Only recently I was summoned to seek out the cause as to why a friend’s bilge pump kept going on at regular intervals. We had left the marina, travelled for an hour to his favourite destination, and were peacefully at anchor. There was certainly no doubt that salt water was entering the boat somewhere, as the automatic bilge pump did indeed keep turning on at regular intervals. Panic immediately set in and we ripped up the various cockpit hatches, followed by the saloon carpets and engine hatch covers. There was quite a bit of water in the bilge, mixed with a little diesel that was leaking from the main supply to the diesel filter which was only hose clipped.

But anyway, the front pulley of the engine had successfully flung this mess to every corner of the engine room. What a mess! But where the hell was the water coming from? We pulled up more carpet from the forward section of the boat, and eventually found the source of the Mississippi.

Luckily there was no hull damage, but he had one of those magical toilets, which work rather well with the aid of an electric high pressure pump. The PVC reinforced hose connecting the pump to the toilet had parted company, allowing the pump to continuously pump water into the boat. Had this been on the marina undetected, the boat batteries would eventually have run flat, the automatic bilge pump would no longer have worked, and a sinking would have been inevitable.

This leads us on to the first application of hoses that are present in your vessel, and their basic functions. Believe me, they are all very different. The correct hose to use on the toilet system is not the same as that needed for the exhaust, and fuel hose should never be used for the coolant system. Fitting the right hose for the right task is crucial. A cockpit drain hose made of PVC will be quickly eaten away if acetone is spilled down it. In fact acetone and hoses are not a good combination, no matter what the material!

You don’t install a standard car heater hose in your boat either. It may fit, but the chances of its lasting may be slim. Appropriate hoses are essential to not only keeping your boat systems working correctly, but also to keeping you afloat. There is no substitute for quality hose and anything less is asking for trouble.

Marine hoses are manufactured in a variety of different types for different uses:


There are two basic types of hose available for this application – PVC and rubber.

PVC is relatively cheap, with features of being flexible and easier to install, but poor quality PVC hose can go hard and brittle after a period of time, leaving it virtually impossible to remove without destroying the hose. If it goes so hard, it is difficult to prevent leaks. Often the suction or water supply hose for the toilet is required to be about 12 mm or 16 mm ID, but the confined situation of the toilet is such that a really flexible hose is required. A word of warning: never use clear PVC hose. This can emit the vile smell of rotten eggs when you first flush the toilet, because the clear hose allows light to assist the growth of bacteria in the stagnant water.

Rubber hose, on the other hand, is more expensive and stiffer to use but is far more reliable. When installing sanitation hoses – either PVC or rubber – avoid creating low spots that will retain effluent. The use of double hose clips is recommended on all hoses below the water line. For tight situations, rubber hose can be obtained with a wire reinforcement to prevent hose collapse. Premium smooth-tube hose designed for open water discharge applications is ideal as this will minimise clogging.

Nevertheless, when choosing sanitation hoses, be aware that in time the inside of the hose will eventually be constricted by calcium deposits if flushing with saltwater.

In your regular maintenance checks, don’t forget the loop vent.


There are not many choices in this area. The hose must be both non-toxic and non-tainting. In common use today are several brands of plastic water piping manufactured for domestic plumbing. These products are generally of an opaque nature and are combined with opaque water tanks, so that no light gets into the system. As a result, water will stay clean and drinkable almost indefinitely. Again, I stress that clear PVC hose should be avoided because of possible bacteria growth. Because of the differing water qualities obtainable, I suggest you fit your favourite water filter. And never use garden hose!


The minimum amount of approved flexible hose should be used in any LPG system. Copper pipe is commonly used with swaged or crimped flexible hoses attached but be aware that copper pipe deteriorate without notice. Hose clips are an unacceptable form of connection.

Every appliance should be served by a continuous fuel line with no joints or connections. Any connections or tees must be made inside the gas bottle locker, which is designed according to standards, and will be sealed and vented overboard. This will keep any gas leaks out of the boat.


Fuel fill and fuel line hoses are specialised. PVC should be avoided in any fuel situation, especially where petrol is concerned. Everyone remembers the fuel crisis, with the cocktail of additives, and the effects that they had on hoses, so it is important to use a premium grade of rubber hose. On petrol engines, because of high ambient temperatures, I recommend the use of a hose labelled SAE 30R7 at the minimum, or if you can obtain it, SAE 30R9.

