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Old 14-11-2013, 03:20   #1
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Placement of Windvane Steering System.

Hello Cruisers,

I have all but settled on a home made trim tab driven auxiliary rudder style windvane for our canoe stern Swanson.

Now I find myself looking at the placement of various windvane steering systems and noting that most seem to be stuck on complex brackets that bring the rudder/blade very well clear of the rear of the boat.

I can understand the need for a pendulum system to be clear of the stern to move freely from side to side, and I can see the advantage of the extra leverage, but I would really rather tuck ours up against the hull, nice and snug, so it does not get in the way when not in use.

I was thinking that if I mounted it on pillow block bearings about 9 inches to 1 foot (edit, per Rebel Heart's post, Inboard or Forward)from the pointy bit of the stern (is there a name for that part of the boat?) it would be out of the way when not in use, while still being well aft of the rudder, and not more than about 6 inches from the centreline of the boat itself.

I see the advantage of the pillowblock mounts as being that they can keep the whole assembly in nice and tight to the side of the boat, eliminating leverage problems and keeping the rig out of the way when not in use plus they can be self aligning, saving a bit of complex engineering and measurement.

BUT, I cannot find examples of people doing the same thing.

When this happens I consider two options:

1. I am a genius making a quantum leap of design improvement on a system that has been around for hundreds of years.

2. I am missing something.

Guess which option I am worried about.

Can anyone shed some light on this for me?

Matt
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Old 14-11-2013, 03:45   #2
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Re: Placement of windvane steering system.

My only thoughts (as a guy with a Hydrovane that extends off the stern by ~3 feet) is that 3' or 1' or 6" really doesn't make that big of a difference as far as having something annoying back there. If someone hits the back of the boat, you're going to have some problems regardless.

I think you really want to get that sucker back there for airflow and leverage.
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Old 14-11-2013, 03:49   #3
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Re: Placement of windvane steering system.

Quote:
Originally Posted by rebel heart View Post
My only thoughts (as a guy with a Hydrovane that extends off the stern by ~3 feet) is that 3' or 1' or 6" really doesn't make that big of a difference as far as having something annoying back there. If someone hits the back of the boat, you're going to have some problems regardless.

Sorry, I might not have been totally clear. That 9" to 1 foot would be INBOARD, as in forward of the stern. A luxury that the canoe stern offers over other shapes. (It would be nice to have something to compensate for loss of useable space implicit in the canoe stern design, I still reckon our 42 footer is more like a 38 footer when it comes to useable space.)

Matt
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Old 14-11-2013, 03:54   #4
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Re: Placement of windvane steering system.

Quote:
Originally Posted by rebel heart View Post
I think you really want to get that sucker back there for airflow and leverage.
Yes, too true, and I am (hopefully) solving the airflow by using a remote windvane (as per my thread on the cluttered stern, there is no good airflow anywhere near the stern of the boat).

The loss of leverage could be an issue, I am just hoping it isn't. Not very scientific I suppose, but I am hoping a LOT if that helps.

Now that I have learned a bit more about sailing the boat and I am using the right sail combinations the helm is very light in just about any conditions, so I am hoping the auxiliary rudder will do the job. I concede that there are risks implicit in what I am doing, but, I have plenty of time to build it and find that it is inadequate before it really matters. I just really like the idea of an auxiliary rudder to supplement the main one, and the auxiliary with trim tab gets around a lot of the problems I face with airflow.

Matt
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Old 14-11-2013, 09:18   #5
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Re: Placement of windvane steering system.

G'Day Matt,

I'm finding myself a bit confused here! What are the benefits of your proposed mounting position over doing it "right" and putting it on the centerline of the canoe stern?

Maybe a sketch plus a photo of the stern would help us visualize your concerns. My memory of the stern of your design is not specific enough to help me... things like the relationship of the end of the WL to the main rudder and to the proposed rudder.

And FWIW I have no doubt that an aux rudder/trim tab gear will steer your boat just fine... if well designed!

Cheers,

Jim

PS: tickets home to Tassie on 15 Dec!!!
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Old 14-11-2013, 11:31   #6
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Re: Placement of windvane steering system.

