42c Repower

[hawkins]

Hello i have a 74 42c powered by 671ti at 450hp.. i am looking to repower to lighten up so i can stay around the same weight after adding another fuel tank to extend range. I have a set of 410hp cummins b series but not sure if that would be enough out of thoes little motors.. i currently cruise between 15-18 knots and would like to do the same or better. If the cummins doesnt have enough what would thanks

[captddis]

The Cummins 450C series is a good fit for that boat.

[Boatsb]

We repowered a 76 42C with cummins 450c series this summer and the outcome was everything the customer wanted. Call me for details.

407-739-5450

[hawkins]

what about any other engine brands besides cummmins personally i prefer cat i know lots of people hate them in boats but i know cats better than any other engine

[jim rosenthal]

Cummins remans are a far better deal than Cat. Do you have the B series or C series Cummins? The C series are a nice choice, big enough, good working room, less fuel burn. And lighter, so she will plane out a little easier.

You could probably fit M11s in there, but it would be a waste of money and power. You don't need them.

[saltshaker]

Hello i have a 74 42c powered by 671ti at 450hp.. i am looking to repower to lighten up so i can stay around the same weight after adding another fuel tank to extend range. I have a set of 410hp cummins b series but not sure if that would be enough out of thoes little motors.. i currently cruise between 15-18 knots and would like to do the same or better. If the cummins doesnt have enough what would thanks
What are you trying to accomplish range wise? you may get the added range from the repower alone. You'll be dropping 3-4K lbs with the repower and the new engines will be much more efficient.

[hawkins]

yes i have a set of b series but i thought they were not big enough so i never did anything with them i to thought i would need at least the c series

[hawkins]

i run the boat out of rhode island and i have a 110 mile hike to the canyons and when you add in a day or two of trolling i have to pack fuel on the deck.. i dont want to pack fuel on the deck its a pain

[Bob Bradley]

Sounds like a familiar story. I run a '79 43C with 435hp 6v92ta engines. Pretty much the same speed and destination (the edge) also out of RI (Westerly YC). Mine run well, so I'm not in a big hurry to change, but I've started to give it some thought. And yea, 495 gallons of diesel isn't enough. I'm also tired of carrying 200 gal in a bladder on the bow.

Whatever you decide to do, please keep us updated. I'm very interested to learn the results.

[Boatsb]

25 Kts with the C series.

I think around a 22 cruise if I remember right. Im not sure of the burn. the 5.9 block is just not enough torque and HP Maybe a 6.7 but for sure the c series.

FWIW the cats are a bad choice for this size. No great deals unless its the dreaded 3126.

Yanmar has some nice engines but for the money the cummins remans are the best.

[hawkins]

does anyone know the difference in weight between the c series and the 671??

[hawkins]

25 Kts with the C series.

I think around a 22 cruise if I remember right. Im not sure of the burn. the 5.9 block is just not enough torque and HP Maybe a 6.7 but for sure the c series.

FWIW the cats are a bad choice for this size. No great deals unless its the dreaded 3126.

Yanmar has some nice engines but for the money the cummins remans are the best.

how much are a set of c remans.. although i was looking to get a set of old ones and rebuild them myself i just have never trusted anyone to any motor work even when a warranty is in effect (parts are cheap.. only being able to blame myself priceless)

[Boatsb]

The reman is not realy a reman. Its pretty much new to original spec by cummins with a full warranty.

a bad injector or head can wreck a motor. They stand behind them.

[Maynard Rupp]

I don't think they sell the common rail B or C series engines as re-mans, only the older mechanical versions. I would love to re-power our 36C with modern B series Cummins at about 380 hp. Our gas engines are great though and I don't want to spend 100K on a boat that isn't worth much more than that with the new engines. It would sure be an awesome boat with those B series engines though.

[George]

Cat C-12 Compact should fit. Juice with performance, light weight, and should move you at 28-29 kts at 1900 provided you can get the right sized prop on it with the right down angle gear.

[saltshaker]

does anyone know the difference in weight between the c series and the 671??

weight will vary a bit depending on what options but a 671 is about 2800lbs, the Cummins C series is about 1800lbs and the B series Cummins is around 1100lbs. These are without gears. You have 410HP B series? If they are that much HP I wouldn't bother with a set of the C series remans as they are only 420HP. I have seen a few 42C with the 6Cta's and the owners were very satisfied with the results. Either Cummins would greatly increase the fuel efficiency of the boat which may allow you to run with your existing fuel. Does your 42C have a waste and water tank? If so they typically are set up to be used as fuel if you plumb them in that way.

[jim rosenthal]

I would guess that you would burn 50-65 % of the fuel per mile with the Cummins engines compared to what you burn with the 6-71s. It's really about your cruise speed, not WOT, none of us run at WOT for more than a few moments anyway. With the Cummins engines you would reuse all your existing plumbing and running gear, but you'd have to make up new mounts for the new gears etc.

