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Old 10-11-2023, 14:47   #1
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Connecting Outboard to Inboard Gas Tank?

Hi again. Well, I've just finished my first season running with an outboard engine (Suzuki 9.9) on my Northern29 with mostly happy results. The A4 that it replaces now lies dormant though will have it's oil changed seasonally in case some future owner can resuscitate it. I've already explained in previous posts about why I made the switch so fixing the A4 is a non-starter here.
Anyway my boat has a 40l internal steel gas tank that I believe is still in good shape so I'd like to use that for fueling the outboard instead of the standard portable jerry can that came with the outboard. Advantages as I see it are greater range without refilling, no more gas can sliding around the cockpit that needs refilling on the go plus weight a little more forward (with the internal tank).
I plan to flush the gas tank to try and remove any sludge or water that may be there then direct a new gas hose from the tank to a water seperating filter then maybe another polishing filter plus squeeze bulb, plus connector to outboard. The tank sits at or just below the height of the O/B fuel pump. It doesn't have an inspection port and would not be easily removed from the cockpit locker for cleaning or replacement. I will still retain the functionality of connecting the external gas tank. I may also install some form of polishing circuit with pump to manually circulate gas through additional filters to further clean the fuel.

If anyone here has replumbed their sailboat's internal gas tank in such a way I'd appreciate your advice on this.

Thankyou
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Old 10-11-2023, 15:03   #2
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Re: Connecting Outboard to Inboard Gas Tank?

I did mine from the start like you are trying to do. New boat of course so I didn’t refurbish but the concepts are the same.

First, make sure that steel tank is good. Any leaks and you are in a world of trouble.

Definitely use the proper fuel hose. The really good stuff. most expensive marine gasoline hose you can find.

what I did is I took the fuel line from the inside of the boat at the tank out to a locker on deck. Kind of like a propane locker. In fact it is a propane locker as well. I call it my explosives locker. All connections with the fuel line and propane are in that locker. There is nothing but straight fuel lines right from the tank to that locker. No joins. Safety.

in that locker is a fuel water separator and filter just like you are talking about. I do not have a polishing system because with gasoline it’s not really necessary. it’s pretty rare to let it sit so long that it’s going to turn into different things. Even after years of sitting a little fresh gas added to some that had been in there for years and years ran just fine through the Outboards.

Diesel can get all of that growth and lumpiness in it. Gasoline really doesn’t. Either it’s good or it’s bad. So you don’t really have to polish.

so while I fuel polishing system is good, and I think it’s not a problem to put one in, I don’t think you really need one with gasoline.

my fuel tanks are at about the height of the Outboards as well when the Outboards are down in their active location. My outboards slide up very far on a slide when they are not being used to come out of the water. But when they are propelling the boat the fuel tank and the outboard are at the same height.

This did not work! I don’t know why, but my Outboards could not pull the fuel through the fuel system and out of the boat to run. I had to add a fuel pump in.

this causes all sorts of problems. The fuel pumps don’t last at all if they don’t have fuel running through them. So you must immediately turn the pump off when the engines are off. if you don’t, and you leave it running by mistake, you will end up with a bad pump. And it will go when you are underway next time. It may not go when you are stopped.

after going through many pumps I figured this out.

The other technique to have the fuel pump work properly would be to set up a return line. For you that would be possible because you have only one tank. For me I have three tanks (150 gallons) It was not possible.

Other than that it is pretty straightforward. There is nothing you really have to do that is very tricky. I did just like you are describing. I left the primer bulb in the fuel circuit down by the Outboard‘s. Doesn’t hurt anything. Why not? Might come in handy.

but you’ll have to see if it works. If your outboard can pull the fuel out of that tank and then back down to them. Mine could not.
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Old 10-11-2023, 15:03   #3
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Re: Connecting Outboard to Inboard Gas Tank?

It would probably be best just to remove the A4, the old, steel gas tank, prop shaft, prop, motor mounts, flange, old fuel line and anything else having to do with that old/ancient engine.

