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Is 1 1/2" Thru Hull Enough?

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  • Is 1 1/2" Thru Hull Enough?

    I'm adding the Wakemakers TankBuster to my 2004 X30 and was ready to add 2 more thru hulls to make sure I had enough water to run all 3 factory pumps at the same time.

    As I was surveying the hull and where I would add the other two thru hulls, I noticed that my current inlet is 1 1/2 inches.

    Now, I'm no math or plumbing expert, but assuming the inside diameter of these hoses is the hose size, I have a 1 1/2 inlet hose feeding 3, 3/4" pump hoses. If not, close enough...

    The surface area of a 1.5" circle is 1.77 in/sq. The surface area of a 3/4" circle is 0.44 in/sq.

    Question #1 - So 3, 3/4" hoses together is 1.32. That being less that 1.77, shouldn't the 1.5" thru hull supply be enough to feed those 3 pumps?

    Question #2 - If the distribution manifold is a bottleneck and not the intake, I could do some plumbing magic, get rid of the manifold, and not need extra thru hulls, right?
    Attached Files
    2004 X-30 5.7L MCX

  • #2
    There's a manifold and some one way valves if yours is like mine. That complicates your fluid dynamics math. WakeMakers recommends the 1" feed per pump because it's easy to plumb and the fill times are improved with this set up.

    Could you come up with a faster solution using the existing 1 1/2? Possibly and I'd be interested in seeing what you did and what your results are. If you don't want the trial and error the 1" thru hull per pump is proven to be faster by several on this site.

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    • #3
      1-1/2 inch line should have no issues filling 3 bags at a time @ ~12gpm each. See the attached head losses from Cameron Hydraulic Data handbook (fluid dynamics holy grail). It's not polyethylene pipe of course but it's close enough and doesn't include pressure loss through fittings/checks etc. Your largest loss is in the 3/4" pipe, going to 1" as noted above is a good idea. Your approach for surface area makes sense.
      Attached Files

      Comment


      • #4
        Add the extra thru hulls and plumb 1" hose throughout. It will be a dramatic improvement on your fill/drain time.

        Comment


        • #5
          Pondo, thanks for the engineering perspective on this. Not being an engineer, I don't know what to think about head losses but will take your word that we are good there.

          Strangely my boat is plumbed with the 1 1/2" hose from the thru-hull to the manifold, 1" hose from the manifold to the pumps, and 3/4" hose from the pumps to the ballast tanks (soon to be bags). I'm not sure why they reduced the hose to 3/4" at the pumps but I am replacing the 3/4" with 1" with the bag installation per your recommendation.

          CheeseSteak1, since it costs me basically nothing to try to maximize what I've got without drilling holes in my boat, I'm going to see how it works. If it takes less than 10 minutes per bag I think I'll leave things be. We always trailer our boat so i've got 10 minutes or so to fill while my wife parks the truck/trailer and another 5-10 to fill while we get things setup. In the end, you might be right.

          Thanks to both of you (and Keith2230) for the responses!
          2004 X-30 5.7L MCX

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          • #6
            If you have time than it's no loss or gain. I just get impatient when setting up. My fill/drain time is 4:45 with everything plumbed with 1" lines, independent thru hulls and no check valves (except for vent lines). Good luck with the new setup and update your thread with the results.

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            • #7
              A 1.5 thru-hull is more than adequate to supply 3 reversible pumps or 4 1200 aerator pumps. Having sad that, cannot speak for the rest of the plumbing schematic. With a good downstream design, there will be no flow difference with this setup compared to each pump on its own thru hull.

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              • #8
                Basically your pressure loss through the 3/4" pipe is nearly 3 times as much as the pressure loss in the 1-1/2" pipe per linear foot of pipe with all 3 ballast pumps on.

                What ballast pump are you using? Maybe I can find a pump curve on it and really give you a good feel on your fill time.

                Comment


                • #9
                  pondo, my ballast pump is the Jabsco Ballast Pump Model: 18220-7123 - See pic

                  PS - After using my incredibly myopic brainpower for a few minutes, I figured out why MasterCraft went down to the 3/4" hose. The input/vent on the factory hard tanks are 3/4" barbed fittings.
                  Attached Files
                  2004 X-30 5.7L MCX

                  Comment


                  • #10
                    OK, let's have some more fun. As I'm adding some ballast bags, (thanks WakeMakers) I see that everything is plumbed with 1" hose to the pump and then reduced to 3/4" coming out of the pump. (See very bottom of my picture above) I want to plumb 1" hose all the way to the ballast bags. Checking the math and assuming my surface area theory is close to correct as pondo said it was...:

                    Surface areas:
                    1 1/2" = 1.77 in/sq
                    1" = 0.79 in/sq
                    3/4" = 0.44 in/sq

                    So, if I leave my KGB on 3/4" hose, I now have (0.79 + 0.79 + 0.44) = 2.02 > 1.77

                    Thus I could keep my rear bags on the same 1 1/2" thru hull but should add another 1" thru hull for my KGB and upgrade that line to a 1" hose as well. But while I'm adding a thru hull, I might as well add 2 of them, right?
                    2004 X-30 5.7L MCX

                    Comment


                    • #11
                      Originally posted by pondo View Post
                      Basically your pressure loss through the 3/4" pipe is nearly 3 times as much as the pressure loss in the 1-1/2" pipe per linear foot of pipe with all 3 ballast pumps on.

                      What ballast pump are you using? Maybe I can find a pump curve on it and really give you a good feel on your fill time.
                      These numbers are likely true, i have no reason to dispute them. however, im not following the relevance in this application. The 1.5 is for a common feed to 3 pumps with a .75 outlet of each pump. The discussion is not between .75 or even 1" outlet compared to using 1.5".

                      With an impeller pump, a smaller passage just increases the velocity. In most systems, the sac fitting is the real bottle neck. In the case of an impeller pump, the flow remains pretty much the same at the sac, as it was leaving the pump.

                      Dont over think flow rates, internal hose friction, head loss and all that jazz. KISS. an impeller pump will remain very close to its rated GPM. A typical aerator will drop off 20% give or take at the sac.

                      .75 t-hull will supply a single ultra ballast or jabsco, 1" for the king
                      1" will supply 2 impeller pumps or a single king
                      1.25" for 3 ultra or puppy's or 2 kings

                      Comment


                      • #12
                        The diameter of the line does matter as his question was if the 1-1/2" inlet will bottle neck his fill time. In my opinion it will not from an engineering point of view. The cross sectional area of the pipe is only one part of the head loss calculation. The driving factor is the fluid velocity as head pressure increases to the square of fluid velocity.

                        The 18220 pump is rated for 9 gpm @ 5 feet of head:
                        http://www.go2marine.com/docs/mfr/jabsco/95774F.pdf

                        @ 9 gpm the ¾” line has 2.5’ of head losses per 10 feet not including fittings OR elevation change.
                        @ 27 gpm the 1-1/2” line has 0.7’ of head losses per 10 feet of pipe.

                        Worst case, you’ll see 8 gpm out of each ballast pump or 66 lb/min. Keep in mind at idle your alternator won’t supply sufficient voltage to keep that rate up. You’ll need 1500+ rpm to do it due to the amperage draw.

                        I wouldn't cut another hole in your boat - KISS like another poster suggested. Using 1" lines in place of 3/4" where you can may give you a bit faster fill times with not much extra work/cost.

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