To increase buoyancy

I want to increase buoyancy on AI tankwell section.
When I load scuba tank to the back it sit too low.

What are ways to do that? Has anyone done it?
I'd love to hear it.

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The laws of physics dictate that the only way to increase buoyancy in a particular place is to increase the volume of water displaced. Therefore, you will need to modify the rear of your hull by adding (for example) a "bustle" like fusioneng added to his TI, or some other external structure, such as floats rigidly attached to the hull. I also note that fusioneng carries scuba tanks in an inflatable which is towed behind his Island.

This is not a trivial exercise whichever way you look at it ..so please keep us informed on the solution you decide on.

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Tony Stott
2012 Tandem Island "SIC EM" with Hobie spinnaker

You are right. I saw fusioneng's back bump. .... I mean tankwell. It looks good. I don't know how difficult it is to make one though.

I am asking just in case someone in similar situation and have done it before. Anyone ?

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Here is a picture of a boat (stearn view) which was at the 2016 Everglades Challenge.




The owner also had a set of external rudder lines using a horizontal, black plate, which can be seen in the picture.

Keith

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2015 AI 2, 2014 Tandem

"Any intelligent fool can make things bigger and more complex ... It takes a touch of genius and a lot of courage to move in the opposite direction." A. Einstein

"Less is more" Anon

Thanks Chekika. That looks amazing.
daft, I searched around half hour under his name. I could not find anything.

If someone has seen Fusioneng's post, can you post the link here?

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Fusioneng's hull mod is in the "ultimate tandem island thread" viewtopic.php?f=69&t=33720&start=375

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-- Chad | 2014 TI

chadbach, That's it. I'll read it tonight. Look interesting. I don't really know i can do that. Will see

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When we are towing our inflatable 4 person dingy we just throw all the tanks scuba gear and ice coolers in the dingy and tow that on a 15ft line attached on the centerline of the stern. You can't tell the dingy is even back there (doesn't effect steering). We spear fish so we need sealed ice coolers and never put catch in the TI. Sharks are pretty bad off key west and bump the boat if they smell blood, nothin like having a bull shark bump your tramp. From first kill to when we have to leave the area is around 30 minutes, sharks can smell blood a mile away I hear (no idea if thats true), All I know is we have a half dozen sharks circling after we kill, no problems when we aren't spear fishing.
When we don't use the dingy we lash the scuba tanks just in front of the rear aka bars (to keep the weight aft). We lash 2 tanks on each side with 1 inch straps, our tramps are strengthened so we can walk on them in full scube gear.
Our planing hull mod (so the hull can plane at high speed) adds about 100 lbs of additional flotation to the TI.
With the dingy I can haul 4 people and 500 lbs of gear (in the dingy), that's around 1200 lbs of weight. However my TI is massively modified and hardened for the task with massive sailsets (up to 260 sq ft), and twin Honda outboards that have been heavily modified for the task.
We are mostly divers and snorklers, and only typically go out in flat water and winds under 7mph (when it's windy and wavy visability goes down to zero). Diving from a sailboat is an oxymoron (who knew lol), can't sail in no wind, thats why I invented my wing crap.
Good luck
FE

Yep, there's a lot of good info in that thread! Instead of trying to increase the capacity of your AI, what about replacing it with a TI? Their capacity is another 150-200 pounds, I believe, with plenty of room for scuba gear.

Fusioneng,
Out of curiosity, with your hull planing mod, how much speed does it take until the boat starts planing? I always thought that would be a fun mod.

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-- Chad | 2014 TI

Without the planing mod the stern squats and gets hung up in the stern wave at around 8mph, and it sucks up huge horsepower to overpower the effect, (the hp requirements go up exponentially)
Watching the wake on a powerboat pretty much describes the effect. On a powerboat when not planing the bow sticks way up and the stern squats. As you speed up and get up on plane the bow drops and the stern raises up, there is a peaked wave just behind the boat. The trick is not to allow that wave to catch up to the boat. Of course on a powerboat when you slow down the wave rushes the back of the boat and crashes into the stern. This is all normal.

With the planing hull mod I can keep that pesky wave a few feet behind the boat and I can overcome that crazy hullspeed theory stuff.
My boat is a custom tri-bred peddle boat design where I use all the available power sources at the same time, (peddle, wing sail, and supplimental power all at the same time. Kinda hard to describe but I have no issues cruising at 8-10mph in very light winds (under 7mph). Actual wind direction means very little, I typically sail almost directly upwind which is kind of cool. I get around 80mpg at those speeds. In better winds (over 12mph) I can easily cruise at 15mph but my fuel economy goes out the window and the motors get kinda loud. I typically cruise with the motors just above idle, and the motors are very quiet and I get around 3hrs run time per tank (1qt tanks).
Like I said I rarely go out in winds over 7mph.
I've been runnin this setup a couple three yrs now with no changes, no desire to do any more, I just use the stuff. Been busy workwise so we havn't gone to our key west place or diving since last April. I travel a lot all over the country for work most weeks (sucks to be me).
FE

Thanks everyone.
fusioneng, after went through all your steps, you are really an innovator. I don't think I can do it like it.

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