Technical Article: #005
Title: Insert New Flexible Water Tanks

Date Added: 17th March 2012

Article Author: Andy
Boat: Hustler 30 – Harriet B
Job Time: 4 weekends around 4 hours per day


Harriet B like all Hustlers has FRP moulded water tanks. I never really thought about any potential issues with FRP moulded tanks until I read the following in my survey report.

“Two moulded FRP tanks externally in good condition where sighted but I could not ascertain full condition due to access. It must be noted that FRP moulded tanks whereby the water is in contact with the hull moulding is not recommended due to possible long term damage to laminate or even osmosis related defects. It would be prudent to investigate via the inspection hatches and if the above is correct then consider having the tops cut out and flexible tanks inserted into these spaces.

It must also be noted that drinking water from this arrangement could contain traces of glycol, styrene etc and therefore an alternative solution should be provided for this purpose”

The last paragraph is what concerned me the most. With this in mind I’d thought I’d take a look in the tanks and see what’s going on…. Oh dear….

Tank Opening Water Baffles inside the tank Another view of the baffle inside the tank Tank Outlet - With debris inside the tank!

The images above are of the main tank (A) the secondary tank (B) was much worse lots of cracks and just no way would I drink water the out of that! It wasn’t worth the effort to try and re-paint the tanks or even patch them up as the space is way too confined. The existing tank ball valves were rusted firmly shut as the previous owner used fittings suitable for a domestic environment.

I then realised there was no way to put water into the tanks externally. The only way to fill the tanks was to run the hose down below and fill the tanks from inside the boat. This is not practical as you can get water everywhere, bunk cushions need to be moved and it then becomes a two man job.

I didn’t fancy poisoning my crew slowly nor spraying the interior of my boat with water every time I needed to fill the tanks, I needed to remedy the situation.

The Plan

I needed to install a new deck fitting, run the pipes through the bulkheads, remove the baffles from the water tanks and insert the new flexible water tanks. The diagram below shows what I was looking to do.


The dark Blue boxes represent the tanks and the inlet pipes and the light Blue lines represent the output from the tanks to the heads and galley pumps.

The original FRP tanks were sized for 54 litres (B) and 145 litres (A) respectively. However, it was obvious upon inspection that the original B tank would never hold a 50 litre flexible tank. So I needed to move the B tank elsewhere. The new location would be under the bench seat. The next challenge was the A tank the space available was simply too small for a similar size flexible tank so I opted for another 50 litre tank with the option to increase the capacity should I decide to later on.

I did think about weight distribution so as not to unbalance the boat. By having 2 x 50 litre or even 1 x 50 litre and 1 x 100 litre tank on the port side the boat will still remain balanced as per the original specification. The only thing I lose is the additional 50 litres on the starboard side. However, if I really needed the extra water for a long distance cruise I’d carry a couple of 25 litre Jerry cans.

The next challenge was when filling the tanks I had to ensure both tanks filled simultaneously from a single deck filling. This meant routing the fill pipe so should one tank fill quicker than the other it wouldn’t matter as it’d fill the other connected tank. In addition both tanks exit pipes are connected together so they drain simultaneously.

Tools and Products Necessary For The Job

The following items are what I needed to undertake this job:`

2 x 50 litre Plastimo Flexible Water Tanks (I’ve used these before and found them reliable)
1 x Deck fitting for water filling
6 metres of 38mm Re-enforced water hose for the tank filler/connection pipes
6 metres of 19mm Blue fresh water hose for the connections to the bottom of the tanks and to the galley and heads sink
1 x 38mm “Y” connector
1 x 19mm “Y” connector
1 x 19mm “T” connector
5 x 45mm Stainless steel jubilee clips
7 x 25mm Stainless steel jubilee clips
1 metre of pipe lagging

Power Drill with Titanium Bits
40mm Hole Saw drill attachment
Cordless 8200 Dremel with clip on cutting wheel attachment
Hacksaw and numerous blades
Epoxy filler
35mm Sanding flapper drill attachment
Safety goggles (essential due to flying debris don’t dismiss this!)
Breathing Mask (essential due to the amount of dust from drilling and sawing)

Work Begins

Before beginning anything I placed all the items that need to be installed around the boat to get an indication as to where to route the pipes, drill holes and place the tanks. This helped enormously with the planning and measuring as to where everything needed to go. I also thought about future upgrades and where those pipes are to run whilst doing this (This is for the heating later in the year).

Installing The Tanks
I didn’t want to leave the hatch off tank A as I wanted to keep the tank semi sealed just to keep things looking neat and tidy. Even though the surveyor recommended cutting the top off the tank it’s something I just didn’t want to do. Yes removing the from the tanks would have made the entire job easier but I wasn’t sure whether cutting the tops off the tanks would affect the structural integrity of the boat as the tanks seem pretty solid!

