A Moebius Skipjack from the land of OZ...

[greenman407]

Thats really good to hear Alec. Next time.......make with the pictures, will ya. I cant see that far.:biggrin:

[alad61]

Time for an idiotic question...

I am really strugling with the c.o.b & c.o.g. I thought it was just me at my first public outing a couple of months backs. This morning I was back to my usual water hole today thinking I had got the trim finally done after some issues required some fix ups, including some more tub tests. However a successful mission on the lake was not to be!!! With the surface trim the boat sits nice and level but when I flood the ballast it settles at about 45 degrees stern down. Now for the idiotic question. Is this a case of adding buoyancy above the desired waterline to achieve a level submerged trim? By the way the adf2 gets the boat leven under power but it just wants to porpoise all the time. Is that also because the c.o.b is off?

[Subculture]

Assuming you have no trapped air, and the CG is bang in the centre of the ballast tank, then it sounds to me you will have to add some buoyancy at the stern, and above the waterline as you suggest although I'd expect this to be the same for all Skipjacks. An advantage with injection moulded subs is, as they are as near as you can get to perfect consistency from kit to kit, unlike a GRP lay-up which has a wider tolerance.

Hopefully there is a enough leeway in the ballast volume to allow for the extra displacement of the foam.

An out of trim boat will certainly get the leveller into a lather.

[Slats]

Time for an idiotic question...

I am really strugling with the c.o.b & c.o.g. I thought it was just me at my first public outing a couple of months backs. This morning I was back to my usual water hole today thinking I had got the trim finally done after some issues required some fix ups, including some more tub tests. However a successful mission on the lake was not to be!!! With the surface trim the boat sits nice and level but when I flood the ballast it settles at about 45 degrees stern down. Now for the idiotic question. Is this a case of adding buoyancy above the desired waterline to achieve a level submerged trim? By the way the adf2 gets the boat leven under power but it just wants to porpoise all the time. Is that also because the c.o.b is off?

Alex
sounds like my very first sub USS Seesaw.

Anyway - sounds not like COG issue but rather you screwed the Trim effort. (COG is important, should be where the centre of the ballast tank sits, and at the half way mark of the profile area (not length) of the sub. To find COG - you could look at my Seawolf thread and others where I grid over a profile drawing, but I figured David would have identified this spot in the documentation for the Skipjack). If he hasn't, let us know and we can get Mike to run him over him with the Jag.

Trimming I always do sub by starting SUBMERGED. If you do so the only thing you have to change, once you empty the ballast tank, is the vertical location of some or all of the foam to achieve designed waterline.
Its sound to me Alex that you have her Trimmed perfect for the surface - and that to me means you can hand your Dolphins back Skimmer boy.
Want redemption? - Make sure you installed the SD EXACTLY where David has designed it to go in the Skipjack, and then with a 100% full ballast tank and the boat submerged start trimming again.

Re the ADF2 - get this boat working in static dive / surface mode first then throttle up and see if problems persist.

Hope that helps

J

[He Who Shall Not Be Named]

I assume the amount of foam is enough to hold the entire boat to a near state of neutral buoyancy -- but, at this point, at an undesired angle. If so, then it's simply a matter of taking some of the foam that is above the waterline and moving it horizontally until the boat assumes a horizontal inclination when in submerged trim. This affects angular change to the boat in submerged trim, but not in surface trim -- which is fine at this point.

M

[alad61]

Thanks Albion I reckon the adf was close to meltdown...

John the SD is set up as per David's instructions. So I reckon that part of the equation is good. On thinking back you might be right as I may have gone down the surface trim road first... Btw it's Alec not Alex, though they are both derived from the word Alexander meaning leader of men or something like that anyway. Alex is the abbreviated form where Alec is the English translation of the Gaelic (Welsh) word for Alexander. :-D

Thanks also David, I kind of thought moving the foam backwards might help. But I reckon it time to rip out the foam, claim the bathroom for the next week & put it back in the test tub.

[Slats]

Thanks Albion I reckon the adf was close to meltdown...

John the SD is set up as per David's instructions. So I reckon that part of the equation is good. On thinking back you might be right as I may have gone down the surface trim road first... Btw it's Alec not Alex, though they are both derived from the word Alexander meaning leader of men or something like that anyway. Alex is the abbreviated form where Alec is the English translation of the Gaelic (Welsh) word for Alexander. :-D

Thanks also David, I kind of thought moving the foam backwards might help. But I reckon it time to rip out the foam, claim the bathroom for the next week & put it back in the test tub.

