Blacktip Scooter- Limited To Weighting, Buoyancy and Trim

[DA Aquamaster]

That sounds like a pretty good approach. I guess I could do that in salt water. But, in fresh water, my BT is dead neutral (with 12Ah batteries and nothing added but a single bolt snap on the nose) with all the internal weight plates removed. So, no way to make it positive at all without changing to smaller batteries.

That's the primary reason I am using 9 Ah Waitley batteries in caves. They allow enough reserve buoyancy for me to weight a BlackTip 2-3 oz positive, which ensures it stays off the floor when placing a jump, etc.

As noted in a prior post, in some situations it works well to place the DPV nose up between your thighs (and the BlackTip's nose up trim is a benefit there). In other situations, you can just let it float beside you and in still others it makes more sense to clip it off to a butt D ring or shoulder D ring. All three are good skills to have but all three benefit from a scooter that is very slightly positive, so that it doesn't sink to the bottom. When using a butt D ring, it also needs to have level trim and slightly positive buoyancy so that it has minimum interference with your legs. That's where the P1 and P2 shine, compared to a BlackTip.

 

[stuartv]

Help, please? @DA Aquamaster?

First of all, I'm confused by earlier posts. My scooter is neutral in Fresh water with 12Ah batteries and 1 bolt snap on a paracord cobra weave leash on the nose.

Other posts in here say that theirs are neutral in Salt water with the 12 Ah batteries and 3 bolt snaps. Have I got that right?

What I really want to know is, my scooter is neutral in fresh water. How much weight (in grams, if possible) do I need to add to my scooter so it is neutral in salt water?

Is it just the weight of 2 more bolt snaps? It seems like it would be more than that, but maybe not...?

I *think* it's roughly around 0.6# that I need to add. I want to get a pretty exact number and then take my thin metal plate and stick stick-on wheel weights onto it to make it the right weight. I'm never going to buy any other weights of batteries. So, I just want to add weight to the thin plate to make it "correct" for salt water with my 12Ah batteries. Then I can just take the plate out for fresh, put it in for salt, and not have to think about it or keep a baggie of weights stored with the plate when I'm diving in fresh water.

 

[Rollin]

Well, it's just physics.

Weigh your scooter as is (neutral in fresh, 1 boltsnap). Multiply that weight by 0.026. Tadaa, tha's the weight to add.

Or, multiply by 1.026, that's the total weight you are aiming at. Assuming 0,998 kg / dm^3 for fresh water and 1,024 kg / dm^3 for your local sea water.

 

[stuartv]

Well, it's just physics.

Weigh your scooter as is (neutral in fresh, 1 boltsnap). Multiply that weight by 0.026. Tadaa, tha's the weight to add.

Or, multiply by 1.026, that's the total weight you are aiming at. Assuming 0,998 kg / dm^3 for fresh water and 1,024 kg / dm^3 for your local sea water.

Sure! Totally simple.

Do you have a scale that will weigh something that is roughly 25# and give you a precise number, in grams?

I don't. I have a digital bathroom scale, which is not that precise. And I have a food scale, which seems to be pretty precise and accurate, but won't take anything that heavy.

I'm pretty sure somebody out there already knows the answer to this. Hopefully, they will see my question and tell me the answer. If I can get a precise and accurate answer, then MAYBE I can avoid jumping into salt water and having to dick around with "tweaks" to dial in the weighting.

 

[RayfromTX]

Weighing yourself with and without the scooter will give you a more accurate result on the digital bathroom scale.

 

[broncobowsher]

You are multiplying by .026
It doesn't have to be that accurate. Off by 1/10 pound is only .0026 pounds of error. (That is a little over a gram)
Next thing is you have to calculate the difference in volume between if you put the weight inside the body or on the outside, since adding a snap bolt outside will increase displacement ever so much. How much more water are you displacing?

Back when I had a Nissan Leaf I calculated the weight of the electricity in the battery. It was .000096g of stored energy. I got that number 2 different ways, one was even the E=MC2 formula. Backed up by a friend who is an electrical engineer doing stuff that goes into space. So don't forget to add that bit of weight into the calculation. Since the power tool batteries are much smaller it will be even less weight. If I get really bored I might try and calculate that again. Probably not going to care enough.

 

[stuartv]

You are multiplying by .026
It doesn't have to be that accurate. Off by 1/10 pound is only .0026 pounds of error. (That is a little over a gram)
Next thing is you have to calculate the difference in volume between if you put the weight inside the body or on the outside, since adding a snap bolt outside will increase displacement ever so much. How much more water are you displacing?

Back when I had a Nissan Leaf I calculated the weight of the electricity in the battery. It was .000096g of stored energy. I got that number 2 different ways, one was even the E=MC2 formula. Backed up by a friend who is an electrical engineer doing stuff that goes into space. So don't forget to add that bit of weight into the calculation. Since the power tool batteries are much smaller it will be even less weight. If I get really bored I might try and calculate that again. Probably not going to care enough.

It's neutral in FW with fully charged batteries. If it's simply neutral in SW with freshly charged batteries, that is adequate for my purposes.

I am going to add weight on the inside. Specifically, I am going to use stick-on wheel weights to stick weight to the thin weight plate that came with the scooter. Fresh water? Take that plate out. Salt water? Put the plate in. Simple. I like simple.

1/10 of a pound is about 45 grams. My digital scale resolution may actually be 0.2 #. Not to mention whatever it's accuracy is. I could easily be off by 90 grams or more.

I can get it close and then tweak from there. I was just hoping to get a more accurate and precise number than "add 0.6 pounds". And more precise and accurate than what I would get by weighing on a bathroom scale and then multiplying by 0.026.

 

[stuartv]

I remembered that I have a digital luggage scale that has pretty much exactly matched airline luggage scales in the past. So, I guess it's reasonably accurate and gives plenty of precision for this purpose.

I weighed my scooter 3 times. The average weight works out to 22.54# (10.224kg).

That, times 0.026 yields a need for additional weight of 264g, which is 0.582# (9.3oz), which is pretty close to the 0.6# number I had picked up elsewhere.

I'm going to add weight to my thin plate until I get it to around 264g, total, and roll with that for my salt water excursion next week. Should be close, I would think.

Maybe that will help someone else.

Thanks for the help working this out!

 

[broncobowsher]

Good call on a luggage scale. I know mine is pretty good as I have weighed bags and then placed them directly on the scale at the luggage counter. They are pretty close.

 

[stuartv]

Well, that was easy enough.

Those weights are marked at 7oz each and they are astonishingly (to me) accurate! The thin plate clocked 109g by itself.