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Besides that, it also comes with the opportunity to get rid of some outdated equipment.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