Repowering a 41 Convertible with cummins 370's.

[jaybyrd83ecu]

I'm about to repower my 41 Hatteras. I'm looking at a pair of cummins 6bta 370's. Currently I still have the 8v53's that run good but its just time for an upgrade. Was wondering if anyone had any experience with this combination or performance info? I'm also planning on running 2:1 gears on the back. Thoughts? Looking for any advice from anyone who has done similar.

[egaito]

My 41C was repowered in the mid-90's with C series, which are heavier than the B's but I can offer a data point based on my experience.

My engines are 320 hp Diamond series. She cruises pretty easily, heavily loaded, at 20-23 kts and tops out at nearly 29. I've never put together a curve, but I'm usually burning about 16 gph at cruise, trimmed out right.

The keel on this hull is pretty deep, and does become a planing surface at the top end of her speed range. If I spent much time running hard, I would shave it down a bit. Others have done this modification resulting in better handling at speed.

With lighter engines, more HP, and probably electronic injection (mine is the last of the C's built with mechanical) your results should be better.

At the time Misty was done, the B's were considered too small to push her and the C's were preferable, but the HP ratings have gone way up on the B's in the 10 years that have passed.

Also, the C's are tight in the engine room with respect to height. They're right up against the salon sole. There is plenty of room on the outboard sides, but if you have a genny on the center line (as I do) there is limited clearance where they overlap.

If you haven't found it yet, there's a lot of good reading to be found on boatdiesel.com

[aclos3]

I don't have experience with the 41C, but I do have some experience with those motors in a 37ft Tollycraft. Your boat is probably a bit heavier, but the old tollys tend to run quite heavy for their size as well.

The engines are great! They were installed in 1999 and the only real problem was with a fuel injection pump fairly early on. This wasn't a cheap fix, but to date, it is the only problem they've had in about 1300 hours of operation. Loaded for extended cruising to northern BC, we cruise them at 2100 rpm for 15-16 knots and about 17gph burn combined. Even though there is a lot left in them (redline is 3050rpm), this has proven to be a sweet spot for range, since the boat gets on a plane around 2000 rpm.

I'm surprised to see that jaybyrd83ecu is able to get so much speed out of his 320s, in what should be a heavier boat. At wide open, which we hardly ever run, we get 24 to 26 knots depending on load.

[Boatsb]

370s will probably require 1.75 shafts. Also they are considerably lighter than the 8v53 so you will change the weight distribution too. I would loom at down angle transmissions and pulling and modifying the stringer caps to accommodate the new engines. I wouldn't use spacers more than 1/2 inch or so.

The panels and electrical system is going to be your big challenge. There are no easy changeovers for that.

All the water and exhaust will be more than adequate. So will the fuel and air vents. My concerns lie with the keel and the shafts.

FWIW I repowerd a 42 hatt with 450c series and a 33 rib with 330b series last fall. I know the3 drill.

[jaybyrd83ecu]

I'm keeping my 1.5" shafts. Not trying to turn it up, just be more economical and a little better cruising speed. What wheel are you turning egaito?

When you say the panels and electrical systems are going to be my biggest challenge, could you expand on that? I know I"ll need to run the new wiring up to the bridge and pull the old stuff out.

[Boatsb]

I'm keeping my 1.5" shafts. Not trying to turn it up, just be more economical and a little better cruising speed. What wheel are you turning egaito?

When you say the panels and electrical systems are going to be my biggest challenge, could you expand on that? I know I"ll need to run the new wiring up to the bridge and pull the old stuff out.

Get your wiring diagrams. Look at how the old systems and new systems differ.

[jaybyrd83ecu]

Ok. Will do. Boat was rewired in late 90's and I have the schematic.

[jim rosenthal]

I think Tom Slane did an identical boat with Cummins 370s, and the owner was pleased with her. Scott is right about both the wiring and the gauges; the Cummins engines come with harnesses that they wire at the factory; you will have to wire those into the boat. The harnesses also work all the instruments, they are set up as plug-in panels. The difficulty may be that there may not be room for the panels as shipped to fit your helm console(s).

In that event, you have two choices: you can revise the way the helm is set up and make room for the panels as they come from the engine seller, or you can remove the gauges from the panels they came in and adapt them to the Hatteras helm console or consoles, if you like the original look. I did that on my boat, and it looks fine, but it did create more work to be done.

My boat, which is lighter than a 41C, has 1.5" shafts and the same hp rating. It has been fine. However I am only running 1.5:1 gears, so the multiplied torque going through the shafts is not as much as it would be with 1.75:1 or 2:1 gears. I would speak with the engine sales people and see what they recommend for shaft diameter. If you need to go up to 1.75" shafts, it's possible you could do this without changing the stern tubes or struts by using thin wall bearings that would get you the 1/4" you need.

Finally, if you look on Seaboard Marine's web site (www.sbmar.com, I think) you will see a listing for Turbocators. These are combined boost and pyrometer gauges made by Isspro. They are a great addition to a boat repowered with turbo diesels; they allow you to find the sweet spot in the engines' range where the output is matched to what the hull requires to plane and run, and they help you also in finding where the boat runs most economically. The one thing I have never been able to find is a good article on interpreting boost and EGT information, but there is some material on Seaboard's web site in their articles section which is very helpful. Just as every boat is different, every installation is different, too, and the boost and EGT gauges let you find out what works for your boat with those engines.

[Boatsb]

Fun install

[jaybyrd83ecu]

^^ That engine room looks tight!

Thanks for the info. I have heard differing opinions from dealers. Most are with me on using 2:1, one said 1.5:1, another guy in FL had 1.5:1's in his 41 with only 330 hp.... Then there is one that used 1.75:1 gears, but that's not an option for me.
I haven't heard of what wheels folks have had on their boats with the different combos though.

I'll look into those boost gauges too once I've got it in front of me. Tach's and temp first!