53MY Repower

[SereneWarrior]

Port engine in Serenity, my 1970 53MY requires a rebuild after 51 years of faithful service. I’m considering my options, including a full repower of the boat. I intend to keep the boat for another 20 years, so amortizing costs makes the project seem more palatable. On one hand, rebuilding one engine is MUCH more affordable, but then I still have a couple of half century old 8V71Ns to deal with. My local marine engineer is proposing a repower with CAT 7.1s and the advantages seem obvious (although much pricier). However, I then have a myriad of other considerations to deal with the 32VDC electrical plant and converting (or augmenting) with 24VDC. I know there are folks on the forum who have been through this and that there are a couple ways to skin this “CAT”.

I could just replace one battery bank & inverter/charger to support the new engines and continue to use the other bank for the 32VDC for household…but that gets real complex, real fast. Most desirable would be to convert the whole boat to 24VDC, but costs for a new genny, potable water pump, inverter/charger(s), heads, etc. will be considerable. As an old Navy guy, it would be akin to a complete overhaul of the boat costing well into six figures and taking months to accomplish.

Looking for comments from those who’ve been through this and any other considerations I may be missing. Thanks in advance!

 

[Bernd1972]

Fresh water pump, toilets, windlass, all that, yes. But where´s the need for a new generator?
Besides that, it also comes with the opportunity to get rid of some outdated equipment.

Besides that, I guess installing a Victron Quattro instead of the old chargers would nice, no?

 

[SEVEN]

Talk to Pascal. He did it.

 

[Cricket]

Been thru 2 repowers with our 50c since 1985.
First repower was with reman 8v92TI's.
Basically a quickie repower keeping most of equipment, but did change the generator which was already 12v.
Second repower with the CATs was full on everything mechanical and electrical, converting the 32 over to 24v, and a new Phasor generator.

My advise is if you're going to go to the expense of installing new CATs go for everything else too. We've had basically 20 years of trouble free boating since

 

[Pascal]

I repowered my 1970 53MY about 3 years ago. Very happy I did

What HP are the cats? I heard that Cat now has a factory reman option like cummins. Not sure if it’s true

I considered rebuilding the DDs, mines were naturals too, but the math didn’t add up. A good rebuild incl the gears would have run $30k each with no or little warranty and still running WW2 era engines. Instead I could get factory reman cummins C-series (435hp) for about 20% more.

I didn’t have to upsize the shafts but replaced them with single piece AQ22HS because of their age. My existing nibral props were just an inch of pitch off despite the higher HP because of the higher RPM of the Cummins Engine beds had to be made which obviously added to the costs

Labor costs were kept low (well kind of...) because I have a very good old fashioned mechanic who specialize is alignment, shafts etc. very good fabricator as well.

Now the boat runs 17kts cruise and 20kts flat out despite having new oversized stabilizer fins

As to vintage, Cummins was charging an extra $1500 per engine for 24v so I went with 12V. I have a dedicated 8D for each engine installed outboard behind the stabs. I like battery redundancy. I converted the boat to 24v with new panel and complete rewiring but that has nothing to do with the engines. Only downside at the moment is that I need the gen to keep the house batteries charged which for now is no big deal. In the future for redundancy when we go longer distances I will add a 24v alternator to one of the cummins.

Again I don’t know the HP of the cats you are looking at but 435hp is the minimum you want in this boat. I did replace the trim tabs with larger model, mounted on the transom instead of recessed. This really helps the boat pop on plane and run flatter. New trim tabs are 12x54

Hope this helps. Any question please ask

 

[SereneWarrior]

Generator isn’t a “must have right now” item, but the Onan mdl3 has been in there since 1996 and won’t last forever…

 

[SereneWarrior]

Pascal, the Cat C7.1s are rated at 450hp and get good reviews re reliability. Local marine engineer thinks the project will take “a couple of months”, but my experience is that any time estimate for boat projects should be at least doubled. What was your experience? How long did your repower take? This is a relatively small firm with only 5-6 folks. They’ve done great work for me in the past, but tend to be overtasked.

