RFII: Cummins 6BTA 370 Repower 28TE

[randyb]

Gooday Albineers!
I'm writing this thread to request for information and ideas (RFI).

Current Setup/Background:

• 1995 28TE with a 250HP Cummins 6BTA
  maintained faithfully
  performs as-well-as expected for its age and horsepower

RFI to upgrade to a 370HP 6BTA:

• Considering repowering to add some umpf. The 250 is just to slow (cruise 14 Knots WOT 19 Knots).
  Don't want to buy another boat or should I? Looking at 28' Carolina Classic
  Found a Cummins 6BTA. What are the "Gottchas?" exhaust changes, fuel, electrical, etc. for the repower?
  Guesses, estimates, experiences on repower installation (not engine purchase) costs?
  Will the 370HP fit with no hull modifications?

RFI on Gear:

• There's a ZF Gear and 1.25 shaft in her now however the ZF label is unreadable
  Can anyone venture a guess on the ZF Gear model for my research?
  Will the 370 work with this gear and the 1.25 shaft be adequate with the considered 370 HP upgrade?

Anything I'm missing? Anyone done this? Regrets, counsel, scolding and anything else encouraged.

Thanks to all replying and helping.

Kind regards,

-randyb

[Tree]

The first thing I'd think that won't be up to the job is the shaft. My Yanmar powered 28 is on a 1.5" shaft and that's 300bhp. With the shaft being 8' long I'd speak to a prop shop first to see if they can recommend a material to suit your sizes that will accommodate that sort of power.

[jetter]

What are your speed expectations? Fully loaded WOT @3050RPM will give me 24Knots. I normally cruise at 15 knots @ 2200 to 2300 RPM. The hull has speed limitations. I do appreciate the extra HP in heavy weather. If you have a need for speed maybe more of a planing hull is in order.

[randyb]

Thank you Russell! My expectation is to cruise at 18-20Knots. Hopefully, that's not unrealistic. You quote your speed -- is your configuration a 370HP?

Today the 250HP, with wind, current, faith and hope in my favor I get 18Knots WOT. That makes for 12Knots in heavy current and a 14-15Knot cruise with the 250HP.

[randyb]

The first thing I'd think that won't be up to the job is the shaft. My Yanmar powered 28 is on a 1.5" shaft and that's 300bhp. With the shaft being 8' long I'd speak to a prop shop first to see if they can recommend a material to suit your sizes that will accommodate that sort of power.

Great counsel tree! Your thoughts on the ZF Gear? Do you recommend investigating new gear and shaft? Any idea on gear/shaft/prop cost for materials, installation? I'm in the investigation stage now and would like to "up" the power if affordable and making sense. IMHO, adding almost 50% HP (120/250) should increase performance by 25% -- cruise at 21 versus 14. I sense apprehension on this task?

[jleonard]

I know you will need at least 1 1/2 inch shaft out of Aquamet 19 or 22, maybe 1 3/4. You can find a calculator on boat diesel for shaft dos but you'll need tranny ratio also for the formula.
Also check raw water intake size.
Cummins publishes an installation manual that will have all this info you should get a copy.

[Tree]

You've got lots of things to consider. I suspect the transmission isn't up to the task since the ZF box on mine is only rated to 330bhp and so far as I know that's standard across the range of the 28's with the Yanmar. You may require a hole new tunnel for the shaft athough it may just be a new cutlass bearing housing, cutlass bearing and new drip less shaft seal. Kevin (Pitou) had a 370 in his 28 and I am sure he will be able to give advice on transmission and shaft diameter as I believe his was a factory fit out.

[jetter]

Hi Randy. Yes I'm running a 370bta. The following is a speed log provided to me by the previous owner:
RPM Speed Knots
600 4.4
800 5.1
1000 6.5
1200 7.5
1400 8.5
1600 8.9
1800 9.7
2000 11.2
2200 13.7
2400 17.7
2600 20.8
2800 23.8
3050 26.7
2POB- Full Fuel-Full water- Bottom clean
I have similar numbers until 2400rpm when I'm getting about 10% less. New bottom this summer may solve that.

