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Old 10-19-2012, 11:14 AM   #1
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Twin Lehman SP90's for 36' GB??

Any comments re my fear that this boat would be under powered?? It is a 1989 Classic and the smallest engines I have seen before were either 120 0r 135.
And your thoughts would be?
Many thanks.
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Old 10-19-2012, 11:38 AM   #2
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That vessel/engine combination should be a great match, if the vessel is propped right. In the past few days I have reviewed power selection for a 90,000 lb new build (at least 3X the GB you are looking at) vessel using JD 130 Hp engines designed to operate at about 50% load.
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Old 10-19-2012, 11:42 AM   #3
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Greetings,
Mr. 68. IMHO, a SINGLE 90 HP would be fine in a 36' GB. I have had previous experience with a 34' MT with a 120 Lehman and THAT vessel was overpowered. The Gurus here will remind you of how many HP are required per ton. I've forgotten. Granted, I'm no expert but it wouldn't bother me at all to have twin 90's in a 36' GB or any other 36'.
Being that the 90HP Lehmans are less common than the 120's I would be concerned about parts availability first off.
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Old 10-19-2012, 11:46 AM   #4
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VERY good point re parts availability....should add that to my list of concerns!!!
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Old 10-19-2012, 11:50 AM   #5
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Newb,
So many GBs and similar boats represented a lot here run on slow bell w much underloaded engines and have no objective need for more power than a single Lehman would do well to have engines totaling about 100hp. On yacht World I saw a beautiful 36' GB twin that had been repowered w two 55hp Yanmars. Plenty of power for the way most guys cruise these days. And the notion that more power is needed to run from storms is basically bunk.

So I would say that boat w twin 90s is considerably better and at least a bit lighter and that is better still. perhaps you better buy it quick before someone else realizes it's value. I'd rather have smaller and lighter engines than that but that cost's money.

Here is a picture of another 36 GB w twin 90s for sale cheap in Craig Alaska. But I think this one has Perkins engines.
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Old 10-19-2012, 12:05 PM   #6
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RT,
I agree w your post but the rule of thumb re HP per ton only applies to full disp boats. The rule varies from 3 to 5hp per ton. Two hp per ton is about the lower limit and only applicable to rather large craft. Of course one could run w less and I'm sure some do. One hp per ton would put me at 8hp. I'm quite sure I could go faster than kayaks and run to and from Alaska without serious inconvenience or safety issues. I know some would/will disagree w that but I'm quite sure I'm right. I'm assuming I could get 4.5 to 5 knots w 6hp.

And sunchaser's example would put the GB in the 40hp category but I suspect that his example was a full disp boat.
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Old 10-19-2012, 12:52 PM   #7
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It all depends on what you want to do with the boat. If you are only interested in running slow than a pair of 90s in a GB36 would be great. But the GB's semi-displacement hull can be run much faster than displacement speed. It takes power to do this, of course, and more fuel, but a lot of GB buyers, particularly of the newer boats, want to be able to get somewhere fairly quickly, cruise the area leisurely, and then get home quickly. This demand prompted American Marine/Grand Banks Llc to put larger and larger engines in their boats.

We cruise our GB at about 8 knots even though it has two FL120s. We have taken it to WOT one time to get data for the prop shop and IIRC the boat was doing some eleven or twelve knots (indicated). We stick to the 8-knot cruise speed not because we like running slow but because FL120s don't do well run hard.

If we have the boat re-engined as we have been contemplating for awhile now we will go with a pair of new 150 or 210 hp engines. If we do this, we will run the boat at ten knots or more if we can get it. This would be impossible with a pair of 90 hp engines.

But our priority--- given engines that can support it--- is speed. Other people's priority is economy regardless of speed. For this, a couple of 90 hp engines in a GB36 would a good setup.

If you are interested in putting the boat in charter, however, the low power may be a detriment. One of the GB52s in the large GB charter fleet in our marina was ordered with smaller-than-stock engines by its buyer. From what I have been told by the charter company, this boat has proved to be fairly unpopular with charter customers because it is so slow.
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Old 10-20-2012, 06:40 AM   #8
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"I have been told by the charter company, this boat has proved to be fairly unpopular with charter customers because it is so slo"

Charter folks pay for fuel and frequently operate on the pin or close to it.

"because FL120s don't do well run hard."

True , so a boat in the charter fleet might be better off with a more robust engine, not necessarily a more powerful one.
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Old 10-20-2012, 01:33 PM   #9
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Quote:
Originally Posted by FF View Post

"because FL120s don't do well run hard."

True , so a boat in the charter fleet might be better off with a more robust engine, not necessarily a more powerful one.

Most boats in charter I think are too new to have the old Lehmans in them. I don't believe any of the GBs in the big Bellingham charter fleet have Lehmans. All these boats are newer than 1990.
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Old 10-20-2012, 07:57 PM   #10
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Quote:
Originally Posted by RT Firefly View Post
Greetings,
Mr. 68. IMHO, a SINGLE 90 HP would be fine in a 36' GB.
Being that the 90HP Lehmans are less common than the 120's I would be concerned about parts availability first off.
Easy enough to check with Brian Smith of American Diesel "www.Briansmithadc@aol.com". There are a few IG32s in Aust. with 80hp Lehman twins, some had raw water cooling instead of heat exchangers so best check that too. BruceK
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