thru hull location

(drknute3) · (drknute3) **Join Date: Sep 2008** 03-06-2009, 7:48 AM

In the final planning stage for my ballast system on the Cobalt. Gonna use 2 Jabsco pumps to fill 4 bags. My problem is where to put the thru hull. If I place it on the bottom, I can fill on the fly. But getting the right spot so it doesnt interfere with the padded bunks is going to be a PITA. If I place the thru hull on the transom, I should still be able to fill while putting around right? I realize I wont be able to fill on plane, but if I can fill while putting around I would be OK with that. Plumbing it from the transom will be much easier as well. Thoughts?

(tl_hereford) · (tl_hereford) **Join Date: Nov 2008** 03-06-2009, 5:09 PM

Might suck in air while "putting" around. Not familiar with your boat but most go through the bottom.

(drknute3) · (drknute3) **Join Date: Sep 2008** 03-06-2009, 5:29 PM

Thanks for the advice. That was one of my concerns as well. Worried about possibly sucking up air or exhaust while filling while putting around. Wondered if anyone had a thru hull on the transom. Not totally against drilling thru the bottom, just gonna be a serious PITA to get it right. Measure 20 times, drill once. lol

(lovin_the_wake)

I wouldn't put it on the transom unless you're planning on sitting still while you fill. Cutting a hole in the bottom of my boat scared the $h|t out of me but after a few beers it didn't bother me at all

(alindquist) · (alindquist) **Join Date: Mar 2004** 03-09-2009, 11:30 AM

you could also "T" of the raw water pick up and not have to put a hole in it all. I think that If I were to do an integrated ballast that's how I would do it. What kind of Cobalt do you have?

(drknute3) · (drknute3) **Join Date: Sep 2008** 03-09-2009, 1:12 PM

Its a 2000 model 226. 5.7 Volvo with Duoprop outdrive. Problem with using the fresh water intake is that the engine would have to be running to get any flow right?

(denverd1)

Nope. Its a open line out to the lake. Will pull water in without any problem.

*as long as you T in before the impeller/water pump.*

(drknute3) · (drknute3) **Join Date: Sep 2008** 03-09-2009, 2:08 PM

Isnt the impeller in the outdrive? This is an I/O.

(towboat_222) · (towboat_222) **Join Date: Feb 2007** 03-09-2009, 3:02 PM

not on volvo the run it off of the crankshaft.

(alindquist) · (alindquist) **Join Date: Mar 2004** 03-09-2009, 3:41 PM

impeller should be behind the raw waterpump housing... (think, it's not the lower unit) not sure on weather or not the boat would have to be running but wouldn't it be anyway?

(cla10beck) · (cla10beck) **Join Date: Dec 2007** 03-10-2009, 5:28 AM

On the Volvo, I believe it has an impeller just like an inboard, on the bottom right or left of the motor (different from mercs), so as long as you "T" the line between the outdrive water intake and the impeller pump, you should be find and you don't need a thru hull. Just wake sure to put a check valve on the line so the impeller doesn't suck you sac dry.

(crushing76) · (crushing76) **Join Date: Feb 2007** 03-10-2009, 7:18 PM

^^^^^^ You definately dont want to have your sack sucked dry!!! Or maybe you do!!

(drknute3) · (drknute3) **Join Date: Sep 2008** 03-11-2009, 6:55 AM

I will have to do some checking when I get it out of storage. Would be great to not have to drill a thru hull as we plan to keep the boat for only 2-3 more years. What would be the best option here. I could do a single T from the intake line and then T it to each pump or do 2 T's off the main line? Anyone know how big the hose is by chance? No problems with engine cooling if I am diverting water to my pumps instead of into the engine?

(alindquist) · (alindquist) **Join Date: Mar 2004** 03-11-2009, 9:15 AM

I have herd of several people doing this without cooling issues. Then again I wouldn't run the boat at WOT with it filling until you know for sure. If I were to do it I would probably just "T" it once off the pick up (and put a manual shut off valve on it) then from there do what you have to do.

(drknute3) · (drknute3) **Join Date: Sep 2008** 03-11-2009, 11:44 AM

I will see how big the feed hose is and plan to T it once, then T that line to each pump. Wonder if it draw enough volume to fill them as quickly as a 1.5" thru hull. Those intakes on the outdrive are fairly small. Back flow wont be a problem as I will have check valves on the lines to the pumps anyway.

(mobv) · (mobv) **Join Date: Jun 2002** 03-11-2009, 1:10 PM

Centurion placed the thru-hull on the transom for a couple years. I never had a problem if I was just idling around. Other people had lots of difficulty keeping the pumps primed. Some claimed the exaust bubbled-up and caused the pumps to suck air. You would not have that problem with an i/o.

(cla10beck) · (cla10beck) **Join Date: Dec 2007** 03-12-2009, 6:59 AM

The impeller pump runs directly in relation to the engine rpm. So if you are running the engine at 3000rpm, it will be 3 times the water flow into the engine than if you were running at 1000rpm. So I would guess that your ballast system won't have enough flow to exceed what your engine would be pulling in at WOT, so you would be safe as long as you aren't filling the ballast while the engine is at high rpm.

(drknute3) · (drknute3) **Join Date: Sep 2008** 03-12-2009, 7:53 AM

That sounds much easier than installing a thru hull. It is also reversible. I think I will start with a T in the intake line and revert to a thru hull if I encounter any problems. this would also allow me to test everything in the driveway using the muffs on the outdrive.

(Message edited by drknute3 on March 12, 2009)