Modifying buoyancy of the rudder on a steel vessel

[jmph]

Hi
I have a steel motorsailor Van de Stadt Norman 40.
The rudder is hollow (a solid stainless steel rudder stock approximately 100 mm and the rectangular 700x1400mm made of 4mm steel plate) and has two holes to fill it, currently oil. Cube about 60 liters.
After adding a stern bow with davits for the dinghy and carrying there the life raft the boat trim aft.
My question is:
Could the trim be corrected if I gain buoyancy at the rudder by emptying it of the oil? Would it affect the correct functionality of the rudder?
Greetings

[Wotname]

Originally Posted by jmph

Hi
I have a steel motorsailor Van de Stadt Norman 40.
The rudder is hollow (a solid stainless steel rudder stock approximately 100 mm and the rectangular 700x1400mm made of 4mm steel plate) and has two holes to fill it, currently oil. Cube about 60 liters.
After adding a stern bow with davits for the dinghy and carrying there the life raft the boat trim aft.
My question is:
Could the trim be corrected if I gain buoyancy at the rudder by emptying it of the oil? Would it affect the correct functionality of the rudder?
Greetings

Welcome aboard jmph.

Well you will gain some lift aft; I guessing about 50 kilos max and presumably the rudder is somewhat forward of the stern so that probably means the equivalent of say 30 kilos right at the transom. This unlikely to have much effect overall but try it, it won't hurt.

I can't see how the rudder functionality would be affected except it will have less mass and therefore a bit easier to move it quickly.

[Ray Perry]

The only reason the oil is there is to help prevent corrosion/electrolysis. You can bet your bottom dollar that the oil has coated all of the interior surfaces.
Your trim is dependant upon the correct distribution of weight of your yacht so try to place the maximum weight near the centre of buoyancy.

[Pelagic]

Ray has it right, corrosion inhibitors is the priority and a designed weight to maintain trim and balance
recommend you leave as is.....
My dutch Rudder is filled with diesel

[GordMay]

Greetings and welcome aboard the CF, jmph.

[S/V Alchemy]

I have a steel custom pilothouse and an aluminum plate rudder; the aluminum rudder stock is transom-mounted and separated galvanically from the gudgeons by Delrin rings. I have the same option to fill the rudder and the same rationale. I estimate adding a bit of buoyancy to the rudder will make the hydraulics a touch more responsive. I would say if you can seal the rudder effectively, it's well worth a try.

[jheldatksuedu]

I have a steel 45 Van de Stadt. 60 liters sounds like a lot, but I haven't looked at the construction of my rudder. I would assume most of the lift would be behind the rudder shaft and when heeled it would tend to lift the rudder to turn toward the wind. 60 liters or 15 gallons would be a little over 100 pounds of lift. Probably not much compared to davits and dinghy but at least a step in the right direction. I would tend to leave the rudder alone and move other weight forward in the boat to trim it if desired. There would not be much affect of a slight increase of draft of the boat.

[bsurvey]

not enough oil to make a difference and you will loose the anti corrosive protection the oil is their for

[UNCIVILIZED]

I'd pass on doing this. The oil is there to protect things for a reason, & loss of steering is one of the top 3 or top 5 reasons people abandon boats. Meaning they trigger the EPIRB & call for help.


Besides, oil doesn't weight anything in water. It floats remember.

[seabreez]

Originally Posted by jmph

Hi
I have a steel motorsailor Van de Stadt Norman 40.
The rudder is hollow (a solid stainless steel rudder stock approximately 100 mm and the rectangular 700x1400mm made of 4mm steel plate) and has two holes to fill it, currently oil. Cube about 60 liters.
After adding a stern bow with davits for the dinghy and carrying there the life raft the boat trim aft.
My question is:
Could the trim be corrected if I gain buoyancy at the rudder by emptying it of the oil? Would it affect the correct functionality of the rudder?
Greetings

I would empty the rudder and fill it with spray foam. It would make it a little lighter and seal it. Every bit helps.

[musher]

I would empty the rudder and fill it with spray foam. It would make it a little lighter and seal it. Every bit helps.

Yikes. This is not a good idea. It will trap any saltwater that does intrude--leading to corrosion. No way to dry or re oil inside of rudder once you've poured it full of foam

Consider: The rudder is either perfectly sealed or it is not.

1. If the rudder is sealed, it will hold air. Air is lighter than foam, so you gain more buoyancy than with foam. Plus, you can still recoat inside of rudder with oil during haulouts.
2. If the rudder is not sealed, foam will not prevent incursion of saltwater and will prevent correcting the problem.
3. If the rudder is sealed now, it may not be sealed later in life.

Hard to say whether rudder balance will be noticeably affected while heeling. You could test it.

Seems like it might be more effective to think about moving some fixed loads (like batteries) inside the hull to trim the boat.

[a64pilot]

Originally Posted by bsurvey

not enough oil to make a difference and you will loose the anti corrosive protection the oil is their for

I think this is likely, to see how much difference it will make, have a light weight person stand in the cockpit with you, then have them step out onto the dock.
I bet you won't be able to see any difference in the waterline at all.

If I did it, I would want a schrader valve in it, I would pressurize it and check pressure infrequently, loss of pressure would indicate a leak of course. I don't think it worth the trouble though

[Pauls]

Regarding all the posts cautioning against draining the oil, lets look at the basic physics. Steel cannot rust in the absence of oxygen. If the rudder is sealed it cannot rust internally, the available oxygen will be consumed and corrosion will then stop. You can drain the oil with complete safety IF you verify that the rudder is hermetic. Do this by draining the oil and then attaching an air pressure line to the drain fitting. You must use a low pressure regulator on this line, use 3 to 5 PSI air pressure. Excessive pressure will deform the rudder. Go over the rudder, especially all welds, with bubble solution. This will show if there are any leaks. If there are, weld them up. When the rudder is hermetic reinstall the drain plug. You can remove the drain plug when you haul out as a further check that the rudder has remained hermetic.

In addition to helping your trim slightly, removing weight from the ends of a boat is always a good idea.

[Pelagic]

[QUOTE=S/V Alchemy;2323349

I estimate adding a bit of buoyancy to the rudder will make the hydraulics a touch more responsive. I would say if you can seal the rudder effectively, it's well worth a try.[/QUOTE]

My steering is hydraulic on Autopilot and pilothouse, but responsive manual cable in cockpit.

I feel that the actual weight of the rudder when hard pressed and heeled over falling to leeward, would help counteract typical weather helm.

No proof, just a feeling.

[Pelagic]

Originally Posted by Pauls

Regarding all the posts cautioning against draining the oil, lets look at the basic physics. Steel cannot rust in the absence of oxygen. If the rudder is sealed it cannot rust internally, the available oxygen will be consumed and corrosion will then stop.

Paul, no argument with the above, BUT practicality comes into play as well as the kiss principal.

Example
Cruising the south pacific and your rudder hits an underwater obstruction. How do you know if you have developed a pin hole leak?

I use diesel specifically because it will penetrate any pinhole and be obvious when cleaning rudder.

That is my simple telltale if damaged