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Old 04-17-2018, 06:49 AM   #41
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Some points come to mind:

1. Those with singles KNOW that the one engine is "mission critical" and tend to take better care of it. Those with twins tend to be a bit more cavalier, accepting starting a trip with known doubts, saying "Hey, I can come in on the other".

2. While they can get in with one engine failed, it still screws up their trip. Most will abort a trip when one engine goes out, then sit at the dock waiting on parts and techs.

3. The accessibility restriction issue is REAL on many boats. Probably half the twin engine boats the outboard sides of the engines are basically no-go zones. Most singles (but not all) you can crawl all around the engine. Hard to maintain things to a high standard if you can't get to them.

4. (very minor point) I find sync'ing engines to be a bit of a pita. On mechanical engines this must be done by ear or by a mech sync box, and the sync will vary a bit. I find the beat frequency annoying.

5. The engines are never identical. One has more oil pressure, one runs a little warmer, one smokes a little more, one uses a little more oil, full load rpm different, etc. I have called out on numerous service calls because of engine differences. Both in spec, but the differences nag many operators.

6. Maintenance costs are probably 50% higher with twins over same total hp single.

I set up my ride as a single, fully aware of the tradeoffs. I am not super anal about maintenance, but if something is iffy, it gets fixed. So far in ten years and over 20,000nm of travel, never had any propulsion system failure that caused a tow or aborted trip. And yes I am knocking on wood! Could have a failure next trip, won't bitch much, just deal with it. Did have one tow due to a tiller arm that broke (casting flaw), but that was a bit of a fluke during shakedown.

My close bud over the same period has had three different twin engine boats and has had at least five trip ending failures. Granted, he is not a gear head, but still pretty up on the care and feeding of diesels. I don't think he will ever run a single!! Seems to get "bit" more than average.

That being said, I would never criticize anyone for demanding twins. It really is a matter of balancing tradeoffs.
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Old 04-17-2018, 07:50 AM   #42
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I grew up with boats in board and outboard all singles 12-68 feet never a bow thruster. Now I have twins with no bow thruster. I think they both have positives and negatives. I have had 1 situation that I did not need to get towed because I had 2
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Old 04-17-2018, 08:03 AM   #43
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I fished offshore for forty years on boats with a single diesel and see no need for two. The "spare" engine theory doesn't work in my mind, for the expense of having a second engine you could be towed in several times. The maneuverability issue is more easily addressed by learning how to handle a boat, I've run single screw boats up to 180 ft. in confined spaces and it's not really all that difficult with adequate crew.
That seems very correct... "... single screw, 180 ft.; with adequate crew." I can well imagine that when you get up to the 180' range, unless you have twins and untold number of powerful responsive thrusters in various locations - even boats with plenty of self-sustainable single hand pilot maneuverability should have adequate crew at hand.
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Old 04-17-2018, 09:05 AM   #44
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So, it has been "decided" that on commercial fishing, large cargo vessels and workboats a single is recommended. Further on smaller boats a single pretty well fills up the ER.

Oh oh, twin powered vessels of all shapes and sizes are selling like hot cakes. Boat magazines and sales events showcase multiple engines. Possibly there is a disconnect between this thread and the current recreational boat world.
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Old 04-17-2018, 09:55 AM   #45
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Me thinks it really boils down to how and where you will use the boat. For us, we plan to do the loop and cruise the inland rivers primarily. Rarely out of sight of land, and rarely out of range of one of the two large tow companies. So a single with its lower maintenance would be fine (bow thruster hopefully). But we won't insist - if we find a boat we love with twins, then ok.
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Old 04-17-2018, 10:24 AM   #46
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That seems very correct... "... single screw, 180 ft.; with adequate crew." I can well imagine that when you get up to the 180' range, unless you have twins and untold number of powerful responsive thrusters in various locations - even boats with plenty of self-sustainable single hand pilot maneuverability should have adequate crew at hand.
It's always nice to have a crewmember that knows how to tend a springline no matter how many wheels you have in the water.
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Old 04-17-2018, 10:27 AM   #47
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So, it has been "decided" that on commercial fishing, large cargo vessels and workboats a single is recommended. Further on smaller boats a single pretty well fills up the ER.

