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Old 09-25-2019, 11:15 AM   #1
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Engine choice on Grand Banks 42

Investigating the GB 42. It really has a wide range of engine options. One brokered boat advertises twin Ford 135 HP with a cruise speed of 7kts and a max of 8kts. But I corresponded with a broker on another boat, same engines, and says cruise speeds of 9 to 12 kts. What can I really expect with the NA 135hp engine.
Additionally I read the V8 engines take up a lot of space compared to the in-line engines. So how hard is it to work on these V8's? I plan on doing as much maintenance as I can myself.
Thanks for your inputs.
Pat
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Old 09-25-2019, 11:25 AM   #2
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I would suspect closer to 9-10 knots WOT but go out on a test ride and see.
Seeing is believing but you’ll get many opinions here. Perhaps 10 knots.
First opinion.
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Old 09-25-2019, 11:34 AM   #3
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I have Cat 3208, naturals. V8s. I don’t like it, but I’ve always been able to perform maintenance; raw water pumps, etc.

Cruising at 1800 rpm gives me about 8.5 to 9.0 kts. Our chosen speed is really more a function of hull shape as opposed to horsepower. Sure, I can push the boat (and a wall of water!) to 12 to 14 kts. However, my fuel consumption increases from 6 gph (sum of both engines) to, who knows, 18 to 20 gph. I like to smell roses!
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Old 09-25-2019, 11:34 AM   #4
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Cruise speed with twin 135hp will be 7-7.5 knots.
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Old 09-25-2019, 12:20 PM   #5
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No way will you get a 12 knot cruise out of 135s. I would bet between 7 and 8 knots will be a realistic cruise speed. If you are going with a trawler then in the range of 7 to 9 knots is a reasonable cruise. We have SP225 Lehmans in a 41’ and cruise at about 8.5 knots at 1400 RPM. Our full throttle is 17 knots.
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Old 09-25-2019, 12:27 PM   #6
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270 (total hp) will not push that boat much over hull speed...if at all. And then it will be producing lots of black smoke. Hull speed is about 8.5 knots. That boat will cruise nicely at 8 knots at 1/2 throttle.
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Old 09-25-2019, 12:47 PM   #7
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I have a 42 grand banks with twin Lehman 135s, MG5011 twin disc transmissions with a 2.44:1 reduction, not over-propped.

With a clean hull we cruise between 8 and 8.3 knots with engine RPM between 1700 and 1750.
WOT yields 2600 RPM loaded, but our throttle limit screws are turned back to where we max out at 2300 RPM.

2300 RPM yields a speed of 11 knots without the faintest haze of black smoke.

The Lehman 135 is not a V8, it's an inline V6. It's incredibly easy to work on, and while they are large, so is the engine room.
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Old 09-25-2019, 12:50 PM   #8
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I have a 42 grand banks with twin Lehman 135s, MG5011 twin disc transmissions with a 2.44:1 reduction, not over-propped.

With a clean hull we cruise between 8 and 8.3 knots with engine RPM between 1700 and 1750.
WOT yields 2600 RPM loaded, but our throttle limit screws are turned back to where we max out at 2300 RPM.

2300 RPM yields a speed of 11 knots without the faintest haze of black smoke.

The Lehman 135 is not a V8, it's an inline V6. It's incredibly easy to work on, and while they are large, so is the engine room.
Very “artsy” looking Lehman’s
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Old 09-25-2019, 06:29 PM   #9
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We had a 42 powered by in line 6cyl 315hp Cummins. She liked to cruise 1750 -1800 rpm and made 9.5 kts. Fast cruise was 12-14 kts, fuel burn jumped from 5 mph. WOT was 17.5 kts, it looked like much larger vessel was creating that wake, but we could roll over the bow wave and actually get on plane. Only did that on rare occasions; sea trial at sale was one. God knows what the fuel burn was at that speed, I did notice that we'd increase speed just a bit if we held WOT for 15 minutes; lighter fuel load I guess.
Plenty of space to get around in the ER.
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Old 09-25-2019, 06:41 PM   #10
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.

