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  1. #1
    Petty Officer 2nd Class
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    Default How do bilge pump thru hull fittings work?

    I'm looking to install a bilge pump and plumb it straight up about a foot and a half feet into my splashwell. So, the pump hose will be straight vertical. What is to prevent water from the splashwell, or discharge from the pump, from entering back down the hose? Do these fittings have some sort of check valve on them?

    Any recommendations for fittings would be helpful.

  2. #2
    Petty Officer 1st Class
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    Default Re: How do bilge pump thru hull fittings work?

    No, they don't have check valves. Why go into the splashwell? Boats are always rigged for overboard discharge.

  3. #3
    Commander BonairII's Avatar
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    Default Re: How do bilge pump thru hull fittings work?

    Plumb it thru the side of the boat....well above the waterline. Don't run it into the splashwell. The splashwell has only 2 small drain holes and a good bilge pump can pump water faster than a splashwell can drain it.
    1975 Starcraft SS-16' / 1977 Evinrude 75hp now w/ CMC power trim and tilt
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  4. #4
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    Default Re: How do bilge pump thru hull fittings work?

    Any thru hull fitting with a check valve would be inappropriate for the discharge line from a bilge pump, so you'll need to find a location which is high enough (well above the waterline) and mounted horizontally. This may require the use of a 90 thru hull as shown here. Whether the water discharges directly overboard (which is the preferred method), or falls into your splashwell shouldn't make a whole lot of difference, but I'd have to see your splashwell to make that judgment.
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  5. #5
    Petty Officer 1st Class blackhawk180's Avatar
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    Default Re: How do bilge pump thru hull fittings work?

    Most bilge pumps I've been around have a pretty high output as mentioned. If you plumb it straight up into your splashwell, you might be creating a fountain. Go out the side like Bonairll said.

  6. #6
    Honorary Moderator Emeritus Don S's Avatar
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    Default Re: How do bilge pump thru hull fittings work?

    If you want to keep the thru-hull fitting lower to the water line, just put a higher loop above the thru-hull well above the water line.
    Don S.


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  7. #7
    Commander BonairII's Avatar
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    Default Re: How do bilge pump thru hull fittings work?

    I'm a fan of mounting the fitting as high as feasible. God forbid that your boat is seriously swamped....you're gonna want the thru hull fitting to be above the flooded water level, so that the bilge will be able to pump it out quickly.

    JMO
    1975 Starcraft SS-16' / 1977 Evinrude 75hp now w/ CMC power trim and tilt
    17p prop- 36 mph @ 5900 rpm ( 2 people, 12 gals fuel, 2 batteries)

    1975 Starcraft Super Sport- Resto currently "in progress"
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  8. #8
    Honorary Moderator Emeritus Don S's Avatar
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    Default Re: How do bilge pump thru hull fittings work?

    Sounds good, but bad when your bilge pump empties onto the dock or someones feet on the dock. Been there done that.

    BP hose.jpg
    Don S.


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  9. #9
    Commander
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    Default Re: How do bilge pump thru hull fittings work?

    Quote Originally Posted by Don S View Post
    Sounds good, but bad when your bilge pump empties onto the dock or someones feet on the dock. Been there done that.

    BP hose.jpg
    don don't you have to have a vacuum break added in the loop line unless you are sure the output will never be underwater

  10. #10
    Lieutenant Commander
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    Default Re: How do bilge pump thru hull fittings work?

    Out the side and high. Don't use a cheap plastic thru hull as the UV will eventually cause it to fail. There are other materials but stainless steel is the best way to go.
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  11. #11
    Honorary Moderator Emeritus Don S's Avatar
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    Default Re: How do bilge pump thru hull fittings work?

    Quote Originally Posted by glenn property of pam View Post
    don don't you have to have a vacuum break added in the loop line unless you are sure the output will never be underwater
    Not as long as it's above the normal water line. Maybe 8 to 12" above the water. Just not so high that it dumps on the dock when tied up.
    Don S.


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