1 or 2 engines coastal waters?

[jon and michie]

Hi - I am wondering if a single diesel engine would be strong enough on 30ft grp boat in coastal waters and the engine I have in mind would be something like a Volvo kad32.
the boat I am looking at generally came with twin engines , however there was a couple of single engine variants.
All opinions welcomed
jon

 

[BruceK]

Stong enough for what? Planing? Doubtful and marginal if at all. You really need to give more info on the boat and end use scenario before anybody can give a valued opinion or answer. I've seen a number of single engined implementations on 27 -30 foot class boats that are normally seen with twins, but the singles were almost always destined or converted for inland waterway use.

 

[Whitelighter]

Boats that had twin KAD32 would normally have a single KAD44. In this instance yes a single engine boat is perfectly fine for coastal work.

A single KAD32 in a boat that usually has twin KAD32 isn't going to plane so is really limited to displacement speed, which in something 30ft LOA is probably 5-6knts

 

[EugeneR]

I can't comment on engines being strong enough, however from a risk perspective, two engines give a lot more comfort.

 

[superheat6k]

For coastal use then a single engine may well suit you, but I would suggest joining Seastart. When I had a single engine I required their assistance twice, and this put me off going offshore or cross channel. Now I have two engines I forego Seastart, but I do carry a decent toolkit and suitable spares.

Virtually every fishing boat out their has only a single. Maintenance costs halve, and fuel consumption reduces very roughly by about a 1/3.

 

[jon and michie]

Boats that had twin KAD32 would normally have a single KAD44. In this instance yes a single engine boat is perfectly fine for coastal work.

A single KAD32 in a boat that usually has twin KAD32 isn't going to plane so is really limited to displacement speed, which in something 30ft LOA is probably 5-6knts

Thank you whitelighter - the boat I am looking at does have a single a kad44
and Yes I should have been a bit more clearer my mistake.

maybe if I do get a single engine boat I may invest in a small outboard in the event of a breakdown (the boat not me)

thanks again
Jon

 

[PCUK]

The outboard option is fine. Also make sure you can make simple repairs at sea. Seastart is a poor substitute and only suitable for the Solent boating lake anyway.

 

[jon and michie]

The outboard option is fine. Also make sure you can make simple repairs at sea. Seastart is a poor substitute and only suitable for the Solent boating lake anyway.

thank you - my intention would be (in the case of a single engine) to fabricate a nice stainless steel bracket that would fix into position should I need the outboard.
I would have a toolkit on board as I am quite confident with a spanner and torque wrench.

thanks again
Jon

 

[CLB]

Thank you whitelighter - the boat I am looking at does have a single a kad44
and Yes I should have been a bit more clearer my mistake.

maybe if I do get a single engine boat I may invest in a small outboard in the event of a breakdown (the boat not me)

thanks again
Jon

A small aux outboard won't work on a thirty foot boat in my experience. You would need something permanently fixed in place and probably of at least 20hp. Most 30ft sportscruisers don't have anywhere to mount such a thing. You will also need to carry a completely separate fuel supply for it. One well maintained engine is fine IMHO, as long as you know how to fix the basics yourself. Things such as belts, impeller and fuel filters are most likely to be what stops you, and can all easily be fixed at sea if you know how and have the right spares and tools. This is coming from someone who has taken a single engine 25 footer across the Channel on numerous occasions. I tried the aux outboard route, lots of different models and sizes, and can honestly say I doubt any of them would have been any use out at sea.

Another way to look at it, having one engine halves the likelihood of something breaking

 

[Richard.C]

Another way to look at it, having one engine halves the likelihood of something breaking

This isn't really true, the likelihood of failure of one engine is the same as the second engine, it is no more or less likely. Having one engine halves the number of things to fail not the likelihood of failure.

 

[TQA]

How many engines do you think fishing boats have? You know the ones that used to go out daily.

 

[Whitelighter]

Thank you whitelighter - the boat I am looking at does have a single a kad44
and Yes I should have been a bit more clearer my mistake.

maybe if I do get a single engine boat I may invest in a small outboard in the event of a breakdown (the boat not me)

thanks again
Jon

Is it a sealine S28?

 

[alancollins]

I used to worry about buying a single-engined boat until I remembered all the single engine fishing boats out there. Then I recalled that our local airfield has dozens of light aircraft, nearly all with single petrol engines. The secret is scrupulous maintenance.

 

[julians]

I used to worry about buying a single-engined boat until I remembered all the single engine fishing boats out there. Then I recalled that our local airfield has dozens of light aircraft, nearly all with single petrol engines. The secret is scrupulous maintenance.

even with scrupulous maintenance you cant guarantee you wont have an issue, just as having 2 engines doesnt guarantee no issues.

I currently have a single engined boat, I dont venture far really, a 60-70 mile round trip is probably the biggest I do, and I'm probably never more than 10 miles from land, but the engine and drive are correctly maintained with no corner cutting, but last year the inner propshaft on the volvo dph drive sheared off, I have no idea why, maybe I hit something, maybe I didnt. But the point is it failed without warning. It wasnt a massive deal because I was only half a mile from home, had I been in the middle of a longer trip it could have been an issue.