The Lehman 135 is not a V8, it's an inline V6. It's incredibly easy to work on, and while they are large, so is the engine room.
Never heard of an inline V6, or is it an inline 6?
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Old 09-25-2019, 06:46 PM   #11
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He meant L6 or I6. And where does the L come from anyway?
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Old 09-25-2019, 07:17 PM   #12
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The hull speed of my GB42 was 8.6 knots and for years I ran my twin Lehman 120s with 2.01:1 and 1.91:1 trannies at 1800 RPM getting exactly that speed. Eventually, I found that 1600 RPM was a vert sweet and quieter spot for those particular engines at 8 knots on the nose. Any more power in this hull is just not necessary unless you are planning to waste a lot of fuel to achieve marginal speed increase.
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Old 09-25-2019, 07:28 PM   #13
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Quote:
Originally Posted by diver dave View Post
He meant L6 or I6. And where does the L come from anyway?
I = inline
L = line

Besides V there are a lot of other configurations. (W, H, U, flat) However none that I know of in the marine world.
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Old 09-25-2019, 10:11 PM   #14
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Cruise speed with twin 135hp will be 7-7.5 knots.
I frequently cruise with a friend who has that boat. I go 8.0 all the time. He waits for me.
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Old 09-25-2019, 10:22 PM   #15
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Thanks guys. Good info on the straight 6's which I know the Lehman's are. You confirm what I have been told about the ease of working on this type of engine.
Giggitoni also confirms the tightness of the V8's ER. As I scour the internet for a boat to purchase I'm seeing more V8's in the GB42's than other options so thus my curiosity about being able to work around them. Some even have stabilizers and that too seems to cut down on maneuverability down below.

I guess if I had my choice I would want a set of the more powerful straight 6's but as we all know everything is a compromise. Give me a real clean, well priced boat with V8's and I might have to buy it.

Please keep your real world stories coming. I need all the knowledge I can get in this daunting task of finding a boat.
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Old 09-26-2019, 06:34 AM   #16
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Even if the engine room looks tight, when you go to look at a boat, crawl in there and see where the common service points on the engines are. It may turn out that either the tight spots aren't as bad as they look or that you rarely have a need to crawl in there and it's not a big deal. Or it may be possible to add a hatch for better access.
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Old 09-26-2019, 08:51 AM   #17
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Cruising at 1800 rpm gives me about 8.5 to 9.0 kts. Our chosen speed is really more a function of hull shape as opposed to horsepower.
Ray, Is that your tender I see in your avatar?
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Old 09-26-2019, 10:00 AM   #18
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Ray, Is that your tender I see in your avatar?
That’s right, Walt! I drag him around a lot. The tender also has a well-stocked frig!
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Old 09-26-2019, 10:01 AM   #19
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I guess if I had my choice I would want a set of the more powerful straight 6's but as we all know everything is a compromise. Give me a real clean, well priced boat with V8's and I might have to buy it.

I don't know that boat or those engines, but the probable hull length at the waterline (40'?) suggests a maximum comfortable cruise speed would be 8.5 kts in "displacement mode"... i.e., not counting any semi-planing a boatload of additional horsepower (and fuel) might allow.

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Old 09-26-2019, 10:07 AM   #20
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I find "cruising speed" has as much to do with the choices the helmsman makes as with the boat and the motor in question.

I had a Grand Banks 42 with twin 120 hp Lehman-Fords which I tended to run at 1600 RPM achieving 8.5 knots. WOT achieved 11 knots.

Over time, though, I realised how fuel consumption-per-mile jumps with each additional knot so I have slowed down.

I now have a Grand Banks 50 with twin 250 hp General Motors V-8s. I can comfortably cruise at 9 knots but, to save fuel I mostly cruise at 7 knots, sometimes as low as 6.5 knots.

Call me cheap :-)
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