above deck fuel tank options/questions

[mikemerrill50]

ok, so there is pretty much no way of me putting a fuel tank below the deck of my boat due to how shallow the bilge is (it doesn't appear there was ever one underneath). so, I am looking at my options for mounting a fuel tank above the deck.

here are the options i have considered, with each option coming to around 40-50 gallons:
1. two above deck tanks, one on each side under a seat
2. two above deck tanks, wedge style, one on each side under the gunwale
3. one above deck tank, mounted under the rear seats (forward of the motor)
4. one above deck mounted in the center of the boat...?
5. several smaller tanks...?

I have a question:
With having multiple tanks, I have been told before in the past, on here and other places, that you should not connect them. I have also been told it's against CG regs. Is there reasoning for this? Do you recommend against it anyways? If I do have multiple tanks, should I get a fuel switch to switch between tanks? If I go with two tanks, I wouldn't want to run on one until it runs low, then have the boat completely off-balance.

I have a few worries about those options.
1. One of course is weight distribution. This is actually one of my main worries about this project. What do I need to take into consideration with weight distribution? Is it ok to mount a tank near the stern, or is it too much weight when combined with a motor?
2. On similar lines, I'm worried about stability. I like to ride in rough waters, and I will be using this boat for some slightly offshore (just to 3nm) trips as well as intercoastal waterway. Would having the wedge styles in the gunwhales make the boat too top heavy? Would putting any tank above deck make it too top heavy?
3. Noise. I don't want to hear the fuel sloshing around the whole time. Of course, I know I can eliminate at least some of this with insulation or soundproofing.

Do you have any other ideas for ways to do this?

Thank you always,
Mike

pictures:
http://rides.webshots.com/album/530653041gHTxRa

 

[reelfishin]

Re: above deck fuel tank options/questions

Other than the fact that your boat appears to be an open bowrider, it looks similar to my Renken 19'. Mine has a single 40 gallon fuel tank mounted at the bow just ahead of the dash, at floor level. Mine also has a place to mount one though in the floor, but I used that space for a livewell now with a giant single lid. I like the weight distribution of having the tank way up front, it offsets the weight of a 400 + pound outboard and I am sure helps me get on plane. The former owner had removed the tank and had intalled two removable tanks on each side of the motor, it not only was not enough capacity, but made the boat too heavy in the stern. With the tank up front, I have to be less concerned about loading or where people sit. It also improved my fuel consumption greatly. I am now in the process of upsizing the front tank a bit since I came across a slightly larger tank, and I want to move the fuel fill off to one side as well. It's tough to reach in the center and makes for some interesting plumbing below.

 

[Mark42]

Re: above deck fuel tank options/questions

I think two saddle tanks would work very well with that setup. That boat has wide gunnels that work well with saddle tanks.

BTW, my tank is right under the dash and I don't hear the gas sloshing around over the sound of the motor and water.

I don't recall any regs against connecting the two tanks, but the best practice is to read about it yourself here:

http://www.uscgboating.org/

 

[mikemerrill50]

Re: above deck fuel tank options/questions

reelfishin, thanks for your reply. i thought about putting a tank up front, but i'm worried about being able to underneath the bow seats.

mark42, so you don't think it would be too top heavy/tippy? That's really the only thing I'm worried about. Although, when I think about it, if there's an even amount of fuel in each tank, the boat should be balanced well, even if the weight is high, right?

Thanks,
Mike

 

[reelfishin]

Re: above deck fuel tank options/questions

With a boat like yours your options are limited. Putting the tank forward would not work on yours, and the bow seats just don't have enough room underneath.
Most that I see have either one or two tanks at the rear corners, I have a 73 Starcraft trihull that has a single 20 at the right rear. It works, but they could have put the battery on the other side to balance the load a bit. They left the left rear wide open for storage.
If it were mine, and I had it all apart already, I would probably look into a huge belly tank of somesort, even if I had to weld one up. You could probably make a long flat tank that sits dead center with a through the floor fill. I've seen a few Welcraft fishing boats set up that way. If your not into the welding, ask around and see which welding shops do tanker repair, they should be able to custom make something for you. Just don't forget to add a vent, a ground strap, and a gauge sender. Even if it's just an aircraft style float and gauge.
Baffles in the tank will cut down on slosh, and I would strongly recommend them in a longer tank.
An aluminum tank will be your best bet for weight and affordability, stainless is heavy and harder to weld and quite pricy in heavier gages.

