Rudder install ?s

I am installing a rudder soon on a project boat. 20 footer, I/B 260 bhp. I have the rudder, stuffing box and associated hardware. I also have an old car manual steering box like used in early Chris Crafts which I might use. I measured 8 inches of travel to turn the rudder a full 90 degree swing with the "tiller arm" that I have now. It is five inches from the center of the rudder shaft to the center of the end of this arm. I am guessing that 45 degrees from dead ahead either way would be a reasonable starting point, thus the 90 degrees.

With that info as background. Are there any standard rules of thumb for rudder installations? Range limits? Force requirements for steering controls/cables? I can't imagine a typical rudder for this size boat would require anything close to OB and I/O requirements. I may use some simple cables and pulleys that I could fashion myself. I literally don't need anything else if I use the steering box I have. It is heavy, but has been rebuilt and operates smoothly etc. Thoughts?

Re: Rudder install ?s

Surface area of the rudder, rudder angle, and speed of the boat are the variables when considering the forces at work. Rudder angle and speed being variable and surface area being fixed. One would need to calculate the forces at the anticipated maximum boat speed and at the maximum anticipated rudder angle that could safely be used at that speed. Straight ahead is obviously not a serious issue as there is little loading on the rudder. One might never use 45 degrees right or left rudder at WOT either but nevertheless, the calculation should include that possibility for safety reasons. It would also be a good idea to add about 20% or more for safety margin since this is a steering system. All components in the system (cables, pulleys, etc.) would need to be sized for the forces they must deal with. As for standards -- standard engineering practices would be called for but I would also expect there to be some documentation somewhere since rudder steered boats and ships have been built for hundreds of years. No sense knocking yourself out if the work has already been done. I'm curious as well so I'll see what I can find. I would suggest getting in touch with some of the antique boat clubs would turn up an "expert" or at least they would be able to give you an idea of hardware sizes on some of the old inboards.

Re: Rudder install ?s

Yeah, your initial assesment is consistent with mine. I assume there are standard calcs etc. already in place and that's what I am looking for. May be in the Glen-L destructions that came with these plans, but I didn't see them at first glance. They sell an inboard install book as well, but that's what iboats is for . . .

Re: Rudder install ?s

I spent about 15 minutes looking at "marine rudder design" and "marine rudder forces" and turned up more reading that one could handle in the rest of my life. It's complicated stuff but great bathroom reading. Who would have thought a rudder could take on so many design characteristics.

Re: Rudder install ?s

all the rudder experience if have is with sail boats, but at hull speed it takes very little rudder to change course, unless coming about.

Re: Rudder install ?s

It should be a pretty straight forward install if you use your steering wheel.
We used to use 1.2" galvanized pipe directly connected to the arms.
A couple of supports along the length these need to allow for the swing of the arms. With adjustable stops along the length or at one end or the other.45 dergree angle is about right for travel.
Depending on the size of the rudder and speed if too much is applied at speed it simply pulls the bow down and stops turning.Of course it will turn easier and sharper to the right. There is no torque feedback due to the design of the steering box.

Re: Rudder install ?s

Yeah, galvanized pipe is how I understand the original Chris's were. I guess I could go that way too. Seems clunky, clugey, goofy, but maybe it's OK. I was considering getting one of these: iboats steering cable deal



Maybe I should use the rack style without the rack, but why wouldn't this work? I would have to make some type of support on each end, but it seems like the simplest and smoothest way to do it . . .

BTW, this is a standard rotation engine and trans (LH prop) so I was planning on putting the helm to port even though I personally don't like that. I am going to use a floor mounted shifter which would be right handed and a left hand Morse throttle control. Anyway I am reading that the rudder should be placed roughly 3/4 of an inch off-center to starboard to:

a) allow you to pull a prop shaft without removing the rudder and

b) to offset some propeller walk from the left hand prop.

Any comments on that?

Re: Rudder install ?s

QC,

I'm no rudder expert but I think I'd go poking around in a Mastercraft, or other direct drive ski boat, showroom.

That may be very educational.

Re: Rudder install ?s

DJ said:

I'm no rudder expert but I think I'd go poking around in a Mastercraft, or other direct drive ski boat, showroom.

That may be very educational.

Click to expand...

Agree, and easy here as there is a big dealer pretty close. But why get off me arse if I don't have to . . .