Get a new 3 gallon or 6 gallon gas tank and place it close enough to your new outboard so all you need is a short fuel line. (a new fuel line)

My external tank is in the aft lazarette locker so it is out of sight and it is secured. I use it if I need to motor 20-30 miles. I have a 5 HP 4 stroke outboard pushing my 6600 lb. displacement sailboat.

If just getting out of the slip and creek, I use the integral tank which is part of the outboard and never even attach the external tank. Sometimes I have sailed for days like this and covered 100's of miles.

Hopefully one day 1,000's of miles using very little gas.

I normally have at most 3-4 gallons or so onboard at any one time in 2 different containers.

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Old 10-11-2023, 16:15   #4
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Re: Connecting Outboard to Inboard Gas Tank?

Thomm225, about your advice to remove the A4 etc, is it possible that doing so might affect boat handling under sail? Wouldn't that 300lbs+ engine (near the keel) have been factored into the boat's balance design ? Maybe not though as the total weight is over 7000lbs!? I do definitely plan to remove the prop.
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Old 10-11-2023, 16:22   #5
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Re: Connecting Outboard to Inboard Gas Tank?

Quote:
Originally Posted by campbdon View Post
Thomm225, about your advice to remove the A4 etc, is it possible that doing so might affect boat handling under sail? Wouldn't that 300lbs+ engine (near the keel) have been factored into the boat's balance design ? Maybe not though as the total weight is over 7000lbs!? I do definitely plan to remove the prop.
I have noticed no big difference after I removed my 10 HP 352 lb. Bukh diesel in 2011 plus all associated equipment to include wiring, a 20 gallon metal fuel tank, copper fuel line, and all the rest I mentioned above plus the controls and linkage.

I've sailed in winds up to 35 knots and have been at anchor in winds to 45 knots or so.

James Baldwin (of Atomvoyages) removed the A4 from his Triton 28 which he sailed around the world on.

https://atomvoyages.com/atom-html/

He also removed the A4 engine from an Alberg 30 and replaced with a 6 HP Tohatsu Outboard. The Alberg 30 displaces about 10,000 lbs.

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Old 10-11-2023, 17:34   #6
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Re: Connecting Outboard to Inboard Gas Tank?

if you do need a fuel pump to assist getting that gas through the additional filters, or gravity pull, depending on your model suzuki it should be possible to fit a rectifier that provides a 12v signal to a relay that operates the electric fuel pump, this way if you or another operator forgets, the pump will stop when engine switches off, that rectifier could also provide some small charge to your batteries.
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Old 10-11-2023, 18:19   #7
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Question Re: Connecting Outboard to Inboard Gas Tank?

Quote:
Originally Posted by campbdon View Post
If anyone here has replumbed their sailboat's internal gas tank in such a way I'd appreciate your advice on this.

I don't have any advice. I mean, it's like driving down the street. Go for it. Get the tank reasonably clean but don't make a fetish out of it. Make sure there are no vacuum leaks. Use a filter. But you knew all that, right?


Here in the land of 10,000 lakes, in my Misspent Youth (tm), I was aboard any number of runabouts that had outboard motors, built-in tanks, and portable tanks. In general the built-in tanks were put there by design to provide fuel to the outboard, but so what? Same result. We would carry a portable tank as a reserve, and switch as needed.


More recently, I've been on 20'-ish foot fishing boats with modern, larger outboards that are connected to a built-in tank. Modern outboards use far less fuel than the two-strokes of the 1970s and so having a portable reserve is no longer a thing.


So go for it. Be sure the tank is vented. Be sure it's clean. Either use a filter or be aware that the relatively small one in the outboard may clog and carry spares. Modern outboards can handle a reasonable amount of lift but won't pull fuel through a clogged filter. If you start running into problems, put a vacuum gauge on the line. A portable one is fine for troubleshooting, don't build something with the idea that it has to be there forever. If there's vacuum then the problem is the tank, filter, and plumbing. If not, the problem is with air getting in or a bad fuel pump. Some transparent line in the system that allows you to see bubbles will tell you which.



Oh, and I put an outboard fuel fitting on my Jeep CJ once and ran it off the portable tank for my boat, because the fuel tank under the seat was leaking and due for replacement... Fuel lines are fuel lines, no magick



Hope this helps, if not, what is it that you're after?
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Old 11-11-2023, 09:17   #8
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Re: Connecting Outboard to Inboard Gas Tank?

