Single or Twin Screw!!

Hello all. We have been looking at a trawler in the 36 to 40' range for some time now. I have had a bias toward a twin screw vs a boat with a single. A single must have a bow thruster to be considered. May I ask from personal experience your preference and why?

Thanks in advance
John

Do a search on "single" and "twins". You will find every possible answer to that question in the thousands of prior posts on this topic.


David

I prefer twins for backup and ease of docking. But in 60 years on the water, I have only have come back on one engine twice. Both times because of lines caught in one prop.
Twins have double the maintenance, but don't use twice the fuel because twins can have less HP than a single in the same boat. But almost all of my experience is with heavy duty engines that never fail and don't have electrical controls or sensors.
I've had single screw tugs and commercial vessels, but never used a thruster. My current boat is twins, 83', and easy to dock.

Go by the boat you like. There are many many many pro's and con's on both sides. Also, a bow thruster is great with 2 screws as well!
Find the boat you like, worry about that later. I have a Mainship 34T, comes BOTH ways. I started out looking for a single screw and ended up with a twin.

It really depends on the boat.

Sometimes twin engines make maintenance very difficult unless you are a contortionist.

It is also worth considering how well the prop(s) are protected. Often twins are much more exposed than singles.

We have twins in our boat. However when we were looking we considered singles also. I would find the boat that meets your needs and take whatever engines it comes with. I personally don’t like Volvos due to the parts cost and availability. If you find a great boat with a single you can always add a thruster if needed.

We ran a single-screw diesel, without thruster, for several years... didn't find it all that horrible.

Have twins now, no thruster, easier, not magic.

Wifey wants a thruster, though, even with twins. Some of that is only about easier (or more graceful?) loitering while we wait for dock hands to eventually get around to doing what they've been asked to do...

In our case, if we were shopping, it'd probably more useful to look for boats that that meet our other specific requirements and nice-to-haves... and we'd decide about engines later.

-Chris

Pulling up to the gas dock, I wish I had twins. Pulling away from the gas dock, I'm glad I have a single. Rolling in bad weather or a beam sea and I wish I had the extra speed of twins, however, doing maintenance, I'm glad I have a single.

Everywhere I happen to roam is within towing range,

Shrew said:

Pulling up to the gas dock, I wish I had twins. Pulling away from the gas dock, I'm glad I have a single. Rolling in bad weather or a beam sea and I wish I had the extra speed of twins, however, doing maintenance, I'm glad I have a single.

Everywhere I happen to roam is within towing range,

Click to expand...

This has to be one of the most profound ,yet succinct posts thats even been posted!

Lepke said:

I prefer twins for backup and ease of docking. But in 60 years on the water, I have only have come back on one engine twice. Both times because of lines caught in one prop.
Twins have double the maintenance, but don't use twice the fuel because twins can have less HP than a single in the same boat. But almost all of my experience is with heavy duty engines that never fail and don't have electrical controls or sensors.
I've had single screw tugs and commercial vessels, but never used a thruster. My current boat is twins, 83', and easy to dock.

Click to expand...

And in five years of ownership I have limped home on one engine three times, all for different reasons. I rather doubt I would ever purchase a single screw boat. Sure, lots of boaters never have a bad experience getting stranded in a single screw. Risk management.

AusCan said:

It really depends on the boat.

Sometimes twin engines make maintenance very difficult unless you are a contortionist.

It is also worth considering how well the prop(s) are protected. Often twins are much more exposed than singles.

Click to expand...

Often true that running gear is not protected. But, a DeFever 44 has a full-length keel the bottom of which is below the level of the props.

djmarchand said:

Do a search on "single" and "twins". You will find every possible answer to that question in the thousands of prior posts on this topic.


David

Click to expand...

This^^^

This subject has been absolutely beaten to death!

And I could argue STRONGLY on both sides.

Advantages of the single:

Simpler, lower maintenance and most likely, easier to do. Harder to dock and the additional cost of most likely maintaining thrusters. Although both have thrusters, the single is more likely to have them and more likely to use them.

Slightly lower fuel cost. In two identical boats, at the same speed, I'd argue that fuel is the same, less the drag of the second prop and gear. So, relatively insignificant.

