above or below deck fuel tank?

[thehermit]

I have a project boat with the deck completely off (22' in length). I am considering a below deck tank but dont really have a heck of a lot of room. I am also considering a 24 gallon above deck tank that would fit in the console.<br /><br />My question is...Is a below deck tank worth the extra effort (and MONEY) to lower the center of gravity of the fuel? Should I be woried about venting/fire/leaks? I was looking at plastic tanks for either application.<br /><br />Epinions welcome!

 

[JasonJ]

Re: above or below deck fuel tank?

Well, the advantage of a below deck tank is it is out of the way. If you do it, you should create an access hatch for removal or repair at a later date. If you go with a poly tank, make sure to follow the instructions to the letter. You can't foam them in because they can expand up to 3 percent in all dimensional directions as they cure from fuel exposure, so you have to make sure there is room. I went with an above deck tank, easy to mount and deal with, and if the fuel gauge goes south I can just look over my shoulder and see the fuel through the tank. Good luck...

 

[thehermit]

Re: above or below deck fuel tank?

JasonJ,<br />Nice call on the expansion of poly tanks. Do they tell you about this when you buy it? I did not know that the other boat I have has a below deck poly tank mounted above deck. I dont think that changed much in dimension but if it did I wouldnt have noticed. On Access. I had planned on possibly framing the surround of the tank so it could be cut out removed and replaced but with no hatch. Looking at it again this morning I think it will come down to room. But I got to tall ya the one thing about the last rebuild I did is if I want to head out for a full day I need to bring additional 6 gal jugs which take up valuable deck space.<br />...still on the fence<br />Jason...what about lowering the center of grav and the effect on the ride/turning?

 

[18rabbit]

Re: above or below deck fuel tank?

A general rule of thumb for fuel tanks is ‘low and in the center’ for stability reasons. There may be some advantages to moving the placement fore or aft on planing hulls. JasonJ makes some very good points. And synthetic fuel tanks are growing in popularity for good reasons. Since you are doing the work yourself you can build an access plate over the whole tank area for future removal. A smaller access plate for the fuel pickup line and sending unit is no big deal, but like JasonJ mentioned, maintenance of the fuel tank is something you are going to be doing, no matter where your tank is.<br /><br />If you install the tank below deck, you can come back later and add that 26-gal above-deck tank should you decide you need the extra fuel/range. That way no fuel tanks are ever left sitting on deck. <br /><br />Venting the below-deck tank is no big deal. If it is possible for fumes from the above-deck tank to drift below deck, you may need to install a bilge blower regardless of what you decide.<br /><br />Good luck! <br /><br />Note: if you do install below deck, remember to leave enough room between the tank top and the bottom of the deck for the pickup hardware, anti-siphon gizmo, sending unit, stuff like that.

 

[JasonJ]

Re: above or below deck fuel tank?

My poly tank, which is a Moeller came with instructions that detailed expansion, but there has been little total expansion that I have seen, but its only been a few weeks. I don't know the timeline. Yeah, the lower the weight and center of gravity, the better the handling. You need at least 2 inches above the tank top for hardware, hoses, etc.

 

[Winger Ed.]

Re: above or below deck fuel tank?

I'd put it below the deck if at all possible.<br />Then, with strap clamps or whatever to hold it, but still be able to take it out and dump/flush it if you ever need to*.<br /><br />* <br />We filled a 60gal. under the floor tank that was foamed in once with gas that we got a a old station, and the station's tank was almost empty. The skimmer in it delivered us about 6 gallons of water and a gallon of sand. <br />*<br /><br />After overwhelming the seperator & filters, it turned into a real bear to clean. Being foamed in under the floor, I had to do everything through the fuel guage sending unit hole.<br /><br />I sure wished I could have taken that thing out and flushed it............

 

[thehermit]

Re: above or below deck fuel tank?

OK so dont foam it in, leave access, and vent. I plan on a 3" pvc chase tube under the pilot house to the stern. This should provide plenty of fresh air. I am looking at a tank that I can incorporate into the pilot house and build it 1/2 below deck (house covers hole-deck self bailing). Or they have a V-tank that I may be able to get under there. Then there is always a custom tank but I'd rathere not. There will only be about 8" below deck and with 2" recomended clearance well it may be tough. <br />Rabbit the problem is a center stringer creating only the 8" space.<br />hermit

 

[E. E.]

Re: above or below deck fuel tank?

Hermit, I'm in the middle of doing the same thing right now. I'm installing an in floor tank wit a 5 stringer setup. My plans are to have the middle stringer go from the back of the boat to where my tank will be. I will run a stringer brace across from the stringers on each side and end my center stringer into that brace. I'll have a void where my tank will set and then in front of that, I'll start my center stringer again. You could compare the setup to a window opening in your house's wall studs. Just framing around the window.

 

[thehermit]

Re: above or below deck fuel tank?

EE,<br />You are going to "cripple" a stinger? I thought of this too is it a good idea? I had thought I could do a bulkhead on either side of the tank. EE how big is your boat? I am going to a budys house to look at his tank (he has hatch off) on a factory boat. It too is in the center. <br /><br />Cripple a center stringer? Epinions????

 

[E. E.]

Re: above or below deck fuel tank?

Hermit, My boat is a 19'7" 1967 Kenner Ski Barge. In my opinion, I think that the cripple joint will be fine. At least this is my plan unless someone convinces me that this is unsafe. There will still be the 1x before and after the tank and I will also be putting in a 2 part foam that was not there before, and that will add to the structure. I'm using the 1x's in the rest of the floor due to a post here that I read about the 1x's being enough structure and 2x's adding unnecessary weight. Here is a look at the stringers right before the deck removal was complete.<br /><br /> http://f2.pg.photos.yahoo.com/ph/skibarge1967/detail?.dir=/d36f&.dnm=fe11.jpg

 

[thehermit]

Re: above or below deck fuel tank?

EE,<br />My stringers are 2x covered with roven woving. Creating a cripple joint would give me plety of room for a tank. I would think it would be wise to keep the lenght of the tank down. Have you thought of nothcing the center stringer?

 

[E. E.]

Re: above or below deck fuel tank?

The tank I have to be installed is 24 1/2" wide by about 48" long. It's not too long and I was planning on 3/4" ply on the deck so this 24" span would be strong enough. It will also be under where my console will be so not much traffic will be on this particular spot. I'm not sure what you mean by notching. Are you referring to notching my cripple joint to the outside stringers?