Repower Opinions

[harnett]

Guys,
I am strongly considering a repower on my 53C. After getting quotes I've narrowed things down to Cummins Recon Engines and zf gears. Cats were over 30k more exspensive. Ok, that being said, here what I'd like input on. If I win the lotto this week I'll likely go with the 700 HP QSM. What I'm considering doing until then is the 500 or 600 hp QSC. A lot less money. This would give me the same HP as my 12v71 with about 10k lbs less weight. I normally run at displacement speed anyway but I want to be able to plane out occasionally if needed. I think with the same HP and less weight I should get at least as good performance as I have now. Might go to taller gear and 4 bladed props to help as well. Won't this work? Is this idea totally nuts!!

 

[cenger]

Curious why you want to reporter versus rebuild your 12v71’s. If you want more power you can get it from the Detroit’s. Hatteras did a Covington conversion on 1271’s that produced 845 hp.

 

[harnett]

I'm going to keep the boat a long time and the advantages of modern engines is just to great. Fuel economy, noise, cleanliness, space in the engine room, weight savings, etc. All in the cost difference isn't that great. To me the rebuild just doesn't make since.

 

[Boatsb]

First the QSC is 8.3 liter vs the QSM at 11.

If that's not nough of a reason your not looking at it right.

The qsm11 would be a great option and it does come in lower hp versions. The QSC would be too small in my experience and would not give you the performance a sportfish should have. Why repower if your not getting the benefits.

 

[harnett]

Are you saying that you don't believe a 600 HP QSC can give the same performance as a 500 12v71N even considering the 10k reduction in weight. Is there a technical reason you believe that? What performance a sportfisher should have is an opinion but if there is a technical reason equal or greater hp can't give the same performance with less weight I'd like to understand that better. Also I've been told that one piece shafts and four blade prop are going to gain a bit themselves. Again, I don't want to go faster, just equal to my current performance.

 

[Boatsb]

A 1271 is about 14 liters. The QSC is 8.3.

A 1271 was at a low power output for the machinery at 500 hp. An QSC 8 3 is at its top.

Will it work? yes. Will it work well? I dont believe so. You will get less than impressive performance with that combination.

Also consider the transmission ratio and shaft size before making a final decision.

I'd say you should consult a real expert (cummins factory or good repower specialist)

 

[harnett]

Thank you for the input. Yes I am working with a repower "expert". The local cummins dealer. He has done two Hatteras's boats this way. A 53 motoryacht and a 58. Equal hp/ smaller motors. The 53 performance was the same and the 58 actually ran 2 knots faster than factory power. I thought I would call Cummins engineering. At one time they had a 53c as a factory test boat. Thank you for your input. This is a big project that I will be living with a long time so I want to gather as much info as possible. Don't want to screw this up.

 

[Boatsb]

2 motor yachts are a poor comparison.

A company that repowers sportys would be a better measure. Most sporty owners dont repower a slow boat to stay a slow boat.

Im woking on a 42 Ocean repower for a customer and we have been discussing the new cruise speeds with different engine packages since day one. Not one discussion of similar performance.

A convertible is usually looking for another few kts cruise.

Theres a few members that repowered 53C boats with QSM11 engines who may chime in.

 

[Cricket]

There's other Hatteras convertible repower threads on here to review.
Since I'm one of the few that have been down this road my advice is to go big or it won't be worthit.There's alot of tricks to a repower so you want to hook up with an outfit or crew that does lots of them. Where are you located or where do you want to do the work? The in and out cost is pretty much the same no matter the size; and you're only going to want to cut the cockpit bulkhead once..
As I've posted before the QSM's are a good option; but I'm a CAT guy. Try looking for some rebuilt/reman 3406e/c15 @ 800hp/850hp or rebuilt/reman c18 @ 850hp/1000hp. Or possibly a new set of the the CAT 12.9 @ 850hp/1000hp. For me the key is to put in as much HP as you can afford and then take it easy on them and they will last forever.

 

[Boatsb]

Dont forget series 60 detroits. I believe 825 hp.

The ones I've been around run great.

