Re: Sea Chest


Thomas Peacock
 

Thanks as always for the tips, Bill.

On the short life of the generator impeller, I have much experience, and a tiny bit of advice.

After we bought our boat about ten years ago, the generator would go through impellers every 15 or 20 hours, obviously a major pain.

When in Martinique, I had Didiere, the local, very experienced diesel mechanic, work on a separate issue. He always looked into the impeller problem, and put a new one in, using some sort of glue-type substance on the Woodruff key that keeps the impeller working correctly. The new impeller lasted only about three hours. (That said, I still think Didiere is a great mechanic).

For the next one, I did three things:

1. I also put a mild glue on the Woodruff key

2. I sanded the inner part of the impeller housing (perhaps the metal is more prone to accumulating residue from the rubber, which then leads to excessive friction)

3. I lubricated the inner housing with Molykote. 

Since, then, I have had no impeller problems, 

Might be coincidence, but it works for me.

Tom Peacock
SM 240 Aletes
Chesapeake Bay, awaiting vaccine


On Nov 27, 2020, at 4:34 PM, Karen Smith via groups.io <karenharmonie@...> wrote:

Chris,

I have taken the photos and annotated them with the parts list.  

All of the fittings I used are standard NPT pipe fittings.  In the case of the outlet fitting on the strainer, that is actually a female 1-1/2” BSP thread.  In this size, the NPT and BSP threads are compatible enough that they will screw together just fine, but they will not make a reliable high pressure seal.  Don’t expect “teflon tape” to help here.  You’ll need paste type pipe sealant.  For the very low pressures seen here, it works fine despite the small mismatch in thread shapes..

We have been running this long enough now, we can confidently say that it works with no issues. Well, no issues that were not already there with the stock Amel manifold.

Here is the only problem we have with the “sea chest” design.  As we sail, air is entrained under the hull.  Some of this air finds the sea chest thruhull and rises into it, displacing the water.  If we are sailing fast, enough air comes through that in a very few hours the strainer and standpipe are empty of water. I am pretty confident that needing to purge this entrained air is the primary reason that the generators on Amel’s have such short lived raw water impellers.  I have a couple of ideas on how to improve this situation, but nothing ready to implement yet.

Our new generator has a hair trigger on its exhaust temperature shutdown which has made this problem more obvious.  Occasionally, and only when we are sailing, the high exhaust temp triggers a shut down right after it starts.  A second start try and it runs fine. If I crack the lid of the strainer and purge the air, it never happens. 

Short of closing the sea cock, I can’t think of a way to keep the air out, so I am trying to figure out a way to easily purge it.

Bill Kinney
SM160, Harmonie
Fort Lauderdale, FL, USA


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Tom Peacock
SM 240 Aletes
Chesapeake Bay

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