Looking at a 50' Aft Cabin MY. Weight is approximately 47,000 lbs. Is it just me or does this boat seem a little under powered. Would be happier with 8-71s? I am a 1200 rpm cruiser. 8- 9 knots. Would really appreciate any feedback on this situation. Thank you!
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Thread: 6-71 turbo in a 50' Aft Cabin MY
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01-24-2023 02:33 PM #1Senior Member
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6-71 turbo in a 50' Aft Cabin MY
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01-24-2023 02:47 PM #2
Re: 6-71 turbo in a 50' Aft Cabin MY
I dunno, but we have a 43DC with natural 6-71s and we run hull speed at 1400 rpms I think typically. 34k lbs.
Also, it really depends on the boat, 100k lb+ 58LRCs have 4-71 standard.
In my opinion, uninformed by this site's standard, is that if you can stick with an inline engine, you are better off.
If you can't, you can't, but, there are a lot more parts on a V engine, exhaust, etc, less room to work, and they are a bit harder to tune.Last edited by brettportzer; 01-24-2023 at 02:52 PM.
Brett Portzer 1972 Hatteras 43DC331
2019- SUPERNOVA Waterford, NY
1977-2019 CAROL-SUE Baltimore, MD
1972-1977 C.VALPRISANN IV Boston, MA
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Re: 6-71 turbo in a 50' Aft Cabin MY
Seems like a great deal of work and expense to install engines which are old and in some ways obsolete. If I were going to go to that trouble and expense, I'd repower the boat with modern 4 stroke diesels, which would cost a fortune. Maybe just decide if you can happily live with the boat desite its limitations.
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Re: 6-71 turbo in a 50' Aft Cabin MY
Straight 6-71 came in many HP tunes that could rival a 8V71.
I always felt, as forgiving as the series 71 are, the straight blocks offered a lil more.
Monster crank shaft with a cap between every lung.
like Cat, Man and Detroit, the engine families in straight 6 make more reliable HP per lung than the V blocks,, per lung.
Give us some more details on the boat, engine marinizer (Covington, J&T, Detroit, other) and HP tune.
If old tech engines don't bother you, Don't let that lil 6 distract you.
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01-24-2023 07:51 PM #5Senior Member
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Re: 6-71 turbo in a 50' Aft Cabin MY
The motors are DD 6v71'sFreshwater boat its whole lifecwith 1372 hours on engines. Beautiful boat. I guess what I am asking are the DD 6v71's enough power for a 50' boat weighing 47k lbs?
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Re: 6-71 turbo in a 50' Aft Cabin MY
Depending on how fast you want to go, maybe yes, maybe no. I think you have to look at the boat as a whole picture, get an idea of her cruise speed, and see if you're comfortable with her as she is. Keep in mind that at the time Hatteras designed the boat, the naval architects who did the design had their choice of engines. I don't know what the performance figures are for that boat, but the listing broker should be able to tell you. Bottom line is that, assuming a satisfactory set of surveys etc, you should make your decision based on the boat as she is built, not on the possibility of a repower. I think those engines are large enough for that boat, assuming you're not trying to set speed records. And fresh water and low hours are both good.
Ralph is right about V versus inline engines- inline sixes and twelves are inherently smoother than any other engine configuration. V6 engines are inherently rougher than any others. Whether that equates to reduced engine life, I don't know. It's plausible. Some modern engines use balance shafts etc to smooth out engines vibrations, but that technology has never been used in DDs, and probably never in diesels.
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01-25-2023 10:42 AM #7Registered Member
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Re: 6-71 turbo in a 50' Aft Cabin MY
If, as stated in your first post, you're an 8-9 knot cruiser, than a couple 6-71TI's are going to be way more than enough. Figure, at those speeds, that boat's only going to need a combined 70-110 HP from those engines. Rather than enough power, I'd be more concerned with enough load to get them up to temp and keep them there.
Backing up a bit, you first say they're 6-71TI's, then you say they're 6V71's in a "50' aft cabin." The 6-71 is an I6 and the 6V71 is a V6. Neither of those were installed in the 50MY from the 1960's; they all had 8V71N's. If you're talking about the newer 50 Sport Deck from the 1990's, then they're 6V92TA's.
Tell us what year the boat is, and nail down the engine model for sure. Or better yet, just post a link to the ad that way we can give you accurate answers the first time instead of having to ask you 20 questions. No matter what, my statement of power requirements for a boat that size remains. And if it's the 50 footer from the 90's, it's a planing hull which isn't going to be ideal for putting around at trawler speeds. Also, if it matters to you, those 90's boats have a 5'6" draft and what could be best described as a vestigial keel, so no prop protection and less directional stability at or below hull speed.Last edited by No control; 01-25-2023 at 11:01 AM.
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Re: 6-71 turbo in a 50' Aft Cabin MY
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Re: 6-71 turbo in a 50' Aft Cabin MY
The Series 92 engines were introduced in 1974
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01-25-2023 08:01 PM #10Senior Member
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Re: 6-71 turbo in a 50' Aft Cabin MY
I knew a guy who had a single 671 natural powering a 65' ice-rated steel hulled tugboat. 210hp was enough to get that 65-ton boat going up to hull speed, though the captain tended to crash-land on the docks. F = ma is real!!! lol
So...is a 671 enough for a 50' boat? The answer is "it depends on how you intend to use it."Last edited by q240z; 01-25-2023 at 08:15 PM.