repower 50 my

[thegreatnomad]

Can anyone give me the best repower option for a 50my?

[jim rosenthal]

Either overhaul what's in there (which is probably 8-71Ns) or get a set of Cummins C 480 hp on their 'reman' program. One of our club members did this on his 53MY, a very similar boat, but it took a while and there were, shall we say, challenges along the way. He is very pleased with the results, though- boat cruises in the high teens and will do over 22 kts, I think.

[thegreatnomad]

Thanks so much for the info. We tore down the port engine today and it was trashed.
I just decided it would be better to repower. I actually thought about powering down
To some smaller yanmars and adopting a trawler mindset as I have no boating background and speed wouldn't be something I miss.

[OBXTucker]

Keep it as close to stock as possible for future resale. You're going to limit your market of buyers when it comes time to sell, if you put small engines in.

Also, there's no reason you can't do 7-10 knots on bigger engines. Just need to blow them out every so often.

[Fanfare]

I repowered my 50MY about 15 years ago with Detroit 6V-92TA, 550 hp each, at Jack Hargrave's recommendation. They have been great, still giving about 21-22 kts. top and a 16-18 kt. cruise, all fully loaded. But the completed cost for new props, shafts, engines, transmissions and many other accessories came pretty close to $ 100,000. It is only worth it if you plan on keeping your boat for many years because you will never get your money back at resale.

Your 8-71Ns are great engines, and infinitely rebuildable. You can run hull speed forever on these. However, to get your boat to plane again you will have to strip out a lot of weight, and it may not be possible. But look carefully at your "trashed" engine. Maybe it's not so bad.

You will certainly never get your money back on smaller new engines, and I would not think this is worth it.

[jim rosenthal]

The boat up here in Maryland is called "Freebird" and the owner installed Cummins 480CEs. I have seen the installation and it is very well done. These engines are similar in power and torque to turbo 8-71s; however, the fact that they weigh considerably less has made the boat quite a bit faster. It also uses significantly less fuel with the 4 stroke diesels than it did with Detroits, even at higher cruise speeds. And of course the engine access is much better, the boat is quieter, the engine rooms are not as hot....the list goes on and on. Clearly these engines are powerful enough for this hull. Cummins M11s would be overkill, IMHO.

Against all this you have to balance several important things: 1) you had better love the boat because the only way you will get value out of any repower of a boat this old will be to use it for decades. The market has declined quite a bit for these boats and the days when you could repower one and spruce it up are long gone. And they aren't coming back. 2) the cost of a pair of "reman" (which are in fact new engines of Tier I specs) C series Cummins diesels will be about fifty thousand dollars. You will also need gears (about ten grand for a pair) and to install all of this hardware. And there will be the "while you're in there"s, which will inevitably boost the costs another twenty or thirty percent.

When you're done ( and all of this will take longer than it's supposed to) you will have a much quicker, quieter, more economical boat. If you do what you should do with such a boat- which is use it a lot and enjoy it and keep it- your investment will turn out to be a prudent one.

The one thing I would NOT do is put in smaller engines and make it into a trawler. These hulls were not designed to do that, and you will have a boat that is absolutely sale-proof. You will own it forever whether you want to or not. You can always run a boat with larger engines at slower speeds and speed up every few hours to avoid loading up the engines. A boat with very small engines that will only run at displacement speeds (which for a fifty foot boat would be in the 7-8 knot range) will be undesirable to any prospective new owner, and possibly to yourself sooner or later. Plus, you will still have to spend all the money for all the labor and refit expense of removing the 8 71s and putting in something else. The cost differential between a proper repower (450hp or so) and a displacement-speed repower (150-200hp or so) will not be that great, because the small engines you are thinking about will not be available for a whole lot less money than the C series Cummins engines on the reman program.

If you wish, PM me and I will try to put you in touch with the fellow up here who repowered his 53MY. They did an excellent job and he is happy with the results.

[thegreatnomad]

Thanks for all the info. Planning on keeping the boat for a long time. We are doing a ton of the work ourselves so depending on the shape of the other engine we will decide on. A rebuild/repower situation. The blower was frozen and I suspect the manifold is cracked. Heads are very clean. Water box/heat exchanger was clogged. We actually dicussed the 6v92 option. I assume the transmissions would be compatible. Having a great time considering the options.