[Russell]

Randy
My 97 28TE had the 250 HP Cummins and I could cruise 16 to 18 knots depending on sea state. The only time it seemed insufficient was fully loaded going offshore in heavy seas. It would labor to climb steep waves and smoke. You might check to see if everything is correct with your engine and bottom before spending big bucks on a repower. Trim tabs in the correct position added almost 2 knots. I chose to purchase a newer Albin myself and the 20 K difference was well worth it. You will spend more than that on a repower which you will not recover and the newer Albins are greatly improved with better sound insulation, better hardware all around, and probably newer electronics.

[randyb]

Hi Randy. Yes I'm running a 370bta. The following is a speed log provided to me by the previous owner:
RPM Speed Knots
600 4.4
800 5.1
1000 6.5
1200 7.5
1400 8.5
1600 8.9
1800 9.7
2000 11.2
2200 13.7
2400 17.7
2600 20.8
2800 23.8
3050 26.7
2POB- Full Fuel-Full water- Bottom clean
I have similar numbers until 2400rpm when I'm getting about 10% less. New bottom this summer may solve that.

Thanks for the stats!!! Great info!

[randyb]

Randy
My 97 28TE had the 250 HP Cummins and I could cruise 16 to 18 knots depending on sea state. The only time it seemed insufficient was fully loaded going offshore in heavy seas. It would labor to climb steep waves and smoke. You might check to see if everything is correct with your engine and bottom before spending big bucks on a repower. Trim tabs in the correct position added almost 2 knots. I chose to purchase a newer Albin myself and the 20 K difference was well worth it. You will spend more than that on a repower which you will not recover and the newer Albins are greatly improved with better sound insulation, better hardware all around, and probably newer electronics.

Russell, sounds like the voice of experience! I'm hearing some wisdom here -- your explanation is exactly what I encounter. I'm finishing the bottom painting this weekend. I'll keep an keen eye on the trim tabs. I do like the boat, the handling and economy yet the sluggishness bores me in a flat sea and a heavy sea while most of our seas are moderate she performs well. I suppose cleaning up my girl and considering a newer one might be in-order. However, I can purchase a low hour 370HP for a good price albeit the repower would be near $20K. As you stated the 20K might be best served on an upgrade in lieu of a repower. Thanks Russell!!!!

[Nancy]

Randy,

What RPMs are you seeing at cruise and WOT?

We have the same year boat and the same engine. The engine is rated for 2600 WOT, and properly propped, you should get 2700-2750.

We cruise at 2200 & 17-18 knots depending on water condition. At 2400 RPM, we get a solid 21 knots. Our WOT is 2750 & 23 knots.

[randyb]

Randy,

What RPMs are you seeing at cruise and WOT?

We have the same year boat and the same engine. The engine is rated for 2600 WOT, and properly propped, you should get 2700-2750.

We cruise at 2200 & 17-18 knots depending on water condition. At 2400 RPM, we get a solid 21 knots. Our WOT is 2750 & 23 knots.

Thanks Nancy! Based on water conditions the absolute best I can get is 20.5 knots WOT and that's not a consistent speed. As stated she can achieve 19 providing the current isn't too strong. I'll call my prop guys while out of the water and discuss. I've never been able to get more than 2650 out of my engine -- even with a new turbo. You've given me something to consider. Thank you.

[Pitou]

Randy -
You've gotten some good quick advice from a number of postings and I'll add to your RFI with what I had under the deck (6BTA 370) and a few GPS screen shots of average RPM's and speed achieved while fully loaded. I've heard on this forum before about the power plant that you're looking at will be very loud and bothersome. Those comments mainly came from those looking at older boats without the sound insulation packages offered in later models. My 2002 28TE had sound insulation under every deck and hatch inside and outside of the pilot house as well as on all bulkheads and therefore this was a nonissue. If you proceed with this project I'd strongly suggest that you also pursue a quality sound insulation package.

With a repower you're looking at a full drive train R&R from engine, gear, coupling, shaft, shaft seal, cutlass bearing, possible work on the stern tube to accept the new cutlass bearing and a new propeller or reworking.

My 28 TE build was done with the following:

ZF gear: ZF 85IV
Aquamet 22: 1 1/2 inch shaft
Tides or PSS Shaft Seal / (include a spare seal on the shaft for down the road)
Propeller: 19 X 20 4 blade nibral left hand wheel
cupping 5 - .073

Here are a couple of helm screen shots / fully loaded with fuel, water and gear:

2400- @ 19.2kts.jpg

2600 @ 21.6kts.jpg

3000 @ 25.8kts.jpg

Engine shots: