Macerator Pump & Thru-hulls

  • August 10, 2013 8:35 AM
    Message # 1362534
    Deleted user
    My new macerator pump has a 1" hose, I only have a free 3/4 it OK to reduce the 1" hose to 3/4" hose to utilize an existing free thru-hull?

  • August 10, 2013 6:43 PM
    Reply # 1362704 on 1362534

    I was hoping that someone else would jump in here, since I do not have a macerator aboard. But, since they did not, I'll try to help.

    The complete answer to your question would depend, to some degree, upon the pump you selected. My my gut feeling, nonetheless, is that this would not be "OK".

    First of all, I'll assume that you refer to the outlet hose and not the inlet hose. (The more typical inlet diameter is 1-1/2" rather than 1". ) Flow rate of a hose is dependent upon 3 factors: hose length, and hose diameter and inlet pressure, and changing any of these three would affect on flow rate. Presumably, hose length would remain constant between the two setups. Inlet pressure could change, based upon the pump's efficiency at the given hose diameter. But the largest contributing factor would be the hose diameter itself.

    Flow calculations are dependent upon several factors, but are ultimately a factor of the cross-sectional area of the hose (or thru-hull if that is the smallest diameter).  A 1" ID hose has a cross-sectional area of 0.7854 sq in. A 3/4" ID hose has a cross-sectional area of 0.4418 sq in. Therefore, reducing hose diameter from 1" to 3/4" would reduce volume approximately 56% (0.4418 / 0.7854 = 0.5625). Clearly, that would have a major impact on the efficiency of the system.

    Using a SHURflow 3200 as an example (which has a1-1/2" inlet and a 1" outlet), the manufacturer's specification is: "Use 1” minimum ID hose on discharge side of pump. Connect to thru-hull fitting above highest heeled point above waterline. Vented loop installations must vent at least 10” above highest heeled point above waterline. Use stainless steel hose clamps on all sanitation connections."  (The JABSCO 18590 has the same size inlet and outlet hose.)

    My advise would be to follow the manufacturer's recommendations, or it's likely that you'll end up doing the install again and possibly replacing a burned out macerator pump in the process. Potentially decreasing the flow by 56% is substantial. At the very least it would make the pump work harder and it would greatly increase the likelihood of a clog. Remember what you're pumping through this!

    Sorry... I know that's not what you wanted to hear. But that's what I would suggest. Might I ask which macerator pump (manuf. and model) you are installing?


    Last modified: August 11, 2013 4:16 AM | Anonymous member
  • August 12, 2013 6:17 AM
    Reply # 1363390 on 1362534
    Deleted user

    Thanks for your help.  Yes, the inlet is 1.5" and the outlet is 1".  The brand? I'm not sure, but I think it's a Jabco Clone.  For some reason, It's not available on Amazon anymore..nervous.

    I'm now trying to find a reasonably priced 1" seacock and thru-hull.  I'm new at boat refitting and have no local accessibility to boat parts and have to order everything online.  From what I can tell, I need a Flanged Seacock, thru-hull, and the piece the hose will clamp to, (don't know it's name).  Since I'm new to this, I'm a little nervous about drilling a hole in the boat but after a dozen YouTube videos about it, I'll hopefully get it right.

    Any more advice is always appreciated.

    Thanks again.

    Last modified: August 12, 2013 6:29 AM | Deleted user
  • August 12, 2013 6:47 AM
    Reply # 1363415 on 1362534

    It's always a challenge trying to find the right part online. Remove the risk and ask the one person who always has the right answer... Bud Taplin.

    If you go to the Parts List page for Thruhulls and Seacocks on the site I built for Bud's new domain, you'll likely find exactly what you need... and likely at a better price! Because your application is somewhat unique, I'd suggest calling (or emailing) Bud directly to explain your needs and circumstances. I'm confident he will get you exactly what you need and get it sent out to you in a timely manor, at a cost-effective price.


    PS: I just took a quick look at your blog... VERY NICE JOB! I'll have to return soon to give it a thorough examination.
    Last modified: August 12, 2013 7:39 AM | Anonymous member
  • August 12, 2013 11:34 AM
    Reply # 1363605 on 1362534
    Deleted user
    Thanks Jack.  I appreciate the help.  I'll check out the parts list.