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Old 11-12-2010, 07:01 AM   #1
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Narrowing the search

We are looking at three trawlers, a 1979 Defever 40 with twin Perkins, 1976 Thompson with twin 453 Detroit's, and 1982 Ocean Alexander 43 with a single 120Lehman. I would like to hear from people with first hand experience with these boats. What kind of fuel economy do you get when you taking it easy? The Defever and OA were designed by reputable architect where the Thompson's selling point is it is built on a shrimp boat hull. (I can find nothing about Thompson 44 shrimp boats on the net).

As far as layout and roominess*we like the Thompson, Build quality would be both the Thompson and Defever as the best.

The Defever is in*good shape, the Thompson in fair shape and the OA in very poor shape. Rot is the best word to describe the OA. Rotten wood on the inside from leaky hatches and windows, I suspect rotten fuel tanks, and the raw water system is rotted from electrolysis.

Keep in mind I will be doing the work myself, and I like to do it.

I would like opinions on these boats.

Thanks.
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Old 11-12-2010, 08:18 AM   #2
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RE: Narrowing the search

The perkins engines will run forever. We have twin 85 hp perkins and burn 1 gal per hour per engine at 8 knots. The manueverability on the twins is what sealed the deal for us. We can back it in almost anywhere.

If the boat is in fair or bad shape you are probably not seeing everything wrong and the chance of new things going bad are much higher on a boat that has not been maintained. Look at the amount of wood on the outside. You will be a slave to it forever.
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Old 11-12-2010, 09:20 AM   #3
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RE: Narrowing the search

If this is your first boat, go with the boat that is in the best shape. Defever, from what I have seen, is a good solid brand and Perkins is a good solid engine. I like OA's, but I'd already want it in tip-top shape.
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Old 11-12-2010, 10:06 AM   #4
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Narrowing the search

If the Perkins are the 6.354 engines be careful if one is "contra-rotating" ( Britspeak) as some parts*are no longer be availble (such as the antifreeze circulation pump).



-- Edited by jleonard on Friday 12th of November 2010 11:07:18 AM
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Old 11-12-2010, 11:07 AM   #5
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RE: Narrowing the search

Quote:
jleonard wrote:

If the Perkins are the 6.354 engines be careful if one is "contra-rotating" ( Britspeak) as some parts*are no longer be availble (such as the antifreeze circulation pump).



-- Edited by jleonard on Friday 12th of November 2010 11:07:18 AM
That's the first I've heard of that.
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Old 11-12-2010, 01:22 PM   #6
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RE: Narrowing the search

Thanks for the response. This is not my first boat and I would prefer a fixer upper. I owned a heavy equipment repair shop that I sold last year. I have been through the 6.354 and the velvet drives before. The sailboat we live on now we bought totaled from Hurricane Ike and we rebuilt it. I am some what new to marine diesels and until I read on this board that Perkins marine add ons were hard to come by I would have recommended a Perkins over just about any other engine. Perkins are all over the world and in every Massey Ferguson tractor that ever rolled into my shop. The parts are by far the cheapest for me to purchase thru my old vendors.

Like I said I have a lot to learn about the marine part of these engines. Both of the Perkins in the Defever were set up the same where on the Thompson*the Detroit's engines were ass backwards from each other. I assumed on the Defever the reverse rotation may have been thru the transmission? I better find out.

None of these boats have wood decks. Anymore!
*
I really want to get a good idea of fuel usage. The more economical the boat the more we can take it out to play. I know if I consider the money and labor I put into a fixer upper I can drive it a long ways. I am like a dog, I like to mark what is mine.
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Old 11-12-2010, 03:20 PM   #7
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RE: Narrowing the search

"I assumed on the Defever the reverse rotation may have been thru the transmission? I better find out."

In that era the rotation change was normally done via backward rotation *engines.*
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Old 11-12-2010, 04:12 PM   #8
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RE: Narrowing the search

Just a guess, the Perkins should burn about 3-4 gph (total) at 7.5 - 8 knots. My 48 DF with twin 225hp Perkins Sabres burn 4.5 gph total at 8 knots in a calm sea state. I'd suggest you do a total rebuild on*the raw water pumps if parts are hard to come by as Jay suggests. A rebuild should easily go 1500 hours with a new impeller every season.*Then just keep looking for a "spare" to rebuild.
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Old 11-12-2010, 05:52 PM   #9
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RE: Narrowing the search

I burn 3gph with a single NA 6.354 pushing a 42' aluminum hull.....
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Old 11-12-2010, 09:12 PM   #10
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RE: Narrowing the search

Fuel burn will be a function of the weight of the boat, the speed you want to go, and most important, the size of the wave you try to pull along with you. The engines will affect this a little, but not a lot. So if your 40 weighs 30,000 lb and you want to go 7.5 knots, your 43 weighs 30,000 lb and you go 7.5 knots and your 44 weighs 30,000 lb and you want to go 7.5 knots, your fuel burn will be the same.
Push your speed up a knot, and you will be pulling a bigger wave with the 40, as you will be exceeding its hull speed, so you will suffer worse fuel economy that on the other 2.
Other considerations, you will have to judge how much work for the savings.
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Old 11-13-2010, 09:12 PM   #11
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RE: Narrowing the search

Quote:
sunchaser wrote:

A rebuild should easily go 1500 hours with a new impeller every season.*Then just keep looking for a "spare" to rebuild.
I purchaced a "spare" 6.354 to rebuild just for fun, but I finally decided I would never use it, as my current engines are about the most reliable engines I have ever owned.* As a result,

For sale:* Perkins 6354 core engine,* $800.00 .............Arctic Traveller

*
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Old 11-14-2010, 07:56 AM   #12
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RE: Narrowing the search

So what everyone is saying here is, Perkins, Detroit or Lehman, twin or single it does not matter. I would suspect that it does. I doubt if twins will burn twice the amount of fuel as a single since the load on the individual engines will be less but there will be a loss.


