Mechanical Sight Gauges

[skinners1]

1985 61 MYNot able to measure at this time. Does anyone have knowledge of the length of the mechanical sight gauges for the forward and aft fuel tanks? I believe they are 1.5”npt and suspect by my memory that they are 36”???

[cww]

I would like to know the same thing for my 1981 53' MY.

I have called Sams two or three times about this but they won't sell them to you unless you can tell them what length the originals were. I explained that I have no way to know because the former owner threw in the towel (these gauges don't have a good reputation for reliability) and tossed them out and capped the holes. He said his intent was to install gauges that you can read at the helm, but he never got around to it, so it has nothing at all.

I want to put them back since I have no way to know how much fuel I have onboard. About 6 months ago this created a pretty interesting situation where I ran out of fuel, lost one engine, and almost hit a bridge. Since then I just fill it up a lot just to avoid that, but I hate carrying all the extra fuel around because the boat runs slower on plane and burns more fuel. Any help would be appreciated.

[Sadey]

Just pull the caps and put a measuring tape down the hole for the correct length.

[bostonhatteras]

I have purchased these Rochester Gauges through E-COMPONENTS #804-462-5679 www.liquidlevels.net I was able to order custom lengths and also in the 8420 series which is 100% brass construction. They are sight dial with leads for remote 240-30 ohm gauge

[SEVEN]

I remove and clean mine about once a year to prevent the float from sticking. I’m guessing but I think they are 18”. I’ll be at my boat on Tuesday. I’ll pull one and measure it unless someone else replies before I get to the boat.

[jim rosenthal]

What Sadey said- just dip the tanks with a measuring tape or stick and give them that dimension. I think they allow an inch or two at the end so the gauge doesn't bottom out as you are trying to screw it securely into the top of the tank.

My fuel tank gauges are the ones which came in the boat. They read low, but predictably so, and I've had her long enough that I know the correction. Or I think I do.

[Sadey]

Sam’s sells the mechanical floats with leads for helm gauges. I believe they are brass as well.

[cww]

What Sadey said- just dip the tanks with a measuring tape or stick and give them that dimension.

I thought about doing that, but how much room are you supposed to leave below the sensor and the bottom of the tank? There's usually a margin built in so you still have a fuel reserve after it reads empty, does anybody know what that translates to in terms of how far off the bottom it's supposed to be? I would need to know that to know what length to order.

The easiest solution would probably still be if somebody else with a 53 MY could measure theirs for me, I'd really appreciate it, and will gladly take you for a boat ride / buy you and the wife dinner / etc., next time you're in the area as a thank you.

[Sadey]

I think you’re over, thinking it. If you measure to the top of the threads, call Sam’s and they will tell you what the proper one is for your measurement. As far as accuracy of the gauge and what’s left in the tank when it reads zero, that’s not something I would ever trust the gauge for. Even in modern airliners we still use time flown/fuel burned as a double check against what the fuel gauges read. It’s a requirement and has saved many a pilots and passengers ass. I know other people on the forum have removed the fuel gauges and took the time to add fuel while marking a dip stick. Excellent technique but takes a little time to stick the tanks on the fly.
I personally filled my tanks as full as I could then went on a long trip using the boat as I normally would, hull speed, generator running and the every few hours throttle up for carbon burn. First chance after a number of hours run and on multiple trips for accuracy I filled the tank back up and just did the math. Time run vs. fuel burned. Distance doesn’t matter because wind and current will change, but a throttle setting and the time it’s been at that setting is constant. I’m assuming since you have a motor yacht you’re running at one particular speed, maybe hull speed. Use this method to get an average fuel burn, mine is around 10-12/hour but I plan 15 and there in is my reserve.
I would never run these tanks down to even close to empty. Mine never go below 1/3. I’m sure there’s a ton of crap at the bottom of these tanks that won’t play nice with the racors. The other issue is the generator. I’m going to assume that there’s a standpipe that won’t allow the generator to run the tank below a certain level assuring you always have fuel for the main power plants.
Hope this helps. I am by far no expert on these boats but I’m learning.