Trim Tab problem

[markc]

Hi

I appear to have a problem with the tabs on the boat being that they are stuck down (I think to their fullest extent, but may be wrong)

The system is Bcs Marine / TwinDisc with twin rams on both tabs and a single hydraulic pump with 2 feeds - 1 for each side. The pump runs and the oil reservoir is full. Operating the tabs deposits a very small amount of oil by each tab.

My feeling is that the valve that would open to allow the oil to return to raise the tabs may be stuck, but I have no idea. How to test. Here are some pics

TIA!

 

[SpectoMarine]

I would start by discontecting the rams from the tab, this will tell you if both are failing or just one. You may find you have one that has gone. We do lots in Palma, if you find one is sized then remove the connections and check the ram is getting fluid, sometimes these rams get siezed very common on the colbolts. You can try to unseize by removing all connection and cleaning ram and either pulling out or pushing in.
If you need any help call me on +34693855862 i am more then happy to help!

Specto Marine Services

 

[QBhoy]

Agree with the above.
Disconnect the hydraulic fittings at the pump and manually work up and down. Knowing a fair bit about hydraulics from a previous career, sound advice is to never leave a hydraulic ram fully out or in. As in max extended or min extended positions. Always back them off a tiny touch the other way. Equally relevant to outdrives and their hydraulic trim system. Just a tiny touch of the button or switch the other way after operation means they aren’t left maxed out and at risk of sticking or perishing seals. Hope this helps.

 

[Kubcat]

Just wondering what the outcome was?

I have a similar issue in that both tabs (with two cylinders each) are not coming back up.

There is only one hydraulic line into each cylinder which I imagine pushes them down, but what brings them back up?

 

[simonfraser]

'sound advice is to never leave a hydraulic ram fully out or in '

always worth reading these threads, do the seals jam up against an end fitting and thus get damaged ?

 

[markc]

Just wondering what the outcome was?

I have a similar issue in that both tabs (with two cylinders each) are not coming back up.

There is only one hydraulic line into each cylinder which I imagine pushes them down, but what brings them back up?

The current position - when I had the boat lifted last year I cleaned up all the rams, thankfully they were OK and not pitted, and was able to manually push the tabs back into position - it was all the crud on them that stopped them moving back into position - they'd been left down by the previous owner. The design is such that the tabs should retract when the hydraulic pressure is released, assisted by springs in the rams. The seals on one ram on each tab had significant leaks, but the rebuild kit was on a 4 week back order, so they're being changed when the boat is lifted this May.

 

[MapisM]

M, I missed your thread, when you posted it.
I think your system is what BCS used to call the 3000 series.
On my boat, I've got the larger 4000 series, with double action cylinders, but only one for each plate.
Excellent stuff anyway, the absolute best available when our boats were built.
Also nowadays, still make Bennett stuff look like toys, in comparison.
You can download a brochure with some technical details at the following link, together with the full technical manual.
But while the first is both in IT and EN, the latter is only in IT, I'm afraid.
Anyhow, I also have the whereabouts of a folk at Twin Disk technical support who used to be a BCS guy before they were taken over, and knows this stuff as the back of his hand.
Actually I'm not sure if he speaks EN, but if you would like to try to get in touch, I can send you his email address - just ask.
WeTransfer link

PS: you (or anyone else interested) should download the files within one week from now, because WeTransfer deletes them afterward.
I couldn't upload them directly here for size reasons.

 

[markc]

M, I missed your thread, when you posted it.
I think your system is what BCS used to call the 3000 series.
On my boat, I've got the larger 4000 series, with double action cylinders, but only one for each plate.
Excellent stuff anyway, the absolute best available when our boats were built.
Also nowadays, still make Bennett stuff look like toys, in comparison.
You can download a brochure with some technical details at the following link, together with the full technical manual.
But while the first is both in IT and EN, the latter is only in IT, I'm afraid.
Anyhow, I also have the whereabouts of a folk at Twin Disk technical support who used to be a BCS guy before they were taken over, and knows this stuff as the back of his hand.
Actually I'm not sure if he speaks EN, but if you would like to try to get in touch, I can send you his email address - just ask.
WeTransfer link

PS: you (or anyone else interested) should download the files within one week from now, because WeTransfer deletes them afterward.
I couldn't upload them directly here for size reasons.

Many thanks P - I have the catalogue, but not the manual, so really useful, thanks!

I am dealing with MIT Group who are the UK Twin Disc / BSC distributors. They have been very helpful. I'm just hoping that a local Fr hydraulic company will be happy to replace the seals etc.

 

[Kubcat]

The current position - when I had the boat lifted last year I cleaned up all the rams, thankfully they were OK and not pitted, and was able to manually push the tabs back into position - it was all the crud on them that stopped them moving back into position - they'd been left down by the previous owner. The design is such that the tabs should retract when the hydraulic pressure is released, assisted by springs in the rams. The seals on one ram on each tab had significant leaks, but the rebuild kit was on a 4 week back order, so they're being changed when the boat is lifted this May.

Thanks for that, I might put on the dove gear and see if I can push them up.

I had asked the yard to see what was wrong when it was on the slip, but they didn’t.

 

[superheat6k]

My tabs are driven by some long obsolete rams with a Volvo Penta QL control pump unit. Having just replaced all the springs and seals whilst testing one of mine stuck in the full down position. It turned out to be a hydraulic lock had occurred when the pressure from the pump was full on into the rams. This seemed also to lock the vent valve.

Cracking the feed tube to release the pressure lock saw the ram return springs take over and then pressing the up button saw the tabs return fully up. I am now careful not to allow the tabs to move to full down position.

 

[markc]

Thanks for that, I might put on the dove gear and see if I can push them up.

I doubt you'll be able to do that when you're in the water, unless you can stand on the bottom. I had to use my shoulder and put a fair bit of effort in to get them back in.

 

[Kubcat]

It’s 7 metres deep at the marina so might have to go for a run.

Thanks for the tip.

I doubt you'll be able to do that when you're in the water, unless you can stand on the bottom. I had to use my shoulder and put a fair bit of effort in to get them back in.

 

[Kubcat]

My tabs are driven by some long obsolete rams with a Volvo Penta QL control pump unit. Having just replaced all the springs and seals whilst testing one of mine stuck in the full down position. It turned out to be a hydraulic lock had occurred when the pressure from the pump was full on into the rams. This seemed also to lock the vent valve.

Cracking the feed tube to release the pressure lock saw the ram return springs take over and then pressing the up button saw the tabs return fully up. I am now careful not to allow the tabs to move to full down position.

That sounds like a good idea to try before diving in.

We have the odd bull shark swimming around the marina so not exactly keen to jump in the water.