Rudder

[Alan Wheeler]

Hi Southernman. Let me just clarify this. Your boat is steel. You have anodes that have lasted 12mths and are onlyjust startign to show signs of wear?
I presume you are permanently moored?

[Alan Wheeler]

I think from re-reading your post again, I can presume yes to all those questions. Just clarify if it isn't.
Firstly, Anodes will be Zinc. How many and where?? well initially that can sometimes be a difficult answer to find. However, there is a really cool device available that a local Marine sparky may lend you to check things. It is a Galvanic meter. You see, you can have either too much or not enough anode. Either can cause harm, just in a different way. If you have too much, a sure sign is that the anode material will form a dirty white'ish layer on it. It looks like a calcium layer built up on it.
An Anode erroding correctly, will be darkish grey and may have a patch or two of shiney meterial which is an "active" area on the anode.
Going back to the Galvanic meter. This measures the amount of current flowing in the circuit of seawater and metals. It will give you a measurement of correct protection to ensure that steel is safe. Different current strengths are required for different metals to ensure they are safe. But steel being kept high in a safe range tends to be good at keeping the bronze prop protected as well.
As a rule of thumb, an Anode would normally be needing replacement every year with each haulout. The actuall is relevant to the "saltyness" of the water. The more salt, the faster the erosion. It can also be helpful to hang a "mouse" over the side. This is an anode on a cable like battery cable that is connected to the steel yacht somewhere and this way you can lift it and visually monitor it for awhile, till you work out what size seems to work the best. As for where to place the anode, well, most tend to place it somwhere near the stern close to the prop. This is so as the prop is offered the greater protection, being the most sensitive to electrolyses.
Oh, and when you test with a meter, ensure you have an electrical circuit on every steel part in the water. This is most important that the shaft is tested. if you have a different reading on the shaft, then you may have to fit a shaft bush to ensure you have a good electrical connection.
Does that help?? ask more if you need.

[BC Mike]

It is possible that the rudder was built to the original design but the design sucks. It is not uncommon on many boats to have a crappy rudder design, even on models that sold 2500 or more.
This is not rocket science. Calculating the area of one rectangle and transferring it to another is grade five stuff. Calculating 17% of that area is still quite simple. Drawing the foil does require some thought, but the coordinates are available via the internet.
Or go outside and look at the wing of a DC6 and copy it, or pluck a primary feather from a red tailed hawk and copy it, or go take a look at a Farr 40 rudder and copy it. If you do it yourself you will have the pride of achievement, spend the winter studying the subject. It takes longer to think about building a rudder than it takes to build a rudder. I bought my Tanzer 22 the week before Christmas. There is a new rudder ready to bolt on in the garage.
I have a new 170% headsail, a spinnaker on order for delivery real soon, a spinnaker pole in the works and will have all the deck and mast hardware required by the end of next week. I thought God invented winter so we could get this stuff done on our boats.
Michael

[Alan Wheeler]

Back to the rudder part. Mike, one main reason I was going to build the rudder in steel was because of time. I am onluy going to be able to have the boat out for a couple of days. Otherwise, I have to hire in two large cranes and lift the boat to a cradle, and vice versa back again. And the yard charges $35/day on a cradle. That is too expensive for me. Ummm, the Cranes that is.
So I thought I could probably wip up a rudder in a day, seeing as the plate has the profile already cut out. A lot of the ribs and sheet can be pre-cut to eld on as soon as the rudder was out and in the workshop.
Wood sounds good, but then the glassing and the painting and thus the time. I will consider it though. Wood will be easier to work with.

[BC Mike]

You can use steel. The balance and the foil are the two critical things as long as the area is close to the original. With a better foil the new rudder can be a tad smaller. On the bigger heavier boats lift is important, on the small go fast boats drag is important. That's why there are different foil shapes, but if you make something that looks like anything I have described you will be fine. You can cut center pieces in a foil shape and wrap around a skin. Warm up the leading edge and bash it around. Weld the leading and trailing edges and grind smooth.
Michael

[southernman]

wheels - I think we have plans for a fijian somewhere in our storage shed that I bought many years ago in auction. I'll see if I can find them. If you are in the marina why don't you remove the rudder in the water to save lift out costs and fabricate one up ready for when you haul her out? I did that on our last boat when I rebuilt the rudder - worked just great!

[CaptainK]

Wheels.

I wish you luck in building a proper rudder for your ferrocement boat!!

[Alan Wheeler]

Thanks CptK.
Thanks Mike.
Hi Southernman, Yes, I had considered that as well. I was considering that we just haul her on the yard trailer and remove the rudder and then use a small boat to take her back to the birth. Then I have all the time I want to do the job. I won't try and take the rudder off while in the water. It is Barn door type in size and I could just imagine being pinned to the bottome by a solid sheet of steel plate. I don't think it would quite work out like the cartoons
Oh and I know what you are all also thinking. No, the rudder doesnt drop witht he stock on this design. The plate is bolted on to the stock under water with a large collar and a dozen or more bolts around it. It unbolts and swings away leaving the shaft stock up in it's place. The bottome of the rudder is held inplace with a bearing/gudgeon, so the rudder then has to be lifted up away from the boat. All to hard and dangerouse I think for his task to be done in the water.
I will see if I can find a photo and post in in the gallery so you can see what it looks like.

