3700GPH for 2 Tuna Tubes? Really?
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Category: Saltwater Fishing
Forum Name: The Work-Up
Forum Description: Game fishing related topics here
URL: https://www.fishing.net.nz/forum/forum_posts.asp?TID=126947
Printed Date: 01 Jun 2026 at 7:02am
Topic: 3700GPH for 2 Tuna Tubes? Really?
Posted By: BeastMode
Subject: 3700GPH for 2 Tuna Tubes? Really?
Date Posted: 21 Jan 2018 at 9:57am
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Hi All, I am fitting two tuna tubes on a trailer boat and trying to get my head around the pump requirements. Do I really need 3700GPH for this (pic below)? That would be 14,000 litres per hour or 233 litres per minute??? (divided by two tubes). Keen to hear from those that have successfully kept tuna alive for the day and what they have? I see a few posts where people have used the 1600GPH Bronze Tournament Rule Pumps but cant find them online here (NZ).  |
Replies:
Posted By: Cocker
Date Posted: 21 Jan 2018 at 10:06am
| Have just fitted a Rule 1600 lph thru hull. Struggling two lift water to top of tube . A lot of head pressure. Replacing with 3700gph |
Posted By: Tagit
Date Posted: 21 Jan 2018 at 10:07am
| 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. |
Posted By: Catchelot
Date Posted: 21 Jan 2018 at 12:39pm
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I think the general rule of thumb is 1500 GPH for two tubes. I have also heard bad things about Rule pumps not being able to last the distance, overheating and burning out, I will see what more info I can dig out...
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Posted By: Tagit
Date Posted: 21 Jan 2018 at 1:24pm
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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. There are other calculations that suggest that you will get close to enough flow velocity over the tune to keep them alive with only 600gph per tube, but in our warmer conditions (lower oxygen levels) my feeling is that you will probably soon be wishing you had bought the bigger pump.
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Posted By: MAD MAX 2
Date Posted: 21 Jan 2018 at 1:26pm
| I have two tubes each hooked up with a 1100 gph rule bilge pumps works really well and a lot cheaper option for the pumps |
Posted By: BeastMode
Date Posted: 21 Jan 2018 at 2:13pm
| Thanks for all the feedback ^^^^. It's gold! |
Posted By: BeastMode
Date Posted: 21 Jan 2018 at 2:14pm
Thanks for this mate. I will go with the 3700. I have now realised I have no idea what I'm up to setting it all up!! |
Tagit wrote:Posted By: BeastMode
Date Posted: 21 Jan 2018 at 2:36pm
Re the charging system output - is there anyway to work this out? All new to me.... |
Posted By: Alan L
Date Posted: 21 Jan 2018 at 2:55pm
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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 ------------- Legasea Legend member |
Posted By: Tagit
Date Posted: 21 Jan 2018 at 3:18pm
| 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. |
Posted By: BeastMode
Date Posted: 21 Jan 2018 at 4:30pm
Thanks. It's a 2009 Surtees Hardtop with a 2009 Yamaha 90hp 2 stroke. Isolator switch thing on the batteries - house/accessories. I will do some googling. |
Posted By: BeastMode
Date Posted: 21 Jan 2018 at 4:31pm
Cheers Alan. |
Posted By: BeastMode
Date Posted: 21 Jan 2018 at 4:48pm
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This me here: https://www.yamaha-motor.co.nz/products/marine-outboard/2-stroke-mid-power/11-90a" rel="nofollow - https://www.yamaha-motor.co.nz/products/marine-outboard/2-stroke-mid-power/11-90a 12 volt 10amp? |
Posted By: Tagit
Date Posted: 21 Jan 2018 at 5:42pm
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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. You could go for maybe a single tube and run a skippy on one side and a big jack mac or Koheru on the other from a live bait tank. Still wouldn't want this off your engine battery though so would be looking at a largish house battery on a VSR setup knowing that it will get run down during the day but that you can charge it from the mains over night. Say you are drawing 8 amps for a single tube pump and can budget maybe 2 amps average from the alternator after running your electronics etc then you lose 6 amps per hour. Allow say 8 hours of tube running and you need ~50A/H and to stop that battery getting killed each day you need to double that so ~100A/H house battery. To be safe I would probably try and go a bit larger if you have the space. If you really want two tubes you could up the battery size and run a larger pump or the other alternative is to put 2 tubes on the smaller pump as you initially asked about and have valves in the feeds so you can run just 1 tube if you have a big skippy or 2 tubes if you have smaller skippies or some other smaller baits (can drop big Jack macs & Koheru etc into the tubes also. Might not give hours and hours of life to a pair of Skippies but could be a workable solution for your constraints.
