The thread to end all "are the ebay scooters good?"

[Mr.X]

Picture mentioned in post above has now moved

http://www.cambridgediveandwaterspo...ourses-07/16_Advanced_Open_Water_April_07.jpg

Paul.

Eh? Is that Dorothea Quarry?

Cheers,

X

 

[DeepSeaExplorer]

I've got 5 cheap scooters from ebay (use them to teach DPV specialty)...

Remind me not to take a DPV class from you...

 

[pdh]

Remind me not to take a DPV class from you...

You've got 5 Gavins have you ?

Unfortunately I don't have £20K spare and recouping that sort of outlay is impossible unless you live next to a lake or the sea and have a lot of rental opportunities.

 

[pdh]

Eh? Is that Dorothea Quarry?

Cheers,

X

Close - it's Vivian. They've been in Dory as well - I take the ballast out and use them to tow me out to the central buoys - it's a long swim with deco cylinders. I just clip them to the buoy at the surface. It's a nice way to get back to shore as well.

P.

 

[DeepSeaExplorer]

I hear ya... generally the point in taking a scooter class is to meet the requirements for diving certain caves. Getting a c-card to zoom around on one of these scooters is kinda pointless isn't it?

 

[Mr.X]

I hear ya... generally the point in taking a scooter class is to meet the requirements for diving certain caves. Getting a c-card to zoom around on one of these scooters is kinda pointless isn't it?

There are flavors to scooter classes. Using a higher thrust/longer endurance scooter in a cave requires cave cert. The UK doesn't really have the gin clear, easy to penetrate and drivable caves as does the US, or Mexico. I know. Been there - ending up just spelunking instead.

In my intro. to scooter classes I used a variety of scooters. At the end the day the students chose their favorite scooters - in short Horses for Courses.

X

 

[pdh]

I hear ya... generally the point in taking a scooter class is to meet the requirements for diving certain caves. Getting a c-card to zoom around on one of these scooters is kinda pointless isn't it?

Maybe in the US. In the south east of England it's fenland - completely flat with no caves and the lakes are lined with clay, chalk or peat so vis is pretty rubbish (that's why we dive in Wales). Most people wanting to use a dpv are going for either advanced open water or want an extra cert for master scuba diver. dpv is a fun option for the aow - some of these divers may only have 4 dives and come straight off an open water course. I certainly would want to give them an X-Scooter or a Gavin for one dive - there would be a very good chance of an injury to them or someone else. You'd also have to sell a hell of a lot of aow courses to cover even one of those scooters, let alone enough for a class of students. I am not knocking these expensive scooters - I'd love one of them, but there is also a market for dirt cheap ones as well. Students love having a go and they don't care that they are not getting their mask ripped off by the speed. I can buy 4 or even 5 for the price of one seadoo and if they break I just throw it away and buy another one, so it's cost effective as well. I also use them myself on trips. As I said before, the 200 watt versions I have can pull me faster than I can swim for very long. It's a nice way to do a scenic dive and conserve your air - especially if the current is against you. Would I take one in a cave or on a serious dive where I had to depend on it ? No chance. Do they break down - sure, but if I get 50 dives out of it with paying customers then it's done it's job.

Paul.

 

[DeusVerto]

(quoted text edited for brevity)"...One last comment, a 200 watt motor is probably more power than the average person can generate for very long...."

It depends on what they're calling "200 watts" and then there's the efficiency of the propeller to factor in. A typical brush-commutated DC motor (the cheap ones used in cordless drills for example) has a peak efficiency of about 60% anywhere near full power. So now you're down to 120 watts at the shaft. Then you have to consider the efficiency of the propeller. A world-class boat propeller efficiency is around 80%, so let's call it 70 to be kind. That's a net of 84 watts out of the original 200.

So how much thrust does one of these things have to have? I have no data on that subject at all, but let's assume 200 net. That means a 500 watt motor...but wait. We can't take a DC brush motor and run it at full power for an hour and expect it to live very long, especially with the need to dissipate 200 watts of waste heat in a sealed (albeit surrounded with water) enclosure. It probably means two such motors in a dual design derated to 250 watts.

The first part we have to select is the battery. This is the most expensive component; all the rest of the mechanical engineering shall be designed around enclosing the batteries and hauling them around. We will need, for an hour dive, 24 volts nominal at 20 amps for an hour. This is not a trivial battery by any measure.

50 D-size NiMH batteries, wired in 25 series by 2 parallel ought to do the trick.

NEVER CHARGE NiMH BATTERIES IN PARALLEL, BY THE WAY.

This will yield an 18-pound pack, and the cells to make the pack itself, sans labor, would run you about $350 USD from a reputable Chinese importer. Want to go Lithium Ion to save space and weight? Double or triple the battery cost.

There's no free lunch here. The more I run myself through the mental design exercise for this (sounds like a cool winter project to make one - my mind is racing), the more I'm convinced that ANY "scooter" sold for less than about $750 USD at retail HAS to be a piece of junk.

That is, if 200 watts net is the number. Any marine propulsion engineers want to weigh in here?

 

[roastbeef]

LOL This is funny.

 

[duartegps]

PDH, would like more information because I would buy one for myself and my son:
1-What is the maintenance?
2-when you use the scooter 2 speeds, how long will the battery, more or less?
Thanks, and sorry my English, I'm Brazilian.