Sending seawater to two devices from single thru-hull-gctid810523

[Solandri]

I need to add a pump for a bait tank, and I wasn't looking forward to drilling a new hole in the bottom of the hull. Then I noticed this nice pre-existing thru-hull complete with bronze seacock and strainer for nothing but picking up seawater to use in the head. And I get the idea of using that for both the pump and head. But being that this is my first non-trivial modification to a boat, I thought I'd run it by you guys first.

Here's how I imagine it working:

[ol]

[li]Remove head pickup tube from seacock.[/li]

[li]Add a three-way T- or Y-fitting to the seacock.[/li]

[li]Attach pump to one outlet of above fitting. (Keeping the pump lower than water level, but also keeping the hose running uphill so there's no place for a bubble to airlock.)[/li]

[li]Wire pump to switch on console..[/li]

[li]Run hose from pump to bait tank.[/li]

[li]Attach ball vale or check valve to other outlet. (To prevent the pump from sucking in air via the head.)

[li]Re-connect head pickup hose to check valve.[/li]

[li]Double-clamp all hose connections.[/li]

[/ol]

So will that work? Anything I'm missing or should change? Should I add a check valve before the pump as well? I'm guessing a Y would work better, since a T may make it difficult to pump water into the head when the bait pump is running. OTOH, with a Y, would it be possible for the pump pulling water up to force water into the head?

[builderdude]

That's how I've plumbed my wash down pump minus the check valve on the head hose (probably should add one) Works great.

[kwb]

Don't do it with something that can't run dry - my washdown pump was sharing with the genset. Washdown sucked harder than the genset, didn't notice it and overheated the generator. I got lucky that it only killed the impeller and no other damage.

[Pcpete]

On our previous boat, I put Y in the flush water line for my wash down, it worked well except when I tried to use the wash down pump to feed a cooler and have it act as a live well to keep crab fresher. The hull fitting wasn't a type that would draw water in while running the boat at its customary 25kn. Idling around, it worked well. Using the electric flush at the same time the wash down was working wasn't a problem.

I completely agree with not doubling up on something that has to have an uninterrupted or restricted flow.

[builderdude]

FWIW my head won't draw any water while on plane, not sure I'd want to use the head while running at speed :whistle: I haven't checked the wash down pump on plane but personally I'll use that to clean fish guts off the back end, wash clams or sand from shoes etc. Dont think I'll be doing any of those things on plane either :silly:

[Solandri]

"Pcpete" post=810539 wrote:
On our previous boat, I put Y in the flush water line for my wash down, it worked well except when I tried to use the wash down pump to feed a cooler and have it act as a live well to keep crab fresher. The hull fitting wasn't a type that would draw water in while running the boat at its customary 25kn. Idling around, it worked well..

Yeah, that possibility occurred to me as well. I figure worst case I can swap out the strainer for a scoop-type; maybe add a pressure regulator to the head pickup so the scoop doesn't force water into the head. The objective here is to avoid drilling a new hole in the hull.

The head is a manual pump, so I really don't foresee that starving the bait pump of water.

[hookemdano]

here is what I have used for years...a great bait pump and has a dual ports...one to the bait tank and the other goes to my washdown pump...this may work for you and very ez to install

http://shurflo.com/marine-products/l...magnetic-drive


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[mister_larry]

How does the bait tank drain? Is it possible to place your Y fitting in the drain outlet and both fill and empty the tank through that opening?

Rather than needing to change out the pick-up scoop on the outside of the hull you could just drop a submersible pump overboard on the morning that you wanted to fill the bait tank. Then retrieve it, stow it, and close the valve on the Y.

I offer this because I suggest caution in any hull modifications that could cause problems when removing the boat from the water.

[Solandri]

Initially it's going to be a bait bag hanging over the transom that simply drains out the bottom. Later I hope to add a proper bait tank in the cockpit (the size and locations of the hatches have ruled out every prefab one I've found). That will probably drain via a hose I stick into one of the scuppers. Both will be raw water fed, not aerated, so the pump needs to be on all the time.

The head intake strainer and engine raw water intake scoop are in-line on the 2556, and positioned so they fit in between the bunks when the boat is trailered. So no issues replacing the strainer. I'm mostly worried about the scoop forcing water into the head. There's a small chance the scoop could disrupt flow into the engine intake. But according to my mechanic that's a secondary intake (main one is on the stern drive), and I don't even need to have it open to operate the engine.

I dropped by the storage yard to take some measurements, and lo and behold one of the POs already plumbed it for a pump. Tucked next to one of the storage boxes, there was already a T-junction, extra hoses, hose clamps, and a shutoff valve. I vaguely recall the PO I bought it from mentioning that another PO had installed a raw water washdown system, was unhappy with it, and replaced it with the fresh water washdown it currently has. The hardware is probably left over from that.

So it looks like this is going to be a lot easier than I expected. Just need a scoop strainer, pressure regulator, pump, and hose long enough to reach the bait tank. I think I'll still buy a transom-mount pump as a backup. It's less than $100, and without a backup, a bait pump failure means losing about $40 worth of bait and potentially wasting $300 worth of gas.

[builderdude]

OEM set up pulls engine cooling raw water through the leg, you sure your other through hull is plumbed into the raw water feed for the engine?

[Solandri]

OEM engine is long gone on this boat. According to the paperwork, the pump impeller disintegrated, the PO didn't notice and drove the boat until the cylinders seized up.

So the scoop is not original? According to the mechanic, both stern drive and thru-hull intakes feed into the heat exchanger for the freshwater cooler. He did say the stern drive intake was enough, and it was unnecessary to open the scoop seacock. I'll take another look and ask him if it'd be a problem repurposing the scoop for a bait pump.

Edit: Hmm, looking at the pic, the hose goes under the engine. I presume it intercepts and merges with the raw water from the drive leg. (The freshwater cooling unit is on the top right side of pic, with the orange radiator fluid hose going to it). I wonder if the PO added it to cool the engine passively via water from the scoop when under way, in case the impeller for the drive leg intake ever went kaputt again. Given he'd paid $16k for a new engine due to a failed pump, I could see him being overly paranoid about this. Scoop seacock has the blue handle, head seacock has the yellow handle. The green T-junction in the lower right is the extra plumbing I mentioned finding. (Stern of boat is left side of pic)

https://goo.gl/photos/7YDjtQ2QYjvRa9Pg9