Bilge Pump Discharge - New Thru Hull ??? - SailNet Community
LinkBack Thread Tools
post #1 of 5 Old 04-30-2003 Thread Starter
Junior Member
Join Date: Apr 2003
Posts: 3
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 0
Bilge Pump Discharge - New Thru Hull ???

Hi Everyone,
Looking for some advise on installing an electric bilge pump in my sailboat. Do I have to install a new thru hull fitting or is it possible to connect the new bilge pump discharge line (3/4") into a "Y" connection that would be installed in the existing (1 1/2") manual bilge pump discharge line ... aft of the manual pump itself ???
Any advise would greatly be appreciated.

Thank you,
Terry Clarke
CAPTIVA, Port Whitby
Terry Clarke is offline  
Quote Quick Reply Share with Facebook
Sponsored Links
post #2 of 5 Old 05-09-2003
Junior Member
Join Date: Nov 2001
Posts: 6
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 0
Bilge Pump Discharge - New Thru Hull ???


I am not heavy in to plumbing, but I do know when you ''Y'' two pumps together like that you need to install check values (anti-siphon, duck bill, etc.) in both lines to keep one pump from pumping into the other. Personally, I think separate discharge lines would be best, but that costs lots of money.

(Actually your bildge line should already have a check value.)

Good luck, Ron
ronbuckles is offline  
Quote Quick Reply Share with Facebook
post #3 of 5 Old 05-10-2003
Senior Member
Join Date: Dec 2002
Posts: 552
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 14
Bilge Pump Discharge - New Thru Hull ???

Yes, you can install two pumps to discharge through a single through-hull; but you should not use an existing (properly sized) thru-hull to also accomodate an extra pump. It may not, therefor, be practical.
1. NEVER install a check valve in a Bilge Pump discharge line. While the valve reduces the amount of water that returns to the bilge, after the pump shuts down; they are VERY prone to failure. It''s difficult for a typical bilge pump to open a fouled check valve (and they DO clogg up) A new & clean 1.5" check valve represents the equivalent hydraulic friction loss of about 14 Feet of SMOOTH-BORE Pipe..
2. You CAN install a "Y", providing a single thru-hull discharge for two pumps.
The "Y" will consist of an assembly that has the free area of the thru-hull equal to not less than the sum of the areas of the pump discharge ports (actually, this is only a close approximation).
The pump hoses will each rise to an anti-siphon loop (risers), then drop to the "Y" fitting, then discharge. This prevents the cross-pummping that Ron mentions.
This riser loop should consist of gentle bends, so as to limit the amount of waterflow turbulance introduced into the discharge line(s). Turbulant waterflow increases friction head, reducing pump output.
3. So, for your example (a 0.75" and a 1.5" pump discharge) will have a "Y" assembly consisting of:
a 0.75" internal diameter upper leg, another upper leg at 1.5" (= 2.2 Sw. In total), and a 1.67" internal Diameter(>2.2 Sq. In.) lower discharge leg. Because 1.67" I.D. not available, you''d have to increase discharge thru-hull leg to 1.75 or 2" diamter.

Perhaps a second 3/4" thru-hull might be easier, after all.

Hope this helps.


GordMay is offline  
Quote Quick Reply Share with Facebook
post #4 of 5 Old 05-10-2003
Senior Member
Join Date: Jan 2001
Posts: 445
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 16
Bilge Pump Discharge - New Thru Hull ???

You know, it is beyond me why anyone would install two outflows in a "Y" fashion on a single discharge thru hull. The idea is failure redundancy, necessitating two thru-hulls. Done it, it''s easy. Go with low amperage auto pump with internal switch at the low point of the bilge and put a higher capacity pump on a manual switch up 8" above that. If those won''t move the water necessary, you''re screwed anyway.
VIEXILE is offline  
Quote Quick Reply Share with Facebook
post #5 of 5 Old 05-10-2003
Senior Member
pirateofcapeann's Avatar
Join Date: Aug 2002
Location: Gloucester, Mass. USA
Posts: 373
Thanks: 0
Thanked 1 Time in 1 Post
Rep Power: 14
Bilge Pump Discharge - New Thru Hull ???

If you''ve got a little daysailer then yea, you can put two bilge pumps on the same outlet and use a check valve too. But if you plan to sail out further then you can swim, you need to installed the second pump as a completely separate entity.
pirateofcapeann is offline  
Quote Quick Reply Share with Facebook

Quick Reply

By choosing to post the reply above you agree to the rules you agreed to when joining Sailnet.
Click Here to view those rules.

Register Now

In order to be able to post messages on the SailNet Community forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.
Please note: After entering 3 characters a list of Usernames already in use will appear and the list will disappear once a valid Username is entered.

User Name:
Please enter a password for your user account. Note that passwords are case-sensitive.


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:


Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page

Similar Threads
Thread Thread Starter Forum Replies Last Post
Glassing hull GreenEarth General Discussion (sailing related) 18 06-19-2009 11:52 PM
High Tech vs traditional-Comments? Pangaea General Discussion (sailing related) 38 08-07-2007 01:07 AM
hull construction cgha33 Boat Review and Purchase Forum 4 05-23-2003 07:11 PM
Bilge Pump Discharge - New Thru Hull ??? Terry Clarke Gear & Maintenance 3 05-01-2003 06:25 AM
bilge pump DQ halyardz Gear & Maintenance 3 06-04-2002 07:36 PM

Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On
Trackbacks are On
Pingbacks are On
Refbacks are On

For the best viewing experience please update your browser to Google Chrome