Custom Ballast Tank

Okay so I have an 85 Sun Sport and I'd like to build a custom ballast tank using marine grade ply and fiberglass/resin and whatnot. Basically I want to construct a box to my specific dimensions to fit under and sorta behind my rear bench seat, then fiberglass in the box to make it airtight. I'm obviously going to have fittings for fill, empty, and overflow glassed into the box as well.

I'm very inexperienced at fiberglassing and stuff like this so I was wondering what advice you guys have. How do you suggest getting the box completely airtight (aka how will I get the last side of the box closed up)?

What materials do you recommend to do the fiberglassing/sealing? I've found some sites with the ply but I was just wondering if anyone has any suggestions for good deals they've found in the past?

Thanks for the help guys!

What about something like this?

http://www.plastic-mart.com/class.php?cat=33

They have many different sizes available.

My thoughts....

1. Would it be quicker and easier to purchase and install a large ballast bag? When filling, the bag will conform to the shape of the compartment.

2. Essentially, you'll want the interior of the box protected from water as well. So, just because you use marine grade plywood, the interior of the plywood will still need to be protected. That'll be tricky. My first thought would be to cut all your plywood pieces, then fiberglass the interior side of each individual piece. Then assemble and seal the box with the pre-glassed interiors. And finally, fiberglass the entire exterior of the ballast box.

With that said, I'm not sure you'd see any benefits of using actual marine grade plywood since it'll be glassed inside and out. You could probably get away with regular ply, or even MDF for that matter.

Another option would be to cut all your pieces of plywood, and assemble most of the ballast box. Leave off a panel large enough that will allow you access to the interior of the box. Apply an epoxy paint to the entire inside of the box, as well as the interior of the final pieces for assembly. Get the paint everywhere, even as you're attaching the final pieces of the box. You want to make sure the interior is really protected. After final assembly of the box, fiberglass the exterior of it. There are guys that build fish tanks out of plywood, and finishing/protecting the interior of the aquarium with epoxy paint.

As far as needing experience for fiberglassing, don't sweat it. Not a big deal.

Its REALLY hard to make something out of wood and fiberglass that would be 100% leak proof. Its really not that hard to build a box and buy a sac to put in it, like scott said. Check out my link below for some ideas. Jet

I agree with all of the above.

To build a water tight compartment, you would need to prelaminate all of the inside surfaces of the box parts, and then you would need to be able to get inside the box to tape the seams for best performance. There are methods for joining panels without fiberglass laminate tapes, but leaks are likely.

A simular box could be fashioned to support a bag, and it would require no fiberglasing, and would not leak, as Jet suggested.

I think the bag suggestion offers less risk, less effort, and better performance.

My $0.2

I agree that building a box to hold a bag would probably be a better option, however I was hoping to come away from this as cheaply as possible. I can't use just a straight bag only because of the support problem for the rear seat.

I've looked into the custom plastic tanks that certain companies will do but I'm just exploring the idea of doing this in the hopes that it's cheaper.

Thanks for the input guys.

Also, there aren't really any bag shapes that are perfect for underneath that rear seat. Some fit, but when anywhere near filled they bulge the three seats and so by the time I would construct a box that would constrain the proportions even more, I would be losing more and more weight.

Keep a couple things in mind here.

1. Unless you want to rework the rear seat back cushion size and mess with the vinyl, you need to conform to the rear seat base dimensions.

2. I'm not sure if you've ever pulled your rear seat, but the gas tank is right behind it, which will limit you utilizing that space. I think the 85 has a built-in ski locker rather than a plastic drop in, right?

3. If you do it correctly, you can build a frame out of 2x material to serve as the new seat base tat is completely open. The standard 400# bag that Skiers Choice uses in Moombas and I think some Supras will work well in this application. The bag measures 10" x 17" x 70". It should fit the space quite well and weighs in at around 400# full. You can use the same bag in the ski locker for another ~400#. There is also a bag size that is really close that would work well...check out this link: http://www.wakemakers.com/fly-high-tube-sac.html For the price that sells for, you're going to come close in resin and glass supplies and make your whole process way more difficult.

If you don't want to buy new and want to save some cost you can probably find stuff used. To get the exact sized bag you need to search for what they make for Skiers Choice or you can find someone wanting to upgrade their factory ballast to bigger bags. That's how I got mine.

Just saw this thread, too. https://forum.supraboats.com/showthread.php?t=8303

That's exactly what you would want for a bag.

Thanks for the advice Okie... all of this is kinda why I just wanted to start this thread, I wasn't sure how much all of the materials would cost/whether it would be worth it or not. My brain started thinking about it after looking at all of the pics of that beautiful Rider helfrich is selling.

I like the idea of constructing a box just from the standpoint of 1)being able to do the exact dimensions and 2) using it as support for the seat.
Using a bag would be nice to avoid the hassle like you said, also it makes storage space available when I'm not using the bag.

Mikey, do I remember something about people at this forum getting a discount at WakeMakers?

The other thing I need to figure out is whether I will be okay with just having 400# under the seat. I can't give up my ski locker because I'm pretty big into slaloming as well and I use that for quite a bit of storage. Last summer I would run 2 330# sacs alongside the engine when I had a large crew, and would add 300# to the space behind the engine and #300 in the bow when I had a small crew. I REALLLLYYYY want to avoid having sacs lying everywhere this summer, I just need to decide if I would be okay with 400 under that seat, and probably another 400 in the bow where Mikey is currently running his sacs.

These pics give you an idea of how it can lay out. You won't get much more than 400# under the seat no matter how you do it.

If it was me, I' put a bag in the ski locker too. When you aren't doing slalom, fill the bag and put the skis on the floor behind / beside the driver seat. Then you get 800# in theback and the only thing on the floor is the skis. You could also put the skis in a tower rack if you have a tower.

You will probably be fine with 400# in the rear and 400# up front. It might not be exactly as big as you want, but you could have a decent wake while still having storage space. If you find it isn't enough, put the skis on the floor and a bag in the ski locker.

Thanks for those pics! That saves me these extra couple of weeks before I could get to my boat and pull that seat out to really investigate. I think you've convinced me to just go with sacs, I'm leaning towards that 400# tube under the seat and around 400# up front as well. By the end of the season I was only running 660# alongside the engine cover and that was plenty for me, any more weight than that just seemed like splitting hairs so 800 spread out like that should be great. My problem now is purchasing the fly high bags and not spending too much money. Right now I have 4 launch pad bags and frickin FIVE pumps, all used, that I will be able to sell but I still don't know that by the time I integrate all of the new stuff I will be able to come out without too much damage to the wallet.

If you know of anyone in the market for 2 330# bags, 2 440# bags, and/or 5 pumps let me know!!! Thanks for the help.

One last question just to be clear Okie, what size bag is that that you have under your seat? And you never have any problems with cushions bulging?

The bag is 10 x 16 x 70. Here's a link where someone is getting rid of that size.

https://forum.supraboats.com/showthread.php?t=8303

Bulging isn't a big issue as long as you watch it. Overfilling the bag can cause some bulging that would push up the cushions a bit.

If that link doesn't work out for you post a wanted ad here and on the Moomba forums. Like I said, that is a standard bag Skier's Choice uses in Moombas and Supras and people commonly look to upgrade to bigger ones and sell their original.