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Old 03-21-2017, 11:49 AM   #61
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Originally Posted by Nomad Willy View Post
Still the biggest difference between singles and twins is weight and power.
Eric,

Not necessarily so. My new to me boat has twin Cummins 5.9 BTA's that weigh 1075# ea (w/o gears) or 2150# for the pair, and produce around 650HP.

Looking around at 600-650HP diesels for a comparison between singles and twins, I found these specs:

Volvo D8-600 - 1852#
Cummins QSC8.3 - 1975#
Cat C8.7 - 2295#
Cummins QSM11 - 2475#
MAN D2840 LE - 2976#
Yanmar 6HYM-ETE - 3047#
8V92 Detroit - 3815#

I threw in the DD just for grins, but you see where this is going. My twins are lighter than many of the singles in that horsepower range. The lighter ones are higher-speed diesels, but all of these are common engines found in planing cruisers and sportfishing boats, where weight is often an important factor.

The very lightest is only 298# lighter, the weight of one big guy with gear!
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Old 03-21-2017, 11:54 AM   #62
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I understand the backup/maneuvering that twins provide and I have only had the single but in the same sized boat I have now I simply like the extra space in the ER that I enjoy every time I go/work below. But, have not had my first break down either!
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Old 03-21-2017, 12:09 PM   #63
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And not having radar and being caught in a scary fog situation.....can change a lot of opinions....like a single quitting in a high current/wind situation without many good options.

But I have a single and just passed 14,000 miles in the last 5 years in this boat.
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Old 03-21-2017, 12:25 PM   #64
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As I shop for a boat, some of the Grand Banks models have single, and some have dual engines.
I've never owned or operated a twin engine boat - my initial impression it is just twice the maintenance, upkeep and cost. But, mebbe redundancy is good.
What are the pros and cons of twin engines? Would you recommend twins, and why?
Thanks.
You have inadvertently entered into a religious debate. Pick a side single or twins. There may be hard liners in either camp. I like to think of myself as a universalist in this debate and will and do use boats with both means of propulsion including sail and paddle and peddle.. God or man gave us the option for twins or singles and we just have to apply it where we want for our own reasons. The right or wrong of it is inconsequential other than bait for a debate.
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Old 03-21-2017, 12:38 PM   #65
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Yep....good arguments in both camps....the real separator is area of use and boat configuration.

Religion? Like many recent discussions on religious fanaticism....it is applicable to the twin/single debate.
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Old 03-21-2017, 01:11 PM   #66
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No need to fear twin engined boat's. Some are better than others and in the end they all have the same view, until you go aground. Here's a design for the groupthinkers to ponder. Click image for larger version

Name:	IMG_3286.JPG
Views:	96
Size:	79.1 KB
ID:	62980Click image for larger version

Name:	IMG_3290.JPG
Views:	103
Size:	76.7 KB
ID:	62981Comes in single or twin. As a recovering sailor I thought I was in the single engine camp. In hindsight I think I was misinformed.
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Old 03-21-2017, 01:23 PM   #67
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No need to fear twin engined boat's. Some are better than others and in the end they all have the same view, until you go aground. Here's a design for the groupthinkers to ponder. Attachment 62980Attachment 62981Comes in single or twin. As a recovering sailor I thought I was in the single engine camp. In hindsight I think I was misinformed.
The best of both worlds!!
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Old 03-21-2017, 02:19 PM   #68
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In commercial fishery, I never owned or operated a boat with twins and when dealing with nets and lines hanging off the back of the boat, it would have been a hardship. Yes, we did break down on occasion and got towed in.

My recreational boats have been a mix of both, but current boat is twin diesel and we love it. It's never been towed. Always managed to limp home on one engine.

You have to take into consideration a lot of factors and where you will be using it. Is there a significant chance of grounding the boat, underwater obstruction, etc. Here in the PNW, with a little care and planning grounding is not likely and most debris is at or on the surface. My current boat has never been grounded and have owned it since 1976.

My best advice is check it out carefully and buy what's within your budget and works best for your boating area.
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Old 03-21-2017, 02:40 PM   #69
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Originally Posted by LarryM View Post
Eric,

Not necessarily so. My new to me boat has twin Cummins 5.9 BTA's that weigh 1075# ea (w/o gears) or 2150# for the pair, and produce around 650HP.

Looking around at 600-650HP diesels for a comparison between singles and twins, I found these specs:

Volvo D8-600 - 1852#
Cummins QSC8.3 - 1975#
Cat C8.7 - 2295#
Cummins QSM11 - 2475#
MAN D2840 LE - 2976#
Yanmar 6HYM-ETE - 3047#
8V92 Detroit - 3815#

I threw in the DD just for grins, but you see where this is going. My twins are lighter than many of the singles in that horsepower range. The lighter ones are higher-speed diesels, but all of these are common engines found in planing cruisers and sportfishing boats, where weight is often an important factor.

