Gavin vs. Silent Submersion

[ucfdiver]

I have the ballast in my X's mounted asymmetrically.

Not that hard to do. Weight pouches that velcro to the interior. Lots of options on where to mount them.

To understand *why* longer smaller diameter tubes are a benefit for high powered scooters that use lighter batteries requires a more complete understanding of the horizontal trim requirements.

For example consider what would happen if you increased the tube diameter by only two inches but left the length the same.

Tobin

I would presume that you would require a ton more weight to negate the added volume, and almost negate the advantage to the lighter packs?

 

[cool_hardware52]

I would presume that you would require a ton more weight to negate the added volume, and almost negate the advantage to the lighter packs?

Bingo! You need the length to allow a lightweight battery to balance a big powerful motor. Blow up the diameter from ~8" to 10" for a 30 inch hull increases the displacement by ~30 lbs.

If you like 80-90-100 lbs scooters there are plenty of monster SLA's to pick from.

Tobin

 

[ucfdiver]

Bingo! You need the length to allow a lightweight battery to balance a big powerful motor. Blow up the diameter from ~8" to 10" for a 30 inch hull increases the displacement by ~30 lbs.

If you like 80-90-100 lbs scooters there are plenty of monster SLA's to pick from.

Tobin

What would tbe downside be if you kept the tube short and fat, similar to a UV18? I know a few people who have NIHM battery packs in those. Slightly more weight I would assume...?

 

[cool_hardware52]

What would tbe downside be if you kept the tube short and fat, similar to a UV18? I know a few people who have NIHM battery packs in those. Slightly more weight I would assume...?

Bingo! You need the length to allow a lightweight battery to balance a big powerful motor.

Not sure what I can add to that.

Tobin

 

[ucfdiver]

Not sure what I can add to that.

Tobin

Perhaps an explanation? Are you saying to keep it horizontally level or what?

 

[rjack321]

Perhaps an explanation? Are you saying to keep it horizontally level or what?

The motor is too heavy relative to the battery weight.

If you took a short gavin and put NIMH batteries in it you'd need the same mass of batteries to get it level otherwise the nose will ride high and the tail down - like most Makos.

Make the tube longer and thinner and you've got a lever to balance out the motor.

But now the thinner tube has less radius to shift weight outward and cancel out torque like you're used to with the fat tubed SLAs.

 

[ucfdiver]

The motor is too heavy relative to the battery weight.

If you took a short gavin and put NIMH batteries in it you'd need the same mass of batteries to get it level otherwise the nose will ride high and the tail down - like most Makos.

Make the tube longer and thinner and you've got a lever to balance out the motor.

But now the thinner tube has less radius to shift weight outward and cancel out torque like you're used to with the fat tubed SLAs.

Makes sense. That sucks. So we're stuck breaking our backs, or driving a scooter that drives like crap for 2 solid hours

 

[rjack321]

Makes sense. That sucks. So we're stuck breaking our backs, or driving a scooter that drives like crap for 2 solid hours

Don't you have lackeys to carry those SLAs?

 

[ucfdiver]

Don't you have lackeys to carry those SLAs?

No, Lincoln put a stop to that back in 1863 here in the south.

 

[cool_hardware52]

Perhaps an explanation? Are you saying to keep it horizontally level or what?

To understand *why* longer smaller diameter tubes are a benefit for high powered scooters that use lighter batteries requires a more complete understanding of the horizontal trim requirements.

Bingo! You need the length to allow a lightweight battery to balance a big powerful motor.

The High output Scooters have big powerful, heavy motors, these are even a bit heavier than the Oceanic style motors.

If you want to be able to achieve horizontal trim you need to balance the mass of the motor with..........the battery.

If you are using a heavy SLA battery it doesn't need to be very far ahead of the motor.

If you are using a lighter weight NiMh or Li-Ion battery it needs to be much further forward of the motor.

As you shove the battery forward the hull gets longer and the displacement goes UP.

As you reduce the hull diameter the displacement goes down.

NiMh in a SLA scooter?

Sure, but it doesn't make the scooter any lighter, the hull dimensions not the battery chemistry controls the "ready to dive" weight.

Li-Ion in a SLA scooter? If you replace the SLA's with a similar mass of Li-Ion you end up with a $5-6K battery with range nobody can actually use and scooter is no lighter.

If you use a smaller capacity (and mass) Li-Ion pack you have to stuff the scoot with lead. Why bother?

SLA scooters are reasonable targets for NiMh upgrade and NiMh scooters are a reasonable target for Li-Ion Upgrade. SLA to Li-Ion is largely pointless.

Tobin