conundrum ... repower engine choice for Uniflite 48 Convertible

Discussion in 'Diesel Engines' started by K_McIntosh, Mar 18, 2018.

  1. K_McIntosh
    Joined: Mar 2018
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    Location: Tsawwassen, B.C., Canada

    K_McIntosh Junior Member

    Again, all very helpul pointers pacblue ... thank you.

    You obviously have a thorough understanding of a range of guiding principles here that come to you easily ... me, not so much ... i.e. "20gph per side gives you a total of 40 gph (ok), and at 0.5 nmpg (based on what exactly?), you may only be looking at a 20 knot cruise (ok, if 0.5 nmpg [is presumed?]), or less if you go below that number." ... so ... how are you arriving at 0.5 nmpg? (in order to yield a 20 knot cruise ... the nmpg # just seems arbitrary to me) And, you say: "less (speed) if (you go) below ... " ... which number ... the nmpg #? Or, the target fuel burn ceiling #? Sorry, but I am a little lost on that one ... how can we know the achievable cruise speed(s, i.e. knots range) at 1800(-2000) RPM w/o actual, physical propping trials? I must be missing something fundamental here.

    And, given the foregoing and your concerns about me falling well short of my cruise expectations ... the way I am looking at this right now is that it seems to me that it will be difficult to know where the RPM hump is (transition to on-step / planing mode) ... would this simply be the peak torque RPMs? Or? i.e. the older Bertram example you pointed me to looks to be very comparable ... on the face of it, it looks to be 3K lbs. lighter and uses the 600HP (602BHP / 610MHP 2300RPM HO?) rated engines instead of the 661BHP / 670MHP 2300RPM HO rated engines I am considering. If that boat will cruise at 26 knots, do you think they are getting that performance at 2100RPM (FYI - per Cummins, for 'HO' ratings [<2800RPM]: WOT RPM less 200RPM for sustained cruise) and simply living with a sustained higher fuel burn rate ... and the accompanying generated heat? Perhaps I should see if I can track down the owner / repower outfit to see what strategies they have employed to manage e.m. / turbo / e.r. heat. Or, maybe there's a (negative) reason why it's only seen 300 hours of use since 2009. Hard to believe a '79 SF is worth $499K USD! Even with those newer engines ... but, to be fair, she looks to be in pretty nice shape ... and, I guess the Bertrams hold their value well.

    Not to belabour the heat thing, but here's an example of QSM 'dry' heat issues ... and ... here's my attempt to zero in on the correct engine choice at the same site / forum ... considering their otherwise good repower rep., the engine recommendation made just did not sit well with me, intuitively speaking, and, I've been trying to get further educated for this proposed project ever since.

    With respect to the fore and aft COG, I would think that lighter engines / gears should, if anything, move the COG aft, however, that situation too bears further scrutiny ... your suggestion to approach Art's son strikes me as a very worthwhile endeavor ... the inverter banks as useable ballast suggestion, e.r. ventilation enhancements recommendations, prop shaft loading cautions and controls upgrade suggestion are all appreciated and well taken as well ... thank you, K Mc
     
    Last edited: Apr 18, 2018
  2. pacblue
    Joined: Apr 2018
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    pacblue Junior Member

    My comparison was an assumption that sportfishers of that era can get about 0.50 mpg at cruise. This is an optimistic number, especially when talking knots, with a lot of variables - just a discussion point, all presumption at this point but still valid enough to steer you away from a Fuel Consumption only perspective.. Here is a table from a 52 Hatteras SF repowered with 900hp Yanmar's as an example:
    upload_2018-4-18_13-3-47.png
    Granted it is in mpg, but you get the idea. Basically 24.9 mph/49.8 gph = 0.50 mpg. Or 0.50 mpg x 49.8 gph = 24.9 mph. For knots, 24.9 mph /1.1516 = 21.6 knots, which is 0.43 nmpg, which is not surprising for a typical heavy and less efficient Hatteras 52 SF.

