Grounding without an Engine

[Aqua Vitae]

I am pulling out my inboard diesel to install an outboard gas engine. All of my electronics are grounded via the engine though. I will retain the prop and shaft to power a generator while under sail. What do I ground to now?

[Chief Engineer]

Power a generator while under sail?

Why not just get a solar panel or windgen?

[DeepFrz]

Ground everything to a good ground bus. Blue Sea has a good selection.

[Aqua Vitae]

Thanks, I will go with the ground bus. Chief, I have a windgen and will be installing panels later. But, the way I see it, I have a prop, shaft, cutlass, stuffing box, etc. Why not just hook up a generator to it as well? Any power source is a good power source in my opinion.

The down side to using the prop to power a generater is that it will cause drag, and reduce speed. Consider, if you go this route, selecting a small generater that will just meet your needs, and going to a smaller prop. This will reduce the drag, and still suit the purpose. I would also consider a shaft lock, and, if you do not already have it, a two blade prop to further reduce drag when you do not need to generate power.
As for the grounding issue, I agree that a bus bar should meet your needs, as long as everything is properly grounded now (i.e. keel bolts, or dyna plate). Although, no reason to keep the cable running to the engine area. You can set the bus bar near the panel, or just run your engine ground directly to the existing bus bar by the panel. Without knowing how our electrical is set up, it is only a guess, but you may have the option just to remove the hot and ground cables that lead to the engine, from the system, and leave the rest.

[Aqua Vitae]

Kai Nui, that is a good point about drag, but I was figuring I would make use of the prop where it is anyways. The way I see it, any power is good power, and I get 6 1/2 knots on a good day anyways. When using a generator hooked up to the prop, a 3 blade prop with at least 14 inch pitch is necessary. You see, the point is now to make it turn instead of feather or fold.
As for the grounding issue: Does anyone else have experience with repowering using an outboard? Without a dynaplate (which I would rather not install), how do you ground? I was thinking the prop and shaft again, maybe with slip rings or something. Not really sure.

[Inthewind]

One of the problems with outboards is when your boat pitches in sea's the lower unit will come out of the water and over rev, unless of course you are under sail only. My advise would be to find a good used affordable diesel engine. You will be much better off when it comes to fuel economy and dependability and you would be using power that the boat was designed for. I had a Watkins with a single cylinder Yanmar and it was underpowered, I would go with at least a twin cylinder. Powering with an outboard is fine but it would not be my first choice for that boat. I find it hard to believe that a prop spinning on a shaft will be able to generate any substantial power at the slow rpm that it would be spinning. This is only my opinion, you don't have to listen.

[Aqua Vitae]

I know, I know, the inboard is better. But, given the age and overall value for my boat, repowering with an engine of questionable history (cheap) or half the value of the boat seems like a bad idea to me. Going with a 15 hp Yamaha which will start, run, and not deafen me or shake the entire stern like the old Yanmar.

But how do I ground without an engine?

[Inthewind]

Ground to the negative side of the battery that starts your outboard motor.

[Aqua Vitae]

That would be my arm.

Really though, so I can just connect the negative side of the battery to the negative bus bar and be fine? Is any real grounding being achieved this way?

[Inthewind]

I was assuming your motor was an electric start, with that being the case, you would have a ground cable connected from the battery to the engine. You would want a fuse panel with the main negative cable leading to your negative side of your battery bank. I don't know what your trying to ground but if it is just small stuff like dc lights, bilge pumps, radio etc, this should be sufficient for your needs.

Simple answer is yes. Just complete the circuit to the negative side of the battery. I think my initial post may not have been clear. If your current (no pun intended) ground system is correct, this is the only thing that needs to be done. If the system is not grounded outside the hull, I would strongly recommend doing so, whether that is using a Dyna Plate, or through the keel bolts. The system will still work without this, but it adds to your ground protection. I do not recommend grounding through the shaft, as you intend to let the shaft spin, and this will create additional problems.
In simple terms, think of the electrical system as a circle. It starts at the positive terminal of the battery, and ends at the negative terminal. Everything in between is wired into this loop.If the loop has a break in it, it is no longer a loop, and will no longer work. I know there are more variables, but that is the simple explanation. The external ground is a separate system, and protects things from outside forces, as well as creating an RF ground larger than the boat. But, that is another story.

[Aqua Vitae]

Thanks for all your help guys. I will be using a negative bus bar to accomplish the "closed loop."

On another note: Anybody want a Yanmar YSM12 inboard?

[Inthewind]

I don't blame you for feeling the way you do about that one cylinder vibrating, hard to starting, underpowered Yanmar you have. I had one in my previous Watkins too. I have come along way since then, now I have the best Yanmar engine that you could possibly put in a sailboat, Yanmar 4JHDTE 125hp and could't be happier, plenty of extra power.