2" Vented Loop Source

[Stevens 47]

Originally Posted by never monday

Why not put an internal pick up for the water pump">raw water pump on the engine.

I can do this and still have the 4000 gph pump as I have already invested in it. Thanks for the feed back.

[NCboatrx]

Hello Stevens 47,

I suggest that you phone the company instead of email. The marine division of Scot Pump in Ft. Lauderdale doesn't use email. The phone # that I supplied earlier works well.

I dont advocate using the engine cooling pump as an emergency bilge pump for two reasons, 1 is the cooling pump has a very small flow for this use and 2 is that if your boat is taking on water, there is also a good likelyhood of stuff floating in the water which will clog the pump intake and thus shut off the engine cooling water supply. If you want an engine driven bilge pump, these are made by both Johnson and Jabsco. The 1" or 1-1/2" emergency bilge pumps have great flow and as long as the engine stays running.

Regards, Stanley

[never monday]

Stanley,
I disagree as always.

A strainer can be added to the bottom of the hose to filter debris to a similar size as a Groco strainer. At the point a crash pump would become necessary. Any means to dewater the boat is the ideal option. A boat of the size as the 47 here will have a decently sized RWP to move water.

good day.


PS you win. Go sell some Betas to these fine folks

[Christian Van H]

Originally Posted by never monday

I Why not put an internal pick up for the raw water pump on the engine.

Most raw water engine mounted pumps could never output 4000 gal. per hour. Even if they could, there is no harm in the high output electric pump. You would need a separate, large volume clutch pump for that. IMHO no pump that empties a bilge should ever have a check valve only to protect a siphon back situation. There is WAY too much stuff in the deepest, darkest areas of the bilge that can easily jamb it. In all likelihood, this electric pump will never run in its lifetime. The smaller pump (a whale gulper 220, in my case) will be the only maintenance pump. On my 42 footer there is a Gulper 220, a 3500 GPH johnson, a Gusher 10 and a Gusher 25, all for bilge water. Next step is a bucket, then a step up into the raft...

[NCboatrx]

Hello Stevens 47,
I would not put the thru-hull high up. You are better off with it fairly close to the waterline. This way, when you are sailing the loop up to your anti-siphon valve should stop water siphoning back into your boat. You can make this loop up to deck level without affecting the pumps capability too seriously. There are arguements for and against a valve on a bilge pump thru-hull. Basically, although it is nice to have a valve on every thru-hull, when you will want the big bilge pump to work, you are likely to just flip the switch because you are in a rush to have it working, so it is better to leave that valve open.
Regards,
Stanley

[Stevens 47]

Originally Posted by NCboatrx

Hello Stevens 47,
I would not put the thru-hull high up. You are better off with it fairly close to the waterline. This way, when you are sailing the loop up to your anti-siphon valve should stop water siphoning back into your boat. You can make this loop up to deck level without affecting the pumps capability too seriously.
Stanley

Stanley am I missing something. If the outlet is at the same level as the vented loop would it not be the same. If in a very heavy sea with green water over the boat it would seam like water would back into the lower outlet and over the vented loop just like it would with the outlet at the same level as the the vented loop? I looked at a 2" genset through hole today with a flapper on the outside and thought this could be the way to go if I in fact installed the it up high. The one of the downside besides the question of what would allow water back into the boat is if for some reason the bilge pump needed to work it would shoot water all over any neighbor in a marina situation, that could be as good as a bilge alarm.

[peterroach]

Run your second bilge pump into your kitchen sink line. I use a Large PVC T and run the bilge pump line WAY up above the water line. The sink acts as a vented loop. You also typically cut down on the length of your hose and often times the rise.

[Stevens 47]

Originally Posted by peterroach

Run your second bilge pump into your kitchen sink line. I use a Large PVC T and run the bilge pump line WAY up above the water line. The sink acts as a vented loop. You also typically cut down on the length of your hose and often times the rise.

Peter,

The only problem with that is all of my sinks (including the galley) and shower drains run into grey water tank inside the bilge. I specially built the tank from scratch and made a place for the Rule 4000 to sit on top of it as it is 10" from the bottom of the bilge to the top of the grey water tank. Interesting idea though.

