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Old 02-10-2011, 02:28 PM   #21
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RE: Not Twins

Yeah,*I saw that on the Discovery channel.* Pretty amazing.
What*would you*want for a 40' - 45' trawler crossing the Gulf Stream, would you prefer a single or a twin? I know there are other factors to consider but overall what is your opinion?
*(I knew I was going to get drawn into this sooner or later).* All the boats that I have looked at so far have twins.*** KJ*
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Old 02-10-2011, 02:32 PM   #22
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RE: Not Twins

Cruise ships typically have multiple primary*diesel engines, five isn't uncommon, and two electric-powered propellers (excluding* thrusters).* The number of engines used depends on the electrical load.* Cruise ships don't operate at a constant speed.* Speed is dependent upon the ship's schedule.* For instance, they hardly move for hours*during overnight trips between Victoria and Vancouver.
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Old 02-10-2011, 02:38 PM   #23
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RE: Not Twins

I pretty much limited my search to keel-protected, single engine/propeller trawlers.* Since I will be boating mostly*in shallow waters, I avoided boats with unprotected propellers and shafts.
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Old 02-10-2011, 04:00 PM   #24
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RE: Not Twins

It's a toss up. With twins you need to keep then synced or the harmonic slightly out of sync drumming will drive one nuts but when one engine overheats or otherwise gives trouble or even quits you'll be kinda glad you've got the other. But it's actually possible you'll need the shallower draft of the twin but you'd need to be more careful unless your twins were as well protected as a single. Of course the single was cheaper to buy so maybe you've got more money to spend in the Bahamas when you get there. When you go to the yacht club you'll be looked up to since you can afford a twin but on the hook w the trawlers you'll be more respected because you've got the guts and perhaps manliness to go forth w only one engine. It's a wash for most but for me I go many places that the loss of my single engine would be big trouble so for me it's a no-brain-er**** ...I'd have twins if I could afford it. And w an airplane I'd have 3 or 4 if I could afford it.
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Old 02-10-2011, 05:03 PM   #25
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RE: Not Twins

Could you hire an expert marine diesel mechanic to sync your twins (if you had them)? *
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Old 02-10-2011, 05:28 PM   #26
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RE: Not Twins

Quote:
nomadwilly wrote:It's a wash for most but for me I go many places that the loss of my single engine would be big trouble so for me it's a no-brain-er**** ...I'd have twins if I could afford it. And w an airplane I'd have 3 or 4 if I could afford it.
It is hard to believe that shipping companies risk millions of $$$ having only one engine in their freighters.* So, maybe it isn't a bad choice for us.

*
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Old 02-10-2011, 05:32 PM   #27
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Not Twins

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Could you hire an expert marine diesel mechanic to sync your twins (if you had them)? *
Syncing twins is done with the throttles and your ears (and your feet because you can feel it, too).* You simply nudge one throttle or the other until the thrumming is gone.* Some engines can have syncronizers installed on them which sync the engines automatically.* The out-of-sync conditon being talked about here is the matching of the vibrations--- harmonic and otherwise--- of the two engine so that you don't get them pulsing against each other.*This "sweet" spot occurs when both engines are running at exactly the same rpm.* Being out of sync a bit makes no difference to the engines, but as Eric says, the sound will drive you nuts.

The engines on a multi-engine airplane need to be synced, too, be they piston or turbojet engines.* You can do it by hand just like*with a boat but most planes have auto-syncronizers.* Our boat does not have engine syncronizers so we do it by hand.* It's so easy even a caveman could do it.



-- Edited by Marin on Thursday 10th of February 2011 06:38:37 PM
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Old 02-10-2011, 05:36 PM   #28
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RE: Not Twins

And then there are all those crazy risk-takers flying single-engined airplanes over the Alaskan wilderness.

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Old 02-10-2011, 05:38 PM   #29
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markpierce wrote:

It is hard to believe that shipping companies risk millions of $$$ having only one engine in their freighters.* So, maybe it isn't a bad choice for us.

*
RickB can give you a*more meaningful response but there is little similarity between the maintenance and skilled labor available to keep the engine on a container ship, tanker, etc. running correctly and the world the engine in a recreational boat lives in.* As I understand it, the engine on many ships can be worked on (to a degree) while the engine is running.* Cylinders can be taken off-line and repaired or adjusted or whatever.* So "single engine"in the commerical world is a whole lot different then "single engine" in the toy boat world we live in

*


-- Edited by Marin on Thursday 10th of February 2011 06:39:30 PM
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Old 02-10-2011, 05:39 PM   #30
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Not Twins

Quote:
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Syncing twins is done with the throttles and your rears (and your feet because you can feel it, too).* You simply nudge one throttle or the other until the thrumming is gone.*...
Seems to me this makes operating twins more interesting, helping to stay the boredom caused by knowing one can afford one engine to fail.

*


-- Edited by markpierce on Thursday 10th of February 2011 06:42:00 PM
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Old 02-10-2011, 05:49 PM   #31
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RE: Not Twins

Mark,
If you spent as money on maintenance as they do you prolly never need a get me home or a 2nd engine. But you're going to bring Janet and her husband and their kids and a coupla his buddies down to the boat to go for an afternoon putz around the harbor. They all just showed up at the house and someone suggested "let's go for a boat ride. Never mind if you haven't been down to the boat for over a month and the battery seemed a little flat and several other maint things are over due they all want to go for a ride and you've always wanted to impress Janet**** ...after all you'll be the captain of the ship.
Lots of trawlers go down to the water in such a state. I think they'd be better off w twins.
Ralph* wrote:
"with twins you are generating TWICE as much heat in the engine room on those hot summer days." If your Naval Architect and/or builder built your boat responsibly your boat would have as much power in either configuration**** ..single or twin** ...and produce the same amount of heat in the ER.
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Old 02-10-2011, 06:01 PM   #32
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Not Twins

My builder says that even in the beamy 35-foot*Coot,*the primary engine and a genset makes the engine room crowded.* Perhaps a couple of beefy gensets and a single (keel-protected)*electric-motor-powered propeller shaft would be "ideal."* Haven't seen that as a builder-provided option, however.

