I actually deleted my message because I remember @notSoGnarly and were talking about this a couple years ago and found the old messages. I was actually looking at the SJS pump, pays to read the full description I guess. I'm planning on adding a second pump to the Bismarck for NATS.
Alright, follow on pump question. I have carved out a 3.5" (basing/tub/area) for the pumps to sit in. Now that I have a much larger area for the pump to take from what is a effective way to secure the pump to the boat? I am not confident my old way will still work.
I've used your exact method, with a rubber band, in the past and it worked fine. If you're afraid there isn't enough "meat" for the screws to grab now that there's not a bunch of water channel material adding thickness to the bottom, I'd drill through the bottom and use a bolt on each side. Drill down from inside the boat, then send the bolt up through the bottom with a nut screwed tight to the hull bottom (creating a threaded stud). The idea is something like this: ^ | | | Exposed Threads of Bolt, acting as a stud | Nut | Washer | Goop/E6000 | Hull Bottom | Goop/E6000 | Washer | Bolt Head From there, attach your pump using your zip ties, rubber bands, make a fancy bracket, whatever.
I was thinking of designing and 3D printing some kind of plastic bracket to hold the corners of the base. But I like the idea of running a couple bolts through the bottom of the hull.
In the past it's always been frowned upon to have a long outlet hose, for fear of vapor locks. In my experience, if there is an effect, it is minimal unless the hose is excessively long. I think the one pump in Bart the hose is at least 9-10" long, and it pumps just fine.
Screen door mesh from a hardware store works just fine. You do have think of the quality of the water your battling in when selecting the size of the screen. For example, our pond up in the PNW has A LOT of muck and silt in the water. Especially when we sink. Our pumps screens have bigger openings. The only thing that has been clogging them up in the last couple years is chunks of balsa wood. If you don't have a lot of silt and muck, you might get away with a finer screen.
yeah so there's this really great metal mesh you can use. @bsgkid117 remember that metal swiss cheese plate y'all were making the pump cradle filters out of for a while?
I don't check this thing as much as I used to. But making your own restrictors is easy and cheapish. A countersink bit from HF and some sharp scissors are the base line tools. Of course a drill press and fancy tapered bits could be used for better? performance. Get some round plastic stock that has the ID you want for the restrictor and an OD that fits your hose. Cut a 2" or so piece of the stock. On one end use the countersink bit to make a 45° ish conical hole. On the other end use the narrow blade of the scissors and spin/drill them to make a long tapered hole. The short 45° is the intake side, the long side is the output. Of course this could be done with various levels of care that maaaay give you some fractional gpm increases. I just got done building a bench for my drill press and at some point will be making some cleaner versions using clamps instead of my shaky hands, some pliers, and a drill.
What Nate described is the Amish Skunkwerks nozzle. Converging diverging nozzles have been a thing for a while now and those much smarter than I figured out what angles produce the best effect. Iirc you want 60° on the inlet and 15° on the outlet, or close to that. Like Nate said, using some plastic round stock from McMaster one can easily make one of these with a hand drill. Get a set of countersinks from harbor freight and a small pair of scissors. The scissor blade will cut into the plastic very easily when spinning in the drill. If people want more details and part numbers let me know.
What’s your material of choice? I’ve bought a few different plastics but haven’t executed yet, stuck to aluminum thus far. Kudos on the spinning blade of death approach, I spent too much on a tapered end mill. I’ve also used smooth screw extractors and stepped bits
I've been using 1/4" Delrin tube. ID is 1/8 but it's usually a little undersized so you can chase it with an 1/8" bit and have a proper sized outlet. Black Delrin® Acetal Resin Oversized Tube, 1/4" OD x 1/8" ID https://www.mcmaster.com/1830T119
Alright I got two pumps ready to put in the Bismarck. would it be better to put both of them in the same area where the single original one was? Or is it better to put one in back and one in front? my thinking is to split them up, one in back and one in front.
You want at least a couple of inches of separation to keep the pumps from scavanging from each other. As to one front, one back, I think it's more a matter of how you think you need the second one. Most people in recent (last decade or so) have used two in the aft as water flows aft during forward accelaration and that's the main direction of travel. A second school of thought is that a forward pump can assist if you switch directions and that same mass of water then tries to move towards the bow.
My first Biz had a pump in the bow and another in the stern. I think I'll try both in the stern and see how that feels. I have the space. It's not like it would be hard to move to the bow later on.
More captains in recent years have been trying the forward/aft pump arrangement. The idea being a bit of a flow chart: You need to keep some space (6" between motor shafts) between your pumps for efficiency. It's better to keep pumps on the centerline, as your boat will list and if you rock/roll the pump on the high side of the roll isn't doing anything. Our boats easily spend 40% of their lives aggressively reversing Lots of ships have a bunch of volume in the bow areas, whereas your typical pump is placed stern biased I ran a bow/stern pump in my Bart 1 and found it to be superior to my later attempts at stern pumps side by side, and often there isn't enough room to do two stern-biased pumps and get good separation. You won't be wasting your time by trying a forward pump and stern pump, but don't build yourself into a box so you can't change later if you want to experiment.
