https://www.yachtworld.co.uk/boats/1981/grand-banks-42-classic-3662666/
Listed speed for twin 120 hp Lehmans on a 38000 lb boat, 10-13 mph.
Listed speed for twin 120 hp Lehmans on a 38000 lb boat, 10-13 mph.
Is this speed realistic
- Thread starter Swfla
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Sure, does it seem too slow?
Comodave
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It seems a bit fast to me. But also it says MPH not Knots. So 10 mph is a bit over 8.5 knots which is about right with 120s.
I too thought it a bit fast. My limited knowledge of trawlers based on reading posts on this forum and looking at listings seems to me 8.5 would be it's top speed. Hoping some GB 42 owners would post here as well. Both of your posts are appreciated. Thanks.
Comodave
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I think that they could go faster than 8.5 knots but you would be pushing the engines more than I would like.
rsn48
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Maximum displacement speed is square root of water line times 1.34. So I assumed water line to be 38 feet and square rooted that and multiplied by the factor to get 8.3 knots.
tiltrider1
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No people, no gear, no water, very low fuel and throttle wide open on a dead calm day. Then just maybe you will see 13 MPH. Reality, it’s an 8 knot boat.
OldDan1943
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Westiculo
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Agreed.
We have a GB 42 with twin Lehman 135s. We cruise between 8.3 and 8.5 knots (10 MPH) at 1800 RPM regardless of weight. It's very comfortable there. We push it every once in a while to 2400 to stretch the legs, at which point we go 10.5 knots (12MPH). 2600 is max loaded RPM for our engines.
rgano
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My twin Lehman 120s in my own 1972 Grand Banks 42 at 1750 RPM would get it to 8.6 Knots (9.89 MPH). What I thought of as a more comfortable RPM of 1600 would do about 8.3 knots (.54 MPH). 10-13 MPH is inflated sales speak..
Nomad Willy
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If it’s fuel burn you’re worried about (you seem to be like many others) just keep shopping until you find a single engined GB36. Why do you need such a big boat?
Once you buy a big twin you’ll be reading fuel burn posts on and on. The problem is that the new buyers had a lot of money and fuel burn wasn’t an issue for them. But for normal people fuel economy is. You probably can’t even count all the threads on fuel burn. But now you’re in a position now to do something about it.
Some say fuel burn is only a small part of boating expenses. Depends on how you boat. Where you moor your boat, where you spend the night like anchored out eating grub from home or at a marina eating out upper end and head’in for other places after ect ect. But if you’re a low-buck boater fuel is a big issue. Why else would all these TF members stress and worry about fuel? And they do.
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Mike Negley
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GB hulls are not displacement boats. They can be pushed faster with more horsepower
A GB is considered a semi planning hull. With more horsepower you can get them to semi-plane along with a lot more fuel consumption. The old 1.3 times the waterline length was never a scientific formula. Sort of like the definition of a good investment is one that turns out that way.
A GB is considered a semi planning hull. With more horsepower you can get them to semi-plane along with a lot more fuel consumption. The old 1.3 times the waterline length was never a scientific formula. Sort of like the definition of a good investment is one that turns out that way.
rgano
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Not here anyway. I did not care about it with the 3.35 GPH at 9.5 MPH on the GB, thinking that it was fairly low, and I don't care about it at about 9 GPH at 16 MPH now because the last thing I want to do is spoil my fun on the water worrying of fuel burn rate.
You misread me. I'm not worried about fuel burn rate. I just wanted to know what the realistic cruise speed is. Sales postings, exaggerate too often. I gave a size range because I'd like to buy in my geographical area and need to be flexible to match availability. My boating skills are honed on twin engines. A single would be fine with a bow thruster. But again, it's availability or going into the yard for a bow thruster. I'm old enough to know my abilities on a single screw. Thanks for your post.
I think a good setup for me would be 36' with bow cabin and second cabin (aft likely). Twin engines like FL 80 or 120 hp or single cummins with bow thruster. Cruising at 8 knots is perfect. A genset is preferred but would consider an inverter setup with ample ah batteries for two days on the hook. Not likely to be more than 48 hours port to port. Don't need huge tanks. Still have a few life situations to get squared away but see myself ready in 12 months. Should give me time to read, look in person, join the power squadron once Covid is behind us. Then actively shop. In the meantime thanks for all the great members who share opinions and or knowledge.
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I consider myself a "normal person" and I burn 28GPH and fuel burn does not concern me. This "normal person" also still has an income. If I were retired(fixed income), then fuel burn starts to become more of a concern. Mama likes going faster. So we will do that for now. But as much as I want a full displacement boat in retirement, we will likely get a big planing boat and go slowly on it with the occasional run up at speed just to keep her happy. Something like a Fleming!!!!.....I wish!!! I also dream of the N57 as it can cruise at 10 knots easily and STILL have a 1500nm range. Obviously, throttle back to 7 knots and you more than double that range.
I guess my point is, Eric, we aren't all like you and you are not the standard of "normal". And I mean that respectfully and kindly....
rslifkin
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For those of us still working, sometimes it's a game of limit how far we travel due to fuel cost or limit it due to time away from work (which is always an issue). When the money is there for fuel, 8 hours at 17 kts gets us a lot further than 8 hours at 7 kts. Makes a big difference in where we can go for a trip shorter than a week or so.
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I cannot like this post enough and exactly the way I feel. It also may increase the usage of your boat. Instead of blowing off a trip because you don't have the time, you go because you can go faster and get there quickly enough to make the trip worth it. Yes I realize the journey is the big draw. But we don't want the entire trip to be the journey. We do want to bask in the glory of our destination for awhile.
rslifkin
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The journey vs destination thing varies by location too. Sometimes it's nice to slow down and smell the roses. Other times, there's a segment where there's really nothing to see, so might as well just speed up and get to the interesting part sooner.
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Not to mention reduce your exposure in potentially dangerous situations.
Nomad Willy
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My god, Eric! That's what the man wants!
HaHa Walt,
Most of us want want more than we can support.
I can’t afford what I’ve got and need to sell it.
But most of us have big eyes and go at it w/o realizing what it really costs to operate a boat. Like we don’t think about insurance all year until we get the bill. All the expenses like insurance, moorage, up-keep and fuel add up to more than many can handle.
Time for me to get out. Can’t afford it any more. And then there’s the old body. But I’ve got plenty of smaller toys that are more manageable. Motor home (small), cars, and other small boats .. canoes and rowboat types.
Like “hit the road Jack” ......
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Nomad Willy
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Good post rslifkin but it’s not how far we go but how much meaningful experience we had. A good row on a lake in the morning and dinner in the camp nearby. Most here think you’re gonna have more fun in a bigger boat w all the bells & whistles.
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markpierce
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Giggitoni
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The sales person may be talking “speed through water” as opposed to “speed over ground”. Around here, as well as many other places, it’s common to have a tide-induced current with a velocity of four to six kts. I have twin Cat 3208na. I often see 12-14 kts (1550 rpm) including the “push”.