 

[harnett]

I respect and appreciate your point of view. People sportfishing want to go fast. The boat I have is a 53 CONVERTIBLE. Highlight on convertible. I've owned her for over 25 years and there has never once been a fishing pole on board. I guess you don't get that not everyone with a convertible wants to fish. I was hoping for more of a engineering discussion on the technical aspects of what I was proposing. The 53 motoryacht I thought was the exact same hull as the convertible. Can anyone confirm that? The motoryacht the guy I'm talking with did had the 6TA at 450 hp installed and she performed the same as with the the 8V71T. That made me believe that my boat could get at least equal performance with equal HP/ lighter engines. I will give Cummins engineering a call to discuss as suggested. Thank you.

 

[Boatsb]

Repowering a convertible with small engines will make it harder to sell and get your money out of it.

Look at other convertibles that have been repaired and talk to the people that own them.

 

[motoryacht lover]

I think what Boat SB is saying is that all things being equal that maximum longevity will be obtained with a larger displacement engine producing the same horsepower as a smaller displacement engine. I am no engineer by a long shot but don’t know if the larger displacement engine will produce more torque at a lower rpm in other words will the large displacement engine keep your boat on a plane at a slower speed and in helping handling in a following sea climbing the backs of the waves, coming in an inlet, etc. I like my power when in a following sea, seems to be less fighting the steering wheel and overall more control.

 

[jim rosenthal]

You are getting all the good suggestions, here. I would not repower your boat with C series Cummins. either get the right size engines, or put the money away and keep saving until you can do it right. Any of the big engine options would do fine for you. The C series option isn't big enough- they may run and move the boat, but sooner or later you will regret not putting in the larger engines.

Looking at the larger picture, 750hp or more per side isn't actually a lot of power in a 53 convertible, especially one that heavy; these were very robust boats and they weigh a lot. While it's good to stay inside your budget, in this instance you will wish you went bigger.

Look in B&H and see if you can find a set of 3406Es or Series 60s, like he said. You could also call T&S Marine Engines in Crisfield, MD, and see if they know of anything. They are Cat and Cummins dealers and also rebuild a lot of Cat engines in their plant.

Good luck on this. Go big now, or keep your powder dry and wait for the right deal to come along.

 

[Cricket]

Scott, Series 60 is a great option, didn't think MTU was still selling them in the marine space but they are so parts would be available for take outs or remans. An outfit like Gregory Poole or Jarrett Bay most certainly have already repowered some 53c's so they could be a good resource. They probably already have the engineering for the mounts which could save a ton of $$$$$. Slane Marine did the engineering for our 3406e mounts, Gregory Poole made them or had them made, and they fit perfectly right on the marks the first time. Also, Ring Power could be a good resource for info.

 

[Boatsb]

The mound design is the easy part


Hang the motor in place.

Make mockups out of duct tape and cardboard.

Have the local certified welder make them out of steel plate 2 sizes thicker than recommended and send for powder coating.

I did this the last 2 repowers I did and it all was fine.

FWIW the custom mounts looked better than the factory ones we compared them too..

 

[krush]

I left this post over on thread about a 46c repower...applies even more to a 53. I think m11 is too small for a 53.

:https://www.samsmarine.com/forums/showthread.php?31569-Repowering-my-1980-46C

Cummins c series 8.3 liter are mechanical are going to be too small for a 46c. I have c's in my 41 and it tops out around 30-31 knots and easy cruise at 18knots doing about 18gph total. The 41c is much lighter and much flatter ass and requires way less HP. A 46c needs m11. Save your pennies and do it right.

 

[jim rosenthal]

Actually Slane Marine did a 53 convertible with M11s, and it topped out at over 28 knots on sea trials. That is fast enough for some of us, esp in an older boat.

 

[thoward]

Pulling 10k pounds will change your COG and likely have an impact on your ride/behavior especially at hull speeds. I would be very concerned about raising the COG, My 60C enclosed bridge with a tower was absolutely miserable in a beam sea. Tim Powell on HOF can give some first hand insight as to the difference in ride of a 52C with QSMs and a 52 with 892s. Yesterday, I had to run 170 miles in 3' @ 3s quartering seas. No way we could do it at hull speed so we ran at 19 knots and I was certainly happy to have that extra displacement.