Don't really see a need to have the vane out of the way. Have sailed for decades with a vane hanging off the back and it's never been an issue. In fact it's an advantage as I use it for a boarding ladder. Not counting the loss of mechanical advantage by moving the rudder forward, there is the issue of off center mounting. Will the rudder be acting in significantly turbulent water on one tack?? How will that effect the steering ability of rudder?? Have fun drilling holes in your boat. Hope you don't have to fill them in later when the vane gets moved to the centerline in the future.
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Old 14-11-2013, 15:50   #7
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Re: Placement of windvane steering system.

OK, a picture is worth a thousand words... so here's three thousand worth.

Now if I have the order right, the first should show the unit in the stowed position, which is the main reason for thinking of this arrangement. As you can see, it would be well out of the way when not in use.

The second picture should show the overall placement from the starboard side (Viking style?) and give the general relationship between the position of the auxiliary and the position of the main skeg hung (barn door) rudder.

The final picture is a top down view of the stern and should show the overall offset.

Matt
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Old 14-11-2013, 15:59   #8
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Re: Placement of windvane steering system.

Quote:
Originally Posted by roverhi View Post
Don't really see a need to have the vane out of the way. Have sailed for decades with a vane hanging off the back and it's never been an issue. In fact it's an advantage as I use it for a boarding ladder. Not counting the loss of mechanical advantage by moving the rudder forward, there is the issue of off center mounting. Will the rudder be acting in significantly turbulent water on one tack?? How will that effect the steering ability of rudder?? Have fun drilling holes in your boat. Hope you don't have to fill them in later when the vane gets moved to the centerline in the future.

Hmm... some interesting points here.

First, turbulence. Well from what I have observed the wake of the Swanson is very calm, so I am HOPEFULL that this mounting position would be in reasonably clean water. But yes, this could be a problem so I will look more carefully on the next couple of journeys.

Hanging the vane off the back for us presents a lot of problems, particularly in the marina where we already stick out like the proverbial dog... er... things. I am expecting, sooner or later, that someone will complain and that I will have to take the dinghy off the davits at the rear when we are in our pen. Also, manoeuvring is not one of our strong points, and any part of the boat further aft will make getting out of the pen that much harder. As it is, when I reverse out, I need every inch we have in some wind conditions. I am have put my hand up for a different pen, but it could be years before that happens, and the next pen might be more crowded.

Drilling and filling holes... well, this mounting method only needs four holes in total, all above the waterline, all in good solid fibreglass and all VERY easy to get to should they need to be glassed in (and of course very easy to reinforce also). Having just glassed in more than ten holes, this aspect does not worry me too much. So I am hopeful that it is worth the risk.

The loss of mechanical advantage is my biggest concern... but I feel that in a way, the canoe stern already provides much of that advantage for me, as the last foot or two are out of the water anyway. Could be wishful thinking I suppose.

Matt
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Old 14-11-2013, 16:00   #9
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Re: Placement of windvane steering system.

cant see much problem with your idea - the aux rudder is only making minor adjustments against a balanced sail plan and a locked main rudder so its position off centre wont be an issue - unless it comes out of the water to a significant degree on one tack. In practice that is pretty rare once the boat is balanced, even going upwind.
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Old 15-11-2013, 16:17   #10
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Re: Placement of windvane steering system.

G'Day Matt,

I've been pondering your query for a while, and can't see that there is really any problem with the off-center aspect (if kept to a minimum).

I am a bit concerned by the proportions of the rudder blade that you show (yeah, I know that it is just a concept sketch, but...). The actual size that will be required to steer your boat will likely have a longer chord than what you show. Further, in order to kick up like shown (and that is a very good thing IMO), the joint must be VERY strong, as must be the blade itself. Remember that the blade and all the associated mounting stuff must be strong enough to steer the boat, and to absorb wave strikes and vigorous slewing as you come down the face of a quartering sea. The loads are vastly higher than those generated by a servo pendulum gear. We managed to break our home built one a couple of times over the years.

At any rate, do give strength a lot of consideration in your planning.

Cheers,

JIm
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Old 15-11-2013, 17:01   #11
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Re: Placement of windvane steering system.

I have a home built auxiliary rudder wind vane on the 33' Murray.

It is hung off the back on center. My aux rudder is huge compared to your sketch.

I like your folding concept...in concept. But I think it has issues. Beyond strength you need to work out the swing radius. As shown it will hit the boat as it rotates forward, rotating backward would be better.

