Hi All, 

I use 2 of these (3700) to feed 4 tubes and I wouldn't want any less. You may get away with less for 2 tubes but I think it will get marginal unless you only ever store small skippies. One thing to watch for on a trailer boat is that the pump current draw added to all your electronics etc may start to push the limits of your charging system at trolling speeds depending on what power plant you are running.

BM - a few considerations. I assume the bronze based pumps are for direct mounting to the hull. If you have an aluminium boat don't use one. If fiberglass or wood hull then fine. I assume that you will have something like a meter or so of head to the overflow point on your tubes? If so that drops a 1600gph pump to probably around 1200gph in a perfect world. Then split that between 2 tubes and you get maybe 600gph with perfect voltage and no parasitic drag on the pick up (they say not to use a scoop as it can damage the pump). Real world after bends in pipes and some pickup losses and allowing for the head etc you could easily be down around 20 - 25lpm for each tube and that doesn't sound like a lot to keep a half decent tuna alive.

Thanks for all the feedback ^^^^. It's gold!

Tagit wrote: I use 2 of these (3700) to feed 4 tubes and I wouldn't want any less. You may get away with less for 2 tubes but I think it will get marginal unless you only ever store small skippies. One thing to watch for on a trailer boat is that the pump current draw added to all your electronics etc may start to push the limits of your charging system at trolling speeds depending on what power plant you are running.

Re the charging system output - is there anyway to work this out? All new to me....

What engine & hull do you have? Model and year? Some later gen outboards have alternators that get close to full output at modest rpms but some older ones don't produce a lot until you get the rpm's up. Should be able to get at least some basic specs online.

Alan L wrote: Depending what motor you are running, (outboard?) it is specified with the motor - ie a query with the agent (model No ) will get you the answer. And there is usually a high output option which can be fitted. If inboard, then it will depend on the Gen specs - may be written on it? - rated in Amps. Alan

Cheers Alan.

There you unfortunately have a problem BM. 10amp seems really low output for a 90hp engine but the 2 strokes tended to have more primitive alternator setups. I would try to double check that number but if that is correct you might only have 5 to 7 amps at trolling rpms and next to nothing at live bait speeds. It wouldn't run a 16amp pump without flattening your battery. 

Just looking at the pump specs you posted, you need a 30+A alternator. That maybe possible. Your agent will be able to tell you how high you can get as a charger unit. But clearly it is going to be marginal power wise. I'm guessing your trolling revs are around 2500+? In which case you will be close to full alternator output/charge.

Have a look on amazon for the pump .atm I think they are around $300-$320nzd landed.locally the cheapest I found was $520-$600