The very lightest is only 298# lighter, the weight of one big guy with gear!
Larry,
And that's the way it should be.
But I was specifically referring to twin FL380 boats compared to single FL 380 powered boats. The twins all have twice as much weight in the propulshion package. Counting the extra fuel and everything else the twin has about 3000lbs more weight than the single. Even if they are both going 7 knots the twin needs to push another ton and a half through the water. Add all the other things in the equation that make the twin less efficient and there's quite a difference.

But this does not say that twins are less efficient. With the same amount of total power twins could be just as efficient as singles .. all other things being equal. And that's the only objective way to compare boats. But in the real world things are not usually equal. Two keels would increase drag unless you made them like the KK twin. And of course most twins need to drag the shafts through the water. And larger engines are usually a bit more efficient ect ect. But if all things were equal their fuel burn would be equal too .. IMO.
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Old 03-21-2017, 02:48 PM   #70
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No need to fear twin engined boat's. Some are better than others and in the end they all have the same view, until you go aground. Here's a design for the groupthinkers to ponder. Attachment 62980Attachment 62981Comes in single or twin. As a recovering sailor I thought I was in the single engine camp. In hindsight I think I was misinformed.
Referring to post 66
Cafesport,
I'm a little confused. Perhaps.
Are there three keels? One on cl fwd and the two that are obvious off cl? I'm confused re that fwd strap not down where the other strap is. Looks like the aft strap could be lifting on the prop shafts. ????
Is this a single mould boat?
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Old 03-21-2017, 04:07 PM   #71
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Not wishing to throw a dampener on your plan, but how will you address the issue, when running on only one engine at a time, especially when it will be by choice and often by the sound of it, of preventing over-heating of the gearbox of the free-wheeling prop, and possibly the overheating of the presumed dripless shaft seal..? Have you already set up a simply and quickly deployed prop-shaft clamping system on each, and a cross-fed water-flow to the shaft seal, or are your engines set up to allow one at a time use without any special tactics needed..? Just curious, because those issues are usually brought up as something that makes just running on one engine at a time to save wear and fuel just not worth it overall.
The subject of running on one engine and what to do about the free turning shaft came up in discussion 2-3 months ago (may have been on another forum). Seems the gearbox is not an issue, but there may be concern with the stuffing box. A shaft brake can be easily fitted ( I have done it in the past with a pipe wrench). I will do more research to confirm that what I am intening to do can be done safely, but I won't be the first to do this.
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Old 03-21-2017, 06:13 PM   #72
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The subject of running on one engine and what to do about the free turning shaft came up in discussion 2-3 months ago (may have been on another forum). Seems the gearbox is not an issue, but there may be concern with the stuffing box. A shaft brake can be easily fitted ( I have done it in the past with a pipe wrench). I will do more research to confirm that what I am intening to do can be done safely, but I won't be the first to do this.
Can't you just put the non functioning engine in gear? That's what I used to do on my sailboat - lock the transmission in reverse to prevent freewheeling while sailing.

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Old 03-21-2017, 06:35 PM   #73
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FWIW, I've had a GB 36 with a single and now have a GB 46 with twins. Love(d) them both. If I were shopping and found a boat I loved I wouldn't care if it had a single or a twin.
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Old 03-21-2017, 07:13 PM   #74
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Can't you just put the non functioning engine in gear? That's what I used to do on my sailboat - lock the transmission in reverse to prevent freewheeling while sailing.

Richard
I'm not sure you could. I believe the transmission needs oil pressure to get it in to gear. That would be convenient if you could. Maybe someone who knows for sure could come back with an answer. My transmission is Hurth HSW 630.
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Old 03-21-2017, 10:20 PM   #75
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Referring to post 66
Cafesport,
I'm a little confused. Perhaps.
Are there three keels? One on cl fwd and the two that are obvious off cl? I'm confused re that fwd strap not down where the other strap is. Looks like the aft strap could be lifting on the prop shafts. ????
Is this a single mould boat?
Nils Lucander design?
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Old 03-21-2017, 10:56 PM   #76
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Can't you just put the non functioning engine in gear? That's what I used to do on my sailboat - lock the transmission in reverse to prevent freewheeling while sailing.

