Retrofitting for a small fireboat

We have obtained a small (10 m) ex military combat support vessel, all aluminum, twin jet drive with two sabre diesel engines. We intend to convert it to a fire/rescue boat for a large recreational lake. We are working on the engines now, once they are running properly I plan to mount a remote controlled monitor on the bow and a largish (500gpm) fire pump aft of the engine compartment. I would like to construct a sea chest to handle the intake for the pump. I am thinking a 3 to 4" metal pipe rising from the hull to above the water line, screened at the hull, with a removable cap on top, and a branch leading to the pump intake with a quarter turn valve. I am pretty confident of my plumbing skills on the discharge side of the pump, but would welcome any advice or resources for the intake side - especially as I have to cut a hole in my boat! It does have two large screens for the jet pumps, but they seem to be pretty self contained, engine, transmission, pump, jet all in a package. I see no easy tapping into them for my intake water.

 

What about considering to use one (or both) of the existing jet drives for fire fighting.

 

Jet drives

I have considered it, but these are high volume, low pressure jets - I don't know how much pressure they actually produce. Also the manifold from the pumps to the jets is quite short, and doesn't look very accessable for tapping into, and finally, I would like both jets available while pumping. Right now I can run the boat only on the starboard jet, and it is pretty tricky to handle. With 500 gpm flowing forward at 60 psi, it will be important to keep the boat on station, much easier with both jets in operation. Still, I will look into it more.

 

Your filling a rather small boat with fire fighting gear, this makes it both heavy (hard to push except with big engines, which with large fuel tanks cause more problems) and expensive to run! It also negates the use of the vessel as a rescue boat - or do you intend only to turn out for fires (whilst dramatic there ain't to many actual fires). What about leaving the boat as it is? use it as a 'platform' to carry portable fire pumps, stretchers, ladders or what ever you need for whatever mode its needed for - phone call "we have an emergency, need divers"; so on goes the diving gear! with room for survivors. "we have a fire"; so on goes the fire pumps! get to the fire, need a pump over there to pump out that boat while we fight this fire, off goes one fire pump (still using the other(s)) reverse the hoses and start pumping - see what I mean! It's cheaper too - all your money can be spent on safety gear rather than fixing it! Just a thought!

 

Small boat, lots of gear

The boat was originally rated to carry 4400 lbs and run at 16 knots, or run at 21 knots with a full crew, so it has got pretty big engines. The pump we are planning to use is a portable one, and can be supplied by hanging a hard suction hose over the side - provided you can get a draft. Portable pumps like this use an "exhaust primer" using the exhaust from the driver engine to venturi the air out of the suction hose and raise the water to the pump inlet. Difficult and messy in a boat, with the hose draped over the gunnels. Hence the idea of a sea chest to attach the portable pump to, so it will be continually primed. Of course, any better ideas would be most welcome at this stage of the game (while the boat is pulled for engine maintenance)

 

I would attempt to mount he pump so low that priming was not needed.
I would use a Y manifold with a seacock on either side of the keel .
Seacocks can easily be push pull cable operated so less danger in having 2 ,3 or 4 inch holes in the boat.

You might consider belting or clutching or HYD to power the pump from the main engine for more reliability.

FAST FRED

 

We have build some fire fighting boat's at this size with aluminium hull and water jets.

We use sea chest and a stationary electrical pump in the engine room or we mount the pump to a pto on the engines(depends on customer choice)

There is a suplier off this in Sweeden and also in Japan that we use.
We have also used from Norway and UK on larger projects.

What kind off spech do you want?

Are you going to forfill anny fi-fi class?

 

I thought those exhaust venturi primers worked pretty well and quickly. Also, there are (or were) 2 cycle 4 cylinder (opposing 4) pump engines which were pretty light and exceeded your 500gpm requirement. They were in a package much like a 5000w honda generator, probably half again as heavy. Vague recollection is that they were Corning pumps. They were light enough that you could have two for the weight penalty of one more conventional pump and plumbing arrangement. Drawback was that they were LOUD!