Single vs Twin: It's Baaaaack!

[Marin]

Last week I had the shocking experience of listening to a man with life long experience in boating more than equal to most here on TF say that a GB was not a trawler.

Well, since American Marine never referred to their Grand Banks line of boats as "trawlers" he was correct. The current company, Grand Banks, Llc, has taken to using the term "trawler yacht" in their promotional material and website but that's simply an acknowledgment of the marketing hype that gave birth to the notion of a recreational "trawler" in the first place.

If your market insists on calling your product a "trawler," then it would be a foolish manufacturer who continued to call them something else even if that something else was actually correct. If everyone started called shoes "footies" instead of shoes, Nike would soon start calling themselves a "footie company," not a shoe company.

 

[Underway]

Skidgear,
Shocked again! What on earth could you base that opinion on? And what boat do you think most represents a trawler?

OK then....I'm shocked that you're shocked that I was shocked!!

The boats represented on this web site are poseurs one and all. Nothing wrong with that mind you.

 

[Marin]

A single engine boat has more room in the engineroom which allowes one to more closely view and monitor the related systems. You are right, one will have more access to and therefore be able to or more willing to do preventive maintance.

You mean the last 14 years that I have spent meticulously maintaining the two engines in our boat--- or having them maintained when doing things like replacing engine mounts, exhaust systems and so on exceeded my experience or time available--- religiously changing the injection pump oil, servicing seacocks, checking hoses, replacing impellers and belts, inspecting for oil, coolant, and fuel leaks, cleaning raw water filters, bleeding the exhaust manifold to ensure there is no air pocket at the high point before every cold start-- something I doubt any FL120 operator does, single or twin--- and so on, most of which require getting to both sides of both engines, I've been doing it wrong?

That for the last 14 years we should have been driving our twin-engine boat with no thought whatsoever to the engines, secure in the knowledge that if one engine fails we have the other one?

I promise to mend my ways for the next 14 years.

"A single owner is more wiling to or able to do preventative maintenance than a twin owner." What an absurd assumption.

 

[bfloyd4445]

You mean the last 14 years that I have spent meticulously maintaining the two engines in our boat--- or having them maintained when doing things like replacing engine mounts, exhaust systems and so on exceeded my experience or time available--- religiously changing the injection pump oil, servicing seacocks, checking hoses, replacing impellers and belts, inspecting for oil, coolant, and fuel leaks, cleaning raw water filters, bleeding the exhaust manifold to ensure there is no air pocket at the high point before every cold start-- something I doubt any FL120 operator does, single or twin--- and so on, most of which require getting to both sides of both engines, I've been doing it wrong?

That for the last 14 years we should have been driving our twin-engine boat with no thought whatsoever to the engines, secure in the knowledge that if one engine fails we have the other one?

I promise to mend my ways for the next 14 years.

"A single owner is more wiling to or able to do preventative maintenance than a twin owner." What an absurd assumption.

[FONT=Arial, Helvetica, sans-serif]you did all that and still had an engine breakdown??......that convinces me, single engine is best. Kinda proves what someone said about it being hard to be thorough with two engines cause of the cramped space
[/FONT]

 

[Marin]

We have never had an engine breakdown. We had raw water cooling problems three times--- failed coolant pump seal on the initial delivery trip from Tacoma to Bellingham after the the boat was trucked up from California, and two instances of raw water exterior intake partial blockages (from outside the boat) that prompted precautionary shutdowns, and one time I let an engine get a slug of air during a fuel transfer for a reason that was totally my fault and we didn't want to take the time to bleed the engine because our guests had to get home by a particular time so we simply finished the run on one.

 

[dwhatty]

To confuse the issue further, our old wooden boat had a "worm shoe". A sacrificial piece of wood running the length of the keel.

 

[psneeld]

I really don't see it as adding to the confusion...the guy who first started using the term "shoe" probably meant it to refer to a "protector part" ...not an integral part of the keel.

To me its easy and logical...but that doesn't always make it correct!

