneeld]

last night thinking about the single vs. twin question that same thought came to mind. Guess that answers the question once and for all. Single engine wins.................wait a minute............the current trend has gone to dual engines in autos. Seems the electric primary motor with a gas engine generator system like the volt is about to take over from the hybrids.
Maybe ten years from now we will see electric powered vessels with a diesel generator powering the motors

so that brings us full circle back to the original question dosent it/

D&D Motor Systems - Electric Boat Motors

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Electric, Hybrid and Diesel Marine Propulsion

 

[RT Firefly]

Greetings,
Mr. 45. Already been done!

Top Gear Build an Electric Car Part 2/3 - YouTube

 

[RickB]

The chain(s) would be oversized solely for the purpose of insuring that the second (remaining) chain would not break following instantaneous failure of the opposite chain/shaft in a high power scenario...a safety consideration...that's all.

If one chain broke at high power the load would momentarily reverse on the other side as it suddenly became driven. Making the chain larger and heavier would only make it more likely to come adrift as that mass was suddenly decelerated with the load reversal then accelerated as the load reversed again.

... the engine runs higher on the power curve at slow speed....possible fuel savings especially if the props were optimized.

OK, so how does it run "higher on the curve" at slow speed and still have power reserves to achieve higher loads and speed? This is right back to the old "cruise prop" fantasy of having it both ways.

 

[alormaria]

The only time you really need twins is when you are buying or selling.

 

[bfloyd4445]

The only time you really need twins is when you are buying or selling.

Hahaha.....I would change that to the only time you need twins is at the marina or when selling

 

[bfloyd4445]

The chain(s) would be oversized solely for the purpose of insuring that the second (remaining) chain would not break following instantaneous failure of the opposite chain/shaft in a high power scenario...a safety consideration...that's all. Thinking in terms of a retrofit of something like a 46 GB with twin 375's or more. (I keep forgetting this is a mostly Lehman web site). Anyway, a 400 HP single would probably get 13-14 knots at max output for occasional use, but run comfortably at 8-9 kts ...where "fast trawlers" operate these days anyway. In fact one of those 375's could be pulled out and the remaining engine might do the job of getting the hull "on plane" for the occasional burst of speed. Objective would be to stay with existing gearboxes...maybe props...or possibly upsize props very slightly. The chain drive arrangement allows a great deal of flexibility in overall ratio. Of course changes would depend on capabilities of existing structure, loads, shafts, transmissions and clearances. Should be an overall weight reduction, the engine runs higher on the power curve at slow speed....possible fuel savings especially if the props were optimized.

seems to me my experiance with smaller boats proved to me that the added hp of twins didnt give much more speed which i blamed on the added drag. A single of the same hp as the two singles would far out preform the twins. But here we aren't concerned with speed but durability and economy right?
This question cannot be answered unless we define it better

 

[bfloyd4445]

single with twin props

This link may be of interest. Testing of twin engined craft converted to single engine dual props.

Can One Engine Drive Two Props? | BoatTEST.com

 

[dhmeissner]

Wow! I haven't logged on in a day and I just dutifully "scanned" from 306 to 378, so now this is my contribution: buy what you like and watch out for cognitive dissidence.

I love boating. Oh, And I own a diesel yacht, not a trawler. And a sailboat.

 

[bfloyd4445]

Wow! I love boating. Oh, And I own a diesel yacht, not a trawler. And a sailboat.

Yep, you said that right. I love all boats and each has its specialty at which it excells. sail, power, single, dual, triple, I love em all

 

[MurrayM]

I don't know about you, but I prefer to keep my dangling-down bits well protected while going over logs or sharp nasty rocks.

Maybe there's a parallel here with my "Big Truck / little penis" theory. Are the twin folks overcompensating as well?

 

[BaltimoreLurker]

Single for me. But I could be talked into twins.

 

[Codger2]

I don't know about you, but I prefer to keep my dangling-down bits well protected while going over logs or sharp nasty rocks.

Maybe there's a parallel here between my "Big Truck - little penis" theory. Are the twin folks overcompensating as well?

:lol:

 

[Underway]

If one chain broke at high power the load would momentarily reverse on the other side as it suddenly became driven. Making the chain larger and heavier would only make it more likely to come adrift as that mass was suddenly decelerated with the load reversal then accelerated as the load reversed again.

OK, so how does it run "higher on the curve" at slow speed and still have power reserves to achieve higher loads and speed? This is right back to the old "cruise prop" fantasy of having it both ways.

I'm not following you here. Both sides would be normally be driven all the time. So if one chain broke, the already driven chain on the other side would get a burst of additional power. Sounds like you're thinking in terms of trailing/freewheeling one side...??

Indeed it would require that the operating envelope of the engine be (re)defined and that the engine be instrumented and operated accordingly.

 

[RickB]

This link may be of interest.

It was interesting ... especially the bits about the MPG ... the writer seems to have forgotten that diesel fuel contains anywhere up to 25 percent more energy per gallon than gasoline so his comparisons are meaningless.

 

[RT Firefly]

Greetings,
Mr. Rick B. Post #385 discussing a question that has no answer and YOU'RE concerned about FACTS? Phffftttt..........

 

[Marin]

Eric-- I respond to posts based on what the posters write. Given all the hoopla about twin engine boats sinking from hitting deadheads I can only conclude that the posters are terrified of deadheads. I respect what a deadhead can do, I've seen first hand what they can do, and we keep a very sharp eye out for debris of any kind in the water which as you know from your long experience in these waters can be problematical.

But I am not terrified, scared, or worried about them. If I was as uptight about them as some posters seem to be we'd never take our boat out of the slip.

I have no issue with people's fears. We all have them. What I object to is applying an individual fear onto everyone with regards to a very broad topic like twin engine boats. In this case, the fear is not even close to being supported by reality. You want reality, read Tom's (Sunchaser) and Eidelweiss' posts.

Regarding the one-engine-two-prop configuration, Rick has satisfied my curiosity if this is something that would provide the kind of twin engine operational flexibility I require..

 

[RickB]

I'm not following you here. Both sides would be normally be driven all the time. So if one chain broke, the already driven chain on the other side would get a burst of additional power.

From where does this "power" originate?

An engine doesn't push power out, the load pulls it out.

If there is X amount of load at Y rpm then that is all the engine delivers.

There may be more available but unless the consumer demands it, it isn't produced or delivered and a sudden excess in capacity is not transfered to the other consumer if it doesn't demand it.

 

[Marin]

Heck, I know of a guy who motored right past a number of suitable boatyards with a 9 square foot hole in his hull! That of course proves it's a smart practice for everybody else and that ripping off a stabilizer is no big deal- at least not for a really manly man.

As you know obviously know nothing of the stabilizer incident or why the decisions that were made were made, your assumptions and speculation about them is as meaningless as your apparent belief that it's just a matter of time before a twin engine boat hits a deadhead, rips out a strut and sinks.

I would explain to you what happened and why but I don't like taking the time for that sort of thing if I don't think the reader would benefit from the information.

 

[markpierce]

Don't blame me. I didn't start this thread even though mine is post #!. A moderator pulled it from another thread.