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Posted By: Alan L
Date Posted: 21 Jan 2018 at 6:23pm
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If your alternator is a 10A (quite feasible) that will be the low end of what may be available. you can probably upgrade that to around 20A. They fit a new system under the flywheel. Not a big job. just enquire with your yamaha service guy. Regards Alan ------------- Legasea Legend member |
Posted By: Alan L
Date Posted: 21 Jan 2018 at 6:49pm
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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. But you are not going to have much leeway. Regards Alan ------------- Legasea Legend member |
Posted By: Alan L
Date Posted: 21 Jan 2018 at 6:55pm
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If you end up at say 1000rpm with a big fish on for a few hrs, you will be sucking your batteries dry, to keep the tubes running. Another option may be to run 2 half size pumps - one on each tube. Then you can drop one tube out if not needed. If you only have 1 tuna left and have to run two tubes - why not drop one out. Or if you are on reduced rpm for an extended period, maybe sacrifice one tube? Alan ------------- Legasea Legend member |
Posted By: 86mad
Date Posted: 21 Jan 2018 at 8:12pm
| 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 |
Posted By: BeastMode
Date Posted: 21 Jan 2018 at 8:24pm
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Alan and Tagit - thanks heaps for the help. I've got some thinking to do! Cheers |
Posted By: BeastMode
Date Posted: 21 Jan 2018 at 8:24pm
Cheers. Smart Marine has a reasonable price on them. Somewhere in between those prices. |
Posted By: Alan L
Date Posted: 21 Jan 2018 at 8:34pm
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Since your power options are marginal, my preference would be to split to 2 x 12v 16A pumps if you can. Gives you more flexibility. I think it is feasible you can get to a 30-35A charging unit for the motor. At which point you are holding your own at troll and beyond. Below troll you are loosing charge. It is logical for the standard charge to run at 10A. GPS/fishfinder/radio = about 5A, so even at idle you are holding your own. But mega pumps change the equation, a lot. Regards Alan
------------- Legasea Legend member |
Posted By: edge01
Date Posted: 22 Jan 2018 at 9:57am
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just to jump in here. Ive got a Yamaha xa200 which shows that It has 43amps of charge. I have two large house batteries linked to give 12 volts ( I can never remember which term it is. parallel or in series) . Do you think this would give me enough grunt to run a tuna tube with the 3700? I have two sounders running of them too. A lowrance lxc and a furuno fcv. vhf, stereo ( which I never use) I run at around 2500 trolling.
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Posted By: Alan L
Date Posted: 22 Jan 2018 at 10:16am
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Your two batteries are in parallel. You have one to run your electronics and one to start your engine basically. And you can switch over to the other if needed? 43 A is plenty, but if you run a 24V pump you will need to reconfigure 2x12V batteries to series to get 24V. Beyond that I am in the dark. if you ran 2x12V pumps (if possible) I think things would be simpler, electrically. Alan ------------- Legasea Legend member |
Posted By: Tagit
Date Posted: 22 Jan 2018 at 10:39am
Are your house batts 2 x 6v cells or 2 x 12v cells? It is more typical to have 2 x 6v cells in series for a house batt but 2 x 12v in parallel is not unknown either. Series is +ve hooked to -ve between the 2 batteries and parallel is +ve to +ve and -ve to -ve. Check what the label on the house batts say re voltage and A/H's. If you configure the the pump to run off your house batteries (I assume that your start batt is fully independent?) then worst case you run the house batt down and have to turn off the pump to get some charge back in it. At 2500rpm with a 43amp alternator I would expect that you should be fine running the setup you have plus the 3700.
