Overpropped...But Why?

[Nomad Willy]

Hey Dan,
Don’t polish it .. burn it.

 

[Sidclark]

"Once I have clean fuel I'll update the speed/rpm numbers..."#88

Would be lots quicker to just borrow an outboard tank and hook it directly to the injector inlet .

Gain a few hundred RPM underway , the cleaning will be worth the effort.

That's a great idea with the outboard tank. I can do that while I wait for the absorbent pads to be delivered.

Ah yup, the benefits of an installed fuel polishing system. You can use a 2 micron filter to capture everything of importance.
What are the condition of your on-line and type of fuel filters?
How is the fuel supply to your generator? Can you successfully load up the generator?
Let's start small. Cycle all fuel isolation valves a number of times to break up any crap at the valves. Next, remove the hose between the tank and the the secondary fuel filter (for now we shall deem them Racors) A bit of air pressure reverse blow .... collect this fuel into a bucket for further inspection. Next, fuel polishing and tank inspection, cleaning the tanks as necessary. Okay, that's the easy stuff.

I've changed all the filters and they're clean. I have a Racor duplex for the primaries. All the valves have been cycled numerous times. Since the filters are clean I believe the lines are clogged before the filters. The starboard tank is so clogged I can't get fuel to the polisher. With this last run it looks like the port side is well on it's way to a full clog also. This doesn't surprise me with the fuel being so old in the tanks. But yeah, once I'm done the tanks will be clean along with every line having been blown threw with compressed air.

 

[OldDan1943]

Hmmm, are the supply lines coming from the bottom of the tank? If so, when you removed the line, do you get a flow out of the bottom of the tank?

 

[Sidclark]

Hmmm, are the supply lines coming from the bottom of the tank? If so, when you removed the line, do you get a flow out of the bottom of the tank?

Using dip tubes, the supply lines actually exit about two inches below the top of the tank. I'm not sure yet how far the dip tubes are off the bottom of the tanks. The absorbent pads should be here on Thursday, then I can start taking things apart and checking flow. The tanks do have drain valves about an inch off the bottom. Will be curious to see what comes out.

 

[Xsbank]

I believe that one of the reasons to over-prop is to provide a bit of a load on the engine in its regular cruising rpm range. If you have a 300 hp motor and you use only 75 hp to get your happy speed, overpropping loads it a bit so you don’t glaze cylinders.

 

[Sidclark]

An update as to progress on the fuel system. Running the fuel line to a five gallon gas tank was a great suggestion so that's how I decided to proceed. I took the fuel line off the Racors and that's when I noticed the fitting at the fuel pump seemed really loose. The fitting comes out of the pump then there's a 90 degree elbow then another fitting to the fuel line. I could turn the fitting 1/8 of a turn and it would tighten up. Turn it 1/8 of a turn the other way and it's just plain loose. Not good at all. I removed the fitting from the pump in order to put some pipe dope on it before I reinstalled it. That's when I noticed it was a flare fitting. I didn't think that seemed right so I called Brian up at American Diesel and asked him what the proper fitting should be. Sure enough, it was supposed to be a flare fitting, but and this is a big but, the proper fitting for that fuel pump has a longer then normal flare portion. The fitting that was in there never sealed at the flare portion, but bottomed out at the "nut" portion of the fitting. There was never a good seal and with it being loose, well that answers lots of questions. Take a look at the picture to see the difference. It's a very small difference indeed. Proper fitting is on the left.

So while waiting on that fitting to arrive I transferred fuel from the starboard tank to the port tank using the Gulfcoast polishing system. Worked like a charm. Opened up the inspection port and inspected the inside of the tank. Looked pretty good. The tank was slightly sloped towards the inspection port and in that corner I removed maybe a cup and a half of diesel "mud". The tank was rust free except for a small portion at the top. There was a light coating from where condensation had formed. Maybe two square feet total. The tank did not look to be original. With that side clean, the polisher then pumped all the fuel back into the starboard tank. The port side tank was much the same so it was cleaned and buttoned up. I had the polisher then pump over to the port side tank to even the levels out. So' I'm really happy about the condition of the tanks. They'll probably outlast me. And the fuel, well, it's been polished almost three times now. I don't think it could ever be any cleaner!

Installed the new fitting when it arrived and changed out the fuel line as well. Since I also changed the secondary fuel filters I knew there was some serious bleeding of air ahead. After about five minutes of pumping that tiny little lever, I thought there had to be a better way. I started looking at the polisher and thought maybe I could arrange the valves in such a way as to use it to send fuel to the filters. It worked. Five minutes later everything is bleed and it's time to fire up the engine. It took about three tries, but she fired right up. Shut her off and tried again. This time took about two seconds and she was purring.

Took her off the dock to run down the river to check things out. I was going to run the RPM and speed numbers, but didn't have the time. I did run her up to WOT and she held at 2300. Remember, before she won't hold 2000. The engine just sounds better too, if that makes sense. Next week I hope to get the RPM and speed numbers again and then decide if I should live with this prop or tweek it. WOT should be 2600. I'm thinking something closer to 2600 should be better for the engine. In the meantime, I'm really happy that I've got a thoroughly clean and inspected fuel system!

 

[FF]

"I'm thinking something closer to 2600 should be better for the engine."

It would be IF you constantly operated near that RPM. Tow water skiers?

Most cruisers prefer about 1K under theoretical hull speed to cut the fuel burn in half.

A 36 ft would run about 6.5K , or for your dock mates 8 (statute MPH) for bragging rights..

 

[Willin]

+1. This is trawler forum after all. Trawlers are f’n slow so don’t need much hp to go 8 knots. My FL powered GB doesnt even pull 2400, but I only cruise at 1750. The “over propped” propeller allows me more torque where I need it, lower down the power curve when I bump the throttle to turn the boat for example. I had a pumped up diesel with after cooler on an earlier boat and I was careful to underprop it a bit because I was using a lot more of the power to make the planning hull go fast.

 

[catalinajack]

Why not use those drain valves as a new supply. No more dip tube problems. But, if you have built-up crud/mud that is above the level of the drain valve, then you still have a problem. Perhaps that drain valve could be used as the draw for a polishing. Bottom fuel feeding is far superior to dip-tubes for obvious reasons.

Using dip tubes, the supply lines actually exit about two inches below the top of the tank. I'm not sure yet how far the dip tubes are off the bottom of the tanks. The absorbent pads should be here on Thursday, then I can start taking things apart and checking flow. The tanks do have drain valves about an inch off the bottom. Will be curious to see what comes out.

 

[Comodave]

Congrats on finding the problem. All it takes is time and money. Have fun with it.