    Hump speed is going to be hull design and loading specific, there are rule of thumbs to calculate it for the design phase but your boat exists now, the best thing to do is sea trial it or find a magazine review with performance numbers. But the transition is lower than 20 knots and I would not really worry about when you are on "step". You want to cruise at 22 knots plus, which kind of eliminates the QSM 11 Fuel Burn limitations as presented in your reference if you chose to use that approach. You will see the 22 knots, but not the "plus" with that approach. I am sure that Bertram 46 repower does not use that approach in practice and they are probably hitting that 26 knot cruise at 2100 rpm, above the 20 gph per engine limits that the reference article prefers. The QSM 11 burns 24.7 gph at 2100rpm (call it 25 gph) per their propeller curve graph. I have always used max cruise as WOT - 200 rpm per the Cummins suggestion, this would be your high cruise, once again, above the 20 gph per engine discussion. For the Bertram, 26 knots / 50 gph = 0.52 nmpg, not too bad! I think your 48 is capable of the same efficiency, if the Bertram numbers are true to life and not "sales speak". And yes, the value of that 46 Bert is a bit off the charts, more like replacement cost, actual value is probably under $200K.

    Tony seems to prefer the QSC 8.3 option, which is a viable choice as well if you are willing to flex a bit on your high cruise. Then you can put the Dry Exhaust Manifold question to rest, you will gain savings in weight and probably more access in the engine room. All things to consider as trade-offs for your repower conundrum. How much does 26 knots cruise mean to you at this point?

    I personally think a reliable 22 knot cruise is ideal in the Pacific Ocean, it matches the prevalent wave periods nicely and you can go from the cockpit to the flybridge while underway without any special gymnastics, and don't need to 'hang on" while you and your gests are on the bridge and underway. In other words, it is a very natural and comfortable speed for an under 50' SF.
     
  3. K_McIntosh
    Joined: Mar 2018
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    K_McIntosh Junior Member

    Thanks pacblue ... your ongoing support of my research and education in this matter is highly appreciated ...

    Your experience with the fuel efficiency of SF's is a solid basis for the nmpg # that I previously suspected as arbitrary ... fair enough ... as for the QSM 11 Fuel Burn limitations route (which, I agree, would be a limitation that would be very beneficial to ignore, if heat concerns were mitigatable), perhaps with everything discussed here so far to alleviate heat build-up, there is the possibility of a 'dry' to 'wet' conversion option for the QSM 11. Unfortunately, there is not a verbose description / explanation at the link provided of what all is being done / referred to (only photos, many of which are not directly relevant ... in addition to the charge-air cooler [SeaWater?AfterCooler, aka SWAC in Cummins literature], in the photos I can see what appears to be a sea?water cooled turbo, however, it is unclear to me if the exhaust manifold is also water cooled, or by what means). I am hesitant to approach Tony again about the latter as he was adamant about the QSC 8.3 600MHP HO rated ReCon engines recommendation for my proposed repower project (which, I take it, you don't find as troublesome [if I was willing to come down on my high cruise expectations] as I do ... it simply does not seem logical to me to be able to replace torquey, low-revving, 2-stroke 12L engines with 4-stroke 8.3L engines in a SF platform [that started out at 45K + 3K lbs. gear allowance and would only get heavier over time] w/o over-stressing the smaller, higher-revving [3000RPM] engines) ... I had thought to obtain more information about potential 'dry' to 'wet' conversion options for the QSM 11 ReCons from Cummins directly ... which, to date, is seemingly just not possible.

    The reason I would like a higher cruise speed (say 26 knots) is because I operate pilot launches and am very accustomed to travelling relatively short distances at a minimum of 26 knots ... we have a couple of ABD / JD twin screw launches that run at that speed and a couple of Kvichak / JD twin Hamilton jets that run at 36 knots [​IMG] ... mind you, these speeds are only achievable in protected or calmer waters ... the Kvichaks in particular slap hard in anything beyond 2' seas and can be most uncomfortable (only the operator gets a shock-mitigating seat). That being said, I find travel at speeds less than 26 knots to be painfully slow (we have those types of launches as well, 20-22 knot capable only, depending on the tide). At least this is my current perception of my desired cruising speeds in my own SF ... your observations about offshore wave periods and overall ride comfort are interesting and well taken. Also, as you noted earlier, my currently forseeable usage (50% highest efficiency displacement mode speed / 50% on-step at highest sustainable cruise speed) may change with actual usage experience ... that remains to be seen ... however, I can appreciate how running a 48K lbs. SF at only 22 knots may prove acceptable ... once fuel burn rate efficiencies have been determined for various on-step cruise speeds ... after all, diesel fuel only seems to be getting more and more expensive. If this entire endeavor was not on my bucket list, I would be more than a little concerned about the potential fragility of global fuel supply and demand ... this type of vessel could be relegated to a floating condominium overnight if there were a major international upset and runaway fuel price spike ... for any of a variety of reasons.
    K Mc
     
  4. pacblue
    Joined: Apr 2018
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    pacblue Junior Member

    The Wet conversion seems to be a bit of a plumbing nightmare, I personally would not sign up for that and if it was that important to me I would start to look at another brand.

