If you have a real breech in the hull, no pump onboard will keep up. A hole only 1 inch (2.5cm) in diameter, 2 feet (60 cm) under water will put over 20 gal/min (75 liter/min) into the boat. That's a scary amount of water. And that's a pretty small hole. This is the reason that knowledgeable sailors love the watertight bulkheads in an Amel!
I think you will also find you are over estimating the amount of water that the engine can pump. Typical ratings for pumps on engines the size we have on Amels are on the order of 5 GPM (18 LPM) at full rated RPM. Look carefully at the exhaust discharge, and collect it in a bucket. You'll see even at 3000 engine RPM there isn't all that much water coming out.
The idea of using the engine pump as a dewatering pump was once a popular one, written about in many classic cruising texts. It has fallen out of favor as people realized that engines really don't move that much water and a rapidly flooding bilge tends to have a lot of debris in the water that very rapidly clogs the small passageways in an engine's cooling system. It is one of those ideas that sounds great in theory, but in practice... not so much.
If you really want to keep up with even a modest hull breech, the only way is with separately mounted large-port engine-driven pump of a size significantly bigger than the cooling water pump. A design target of 100 gal/min is not unreasonable for a pump designed to keep a boat from flooding. Such a flow rate would require something on the order of a 2 inch diameter discharge hose.
I am not suggesting that a second back-up bilge pump on an Amel is not a good idea, far from it. A redundant system here is important (to me anyway!) I am suggesting that your design goal of pumping out a significant hull breech is unrealistic, and using the engine cooling pump is not a really a practical idea.
---In amelyachtowners@..., <mshirloo@...> wrote :
Hello Every one;
I've always had a concern about keeping up with pumping out the bilge area water in case of any type of breach in the hull, thru hulls, etc. The current pump capacity would be overwhelmed by even a minor breach. Although the water tight bulkheads will prevent most events that would lead to sinking of other boats, flooding a compartment does lead to significant other damage that may be preventable, given added time to diagnose and correct any breaches.
There are several existing pumping capabilities in the engine room. They are engine raw water cooling, generator raw water cooling, anchor wash, refrigerator and A/C pumps. Some of these, e.g. the main engine raw water cooling, can pump an enormous amount of water at high RPMS. Also the amount of the pumping can be adjusted by adjustments in the main engine throttle setting.
One option I was looking at was to add an inlet to the raw water distribution manifold and use that as a secondary pickup (installed somewhere in the bilge area) with a shutoff valve. When needed, the main raw water thru hull can be closed, this added valve could be opened and any of the other pumps in the engine room could be turned on to add pumping capacity.
I would like to hear if others have put any added pumping capacity and all opinions about my proposed solution.
Mohammad and Aty
Amel 54 #099