Scratch built Typhoon advice needed

[Mermod]

I have a Typhoon project I've been playing with over the last 25 years or so that I really would like to get into the water, there was very little access to the net when I started so my best option at the time was to buy the Dragon plastic kit and scale it up to 1.8m long, it involved taking all the measurements from the kit and making a 2 piece solid MDF plug with all the tile details scribed into it then the usual process to make the final glass hull, my thinking back then was to make it tough so its a lot thicker than necessary and as such is now extremely heavy.
Around the time Engel released their Typhoon I eyeballed it and decided their single watertight compartment with twin piston tanks was pretty cool so I installed a similar WTC in mine and made some rudimentary tanks but again I've over engineered the tanks so they draw way too much current and weigh far too much and to be honest I'm pretty impressed with the simplicity of the pump driven systems put out by OTW.
So the question is am I crazy for wanting to remove the compartment already in it and go the pump route? im hoping a single cylinder with a central tank might be enough or should I seriously be looking at a tank either end. perhaps I should keep the engel type compartment and put a pump driven tank in instead (I don't mind this idea)
Any thoughts would be appreciated and I do have a few more questions but I'll leave it here for now, I hope the attached photos help.

Regards
Phill

[Subculture]

Piston tanks shouldn’t draw an excessive amount of current. What are you using for piston seals, o-rings?

[Mermod]

Piston tanks shouldn’t draw an excessive amount of current. What are you using for piston seals, o-rings?

Yes O rings, plus I'm not thrilled with the gearing, I really would like to simplify the whole setup.

Phill

[Subculture]

They do tend to be higher in friction than the pneumatic seals Engel use, If you keep squish to a minimum it helps a lot, quad rings are useful for this application as they won’t spirally twist. Specialist seals like the type Engel use along with others like Airzet are really nice, but only come in a limited range of sizes, which often don’t align with tubing. Are you using aluminium pipe on the tanks? If so it’s not ideal, aluminium is quite a high friction material and tends to corrode unless coated. Plastic pipe much better and lighter. You can simplify gearing by using planetary geared motors, then you only need a single stage to clear the spindle. I’d stick with the piston tanks, but it’s your build. If you want to step a2ay from the tanks I would consider a hybrid ballast system using an air pump an aspirated tank to get the decks awash, then use a smaller trim tank perhaps with peristaltic or geared pump for that last bit of trim, the tank could be something simple, like a bag, or a syringe mounted vertically inside the main tank.

[Mermod]

Yep guilty on all counts :) aluminium tanks and O ring seals, I do like the aspirated tank idea though, would that be a single central tank or best split one either end?
One more question on piston tanks, mine draws the threaded rod back into the hull where it hits a limit switch inside, I have seen some that the piston tank has an open end outside the cylinder with a microswitch in the flooded area, are these a special switch or is a standard switch ok in fresh water, not a pressing issue, just something I've always wondered.

[Subculture]

You could use either tank arrangement, but I would use a single tank unless you have some sort of proportional feedback for ballast volume e.g. small piston tanks. The tanks with a limit switch in the drink are the R&R units. They use this as they have a fixed spindle which requires a stuffing box on the piston to seal the thread. These tanks slot the feed on negative (low side) leg to prevent the anodic reaction furring the contacts, and so require a slightly different control arrangement. This all harks back to a time when a large SLA battery was the state of the art for powering subs, and the lack of threaded spindle retracting into the hull saved valuable real estate. These days with high capacity lithium batteries, it’s less of an issue. Ron no longer builds the piston tank based systems as he found most customers favoured the cheaper pump systems and required less maintenance.

[Mermod]

OK I think I'm creeping closer to a decision, I do prefer a single tank so that works, I have some 100mm OD and some 110 OD polycarbonate tubing on it's way, I'm thinking remove the existing pressure box arrangement and just fit the cylinder, drive motors obviously wont fit in the tube so I'm thinking of giving each motor it's own mini WTC, I would like to go brushless and I do have a pair of Hobbyking Donkey 820KV motors I could use if you don't think they're overkill.
Another random question, endcaps, can I use acrylic? I have access to a laser cutter and can simply cut discs to make up the O ring grooves.
Instead of the aspirated system could I simply use the pressurized type where the waters forced in then sucked out? I do believe I've found a Shurflo Nautilus pump for just this purpose.

