Installation of a desalinator on a boat

Are you planning on Installing a desalinator on your boat?

Installing a watermaker on a yacht or sailboat is something most boat owners tackle only once and understandably got some respect from this task. Understandably – It’s an expensive system with quite some components after all.

Various questions pop up again and again during our talks with clients. In this blog post we will handle the most common questions in order to provide you some initial guidance.

Topics covered in this article:

What components need to be placed and general considerations
Sea water inlet & Thru hulls
Placement of feed pump and filters
Placement of the High-Pressure pump
Membrane location and orientation
Installation suggestions

Where to place a watermaker in a boat?

One of the first questions to be answered is: Where to put all the parts of a watermaker?

Lets have a look at what’s part of a system first and then go into the details.

Strainer & Feed pump
Sediment filters
High pressure pump
Membrane unit
Control panel
Junction Box

That’s apparently quite some components that all need to find their place and this is why we strongly believe that a modular watermaker is the best fit for most boats compared to a compact, framed system that facilitates all components in one large block.

Despite the actual space demand there is a few other aspects to consider when planning an installation.

Noise during typical usage
Keeping hose and cable runs short
- Especially for DC systems due voltage drop

The importance of the seawater inlet

For any watermaker it’s crucial to avoid air coming into the system. Therefore its important to choose the seawater inlet location be in a place of the hull that will never come out of the water.

For sailboats: Typically mid ships around the keel
For fast motor boats: Further aft, midships

The other aspect is suction pressure for the pumps. No pump should see excessive low pressure during operation.

But what happens at the outside of the hull while sailing? Due to the movement throughout the water the water pressure at the hull drops which is why you observe the boat “sinking” into the water when sailing fast.

This is exactly why you should install a scoop type inlet with the opening facing forward. This way you always retain a positive pressure on the water inlet allowing your pumps to run reliable in the long term.

Shared through hulls and sizing - What is possible?

One of the most common questions regarding the through hull is whether or not you can share them with other utilities.

For the outlet – the brine discharge: This is a very general yes as the water will always get pushed outside.

For the intake: It’s a “depends”. Will both or all the utilities on the intake run at the same time and how big is the intake compared to the combined water demand?

Your boats engine or air condition can have quite a significant water flow. If they’re hooked up e.g. on a small 1/2″ intake the result could be a low pressure on the suction side again which is not ideal.

If you plan sharing an intake with some other equipment that may run at the same time than the watermaker and got a significant water demand – Make sure the inlet is large enough – At least 3/4″ or better 1″ depending on the utility and size of the watermaker.

Considerations for placing the feed pump and filters of a desalinator.

The feed pump and strainer of a watermaker are usually low in maintenance and it’s only about washing the strainer occasionally. So accessibility is a factor but not the most critical. Our Ocean-Spring Watermakers use only magnet driven feed pumps which are very quiet but not self priming. Means you will not have a noise issue coming from this pump but the strainer and feed pump need to sit below the water line.

Again to avoid suction pressure on the inlet side of the pump its advisable to locate both items close to the intake thru hull and rather have a longer piece of hose in between the feed pump and the high pressure pump.

The sediment filters: These are the items that you will touch the most maintenance wise. Depending on the seawater you will need to change them every now and then and therefore accessibility is the most important aspect when choosing their location.

Placement of the High-Pressure pump

The High Pressure pump is the source of noise in any conventional desalinator. Especially on sailboats that don’t have large sound proofed engine rooms this can be an issue.

To reduce the noise there is a few attempts:

Make a solid and stiff base that is in itself again decoupled from the boats structure
- E.g. a solid piece of marine plywood that you fix with dampers or some elastic material such as a thick bead of assembly adhesive.
Provide some sound proofing in the installation compartment
Choose a location further away from your typical hang out areas while at anchor or sailing (eg in the forward cabin)

Looking at these criteria and advices another common question comes to mind:

Can the watermakers pump be located in the engine compartment?

The answer is again a “Depends”:

Ventilation: Any typically used electric motor requires some air cooling. In order for this cooling to be effective the ambient temperature for operating the watermaker must not exceed 40°C. This requires a good, forced ventilation for the engine room.
Using habits: Ventilation or not. When shut off the engine will still have residual heat while the ventilation is not running anymore. If seawater is left within the desalinator after finishing the production the additional heat might cause corrosion problems shortening the life span of your HP pump. Consequently performing a fresh water flush after usage mitigates this issue.

The membrane unit of your desalinator

As one of the most clunky items of a watermaker the membrane unit can be a challenge to locate especially on small sailboats.

Lets look into a few typical aspects:

Does orientation matter?
- Not that much. You can put it horizontal, vertical or any orientation in between. Just make sure the installation allows air to escape. That means in vertical or inclined installation the outlet of seawater and product water must be on the highest point so air can bleed out there.
What about the engine room?
- Again heat is a concern. Less because of corrosion but more because of biological growth which is also accelerated by elevated temperatures.
- The fresh water flush also helps here and using membrane cleaners on a regular base also helps but ultimately its better to put the membrane unit in cooler place as it also doesn’t emit noise.
The length as primary issue on small boats:
- 40″ is the most common length of reverse osmosis membranes and therefore the most cost effective solution. However on small boats this length poses a challenge to find a place for the membrane.
- Below a bunk, or below the ceiling of an more technical place are good examples where you can fit this length on most boots.
- If you still find it a problem: Look into 21″ membranes that reduce the space requirement significantly.

Inspirations of where to place your watermaker on a sailboat.

There is a huge range of boats out there so there that are used I very different ways so there is not the one place to recommend for placing a watermaker. But we would like to give you some inspiration based on a typical production sailboat layout.

Example 1: Installation in the Space below the V-Berth

The inlet and feed pump are place closer to the keel
HP-Pump and Membranes are placed inside the V-Berth compartment – far away from the cockpit and in a space that is usually inconvenient to access for storage purposes.
The control panel could be placed facing to the entrance of the cabin at the V-berths bulkhead or inside a locker for a more subtle appearance.

Example 2: Aft cabin and engine room

The pumps are placed in the isolated engine room keeping benefitting from the sound proofing and utilising usually unusable space.
The membrane unit is place eg under the aft cabins berth next to the engine room. Benefiting from low temperatures.
Same as in example 1 the control panel could be placed in a locker or at the bunks front side for convenient access.

In both these examples the noise level in saloon and cockpit are reduced and the chosen installation spaces are usually on all boats long enough to host a standard 40″ membrane.

You still got questions regarding installing a watermaker on board your boat?

Whether you own a sailboat, motor boat or yacht – They all are different just like peoples preferences and questions. So don’t worry in case you got questions left to be answered – give us a message and we will see how we can help with your specific questions!