I've had Cats, and I would not have them again, although I think they have made a lot of progress on reliability compared to the 3116 and 3126 engines. But they had nowhere to go but up, essentially. I think the Cummins are a far better choice.

Because the size of the Cummins diesels is so much less, your service access will be better as well. You'll have to keep your boat a long time to get your money's worth from the repower, but most of us on this forum keep our Hatteras yachts a long time, and get a lot of enjoyment out of them. Go for it.

[hawkins]

I would gladly put cat c12s in but i dont want to change shafts props and angles just way to mich cost and work.. i do have the b series but i am jist not sure if they will do the job is it hp or torque that a boat needs to get out of the hole?? There is lottle difference in hp between the b and c but there is a big torque difference.. i almost want to drop engines and gears in and be done maybe get a little more pitch on probs but the least i have to do the better.. i do have waste and water tanks but i want to leave them as is and add a new tank for fuel to kinda offset the 2000lbs diet that the new motors would do. I like the way it rides now so i kinda wanna stick to the same weight i got.. or maybe i am just thinking about it wrong

[Bob Bradley]

Where would you fit the new fuel tank? I don't want to lose my water or waste either.

[Boatsb]

First a 42c going much over 25 kts is scary. Light load on the one I repowerd this summer had us about to lay over on the side.

It is not an efficient hull and cummins did not recommend the 5.9 block in any horsepower. The 450 c will bring the boat to the the limits of speed very nicely. No need for bigger or higher hp. The 6.7 is their new block and goes up to 650 hp with less torque that the 450c.

[jim rosenthal]

Agree with Scott. If you contact Cummins they will tell you that the preferred engine for repowering that hull will be the C series. It IS about torque. Hp is calculated from hp in any case.

What is the reason for a repower on this boat? Fuel economy is a good one, quieter performance another good one, higher cruise speed another. Higher top speed is pretty much pointless IMHO. It is only worth doing if you really love the boat and plan to keep her a long time and get your money's worth out of the new engines. Cummins remans may be available in the common-rail engines, but I don't think you need them. (and they are not really remans at all, they have a few noncritical parts that are used in them, but they are essentially new for all practical purposes) I think what you need is mechanically injected C series engines at about 480hp per side. Gears to match. Your boat will perform better, it will use less fuel, and be less noisy. I think that is all the power you need to make that hull perform brilliantly, within its design limits. And I don't think you will need to add fuel storage space to reballast the hull.

[saltshaker]

First a 42c going much over 25 kts is scary. Light load on the one I repowerd this summer had us about to lay over on the side.

It is not an efficient hull and cummins did not recommend the 5.9 block in any horsepower. The 450 c will bring the boat to the the limits of speed very nicely. No need for bigger or higher hp. The 6.7 is their new block and goes up to 650 hp with less torque that the 450c.
But if he already has a good pair of 410HP B series why not use them? How would a pair of 420HP C series perform better? I agree if I was shopping for the engines. I'd opt for the C series but if I already had a good pair of similar HP smaller displacement engines, I'd be hard pressed to buy another set.

[hawkins]

Agree with Scott. If you contact Cummins they will tell you that the preferred engine for repowering that hull will be the C series. It IS about torque. Hp is calculated from hp in any case.

What is the reason for a repower on this boat? Fuel economy is a good one, quieter performance another good one, higher cruise speed another. Higher top speed is pretty much pointless IMHO. It is only worth doing if you really love the boat and plan to keep her a long time and get your money's worth out of the new engines. Cummins remans may be available in the common-rail engines, but I don't think you need them. (and they are not really remans at all, they have a few noncritical parts that are used in them, but they are essentially new for all practical purposes) I think what you need is mechanically injected C series engines at about 480hp per side. Gears to match. Your boat will perform better, it will use less fuel, and be less noisy. I think that is all the power you need to make that hull perform brilliantly, within its design limits. And I don't think you will need to add fuel storage space to reballast the hull.

Only reason to repower is extending range and putting in modern engines..I plan on keeping for a long time or untill something better comes along but right now this boat still fits my needs just need it to go further than currenly can my goal would be around 5-600miles

[Boatsb]

Its all about displacement. 5.9 vs 8.3 ltr.

the 5.9 would be great for a series 1 41c. The 8.3 wont fit. Also the 42 needs more torque to get up and go. The hull is heavier and will need more ho and torque to plane.

My customer has 150 hours on the engines I installed last summer. He loves the package. It was not a problem with the same shafts. Down angle transmission is a must.

[daniel r morrison]

I installed cummins 480ce 5 years ago and they were a perfect fit. needed new gears, stuffingboxes shafts, struts and props to make it work. the old 671 ti's weighed so much that the transom water line came up over 6" to 7" with the new engines. 1800 rpm gives me 18 to 19 mph and almost 1.25 miles per gallon for a slow cruise. 2400 rpm will yield 24mph at about one gallon per mile. top speed, I am slightly underpropped , is 29mph is top speed at 2600rpm. the 42's really like that 20 mph cruise speed. troll at 1000rpm all day at 9mph and get almost 3 miles per gallon

[bhostrawser]

Its all about displacement. 5.9 vs 8.3 ltr.

the 5.9 would be great for a series 1 41c. The 8.3 wont fit. Also the 42 needs more torque to get up and go. The hull is heavier and will need more ho and torque to plane.

