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Old 07-14-2016, 12:58 AM   #61
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Back in the 50's my dad had an old wood tug with a Fairbanks Remorse in it, about 150HP. He then repowered to a 6-71 and liked it a lot. He went back to back with another tug with an older eng of similar HP, forget the make but it was an old heavy duty of some sort. The 6-71 quickly pulled the other tug backwards, the skipper freaked because he had an open hatch on the back deck and water was running into it! I spent a little time around a 6-53 in one of dads trollers, good engine but horribly noisy.
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Old 07-14-2016, 01:12 AM   #62
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I think if you run the 53 at about the same 1800 rpm they will
be a lot quieter. That's the way I ran the 3-53 I used to have.
Those 3 cylinder models were sure smooth!

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Old 07-14-2016, 07:19 AM   #63
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I recall that my 6-71 Grays generated about 16 hp per gallon-hr and were rated 160hp. I don't recall the injectors but were likely N50 or N55.

Those were 2 valve heads.

So if the engine had 4 valve heads (which I believe would bring the power up to 180 hp) would that also increase the fuel efficiency?
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Old 07-14-2016, 04:14 PM   #64
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would that also increase the fuel efficiency

Not much , but it would increase the ability to burn more fuel, if you want higher speeds.

"Screaming jimmys" need RPM for high power output.

But for many boats 1200-1500 RPM will so the sq rt of the lwl , a nice efficient speed with little noise.
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Old 07-14-2016, 05:01 PM   #65
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All engines need high (relative) rpm to make their best power. OB engines are known for high torque but but two stroke engines are known for wild power near the top but weak down low. Early scream'in Honda motorcycles did'nt have much low end but in all these cases it was the state of tune that dictated where the "relatively" good power was.

However my only significant experience w DD engines is riding the Greyhound busses when I was young. When the power and rpm fell off on a hill the downshift did wonders to save the receeding power but the lower gear had a lot to do w it too. I suspect that power low down has mostly to do w valve overlap and the amount of stroke or time of the cycle that delivers compression and pulls in the fresh air. But the DD has the blower to help however at low rpm can't help much. Hmmm .... It's a complicated relationship (rpm and power) and differs w every engine. But nobody's favorite engine has a corner on low end grunt. The Buick straight eight had a rep for great long stroking torque but when Buick came out w their very short torque V8 it had more torque than the old long stroker.
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Old 07-14-2016, 05:11 PM   #66
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Re the thread,
Boats don't need much low end power or torque. The prop dos'nt present a large enough load at low rpm to develop much power. But because of the hull's resistance very little power is needed. The load curve of a prop on a boat ramps up steeply at the high end and that's where the power is needed to maintain speed. Cars and trucks are frequently going up hills and accelerating so there's much use of low end power and torque. But not so w boats.
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Old 07-14-2016, 06:21 PM   #67
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At idle, my boat moves at nearly half speed. At 2200 RPM, it reaches hull speed. (14-ton boat, with NA JD 4045)
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Old 07-14-2016, 08:19 PM   #68
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Twin Detroit 453's recently rebuilt due to spinning the main bearing in the starboard engine at 3600 hours. We cruise at 1559 to 1650 rpms , they don't leak at all, and we do not find them noisy. Parts everywhere. I own them so of course I love them. 👍
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Old 07-14-2016, 09:52 PM   #69
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[QUOTE=
Every engine manufacturer makes some less than reliable efforts one time or another. Among them, Cat 3116, Yanmar 6LP (a Toyota block), Detroit 8.2, and so on. Then there are the best ones: Lehman 2715, Yanmar 4lh, Perkins 4-236,
Deere 4045, and so on. And Aluminun problems, well that's bad metallurgy, cheap aluminum, and it happens. Westerbeke is famous for it. Ever seen a solid brass Detroit diesel? They built them, and aluminum too.


The Yanmar 6LP is a well liked engine from my research. There was a run with some valve issues but other than those particular engines they were/are well liked by most owners. I know Tony Athens on Boat Diesel has been quite positive about them if used for their intended purpose and he seems to be a pretty knowledgable fellow.
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Old 07-15-2016, 06:18 AM   #70
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"But nobody's favorite engine has a corner on low end grunt."

Todays 4 stroke engines (gas or diesel) with a turbo have great low RPM power.

The new touring buses in EU land have the green zone on the tach at 1200 RPM.

The 6-71 and 8V71 that Greyhound ran used 1650 RPM , tho most were tweeked to at least 1800.

If boaters could get over the sillynes of wanting MAX rated power at Flank, cruising a good sized engine at minor RPM , with great fuel use and low noise and vibration.

With the electronic injection and control, overloading from an unskilled operator would no longer be a concern.

But a diesel advantage , once its running nothing but fuel is needed would be lost.

