Twin or Single?

[BarryD]

Cruising tryo here - can someone help me with the difference between a twin and a single engine? I understand the safety aspect of having two engines, and I'd guess it will accelerate quicker but at twice the fuel burn. The other aspect I suppose would be emergency steering and an increase in manouvering capability.

But that aside - there seem to be a fair number of single engined boats. I ask as I've got details on an 84' Fairline Sunfury (26') with a single that looks quite nice. It's got about a 1000 hours on the engine and they are asking £25,000 - is that a reasonable price (I can't find the equivalent of Parkers for Cruisers!)

Many Thanks.

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[Guest]

I've got a Sunfury with a single turbo'd and after cooled diesel as an original fit. Not very common but cheap to run with good performance. The single is a bit of a pain for low speed manouvers and trim tabs are a definite must. There is plenty of room in the engine compartment.
I'm happy with the boat.

 

[Guest]

IMHO

Twin engines better than single, particularly handling and performance, lots of boats only have one engine with no safety issues. £25k sounds quite expensive, there are a lot of twin engined petrol ones around at about £19k. I have seen a twin engined diesel one advertised for about £25k recently.

As a boat it is excellent. I had one a few years ago and did a lot hours and miles with no real issues.

Colin

 

[Guest]

Re: perhaps single

I was going to post about this myself. For two reasons.

1. One of our engines lost a cable. So bumbled along on one engine, and miserably failed at a tight med mooring, had to be dragged in with ropes, phew.

2. I'm a bit aeroplaney. Do you know that there are TWICE as many air accidents with multi-engines than with singles? From today airplane-based crises, the difference can only get worse. Note that the single engines stuff inlcudes all the loony home-built and kit planes. As with my experience on the boat, the second engine "takes you to the scene of the accident" . Lindbergh had only one engine when crossing the atlantic.

Now, boats and planes ain't the same. But if perhaps, you're mostly coastal or inland, and happy with the performance, and if praps you had a get-you home cheapy outboard for emergencies, and if of course you kept up with the maintenance far better with one engine in a roomy engineroom rather than clambering around two when all us lot with twins do is make sure that they both have the same readings, both got oil, that's it , let's go....

...then maybe the lower cost single will be fine. Or better? Priddy has just the one engine for his mega-trips round britain etc.

 

[BarryD]

Re: perhaps single

Matts, I'm also aeroplanny (OK PPL stude - do you PPRuNe?) and I thought the problem with twins in the air is workload (much higher scan rate), asymetrical power - much greater than in a water craft, and over loading - pilot assumption that one donk won't quit, and so busts maximum load. I did a two hour X country in a light single at the weekend - trying to hold it at 2,500 and fly corrected tracks and make RT calls including a MATZ penertration was enough for me. Boating is so much more fun.

However - the consensus seems to be that two engines are better than one, I'm not sure how you could fit an outboard to the bathing platform and my arms aren't long enough to row!

I'm guesing that as so many craft are fitted with only one that it becomes an owner choice as to the level of safety.

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[Guest]

Re: ppl

I am aeroplany cos wife is PPL (private Pilots licence) um evidently not up to speed wiv um jolly secret code. RT is radio telephone but the MATZ thing sounds a bit rude, wot is it?

Nice new planes have buttons with "hold this level" rather than being like an austin a40 with wings like noprmal PPL junk.

But you're right about boating being nicer. There are no drinkies in someone else's plane and there's no hanging around outside to wash or tinker with the plane. Not allowed. Git orf the apron, we have an rt412 due at sixteenfifty hours, 10-4 barbecue foxtrot hold at juliet.

I sit in the spare seat, and say things like What's that buzzing thing, sounds like an alarm? Oops we've just taken off with the flaps out, never mind she says. Erm just a minute, I said, that was the stall warning, doesn't that mean we risked instant death? Hmm.

 

[BarryD]

Re: ppl

Whoops dropped into jargon. MATZ is Military Air Traffic Zone. You're not allowed to fly across them without their permission.

Now the drinking thing is one of the things I like about boating. That and the hang-on you take over whilst I go for a pee, try not to hit anything. If you give control to a novice in a plane - you are going down, rapidly. No autopilot on a Cessna 152!

And don't start me on the cost thing. For a decent four place with less room than a mini you can buy a very, very nice power cruiser.

Switching allegiance as we speak!



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[duncan]

A well maintained single diesel, of appropriate power, fed from two switchable tanks, filled from different sources, switchable filters, proper dual batteries and a bow thruster must be the best compromise on performace, safety and economy.........................oh - and carry spare props in case they fall off.

 

[ChrisP]

The best part of 2 engines is the manouverability. As far as the reliability goes, take the same action as my dad did when we went on holiday. He always serviced the car and made sure every thing was in good shape before we left. We always arrived without any breakdowns and had a great time. The amount of grief that you get out of a single engine installation is entirly your choice. Do the work and you'll be ok. By the way I've got twin engines because I like looking at all the dials and switch's.

 

[Guest]

If I remember rightly, The Fairline Sunfury 26 had outdrives, so from the manouvreability point of view there is not such a huge advantage in having two engines. We had a Sealine 22 Sport for many years with a single BMW Turbo diesel engine/outdrive and with practise I could get it into most spaces without too much hassle.
Looking at reliability, I would be more concerned with the outdrive/s at this vintage, rather than the engine/s especially if they were diesel/s.
As mentioned elsewhere, a good reliable outboard should suffice to cover the emergency situation.
The Sunfury's were a popular boat and I wished I could have afforded one at the time!!
Good Luck
Peter.

 

[milltech]

Re: design criteria count most

I've had both and since you say you understand the twin engine reliability issue lets leave that aside.

I have owned all kinds of boats, planing and displacement, single and twins. I owned a yacht built MFV, 63' and 70 tons with twin 8LXB Gardners. Lovely boat but a pig to handle in a tight location. The only way a twin installation manouvres better is if it has ram rudders astern of each prop, most big yacht TSDY's have a single rudder so there is no steerage until you get moving, a centre line rudder and twin engines is the worst combination you can get!

This boat had a 2.4m draft, put one ahead and one astern at full throttle with any kind of beam wind and absolutely nothing happened at all.

My most recent boat, sold last week, was a single engined MFV, 64 tons, single 6L3 Gardner. This turned "on a sixpence" with a big rudder right behind the screw, the trick is loads of throttle on a full rudder angle and take the power off before you get forward momentum. Going astern you must be brave enough to get some speed on, crabbing correction can then be made with a touch of ahead without losing sternway, so when you go back into gear astern the crabbing is not repeated.

Now people say that planing hulls with ram rudders and twin screws are easier to handle, but usually the lack of draft and windage negates any benefit from the twin screws. At least the deep draft SSDY goes where you send it and stays there for a period before the wind has an effect!

However the bad news about TSDY's vulnerability in wind is worse still if you have a planing hull with a single screw, or with twin screws that don't counter rotate. I had a Fairey Spearfish, probably the best dry high speed hull shape ever designed for the leisure yachtsman, but she was a real pig in a marina.

I feel comfortable with twin screws because I am not an engineer. My single Gardner never let me down, but in mid Channel there's no doubt I was constantly nervous about the lack of back up. However close quarters manouvres were not a concern. Of course I couldn't get into marina berths unless i could turn in because I couldn't "park" and turn 90 degrees, I needed a little room to swing, but most marinas have suitable places on hammerheads on in the first two or three pontoons from the sea.

Finally, the most important thing is to practice with your boat. I have seen TSDY's with bow thrusters make the most terrible balls ups in the simplest of locations. If you understand the limiations and characteristics of your own boat you will be able to do most things with it. In particular most people seem to have forgotton the use of springs, with my SSDY I could come alongside, get a forward spring on and leave the boat ticking over "ahead". Depending on the wind direction I'd need a light port or starboard wheel correction to leave the boat alongside for minutes whilst I made up the warps. Similarly leaving, drive against a forward spring and the stern comes away from the quay like a dream, you just don't need twin screws or bowthrusters to achieve good boat handling, just a bit of practice and always have A PLAN IN ADVANCE. My only problems occured when I didn't plan or changed my mind halfway through, like leaving the pontoon with the power cable attached - a particular favourite of mine.

 

[adrianm]

I spent a lot of time looking into this very subject for the new boat I'm having built.

I started off wanting twin engines because that was what everyone in Britian seem to have. However when I started investigating the American market I found a lot more people seem to have one engine.

What really made my mind up was a report I found on one web site (I forget which) that showed a comparison between two models of the same design. One with twins and one with a single. The performance was near enough the same apart from the fuel consumption: the single was over twice as efficient at cruising speeds.

I'm having a single with a bow and stern thruster in my boat coupled with a 'get-you-home' wing engine that doubles as a generator. I'll save a bomb in fuel and it should work out to be about £30k cheaper as well.

 

[Guest]

When looking at the American boats, it is true the majority of the boats at the lower end of the scale have single engines... and petrol at that. Perhaps the reason for this though is because a very high percentage of the boats are only ever used on lakes and estuaries. Could this be the reason why?

Personally, after having several engine problems whilst cruising, and not being able to fix the problem myself, I am extrememly glad to have twins. I would never buy another boat with just a single engine ( oh, apart from a tender :-> ).

Lee