Hydraulic steering help - Part 2

Cardo

Cardo

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www.yacht-tinkerbell.co.uk
So...
Following the palaver we had back in the summer, we're now in Corfu, hauled out and ready to be worked on.

My plan is to fix up the steering so it uses linkages to turn the rudders from a ram mounted inside the transom. Our current hydraulic "helms" push 50cl fluid per revolution.
I'm looking at one of these as a ram:
http://www.vetus-shop.com/vetus-hydraulic-steering-cylinder-mtc72-10mm-tubing-p-173.html
The dimensions all look right for what we're doing. I guess the question, apart from the obvious general suitability, is will this take the forces from the rudders ok? I don't know the exact dimensions of the rudders, but the boat is 10.5m and we don't really go much above 6 knots tops. Though, I will say the rudders are probably on the larger side for the size of boat.

This ram would give us approx 3 turns lock to lock, which is what we currently have, and seems to be a suitable setup.

Once we've returned to the UK and have some more spending cash, I'm hoping to overhaul the system further, replacing the helm pumps with probably these:
http://www.vetus-shop.com/vetus-hydraulic-steering-pump-htp42-black-10mm-with-valves-p-160.html
and replace the current autopilot with a hydraulic autopilot. We'd end up with 3.5 turns lock to lock, which again would be fine.

Any advice, as always, very much appreciated.
 
3.5 turns is what I have and quite happy with it.My ram drives a stub tiller arm about 12 inches long;the steering pump is a vetus which I fitted several years ago to replace an old pump.The piping runs through non return valves necessary as I have a hydraulic autopilot(a lovely sharps analogue solid state one.
I
I love the way I can go and make a cup of tea whilst the steering remains where I left it.The lack of mechanical feedback from the rudder did take a bit of getting used to at first.
 
OK I have the same ram fitted to my HR Rasmus which is also 10.5 metres but probably not quite so heavy. Its lasted 3 years so far with no issues and I have quite a heavy unbalanced barn door rudder hanging on the end of my long keel

I also have an HTP 30 steering pump but without the NRVs. That way i get feedback when steering. When using the autopilot I just lock the helm using a wheel lock on one spoke

Vetus have a calculator for selecting the correct kit so should be able to verify equipment is suitable for your boat.

BTW I discovered they also do conversion bosses so you should be able to fit your old wheel to the new pump even if it has the old style of taper and the pump has the new one

This guy has also done the same. See his website for calculations http://www.lizardheadone.com/Hydraulics.html
 
Thanks for the tips so far. Looks like I'll be popping down to the boat tomorrow to measure up some rudders. Guesstimating, I think the mtc72 should just about be butch enough for us. Seems weight of boat is irrelevant, but the size of the rudders (as expected) is key. Our custom twin rudders are pretty hefty, though they are slightly balanced, so will be interesting to see what kind of torque they produce.
 
So I've popped down to the boat and done some measurements. This is what I have:
Height of rudder in water = 0.8m
Width of rudder in water = 0.59m
Balance distance = 0.12m
Our max speed is going to be nowhere over 6.5kts tops, so I reckon 12kph.

Using Vetus's formula:
F=23.3 x A x v^2
gives me
F= 23.3 X (0.8 x 0.59) x 144 = 1583.65 Newtons

To get the torque, M = F x b
b = (0.37 x width) - balance
b = (0.37 x 0.59) - 0.12 = 0.0983m

So,
M = 1583.65 x 0.0983 = 155.67Nm per rudder.
We have two rudders, so 311.35Nm total.

The MTC72 is rated to 706Nm, so we should be laughing all the way to the madhouse.

Seeing as the torque values have come out surprisingly low, I'd appreciate a sanity check on my figures!
 
And for my next question...

This page:
http://www.vetus-shop.com/vetus-hydraulic-steering-cylinder-mtc72-10mm-tubing-p-173.html
says 10mm tubing. We currently have 1/4" hose with, as I understand it, 1/4" connections.
The catalogue says the ram can take 6mm x 10mm or 8mm x 12mm nylon hose or 8mm x 10mm copper tube. I'm assuming that's ID x OD. Would I be right in thinking this won't be an issue, as long as I have the appropriate connections on the end of the hoses?
 
EuanMcKenzie said:
I also have an HTP 30 steering pump but without the NRVs. That way i get feedback when steering. When using the autopilot I just lock the helm using a wheel lock on one spoke
Click to expand...

Could you elaborate, please. How does the autopilot engage if the wheel is locked and there are no non-return valves, or do you have relief valves in the set up?
I have a Vetus helm pump driving an unidentified ram. The autopilot (goosed) and valves were removed to get me going but I would now like to install a more modern set up. I doubt if the old Bamar fluxgate and course-setter are servicable anyway.
 