With a previous twin engined boat (sealine s34) , I had an overheat on the first engine, no problem, shut it down and continue on the remaining engine. The only problem was the engine I shut down drove the power steering pump, you'd have thought that wouldnt be a big deal, steering is just a bit heavier than usual, but should still be fine to get you home. after a couple of miles of driving without power steering, something sheared in the steering system because it couldnt take the load of the steering without the power assistance. Leaving me with one running engine, no steering, with the drives pointing left. At this point we werent far from home, so radio'd the nearest boat and got a tow home.

Essentially you can reduce the odds of having an issue but never eliminate them. You just need to be as prepared as you can for the various eventualities, but never be complacent that you wont have a problem.

 

[jon and michie]

Sorry for the delay in replying - the single engine in question is a Kad 44 (edc compressor).

jon

 

[dragoon]

This isn't really true, the likelihood of failure of one engine is the same as the second engine, it is no more or less likely. Having one engine halves the number of things to fail not the likelihood of failure.

Each component has a probability of failure - increasing the number of components increases the likelyhood of something failing. That said, there are 2 engines so overall system availability is increased. But, in smple terms, the more engines, the more bits, the more likely you'll be fixing stuff....dont ask me how I know, 4 cars, a twin engine motor boat, 3 dinghys, 2 lawn mowers.....it's only breakfast and I have a misfire to fix on SWMBO's Volvo.....

 

[oldgit]

Just thought on the singled engined argument.
Agreed most "small " commercial fishing boats have single engine,however there is probably somebody aboard who will be responsible for fixing that engine including being able to undertake some very serious repairs while offshore and perhaps even while underway.
There will be other crew members able to keep a look out and carry on all other safety tasks as well.To get at the engine will probably NOT involve moving all the furniture and shifting all the carpets and flooring..
Further,should assistance be required,good chance that somebody else will be fishing not far away or failing that, a radio or telephone will produce a boat from your home port to come out and get you.

Engine failure in rubbish weather on a leisure boat normally has one outcome.It usually involves the lifeboat. It is best the call is made before embarrassment turns into something worse . ?

 

[Richard.C]

Each component has a probability of failure - increasing the number of components increases the likelyhood of something failing. That said, there are 2 engines so overall system availability is increased. But, in smple terms, the more engines, the more bits, the more likely you'll be fixing stuff....dont ask me how I know, 4 cars, a twin engine motor boat, 3 dinghys, 2 lawn mowers.....it's only breakfast and I have a misfire to fix on SWMBO's Volvo.....

I see where you are coming from but the same or similar diesel engines will have more or less the same level of reliability, so the one engine in the single engine boat is just as likely to fail as one of the engines in the twin engine boat. I just struggle with the concept when it is inferred that a single engine boat is more reliable than a twin engine boat.

A lot of people are making comparisons with fishing boats in this thread, I don't know the answer to this but do any fishing boats use the small capacity relatively high revving Volvo engines that are referred to this thread, i.e. KAD 32?

I've always worked on the premise that RPM and reliability are inversely proportional so would have assumed a fishing boat used low revving diesel technology without turbo's/superchargers etc.

 

[dragoon]

I see where you are coming from but the same or similar diesel engines will have more or less the same level of reliability, so the one engine in the single engine boat is just as likely to fail as one of the engines in the twin engine boat. I just struggle with the concept when it is inferred that a single engine boat is more reliable than a twin engine boat.

Agreed, a twin engine boat will be more reliable - both engines have to fail AT THE SAME TIME for the boat to fail. H

However, with two engines, statistically you're more likely (not twice as likely, but more likely) to have one of them in a failed state at any one time.

Increase the complexity, and increase the points of failure, even if the overall reliability is increased. Ultimately, it's plate spinning - you call always keep one of them spinning, but it's much harder to keep them all spinning at any one time.

 

[Hugin]

I just struggle with the concept when it is inferred that a single engine boat is more reliable than a twin engine boat.

It depends of the scenario, of course. A twin engined boat obviously have a limp-home capability the single engined boat doesn't have if scomething breaks down while at sea. The capability to get you out of a bad situation is also a sub-set of reliability I suppose.

If we on the other hand consider the likelihood of something.... anything...... not working at the time you want to go somewhere then the single engined boat will be superior. If you own a twin engined boat and one of the engines doesn't work, would you then even leave the pontoon with just one functioning engine? I guess almost no one would...... if for no other reason they would be limited to displacement speed on a boat pulling to one side. Let's assume for the sake of discussion, all things else being equal, that any single drive train has a failure rate of 2% on any given day. In that case you will go out on your single engined boat 98% of the days you want, while you will only go out on your twin engined boat 96% of the days. Here the single engined boat is clearly superior.

The single engined boat certainly also has superior overall economy; cheaper maintenance, less fuel consumption.

A lot of people are making comparisons with fishing boats in this thread, I don't know the answer to this but do any fishing boats use the small capacity relatively high revving Volvo engines that are referred to this thread, i.e. KAD 32?
I've always worked on the premise that RPM and reliability are inversely proportional so would have assumed a fishing boat used low revving diesel technology without turbo's/superchargers etc.

Yes, agreed.... it's not a very relevant analogy. I suspect diesels on fishing boats don't even have turbos. That simplifies things a lot; boosting reliability.