rnli atlantic ribs

gtflash · 21 July 2013, 08:01

I noticed the local lifeboat has a water ballast tank. Anyone know how big it is on them?

m chappelow · 21 July 2013, 08:44

200 kgs in weight on the A85 .

whisper · 21 July 2013, 08:52

We went to see the the one at Cowes but they didn't mention anything about a ballast tank, anyway here's some pics if you like the 85's...

http://www.rib.net/forum/f8/cowes-rn...day-55492.html

Loved the knifes located on the cone ends and also the water supply to the legs so that they can start the engines before it hits the water

chris123 · 21 July 2013, 11:10

Quote:

Originally Posted by whisper

We went to see the the one at Cowes but they didn't mention anything about a ballast tank, anyway here's some pics if you like the 85's...

http://www.rib.net/forum/f8/cowes-rn...day-55492.html

Loved the knifes located on the cone ends and also the water supply to the legs so that they can start the engines before it hits the water

In your first group of photos, you can see the control cable (red outer) between the two outboards - it leads from the helm seat to the tank control valve on the transom:

And in your second set of photos you can just make out the control lever at the helm seat (stainless lever with black knob on the end, just inboard of the throttles)

Cheers

Chris

whisper · 21 July 2013, 11:27

A few more pics added but none of the ballast equipment...

chris123 · 21 July 2013, 11:32

Quote:

Originally Posted by whisper

A few more pics added but none of the ballast equipment...

The stainless steel component in the centre of your photo:

Is the ballast tank valve.

Cheers

Chris

whisper · 21 July 2013, 11:36

So can they fill and empty the tank on the water?

chris123 · 21 July 2013, 12:08

Quote:

Originally Posted by whisper

So can they fill and empty the tank on the water?

Yes they can - in fact I think (not 100% sure) they can only fill on the water. The lever at the helm seat has three positions - hold, fill and drain - the helmsman adjusts as required depending on conditions.

Cheers

Chris

JamesF · 21 July 2013, 12:10

The Sidmouth Arctic 24 has a ballast tank as well. About a quarter of a ton, and takes just a few minutes to refill at sea, if I remember rightly. I forget how quickly they can dump it.

SimonCh · 21 July 2013, 18:24

the ballast lever essentially opens a flap, which when under way forces water in to the bow. When its full up, water runs out of a tell tale inboard at the bow, and runs down the deck. at this point, the water can be 'held' or 'drained'. I am sure on the A75 its only around 60kg, but dont quote me on that. The boat needs forward momentum to fill the ballast tank, and cant be done on the spot

kubcat · 22 July 2013, 10:18

Quote:

Originally Posted by JamesF

The Sidmouth Arctic 24 has a ballast tank as well. About a quarter of a ton, and takes just a few minutes to refill at sea, if I remember rightly. I forget how quickly they can dump it.

We have ballast tanks on the race boats. As mentioned they fill very quickly, ours fill a couple of hundred litres in well under a minute, but that's probably due to our high speeds and the ram effect. They take a few minutes to empty as it just relies on gravity. On the twin hull race boat we have a tank each side and can fill just one if required. Our tanks are baffled so we can run them half full.

ribrunt · 22 July 2013, 16:21

A75 has a 180kg tank and can only be filled on the run or by hose when ashore (i.e. for dodo launches into surf). Fills in c. 30secs at full chat - you can visibly see the nose sinking in front of you. Overspills when full - move lever to hold.

It dumps quite quickly at speed also due to venturi effect, IIRC, but slower at rest/slow speed, approx 2 mins I think.

HTH