By the sound of this thing, you may want to add a lifting eye while you are fabbing things. Next time it can be lifted out with the boom
Major computer problems with my other computer, so I won't be scanning tonight. I will drop the magazine in the mail tommorrow. PM me a mailing address.

[Alan Wheeler]

Thanks Kai Nui, much appreciated. Hey if ya can slip ya self in that envelope, I'll shout you a beer. I can post you back on the next mail out.

Hey if anyone is interested, I just uploaded a photo of the Rudder. Not great, but you'll get the idea. If you look careful, you'll see the row of bolts ont he flange at the top of the stock/rudder area.http://cruisersforum.com/photopost//...php?photo=1620
Hope that links.

[CaptainK]

Wheels.

I can see why you want to build a new one. That rudder looks a bit small for that design?

She's a fine boat you get there. A nice ferro boat!!

[BC Mike]

The picture explains heaps. Going back to your original post. The weather helm may be a function of the long keel. That happens, but it may be improved by a foil shaped rudder. Your building ideas are fine. Make foil shapes and weld them to the central slab, then cover with a skin. You can not change the balance, there is no room forward of the pivot point. The leading edge looks rounded. I would stay with that and blend the foil into the rounded part. The size looks fine to me. Was the boat managable in the last hurricane. If it was then the rudder is big enough. For another opinion send a message to John Welsford. He is near Waihi Beach in the North Island and a designer. He also has a magic C&N formula for drawing foils. Your rudder looks to be about 50cm front to back. Is that about right ?
A foil thickness of about 75mm would probably be enough. Of course looking at the boat directly might give a different impresion.
Michael

[Alan Wheeler]

Thanks Mike. The leading edge is indeed the shaft stock. It would be a good 2" shaft. Yes I imagine the cord width to be about .5m. The Rudder is about 2m in height.
I did have some much better photo's at one stage. I took a heap of detail and measurements when she was up. But I somehow have filed them in bin 13. Can't find them anywhere.

I have haydraulic steering, so not having a balanced rudder is probably not a huge issue. Or is a balanced rudder nothing to do with steering feedback force???

Here was another thought I had last night. I could make up a timber foil section as you suggested. But keep it in two halves. Then epoxy and bolt it over the steel plate when the boat is up. Glass it all over to seal it and then epoxy paint. Could do that in say two- three days or so, cause the glass and epoxy paint doesn't have to be fully cured before emersion. A quick anti-foul before it goes back in and bob's ya uncle.

[Boracay]

The boat that I built was a Hartley RORC 32.
My memory is a little hazy, but from what brain cells I have not destroyed I recollect that I made the rudder from two thick planks at about 30 degrees to each other, shaped according to plan. It was held together by epoxy and copper rivets through bronze fittings. Not expensive in those days, but it would not be cheap now.
The rudder was "balanced" in that 15% of the area was ahead of the stock.
It sounds like this comes into the essential for cruising, must be done long term but will not sink the boat today category.
If a steel rudder has worked for a long time then it may be best to stick with a steel rudder.
In a perfect world one could weld up a rudder with a nice shape, have it galvanised, primed and painted ready to go on the boat. This would take time, and money, though I am not sure that a nice shape would do that much for your steering.
The cheapest and easiest would possibly be to take the rudder off, repair the damage and bolt it back on.
Galvanising would not be prohibitivly expensive, and would do much for your peace of mind.
A hole in the top where lifting gear or emergency steering could be shackled on could do likewise.
If the Tahitian is anything like my 32' was then your steering would possibly be best improved by concentrating on reducing the topside weight, and placing all weight is as low as possible in the boat, and by making sure that sail area can be reduced quickly and easily.
There have been some reports that some aspects of steering can be greatly improved by the use of a suitable feathering propellor, so a long term focus on this could be beneficial.
Hartley and Brookes may sell a set of plans at a reduced price if it is only for the information of the owner. I do know that they continue to support their plans so a chat with them could also be beneficial.
As a matter of curiosity, is your rudder shaft mild steel?

[BC Mike]

Yes that is what I had in mind. Build it whichever way is easier.
Cloth will not wrap around the sharp trailing edge, just run it straight back a smidgeon on one side and then overlap it a smidgeon in the other side. This will create a bit more resin on the trailing edge that can be filed flat about 2 to 3 mm even up to 5mm. Do not round the trailing edge. Having 17% maximum of the rudder forward of the pivot point is a bit like having power steering. It is quite noticeable on smaller boats with tillers. With hydraulic steering on a bigger boat you will not get the same feedback. If you get weather helm you can probably only flatten the main and ease it a bit and that is about all. I have not sailed on a full keel boat so for me it is just theory.
Steering in a straight line is as much a function of the hull as anything else. If the hull is properly balanced you can hang just about anything off the bottom.
Michael