Re-power 1984 Uniflite 48 Convertible

[Kevin McIntosh]

Hey all … I’d like to study the feasibility of using Cummins Recons to replace DD 8V-92TI’s (2-stroke diesels – Turbocharged, Intercooled, 570 Crankshaft HP / 550 Shaft HP @ 2,300 RPM, 12.07 litres, each, 3,815 pounds, each, with Allison ‘MH’ Marine Gears, highly likely 1.97:1 ratio [all from DD datasheet 4SA104 2-78]) in an example of the Subject vessel that is currently available in the San Diego area.

“Port engine is recently overhauled. Starboard engine is inoperative and partially disassembled.” … is all I have to go on for the moment, aside from interior / exterior photos. The broker representing the vessel is, so far, unresponsive, forcing me to commit to a preliminary viewing trip to further assess.

I should say I’ve had a long love affair with Uniflites due to their robust construction and weight … I wanted a 42 DCS for its’ onboard spaciousness (I have focused on my local market [PNW] but have yet to find anything suitable after some 20 months of looking / dealing) but am now also considering the 48 Conv which offers the spaciousness + fishing! (the 42 Conv or 48 YF are, IMO, unsuitable variants of the 42 hull mold) … I think the Subject vessel would make an awesome fishing boat with the correct engine refit.

I have read up some here on the QSC 8.3 600HO’s.
This THT thread (https://www.thehulltruth.com/boating-forum/259862-cummins-qsc-8-3l-600hp-any-opinions.html) gives me pause as to the QSC engines being robust enough for this 48,000 lb boat.

The QSL 9’s offer an additional 0.6L displacement but no power ratings comparable to the DD 8V-92TI’s.

The QSM 11’s, while more equivalent displacement-wise and offerring an HO power rating of as much as 715MHP, seem to be somewhat more complex in their application due to their ‘dry’ exhaust manifold / turbo nature. After reading Tony’s Tips article ‘Propping the Cummins Marine QSM 11 to Prevent Exhaust Issues’, if I understand correctly, excessive heat must be avoided by underpropping … to the extent that the fuel burn is maintained 0.5-1.0gph below 20gph at cruise RPMs (1,900-2,000). The 715’s WOT rating is 2,500 RPM … is it unrealistic to think this boat could be comfortably cruised at 26 knots while still observing the fuel burn / propping constaints of the QSM ‘dry’ series?

Application:
strictly recreational fishing / cruising … likely only 200-400 hours annually, as I am in the great white north and most activity is typically in late spring, summer and early fall.

Duty cycle:
50% fastest fuel-efficient displacement mode / 50% ‘on-step’ cruising (22-26 knots) … ideally, the engine choice / propping would allow for more than adequate available torque to get this vessel on-step quickly … without the engines laboring too long to get there.

I am hoping to draw on sbmar’s and this community’s collective experience for some further input on what re-power parameters to focus and read up on.

Thanks, Kevin Mc

Topic

[Tony Athens]

Small typo–“NVH”

Noise, Vibration & Harshness

Buying the engines with the proper gears is the easy part of the overall equation,, Around $100-110K for what you will need… It’s all the rest that will make or break the project..

Keep your research moving forward..

Good luck

Tony

[Kevin McIntosh]

Tony … thank you for your detailed Reply to this topic …

I was not aware of Greg Slayton / Delta Performance Marine’s (THT username ‘Greg Dpm’) track record … I just now did a little searching and reading and it seems he’s not someoneI would deal with (thank you for that) … that being said, his 2 contributions (out of 32 posts, overall) to the THT thread I referenced (which actually got kicked back to life at post #13 in May, 2017) do not neccessarily negate the observations of the balance of the thread participants, most of whom cite personal, practical, real-world experience. I got the overall impression from that thread that perhaps the weight of the Subject vessel to be re-powered could be an issue in the case of the QSC’s … obviously I need to be sure one way or the other.

OK, so you don’t consider the vessel weight combined with my ‘needs’ (my previously defined usage) to be an issue for the QSC 8.3 600HO’s – so be it, like I said, I am just being careful and will try to perform further due diligence on the matter.

And, sorry Tony, what do you mean by “major NVA improvements”? Fewer exhaust emissions? Undoubtably … and to CARB standards no less.

As for the re-power expense (and my budget), that is what I’m attempting to nail down in this topic … obviously there comes a point at which major expenditures on a 34 year old hull stops making economic sense … I asked for a Cummins Recon engines recommendation and a preliminary, broad strokes expense estimate … now that I have that information, I can make some decisions moving forward.

The Subject vessel would have to be purchased dramatically below market … that’s the only way I could justify moving forward with this re-power project.

Tony / sbmar experts, I did not arrive at your doorstep by accident … rather, I chose to approach sbmar first … after extensive online reading … at places like BD & THT … I’ll get back to my topic here as this develops further.

Kevin Mc

[Tony Athens]

Kevin,

IMO, the best way to approach your post is to get down to the most basic things that would go along with a repower of this stature…………….. To me, it would go like this:

#1————Your Hull Truth link is 100+% bogus for 2 real reasons.. 6 + years old, but the big one is the response from Greg Slayton—If you do not know what I am referring to, then go to GOOGLE and look up that name or “Delta Performance”.. I need to say no more on that subject as some independent research will say it all.

#2————— A repower done right using the QSC 8.3 600 will do you long term right as to performance, major NVH improvements, very real & measurable fuel economy improvements, major improvements in serviceability & access and the costs to service the engine, plus you will actually like to use the boat and not have to make any excuses when you lift the floor boards to show some your engine room to your friends.. With that said, the most important part of #2 is “done right”.. This is a very modern engine and requires “new completely new approach as to a proper install & set up—What that means in this——–“Detroit Mentality” does not apply to anything as to how this engines needs to be installed or “set up”..

#3—QSL 410 vs the QSC 600………”Apples for Apples”, the QSC at any HP rating ( 500, 550 or 600) will give you a faster vessel AT WOT with one caveat—How important is WOT to the end product of the repower??———-If you were a “cruiser” only and wanted to run around at a nice planning speed in the 18 -22K range to go from Point A to Point B and were doing this for 1000+ hours at year and a 50+++% duty cycle, then the QSL would shine over the QSC as overall robustness and ease of service. But you would lose the option for higher short term lower duty cycle cruise speeds that may require a fuel burn of over 20 GPH per engine to satisfy you need for speed. .

#4——Putting the above in perspective & basing it on your “needs”, then there really only is one choice.. The QSC 600.. But again, it will all come down the to install and overall set-up on the engine..

#5 —————–And of course here is the really BIG one.. Do you have a the maybe $175K ( bare bones and you do much of the job in-house) -$250+K budget that it will take to make this happen? Here is where YOU have to become very realistic!

Tony

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