My customer has 150 hours on the engines I installed last summer. He loves the package. It was not a problem with the same shafts. Down angle transmission is a must.

Yes, definitely the 8.3L's. Now, whatcha gonna do with those 5.9s? :D

[season]

I installed cummins 480ce 5 years ago and they were a perfect fit. needed new gears, stuffingboxes shafts, struts and props to make it work. the old 671 ti's weighed so much that the transom water line came up over 6" to 7" with the new engines. 1800 rpm gives me 18 to 19 mph and almost 1.25 miles per gallon for a slow cruise. 2400 rpm will yield 24mph at about one gallon per mile. top speed, I am slightly underpropped , is 29mph is top speed at 2600rpm. the 42's really like that 20 mph cruise speed. troll at 1000rpm all day at 9mph and get almost 3 miles per gallon

Those are very impressive performance improvements. Does anyone have an idea what a 45 or 46C with the VT903 or QSM11's would do in cruise and hull speed conditions? There are a few of them on YW currently and I am curious about just how much better performance you could expect.

[jim rosenthal]

Yes. One of our members, Lonnie Cooper, repowered his Series II 45C with M11s a few years ago (when they were "only" 650hp or something like that) and she did 34 knots WOT on her sea trials. The load readouts showed only 93% loading at that speed. In other words, she could have accommodated another two inches of pitch on the wheels- and maybe hit 36 knots. That is faster than I need to go.

[hawkins]

Thanks for everyones thoughts on this but now if i can fit a cummins c series engine in the 42c wouldnt a cat c10 or c12 also fit? i know they get all kinds of power out of them but if i were to run them at 450-500hp wouldnt they outlast the cummins (less hp per cubic inch)???

[Avenger]

Also look at power to weight ratio. While it's not always the guiding factor it's usually where CAT falls down in recreational marine propulsion.

[Boatsb]

Also look at power to weight ratio. While it's not always the guiding factor it's usually where CAT falls down in recreational marine propulsion.

The 450c cummis is not a short life engine. Run responsibly I would say well over 5k hours maybe up to 10k.

Also remember cats motto. "Turning iron into gold with yellow paint".

[hawkins]

Haha good one... so if i run the 6cta's at 1900rpms or so i souldnt have much problems and last awhile?? Also how much fuel do they burn at 1900??

[saltshaker]

Haha good one... so if i run the 6cta's at 1900rpms or so i souldnt have much problems and last awhile?? Also how much fuel do they burn at 1900??
I would think 1900RPM would be dogging them. Aren't they 2600RPM engines? The 6CTA is a great engine. Rarely see them needing an overhaul without a ton of hours on them. A friend of mine just sold his boat with one in it. 3900 hours and surveyed flawlessly.

[Avenger]

The 450c cummis is not a short life engine. Run responsibly I would say well over 5k hours maybe up to 10k.

Not only that they're a wet-liner engine and very reasonable to overhaul.


Also remember cats motto. "Turning iron into gold with yellow paint".


Yeah, ha ha good one. Where'd you get that? ;)

[Boatsb]

Not only that they're a wet-liner engine and very reasonable to overhaul.




Yeah, ha ha good one. Where'd you get that? ;)

Ever buy Cat parts?

Make you wonder. I think I saw it on a wall in the parts department by the way.

[jim rosenthal]

Rather than run them at a specific rpm, I think you'd be better off to invest in boost and exhaust gas temperature gauges and run them at 900 degrees EGT and about 10-12 lbs boost- find the place where the boat is planing and the engines are happy and run them at that speed, whatever it turns out to be.

There is a combination boost/EGT gauge made by Isspro called a Turbocator that does exactly that. Not expensive by our standards, and works very well. Seaboard sells them, too.

[hawkins]

Hey Scott
the 42c you repowered with the 450c what gear reduction did you use? would i be able to use 1 1/2-1 or what would be best?

[Boatsb]

Hey Scott
the 42c you repowered with the 450c what gear reduction did you use? would i be able to use 1 1/2-1 or what would be best?

Ill have to check. I dont want to spout out answers and be wrong. Also what size exhaust do you have?

[hawkins]

ahhhhh stove pipe size has to be 8 or 10inch..

[Boatsb]

Double check. I believe you want 8 or larger

[hawkins]

i am sure they are at least 8inch

[Boatsb]

Thats good. Ill make you a deal. Ill get all the specs for the 450C engines in exchange for the 5.9's.

they would fit in my 41c.

[hawkins]

Did you say specs or real good deal

[Boatsb]

And Ill get you a deal on the 450s because your a nice guy too :)

[Maynard Rupp]

I would love to repower our 36C with those B series engines. I keep trying to justify it though. I figure $100,000 total to get the job done. Make me an offer that I can't refuse for those B series engines and transmissions.