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Old 08-27-2014, 06:55 PM   #1
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GB 36 Classic with Twin Lehman 90s

Have been looking for our next boat and really like the Grand Banks classic. Have come across a 1985 that looks to be in excellent condition.

According to the listing, it has factory twin Lehman 90s with about 2600 hrs each. I've heard that perhaps the smaller 90s make this a much less desirable boat, or at least might make it more difficult down the line to sell.

What are the thoughts among the forum of the pros and cons of twin 90s versus the twin 120s???

Thanks.

John
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Old 08-27-2014, 07:07 PM   #2
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Twins fitted to the (not dissimilar to GB 32) Island Gypsy 32 were typically Lehman 80s. Maybe 90s came later, like the 120 going to 135. Beware, some 4cyl Lehmans were raw water cooled, not FWC, that won`t help resale.
Most Blue Seas 36s had a single Lehman 120 and manage well. I suspect there will be some prejudice against twin 90s in a GB36, but it may lack a sound basis. Let`s hope an owner pops up to comment, or Marin, or you could take it to the GB Owners Forum. 180 total hp sounds adequate to me.
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Old 08-27-2014, 07:14 PM   #3
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Thanks - These are FWC 90s. Let's see if an owner pipes up.
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Old 08-27-2014, 07:15 PM   #4
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Greetings,
Mr. JKW. Welcome aboard. In spite of the fact I've never seen a Lehman 90 I would expect they are smaller physically (two less cylinders) than the 120 so, it follows you may have more space in the ER.
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Old 08-27-2014, 07:15 PM   #5
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First, ask your question on the GB owners forum Grand Banks Owner's Resources You should get a fair amount of opinions from the GB owners there.

Second, having owned a GB36 with two FL120s in it for the last 16+ years, I personally would not want this boat with any less than a pair of 120s. For this boat, we would actually prefer a pair of 200+hp Cummins, John Deere's or Luggers. But the two 120s are tolerable.... kind of.

It's not that a pair of 90s won't move the boat along okay, but they'll be working harder to do it. Also, being 4-cylinder engines, they won't be as smooth as a pair of sixes but since there are two of them the vibration may not be much different.

There are people who say that even with just one FL120 a GB36 is overpowered. However these folks are all in the "displacement speed is all you need" camp, which I don't agree with at all. The GB hull is a semi-planing hull, which means it can be driven fairly efficiently at speeds higher than displacement speed, which with a GB36 is a tad under 7 knots. So even with our two FL120s running at a pretty conservative rpm setting, we exceed hull speed, which is nice. To do the same thing with a pair of 90s you'll have to run them harder, which this paricular group of engines don't especially like over the long run.

Depending on the engines one has, it's nice to be able to run the boat at eight or nine, or even ten knots if the power is there and the fuel bill is acceptable to the owner.

So I would regard the GB36 you're talking about as being too underpowered and would not buy it, were we in the market again for such a boat.

But this sort of thing is a personal decision based on whatever one believes a boat should be. Not only would we never buy what we considered to be an underpowered boat, we would never buy a single engine boat, either, which at least the boat you're considering isn't.

A pair of 4-cylinder engines in the engine room will give you more working space, which is nice. The 90 is the sawed-off version of the FL135, where the 80 is the sawed-off version of the FL120. So the 90 is a little more advanced of an engine than the FL80. I'm not sure, but you may not have the injection pump that needs it's lube oil changed every 50 hours like the FL120/FL80.
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Old 08-27-2014, 07:16 PM   #6
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I think they are perfect...unless you want a lot of speed...and even the 90's should give it to you just as well as the 120s...just nearer to a high cruise rpm than a lower setting probably for the 120s.
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Old 08-27-2014, 07:27 PM   #7
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Thanks for the thoughtful replies.

I've registered on the GB site and will post there as well.

I must admit that we've been wrestling with the single vs twin decision. Our Chris has twins and I really like the spin-on-a-dime maneuverability and handling, plus the entire redundancy issue. I think we'd feel more comfortable with the twins.

I'll listen to all opinions regarding whether or not the boat would be underpowered with twin 90s. I'll see what the folks on the GB forum have to say.

Thanks for the help!
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Old 08-27-2014, 08:38 PM   #8
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I would not write off a 36GB with twin 90s quite so fast.

While it MIGHT be less desirable, It's still a very viable boat. And I don't believe most people would consider it under powered. Especially if you figure many 36s only have a single 120 or 135hp Lehman in them.

Unless of course you want to run around burning a bunch of extra fuel to push it to 9 or 10 knots than yes, this is not the boat for you. But if that is the case than get something with real HP in it and really plane it off when need be. But if you just want to run it at or slightly above hull speed where the vast majority of owners run them, then you'll be fine.

Sure they might be working a bit harder than the 120s or 135s. So I guess that means you only get 10,000 hours out of them instead of 15,000.
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Old 08-27-2014, 08:48 PM   #9
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We run our two FL120s at 1650 rpm. This gives us a wee bit over 8 knots and we burn 5 gph total.
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Old 08-27-2014, 10:17 PM   #10
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I have twin 90's on my boat and love them. Even though it's not GB I would think the performance would be comparable. I burn 2gph total at 1600rpm averaging 7.5 knots. Vibration and noise are not a concern. These engines are highly regarded by Bob Smith, because I have conversed with him through email many times. Mine are 1985 with approximately 2600 hours and perform beautifully. They were one of the main reasons I bought this boat.
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