steering geometries between engine and rudders...

[restless]

It has always been a source of disquiet to me when I go lock to lock and notice that the engine always swung significantly less than those wobbly old blades.
Since our first somewhat fraught escapades I have been re-engineering the steering to something appropriate for the reliability I would like to have, especially should things turn a little tricky.
In the process of this I removed the drag link off our nissan 50 and linked the bar with a slim fork onto a portion of the engine steering arm about 2 1/2" closer to the engine fulcrum. There happened to be a handy hole there. I gained about 10degrees of extra swing straight away and was for a while placated.
However, as the braces and bushes and balljoints and shims go on, this issue comes to plague me again.
It seems the turning radius of my engine fulcrum (already reduced) is now roughly 7" whereas the rudders are a touch under 5"!!!
Therefore, if I extend a rudder bracket and add a motor fulcrum with a similar radius I should get the engine to swing in parrallel to the rudders, which in turn should make it a bit more possible to get off a pontoon when in a gale on the windward side by having enough directional thrust in reverse to get the stern out and escape for some exciting sailing. In said conditions I only made it with the help of some curious bystanders who helped kick me out.
So, I'm curious to know if others have this strange set up of non parrallel gear... maybe my boat was put together by some random freak, perhaps there is some sound reason for this to be found in the fluid dynamics area of physics which so far eludes me. I would be pleased to hear as I seem to have a fairly standard set up. How could this affront to efficiency be allowed?
Many thanks.

[Catigale]

The forces the rudders and the motor put with respect to turning the boat are by no means equal, so there is no reason that the swing radii should be equal....other than aesthetics...

[bscott]

I installed a Power Thruster on my engine and it vastly improved slow speed maneuvering around the dock.

Bob

[restless]

Any more info on that Cati? I would indeed love to put this to bed without further sea trials and their associated mods to see if I can't improve what to my mind is a flawed tandem operation.
cheers

[restless]

yeah.. those thruster things have been calling for my attention... sound pretty good!

[Hamin' X]

I use a spring line to swing the bow, or stern out from the dock. Duane Dunn has an animation on their use.

http://ddunn.org/BoatHandling.htm

Try it, you'll like it.

~Rich

[restless]

Aft spring line (bottom of the page) was the technique I used to get off the sticky pontoon except I was reversing the stern out. I suppose it would be worth a try.. not overly keen on all that force on the bow fenders... I imagine it would make an 'orrid sound and require a load of gelcoating and sanding and polishing if a fender slipped Still.. I shall certainly give it a go.

However... I still really want to know why the engine swing is less than it could be. I seem to be one of those lucky sort of chaps who always ends up in particularly challenging situations so I like to maximise my options. I've been considering a thruster tube thingy as then I won't have to make shoal rudders or some complete new steering gear like on a first 21 (look at that... drool drool... I know one morning I'll see the solution)



so if I've got my rudders up and a tube on, surely would I not want the full lock to lock swing of the outboard (as designed by the manufacturers and of the steering gear And Engine... anyone seen a speedboat with lock-stops on??) to be at my disposal? I can't get this feeling out of my head that there is something not right here. I am planning on crossing France through the canal system. I want the absolute best low speed manouverability I can get.

[Catigale]

With my I can "back and fill" or spin the boat on the centerboard axis while stopped
I do have some asymmetry in the engine movement, but the boat will rotate in either direction equally

I don't think there is functional value trying to equalize the motor steering

[restless]

so can I, and I'm not particularly unhappy with the boat as it is now but I still think I could do even better! Especially when everything is up.
My regular slip normaly has a cross wind so most of the time I coul really do with all I could get.
That's the bug

[raycarlson]

this is going to be my winter time project this december.I have a nissan 50 that still has 25-30 degrees of unused steering angle available both left and right.I want that extra directional control as nothing you can do will equal the power of a propeller pulling or pushing your ass end around in tight quarters.I'm going to use a second push pull steering cable coupled with a lever to increase the swing arc of the engine which is about 40 degrees under used with the factory L shaped puh-pull tube hooked to the port rudder lever.I hope to have my motor swing in a wider arc than the rudders as slow speed manuvering at 700rpm the rudders have no effect at all.

[restless]

Hooray! my sentiments exactly.
I do think a second set up is excessive as my calculations show I can get full engine lock to lock on the 'standard set up' by simply changing where the engine link attaches. Both ends are a tad awkward, but not impossible IMHO

[magnetic]

Ask Highlander about Jackplates

[Indulgence]

My opinion- if you think about rudder function and motor thrust function
wouldn't you want the rudders to move through a lesser arc? If the rudders
throw all the way over they just stall the boat. The motor on the other hand
will provide thrust and control in whatever direction it points. So if the rudders
don't stall the whole shebang works better, does it not?

I was under the impression rudders cease to be efficient somewhere around
an angle of thirty degrees off.

[restless]

wouldn't you want the rudders to move through a lesser arc?

I'd be happy with that.. only the damn shebang works the other way round. I'm perplexed as to why the motor lock/swing has been limited, as Raycarlson agree.

[Catigale]

Make sure that ...

- You cant bring the rudders and prop into contact (

- you dont limit the engine movement by wires instead of stops ...also

Good luck with that!!