Richard
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I'm not sure you could. I believe the transmission needs oil pressure to get it in to gear. That would be convenient if you could. Maybe someone who knows for sure could come back with an answer. My transmission is Hurth HSW 630.
Yes, but Brittanica, that was because in your sail boat it would have been a drive similar to outboard motors, with actual gears to mesh. That's the problem with what would otherwise be an easy solution for one of the issues at least, and if it stopped the shaft turning, the shaft seal issue as well, with boat gearboxes. These gearboxes are not meshing teeth like in a land vehicle with a manual tranny, but more like the auto tranny in automatic car gearbox, and need oil pressure to actually engage the drive in either direction, so I doubt it would work, as Nightsky has indicated. Unless the turning prop generated enough pressure to lock it up..? But then as soon as the prop stopped turning, you'd lose oil pressure and the locking effect and be back to square one, so I think not...
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Old 03-21-2017, 11:05 PM   #77
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Our primary reason for twins is simple. Power and performance. It's not redundancy, it's not handling. Those are all additional reasons but they don't even come into play in our decision making because we've already chosen twins to have the power.

As to the article pointed out, it talks about "commercial boats" but it really speaks about a small part of the commercial boat population and it's not accurate. It states, "Did you know nearly one hundred percent of the commercial fishing and workboat vessels (of all sizes) are single screw/one engine boats? Scallop draggers, lobster boats, charter fishing boats, longliners, crabbers, seiners, whatever- these vessels are all powered by a single diesel engine."

The "of all sizes" is where it really falls apart. Most larger commercial boats are multiple engines. Charter fishing boats in most areas are primarily twins. We just had someone here go fishing out of Westport WA. Tons of charter fishing boats there and nearly all are twin diesels.

What about all the commercial boats in the Gulf serving the oil industry? They're not singles. Add to this that the vast majority of boats of all types in excess of 60' are twins or more. Yachts? SF's? Only a few trawlers are not but they are the minority, not the majority of boats.

When an article leads with a basic falsehood, then it hurts it's entire credibility.

The information in the article is mostly correct when you turn the discussion to trawlers 60' and under which is relevant to this forum. However, the statements made early are blatantly misleading and the article is clearly written to express one view, not to give a broader view. It is a conclusion reached, now lets prove it sort of article. I would be just as guilty if I listed all the reasons to have twins including redundancy and handling and went on to state why twins were the only way to go when the reality is we choose twins for the power and for all the other arguments there are valid contrary arguments.
I am not sure what you are getting at. I think the point was most commercial SHIPS and trawlers are single engine. And that is a true statement. Yes, 1000 foot tankers are single engine. There are NUMEROUS 100 foot shrimp boats here on the gulf coast and pretty much all are single engine.....and no bow thruster.

If you are talking about charter sport fish boats then of course they are twin engine. But a sport fish is not BUILT as a commercial boat. I think the author's point was boats built for commercial purposes are singles. The reason why support vessels in the GOM are multi engine is because they need the speed.

How about we say that commercial vessels that are built for commercial purposes that do not need speed(ie travel at hull speed) are single engine.

My only reason for having two engines is I like to run on plane. If they made my boat with a single QSM Cummins rated at about 700hp, I would likely go that route. But they don't. So I have two at 330hp a piece.
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Old 03-21-2017, 11:21 PM   #78
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My preference would be single with a bow thruster. If it were a passagemaker, it would be single with a bow thruster and wing engine. My current boat is my first twin and I consider myself a pretty good boat handler(because all my previous boats were singles). But I think I am better with a single and bow thruster.
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Old 03-22-2017, 12:15 AM   #79
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I am not sure what you are getting at. I think the point was most commercial SHIPS and trawlers are single engine. And that is a true statement. Yes, 1000 foot tankers are single engine. There are NUMEROUS 100 foot shrimp boats here on the gulf coast and pretty much all are single engine.....and no bow thruster.

How about we say that commercial vessels that are built for commercial purposes that do not need speed(ie travel at hull speed) are single engine.
.
Many of the Maersk container ships I believe are twins. The supply vessels and service vessels I'm familiar with in the Gulf of Mexico are twins. All the tankers I'm aware of are single as you indicated. Tugs are generally twin I believe as are Ferries. Commercial Trawlers single. I'd classify all those listed as commercial vessels.

I can't argue with your statement if we put a most in it, Most commercial vessels that are built for commercial purposes that travel at hull speed are single engine. I just felt the article started with a conclusion and went in search of support for it and was a bit broad in it's statements. You've qualified well which commercial vessels you're talking about.

Regardless, I do not claim twins are better or preferable now will I buy singles are for recreational trawlers. I don't agree with the article's conclusion that singles are always best, nor would I agree with a conclusion that twins are absolutely necessary. And, as I freely admit, out choice of twins has nothing to do with safety or redundancy or any of the other issues, but is very simply for power and speed.
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Old 03-22-2017, 12:18 AM   #80
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My preference would be single with a bow thruster. If it were a passagemaker, it would be single with a bow thruster and wing engine. My current boat is my first twin and I consider myself a pretty good boat handler(because all my previous boats were singles). But I think I am better with a single and bow thruster.
Your post alludes to something I think is important. Many automatically assume or even claim that a twin engine boat makes up for and doesn't need thrusters. Many very much need them, depending on where and how the boats are used.
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