-- Edited by markpierce on Thursday 10th of February 2011 07:02:12 PM
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Old 02-10-2011, 06:42 PM   #33
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RE: Not Twins

Quote:
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Seems to me this makes operating twins more interesting....
One reason I like multi-engine boats is that I like operating the engines and what you can do with them.* This is not to say that one can't accomplish the same maneuvers with a single engine boat. I just like manipulating the engines to put the boat where I want it.

Years ago I filmed on board an oil rig supply boat out of Santa Maria, CA.* This particular boat had three engines.* The skipper had to hold the boat exactly on station under the rig cranes while pipe and whatnot were picked up off the deck.* Port of my filming was of the skipper manipulating his three throttles and shifters to hold the boat in the same spot despite the efforts of the wind and waves to move it.* It was impressive to say the least.* I'd love to be that adept at maneuvering, and that experience is one reason I like running multiple engines.

*
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Old 02-10-2011, 08:30 PM   #34
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RE: Not Twins

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nomadwilly wrote:

But about the different brand twins** ..it would be nice if we had someone on here that had experience with such a system and is willing to share.
Eric--- I will pose your question to the GB owners group and see if anyone responds.


Eric--- FWIW, here is a response I got from Bob Lowe who founded the GB owners site and has many years of working on these (and other boats) as the owner of Oak Harbor Boatworks.* Part of my question was if the differnence in power between the two engines*was compensated for with prop pitch.

(quote)

"Same pitch and diameter and same rpm = same speed, regardless of max hp capability. Assumes props have been sized for any differences in transmissions as in GB twins."

*
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Old 02-10-2011, 09:19 PM   #35
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Not Twins

Marin wrote:

""Same pitch and diameter and same rpm = same speed, regardless of max hp capability"
Of course. If youv'e got a 500hp engine on one side and a 100hp engine on the other and both shafts are turning 1200rpm both engines are synced and both shafts props are producing the same thrust and power. I thought I covered that. Let us know what comes of the GB site inquiry. In this different engine caper one could get unfortunate enough to wind up w the service side of the engines both on the outboard side.

Mark,
Two small engines (in your case 40hp) shouldn't take up much more (if any) more room than one 80hp engine.

-- Edited by nomadwilly on Thursday 10th of February 2011 10:21:51 PM
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Old 02-10-2011, 09:27 PM   #36
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RE: Not Twins

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In this different engine caper one could get unfortunate enough to wind up w the service side of the engines both on the outboard side.

You could, I guess.* In the case of the AD 150 hp diesel that's a drop-in replacement for the FL120 the base engine for the AD 150 is a new but somewhat similar Ford of England engine.* So the main components--- injection and exhaust--- are on the same sides as the FL120.

*
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Old 02-10-2011, 10:00 PM   #37
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RE: Not Twins

Yes but the example was w a Perkins and all that service side exhaust side stuff may be or probably is different. Location of engine mounts, throttle, fuel lines, alternator, oil coolers and lots of other stuff will probably be different. Most would be easy to change though.
I joined the GB site but had difficulty w the profile page*** ..the avitar I think.
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Old 02-10-2011, 10:02 PM   #38
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RE: Not Twins

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I joined the GB site but had difficulty w the profile page*** ..the avitar I think.
Which site did you join?* There are two GB owners sites, the International Association of Grand Banks Owners and the GB Beacon site which is hosted by Grand Banks.

The one with the most participation is the IAGBO site.

*
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Old 02-11-2011, 11:59 AM   #39
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RE: Not Twins

Eric--- Here are a couple of other comments on unmatched twins from the GB site. First one is from a fellow in England who completely rebuilt a near-derelict and rotted out GB32 woody into a near-perfect example of the type and who has a lot of professional experience with engines. Second one is from a local owner of a GB42 woody.

------------------
(1)
Theoretically ? If you had one engine that only developed (say) 70Hp and the other was a 120 you wouldn't notice a difference until the smaller engine couldn't keep up. This would depend on where the power range is on the smaller engine. (look above I stated THEORETICALLY). I don't think anybody would use full power whilst traveling, That said in rough waters pushing against waves etc, the torque difference would begin to show if they were so far apart on the power scale.

With a 120 to 150 I would assume their torque curves would be fairly close.

---------------------
(2)
I second that, if the power band is close at cruising RPM it will not make much difference. As the RPM moves upward and the stronger of the two start developing more and more power, it will make a difference if the gap is large enough. However for a 120 and 150 at 1,800 RPM, the torque curve is close enough between the two engines to make virtually no difference. Give them full throttle and you will have to compensate slightly with the rudders as the power curves separates.
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Old 02-11-2011, 01:31 PM   #40
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RE: Not Twins

Would it be reasonable to expect that a boat owner would try to match the older engine as close as possible regarding HP,*and torque, as well as any other variables to be considered, well before the new one was installed?**** KJ
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