Scratch built Typhoon advice needed

[Subculture]

If you have Norbert Bruggens book, there's a formula in there which enables you to calculate the reduction in metacentric height for a part filled ballast tank.

I plugged the numbers for your boat, assumed 22kg overall displacement- same as Engel- and would get worse if the boat was lighter. Bear in mind that the metacentric height for a Typhoon would probably be 15mm if you're lucky.

[Mermod]

All this seems to bring me back to the aspirated tank system, perhaps I should change my thinking, or just go with the sealed tanks just to get moving.

If the long sealed tank will no doubt reduce stability just how much can the APC be relied on to counteract it?

Phill

[Subculture]

Engel Typhoon is about the same size and construction as your boat, that has 1650ml of ballast tank volume split over two 825ml piston tanks. So I'd take that as a ball park and somewhere between there and 2000ml if your laminate is on the chunky side. In general resin rich GRP tends to be around 20% denser than water, but can go higher depending on how glass rich your layup is. Therefore I'd expect your hulls upper half to displace around 2200-2300ml of fresh water, and as the waterline is slightly above the hull break, I'd say that around 2000ml would be about the right, but ultimately an empirical analysis is the only accurate way for a hand laid composite hull.

For 110mm tubing- likely 104mm ID, a tank volume of 4000ml (half filled) gives a tank internal length (less bulkheads) of around 470mm, any baffling inside would have to be additional, making the tank longer still.

Regarding stability, such a long tank part filled is bound to reduce it, baffling will be essential and will help, but can't eliminate it completely. I favour tanks that fill completely with no air bubble. That tends to mean piston tanks, flexible bags, or aspirated fixed tanks.

[Mermod]

That is essentially how the Eden/Sheerline system works, except they tend to use a centrifugal pump, and the hose is checked by pinching it with a cam controlled by a servo. The same servo is also used to actuate a micro switch which powers the pump when filling the tank. Very simple and inexpensive.

The downside of this system is the tank tends to be large as the system half fills the tank. You also needs to be very diligent with the baffle design to limit sloshing.

That all sounds very cool, I'm seeing a plan come together, a large tank is not problem as I certainly have the room, I'm thinking waterproof junction box in the rear for motors, rear planes and rudder, possibly pump depending on the size of box I find, another box in the bow with servos for bow planes, retracts, bow thruster ESC and stuff and as for battery maybe a big gel cel in the free flood area.

I can go crazy with the baffles as I have plenty of access to acrylic sheet and a laser cutter :)

I would appreciate some guidance/advice on ballast tank size, boat is 1.8m long and weighs 10kg, removable top half weights 2.8kg and the separation is pretty close to the waterline, there is still a section of the top with the rudder area that is permanently attached to the hull that cant be weighed.
I'm hoping a central tank won't cause see sawing but I could be wrong but what size should this tank be? or perhaps two side by side tanks? I don't know and could do with some guidance.

Phill

[Subculture]

That is essentially how the Eden/Sheerline system works, except they tend to use a centrifugal pump, and the hose is checked by pinching it with a cam controlled by a servo. The same servo is also used to actuate a micro switch which powers the pump when filling the tank. Very simple and inexpensive.

The downside of this system is the tank tends to be large as the system half fills the tank. You also needs to be very diligent with the baffle design to limit sloshing.

[Mermod]

I took the plunge yesterday and cut out the big tank I glassed in all those years ago, I'm glad I did as I weighed the sub before and after and it turns out it was 2.2kg! so I think I may have overdone it just a tad :)

I've given up on the piston tanks completely as the cost of re-working them with planetary geared motors and all the work involved was more than I wanted right now so I'm on the hunt for the perfect geared water pump, I can't believe how hard it is to find one that would suit the pressurized system, there are however plenty of diaphragm driven one way pumps, not reversible of course but instead of pumping the water back out could a solenoid be added to let the internal pressure push the water back out?

Thanks' again for all the help.
Phill

[Subculture]

So many of us have been there with the ‘gotta be a biggun’ desire, some never quit, but most downsize once they realise what a hassle dealing with a big model is.

[Mermod]

Yes I'd love to have a chat with 25yo me about our future back and brain surgeries and point out a large sub might not be ideal in the future :) must be something wrong with me though cause I'm still starting that 66inch Nautilus.

[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

[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]

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]

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

[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?

[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]

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