[GordMay]

Pat:
What approximate flow rate would you expect from the raw water pump on a typical 50 - 60 HP diesel, operating with minimal head, and at cruising RPM?
I’ve never been able to find pump curves or specs on these pumps.

[Christian Van H]

Gord, just look at your tailpipe...not really an impressive flow,eh? Oh, and I can imagine a sink geyser by plumbing a 4000 GPH pump into the sink drain. If you ever developed a regular leak, people would gather around the galley and wait for it to go off. Old bilgeful?

[NCboatrx]

Gord May. Raw water pumps for the average 40 to 60HP engine that is heat exchanger cooled will pump between 20 and 35 litres per minute depending on engine speed. Here is the link to the correct page on the Depco website which has links to the data sheets for most pump manufacturers Depco Pump - Brands, Vendor Links & Data Sheets

Stevens 47, The vented loop must be above the pump and the thru-hull or it cannot work. When the boat heels and lets water in the pipe, the water level in the pipe will rise and when the boat levels again the water will flow out of the hose back into the ocean. This is why we always ask installers to make the loop as high as they can to provide a safety factor. In an ideal world, the vented loop will be at or above deck level on the boats centerline but every boat is a compromise for one reason or another. A flap over the thru-hull outlet will help.

Regards,
Stanley

[Stevens 47]

Stanley I understand the purpose of the vented loop and the need to have it as high up inside the boat. My point is if a direct discharge outlet and a vented loop are at the same level on the side of the boat, what is the difference? It would seem that water rising above both will cause some intrusion. I am not saying that I am going to install the outlet as I am discussing. However using tables on friction loss Nigel Calder's book, a 180 vented loop and the associated hose would add about 1.7 feet of head to the discharge line. A discharge at the level that we are discussing adds about .63 feet of head. This equates to an approximate difference of between 150-200 gph of discharge potential at optimal voltage. I admit this is not significant in the overall scheme and the best install would allow less water back into the boat. Do you or anyone else think that a installation with the conventional vented loop install would keep out more water compared to what I have described. If so I would like to know your reasoning is or your experience.

[GordMay]

Stanley:

35 Litres per Minute equates to 9.23 US Gallons per Minute, or 554 US Gallons per Hour (462 Imp. GPH); not exactly what I’d call an emergency crash pump.

Are those (20 - 35 l/Min) “Open Flow” ratings, or as typically installed?

Can you direct me to a particular manufacturer (name) of Engine Raw Water Pumps? Most of those on the Depco site are not.
__________________

Approximate Flooding Rates, for smooth holes at specific depths, are calculated using the formula:

Flooding Rate in GPM [Q] = 20 x d x ?h

where:
d = diameter of hole in inches
h = depth of hole underwater in feet (head)
?h = square-root of h

Hence, for a 2" diameter hole at a 3 Ft depth:

Q = 20 x 2" x root 3 = 20 x 2 x 1.73 = 69.2 gpm (4,152 Gal per Hour)

The actual initial flow rate ('Q') will be slightly less than calculated above, due to frictional & turbulence losses at the aperture, and.
__________________

[Christian Van H]

You guys think 2" is large for a bilge pump? I just found out that Rule makes a 8000! GPH pump, with a THREE INCH OUTLET! Whoa, now there's a crash pump! Rule 8000 > Bilge Pumps > Pumps > Rule - ITT

[NCboatrx]

Gord,
The flow rates that I gave are for engine cooling pumps, not bilge pumps. Sorry, I thought that that was what you wanted. The Depco site has links to Jabsco and Johnson which are the two brands that we use.

The Johnson clutched bilge pumps have flow rates up to 75 litres per minute or 210LPM or 275LPM or 380 LPM depending on size. Here is the link to that page Johnson Pump
I have used the Johnson pump # simply because that is the pump # that I remember. These (and the Jabsco versions) make great emergency bilge pumps as they are engine driven and have a clutch on the pulley.

My replies may be spotty over the next week as I am on my way to Miami to exhibit at the Strictly Sail boat show. I am looking forward to some warm weather as well as hopefully, some sales.

Regards, Stanley