[Subculture]

It'll certainly motor along if you're running a 12v system, but the motors will be up to it.

Endcap material , acrylic will work fine, almost any sheet plastic material will suffice.

The Shurflo Nautilus pump probably isn't a great choice if you're intending to run a system with a sealed tank. They max out at 15 psi, and flow is very poor beyond about 7psi. See the attached image.



To half fill a sealed tank will require 14.7psi, I expect this is why the OTW system vents into the dry spaces to keep the pressure down, but then you need some electronics to monitor the water level. It would work fine with an aspirated tank with or without a valve/snorkel.

For sealed operation you need a pump which can effortlessly make 15 psi pressure, which means either a gear pump, peristaltic or a good centrifugal pump- the latter of course not being bi-directional.

[Mermod]

Does that then bring me back to those Nidec pumps you suggested for my 66inch Nautilus? there doesn't seem to be much else that capable in a small size.

https://www.aliexpress.com/item/1005008638033447.html

[Subculture]

One option, although you’d need pair for sensible dive times, even then it’ll be slow. Kavan pumps are another option, higher volume but more expensive.

This is why I suggested using air, fast, and the pumps are cheap. I’d still use the tanks you have though.

[Mermod]

One option, although you’d need pair for sensible dive times, even then it’ll be slow. Kavan pumps are another option, higher volume but more expensive.

This is why I suggested using air, fast, and the pumps are cheap. I’d still use the tanks you have though.

As in persevere with the piston tanks or just use those tanks with an aspirated system? If I went down the pressurized route but let it equalize into the outer chambers with a water cut off sensor is there a pump you would recommend?

[Mermod]

These seem a pretty capable pump, physically too big for my tubes but could be in it's own box, not sure what "type" it is though.

https://www.ebay.com.au/itm/286801904763?chn=ps&_ul=AU&_trkparms=ispr%3D1&amdata=enc%3A1eeQ4AjB5Rr66Z4-Rtpzt5A0&norover=1&mkevt=1&mkrid=705-173151-935305-0&mkcid=2&mkscid=101&itemid=286801904763&targetid=2370046502538&device=c&mktype=pla&googleloc=9072402&poi=&campaignid=21766134162&mkgroupid=175112620264&rlsatarget=pla-2370046502538&abcId=10047381&merchantid=7364522&gad_source=1&gad_campaignid=21766134162&gbraid=0AAAAAD97CxRASPOSpop0S-lur_T476b9f&gclid=Cj0KCQjwrc7GBhCfARIsAHGcW5UYPZ61Etm2UY3dTmC4YZZisRgyw0-JcvxHk9lxwH1NIDCLGnc8JcoaAlGoEALw_wcB

[Subculture]

Yes, the piston tanks. They look well built and I’m sure can be made to work well. Also cheapest solution as you already have them. Not familiar with the pump you show, looks a bit too big though.

[Mermod]

I guess that I was also hoping to reduce overall weight, I'm guessing that big watertight box is going to need a lot of lead ballast to offset it.

[Subculture]

Shouldn't build a big Typhoon if you want a light boat, regardless of dry weight they'll still be heavy to pull out of the drink. The snag with boats built light is that they tend to react in an unscale fashion on the surface and are more susceptible to torque roll if single propped.

Why not put the tanks into a cylinder, or cylinders, side by side like the original. You will need a reasonable volume for the tanks to compress into, Engel aim for the tanks to represent 10-15% of the wtc volume, giving about 1.5-2.25 psi pressure raise, but you can go a little higher without compromising hull seals. If your tanks match the Engel Typhoon volume of 1650ml, then you'll need a volume of around 11-12000ml, but you could go as small as 8200ml