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 Post subject: rudder tunning
PostPosted: Tue Jul 29, 2014 10:08 am 
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Joined: Thu Jul 17, 2014 4:42 pm
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hey everyone, ive got me a a 81 H18. I got it a couple months back, still working out the kinks. I have tremendous pressure fighting against my hand on pretty much any heading I take...especially when heeling over. ive inspected the rudder system somewhat, and the blades are quite loose and I have already installed 2 of the newer black rudder bushings on the newer style gudgeons. I tried putting 4 but they just didn't fit. might be part of the problem? and ive put a nylon washer on each side of the rudder attached to the lower part of the casting. but the problem I see is that there is still quite a bit of gap between the rudder blades and the upper and lower castings (well beyond what a pair of nylon washers may stiffen up). I don't want to over tighten the bolts as I am afraid that this will damage the castings.

is this a matter of shimming the spaces with whatever I can find? any suggestions?


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 Post subject: Re: rudder tunning
PostPosted: Wed Jul 30, 2014 2:46 am 
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Joined: Mon May 09, 2005 10:25 am
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Location: Jersey Shore
Do you have the old-style or the new-style rudder castings? Are you locking the rudders down fully (i.e., is the upper casting "latching" in to the lower casting)?

Helm issues are more likely to be caused by improper rudder rake than by side to side shim issues (and the most common cause of improper rudder rake is not locking down the rudders completely).

sm


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 Post subject: Re: rudder tunning
PostPosted: Wed Jul 30, 2014 8:32 am 
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We've seen a few new hobie sailors this year pickup boats with "new style" rudder castings that have become loose. There are two adjustments that can be made to adjust rake. The common issue is that the adjustment screw/bolt on the top rear of the casting is loose and the rake is set too far aft. In the locked down position loosen the bolt on the top and slide it forward so that the rudder is firmly held, and then re-lock and re-check. Lube, clean etc. to ensure everything is moving properly, there are many threads on rudders here to browse through.

This thread has some photos and diagrams of the old style, so if you're castings look like this, you have no adjustment other than re-drilling holes or toe-in toe-out adjustment.
viewtopic.php?f=13&t=48470&hilit=h18+rudder+rake

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Tom
Fleet 259, Central Coast CA
H18 ('81)
H18 ('85)
H20 ('97)
H18 ('78)


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 Post subject: Re: rudder tunning
PostPosted: Thu Jul 31, 2014 11:33 am 
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Joined: Thu Jul 17, 2014 4:42 pm
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I believe I have new style components. Definitely new style gudgeons, and I have tension adjustment screw on the lower casting and I have the sliding bolt and plate on the upper casting. I'll make some of gees adjustment over the weekend and see what happens. Thanks for the assist.


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 Post subject: Re: rudder tunning
PostPosted: Thu Jul 31, 2014 5:35 pm 
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Location: Jersey Shore
If you have the slider plate in the upper casting, then you have the new style castings.

Do you have a good understanding of how the system is supposed to work? When the rudder is down, the upper casting drops down and trips the plastic cam in the lower casting and this locks both the rudder and the upper casting down. If the rudders are locking down properly, then the next thing to check is the gap between the front edge of the rudder and the inside of the lower casting. In general, when the rudder is locked down, the front edge of the rudder should be no more than 1/4" away from the inside edge of the lower casting. Many times, the rudder will be right up against the casting. If the gap is too large, it means your rudders are raked too far back and this will cause excessive helm.

Another possibility is that the pivot holes in your rudders are not drilled properly. Since your boat is a 1981, it would have come with the old style rudder castings. It's possible that someone upgraded the rudder system but did not re-drill the rudders to match the new system. There is a template that you can download from this site to check the hole positions. The best way, however, is to find someone with a boat that has properly drilled rudders and lay one of their rudders up against yours to compare the hole positions.

sm


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 Post subject: Re: rudder tunning
PostPosted: Mon Aug 18, 2014 3:20 pm 
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Joined: Thu May 15, 2014 11:51 am
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If everything else ends up being mechanically sound with the daggers full down, there is a point when close hauled (which is 95 percent of the time on a H18 in decent wind due to the high apparent wind) that the boat should slightly tend to turn into the wind. Adjusting this can be done on old style castings by filling and drilling the holes in the rudder. Without weather helm, if you fell off, the boat would maintain course as it sailed away from you. By raking the rudders forward you can rebalance the rudder get less weather helm. Again, too far forward is dangerous. I don't know of any objective way to tell you how much weather helm is correct.