That boat looks pretty well built with that many stringers, the last one I did only had three, with a few crossbraces. You could most likely modify an area in the center to allow a long narrow tank.

As far a hooking multiple tanks together, I just stripped out a SeaRay that had three tanks, they were all connected to a single 4 way port at the fuel filter, only the front tank had a gauge. They had to be factory since I had to cut the upper deck section to remove them. My last boat had two 80 gallon tanks that were both connected together at the filter, they had separate guages, but were both drawn from at the same time.
There may be a regulation as far as joining them in series, or using a common fill point. There would be a problem with safety as far as the type of hose that linked them as well as posible ground spark or fume concerns. Always make sure that you tank and fill neck ring is grounded, the nozzle tends to spark when filling, especially with plastic is involved.

Look at it this way, you are only doing this one time, after that your going to have to live with your decision, so picture it in your mind how you want it to be, and do it that way, what ever it takes.
I don't know if I would like having the tanks on each side, not just for weight distribution, but for cosmetic and space purposes too. If you do custom build a tank for the floor, make sure you leave a way to get to it to inspect it or simply to access fuel conections. A buddy of mine did his floor, and failed to put back all the access panels that were in the old floor, when the fuel lines began to leak, he realized why the factory had those panels there.

 

[tashasdaddy]

Re: above deck fuel tank options/questions

mike, i'm very familar with that boat. true there is no room for an under deck tank. i would use gunnel area for storage, batteries, under each side of console as a foot rest. 18 / 24 gallon tank under the motor well, and 2 tanks under back to back seats. the batteries in the front helps balance the weight of the big tank under the motor well. run on the tanks under the seat first..

that boat was originally designed to be a family boat with 2 6 gallon tanks, and battery under the motor well.

 

[mikemerrill50]

Re: above deck fuel tank options/questions

reellfishin,
I looked into having a tank made for underneath the floor, but there really isn't any room. I'm hoping to push around or over 30 gallons in it. Believe it or not, there's actually enough room to do them under the gunwales. The tanks only go about 8 inches out at the top and 5" at the bottom, which would be fine with the seating I am doing.
However, putting a tank under the rear seating would be ideal for me. The problem I see here is weight distribution. At least with side-mount tanks, I could mount them in the center of the boat for equal distribution. In the rear, I see problems with planing. It would take alot of stuff in the bow to balance the weight of 20 gallons (or 30!) in the stern, along with the motor.

tashasdaddy,
I still worry about having too much weight rearward with that setup. I also would like to have a setup in which fuel is drawn equally from the tanks. I would like to just buy the seats for the boat, and I cannot find a fuel tank that will fit completely underneath any of the seats I can find. I guess I could get custom fuel tanks mounted that would fit underneath those seats to go with tanks mounted under the gunwales, but I want to try to keep the tanks plastic if possible.

Would it be ok to have a 20 gallon tank in the rear?

 

[reelfishin]

Re: above deck fuel tank options/questions

You have to make that call yourself, as far as what will fit where since you have the boat in front of you.
Depends how high on the sides the tanks will sit how much its going to affect the center of gravity. My concern would be making sure both empty at the same time, what if one tank was lighter than the other? It can be tricky getting two to draw at equal rates. fuel line length, diameter, fuel filter/fuel control blocks will all have to be figured into the plan. I ended up having to restrict one tank slightly on my last boat to get both tanks to empty equally.
Twenty gallons at the rear will be quite noticable in a small boat, the farther forward you can get the tanks the better as far as getting on plane.
Myself, I like extra fuel capacity in all of my boats, I hate not having at least 40 gallons on board and even then I carry a reserve tank.
My one trihull is in the category of 'No other choice" and runs with only one right side rear 20 gal. tank. It's good on fuel and I don't go too far in that one, so it's not a major concern. On that I have no floor area since the hull has two high spots on each side and is flat towards the rear. The seats are pedestal type and the forward storage boxes are barely large enought to shove a few life vests in. The gunwales are narrow and anything that sat there would be under toe while fishing and restrict side access when boating a fish.