Oh oh, twin powered vessels of all shapes and sizes are selling like hot cakes. Boat magazines and sales events showcase multiple engines. Possibly there is a disconnect between this thread and the current recreational boat world.
There may be a "disconnect" between this thread and the recreational boat world but there isn't one between going to sea and sound seamanship.
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Old 04-17-2018, 11:51 AM   #48
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There may be a "disconnect" between this thread and the recreational boat world but there isn't one between going to sea and sound seamanship.
The ultimate blue water vessel I’m familiar with is Dashew’s Windhorse. Powered by twin JD 4045s. All sorts of craft out there that are blue water capable whether with singles, get home, twins, sails or row boats. KK makes some marvelous twins as does Nordhavn.

But you are partially right, seamanship counts - but so do mechanical and electrical skills. The list of blue water crew and vessel attributes can get long quite quickly.
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Old 04-17-2018, 12:00 PM   #49
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I would consider electrical and mechanical skills to be a part of seamanship, anything pertaining to the operational safety and efficiency of a vessel at sea. I've always gone by what an old salt said to me almost fifty years ago "It's no sin to be ignorant, it's just a sin to stay that way", and the more I learn the more I realize what I don't know.
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Old 04-17-2018, 07:13 PM   #50
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Just want to throw this in...


Depending on the arrangement of many twin engine boats [size, placement, product capabilities or lack of capability... etc... as well as the speed desired] it is not difficult to run on one engine at time in the lower speed range. There are numerous variables that come into play... however... just because its twin screw doesn't mean both screws need to always run consecutively.
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Old 04-17-2018, 08:43 PM   #51
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It's always nice to have a crewmember that knows how to tend a springline no matter how many wheels you have in the water.
Ain't that the truth!
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Old 04-17-2018, 10:27 PM   #52
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Just want to throw this in...


Depending on the arrangement of many twin engine boats [size, placement, product capabilities or lack of capability... etc... as well as the speed desired] it is not difficult to run on one engine at time in the lower speed range. There are numerous variables that come into play... however... just because its twin screw doesn't mean both screws need to always run consecutively.
I actually disagree with that Art. Running a twin on one is only an indication that one has the wrong boat. The only two reasons for running on one is that the other quit or you’re trying to make an unsuitable boat into a suitable boat by running on one so the fuel burn is less. IMO you can't afford that boat. Just my opinion.
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Old 04-18-2018, 12:44 AM   #53
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I actually disagree with that Art. Running a twin on one is only an indication that one has the wrong boat. The only two reasons for running on one is that the other quit or you’re trying to make an unsuitable boat into a suitable boat by running on one so the fuel burn is less. IMO you can't afford that boat. Just my opinion.
In my opinion, your opinion is incorrect, my friend, Eric.

I only run on one of the two 255 hp. each engines very occasionally... i.e. when wanting to take some lazy hours of s-l-o-w cruising in stretches of low speed areas... such as 5 mph restricted areas deep into the Delta. Anything much above 5 knots I run on two. Reason I like planing boats [with powerful twins - such as ours] is because when in open water we can easily cruise at 16 to 17 knots and get places much more quickly than a boat with top cruise 6.5 knots; top end 8 knots. And, when needed our Tolly will hit a continual 20 knot cruising speed somewhat before WOT which does about 22 to 23 knots.

One BIG difference in cruising between your boat and my boat is that above hull speed for yours is impossible. And, above hull speed for mine is when she just begins to really stretch her cruising legs; up on plane.

Regarding overall fuel economy - your boat wins. However our Tolly ain't too shabby on slow speed economy. One engine running at 5 knots our Tolly gets right next to 3 nmpg. With both engines on and traveling at 6.5 to 7 knots... just below its hull speed of 7.58 nmph... she's at 2 nmpg. And yes, when up on plane doing 16 to 17 knots the twins are sucking down 1 nmpg worth of fuel. Yea Doggies!

There IS a Trade-Off for Everything! One of the first and most important things to understand regarding life - and, to know about pleasure boats especially!!!
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Old 04-18-2018, 01:44 AM   #54
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My own two penn'orth, it depends on several factors, where you cruise, what time you have available to cruise, how handy you are with the spanners,how deep your pockets are and how good a seaman you are.

Where you cruise, a twin engine boat is fine in big deep shipping canals but smaller canals need much more care or you'll be repairing one prop a year, plus lift out costs. I've seen some rich men with twins and they're like a ploughman riding a racehorse.

If you're working and only have a short cruise window then a, you have plenty of money for diesel and b, you have to get there and back on a tight leisure/work window. i.e What time you have available.
In my own opinion any person who puts to sea without having done a basic maintenance course is just plain stupid. You should know how to service your engine at the minimum, even if you pay a mechanic to do it, not all of them are meticulous.
How deep are your pockets ? are you a speed freak ? are you retired ?