[SeaEric]

Call Deckemans Long Cove Boat Yard. I know they have a pair of low time SMOH 871's in stock. I bet you could make a nice deal and save a lot of $$. 410-778-6777. Always easiest to go back with the same power of you can.

[Fanfare]

My repowering saga began by my trying to get just a few more horsepower out of my 8-71Ns so I could keep my boat on plane. As I was contemplating a rebuild anyway, I was hoping I could just add turbochargers and thereby keep up with the newer boats. I learned my older blocks couldn't take the additional heat from the added horsepower. Something about "fire above or below" the something or other. Further, the Allison Model M transmissions were marginal with 350 hp. I think later versions have the Model MH. Having learned all this I gave up trying to improve on my 8-71Ns.

My 6-92TAs have been even more bulletproof than the 8-71s. Of the three times I had to come home on one of my old engines one was a sheared fuel pump shaft (very rare) and two were transmission problems. I have had not a single problem with the new ones. Still, if I were repowering today, I would start from scratch in reviewing the newer generation of diesels.

As I wander the docks I seem to be seeing A LOT of mechanic's trucks working on the newer boats. Many of the problems seem to be disabling. Lots have an engine removed for service. In speaking to owners I hear reports of annual maintenance costs for some of these fancy new engines literally in the tens of thousands of dollars per year to maintain factory warranty. So there is much to be said for older, totally reliable engines whose development costs were paid for during WWII and tested over sixty years. The newer engines seem to be a bit more fuel efficient and emit fewer emissions, but at the cost of enormous complexity.

[rsmith]

My repowering saga began by my trying to get just a few more horsepower out of my 8-71Ns so I could keep my boat on plane. As I was contemplating a rebuild anyway, I was hoping I could just add turbochargers and thereby keep up with the newer boats. I learned my older blocks couldn't take the additional heat from the added horsepower. Something about "fire above or below" the something or other. Further, the Allison Model M transmissions were marginal with 350 hp. I think later versions have the Model MH. Having learned all this I gave up trying to improve on my 8-71Ns.

My 6-92TAs have been even more bulletproof than the 8-71s. Of the three times I had to come home on one of my old engines one was a sheared fuel pump shaft (very rare) and two were transmission problems. I have had not a single problem with the new ones. Still, if I were repowering today, I would start from scratch in reviewing the newer generation of diesels.

As I wander the docks I seem to be seeing A LOT of mechanic's trucks working on the newer boats. Many of the problems seem to be disabling. Lots have an engine removed for service. In speaking to owners I hear reports of annual maintenance costs for some of these fancy new engines literally in the tens of thousands of dollars per year to maintain factory warranty. So there is much to be said for older, totally reliable engines whose development costs were paid for during WWII and tested over sixty years. The newer engines seem to be a bit more fuel efficient and emit fewer emissions, but at the cost of enormous complexity.


I remember in the 90's when the DDEC's came out I ran across a # of 65's stranded in the Bahamas with engine problems. Most of the mechanics I talked to said it was the electronics and salt that caused fits. I still see newer boats with dead engines waiting on a new computer or a mechanic to fly in with test equiptment.( I dont even want to think about what the duty is on a computer) I dont think there is any question that the new engines are lighter and more efficient. But for reliability in bad weather and remote places I would stick with mechanical engines.
I know all the believers will say the reliability is much better now but I've had enough problems with computers in cars and trucks. I Don't think I want to have an engine shut down in the middle of a inlet or waiting on a bridge opening in a bad current because of a computer problem.

[thegreatnomad]

I think I have my answer. We spent the whole way home discussing the pros and cons and decided it best to rebuild both engines. The 8v71s that are in the boat are proven strong motors and I would be better off learning everything I can about them. This project is about the whole experience and I know I will get more satisfaction out of understanding whats going on inside DDs than wondering how the computer does it. It will also give me time while the DDs are out to totally clean and degrease the engine rooms and paint. There will be some rewiring required as well and I will replace the generator. We have two 8v71 blocks in the shop and It might not be a bad Idea to build one while we are at it just to have a spare. Going to replace the old heads and add holding tanks. The good news is the air horn works perfectly.

