Engine choice on Grand Banks 42

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Pat T

Senior Member
Joined
Sep 6, 2019
Messages
224
Location
United States
Vessel Name
Moondance
Vessel Make
Grand Banks CL 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
 
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.
 
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!
 
Cruise speed with twin 135hp will be 7-7.5 knots.
 
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.
 
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.
 
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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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 :thumb:
 
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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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.
 
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.
 
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.
 
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? :hide:
 
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.

-Chris
 
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 :)
 
I also do all my own work and prefer inline engines. They also have fewer wear parts such as heads, exhaust, turbos, cooling tubing. Easier to access the outboard side as well
 
inline engines. Easier to access the outboard side as well

That one is somewhat engine specific. Depending on the manifold layout, a fully assembled inline can be just as wide as a V block, at least for a crossflow inline (where the intake and exhaust manifolds are on opposite sides).
 
So far I’m seeing 7.5 to 7.7 knots at 1500 RPM with Lehman 120’s. I can get a bit over 8 knots at 1800 RPM but the engines seem happiest at 1500.
 
I'm late on this one, but my two cents. My 1982 GB Classic 42 has been repowered with a naturally aspirated single John Deere 6086. She hums along at 7.5 knots burning 1.5 gph fuel, at 8 - 8.5 knots I'll burn about 2 gph. I love my powerhouse, I found I had enough torgue to get me out of some crazy currents in tight spots heading up the inside passage last summer. She is not underpowered thats for sure.
 
So far I’m seeing 7.5 to 7.7 knots at 1500 RPM with Lehman 120’s. I can get a bit over 8 knots at 1800 RPM but the engines seem happiest at 1500.

That dosn’t have much meaning unless one is privy to the WOT rpm.
 
I'm late on this one, but my two cents. My 1982 GB Classic 42 has been repowered with a naturally aspirated single John Deere 6086. She hums along at 7.5 knots burning 1.5 gph fuel, at 8 - 8.5 knots I'll burn about 2 gph. I love my powerhouse, I found I had enough torgue to get me out of some crazy currents in tight spots heading up the inside passage last summer. She is not underpowered thats for sure.



4nm/g is awesome for a high windage, 17 T powerboat.
 
I'm late on this one, but my two cents. My 1982 GB Classic 42 has been repowered with a naturally aspirated single John Deere 6086. She hums along at 7.5 knots burning 1.5 gph fuel, at 8 - 8.5 knots I'll burn about 2 gph. I love my powerhouse, I found I had enough torgue to get me out of some crazy currents in tight spots heading up the inside passage last summer. She is not underpowered thats for sure.

Those fuel numbers equate to a horsepower draw of approximately 36 HP at 8.5 knots on the JD 6068. How do you measure fuel used?
 
Although brokers "should" be very knowledgable just like realtors should know real estate and car salesmen should know cares, the truth is that some are strictly salesmen and will tell potential buyer anything he/she thinks they want to hear.

Some supposedly nautical people really don't know the difference between knots and mph. If someone tells them a boat can obtain 8 -9 knots which is "sort of" 10 or 11 mph it may become 12 + knots in the retelling.

Twin F.L. in that boat is about the best engine/boat combination you could dream of. Buy it !!

pete
 
I'm late on this one, but my two cents. My 1982 GB Classic 42 has been repowered with a naturally aspirated single John Deere 6086. She hums along at 7.5 knots burning 1.5 gph fuel, at 8 - 8.5 knots I'll burn about 2 gph. I love my powerhouse, I found I had enough torgue to get me out of some crazy currents in tight spots heading up the inside passage last summer. She is not underpowered thats for sure.


You have one of the best motors made for a boat, we saw very similar #s over the 9 years we had the same motor in Volunteer. I tracked the fuel consumption with a 100G day tank that was very accurately marked. We ran 8kts in no current and burnt 2.2-2.3 gph including about 4 hrs a day of 4kw gen time on non travel days. Either that motor or the famed Gardiner would be my go to engine in a trawler.


HOLLYWOOD
 
I've a Floscan flow meter. I've not checked the accuracy of this meter but I had a similar one on a fishing boat that burned gasoline, it was accurate in that application. I know flow meters can be affected by viscosity, and other variables and to be sure should be calibrated. I have a diesel generator and heater so doing a simple gallons burned divided hours on the engine will give me a close approximation at best.
 
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