It is just so nice to simplify the whole thing by getting rid of all the old crap (engine, fuel tank, and all associated equipment) then glassing over the old prop shaft thru hull.

Then get a new tank and fuel line and that should solve the problem. Plus the boat will be a little faster without the weight and prop drag.

Also, you can really clean and paint the bilge in the process washing out all the old oil and gas residue which by doing so removes that smell also.
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Old 22-03-2024, 16:40   #9
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Re: Connecting Outboard to Inboard Gas Tank?

Hi All. I have one further question to add to this thread regarding plumbing my outboard to my builtin gas tank. It is whether it's advisable to install a fuel pressure gauge? I'm thinking so in order to visually verify that the fuel lines from the tank to the motor are sufficiently pressurized. Would anyone know what PSI range is normal for a Suzuki DF9.9/15/20 motor? My plan is to connect the fuel tank (with shutoff) first to a water seperating filter (10micron), then to a priming bulb then to the outboard, all using appropriate fittings and standard Suzuki 5/16" hose. I might also add a check valve to prevent drainage back to the tank.
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Old 29-03-2024, 09:21   #10
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Re: Connecting Outboard to Inboard Gas Tank?

Outboards use vacuum to pull fuel from the tank. Some people fit vacuum gauges as confirmation that the filter and fuel pickup are not clogged. With outboards you can just look at the primer bulb and see if it's collapsed.


To be useful a fuel gauge would have to go between the fuel pump and the fuel injection system on your Suzuki. I have no idea what sort of pressure they use.
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Old 29-03-2024, 10:01   #11
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Re: Connecting Outboard to Inboard Gas Tank?

Thanks, Jammer!
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Old 29-03-2024, 10:53   #12
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Re: Connecting Outboard to Inboard Gas Tank?

There is (well, should be) an anti-syphon valve fitt toed permanently installed gas tanks. It takes a fair bit of force to pull gas through the valve. Generally, small outboards don't have enough vacuum to overcome the valve. An aux fuel pump is probably needed.
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Old 02-04-2024, 13:59   #13
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Re: Connecting Outboard to Inboard Gas Tank?

The (existing) built-in tank has, as far as I know, just a vent pipe and the gas line outlet (with shutoff). The hose went to the A4's carb via a facet fuel pump, both located 2-3 ft below the level of the bottom of the tank. The new arrangement would have the outboard (fuel injected) inlet about 2 ft above the tank bottom. In the line would be the shutoff, a (new)check valve, (new)water seperator then (new)primer bulb before the fuel inlet. The bulb and the check valve should keep the gas from draining back to the tank. My Suzuki dealer seems to think the OB's fuel pump should be able to suck through that okay. Suppose I'll find out soon enough how well it works.
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Old 02-04-2024, 15:14   #14
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Re: Connecting Outboard to Inboard Gas Tank?

Gday

I love my outboards on my boat, but it is a cat. I would be much more wary of using any older style fuel tanks in a mono. My fuel is stored in lockers with no ability to have fumes drain into the rest of the boat. Many cats use petrol outboards but they can store large amounts of fuel in the bridgedeck, with fully vented and separate compartments.

I would be very keen to make a separate fuel tank area, that gets vented and has no possible way of allowing fumes from any leaks into the bilge. Petrol fumes and electronics can be a terrible combination. A few pieces of plywood and epoxy would allow you to make a separate part of a locker and then you can either store extra cans (like I do) or install a new plastic tank.
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Old 02-04-2024, 16:30   #15
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Re: Connecting Outboard to Inboard Gas Tank?

Thanks, but I don't see how my proposed setup increases risk due to gas fumes than the original design. The gas tank in question is in the starboard cockpit locker. It has it's own vent line to the outside and (being in the cockpit locker) is already somewhat vented to the outside. My 1974 Northern29 design has the fuel flowing down to the midship saloon level (where the A4 was), which I'd think should surely pose a greater hazard for explosion risk than where I plan to run the fuel lines. I do intend to have a "gas catcher" mounted under the fuel filter in case of drips. Is there something I am missing?
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