E

[REBrueckner]

There is I believe a good cross section of advice above for you to consider.

While I like most of Jim's post #6, I think that the idea that "smaller engines will kill resale" is likely becoming an outmoded idea. In other words, a majority of people buying a classic MY will not be looking for speed but rather economy and ease of maintenance.

If someone looks at an older Hatteras MY clearly their interest is NOT speed...or if it is, they'll stop looking pretty quickly. And the difference in COST between an older trawler and an older MY is ridicuously large for anyone on any kind of a budget....a cost difference that if people looked would rarely be recoverable. And what's the difference in fuel efficiency between a trawler and MY at or near hull speed....not very significant. [Range could be more of a consideration for a few.] Sure, maybe in theory a trawler can handle 120 MPH winds and a MY only 90 MPH in open seas, who cares...unless the individual is among the 5% who do long range open water cruising...

One correction:
"Further, the Allison Model M transmissions were marginal with 350 hp.."

Not so, they are used with 8V71TI's at 435 HP with good results...


Unless you are going to run very high annual cruising hours, say FLA/Bahamas to Mass roundtrips for a number of years, and so use huge amounts of fuel, the most economical option is clearly to either rebuild the existing 8V71 or replace it with one that is already rebuilt. Modern four cycle electronic control engines WILL save you about 15% or 20% in fuel, but using up an additional $50K or $75K in first costs will take forever.

For example, say you would use 3,000 gallons of fuel annually with
8V71's...and you could cut that by even 25% with small modern engines...thats 750 gallons saved with modern engines at, say, $4 a gallon diesel fuel cost or a $3,000 annual saving.....assume a $60K difference in first engine costs....that's over 20 years payback....

use your own numbers to get some insights on this one aspect of repowering....At $6 gal, for example, it's still $60,000/ 750 x $6 or well over 13 years....

[thegreatnomad]

I found some manifolds that aren't too expensive and all the other parts we already have. We have never attempted a rebuild on a marine transmission so If anyone knows a good place to send the transmissions let me know. The boat is in Savannah GA. I really appreciate everyones input.

Edwin

"Instant Karla"
1968 50MY

[REBrueckner]

Just saw your post above...using 8V71's makes a lot of economic sense....

And one other thing: I have personally seen a nice big, beautiful 50 or 55 SEARAY nearby in my former marina....One engine died and the mechanic working there was the guy who did my engines....so as usual I sat and watched: He had already started up the port engine and he told me raw water from a loose hose clamp had sprayed water all over the place.

The stbd engine was "dead".....He opened the "waterproof" electronic control box cover and water poured out.....that box was located down low on the engine, between the port and stbd engines....two LOUSY features....

Add to that stories posted in this forum of electronic speed and throttle control issues.... and the possibility of battery/electrical system failure, and you can begin to see all is not well with "modern" engine arrangements ....After all diesels had been touted for 50 years as free of electrical requirements once started...no more!!!!!!!!!!!!!!!!!!!!!

[thegreatnomad]

I Have a question about transmissions. Would it be better/possible to upgrade to a twin disc set up?

[SportFishCruising]

Welcome to the forum nomad, please keep posting often during your progress.... this is a very interesting topic/thread!

[Boatsb]

I have some issues with the newer TD designs. Special tools for basic tasks and such. Look at ZF's

[saltshaker]

Acadian Marine is the best source for parts for Allison gears. They can rebuild or sell you a rebuilt gear with a core exchange.
http://www.acadianmarinetransmission.com/site.php
If you want to change gears you might as well go for the new power package. The new gears will cost big bucks and the bell housing on the 8V71's will have to be changed as they are set up for the Allison gears. If you went that route you would need to modify the engine beds and most likely will need to move the engines forward or aft depending on the gear selection. If your going through all that, it would seem a waste to stick with those old Detroits that need to be rebuilt anyway. Figure out what the total cost to repair what you have will be and weigh that against a repower with something like Cummins C series remans. If the cost to repower isn't that much more, I would go with the new engines. Either way you will be spending more money than you will ever see back in terms of resale. That doesn't mean its not worth doing for your own enjoyment. Make the boat the way you want it and use it well for many years.

