CR4 - The Engineer's Place for News and Discussion ®


Maritime Technology Blog

Maritime Technology

The CR4 source for all nautical topics—from boating and shipping, on salt or freshwater, for fun or commerce—all aspects of marine engineering and technology reside here. This also includes related topics such as marine products and electronics, offshore energy, marine conservation, navigation, naval defense and innovation, climate and weather, and perhaps even some relaxation and recreation.

Previous in Blog: The Sailboat Diaries: Fiberglass-By-Numbers   Next in Blog: Could Driverless Boats Boost the Shipping Industry?
Close
Close
Close
7 comments

The Sailboat Diaries: Building a Bilge

Posted July 20, 2017 2:07 PM by HUSH

For what it’s worth, I’m several projects ahead of my blog updates. I just haven’t had as much time to blog lately as I would like. Let’s hope that changes in the near future. (Also, kicking myself right now for not naming this blog series Ship’s Log!)

The bilge of my boat is to scale for a ‘pocket cruiser.’ It is considerably shallow (between 1-1.5 in. deep), and isn’t much larger than the sole of the cabin (roughly 8 ft. long by 4 ft. wide). It’s a small boat and like many smaller sailing dinghies it isn’t usually outfitted with a pump. It acts like a basin for the occasional topside leak, rain ingress or dripping-wet swimmer. Sailors with this type of bilge will typically empty it with a sponge or small siphon once back on land or at the dock.

Yet there are a few reasons why I need to install a bilge pump. First, there is a small hull leak around the keel trunk and on my shakedown cruise last October it was enough to fill the bilge in an hour’s time. (Apprently she was waterborne for most of 2016 with that leak.) Even though I intend to fix this leak completely, the ability to evacuate water from a 50-year-old boat cannot be undervalued. Also, to find and fix the leak, I’m going to need to fill up the inside of the boat with water; eventually all that water will have to be pumped out.

Lastly, my state is quite strict about invasive species and all bilges must by dry before a boat can be launched in a new lake. Several law enforcement agencies inspect and regulate this heavily!

Ideally my boat will have two bilge pumps for redundancy’s sake, but for now one will have to do. I elected a manual design because I didn’t want to have another appliance drawing electricity and also because most electric pumps are submersible, and none (or quite few) would fit the very shallow dimensions of my bilge area.

The Boat Owner’s Association of the United States recommends a pump output of 450-700 gallons per hour for a 20 ft. boat, and using this as my guidelines I bought the Whale Compac 50 (for myself, for Christmas, back in 2016).

Installation started by drilling a 3-3/8 in. hole into the storage locker underneath the port side quarter berth. I selected this location because it provided ample space to stroke the pump and also observe the bilge level from the cabin. The bilge gasket and deckplate installs on the outside of the locker and a removable handle ensures a clean aesthetic when the deckplate is closed. Installing the pump in the locker was painful because there are four screws the needed to be blind-threaded from the deckplate into the pump. After two hours and some blood loss I eventually got it aligned and tightened.

Bilge exhaust plumbing requires a mechanism known as a vented loop. This mechanism prevents water from siphoning back into the boat should the bilge exhaust ever find itself submerged. This is perhaps a little bit overengineered because my bilge exhaust is above the waterline and the manual pump should prevent water from siphoning all to way back into the bilge (which should only potentially happen on trailer launches and haul-outs). On my Matilda, the vented loop is positioned high along the inside transom wall, not far from the repair shown in Fiberglass-By-Numbers. It was screwed into a painted piece of wood that is epoxied to the fiberglass.

The 1 in. diameter pump intake hose runs underneath the boat’s kitchenette(-ette?). The sink currently drains right into the bilge so I ran the hose alongside that drain line, but continued the hose underneath the cabin sole. The end of the intake hose has a plastic screw-in strainer. The pump output, also 1 in., runs along the locker area before it has to extend underneath the cockpit floor so it can meet the vented loop. The loop is connected to a 90° stainless steel through-hull located on the upper starboard side of the transom. The hose connections are held tight by hose clamps, while the through-hull was secured with some 3M 5200 marine sealant and a plastic nut.

Today, I’m happy to report that my Matilda can expel water whenever she needs to.