 

[bfloyd4445]

We have never had an engine breakdown. We had raw water cooling problems three times--- failed coolant pump seal on the initial delivery trip from Tacoma to Bellingham after the the boat was trucked up from California, and two instances of raw water exterior intake partial blockages (from outside the boat) that prompted precautionary shutdowns, and one time I let an engine get a slug of air during a fuel transfer for a reason that was totally my fault and we didn't want to take the time to bleed the engine because our guests had to get home by a particular time so we simply finished the run on one.

humm...so you have had more than one failure with twin engines....So maybe since two is better than one engine that three engines would be even better than one impecably maintained engine? Or maybe that single engine failure is less common cause they never make it back to port for documentation creating the illusion that twins may be more dependable/

three engines...wonder if there are any. Is'nt this like in the early days of aircraft when extra engines were seen to increase dependability? The trend has been to fewer engines and for good reason


In fifty years of boating, none in a trawler, i never had a single engine failures.One duck blind, one loose anchor rode, one gravel bar, caused my engine to stop in fifty years but none because of engine or related systems failure all because of my failure.

 

[RickB]

three engines...wonder if there are any. Is'nt this like in the early days of aircraft when extra engines were seen to increase dependability? The trend has been to fewer engines and for good reason.

Lots of 3 engine boats around.

Early flying machines added engines to provide enough power to get off the ground ... they couldn't make a single engine with enough power so they just kept adding them until the thing would fly and carry a load. Take a look at the Linke-Hoffman R.II for example.

If we had giant turbofans around in the 1950s we probably wouldn't have had so many 4 engine planes. Marin can probably supply some good leads on Boeing's take on that subject.

 

[bfloyd4445]

Lots of 3 engine boats around.

t.

this isnt exactly what i had in mind
Motor Yacht Pershing 108´ - a Pershing Superyacht

all the fishing trawlers and pleasure boats i could find were two engined

 

[Underway]

Lots of 3 engine boats around.

Marin can probably supply some good leads on Boeing's take on that subject.

No you fiend....anything but that.....

 

[Marin]

humm...so you have had more than one failure with twin engines....So maybe since two is better than one engine that three engines would be even better than one impecably maintained engine?

You are absolutely determined to remain clueless on this issue, aren't you?

We have never had an engine failure. We have never had an engine stop running for some reason except one time and that was totally my fault and had nothing whatsoever to do with the engine or its maintenance.

In three of the four instances we shut the engine down as a precaution. On the fourth instance I shut it down inadvertently.

The only instance that actually had anything to do with the engine was during the delivery trip when toward the end of it the coolant pump (not raw water pump) began leaking coolant from its mounting gasket. But this was the first run of the boat after buying it. So it's anyone's guess how long the pump had been on the engine or what condition the gasket was in.

The other two times were due to cooling problems that had nothing to do with the engine and would have occurred had we had one engine or twenty.

And the last occurrence was, as I said, totally my fault for mismanaging the fuel system during a transfer. Lesson learned. And it would have occurred no matter how many engines the boat had. But since we had two it was a non-event.

None of these things other than possibly the first one had anything to do with how well the engines had been maintained.

You need to learn the difference between an engine shutdown due to circumstances that are not connected with engine maintenance, and shutdowns (or outright failures) that are.

You also need to learn the difference between potential failures that can be prevented because you can see evidence of a potential problem developing, either by inspecting exterior components, removing covers and inspecting what's inside, or changing high-wear components out on a regular schedule, and failures that occur just because they occur and there is no way to predict their occurrence.

Examples of the former are a drive belt or raw water pump impeller failure. Examples of the latter are the sudden pinholing of an injector pipe or a transmission damper plate spring breaking.

 

[markpierce]

Marin, you need a new avatar where you aren't displaying fenders.

 

[psneeld]

I think a lot of people need to be more specific between an engine problem and failure.

A twin guy might shut down an engine because it has a "problem" and call it an engine failure.

A single engine guy will figure out how to handle the same "problem"...keep going till safe haven and call it an engine "problem"...not a "failure".

I've had hundreds of engine "problems" through the years on all kinds of boats, singles and twins...never an engine "failure" ... and I have tens of thousands of hours underway in vessels from 20-399 feet.

Actually the only failure I've had was when an outboard fell off my second sailboat....I'd call it a failure to hang on!!!

 

[BruceK]

To confuse the issue further, our old wooden boat had a "worm shoe". A sacrificial piece of wood running the length of the keel.

The Yard I use calls those "docking boards", because it is what the boat sits on when docked (ie dry-docked/hauled, or as we say "slipped").
They would also be good in a grounding. The Yard used freshly felled and milled un-dried turpentine timber for the boards, an oily tough timber.

 

[Marin]

If we had giant turbofans around in the 1950s we probably wouldn't have had so many 4 engine planes. Marin can probably supply some good leads on Boeing's take on that subject.

Rick summed it up well.

The only reason airplanes acquired more engines was to be able to take off with a full load or go faster or both.

