integral fuel tanks - construction

[pescaloco]

hello, all
my plans are to build integral fuel tanks in my 27ft sportfisher, in a saddle type configuration. the tanks will be out board of the stingers, esentially built into the hull sides and bottom. the plan is to use divnycell 3/4 foam, poly resin 1801 nytex and 1 oz matt as materials, to construct tanks and coate inside with isotholic gelcote, the tanks will hold diesel fuel 100 gallons each.

what I am thinking is to make a full box (all 6) panels out of foam and glass with stainless steel fittings laminated inside the tank. having never done fuel tanks like this before I know it has to be done perfect, so any advise or publication on the subject you all could provide would be very much appreciated.

thanks, mark

[dougfrolich]

I would not use Poly Resin for this.

[jimslade]

I'm not a fan of built in tanks. separate tanks are better.and safer.

[Mikey]

Vinylester, poly resin should not be used for integral tanks

[pescaloco]

Thank you for the replies, I am going on a suggestion, but am certainly open for others. The point of the integrals is to provide additional hull structer & stregenth,and avoid the pit falls of non servicable aluminum tanks, also being a home builder it is just one more thing I can do my self.
The engine compartment bulk head is 142" from the transmom wall and it is a wide hull 8.5 ft at the water line 9.6 to top of the sheer, so I need support and stregenth for the hull sides and deck. so given all these factors the integrals seem to make sense.
If you have any other advise on how do this sucessfully, or a different plan would like to hear your thoughts on the subject.

thanks, mark

[dougfrolich]

Repeat:
If this is a Gasoline powered boat, be very carful with your choice of resin, ethanol or alchohol in ethanol is a real problem with all types of FRP fuel tanks.

[SamSam]

You're sort of playing with fire. At 100 gals diesel, the weight will be almost 700 lbs, so you have to design to prevent sloshing and I don't know what else. This book has a chapter on making fiberglass tanks...
http://www.boatdesigns.com/prodinfo.asp?number=12%2D435
and this site...
http://newboatbuilders.com/pages/fuel.html
has info and links to AYBC, Coast Guard and others. The owner of the site, Peter Eikenberry, is a member of this forum, so maybe you could chase him down and ask more questions if you have them. Sam

[Ike]

Thanks Sam, I have been sort of lurking in the background of late;

Well, I too am not a big fan of integral tanks, although they are allowed on diesel boats, but not on gasoline powered boats. Additionally with all the problems with fiberglass tanks these days, I would be very apprehensive about building them. I prefer roto-molded polyethylene, but they aren't seen much on diesel boats and you get into the baffle problem.

If you need to reinforce the structure I would just do that, and then install some premade tanks that have built in baffling. You're talking about a lot of fuel sloshing around in a 100 gallon tank. And if you build twin tanks, then you need a cross over valve to equalize the weight on either side, and a selector valve for selecting which tank you are drawing from, which you will need no matter what material you build in. Aluminum is a good choice, because the baffles will be built in and if you install them correctly (lots of air space around all sides, top and bottom of the tanks) they will last 20 years or more. And you can buy aluminum tanks off the shelf from quite a few tank makers, just tell them what size you want, such as Florida Marine tanks or RDS. There are others. A google search should find them.

[pescaloco]

thanks, for the replies (Ike thanks for the links, will check them out)
the plan on the tanks is to have several baffles, solid panels in a more or less rectangular box (the shape of the tanks) then whole sawed cut outs in the ceneter, with the bottom corners cut off at 45 degress (2 or 3 baffeles like this should work quite well)

my main point of concern is if a person does go with integrals
is it ok to support the decking on the top of the tanks?
and how are the vent and pickup and cross over fittings installed and sealed for a one time no problem installation.

mark

[dougfrolich]

http://www.proboat-digital.com/proboat/200612/

There is a brief discussion here re intergal tanks.

[pescaloco]

thanks, doug