 

[SereneWarrior]

Pascal, the Cat C7.1s are rated at 450hp and get good reviews re reliability. Local marine engineer thinks the project will take “a couple of months”, but my experience is that any time estimate for boat projects should be at least doubled. What was your experience? How long did your repower take? This is a relatively small firm with only 5-6 folks. They’ve done great work for me in the past, but tend to be overtasked.

 

[Pascal]

It took about 5 months in the yard but we did other things too like new TRAC stabs, barrier coating, reinforcing the hull outside the ER stringers for the larger stabs, new exhaust etc

Speaking of exhaust, if you have to upsize from the natural’s 6” to 8” as for the C series it’s a big job getting access. In my case I had most of the interior gutted anyway since I combined the mid ship and master.

 

[Pascal]

Here is a video of the DD removal.

https://youtu.be/nvjsv4KzCb8

There are a couple more on my YouTube page

 

[Boatsb]

The 7.1 cat is too small. Not enough mass to get a good life out of them.

Keep in mind the old engine was over 9 liters and heavy duty. That's why they lasted.

QSM 11 would be far better. Or talk to Sky Cheney. He's doing it right now with cats. He's putting in 8.7 liter engines.

 

[bigbill]

when my boat was repowered the PO left the 32 volt stuff in place and put an 8d in each engine room, 1 for each engine. they also had a 12v battery to run 2 heads and a 12v battery for the generator. i have since swapped everything over to 12 volt

 

[SKYCHENEY]

View attachment 54383

 

[spartonboat1]

Pascal, the Cat C7.1s are rated at 450hp and get good reviews re reliability. Local marine engineer thinks the project will take “a couple of months”, but my experience is that any time estimate for boat projects should be at least doubled. What was your experience? How long did your repower take? This is a relatively small firm with only 5-6 folks. They’ve done great work for me in the past, but tend to be overtasked.

Just for grins I ran the re-power duration numbers through the old project management estimator, "PERT". Its old but works, plus has statistical analysis capabilities. I will skip all the wild PM PERT stuff, which requires full coursework.

What I used, in months, per the conversations here:
Optimistic 2 Mos
Likely 9 mos
Pessimistic 24 mos

PERT tool sez [ Optimistic + (4 x Likely) + Pessimistic ]/6 = [ 2 + (4 x 9) + 24 ]/6 = 62/6= 10.3 mos Probably duration.

It would be fun to know how close the tool is to actual experience.

Long time PM guy... Note: Per the remarks as well, you need one or more "stars" on your projects, i.e. people who really know their stuff!

 

[jim rosenthal]

There is a 53' my in our cruising club which was repowered w C series Cummins. Performance numbers about like Pascal's and has run nicely for years. I'd look at those. I don't know which Cats are the 7.1s, but if they are related to 3126s I'd avoid them/

 

[piripucha]

My friday "Dream proyect" is to repower my 58 YF . I am considering the Scania 6 cil 500 hp engines. My plan is to leave all the 32 V systems intact and add a 12v system for the engines only. The problem with a proyect of this size is the "Since" word. That is what takes the cost trough the roof.

 

[Scarlett]

Sky, I must have missed something, this is the first I have heard about your repower could you start a thread and keep us posted as to your progress, I think most of us would be interested. John

 

[johnjen50]

Agreed. Sky that looks like it’s going to be awesome. All I’m thinking is that’s 200 more horsepower than I have now and how great the boat would perform with the extra ponies. New engine beds I’m sure but what about shafts? You had the 6-92’s before right? What were those, 500 up?

 

[SereneWarrior]

Thanks, everybody! Some great inputs here and lots to think about. Keep it coming as you think of any other considerations. As always, this forum rocks!

 

[SKYCHENEY]

Agreed. Sky that looks like it’s going to be awesome. All I’m thinking is that’s 200 more horsepower than I have now and how great the boat would perform with the extra ponies. New engine beds I’m sure but what about shafts? You had the 6-92’s before right? What were those, 500 up?

The 692's were 465, the Cat 8.7's are 650. New engine beds, new struts, new shafts. Its a big project. I was waiting to post until I finished and had some performance numbers, but I might start a thread since the CAT is out of the bag, so to speak.