The FAA, JAA, etc. requirement for multi-engine commercial airplanes is very simple and does not define how many engines one needs to have. The rule is that a multi-engine airplane has to at full gross weight be able to continue a takeoff and climb out at a safe rate of climb in the event of the loss of ONE engine. So a 777 has to be able to meet these requirements with one engine, a 747 has to be able to meet them with three.

Lose two engines on a four engine plane and it is a Not Nice situation to be in.

So the only reason the 747, A340, and A380 have four engines is to be able to take off, climb out, and fly safely with engine one not running.

The advances in turbofan technology as well as airplane systems have made today's engines powerful enough to only require two in all but the largest transports. I will be surprised if any of the commercial airframe manufacturers design a plane with more than two engines in the future unless very high speed becomes part of the formula. But I don't see that happening until there is a less expensive, cleaner, and more efficient source of propulsion energy readily available.

SomeSailor may have a more engineeringly-accurate take on the situation but that's mine. Sorry Skidgear........

 

[Marin]

Marin, you need a new avatar where you aren't displaying fenders.

Why?

 

[markpierce]

Why?

Because I'd like something new/different.

 

[koliver]

I too have Velvet drive transmissions on my engines. Several years ago I hit something and thought I might have damaged a prop. This occurred at the second day of a two week trip through the Gulf Islands so stopping for repairs was not going to happen. We continued on, using only one engine for the rest of the trip. My hour meters showed 35 hrs of single engine use.

This all occurred long before I ever started looking at sites like this, so I had no idea that dragging one prop might damage a transmission. I did go a little slower while on one engine, likely 1 knot below normal cruise.
Three years later, when I swapped out the engines, the transmissions were both still working well and inspection did not reveal any difference between them. I haven't ever worried about freewheeling, and apparently there is no damage done to a Borg Warner Velvet Drive in those circumstances.

 

[Marin]

Because I'd like something new/different.

I agree with Eric's take on avatars in that consistent avatar photos are a benefit to forum readers because they will know immediately who a post is from and thus be able to determine at a glance whether they want to bother reading it or not. In my case the decision is probably more often not, so by using the same avatar since 2007 I feel I am doing the participants in the forum a service by helping them know instantly what to avoid. That much less drivel for them to wade through.

 

[markpierce]

Marin, as you are the most active poster, I find it hard to believe people won't recognize you regardless. ... I haven't noticed people failing to recognize me despite changing avatars frequently. Think I'll do it now.

 

[BruceK]

I too have Velvet drive transmissions on my engines. Several years ago I hit something...We continued on, using only one engine for the rest of the trip. My hour meters showed 35 hrs of single engine use.

This all occurred long before I ever started looking at sites like this, so I had no idea that dragging one prop might damage a transmission. I did go a little slower while on one engine, likely 1 knot below normal cruise.
Three years later, when I swapped out the engines, the transmissions were both still working well and inspection did not reveal any difference between them. I haven't ever worried about freewheeling, and apparently there is no damage done to a Borg Warner Velvet Drive in those circumstances.

Koliver, Your practical experience is much appreciated. I also respect Marin`s views about preventing unpowered rotation and the 'trolling speed" limit BW mention. My PO ran my boat a while on the port engine after the stbd gearbox imploded, the port g`box seems fine, no idea if he locked off. Are there any other experiences out there?

 

[psneeld]

I have run dozens of boats with one engine off...it all depends on the tranny and many are just fine if keeping it below 10 knots. Some recommend starting the engine if possible for a little to get the oil circulating but again it all depends on the manufacturer.

As far as drip-less packings...again it depends but many boats have crossovers...when I was runnin g the older Sea rays that lost engines...we dragged the props/trannys and just pulled the water feel to the drip-less off to let a flow into the bilge to keep the drip-less cool and as long as the bilge pump was working...no big deal.

 

[Marin]

Water feeds to shaft logs are not limited to dripless packings. Our shaft logs have conventional packing glands (w/flax packing) but they also have water feeds. The reason as it was explained to me is that the design of the GB's shaft tunnels and their installation of a pair of cutless bearings in the shaft tunnel back to back means that underway there is little to no cooling/lube water getting to the forward cutless bearing in the tunnel and the shaft log. Hence the water feed from each engine's raw water cooling system to the shaft log.

This is why we have to tie the shaft off if we shut an engine down. It has little to do with the transmission but everything to do with the rapid overheat and extreme damage that will occur to the log and possibly even the shaft if the shaft is allowed to freewheel without the water flow from its associated engine.

