Rudder trim

I bought a Hobie 18 Magnum early this spring to match my 17 Sport. Beautiful boat but, it had the old rudder system. I sail in Ocean Springs / Biloxi and the water can be less than 2 feet deep over 300 feet from shore. So... I bought a new style rudder system. I measured carefully, took my time researched and installed it perfectly. Now for the problem. If I trim the sails correctly I can lay the tiller and the sheets on the tramp and she sails all by herself. This is horrifying!!! What if I fell off? Would she stop when she hit Cuba?
How do I induce some helm to her to make her round up in the event of an overboard situation? I don't want to fight her but, I don't want her to leave me either. I sail solo a lot.

adjust the rudders so the bottoms move forward, that will induce a little weather helm.

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Chris
'88 H18SE Arís

I think you mean move the bottoms of the rudders aft.

Raking the rudders back creates more weather helm, raking them forward reduces weather helm. This is very easy to adjust by just loosening a bolt and repositioning the slider plate on the upgraded rudder system.

You can also increase helm by raking your rig back by changing the setting on your forestay adjuster and shrouds.

Regarding falling off the boat, even if you have weather helm, if you fall off the boat, it is very likely that you still won't be able to catch up to it by swimming. I recommend you take some additional precautions when sailing offshore such as sailing with friends, filing a "flight plan" with someone on shore, carrying a cell phone, VHF, and/or EPIRB on your person.

sm

I believe that raking the rudders is only effective for changing the amount of force on the tiller, not for changing the helm characteristics of the boat.

For the following explanation, please refer to the diagram on page 4 of this article on rudder rake: http://w1dm.com/11%20Winter%20Hotline%20TOH.pdf

I know there is a bit of confusion out there on rudder rake and helm, as many sailors sometimes simplify weather helm as the amount of pull on the tiller. While excessive weather helm will result in excessive tiller pull, the two are distinctly different. Weather helm, or the tendency of the boat to turn into the wind when no input is received from the rudders, is caused by the moment arm created by the difference in longitudinal position of the center of effort (CE) of the sail plan and the center of lateral resistance (CLR) of the daggerboards and underwater hull. The CE needs to be aft of the CLR in order for the boat to have weather helm - the resultant force on the sails tends to rotate the boat around the CLR to turn the boat upwind. The rudders are then used to counteract that moment and keep the boat on a straight course, by creating an additional force to help oppose the resultant force on the sails and balance the two, thereby cancelling out the moment it creates. Neutral helm (boat sails straight with no steering input) is the result of the CE and CLR being in the same longitudinal location, and Lee helm (boat tends to turn down away from the wind) is caused by the CE being ahead of the CLR. The only way to correct the latter two is by raking the mast further aft or altering the sailplan - smaller jib, jib furled, bigger/more efficient main, etc. Weather helm is desirable, as you have mentioned, to keep the boat from sailing away on it's own.

Rudder rake, on the other hand, primarily adjusts the amount of "pull" the tiller has when sailing upwind. Raking the rudders further forward moves the hydrodynamic center (HC) of the rudders closer in line with the axis about which they pivot, reducing the amount of pull you need on the tiller to keep them straight. Raking them further aft moves the HC of the rudders further from the axis of rotation, increasing the force on the tiller arm required to keep them straight.

If the problem is too much/too little feedback from the tiller, rake the rudders fore or aft (respectively). If the problem is with excessive weather helm, neutral helm or lee helm, rake the mast fore or aft (again, respectively) to correct the problem.

As srm said, weather helm alone is not enough to keep you safe when sailing solo. The boat can cover a long distance before turning head to wind, or there could be waves or current that conspire to keep it sailing/drifting away from you. If you're not going to be around other boaters, use extreme caution and either file a "sail plan" or keep your phone, a marine radio, gps, EPIRB, etc. on your body.

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Mike

'79 H18 standard 'Rocketman II' sail #14921 RIP
'78 H18 (unnamed) sail #14921
'08 H16 sail #114312
'97 H21SC sail #238

I agree, it is a balancing act between rig rake and rudder rake. However, since presumably his boat was properly balanced before he swapped out the rudder castings, then the only thing that should have changed would have been the rudder rake. So most likely, it would just be a matter of dialing in a little bit more helm by raking the rudders back a little bit at a time until the desired force on the tiller is achieved.

sargentwu10 - did you fill and then re-drill your rudder holes when you swapped out the castings? The holes in the rudder for the old vs. new system are not the same.

sm

Oh yes, I did fill and redrill the rudder holes. (using my Sport 17 rudders as a templet) Sounds like the first thing I will do is increase my mast rake by moving my forestay 1 hole. I like to make small adjustments. Then I'll change rudder rake. The only other comment I have about the new system is at speed my rudders "sing" loudly.

Yes, I do sail alone often. Never without my PFD on. The Ocean Springs Yacht Club is a GREAT hobie club. Lots of boats, friendly people, always people around and they monitor VHF. We all carry VHF radios, everyone ask where you are going, and the new GPS locators are becoming more common. If any of you ever have a chance to get in our area please drop by as my guest.

That is the result of the trailing edge of your rudders needing to be "tuned" and/or you need to add shims to tighten up the rudders in the castings. It really isn't related to the castings themselves.

sm

My EPO's hummed like that when I first got them. Sounded like I was singing with the whales! I took a file and flattened out the sides of the trailing edge, and flattened out the trailing edge itself. No more hum!

You may have already seen it, but if not, check out page 20 of Hobie Hotline spring 2011 issue (page 22 of the pdf): http://www.w1dm.com/projects/hotline/11 ... OTLINE.pdf

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Mike

'79 H18 standard 'Rocketman II' sail #14921 RIP
'78 H18 (unnamed) sail #14921
'08 H16 sail #114312
'97 H21SC sail #238

Correcting rudder hummmmmm: http://www.hobiecat.com/forums/viewtopic.php?f=18&t=12859

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Matt Miller
Former - Director of Parts and Accessory Sales
Warranty and Technical Support
Hobie Cat USA
(Retired 11/7/2022)

thanks Steve, ahem. I was apparently facing the wrong way.

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Chris
'88 H18SE Arís

I am for sure going to"tune" my rudders. Thanks for the links. Sometimes a picture is worth a thousand words. Thanks for all you help guys.