Following on from my connections query:
The page also mentions G1/4 female pipe thread for the connections. Is this simply female 1/4 inch connections? If so, that sounds fairly easy, especially as I have some male to male 1/4" connectors here also.
 
ffiill said:
3.5 turns is what I have and quite happy with it.My ram drives a stub tiller arm about 12 inches long;the steering pump is a vetus which I fitted several years ago to replace an old pump.The piping runs through non return valves necessary as I have a hydraulic autopilot(a lovely sharps analogue solid state one.
I
I love the way I can go and make a cup of tea whilst the steering remains where I left it.The lack of mechanical feedback from the rudder did take a bit of getting used to at first.
Click to expand...

You can get steering feedback if you buy a helm pump without check valves and insert a single manually operated ball valve with a lever close to the steering, this can be in either of the two hoses going to the helm pump. You simply lock the steering by closing the valve every time you actuate the autopilot, you soon get used to remembering to open it again when you come off autopilot. I get more steering feedback with my hydraulic system than I did from the old Whitlock Mambo system that I took out.
 
hose size is important for one reason. the pressure drop will be greater with increased linear velocity in the tube. If you need to pump a fixed volume through the pipe to move a cylinder a fixed stroke then the velocity of that fluid will increase as the pipe size decreases. This friction results in higher resistance at the helm,the pipes getting warmer, and higther pressures in the system given greater risk of bursting a pipe.

That said I went for 10mm od hoses and its fine for my system. Don't scrimp and buy 1mm thick hose from the interweb. It won't take the pressure, I have the tea shirt and it resulted in a frantic run for the emergency tiller near the shore in the west Kyle of Bute.
 
Hi Gordon,

Saw your boat in Rothesay on Saturday when passing through via ferry to Port Bannatyne. Were you cruising of are you laid up there?

The autopilot pump is plumbed in parallel with the helm pump. The autopilot pump has non return valves so when the helm is in use it is effectively dead to the system.

When I switch on the autopilot I lock the helm and the helm pump resists the force from the autopilot so the cylinder moves. If you release the wheel lock the helm spins instead of the cylinder moving.

I prefer it as I get feedback at the helm when sailing by not having the non return valves at the helm pump.

Bit heath robinson but it works for me.

Euan
 
EuanMcKenzie said:
hose size is important for one reason. the pressure drop will be greater with increased linear velocity in the tube. If you need to pump a fixed volume through the pipe to move a cylinder a fixed stroke then the velocity of that fluid will increase as the pipe size decreases. This friction results in higher resistance at the helm,the pipes getting warmer, and higther pressures in the system given greater risk of bursting a pipe.

That said I went for 10mm od hoses and its fine for my system. Don't scrimp and buy 1mm thick hose from the interweb. It won't take the pressure, I have the tea shirt and it resulted in a frantic run for the emergency tiller near the shore in the west Kyle of Bute.
Click to expand...

The pipes I have are pretty thick, I doubt they'll struggle to take the pressure. They're probably around 12 or 13mm OD.
 
Ahh...
Understood. The system on my boat had a single non-return valve between the helm pump and electro-hydraulic pump. I still have the valve so I guess I could get a suitable pump plus the plumbing, then concentrate on the electronics. The fluxgate and course-setter are located midships under cover so "might" have survived.
I took Farewell into Rothesay just before Christmas before I went abroad for the Festives. She'll be in until March, although it may be longer if they can't fix the swing bridge. The electrics were goosed in the January 3 surge.
I was up on Saturday, although I took a run round to Port B for a while to check out the Ossian in the Anchor.
Maybe catch up with you another time.
G.
 
complete thread drift but i helped build inveralmond brewery where Ossian comes from. I went to uni with teh owner and we worked at Scottish & Newcastle together before he went independent.

He is very diligent and takes enormous pride in his products. Good to see it hits the spot

I will be out of PB & back to Largs in the next few weeks anyway.

I have a CETREK autopilot that was knackered because the main controller got drowned.

I managed to find a complete set less the hydraulic pump which gave me more than enough to get it going again for buttons compared with a new set.

I have a spare

fluxgate compass, rudder positioner, & 3 helm interface panels but obviously used the main processor. you have a pump i take it

you need a cetrek 930 680 make a complete set and that might get you away

you may also pick up a set that someone else is ripping out of their boat to upgrade

that may be a way forward if you're looking for an autopilot at sensible money

anyway apologies for the thread drift

Euan
 
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