How good a seaman are you ?
We all think were Gods gift to cruising but you need to have proper training in boat maintenance, handling (using springers and lines) and navigation. not solely with electronics but basic chart work just in case.
Information is an easy burden to carry and leads to a far more relaxed enjoyable boating experience, not only for you but your crew will also have greater confidence in your leadership.
Every person has different criteria and outlook on life and I respect that, the points I raised are just my thinking.
What do I use ? A single engine, old fashioned charts backed up by a simple Garmin 72. K.I.S.S
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Old 04-18-2018, 06:11 AM   #55
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I actually disagree with that Art. Running a twin on one is only an indication that one has the wrong boat. The only two reasons for running on one is that the other quit or you’re trying to make an unsuitable boat into a suitable boat by running on one so the fuel burn is less. IMO you can't afford that boat. Just my opinion.
I agree with Nomad and would only add that a vessel designed to operate with two engines will never be as efficient as one designed for one when operated as a single, regardless of weight to horsepower. I understand that some don't share my particular fascination with efficiency, perhaps it's my Scotch ancestry.
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Old 04-18-2018, 06:54 AM   #56
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Some boats CAN gain by using one engine.

The fish boats that tow nets require large HP to function.

On a long transit removing one prop will allow the boat to procede on one engine quite well and save fuel and engine hours .

For most folks the hassles with transmissions and a free wheeling prop, or the difficulty in locking a prop ., is seldom worth the effort.
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Old 04-18-2018, 07:59 AM   #57
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Some boats CAN gain by using one engine.

The fish boats that tow nets require large HP to function.

On a long transit removing one prop will allow the boat to procede on one engine quite well and save fuel and engine hours .

For most folks the hassles with transmissions and a free wheeling prop, or the difficulty in locking a prop ., is seldom worth the effort.
Aside from the difficulty and expense of removing one wheel there exists the inefficiency of having both rudders having to fight the water flow to maintain course as well as the shaft and strut adding drag. Using a mechanical device of any kind in a fashion inconsistent with it's designed method of function is seldom advantageous, but that by no means implies that I wish to tell others what type of boat they should own or how to operate them.
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Old 04-18-2018, 08:12 AM   #58
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Some boats CAN gain by using one engine.

The fish boats that tow nets require large HP to function.

On a long transit removing one prop will allow the boat to procede on one engine quite well and save fuel and engine hours .

For most folks the hassles with transmissions and a free wheeling prop, or the difficulty in locking a prop ., is seldom worth the effort.
I'm sure locking a prop so that freewheeling does not hurt transmission can become PIA if done often and not having specialized, easy to actuate shaft-lock apparatus.

Luck for us locking is not needed. BW Velvet Transmissions our Tolly has is fine for freewheeling without hurting it; especially at the low speeds we travel when purposefully using just one engine. In addition, I alternate engine use on regular basis during the very slow cruise to keep use-hours similar as well as to not constantly let just one trany experience free wheel stress... no matter how OK it is according to BW experts.

And... because freewheeling is no problem... the freewheeling prop causes less drag than prop locked rigid in position. Which is another assistance to getting near 3 nmpg at 5 nmph, on single engine use, slow-cruise in a planing boat that can also easily cruise at 16 to 17 knots - or above.
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Old 04-18-2018, 08:31 AM   #59
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I'm sure locking a prop so that freewheeling does not hurt transmission can become PIA if done often and not having specialized, easy to actuate shaft-lock apparatus.

Luck for us locking is not needed. BW Velvet Transmissions our Tolly has is fine for freewheeling without hurting it; especially at the low speeds we travel when purposefully using just one engine. In addition, I alternate engine use on regular basis during the very slow cruise to keep use-hours similar as well as to not constantly let just one trany experience free wheel stress... no matter how OK it is according to BW experts.

And... because freewheeling is no problem... the freewheeling prop causes less drag than prop locked rigid in position. Which is another assistance to getting near 3 nmpg at 5 nmph, on single engine use, slow-cruise in a planing boat that can also easily cruise at 16 to 17 knots - or above.
Just for reference my 38' dragger weighing 50,000 lbs would use less than a gallon an hour at 5kts.
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Old 04-18-2018, 08:58 AM   #60
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Just for reference my 38' dragger weighing 50,000 lbs would use less than a gallon an hour at 5kts.
And... there we have the basis of boating choices - trade offs!
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