I stripped one boat a few years ago for parts, it was a mid sixties 15' lapstrake hull like yours made by Crestliner, a former owner had gutted it for fishing, built a platform up front to fish from, then placed a forward 30 gallon tank underneath, then pulled up the floors, boxed and repositioned the center stringer and welded up a v shaped tank that ran from the dash to about 6 inches from the transom. It was about 6 inches deep in the middle and about 2 at each side and maybe 18 inches wide, but it was nearly 7 feet long with the fill in the floor, a vent the exited the forward edge and went to a through hull vent just below the rub rail about midship, and the fuel was drawn at the rear top. I was going to save it but never got around to it, he had foamed in and it was made of plain steel and painted black, and it had been used in saltwater for a few years by then. That tank had to be at least 30 gallons, if not more. I never tried to fill it and check, but I remember pumping out three or four 6 gallon gas cans full from it.
The boat also had it's original tank, a 6 gallon metal Evinrude tank strapped and rusted to the floor on right side of the engine. I guess they figured it was too much trouble to remove. The forward and mid tanks in that both had separate lines and fittings, I guess they were just manually switching tanks, but I guess it worked. Both those tanks had fuel in them. I had stripped that boat a few years ago, I wish I had pics of it to show you, it did look somewhat professional, at least as far as the tank and stringers, the floor was another story, they used indoor plywood and scrap foam as filler, so that part looked bad, real bad. The cut stringers were boxed, gusseted and bridged, so there was no real loss there. Besides, that had all been done long before I got it and stripped it for it's motor and controls.

 

[tashasdaddy]

Re: above deck fuel tank options/questions

Mike, i have to ask what are you wanting to do with this boat? it really sounds like you are trying to rig it for something it is not and will not be safe for.

this is my fishing boat, inshore and off shore. 18' it carries 22 gallons, with a 90 hp Johnson, i've never used more than 18 gallons in a day. i does have a belly tank and it is a very deep v hull.

 

[mikemerrill50]

Re: above deck fuel tank options/questions

reelfishin:
thanks for the input. the high center of gravity is what worries me about the gunwale setup. The tank would go about 18" higher than the floor, which worries me. i am like you in that I want lots of fuel capacity. However, I may just settle for less. I may go with smaller tanks, maybe under the seats. Even though those will be above-deck, they will at least be low to the floor.

Admiral:
I want to be able to use this boat for a variety of purposes, including creek riding, fishing, playing, and riding to about 3-5nm offshore. Here, 3-5nm offshore is not typically that rough, but it's not flat either. I like to ride to new areas. The reason I want high capacity tanks is so I can ride up the intercoastal waterway. I like to ride far up to areas I haven't been before. I also just simply like the idea of having plenty of fuel. I would be putting about a 115-130 on the boat, so I know it will use a bit more consumption. I'm leaning towards just going with 20 gallons or so, but if I can take 30 gal with the boat still being safe, I will do it.

 

[Yacht Dr.]

Re: above deck fuel tank options/questions

mike..lo m8..

Now that I understand your delema of going far far away from port I can mebbe put in some 3 cents..

Trust me..I realy do understand you wanting to go 300 knots without changing/adding fuel ( not like you dont have loads of marinas to refuel on the way..no you want or have to go go go )..oh no..I do understand. pulling into a gasup can cost you an hour with no wake zones..

So... my solution would be instead of modifiying your tanks and where..and how..just do it simple..

put your tanks ( couple 10 gals here and where you should get them accessable ) and just fill up some 5-7.5 gal fuel jugs and stash them where you want your ballast to be..( along with some 20 gals of water and canned beens just in case your motor takes a crap ) .. you know ?

Id rather have 20 gals of H2O than 20 of firebreathing gas on my runner when things go wrong...

Thats just an ol' boater talking though..

YD.

 

[eli_lilly]

Re: above deck fuel tank options/questions


I use two 12g portables under the splashwell of my 17' closed-bow fish/ski and have never had a problem getting on plane. It's only about 170 pound of fuel, less than the weight of a single person.

-E

 

[mikemerrill50]

Re: above deck fuel tank options/questions

yeah, i started thinking about that. 25 gallons of fuel weighs approximately 150 lbs. maybe I will just put it in the rear with everything else towards the front...