Single or twin?

[Guest]

Looking about at potential new boats, I find myself increasingly attracted to single engine boats, possibly a motor sailer. However just reading the last thread, a single engined steel boat might be OK or even a single engined GRP job. It appears however that everything over 30 ft is twin engined until you get to about 200ft and over. Then nearly everything is single engined again apart from liners and the like.

The advantages appear to be:

Better fuel efficiency
More space in the machinery areas
Less weight and therefore more available for gennies/larger fuel/water tanks/other goodies = amongst other things better range
Lower repair costs

The downside appears to be

Less back up in case of failure
Less maneuverability (subject to bow/stern thrusters)
Usually less speed

Why are 30 -40 ft cruiser not available with a single large engine option e.g. instead of twin 200hp why not single 350-400hp? - may be with single 50hp clutched to main shaft for backup/genny/canal work.

Just a thought.

I defer to the panel

Nick

 

[longjohnsilver]

Copycat!!

That was the gist of my post a few weeks back!! Same title as well.

You must be celebrating Burns night early up there.

Single. There, that's answered it, no fred drift here.

 

[hlb]

Nick. Oh god yer back. And with the latest, as usual most dificult post. You know the answer before you started.
Two engines (Big Ones) means loads of wuuumff. One engine means sencible potter along. All dependant on what you want.
Cant quite see you in the plodding sceen. but oh well if its what you want!!


Haydn

 

[Piers]

Apart from sheer grunt and power for speed, it's safer with two. Twice I've lost an engine in "confined" areas - just off the Needles (plastic bag over the water intake) and on the Seine (belt failure).

When I used to fly commercially, the saying was "I fly an aircraft with 4 engines simply because they don't make one with 5...."

Piers du Pre
MBM Cruising Club enthusiast
www.dupre.co.uk

 

[oldgit]

With regard to number of engines most boats in rivers prob do not not need twin installation if something goes wrong simply drift to bank etc.Off shore different matter maybe,But look at the number of fast fishers Lochin/Mitchell etc with ginomus single diesels very very fast and out in weather that would have a lot of twin engine white carpeted bubble boats heading for home.On the flying side I have no doubt that I have no experience at all compared to Piers, But the new turbine single Caravans are supposed to be oodles more reliable that some twins (piston).IMHO.Cost of twin engines maintainence horrendus if twin setup not really needed. Most repair work required because of lack of use not because worn out with lots of use.

 

[Rabbit]

Hi Nick, We will all have our own views i know. Please Consider this. IMHO breakdown at sea is often caused by lack of use condined with poor maintenance. With two engines, maintenance can be difficult. Result, some jobs being neglected. Hey no worries ive got a spare! The other most commen cause is POOR QUALITY fuel. Now one or two engines. One or two tanks! How many people fill both tanks from the same supply? Just a thought.
regards.

 

[longjohnsilver]

Comparisons with twin engine planes is not exactly comparing like for like. Planes usually do not have engines only inches apart with no room to work or check many of the basics. On most twin engined boats the opposite is true and I would guess that is the reason ie lack of space, awkward positioning of filters, belts, pumps, injectors etc is the main reason that many peeps do not bother to check in the end, they just give up cos of all the hassle.

I have spent many an unhappy hour in my engine room, but if I had a twininstallation I probably would not even be able to get down there on account of being very tall fat bastard (before anyone else points it out!!) and things would get neglected.

Still, wouldn't mind a twin engined boat sometime, but access would be priority.

 

[hlb]

Singe engines will be fine in fishing and comercial boats.
But hopefully there not saddled with Volvo leasure engines, gear boxes and outdrives.

Can hardly remember a car braking down all my life.
But boat engines, I would think I average three or four engine failiers per year. Of course, I include everything from plastic bags under water intakes, to smashed gearboxes. Rubber insert in prop failier. Dirty diesel, water in diesel, pipes drawing air in, ropes round prop. Prop comming loose. (On a new boat), shafts in outdrives breaking. All mean that engine dead.
None of the above could have been avoided by more servicing, except maybe the water- muck thing. But then I change filters at least twice a year and maybe more. Other than that. Its guess work, which was the bad load of fuel.
Anyway these problems dont cause to much trouble cos change filter and all ok again. (Hopefully) But not good if it happens at the wrong time. As presumably "Willy" in Plymouth sound, the other week. Engine stopped miles out to sea, is not much of a problem. Theres time to mend it. If simple. Or call for help. Narrow channel, strong wind or current. Rope round prop or other normal minor problem and. Up on the rocks very quickly.

