1983 ski Nautique 2001 blueprints

John Thacker

205-755-9035

Verbena, AL

I'll try to explain a ballast tank idea thought up after your post today, not to scale and funny looking but think it work.

Get some melamine board, frp or masonite, the masonite has been successful for me, so has pvc board.

Remember to store your frp on a flat surface like the bed in the spare room, but keep the melamine and masonite out in the shed unless or untill you have to put it in the dining room so the balsa core can be cut to fit the transom template for a patio table project which oddly enough is in progress right now. 

Actually for some ballast tanks to make the mold in this case i'd use masonite because it's light and easy to work with, and with some planning can be used over and over.

It ends up being a funny looking half a box with the hullside and bottom closing it up.

Fit masonite to the hullside by scribing to fit, once you have 2 pieces cut a top and face.

It will go from the hull bottom up to the gunnel but not up under it because you need room to fiberglass it into place.

A fiberglass box could be fitted along the hullside next to the engine, another behind it that goes almost all the way back to the transom.

A big one under the deck would make 5 ballast tanks that dont take up floor space beyond the gunnels.

Lay your masonite box down and install some dowel rods, say 1/2 inch dowel for a 1 inch hose.

(fill, vent, drain tube locations in the box would have to be determined and some pump research is in order to see how many and what size tubes you need) ( think i'd fill them thru clamshells and forward motion, pump to drain) 

Glass up the box and wrap the dowel rod until you have the diameter you want, after the glass dries, pop it off the masonite, drill out your dowels and bingo ya got some molded in hose barbs.

Glass the 1/2 boxes right onto the hull sides and hull bottom

3-5 coats of meguires #8 maximim mold release on every and anthing you want to pull fiberglass off of

5 x18 x 48 inch tank is 18 gallons, say you got 2 tanks with 30 gallons a side and another 40 under the deck,

100 gallons 700 pounds spread out from front to back, it might go red october better ask how much extra weight that hull is good for.

Apologies for taking so long, but here are some pictures of my setup. And apologies for the untidy state of things in the pictures, but I have a few things I'm working on, hence the cardboard/paper covering etc.

I had stringers and floor replaced when I bought the boat (all wood replaced with Nidacore), and the shop that did the stringers and floor for me also built and installed the tanks for me. For regulatory reasons I had to have a lot of foam added under the floor for buoyancy, so the factory battery box etc. all had to go. The tanks work really well as seating in the boat. Only drawback is that the side tanks cut down quite a bit on working space around the engine when one has to work on the engine.

The port and starboard tanks cover most of the space from the stern to the front of the boat, to a point in line with the front of the engine cover.They fit in snug below the coaming pads. They're bonded to the floor with 4200, and have a piece of fibreglass attaching them to the hull at the front. The tanks (except for the front) have sight windows with float level indicators.

The aft tank fits in between the two side tanks. It has two 'wings', which slide in behind the side tanks and keeps it from moving forward. It rests on the stringers, which have a small step in them (marked in red in the picture below) which the tanks snugs up against, preventing it from sliding back.

The green thru-hulls supply the pumps which fill and drain the tanks.

The front tank is fitted under the bow, held in place with a bit of fibreglass. It is shaped to accomodate the battery. It does make it impossible to access the navigation light without pulling the tank (likely a big job), but so far I haven't had to do that.

The pieces of wood glassed onto the front tank is for screwing a kick panel onto, which holds speakers, amplifier and fire extinguisher (regulatory requirement in South Africa).

Each tank is drained and filled with its own pump. The pumps are mounted at the back of the two side tanks, and against the sides of the hull next to the fuel tank.  Each pump is mounted on a piece of PVC foam core material that is bonded to the tank/hull with 4200. Mounting and plumbing those pumps was a major PITA, because there is very little space to work with.

The side and aft tanks fill/drain fittings as well as the overflow/vent fittings are at the rear. In hindsight the overflow/vent should have been at the front, as I do lose some water through the overflow while underway, with the bow of the boat higher than the stern. I intend  to plumb in a long loop under the gunwales for each tank to address this issue.

The hard tanks does add weight to the boat, so if you're concerned about keeping the smallest slalom wake possible, ballast bags may be better. But filling and draining the hard tanks are much less of a hassle than bags, and as I said, the tanks serve as really convenient seating as well, so overall I'm very happy with the setup.