What am I missing?

[Steven Borcherding]

I have a 37 foot 11.5 beam 20,000 pound Roughwater that is currently powered by twin 250 HP Detroit 8.2s. After a fire in a nearby marina I was able to purchase the motors from a 2007 Meridian that had external damage from the fire, it was not the boat that burned but moored next to it. ( check your shore power connections in winter!)
I got two low hour, very well maintained 330 HP, 6bta s with ZF 80 A – 2 gears at 1.5:1, the mixing elbow, gauges, pretty much everything.
 I currently have 1 3/4 shafts which are newer, newer 5.5″ wet exhaust with new water lift mufflers and Morse cable controls for throttle and shift. The fuel tanks are two years old. The current mounts are the correct width on the stringers. I will have to modify them for the length and height but should be straightforward as they are welded steel plates that straddle the stringer. 
I posted photos of them in my other post when I was searching for engines. My question is based on experience, what am I missing? I know I will most likely need to replace the props, The cutlasses and struts are two years old. The motors fit under the floor. I am having  a local shop do the swap and want to avoid nasty surprises. I think that the mixing elbow and dry exhaust will work as the installation in the Meridian was very similar as far as top clearance for the engine compartment and height of installation above the waterline. I have reviewed the tips section on exhaust system design and it looks pretty good on my boat. Would love to hear any feedback or ideas about the project! 

Topic

[pwrobert]

Replied to earier Post

Here is an overlayed picture of the Detroit 8.2L (Red) with 502 Trans with a Cummins 6BTA with ZF 220A (Black).  By superimposing the scaled diagrams in Photoshop and lining up the Faceplates of the transmission output flange you can see how they stack up.  Same degree of down angle.  Detroits are wider and the Cummins are a couple of inches longer.  The Cummins/ZF packages save about 1500 lbs on the install.

Only other somewhat issue was the Cummins were wider at the block/transmission bell housings and the narrow engine beds for my boat required slight notching of the stringers in a couple of places – but no biggie.

 

[Steven Borcherding]

Which Gear??

I have taken careful measurements of the new engines and I could go with the ZF 80 A gear boxes that are coming with the engines or the MG 502 that I have with my current Detroits. If I re use the MG the front brackets for the engine need to be cut down, if I go with the ZF I need to cut down the rear and add an inch to the front brackets. As I have a fab shop at the yard it is six of one… My question is which would be the better gears? (Yes I know, none of the above but budget and wife considerations) If I use the ZF, I have the 4 blade props off the other boat that every prop calculator I look at says should work. I may need to remove some pitch as they seem to be pretty steep. (23 X 25). If I use the MG I will need to get new props, but if that is the better choice.
I had a chance to look at the same boat as mine that the guy repowered with 250 HP Yanmars, I think it was a crap job to be honest… But he did do what I was thinking and reuse the brackets mounting system by simply sliding them on the stringer. I am baffled why he did not just make new brackets rather than the shims but this photo of the install, and my current setup gives the idea. What is you take on the ZF 80 As?

[Steven Borcherding]

502-A ???

I was told that the 502 A woudl not handle the torque of the 6bta 330. If I can use the MG 502 gears that will be my plan! It makes this whole thing a lot eaiser.

[Tony Athens]

As to a drawing of a 6BTA and a ZF80 or 85A?  If you have the engine/gear in your garage or ??, then you have all the measurements you need.. I’ve attached a critical dimension drawing but it will not help you as to the mounts.. There will need to be 100% custom.

 

 

[Tony Athens]

Why not just use the MG502A that you have–These are very good gears? Also, the ZF220A was a close to and exact “plug & play” copy but with much higher ratings than  the MG502A..

[Steven Borcherding]

Follow-up

The photo above shows the mounts in my boat with the Detroits. My current tranny is a MG 502 with 10 % down angle.
The 6BTA has a ZF 80 A with a 8% down angle. I was thinking of making up the 2% by modifying the mounts. Is it Kosher to set the engine at a angle below well 12% to make up the difference.. It looks like the ZF has the output about 1″ lower than the MG on the Detroit so I will lower the mount pedestal on rear. I can raise the front to get the balance. There is a metal fab shop at the yard so I was just going to have them make new pedestals for the mounts. One of the outboard ones is pretty rusty anyway.
The motors going in are really nice. It was a freshwater boat with one owner who was very current with maintenance and kept excellent records.
One of my challenges is that I cannot find a drawing of the 6bta with the ZF 80 gears. It would help if I could fab a mock up to get the mounts figured out before I get the engines on site.
We were starting to have a lot of small issues with the Detroits and we use the boat on the Washington coast between Neah Bay and Astoria. It is not a place where you want to need a tow!

[Tony Athens]

What are you missing? 

 

1) The other post you are talking about,  all in the same thread

 

2)  Good pictures of everything you are trying to describe..

 

No crystal balls on this forum..

 

 

[Author]

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