Haydn

 

[ArthurWood]

LJS - your point is well taken and today I shall be experiencing getting part of my large form behind my twin Merc 7.4ls to replace the bilge blowers, both of which crapped out within days of each other. To do this I have to almost stand on my head as there is no way that I can actually get right down there. Well, I might be able to, but I would never get out!

 

[Guest]

Re: Some research

OK I have had a look at the Volvo site to get some comparisons. If you take a typical mid sized boat such as say a Princess 35, it has twin 200hp volvos giving maybe 25knts flat out? If, instead, it had a single TAMD63 giving 370 hp, would it not be just as fast, if not faster because the whole installation would be significantly lighter - the TAMD41's weigh with gearbox 503kg x 2 = 1006kg. The TAMD63p & gearbox weighs 833kg. Flat out fuel consumption on the twin 41's would be maybe 25 gal/hr. On the single 63p it would probably be under 20 gal/hr. I could stand corrected on this as it is only semi intelligent guessing on my part. The 63p is actually shorter in length than the 41p (I had to re-check that but that's what it says) but is a bit taller and wider. Obviously the width does not matter but the height might. On the other hand, a centrally mounted engine can sit lower in the boat.

I sort of take the reliability issue on board but it seems to be OK for commercial craft. You could work on a certain amount of redundancy like having two cooling inlets with alarms so that if one is blocked, it is unlikely to cause a problem - twin fuel tanks with an emergency reserve, etc.,etc. Fouled props are maybe also a problem although if one prop on a twin gets fouled, there's a good chance both will.

I know I have wittered on before about wing engine arrangements but having a smaller engine for back up and lengthy slow speed work could work - depending on the size of boat, maybe a diesel outboard? Alternatively, something about 50hp clutched to and driving main shaft through a reduction gearbox. A Volvo D2 gives 55hp, is pretty small and its weight plus the big engine would be about the same as the twin installation.

Would'nt this give a pretty useful all round boat, properly engined for offshore as well as inland work? The small engine when not needed for the main drive, could also run a genny.

Its all in the imagination!

Nick

 

[hlb]

I think that when you've done all that Nick. You may as well just stick to the two engines.
Any way have you thought who's going to buy this thing with one big engine and one little one, off you!
Its hardly conventional.
In any case its a planing boat and totaly, hardly steerable on one engine. Lest you get the outboard going backwards on one corner, or mount a bracket on the front and use it as a bow thruster!

Haydn

 

[Guest]

Okay the thing about an auxiliary engine is a bit of a red herring but I still think that your princess would probably be just as fast, if not faster, with a single 370hp as the current twin 200hp with the plus that it would have

greater range
better fuel consumption
better servicing access
cheaper to buy - one 370hp = about 65% of cost of 2 x 200hp

A bow thruster would make it just as maneuverable at close quarters

I rest my case!

Nick

 

[tcm]

Re: Professional boatbuilder please

Um, weel thrre must BE a reason. Cd a lurky boat industry design type get invilved please, use a pseudonym and tellus why they don't have one monster engine stead of two smaller ones. Issit just the reliabilty thing? Might it not get approval or summink. Is it a marketing thin- they think it wdn't sell?

 

[hlb]

Re: Professional boatbuilder please

It just dont have the ring in it for me. I mean Waiting for locks and things. Its fun to bang one engine forards and one back, and wiz round in circles. then go other way round for a change. Just cant get impressed with this idea.

Haydn

 

[Deleted User YDKXO]

Technically you're right but the fact is that the market wants twin engined boats above say 28' and its going to be really difficult to sell your single engined boat on afterwards. Having limped home on one engine myself on more than one occasion following prop fouls, I reckon the extra safety margin outweighs the cost and maintenance argument
Yes there are plenty of fast fishing boats out there with large singles but, given the much greater engine hours these boats do, the cost savings are correspondingly much larger

 

[DepSol]

THANK YOU, how many times have I said this.

Dom