because each of the six cylinders had its own injection system they were hard to kill, you might loose the injection on one cylinder or more but it didn't stop the others from running unlike most engines that use a single injection pump and injectors.. if the pump goes bad the engine is dead. im not sure if they were developped that way for the navy for WW2 but it was an ingeneous design, years ago I bought a WW2 landing craft that had one in it.. and my " big " sailboat did as well untill I repowered. a supercharger is simply a mechanically driven compressor compared to a turbo that uses exhaust gases as a power source, a turbo is more efficient as supercharger workes better at low rpm. and of course a 6-71 would not run without the blower as it is needed to force the air into the cylinder as it does not have intake valves but ports in the cylinder that become exposed when the piston reaches the bottom of its stroke.
Eric ----- Original Message ----- From: jack courrier<mailto:[email protected]> To: [email protected]<mailto:[email protected]> Sent: Saturday, June 12, 2010 5:17 PM Subject: Re: [UnifliteWorld] Re: Uniflite 42' vs Trawler It's pretty tough to argue with the extreme reliability of a DD 671N (supercharger much different from a turbocharger.) I ran a pair in a 42 convertible for several thousand hours and repowered 5 years ago to 4 stroke turbo diesels. They do burn more fuel and definitely make more noise but give 'em fuel and air and they will get you home. Incidentally my new engines and gears weigh almost the same as my 671's did and the dimensions are very similar. Definitely do not miss the noise but those old girls will be running when my grandkids are boating. The repower was a "fun" project though. ----- Original Message ----- From: e b<mailto:[email protected]> To: [email protected]<mailto:[email protected]> Sent: Saturday, June 12, 2010 9:30 AM Subject: Re: [UnifliteWorld] Re: Uniflite 42' vs Trawler personally I would stay away from 6-71's, or any two stroke diesel. it seems kind of odd to call a 6-71 naturallly aspirated ( NA ) as there is no such thing as they all have a roots blower... they are good reliable engines but noisy and fuel effiiciency was not a concern back in the late 1930's when the 6-71 was first built. a two stroke is a two stroke, not efficient, even with upgrades and changes over time a two stroke will always burn substancially more than a four stroke diesel and thank god we don't have to deal with emmissions, it would be impossible to make them meet any standards... I would think there should be boats on the market that have been upgraded with a newer style diesel that are half the weight, twice the power and 1/3 rd more efficient. in their days the 6-71's did make more power than a comparable sized four stroke, two strokes always do, but that has all changed in the past 20 years... for those who own them there is no reason to justify the cost to change them out but if I was in the market for a boat I sure as hell would stay away from them. some designs despite beeing good simply get outdated and replaced by better and newer technology. when I was a kid 40 or more years ago I spend hours in the engine room of my parents boat as the 6-71's pushed us along... I'll keep the fond memories. I do have a 6-71 cranshaft in front of my house holding up my mailbox... eric ----- Original Message ----- From: Rocco<mailto:[email protected]> To: UnifliteWorld<mailto:[email protected]> Sent: Saturday, June 12, 2010 7:11 AM Subject: [UnifliteWorld] Re: Uniflite 42' vs Trawler Somewhere on the site we should have a FAQ section and model description section. This piece should definitely be included as it's exceptionally well written. On Jun 11, 12:43 am, waterguy <[email protected]<mailto:[email protected]>> wrote: > If you're looking at trawlers in the 42-foot range, you're probably > looking at twin engine boats anyway, unless it's a real cheap-and- > nasty Taiwan or mainland China boat that was built to a price. And > you already know about the problems with those boats (fiberglass-over- > plywood deckhouses that turn to pulp due to window frame leaks, ditto > teak plank-over fiberglass-over plywood decks, electrical gremlins, > etc.) > > That 42 Uniflite you're looking at is far superior in construction > quality to almost any trawler built in the last 20 years. > > The differences in design are going to be that the trawler will have > slightly safer outdoor walkaround decks (because they're wider and > have raised gunwales). However, the drawback to the wide side decks > is cramped interior quarters. The Uniflite will have a much roomier > cabin. This tradeoff may work for you as a liveaboard. > > If the engines are original, they may be GM/Detroit Diesel 6-71NA or > 6-71TI's (great engines, IMHO, a little noisy and a little less fuel- > efficient than 4-stroke diesels, but more powerful for a given > displacement, and repair parts and mechanics who know them are > everywhere), possibly the Cummins 903's, or just barely possibly the > Caterpillar 3208's. Some 42's were fitted with Chrysler 440's or Chev > 454's. Avoid those unless you know that (1) the engines are new; and > (2) you're never going to run it above hull speed. Gas-powered 42's > have seriously overstressed engines. > > The other difference in design will be that the Uniflite, as a planing > hull, has sharp chines and no keel, so when you're stopped or going > slowly in a cross sea, there's a tendency to snap rolling, which can > be uncomfortable. The trawler won't roll as sharply in a cross sea. > > To me the biggest factor is the safety margin given by the planing > hull and big engines. As noted by other posters, your fuel economy > won't be too much worse than the trawler when you're running at > trawler speeds, but if the weather turns nasty, you can do what a > trawler can't -- shove the throttles forward and run for a safe > anchorage. Only thing is, if the boat has Detroit Diesels, know that > they won't tolerate being run at constant low speeds. > > May I suggest one other boat to look at? That would be the 1967 to > (about 1975) Chris-Craft 47-foot Commander. Built like a battleship; > it was Chris-Craft's first fiberglass boat; and I think that Chris- > Craft's designers decided, "Well, we use 3/4-inch mahogany in our > motoryachts, let's lay on 3/4ths of an inch of fiberglass mat!" The > hulls are literally bulletproof (I know of one that stopped a .38 > Police Positive round). The older style flush deck design may be > offputting because it causes the windows in the cabin to be above head > level when you're sitting down. Look for a 1968 or older, as they > have beautiful interior woodwork in the classic Chris-Craft style > (became more wood-grain Formica in later years). > > Most were originally underpowered, having GM/Detroit Diesel 8V-53's > (about 250 HP) or 427 Ford sideoiler gas engines (about 325 hp, > equivalent to the 250 hp diesels), so you almost have to plan on a > repower. A boating magazine a few years ago had a feature on a 47 > Commander that had been repowered with 350-horse Perkins diesels. She > ran 26 knots at 20 gph. The 47 Commander had a very efficient hull > for high-speed cruising. > > There are a couple of layouts; standard was a large aft stateroom with > private head; there was an option for two aft staterooms with a shared > head opening off a companionway; this is the one you'll most likely > see. > > Presently, these boats are selling in the mid-to-high five-figure > range. A hell of a lot of boat for the price. -- You received this message because you are subscribed to the Google Groups "UnifliteWorld" group. To post to this group, send email to [email protected]<mailto:[email protected]>. To unsubscribe from this group, send email to [email protected]<mailto:[email protected]>. For more options, visit this group at http://groups.google.com/group/unifliteworld?hl=en<http://groups.google.com/group/unifliteworld?hl=en>. -- You received this message because you are subscribed to the Google Groups "UnifliteWorld" group. To post to this group, send email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/unifliteworld?hl=en. -- You received this message because you are subscribed to the Google Groups "UnifliteWorld" group. To post to this group, send email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/unifliteworld?hl=en. -- You received this message because you are subscribed to the Google Groups "UnifliteWorld" group. To post to this group, send email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/unifliteworld?hl=en.