If you are closer than 45 degrees to the wind, a tightly sheeted boat will have strong weatherhelm because there is no way the jib can generate the necessary lift at such a low angle of attack (the jib has a much lower angle of attack than the main because the jib cars are mounted away from the centerline, greatly lowering the angle of incidence by design). Try moving your jib cars back 6 inches from where you have them now.

The trim of the jib can greatly effect the balance of the boat. (Imagine that with no jib or rudders, the main is a pretty effective weathervane and will always try to turn itself into the wind since most of it is behind the pivot point of the hulls. Are all four telltales on the jib flying perfectly when you have this strong pressure on the rudder? Are you sheeted in hard with the pocket in the main pretty far aft? As the center of pressure (lift) of the main moves aft you'll get more weather helm. Mast rotation, outhaul, and batten tension all have some input on the moments that the main generates. The strongest effect is from lack of proper jib trim (where are your cars, all the way forward?) and oversheeting the main because flying a hull is more fun than properly trimming the main.

To get a neutral helm, the leeward moments of the jib and rudders has to equal the weather moments of the main. The moment of the hulls and daggers can help with proper boat trim (weight forward or back) The boat will always have some slippage to to leeward, so if water pressure is too much from the side of the rudder (lots of sideslip while pointing too high and/or heeling) the rudders will try to force the boat further upwind to weather. (A lot to slippage to leeward results in a windward turning force felt at the tiller because water of water pressure on the side of the rudders If you are flying a hull with lots of weight aft and insufficient jib trim, that rudder in the water has to do a LOT of work

I'm fairly new to multihull sailing, so don't take this as canon!


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 Post subject: Re: rudder tunning
PostPosted: Tue Aug 19, 2014 11:56 am 
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Joined: Wed May 25, 2011 3:15 pm
Posts: 118
Location: Buffalo, NY
Aaron,

That was a very thorough explanation. However, one thing to be aware of is that adjusting the rudder rake on an H18 does not change the amount of helm on the boat by any appreciable amount, it mostly just changes how much your rudders pull against the tiller. Adjusting the fore and aft location of the center of effort of each the main, jib, rudder or daggerboard would affect the helm of the boat. Raking the mast, for example, significantly moves the center of effort of the sails, as does changing sail trim. Raking the rudders moves the center of effort of the rudders very little (because they're much shorter than the mast), but it moves the location of the blade area relative to the rudder pin drastically. The reduced pull on the tiller is largely due to the change in pivot point.

For this reason, the Hobie 18 Performance Manual recommends raking the mast to maintain a weather helm. The rudders should be raked forward to a point that the pull on the tiller is noticeable, but not excessive. That pull allows the skipper to have a "feel" for the boat, minor changes in wind strength/direction, etc.

On that note, josh, fore & aft slop in the rudders can cause excessive pull on the rudders, by allowing the rudders to shift further aft while underway. As srm explained, the leading edge of the rudder blade should be pretty close to "bottoming out" on the rudder casting. If you can grab the rudder blade when it is locked down and pull it back any appreciable amount, that is a contributing factor to the excess pull on the tiller. I don't have the newer style castings, but hopefully adjusting and locking down the slider plate will resolve the issue. Otherwise, check that the upper casting is locking down, check the bolt holes in the rudders & castings, and check the pins/gudgeons for slop.

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Mike
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'79 H18 standard 'Rocketman II' sail #14921


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 Post subject: Re: rudder tunning
PostPosted: Tue Aug 19, 2014 1:04 pm 
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Joined: Thu May 15, 2014 11:51 am
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SabresfortheCup wrote:
one thing to be aware of is that adjusting the rudder rake on an H18 does not change the amount of helm on the boat by any appreciable amount, it mostly just changes how much your rudders pull against the tiller.


That's a great point, chang ing the hinge point of the rudder just changes tiller input force required, it doesn't really change the boat trim though (unless perhaps you raked so far forward that the rudders became unstable, which might not even be possible on this design)

SabresfortheCup wrote:
Raking the mast, for example, significantly moves the center of effort of the sails, as does changing sail trim.


I forget about things I haven't adjusted in a while, but you are right, mast rake is probably the biggest change you can make that affects weather helm tendencies when you initially rig the boat. So @JoshCohen, if the rudders check out ok, you might want to rake forward one hole on the forestay to see if that helps! The performance manual has a median rake of 105 7/8" from the bridle to a point 48" up the mast but shouldn't be more than plus or minus 3/4" from that. It's a pretty narrow range of measurements that work, so measure accurately!


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