===

Advantages of the twin

Easier docking
Redundancy to get home if one quits. (and, yes, they do quit, not often but sometimes for the craziest reasons)

=====

That's basically it... your choice.

My future boat will have twins. Why? My number one priority is peace of mind and safety whether real or psychological. I can understand if on a single and the engine fails in a safe place but what if you are crossing the Gulf Stream and it cuts out, or you are leaving or returning through an inlet and it cuts out, or you wake up by an anchor alarm and are close to rocks or other boats and the engine won’t start. A second engine will give you the extra security. That has a lot of value to me and the wife. Please no comments that most engine failures are due to foul fuel which will effect both engines.
PS the OP asked your personal opinion on your preference. Tired of responses to just do a search. Probably 99% of questions can be answered by search and this forum would just turn into another social media site. Not!

I know what it's like to have too many toys with too many engines. For example i've had 3 motorcycles at once, 2 boats, and 3 cars.. All engines suffered neglect(only so much attention to go around).

I prefer a single in tip top shape.. Bow thruster vs doubling your fuel burn? C'mon.

36-40' and i'd bet you're not looking for a transatlantic passagemaker so play it safe with a single.. Most of us are never more than 50 miles from land and towboat/seatow will come get you if something goes wrong.

Add to the fact that if you have X amount of hours to maintain an engine it's divided by 2 with twins and these engines are incredibly reliable.

You could argue both ways but great loop style boats don't need twins.

I ended up with a single, simply because twins are not available in the type of boat I wanted.

If you want the seaworthiness and efficiency of a full displacement boat under 40 feet, I am not aware of any twin engined boats in this category. With the round bilges and narrower aft section most FD hulls have, there just isn't enough space to fit two engines. The choice is easy.

Have a single with thruster because:

1. The desired boat only came with a single,
2. Local waters are often shallow and wanted keel-protected prop and rudder,
3. Less maintenance and repair (two engines break twice as often as one), and
4. Reliability of having just a single is not a significant concern.

Regardless, the great majority of high-speed trawlers have twins, and many boaters want to go fast; so you'll probably end up with twins.

Mrwesson said:

I know what it's like to have too many toys with too many engines. For example i've had 3 motorcycles at once, 2 boats, and 3 cars.. All engines suffered neglect(only so much attention to go around).

I prefer a single in tip top shape.. Bow thruster vs doubling your fuel burn? C'mon.

36-40' and i'd bet you're not looking for a transatlantic passagemaker so play it safe with a single.. Most of us are never more than 50 miles from land and towboat/seatow will come get you if something goes wrong.

Add to the fact that if you have X amount of hours to maintain an engine it's divided by 2 with twins and these engines are incredibly reliable.

You could argue both ways but great loop style boats don't need twins.

Click to expand...

Mrwesson,

Good points, but some prefer a twin, both in top shape, and I could argue for that.

Engines DO quit and I know of several that have failed on Loopers, some in very awkward spots, like a lock. Loosing one on the Ohio, with current and traffic would be more than a minor inconvenience. And there are place where SeaTow isn't available and yes, we can be over 50 miles off shore.

You don't divide your maintenance time between two engines, your just about double it. That's the price for twins.

Now, I could argue that the risk benefit of a single could be argued as they rarely quit.

Do you really need a twin? Maybe, if that's your comfort zone.

My boat was only offered with twins and I'm glad. Three times I've made it safely to the slip on one engine, the longest trip was 89 miles.


Being in Surrey you're going to be boating in some pretty stiff tidal currents. The added security of being out there with twins vs a single would be worth a lot to me. If wind is also a factor in your area you're going to be loving the twins whenever you dock in a crosswind.


Also, a bow thruster can be your best friend.

It's area dependant as well.

BC's north coast has many large rivers in narrow mountainous valleys, so forest debris (including old growth trees with root wads attached) are continuously being flushed into the ocean. Some of them become waterlogged to the point of neutral buoyancy and hover at or just below the waters surface, making a single engine with keel shoe protected prop & rudder a good idea.

Most boats up here have a swimstep mounted outboard for salmon trolling which is also useful for getting to a safe anchorage if the main engine dies.

Getting into and out of our slip is a secondary concern...the boat is made to go places, not stay in a marina!

