Thru Hull Pickup?

No0ne · Criminal Joined: 02 May 2003 Posts: 65

Hi,
What would be the advantages of using a thru hull pickup as opposed to a hole in the transom as a pickup? More pressure while underway? So pumps work less and fill faster? Could that be a hinderance in terms of loading the line with a bunch of pressure at say 40mph?

Ooh yah one more, any math guru's know the size of hole I will need to have so as not to choke the flow of 3 Simer pumps for ballast system?

Thanks, Gerrit

No0ne · Criminal Joined: 02 May 2003 Posts: 65

70 + viewing's and nobody has adviceor a suggestion!!.....wow

MrBlean · Posted: Mar 13, 2004 12:06 am Post subject: Hole size

The pumps don't allow any liquid to pass when they are not running so pressurising the input on the pump will make almost no difference. Hence there will be no discernable difference (if any) between a thro' hull and transom mount.

However, a transom mounted hole may end up being above the water line when underway or be in an area of aerated water so that it's effectively sucking in a lot of air too. That won't be good for the pump(s) and will also slow the fill rate.

In terms of pipe size needed, it's not just the diameter that's important but also the length of pipe. The longer it is, the more frictional losses (back pressure) there will be. Over few feet from the inlet to the pumps this should be an issue. However, it may be an issue from the pumps to the front sacs. I mounted a front and rear sac supplied from a T-piece fitted to a single Jabsco pump and virtually no water runs to the front sac until the rear is full. Hence I put a restrictor in the line to the rear sac so they fill at the same rate.

In terms of area, the Simers probably have a 3/4 inch diam cross sectional area to their inputs. Ideally, any common supply line to three pumps needs to have 3 times the cross sectional area of a single pump. The cross section of 3/4 pipe is 0.56 inches square. The diameter of a pipe with the 3 times that cross sectional area is 1.29 inches (call it inch and a quarter). If the pump inlet diameter is 1 inch, then the common pipe needs to be inch and three quarters.

Not as big an increase as you would think, huh?

For other diameters, simply take the square root of 3 times the diameter of the pump inlet pipe. If you had two pumps, it would be the square root of twice the diamater and for four pumps, te square root of 4 times the diameter.

Hope this helps Exclamation

No0ne · Criminal Joined: 02 May 2003 Posts: 65

Jeff(MrBlean),
Thank you, thats exactly what I was looking for. Thanks Again so much, you've got me a ton closer to starting.
Thanks, Gerrit

MrBlean · Posted: Mar 13, 2004 2:22 pm Post subject: A ton closer

Glad to be of service and know that my education wasn't competely wasted!