    I am sure the factory knows about any dry engine exhaust issues and if deemed necessary they would have their own wet conversion kit engineered/tested/available. The recon's have a 2 year / 2000 hour warranty, you may be able to negotiate and extended warranty as well. Maybe the factory knows they will get the 2 years out of the dry set-up without many early hour issues. Then it is up to you. You have a clear requirement for a 26 knot cruise, which would surpass the 20 gph fuel burn, and that appears to be your conundrum.

    I would try to see if you could talk to an existing owner who has 2000+ hours on QSM 11 670hp recons and see what they have to say.
     
  5. K_McIntosh
    Joined: Mar 2018
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    K_McIntosh Junior Member

    pacblue ... thanks for the 'dry' to 'wet' conversion plumbing assessment ... I'm not even sure exactly what's going on there ... without asking a lot of direct questions of Tony ...

    As I've mentioned, I still don't seem to be able to get a lot of specific info from Cummins ... and I went right up the chain to Jim Schacht, Executive Director, Marine and Oil & Gas Markets.

    I've just now made a last ditch effort to get a response from him / them ... we'll see what happens.

    Finding an existing owner of 2000+ hour QSM 11 670MHP ReCons would be great ... so far, I've not identified anyone like that in my various forum postings ... perhaps I'll try a fresh topical thread here ... and elsewhere ... i.e. sbmar, BD, THT ...

    Thanks again pacblue for all of your help, K Mc
     
  6. pacblue
    Joined: Apr 2018
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    pacblue Junior Member

    If the Dry Exhaust Manifold design and service life are too big an issue to overcome in your analysis, I would not hesitate to go to the Volvo Penta D11 - 670hp. It stacks up well on the Torque comparison, and at 10.8 liters is the same displacement as the QSM 11 , but it has the wet exhaust manifold design.

    upload_2018-4-20_9-29-13.png

    At a dry weight of 2,524 lbs. it would be a nice fit for your application.
     

    Attached Files:

  7. K_McIntosh
    Joined: Mar 2018
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    K_McIntosh Junior Member

    I was not specifically aware of that V P engine model (in truth, I haven't looked at any other new engine options ... due an assumption on my part that they would simply be too pricey ... I have now requested a price quote locally, here in Canada) ... I note the datasheet you uploaded pacblue specifies an optional wet exhaust elbow ... no mention of e.m. or turbo ... V P online does refer to a water-cooled e.m. but does not elaborate with further technical descriptions of the entire cooling system ... i.e., all components, what portions of same are permanent, captive coolant vs. seawater and whether the turbo itself is water-cooled ... still, absolutely worth looking at ... too bad they don't accept technical inquiries online to facilitate sales ... that task seems to be offloaded to their dealer network.

    I see you took the trouble to add the V P torque vs. % throttle curve to your graph ... interesting how it rises steeply, earlier than the others ... although I imagine the old DD rises sharply up to 1200RPM ... anyways, thanks for doing that ... say, any chance of me looking at your file used to create the graph? The PM system here (Conversations) is kinda' different and, apparently, doesn't allow attachments ... however, my outside e-mail addy is my [username][at]telus[dot]net if you don't mind sharing it. Thanks, K Mc
     
  8. pacblue
    Joined: Apr 2018
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    pacblue Junior Member

    Well, now you have 2 nearly identical physical solutions with a dry and wet exhaust manifold configuration. I think the dry and wet turbo is really a non-issue for operating, turbo blankets/shields are fine in terms of operation. I think the Cummins and VP both have dry turbo's, but you can verify with them. The VP Turbo seems to be under a heat shield and the picture does not give a full view, but it certainly has a wet cooled exhaust manifold from the spec sheet.

    As far as cost goes, one can not provide what the other can, so if you get a VP quote, that tells you what a Wet Exhaust Manifold costs for your application. That will be the price point to get what you are looking for and leave the uncertainty behind the dry QSM 11.

    Attached is my crude spreadsheet, just thrown together off of internet data, use it for whatever you wish.
     