The 6-71 graph on another post shows 100HP available at 1000RPM

As most of our sized boats need less than 100HP,, 6 or 7 GPH it could be a place to start for a cruiser.
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Old 07-15-2016, 12:42 PM   #71
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[QUOTE=jarod;460763][QUOTE=Ever seen a solid brass Detroit diesel? They built them, and aluminum too.[/QUOTE]

DD even made stainless steel engines for minesweepers. If I recall right, they were the big 16V-71s.
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Old 07-15-2016, 02:35 PM   #72
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The stainless steel 671s came after the aluminum ones. Also, bigger GM 8-268a engines were made of ss for bigger minesweepers. There's an ex-Canadian minesweeper on the US West Coast with those engines.
Here's one with a quad (4 671s on a single shaft): 1958 Bellingham Shipyard Minesweeper, Olympia Washington - boats.com

I have been told the 4 valve head gives better economy by allowing better exhausting of spent gases, but would need to be used many hours to pay.

16v71s are two 8v71s bolted together. There are other dual models, too.
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Old 07-15-2016, 04:34 PM   #73
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"Low end power" has no relevance for me, as in lack of. Sure, my boat vibrates at idle-speed while in gear, but less than some others. Idle moves me near half speed (three-something knots), but push the lever controlling the engine's fuel consumption provides quite sufficient power, thank you.
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Old 07-15-2016, 04:41 PM   #74
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Quote:
Originally Posted by Nomad Willy View Post
Re the thread,
Boats don't need much low end power or torque. The prop dos'nt present a large enough load at low rpm to develop much power. But because of the hull's resistance very little power is needed. The load curve of a prop on a boat ramps up steeply at the high end and that's where the power is needed to maintain speed. Cars and trucks are frequently going up hills and accelerating so there's much use of low end power and torque. But not so w boats.
I am going to have to majorly disagree with you. A boat is continuously under load...WAY more than a car or truck. They need that low end grunt to get them up and going. I know we are on trawler forum. But the vast majority of larger planing boats are diesel powered for a reason and that is TORQUE!!!...POWER!!! I have been on a Viking 68 sport fish doing 40kts. I think the power setting was around 1900RPMs...right in the meat of the torque curve. That is an extreme example but I cruise ar about 2300. Again...right in the meat of the power. I may have misunderstood you. But boats need torque way more than a car.

To put it another way, boats are going uphill continuously...
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Old 07-15-2016, 04:48 PM   #75
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best trawler engine

Boats are climbing uphill all the way through the power band. Don't believe that, cut power to the engine and watch what happens. Adequate torque to fulfill the mission is vital.

Edit: just saw Bakers last sentence added.
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Old 07-15-2016, 05:02 PM   #76
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My maximum torque is at 1400 RPM (about five knots), providing "slow cruise." Don't operate above that until engine is sufficiently warmed. Typically run at 1800 (a knot below hull speed) while maximum WOT is 2400 (a waste: greater than hull speed that is reached at 2200). (Beware: boats and engines are unique, and my boat has a full-displacement hull.)
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Old 07-16-2016, 01:03 AM   #77
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There's an ex-Canadian minesweeper on the US West Coast with those engines. Here's one with a quad (4 671s on a single shaft)...
Wow, looks like a great hobby to keep you busy full time during retirement! Few comments though:

1) What's that pointy thing on the bow??? Can't be an anchor for a boat that size - perhaps its a toothpick for whales?
2) Love that huge steering wheel at the helm, looks to be about 4ft diameter. Do you know if the boat has cable steering?
3) Four 6-71s to maintain. No thanks. I didn't like having two, so for now on I'll only be sticking with one engine.

BTW, perhaps I read your post wrong, but those "stainless 6-71s" seem to be suffering from a god-awful amount of rust.

cheers
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Old 07-16-2016, 04:39 AM   #78
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"Best trawler engine" . If You want the latest, most fuel efficient, lightest, smoothest, quietest, least emmision, easily serviced engines, You simply go with Volvo Penta full stop. Even M.A.N. or MTU canīt compete with them. And NO, CAT or Cummins are not even near. Compare to what You are driving on the road. Tedious - Sorry for sore feet, a little.
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Old 07-16-2016, 05:23 AM   #79
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"Best trawler engine" . If You want the latest, most fuel efficient, lightest, smoothest, quietest, least emmision, easily serviced engines, You simply go with Volvo Penta full stop. Even M.A.N. or MTU canīt compete with them. And NO, CAT or Cummins are not even near. Compare to what You are driving on the road. Tedious - Sorry for sore feet, a little.
Clarify how you come to this conclusion for a trawler engine (versus a high speed craft). Granted I've owned good VP gas sterndrives, but when reviewing their website for a typical 225 hp inboard, the specs show:
  • 4 cylinder
  • tiny 3.7 liter displacement
  • 3500 rpm
  • 18.75 gal/hr-hp at full throttle, which is typical for any T-4

Perhaps the engine would be great for high speed, but for a trawler we're usually looking for a commercial rated, medium speed, engine, not a recreational-rated engine. Also, there are a lot of comments about the company's support for its product, but others would have to chime in on that.
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Old 07-16-2016, 06:37 AM   #80
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"there are a lot of comments about the company's support for its product, but others would have to chime in on that."

In one word , FORGETABOUTIT
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