 

[Peter B]

Marin, you need a new avatar where you aren't displaying fenders.

Mark, you leave Marin alone. Fenders are the new cool....and I agree with the consistent avatar thing in the main. Heck I only recognise you these days because you usually attach a photo of the Coot, you change yours so often, and as for RickB....
Actually usually do recognise him because his avatars are usually BIG boats or BIG boat bits - that and his acerbic wit....

 

[bfloyd4445]

<<<

You are absolutely determined to remain clueless on this issue, aren't you?>>>>

......chuckle, or so it seems like it to you. The question in my mind is" which is better, single or twin engines". I may have jumpted to a conclusion regarding the incidents you mentioned from lack of data and i thank you for filling me in.

The raw water pick up issues you experianed are something everyone has to deal with at some time or other.

anyway, my point was that you have had more than one instance when you found it necessary to shut down an engine and the question that comes to mind is this: Does haveing a twin engine boat tend to make the captain less diligent because he feels confident that if he has a failure he will still have one dependable engine system.

To approach the original question scientifically we would need to first get a feel for the total number of single screw and twin screw trawlers in say the state of Washington. Then obtain insurance company statistics on the amount of accidents resulting from engine system failures. From this information we could determine which system has the highest failure rate resulting in damage. Even this would not answer the question because i believe the single screw craft may be used more because of the economy than twins and so would have a greater exposure to hazards. I'll bet one could write a book on this issue?/ We need a writer...Marin.....chuckle...wanna write another book?

 

[Marin]

<<<

Marin.....chuckle...wanna write another book?

No, I'm having enough of a job with the current one and I was just hired to work on another one. Or rather work more on one I thought was done.

I don't know about the singles vs twins in terms of which gets used more. If you're limiting it just to recreational diesel cruisers I'd be tempted to say there are more twins out there being used than singles. At least in this area where Bayliners are probably the most numerous of all makes. Grand Banks are also very popular in this area and most of them, at least since the 1980s or so, are twins.

Judging by the number of power levers I see on the boats I have paid attention to in our marina over the years, I would have to say that far more larger cruisers are twins than singles. Exceptions are the very few number of Nordhavn's around and the handful of single-engine GBs I'm aware of, all of them 36 or 32 feet long. The big Tollycrafts are mostly twins, as are the larger Uniflites.

CHBs and the like tend to be twins more than singles of the ones I've seen around us and in the yard. Likewise the Island Gypsies.

The tugs--- Nordic and American--- are singles or mostly singles.

So while it's impossible to say without a lot of data that is either too hard to round up or doesn't exist whether or not singles are used more than twins, my tendency would be to say it's the other way round based on what we see on an annual basis.

Our slip is opposite the fuel dock in Squalicum Marina, and this is the only fuel dock with diesel in the bay. So everything comes through here including the USCG. And from what we've observed over the years, summer, winter, spring, and fall, the larger powerboats, by which I mean 35 feet on up, are for the most part twins.

But that's just here.

 

[sunchaser]

Ah, twin skegs. That is just what the new boat Doctor ordered. Check out KK's 52, 55, and 58 brochures. Since one skeg is great according to Mark, Benn etc - two must be twice as good.

 

[Nomad Willy]

Floyd writes;

"The question in my mind is" which is better, single or twin engines".

That's simple. The twin is considerably more expensive and lots of boat buyers opt for the twin. They pay considerably more money for them so it can be assumed that they are better. Why else pay more?

And one should keep in mind that here 90% of the twin/single conversation is centered around twins w twice as much power and twice the engine weight as the singles. Any objective conversation about this should be regarding single engined boats and twin engined boat having the same total amount of power. As in a 200hp single and a twin w two 100hp engines. So this discussion is rarely apples and apples on this forum. If you are having a Naval Architect design a boat for you .. a boat of either configuration will be assumed to have the same amount of power.

And yes Tom, I think the KK twin keel/engine boats are the most desirable propulsion system available.

Peter, I agree w you but it's a much bigger PITA on FB. You will notice I changed my avatar about a year ago and made a point of making the new look very much like the old avatar. It's recognition. But I wouldn't go so far as to criticize others for doing it. By the way Rick what is that V16 engine in your new avatar? Sure glad you dropped the old one. Couldn't even make out what it was.

 

[FlyWright]

Wow!! 300 posts and we still haven't settled the question. Let's hope we'll get to the bottom of this in the next 300 posts.