Other completed tasks:

  • Installed six vents around the cabin and cockpit to increase airflow in storage lockers
  • Replaced all hardware on rudder assembly
  • Installed new tiller
  • Painted bilge cover boards

Reply

Interested in this topic? By joining CR4 you can "subscribe" to
this discussion and receive notification when new comments are added.
Guru

Join Date: Mar 2011
Location: Lubbock, Texas
Posts: 11586
Good Answers: 137
#1

Re: The Sailboat Diaries: Building a Bilge

07/20/2017 3:34 PM

But you still have to operate the pump by hand, correct?

__________________
If it ain't broke, don't fix it. Just build a better one.
Reply
Guru

Join Date: Mar 2007
Location: at the beach in Florida
Posts: 18333
Good Answers: 1064
#2
In reply to #1

Re: The Sailboat Diaries: Building a Bilge

07/20/2017 7:04 PM

Correct...

__________________
Life is like riding a bicycle. To keep your balance you must keep moving. A.E.
Reply
Participant

Join Date: Sep 2016
Posts: 2
#3
In reply to #2

Re: The Sailboat Diaries: Building a Bilge

07/21/2017 11:09 PM

As a suggestion, the dynamic bailer on a Sunfish works pretty good. Just unscrew the plug and the rear facing clamshell sucks it dry while underway and a captive ball seals it off at rest

Reply
Guru

Join Date: Oct 2014
Location: Hemet, Land of milk and honey.
Posts: 1022
Good Answers: 20
#4

Re: The Sailboat Diaries: Building a Bilge

07/22/2017 1:11 AM

The only interaction I've had with boats that are seaworthy was when I was 17 and I went on a fishing trip for 2 months aboard my friends father's 24' converted 1930ish tugboat. The craft had two manual bilge pumps and a single cylinder diesel engine. We were fishing for albacore about 500 nautical miles west of Baja.

Just an observation, I noticed in the images that the inside of the vessels shell appears to be very rough, while the outside appears to be very smooth and has a sheen. Will the insides surface texture contribute to the distribution of invasive species ?

Reply
Guru
CR4 Admins - CR4 Moderator - CR4 Moderator Technical Fields - Technical Writing - New Member United States - Member - New Member

Join Date: Dec 2011
Location: Crime Alley, Gotham City
Posts: 519
Good Answers: 2
#5
In reply to #4

Re: The Sailboat Diaries: Building a Bilge

07/24/2017 9:18 AM

Possibly in the bilge area, where something waterborne could survive. However, pumping out the water and letting it air dry for a few days should resolve that.

Also, while there will definitely be occasional trips to the shore, the plan is for the boat to live on a single lake each year, so cross-contamination shouldn't be much of an issue.

My neck of the woods has many, many lakes that have been infested with zebra mussels. The spawn quickly and once dead the shells break apart and wash up on beaches and shores as sharp fragments.

__________________
HUSH
Reply
Guru
United Kingdom - Member - Not a New Member Hobbies - Musician - New Member Hobbies - Fishing - New Member

Join Date: May 2006
Location: Reading, Berkshire, UK. Going under cover.
Posts: 9478
Good Answers: 447
#6

Re: The Sailboat Diaries: Building a Bilge

07/25/2017 10:56 AM

I notice that the performance data on the pump datasheet states the pumping rate as 9 USgal/min @ 45 strokes/min and only 9.2 USgal/min @ 70 strokes/min. Struck me as a bit odd.

__________________
"Love justice, you who rule the world" - Dante Alighieri
Reply
Guru

Join Date: Mar 2011
Location: Lubbock, Texas
Posts: 11586
Good Answers: 137
#7
In reply to #6

Re: The Sailboat Diaries: Building a Bilge

07/25/2017 11:02 AM

It's not how well you mow, it's how well you mow fast.

Now extend that to hand operated bilge pumps. It could be that this pump cannot support suction transfer past the 45 strokes/min. Just a W.A.G.

__________________
If it ain't broke, don't fix it. Just build a better one.
Reply
Reply to Blog Entry 7 comments
Interested in this topic? By joining CR4 you can "subscribe" to
this discussion and receive notification when new comments are added.
Copy to Clipboard

Users who posted comments:

HUSH (1); James Stewart (2); JohnDG (1); SolarEagle (1); tonyhemet (1); trackfodder (1)

Previous in Blog: The Sailboat Diaries: Fiberglass-By-Numbers   Next in Blog: Could Driverless Boats Boost the Shipping Industry?

Advertisement