MKI sugar scoop transom bilge pump back-flowing seawater?

[Noah]

I had a couple of gallons or so of seawater in the low point of the bilge the other day AFTER an outing and have checked "everything" for leaks! None!  I usually have a dry bilge. Nothing is/was wet aft or under the engine. Not from stuffing box, etc. I suspect that my electric bilge pump hose (being low to the water positioned on the edge of the sugar scoop) is back-flowing seawater into the bilge when the stern gets buried. Has anyone with a 1990-vintage sugar scoop transom boat experienced this issue? I will try and plug/cork/bung the bilge pump thru-hull outlet then deliberately bury the stern by using high RPMs or backing, etc. next sail to see if it may be the cause.

[Dave Spencer]

Hi Noah,
I think your assessment of back-flowing from the bilge pump discharge is accurate.  It looks like you have two separate discharges for your bilge pump(s), the one in the middle is likely the manual pump discharge and the one to starboard looks to be an additional discharge added for the electric pump.
I only have one discharge located where your centre discharge is located.  My electric pump hose joins the manual pump discharge hose just after the manual pump thereby creating a loop that is higher than the waterline preventing back flow.  I think this is the OEM setup.
I am slightly worried about the location of the bilge pump discharge as it is subject to being submerged; especially when motoring.  I am very keen to replace my aging bilge pump hose at the discharge fitting to something more robust as I don't trust the light bilge pump hose to serve "below the waterline" (albeit only periodically).  Access to the fitting under the swim platform will be interesting.  Has anyone done this on Mk 1.5 or Mk II boats with the swim platform?

[Ron Hill]

Noah : Is this an "all of a sudden" occurrence?? 
It appears from the location of the bilge pump exit that backflow would be happening all of the time when you motor!!

A thought

[Noah]

Ron- I have had some small amount of mystery seawater in the bilge in the past but ignored it. Now I am paying more attention. Rarely does my stern submerge when motoring except recently with full aft tanks, high RPM and lots of crew in the cockpit.

[derekb]

Noah, after purchasing my boat my first sail was from Williamstown to Geelong (about 6 hours) in a following sea. After about 3 hours sailing, I noticed the bilge had filled up to just below the floor-boards due to waves slapping against the transom and back-flowing down the bilge-pump hose. The transom was not submerged, it was just the wave action. Changing direction slightly stopped the waves splashing on the transom, and a faulty bilge pump led to some bucket bailing! Then I blocked the bilge-pump outlet with a stubby-holder and sailed the rest of the way without incident.

I have a Mk 1 boat without the sugar-scoop, but the bilge pump outlet is in the same place as shown in your photo. I've replaced the bilge pump, and I'm about to replace the bilge-pump hose. The hose runs in a straight line from the pump to the outlet - so any water flowing into the outlet flows directly down into the bilge. I plan to incorporate a small anti-siphon hump to prevent splashes on the transom flowing down into the bilge.

Regards,
Derek

[Jon W]

When I added a second electric bilge pump I ran new bilge pump hoses without check valves, and added anti-siphon loops. The anti-siphon loop for the 1 1/8" hose is mounted in the galley above the drawer and under the galley sink. The anti-siphon loop for the 1 1/2" hose is mounted under the manual bilge pump in the aft lazarette. Photo of the 1 1/2" attached. After the anti-siphon loop it joins the manual bilge hose with a Whale 1 1/2" Y connector. Photo also attached.

[Noah]

If back syphoning is my culprit; I would be interested in opinions as which route would be safer/more effective: an anti-syphon valve, verses a high loop, verses a check valve, (considered not safe), verses teeing the electric pump's discharge into the manual pump's  discharge—which basically is a highbred of a high loop and anti-backfow valve—using the manual pump's placement, high in the cockpit,  to accomplish both. In that case, I would need to abandon (cap or remove) my electric pump's stern thru-hull.

[Jon W]

I'm biased because I did it on my boat. My 2 cents is to keep the electric bilge pump hose separate from the manual bilge pump hose. If your boat is like the MK 1, the electric bilge pump hose runs by the galley sink. Putting an anti-siphon loop up high between the galley sink bowls gives a secondary benefit of minimizing water run back into the bilge when the electric bilge pump shuts off. No check valves in the bilge pump hoses.

[Noah]

Thx jon, I am inclined to keep a separate hose and outlet for each pump as well.  I will investigate where to put an anti-syphon loop/break. Working under the galley sink is a bit more pleasant than working in the after locker. But there might be more advantage to having loop closer to thru-hull. Limiting a long run of seawater staying/fermenting in hose is one thing I wouldn't want.  Either case, I will need to cut the hose and tee in some length to make the loop, as there is no slack available. I have heard from some other sugar scoop owners who have the same set-up as me—two discharge thru-hulls on transom—and they report mixed reviews. Some have had back-flow problems and others no issues. Curious...

[KWKloeber]

I don't have this issue because my bilge hose has a high hump (as high as one can go) in the sail locker.  So no sea water backflow.

But would a flapper-do-hickey help/work?
You can buy just the butt-end shown, which you screw onto the outside of the existing thru-transom, no change-out necessary.

[Noah]

Thx Ken. That might work. Once I remove all kinds of barriers and equipment; shelf, propane locker, giant mounted halotron fire extinguisher, manual bilge pump, etc. and manage to squeeze down the helm seat locker hole (or get someone younger and smaller) to reach the transom thru-hulls, I will see. I may also try and go through aft cabin, but that also invovles removing bulkhead and aft water tank and still my below deck autopilot may prevent me crawling back there. The bilge hoses were replaced 4 yrs ago, but do not know about the thru-hulls, which may be old nylon and brittle and need to replaced anyway. Just very tough to get to on. 34 MKI sugar scoop.

[Dave Spencer]

Hi Noah,
I'm battling the same conditions to get to my through hull under the swim platform.  And I don't have the piece of mind knowing that I changed the bilge hose only 4 years ago.  As far as I know, the hose and through hull are OEM from the early 1990s.  Like you, I'm thinking through changing my bilge through hull fitting, possibly with a bronze or stainless substitute.  Did you use bilge pump hose when you replaced it a few years ago or did you use a more robust "below the waterline" hose?  It must have been a bear to get to the fitting!  I can see my bilge pump hose heading to the through hull but certainly the aft water tank will have to come out for me to access the hose and fitting and get the job done.  Any tips you or anyone else has would be most welcome.

[KWKloeber]

Noah

Not sure if you missed my point- you don't need to change anything unless you want to. I simply applied the flapper-doohickey to my OEM thru hull.

There are more expensive/elaborate ones available.

[Noah]

Sorry, Ken,  I DID miss your point on just using the flapper end section. It might work. I will investigate. Thx.

[KWKloeber]

Noah, You can barely see it, but.... screwed to the face of the thru hull.