    Attached Files:

  9. K_McIntosh
    Joined: Mar 2018
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    K_McIntosh Junior Member

    Thanks pacblue for the spreadsheet ... so ... the V P people have yet to get back to me ... the marine engine sales business must be good ... no sense of urgency that I can detect ... I guess I'll eventually hear from them ... when I do, I'll get more info about the V P D11 cooling system and post back. K Mc
     
  10. pacblue
    Joined: Apr 2018
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    pacblue Junior Member

    The recreational and commercial marine business is going full tilt at the moment for many suppliers. I am not surprised you have not heard back from VP, internet/over the phone inquiries are usually bottom rung. This industry is more relational, with face-to-face action getting best results. On their side, they have limited sales/engineer resources and there was just a big trade show in Victoria, Mari-Tech, where they are probably chasing the strong leads they gathered in person.

    An over the phone or internet inquiry price will get you list price at best, best to make an appointment and meet with them in person.
     
  11. K_McIntosh
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    K_McIntosh Junior Member

    Still haven't heard from V P or their dealer ... it amazes me that I have to track down someone at a dealer's just to get detailed info on their product ... in this regard, both Cummins and V P are similar.

    Will get back to my thread here when I clarify the V P D11 cooling system design.
     
  12. K_McIntosh
    Joined: Mar 2018
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    Location: Tsawwassen, B.C., Canada

    K_McIntosh Junior Member

    So, I was able to coax some info out of V P of the Americas in Virginia ... here's the Cooling System info I was provided for the D11-670 R5 engine:
    upload_2018-5-7_9-10-2.jpeg
    upload_2018-5-7_9-10-59.jpeg
    upload_2018-5-7_9-11-28.jpeg
    ... so, the turbocharger bearing housing is cooled by captive coolant (i.e. antifreeze solution), as well as by the partial cooling effect of the engine lubricating oil (V P has yet to quantify the extent of the cooling effect) pumped to the turbocharger bearing housing ... all in all, a pretty good design.

    Pricing-wise, for two engines / rev. gears, I am told by my local dealer I can expect 5-10 points off of this single station package pricing offered here in Canada:
    upload_2018-5-7_9-23-18.jpeg
    ... $ not as steep as I expected.

    V P warranty: " ... warranty commitment to 2+3 years or operation hours (having trouble nailing this hour figure down for the D11-670 R5 engine), whichever occurs first. For the first 2 years, the warranty covers the complete engine package and for the following 3 years, major components. Accessories bought simultaneously with engines will also benefit from an extended warranty period." Seems superior to the Cummins ReCon warranty, provided the hours covered are at least 2,000.

    K Mc
     
  13. pacblue
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    pacblue Junior Member

    Lots of good info.
    I would weight warranty time more than hours, you typically would not be putting 1,000 hours per year on a recreational vessel?
     
  14. pacblue
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    pacblue Junior Member

    Hope all has gone well for you did you ever make a decision on this project?
     

  15. K_McIntosh
    Joined: Mar 2018
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    Location: Tsawwassen, B.C., Canada

    K_McIntosh Junior Member

    Hello pacblue ... as it turned out, the '84 48' Uniflite Convertible I was to potentially re-power did not sell to me ... KATY B continued to sit on the market at an unrealistically high asking price until just recently (12DEC18), when it apparently sold for $42K USD ... $18K USD below the then asking price and $12K higher than I was prepared to pay for her in her condition (Stbd DD 8V-92TI engine torn-down and sitting apart for two years, the other a suspect rebuild, per the mechanic to last work on her) ... so ... all of my research (and the extensive help of yourself and others) did not come to fruition, however, the exercise was tremendously helpful to me in terms of learning what all is involved with a re-power project of this magnitude ... maybe it's a good thing I did not go that route with my time, energy & $ ... time will tell ... I've since settled on focusing on a '79 42' Uni DCS w. DD 6-71N's ... that will come to me within days as a local, boathouse-kept, low-hour, running vessel for the same money I was prepared to pay for KATY B ... no re-power required.

    For a guy with bad knees, maybe the climb to the flybridge on a Convertible sport-fisher was a bad idea anyways ... the 42' Uni DCS is not the same type of boat at all (except for the build quality /era specifics ... and ... blisters), however, it will satisfy my requirements as a coastal cruiser, and, I will do most manners of fishing from her ... the 48 would have been interesting tho ... here's a local example that I would seriously consider buying except for the fact that it has previously been sunk ... then re-fit ... the re-fit job appears to be good, however, there's still the DD 8V-92TI's there to contend with.

    Thank you again pacblue for all the help you provided ... I hope all's well at your end, and, Happy New Year to you and yours.

    K Mc
     
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