I can't back well at all with the vane in the water. I have even considered mounting a tiller on it and steering in reverse using BOTH rudders. Makes me head hurt but might work. So I end up remounting it, but it's pretty heavy and takes up space.

Who's design will you use? Mine is by John Belcher.
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Old 15-11-2013, 18:22   #12
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Re: Placement of windvane steering system.

Since you have designed a fold up, you should consider a weak link/breakaway, so if you catch something it folds or breaks away without doing major damage. I also suspect that it will function different on one tack, than on the other, due to turbulence.____Good Luck with it_____Grant.
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Old 15-11-2013, 18:47   #13
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Re: Placement of windvane steering system.

It's not recommended to off-set the servo-pendulum (paddle) due to it lifting out of the water when heeled and too deep in the water heeled the opposite direction.

For a little education go here.
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Old 16-11-2013, 00:20   #14
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Re: Placement of windvane steering system.

Thanks all, good points all round.

Yes, those sketches are really rough, I think that the area of the auxiliary rudder needs to be about one third the area of the main rudder, but I will look that up before I start welding, just be sure. Hpeer/Jim Cate, do you remember the size relationship you used, and were you happy with what you settled on?

I believe I have a strong enough hinge design in mind, I was planning to weld two strong plates either side of the rudder shaft and have them overlap the rudder blade by a good 9 inches beyond the hinge point. I have borrowed the idea from a catamaran I used to sail which had the same thing but on a smaller scale. That particular boat had a habit of becoming completely airborne when at speed so needed very strong rudders for when you "touched down", by which point there was often a fair bit of sideways velocity. The plates would also give me the offset forward that I need for the blade to fold up flush against the shaft and also for the mechanism I have planned for the trim tab servo arm to engage with its driver when the blade is locked into its running position.

Gjordan, a shear pin would be good, particularly as the blade has to fold up forwards to address two concerns I have with a folding blade. The first concern, familiar to many a trailer sailor captain, is the problem of keeping the darn thing DOWN when under way at speed. And with ANY kind of lifting of the blade, the loss of balance on the rudder would make the servo tab useless and render the thing inoperable. Hence I have planned for it to fold down into the running position, allowing me to fine tune the position and balance with some kind of threaded stopper bolt.

The second advantage is it allows the trim tab servo arm to swing up into a socket on the driver arm as the blade is swung down into the water, meaning there would be no fiddling around to engage the thing when I want to use it.

Hpeer, to get the blade to swing up out of the water it would need to be turned to about 45 degrees to port, at which point it would clear the hull, but I admit this bit has me worried. This means the blade simply could not be lifted if the boat was under way, the forces would be too great. Also lowering into the water would require the boat to be travelling very slowly also.

I am hopeful that this will not prove a problem, as the blade should trail in neutral without affecting the course of the boat allowing me to lift it or lower it after I have stopped, or to heave to for a moment to move it. At the moment, I feel this disadvantage is outweighed by the simplicity of keeping the blade trim optimal, but time may prove me wrong, in which case it would be matter of drilling a new hinge point on the trailing edge of the blade and a corresponding hole in the trailing edge of the side plates. Actually, I might as well pre-drill and fit these when I build the blade, just in case.

Finally, nobody seems to have any particular thoughts about the pillowblock bearings, which was the bit of this design where I really felt I was breaking away from the norm. Aside from the loss of leverage issue, I feel they make the whole thing very strong and compact, but I am keen to know if anyone can see any problems with the idea.

Matt

P.S. I have finalised my Lego prototyping now and have sorted the issues around the trim tab servo plus the folding offset, the next thing will be a plywood and pine mockup in full size to see if there is some bit of the boat that gets in the way.
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Old 16-11-2013, 00:22   #15
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Re: Placement of windvane steering system.

Quote:
Originally Posted by delmarrey View Post
It's not recommended to off-set the servo-pendulum (paddle) due to it lifting out of the water when heeled and too deep in the water heeled the opposite direction.

For a little education go here.
Thank you Delmarrey, you are absolutely right, but I have decided to avoid servo pendulum and go for the auxiliary rudder with trim tab, mainly because I liked the the idea of an auxiliary rudder as a backup, after all I have read on CF about rudder failures.
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