Diesel fuel hoses are often overlooked as diesel is not considered as dangerous, but all the same it does make a terrible mess if it escapes. I stress again that PVC should be avoided as it hardens with age and is hard to seal.
Engine manufacturers such as Detroit, Cummins, etc. all use SAE 100R5 type hose (fabric external cover) for their oil and fuel lines. This hose has a wire braid as a reinforcement and has a special range of reusable or crimped couplings matched to the hose. The result is a robust fuel or oil hose that will withstand someone climbing around the engine room, often in poor light or access. An important fact to consider in diesel supply lines is that the hose and couplings are particularly airtight to prevent air getting into the diesel pump and injectors.

Fuel vent hoses should be of an equal quality and large enough to vent adequately when refuelling.


From the skin fitting to the suction filter to the pump, a premium grade suction hose should be used. There have been some failures of water pumps in stern drive trailer boats caused by the use of ‘ear muffs’ connected to the garden hose when there is insufficient pressure available to feed the demand of an engine being flushed at too high a speed. Flushing using earmuffs is OK in most areas on a city water supply. At cruising speed most modern marine engines would pump at least 45 litres per minute, far more than you would get out of your city garden hose. 

If you are using a gravity-fed hose from a water tank, you may just get away with it if you operate the motor only at idle.
Generally, marine engines are fitted with heavy-duty, wire and fabric reinforced hoses between the raw-water pump and the heat exchanger. But all too often the engine installer will use a light-duty rubber or plastic hose (i.e. automotive heater hose) to connect the raw-water seacock to the pump. Although heater hose is generally designed to tolerate temperatures as high as 105°C and pressures to 400kPa, it is relatively thin-walled and soft. If the inlet becomes blocked, the vacuum pulled by the raw-water pump will collapse the heater-hose, starving the engine of water. However, there are many wire reinforced hose suitable for the job.

Again, all water hoses, especially those below the waterline, should have double hose clips.


Use only approved exhaust hose. Approved exhaust hose means that it meets certain criteria of being able to withstand total loss of cooling water for a period of time. Double clamping using nut and bolt ‘T’ clamp with lock nuts is recommended on all exhaust connections. Regular inspection for tightness is also recommended.

Exhaust hose requires a heavy-duty rubber, wire and fabric-reinforced construction. It is recommended that hoses longer than four to six times the inside diameter of the hose or those with relatively tight curves be wire-reinforced. This eliminates kinking on bends, and sagging or pulsing from the constant pressure changes that occur in the exhaust.

Care should be taken on wire reinforced hose as the wire is nasty stuff to cut, often leaving a razor sharp piece of metal sticking out of the end of the hose. And if the hose isn’t a perfect fit on the nipple, the wire may make it difficult to get the hose to seal properly.

If you need long exhaust hose runs you can avoid using hard-wall by including lengths of fibreglass marine exhaust tubing.


There are several options for hose or pipe in this application. The one factor to bear in mind is that you want a hose that has virtually no expansion or contraction. This rules out using rubber hydraulic hose as a satisfactory product because its elasticity can result in a spongy feel in the steering, particularly at high speed.

Satisfactory products are high pressure thermoplastic type hoses or copper tubes.


How do you tell a quality hose from one of an inferior quality?

Firstly, look for recognised brands and check that the hose is labelled with its manufacturer’s name and specs. It is also important that the hose has an SAE rating, or US Coastguard approval, and that it meets M & I approval or survey requirements.

Having the right hose for the right job is probably more important than most of us realise. On the face of it most hoses look very much alike, but identical looking hoses may have all sorts of differences in the chemicals that have gone into the hose compounds, the type of reinforcement and its quality of adhesion between different layers of hose.
It is best to buy from a recognised dealer or distributor or listen to their advice.

A quick tip on maintenance. Don’t leave it a few seasons before checking skin fittings, seacocks and hose clamps. A faulty hose is a potential disaster waiting to happen. What could be merely an annoying inconvenience in a car could be a fatal disaster in a boat.

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