I appreciate those who are giving me examples of economy the are getting. I do understand that LWL and theoretical hull speed play a role along with weight and hull design. Hearing what people actually get really helps.

As far as weighing the cost of buying a fixer upper against one ready to go, I enjoy doing this kind of work.
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Old 11-14-2010, 09:57 AM   #13
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Narrowing the search

All of those engines are very durable. The DD is probably the smoothest and the noisest and the heavyist but at our speeds weight is not a big issue and noise can be controled. But the DD has twice as many power strokes as a four stroke so a 4 cyl DD will have as many power strokes as a Buick straight 8***** ....and THATS smooth. They should all last forever unless your'e 25 yrs old and that would make you unique among us. If it's a late model Perkins that could be the best engine but if it's an old Perkins the Lehman and the Perkins are not much different. I've been looking at lots and lots of boats on Yachtworld and it's amazing how many old boats w Lehman's STILL have their original engines. Very few have been repowered! I know other boats about the same age and 1/3 of them have some other engine. The same or much the same can be said about the Perkins so if you buy any of the three boats and get a good survey from a good surveyor you should be set for a long time. We all have grand plans about extensive cruising but most of us only do a fraction of our dreams so don't stress about fuel burn.
Chances are 90 to 98% that fuel burn will be fly stuff in the overall scope of things and in the case of the DD (known that it burns more than others) I think is only about 20% more. Check w FF about that. He is our DD expert. And I should say that the answer to your question is that it really dosn't matter much what engine you get and the boat is more of a variable than the engine. The ideal boat will have just been repowered and re tanked. Old black iron tanks are a bit of a time bomb as they scost so much to replace.


-- Edited by nomadwilly on Sunday 14th of November 2010 11:06:45 AM
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Old 11-14-2010, 10:22 AM   #14
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RE: Narrowing the search

Eric is dead on about the fuel burn. It really works out usually to be a small percentage of your owning/ operating costs. We travel a good bit and I suspect our fuel purchases this year are under $1800. Much less than our insurance. Then there's the slip fee, those new outside cushions, electricity, generator water pump, stbd trans oil cooler, ........I could go on
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Old 11-15-2010, 10:40 AM   #15
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RE: Narrowing the search

Single is definitely more fuel efficient than a twin (for old Perkins FL etc).* One reason is that the old transmissions are not as efficient as newer ones.* You lose a certain number of HP just to turn the transmission, so it follows that if you have two of them you lose even more, not to mention extra drag from struts etc.

That being said, my twin Perkins 6.354 have been getting 2+ MPG, somewhere around 2GPH per motor.* Having a single I might save 1GPH, maybe a bit more driving a bit slower.

Having two is more expensive in parts, filters, oil, and time maintaining them.* So far it is worth it to me in extra maneuverability and having had a transmission fail, the ability to get home after a catastrophic problem.
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Old 11-15-2010, 10:58 AM   #16
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RE: Narrowing the search

"Single is definitely more fuel efficient than a twin"


I will say that's not a givin. I for one think the opposite is true but I don't want to get into an argument about it as we've done that at least once. See the archives if interested. But the cost thing is almost irrelevant in that most of the parts are half the size on a twin and the fluids are half as much ect ect. The difference is really small in efficiency AND cost once you get by the initial investment of twins. And of course if your'e going to talk about which is more efficient or how much each costs you must compare boats w the same total power and with engines of similar design.
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Old 11-15-2010, 11:30 AM   #17
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RE: Narrowing the search

Let me rephrase that...

A Monk 36 with twins is less efficient than a Monk 36 with a single.* That would be two Perkins 6.364 (270 total*HP) vs. a single Perkins 6.354 (135 HP total).* I don't know how twin 135s stack up against a single 270 however.* Consider also that anything over about 7.5 knots is wasting fuel anyway.
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Old 11-15-2010, 12:51 PM   #18
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RE: Narrowing the search

Quote:
nomadwilly wrote:But the cost thing is almost irrelevant in that most of the parts are half the size on a twin and the fluids are half as much ect ect.
I'm not sure I follow the reasoning here.* We have a twin GB36 with two FL120s in it.* A lot of GB36s were made with a single engine, but it was still an FL120.* So same parts, same volume of fluids, etc. in the engine in the single as in one of our engines in the twin.* So our twin is twice as expensive to service as a single because we're buying two times as many of everything, from pump belts to lube oil to impellers to filters.

In terms of GBs, this held true until GB stopped making single engine boats in the very early 2000s.* Even though the motors were modern--- John Deere, Cat, Cummins--- a twin-engine boat used two of them and the single engine version of the same boat used one of them.

*
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Old 11-16-2010, 04:13 AM   #19
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RE: Narrowing the search

The worst marine trannys only loose 3% in mechanical losses.

Not sure the usual owner could find 3% or 6% in the annual 100 hours of engine time.
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Old 11-16-2010, 08:22 AM   #20
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RE: Narrowing the search

Hydraulic transmissions like the BWVD need a hydraulic pump to function and I was told it takes 5 hp to run the pump so it seems mechanical gears are more efficient but like the difference between the efficiency of various engines it dosn't amount to much. Since I only have 37 hp to apply to my BW I had a much smaller gear installed in the pump so my losses are less but I've only got 37 hp. If I got an 80 hp engine I'd need to put the standard gear back in.
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