Hatteras 46C series 1 rebuild or repower?

[chicco]

Hi Gentlemen,
I've read several threads about repower a 46C but I'd like to ask you some suggestions or tech specs about my idea.
My hat has 8v71 rated @435 hp and it's time to rebuild them or repower. Honestly I don't want to rebuilt them, I need a faster cruising speed. My engines have aprox 8000hrs and the cruising speed at 2000 rpm is low 16knots, have 1:5 ratio gbox.
I don't have the money to buy QSM11 :-(
I have the chance to buy very well mantained and serviced 8V92TI rated @650hp with 2:1 ratio gbox. I know these engines were available for 46C series 2, the one named HP version. I know the HP version had some differences regarding the hull.
Another option could be looking for 6v92 rated @550 hp.
I think both pair of engines could fit nicely inside the my Hat.
I had an hand made tower and usually I cruise loaded of diving gear, underwater archaeology is my work.
I use the Hat for 7 months per year, quite everyday, 1500 nmiles per year.
What could you suggest me? and in case I wll choose 8v92 do you have some good suggestions about propellers or any others tech specs?
Thank you

[Boatsb]

The hp also had a larger er. If you go 8v92 theres a good chance you will need to change running gear and do some hull modifications.

[chicco]

The hp also had a larger er. If you go 8v92 theres a good chance you will need to change running gear and do some hull modifications.

8v92’s came with their Allison 2:1 ratio Gearbox. I made some calculations and at 99% they will stay really close to the living floor.With 6v92 maybe I could use my gearboxes that are Allison M15R ratio 1.5:1 My big thought is about hull modifications...very hard to think it could be possible where I am. Will I have problems if I won’t modify the hull repowering with 8v92?Tnks

[jim rosenthal]

How much weight difference will there be for the two 92 series?

Just looking at your alternatives, I would think you would be better off with the 8-92s, as they are less stressed at the 650hp rating than the 6-92s are at 550 hp.

Have you looked at take-out M11s or Cummins reman M11s? You could call Tony Athens in California. Also you could call T&S Marine in Crisfield- see if they can find you a pair of 3406s which might be the best choice of all.

[Scope]

What cruise speed are you trying to achieve? My 46Hp with 650hp 8v92 cruise is 20knts at 1850rpm
26x28 in three blade wheel. that is with 1.5 to 1 gear. I would suggest a 28x35 4 blade to start and adjust from
and adjust to hit 2350 rpm. Pm me if you want more information

[Cricket]

Would look for some rebuilt or used take out QSM11's or CAT 3406E/C15 or 3196e/C12 or DD Series 60?
If you're going to go through all the work and expense of a repower go for some modern 4 stroke engines.
Shaft wise you may be able to use high strength Aquamet 22 shafts, especially if you keep the ratio @ 1.5:1.
As far as having to modify the the hull it depends on how fast the boat is going to end up going. As I've posted before, big believer in overpowering and then running the engines slow so they last.
As an example a CAT engine with 2300rpm WOT being cruised at 1750, or less, will last a very long time compared to running them @ 2000 rpm cruise.

[chicco]

Would look for some rebuilt or used take out QSM11's or CAT 3406E/C15 or 3196e/C12 or DD Series 60?
If you're going to go through all the work and expense of a repower go for some modern 4 stroke engines.
Shaft wise you may be able to use high strength Aquamet 22 shafts, especially if you keep the ratio @ 1.5:1.
As far as having to modify the the hull it depends on how fast the boat is going to end up going. As I've posted before, big believer in overpowering and then running the engines slow so they last.
As an example a CAT engine with 2300rpm WOT being cruised at 1750, or less, will last a very long time compared to running them @ 2000 rpm cruise.

I'd love to repower with modern 4 stroke engines but here in Italy it isn't so easy to find them and even if you could find something the big issue is always their history...and of course the price. With the same amount of money I spend to rebuild my engines I can change them with 8v92TI's. From those I know their history and the seller. Honestly I don't know the US market price but talking about the Italian a pair of well mantained QSM11s will cost 50k euro, plus gearboxes (I cannot use mine), exhausts and more...at the end it will be too much money for me.

[Fanfare]

When I started thinking about repowering 25 years ago I went straight to the top. Jack Hargrave wrote me saying I should replace my 350 hp Detroit 8V-71 naturally-aspirated engines with 6V-92TA 550 hp engines. He said do not go for larger eight cylinder engines because these would not fit in the engine room of my Hatteras 50 Motor Yacht. I have measured a number of dimensions in early 53MYs and 58MYs and these are identical to my cabin sizes, at least up to the one foot wider salons. (Hatteras probably used the identical interior jigs on all.) I have not measured my engine room length, but I would bet it is also the same. So watch out for this.

Compared to my 8-71 natural engines (568 cu. in.) the 6-92s were lower displacement (552 cu. in.). All the additional horsepower came from the turbocharging which was jamming more fuel into the cylinders. To handle this additional power the heat exchangers for the engine and engine oil coolers on the front of the engines were considerably enlarged and probably exceeded the length of the older engines despite having fewer cylinders.

On the good side, my 6-92s have been nearly flawless in 25 years. I try not to run them hard, probably 70% of their roughly 3,000 hours at 1,950 rpm, 30% at idle to 1,300 rpm hull speed (9.2 kts.). Detroit Diesel wanted me to get their brand new DDEC engines but I decided to stick with the well tested mechanical engines because I knew how to fix them. They still do not burn oil. The Twin Disc transmissions seem significantly stronger than Allisons. Because one of my new transmissions essentially always runs in reverse both my 6-92s crankshafts turn in the same direction. I have heard Allisons cannot stand up to this. But because your 8-71s have greater horsepower than my older ones you may be able to use your present transmissions. That's over my paygrade!

I think Roger Pensky's ownership of DD really paid off in my newer engines with improved metallurgy and sealing. No oil leaks!

Good luck in your decision.

[sixty]

My vote is either rebuild what you have or find modern 4 strokes that would be worthwhile for a repower. Repower to 8v92's will cost ALOT more than you think and take much longer with fabbing and new parts and possibly crowd your engine room.

Hull modifications may only be a requirement if you plan on greatly exceeding your current top speed. this usually entail cutting down the keel and making transom modifications. A lot of trial and error.

[Tim Powell]

Would look for some rebuilt or used take out QSM11's or CAT 3406E/C15 or 3196e/C12 or DD Series 60?
If you're going to go through all the work and expense of a repower go for some modern 4 stroke engines.
Shaft wise you may be able to use high strength Aquamet 22 shafts, especially if you keep the ratio @ 1.5:1.
As far as having to modify the the hull it depends on how fast the boat is going to end up going. As I've posted before, big believer in overpowering and then running the engines slow so they last.
As an example a CAT engine with 2300rpm WOT being cruised at 1750, or less, will last a very long time compared to running them @ 2000 rpm cruise.

CRICKET IS ON THE RIGHT TRACK FORGET THE DD
HOW DOES THE SONG GO Save my nickles and dimes and buy a qsm 11.