Alec - first sorry re your your name.

Take your time on ballasting - yes please do seize the bath tub. Make sure the tub is deep enough to get her to where you need. I always set my boats up a little positive. Bit of a safety factor.

Looking back on this thread, I'm glad you had to tinker with the servo for the ballast vent, had a bum seal I had to replace awhile back, its a bit of ******* to get to but its all learning. You are doing a great job. keep at it.

Best

John

[alad61]

Thanks John and yes our bath is more than deep enough. Maybe one day I'll actually use it for its intended purpose... lol
Even with a bout of the flu I still tackled the trim... the first picture shows submergered trim and the second is with an empty ballast. All in all it took about three hours this is what I ended up with on the submerged trim. It's hard to tell with the water refraction but I have the sail sitting with about half an inch above the water. Tonite whith everything dry I'll glue in the foam and to make sure its all going in the right spots I took some happy snaps. So once the rtv is fully cured I'll dip it back in the tub and see how it looks

[Slats]

Thanks John and yes our bath is more than deep enough. Maybe one day I'll actually use it for its intended purpose... lol
Even with a bout of the flu I still tackled the trim... the first picture shows submergered trim and the second is with an empty ballast. All in all it took about three hours this is what I ended up with on the submerged trim. It's hard to tell with the water refraction but I have the sail sitting with about half an inch above the water. Tonite whith everything dry I'll glue in the foam and to make sure its all going in the right spots I took some happy snaps. So once the rtv is fully cured I'll dip it back in the tub and see how it looks

Good man Alec,
and if I may say so - nice job on the sub.

I'd suggest for your next outing you head down to the swimming pool.

Lake temperatures even here in Sydney are starting to head towards dangerous levels.

Best

John

[alad61]

Thanks for the compliment I did mute the front sonar covers as the colours specified look to bright & clean for me. I don't know if the escape bouyies would be the international orange when on active patrol but I kept them as visual reference.

Yes even for Brisbane the days & water are getting cooler than previous years. Most of the local pools are closed here as well as I have been told by the shore council that rc vehicles aren't all that welcome in our council run pools. Yet they do little in maintaining any community lakes in the shores park lands!

[Slats]

Thanks for the compliment I did mute the front sonar covers as the colours specified look to bright & clean for me. I don't know if the escape bouyies would be the international orange when on active patrol but I kept them as visual reference.

Yes even for Brisbane the days & water are getting cooler than previous years. Most of the local pools are closed here as well as I have been told by the shore council that rc vehicles aren't all that welcome in our council run pools. Yet they do little in maintaining any community lakes in the shores park lands!

Alec
are you a Triple S member?

Re the International Orange - IMHO good to have that on the model for visual reference.

Also how do you find the snorkel valve operation for the SAS? Any teething problems?



J

[alad61]

Re Triple S, I'm indeed a member and although Boondal is a 20 min drive from home. The water there is pretty much a giant billabong with not much circulation. It can get pretty murky and still So much so that were you to stick your arm in up to the armpit you'd be hard pressed to see your fingers. To be really honest you could drop a ton of gold bars in there and I still wouldn't dive in after them with the water there. On top of that they have been struggling for years with the weed. When I put a sub in there it's down to periscope depth only and if I do go deep to avoid a surface runner it's havoc on the nerves... LOL.

Regarding the SAS & snorkle. The first couple of trials both in the tub & in open water produced some water in the SD but I have tweaked it and now not so much. I reckon that any water it takes in now is that from water hanging around the top of the float valve as it is a strong pump. Jim suggested using those little silica satchels you get in a vitamin bottle to absorb it and reduce the risk of it sloshing around. I also think that when the sub runs level without the porpoising then that'll help keep the float firmly against the valve which will reduce any water being "pumped" into the induction tube as the float moves up & down with the motion of the sub.

[He Who Shall Not Be Named]

A reminder: Inverting the SD in-water will unseat both the snorkel and safety float-valves, letting water into the SD. However, any angle less than 45-degrees (pitch and/or roll) will find the valves firmly shut.

M

[vital.spark]

David, Yes and what is the result of a collision with a a target or other sub? Thank you but I'll stick with your gas system and LPB.

[He Who Shall Not Be Named]

Myron,

As long as the boat does not pitch or roll excessively, things are fine. If the induction line between snorkel and SD parts, the safety float-valve will keep the water out.

Other than the 2" Kilo SD and 1.25" SD's we gone entirely to SAS, with gas as a retro-fit option.

M