The original Tank B wasn’t going to be touched. I may convert that to a storage area for tools instead. Tank B was to be relocated and was to go under the Dinette seat so that wasn’t a problem to install.

Tank A however proved tricky to install simply due to the inflexible nature of the filler pipe and the inclusion of the water baffle.

Water baffles are fitted inside the moulded tanks to stop the water from sloshing around and making too much noise. The baffle needed to be removed in order to install the flexible tank. To do this I used the Dremel and the cutting wheel to slice out the baffle. This generates a LOT of dust and a breathing mask is essential.

Rough Ridge remains from the Baffle

Removal of the baffle took around 4 hours as the Dremel kept overheating and shutting down. After finally reading the Dremel manual it appeared I was covering the air intakes to cool the thing down with my hands. Then they became clogged with the FRP dust. As a result I needed to wait a while before I could use the Dremel again so in between Dremel sessions I used the trusty hacksaw and shredded my knuckles in the process.

I found it impossible to get a straight cutting line due to the awkward position of the baffle and the limited space within the hatch. So I cut what I could then sanded down the remnants with the sanding flapper. I was then worried about the possibility of chafe against the flexible tank. I epoxy glued some pipe lagging over the ridge to tidy up the ridge and to prevent chafe against the tank. As I inspect the tanks every season I’ll be able to keep an eye out if this lagging is working or not.

Pipe lagging laid across the remaining ridge

In addition to removing the baffle I also needed to drill a hole in the bottom of the tank for the pipe that connects to the “T” piece. This then connects to the pipe from tank B and eventually connects with another “Y” piece that connects to the Galley and Heads water pumps.

With the lagging in place, lower holes drilled in the existing FRP tank I could now place the flexible tank inside the old FRP water tank.

Routing The Pipes
This was the toughest part of the installation. Mounting the deck filler and running the pipes through bulkheads. I can’t stress enough how important it is to pre-plan where the pipes are to run. Be aware that 38mm re-enforced water piping isn’t that flexible and quite tough to run. On the flip side it’s very strong doesn’t crush making it ideal to route through cockpit lockers.

I had to mount the deck filler in the aft part of the cockpit simply because there wasn’t enough room to mount on the side decks. If I did the pipes would have been visible inside the cabin or the pipe routing would have caused issues under the seat especially if filling two tanks simultaneously.

Drilling 40mm holes through the bulkheads wasn’t easy. The Hustlers have a a varied layup in some places the FRP it is the standard thickness and in others it’s 4-5 inches thick. These boats were heavily laid up when made… very reassuring! :-)

38mm Pipe running into tank A and to tank B via the "Y" connector

The image above shows the hatch screwed back on tank A with the 38mm pipe being routed through the hatch after the flexible tank was installed. It looks like it’s a pretty awkward angle and it is! The re-enforced 38mm pipe either bends as a long sloping curve or at extreme right angles with no play in between. Whilst it looks as though it’s bent there’s enough space for water to run quite freely to fill the flexible tank.

The flexible tank under the dinette seatThis is the 50 litre tank under the dinette seat. As you can see there is plenty of room for a bigger tank should it be deemed necessary. You can’t see it in this picture but the outlet pipe runs into the bilge area and connects to tank A and then to the relevant pumps for the Galley and Heads.

With everything connected together I get this…
Lovely clean water!

I then filled and flushed the tanks multiple times to remove the traces of plastic taste from the new tanks. I now have lovely clean safe water… cheers!


This was quite a time consuming job that needed all my powers of contortionism to get into all the nooks and crannys of the Hustler 30! (I can confirm that the Hustler 30 primary cockpit locker can indeed hold a 6ft 5 man).

Cordless drills are useless for drilling holes with a hole saw attachment. Only a proper cabled drill was man enough for the task of drilling 40mm holes in everything from inches thick FRP to wood.

Whilst it’s possible to buy the rigid tanks, they’ll need to be custom made and they cost a lot of money. I found the approach I’ve taken here to be the most cost effective and flexible (excuse the pun) when it comes to maintenance of the water tanks out of season.

Now I can just drain, disconnect and store at home knowing they’ll be clean for the next season. If I want to expand my water capacity I can simply by buying a larger flexible tank. I can also fill my tanks outside and by a single person.

Most important of all I have no worries about quality of water. I hope you’ve found my experience informative!


Additional Future Modifications
Whilst I’m happy with what I’ve done so far I’ll also be fitting an inline cartridge water filter and a ball valve to shut each tank off if necessary later in the season.

HOA NOTE: The article above is related to works that the author has carried out to their own boat at their own risk. This article is intended to share the authors experience with other readers only. It is not intended to be a comprehensive step by step instruction guide. Anyone choosing to do any work as a result of reading this article do so at their own risk. If there is any doubt about whether to conduct work on your own boat call a professional to assist.