[saltshaker]

I have some issues with the newer TD designs. Special tools for basic tasks and such. Look at ZF's
What issues? I put brand new Twin Disc 5111 gears in back in 2002 and they have performed flawlessly.

[Boatsb]

What issues? I put brand new Twin Disc 5111 gears in back in 2002 and they have performed flawlessly.


I believe the special tool needed to pull a coupling to change the rear seal was one of the big ones. 2 Transmission shops both told me they will not invest in the tolls because the price was ridiculous.

They run great but servicing them could be an issue later on.

[saltshaker]

I believe the special tool needed to pull a coupling to change the rear seal was one of the big ones. 2 Transmission shops both told me they will not invest in the tolls because the price was ridiculous.

They run great but servicing them could be an issue later on.

Thanks Scott. I haven't heard that but will keep that in mind.

[jim rosenthal]

I think if you are going to major the 8-71s and put them back in, you might as well put the Allison gears back in. It's hard for me to see what your advantage would be to put in newer gears and NOT put in newer engines; I'd send the Allisons out and have them gone through, and they should last another several decades. We have Forum members with Allison gears that are probably forty years old.

Under the heading of "while you're in theres" you might think about having the shafts trued, the cutlass bearings replaced, and the wheels tuned up with PropScan or something like it.

[ron6785]

Thanks for all the info. Planning on keeping the boat for a long time. We are doing a ton of the work ourselves so depending on the shape of the other engine we will decide on. A rebuild/repower situation. The blower was frozen and I suspect the manifold is cracked. Heads are very clean. Water box/heat exchanger was clogged. We actually dicussed the 6v92 option. I assume the transmissions would be compatible. Having a great time considering the options.So far what you're describing is not a trashed engine. Now if the crank, pistons etc are gone that's a different story, however the 8v71 naturals are good engines for that boat. The problem is these MY's are not on trawler hulls so if you put small engines in them and plan to cross any type of significant open waters with them you are at serious risk if you get caught in a storm. The 71 naturals may not get you on plane but they are fast enough to keep you ahead of wave speed so can navigate adequately in rough following or quartering seas. All my friends who have trawlers are quick to point out how economical they are, but it's their only advantage in every kind of condition we have been exposed to, (which includes some rough weather crossing the gulf ) they are at a disadvantage and while the trawler full displacement hull is ultimately stable they still roll like hell and surf like crazy in following seas.

That being said, if I could have afforded a 58LRC when I was looking I would have jumped on it.

[Capt K]

[QUOTE=jim rosenthal;167277] We have Forum members with Allison gears that are probably forty years old.


1965 50' motoryacht, hull #8, with 871n's and Allisons. All still original, so far.

I know someone who repowered a 50' and is thrilled. I 've been daydreaming about just this question all summer while cruising. This thread has really driven home the point that a repower makes no real sense unless the bank account can handle it, and/or you cruise at least 200 hours per year.

All good info, as usual!

Capt K

[Walter P]

Lots of good points regarding the pros and cons of rebuilding or repowering. Can't argue most coments from a practical level, however........ There is nothing practical about grown men and women playing with their expensive toys on the water so let's forget about whether it's a good investment or not, it's not, at least from a practical point of view.

Now consider the real reason we are into boating (or any other hobby). Pure pleasure for us and our familys and friends. Statiscally familys that are involved with activities together are generally happier folks. Humans are social animals after all. It (boating) provides us with a level of pleasure that is hard to match any other way. I could go on but you all get the point. If you have the sheckels ($) and you get a certain rush thinking about what if I did this or that (new engines, paint, what ever jingles your chain) then just do it. In all my 70 some years I have unfortunately or fortunately been to too many funerals and have never seen anyone laid out on a bed of money. Remember the famous words of Malcolm Forbes "he who dies with the most toys wins".

Walt

[thegreatnomad]

I have a plan in place that includes checking the shafts, props, bearings bottom paint. Transmissions will be rebuilt along with both 871s. Found a low time generator 21.5 kw to replace the old onan. Lots of work ahead.

e