Through the years I have had the following: Single screw, twin screws and twins with bow thruster.
My absolute preference is the twins with thruster. The main reason for this choice is the home port where I dock my boat. She is a 36 footer with some windage issues and when I bring her in stern first with a strong outgoing tide and the afternoon southwesterly's, docking becomes a real challenge. The set up with twins and thruster helps tremendously.

Started the tractor, attached the plough, but found the paddock has been ploughed, many times, already.
I prefer twins. I`ve had a single. Essentially I like the redundancy and the maneuvering benefits. I`d like a bowthruster as well. No point being hairy chested about it, if there are helpful features at reasonable cost why not have them.

I prefer the redundancy and maneuverability of twins but it depends on each boat.
You've got to be able to reach the essential maintenance items on each engine. I've seen a single with an ER the size of a large tuna can. My twins are sitting in a 12'x20' ER.

FlyWright said:

...
You've got to be able to reach the essential maintenance items on each engine. ...

Click to expand...

Agree. Despite a small engine compartment, my single has easy access from starboard, port, and above, without any crawling. My engine mechanic loves it. (It's easier to concentrate loving attention on a single engine than on two.)

Having had a twin I never thought I could / would go "backwards" to a single.
After looking and considering the +/- and my situation of inland / Great Lakes boating the single looked reasonable.
The Mainship I found and liked was a single and already had B&S thrusters which might be the best of both worlds.
I can live w/o redundancy and the PM is a dream w SPACE in the ER.

I prefer a single with a bow thruster for many of the above reasons. What I will add is that how a single engine boat is setup makes a huge difference in being easy to handle. Slow speed maneuvering with a single and small rudder can be very challenging. The rudder needs to be substantially larger and should swing 40 degrees to either side for outstanding slow speed and docking handling. The larger rudder and degree of turn allows you to push the stern to the side with very little forward motion. This makes stern in docking with the "back and fill" technique, quite easy. Also, being able to push the stern to the side with little forward motion and pushing the bow with a thruster, allows you to push the boat sideways to the dock for essentially parallel parking. There are other ways to accomplish this with spring lines, but a well setup single screw boat can be very easy to dock.

Ted

NewbieFromNJ said:

PS the OP asked your personal opinion on your preference. Tired of responses to just do a search. Probably 99% of questions can be answered by search and this forum would just turn into another social media site. Not!

Click to expand...

I don't quite understand your complaint.

A decent search usually turns up the "personal opinion" or "preferences" many have already written -- over and over and over and over and over again, on popular and generally unchanging topics like this -- so the OP's results would be the same.

Might be different if the query is about some kind of new/emerging technology or maybe a topic that's in flux for some other reason... but generally discussions about the pros and cons of singles/twins, anchors, and a few others, probably aren't gonna surface much if any new factoids, opinions, preferences... Somebody might say something in a different way than they've said it 30 times previously, and the different wording could perhaps be useful... but that's kind of a reach.

"Decent search" usually means using the Google or at least the Advanced versions, given the site's base search tool isn't great. And many new users don't know the base tool is so limited, so they don't always find much if that's the only tool they've tried...

Anyway, what do you see as the advantage of asking a commonly-asked question all over again? FWIW, I don't see it as a bad thing, just usually slow for my own purposes...

-Chris

I've been boating more than 30 years and have always had single engine boats.
Once I learned I have only had trouble maneuvering once or twice.
Had fuel issues a few times, always got them resolved (learn your boat).
Lost a belt once...keep spares aboard and do your PM. Easier to do with one engine.
Etc.

One interesting advantage of twins that I’ve never heard mentioned: I woke up in an anchorage 25 miles from home to find the Schrader valve in the air-over-oil tank in my Hynautic steering system had failed, leaving me without steering. I decided to try throttle steering home; I cruised up the harbor, through the creek, down the canal and home, all at my normal speed, with no problem. Interestingly (maybe only to me), I found it much easier to hold the boat on course into the wind with the throttles than with the wheel. It makes sense when you think about the forces involved, but it would never have occurred to me to try it. And yes, I now carry a spare Schrader valve.

I like large deep draft boats turning a single large propeller, a rudder to match and one good deckhand, but I'm sort of weird anyway. I've run singles, twins. triples, quads, bow thrusters, stern thrusters and oars but a single is my preference for just having fun at the dock.