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Posted By: RH580ikanui
Date Posted: 22 Jan 2018 at 10:53am
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Gidday BM I have a Shurflo 2000gph 12v running on my 5.5 surtees with 90 etec. Runs 2 tubes plus my live bait tank piece of piss. http://shurflo.com/marine-products/livewell-pumps/shurflo-high-flow-livewell-pumps/60-shurflo-livewell-2000-12-vdc" rel="nofollow - http://shurflo.com/marine-products/livewell-pumps/shurflo-high-flow-livewell-pumps/60-shurflo-livewell-2000-12-vdc I bought mine from Walmart out of the states. Heaps cheaper than buying one here. I prefer this type as it has an inlet pipe rather than a scavenge setup like a bilge pump. Mounted mine on a bracket with just the inlet hosetail protruding below the hull. works a treat,
------------- "IKANUI" RH580 SUZUKI DF140 |
Posted By: Tagit
Date Posted: 22 Jan 2018 at 11:28am
| Looks like 90 Etec is over 20amps charging at 2500rpm and provides up to 45amps of usable charge at WOT. Bit different to the old 2 stroke Yammie at 10amps max. Charging rates on outboards are all over the place depending on the manufacturer. Only reasonably sure thing is that later designed engines will probably have bigger alternators than earlier designs as the amount of electronics on boats has increased immensely. |
Posted By: Alan L
Date Posted: 22 Jan 2018 at 4:09pm
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That Shurflo 2000 only uses 10A according to specs. With an upgraded charge system you will bolt in. I recently parted with an older Mariner 50 that had a 30A charge system. It was an upgrade from the basic unit. But I expect most if not all 90HP motors would be upgradeable to around 30A and maybe a bit more. Alan ------------- Legasea Legend member |
Posted By: BeastMode
Date Posted: 22 Jan 2018 at 6:22pm
Cheers. Spoke with someone today that said my motor couldnt be upgraded
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Posted By: Alan L
Date Posted: 22 Jan 2018 at 6:46pm
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seriously? That's weird. if not, then you are a bit screwed. 2009 Yamaha 90? Most manufacturers offer at least 2 options. I would get a 2nd opinion. Regards Alan ------------- Legasea Legend member |
Posted By: Tagit
Date Posted: 22 Jan 2018 at 6:54pm
| Might have been manufactured in 2009 but it was probably designed in the 1990's, or maybe even core design back in the 1980's. |
Posted By: Alan L
Date Posted: 22 Jan 2018 at 7:06pm
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Not saying the guy who gave the advice is wrong - presumably he knows what he is doing. My experience is with mercury/mariner and they are old time engines - simple and robust - 2 strokes i am talking about. And they have had 2 options - high /low as long as I recall. the 50 HP Mariner kept blowing regulators every 2-3 yrs. At some expense. Until they realised it had the high output alternator. problem solved. 2 different colours under the flywheel. to think a manufacturer would limit themselves as late as 2009 to low output is hard to figure. My Mariner was 90's. regards Alan ------------- Legasea Legend member |
Posted By: edge01
Date Posted: 22 Jan 2018 at 7:47pm
No I have a totally separate start battery on a vsr. the two batteries are in parallel. I think that the batts are 600 amp hours from memory but I would have to check that to be certain. I know that the start battery is 1000cca. These are big batteries and they are not cheap
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Posted By: Tagit
Date Posted: 22 Jan 2018 at 7:56pm
| Most likely they won't be 600A/H. If they were they would probably be around 200kg+ each. The more common 'big batteries' for house circuits are often around 200A/H. They tend to be around 60kgish per batt in 12v cells from memory. Anyway it sounds like you are plenty well equipped. Just as a footnote most large Yamahas have a twin charging harness which eliminates the need for a VSR. It's about the same price as a VSR probably but saves a bit on the extra cabling. |
Posted By: [email protected]
Date Posted: 22 Jan 2018 at 8:56pm
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Definitely need the volume of the 3700's. Im in tagits Camp and run 4 tubes with two 3700's. catchelots statement on longevity is a mystery to me. I do 100's and 10o's of hours of pump use each year and have never had a failure and pumps are now 7 years old.
------------- http://www.blackbillsportfishing.co.nz/" rel="nofollow"> 
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