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Old 09-09-2018, 05:47 PM   #21
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Might use aluminum if I try it again... softer, yes, but significantly easier to work with.
If your rudder is ss, your aluminum plates will disappear through galvanic corrosion.
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Old 09-09-2018, 05:50 PM   #22
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Twist,
I agree.
The propwash is way above boat speed. I moved one of my zincs up to the top of the rudder to get them out of the propwash.
As we used to say in aviation the propwash is trying to blow the tail backwards. So it pulls back on the fuselage. Rudders pulling back on boats dosn’t help efficiency.
No noticeable loss of efficiency or fuel consumption at 7 knots (as measured between Toronto and Bahamas), actually no noticeable difference in any way except the ability to do tight turns at low speed and a moderate improvement going astern.
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Old 09-09-2018, 05:58 PM   #23
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...about $100 Cndn dollarettes, I believe that's about ten bucks US
Been cruising in the Ďol US of A?

Your dollar is worth a dollar in BC...you should come up & over, down and around, or across at 100kph for a visit
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Old 09-09-2018, 06:17 PM   #24
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Been cruising in the Ďol US of A?

Your dollar is worth a dollar in BC...you should come up & over, down and around, or across at 100kph for a visit
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Old 09-09-2018, 08:23 PM   #25
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There is a commercial rudder addition made for single screw ships, tugs and large commercial boats. About 20% more rudder tail is added with pivots and linkage so in a turn, the further the rudder goes toward full, the further the extension moves. I've seen a homemade one with ss cables and attachments along side the rudder post. A ship will make a turning circle about 20-25% smaller.
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Old 09-09-2018, 10:42 PM   #26
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The million dollar question...

How big of a fishtail to improve turning but small enough to be insignificant drag at cruise?
Guesswork
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Old 09-09-2018, 11:43 PM   #27
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Guesswork
It is guess work but easily and inexpensively changed if bolted on. A buddy who is a naval architect saw my effort after the fact and said my 6" fins at 15 degrees on a 38' displacement hull was right about what he would have prescribed.
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Old 09-10-2018, 05:34 AM   #28
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Originally Posted by Lepke View Post
There is a commercial rudder addition made for single screw ships, tugs and large commercial boats. About 20% more rudder tail is added with pivots and linkage so in a turn, the further the rudder goes toward full, the further the extension moves. I've seen a homemade one with ss cables and attachments along side the rudder post. A ship will make a turning circle about 20-25% smaller.
Articulating rudder, a very different animal than adding to existing rudder.
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Old 09-10-2018, 08:11 AM   #29
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If you want great slow speed turning, the 3 components to success are:

A large rudder.
A significant leading edge (up to 28% of what's behind the pivot point, put in front of the pivot point). Without a leading edge, you lose half of the prop wash.
Being able to pivot the rudder 40 degrees.

This is the rudder on my trawler. It's a foil style, designed for slow speed. There is a significant leading edge and it will pivot 40 degrees. You can push this boat sideways by pivoting the rudder hard over, going forward at idle and pushing the bow with the bow thruster. There is an incredible amount of sideways push with this rudder hard over!

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This is the rudder we built for my Bruno & Stillman. Large leading edge and 40+ degree pivot. This boat turns on a dime and gives you a nickel back.

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Ted
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Old 09-11-2018, 05:34 AM   #30
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I made a similar rudder mod but also added end plates. My thoughts were that it would help prevent the water taking a short cut and bypassing the rear strip. It has had a massive effect on the hull and I am still evaluating the effects. It must be costing fuel as there seems to be a lot of ocean chasing the boat about the harbour that there wasnít before, and the wake leaves the hull from further back on the sides of the hull. Steering is much more direct and low speed manoeuvring has improved ten fold which was expected (planed -hoped more likely). What I didnít expect was a higher top speed and the hull traveling much flatter. Itís intriguing and got me thinking of removing it next season so I can make more accurate comparison as I didnít make enough observations of the earlier set up. I think what may be happening with the increase in top speed is that the schilling strip is dragging a lower pressure behind the rudder that is being filled by water that would of otherwise continued to travel below the keel and rudder. This upward movement of water I suspect is creating lift at the large flat area at the stern and keeping the boat bow down increasing the effective waterline. The bow stays flat at all speeds so it will be interesting to see if it climbs over big seas on the bow or attempts to punch through them ??. Iím really surprised at what a huge change something so subtle can make. I suspect the designer would be horrified at what Iíve done but gosh itís interesting. I can post a couple of pics if anyoneís interested. I would also be interested on anybodyís ideas on whatís really going on.
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Old 09-11-2018, 06:07 AM   #31
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BeeJay,


Pretty interesting that you got some stern lift from the mod. Got any pics?
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Old 09-11-2018, 06:18 AM   #32
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If your rudder is ss, your aluminum plates will disappear through galvanic corrosion.
Yes that would be and issue, but one could separate them with non metallic washers. But mine's not SS anyway.
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Old 09-11-2018, 06:21 AM   #33
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Beejay,

Yes, pix would be interesting. I also a bit intrigued with the rudder designs and the shilling, fishtail, etc. mods.

Considered the articulating rudder at one time, but just don't like moving parts down there, plus it's expensive.

All this rudder modification stuff solidifies my decision to get a twin next time.
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Old 09-11-2018, 10:52 AM   #34
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The main purpose of the leading edge of the rudder, the bit in front of the post, is to lower the effort needed to turn the rudder. My mod lowered vibration in the rudder, has no effect on cruise speed and improved my low-speed handling immensely. Itís up to you to decide if ďimmenselyĒ means anything.
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Old 09-11-2018, 11:17 AM   #35
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I had a piece of 2" angle welded to the trailing edge of MOJO's rudder. No change in speed that I can discern but it does seem to make slow speed handling a little better. I suspect it's a little too small so I may try a larger piece at next haul out. Easy to cut this one off and weld on a 3" or 4" angle.Click image for larger version

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Old 09-11-2018, 11:30 AM   #36
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Our big 45 degree rudder leaves me not in want of anything else.
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Old 09-11-2018, 03:27 PM   #37
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Rudder mod pics
Attached Thumbnails
Rudder mods.jpg   Rudder mods 2 .jpg  
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Old 09-11-2018, 04:15 PM   #38
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Our big 45 degree rudder leaves me not in want of anything else.
That’s because your boat has a small, pert, slippery rounded arse compared to our large, squat, heavy, water dragging square ones
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Old 09-11-2018, 04:20 PM   #39
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That's the kindest thing that somebodies said about my rear end in a long time .....gosh thanks Murray (blush blush)
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Old 09-11-2018, 04:35 PM   #40
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That's the kindest thing that somebodies said about my rear end in a long time .....gosh thanks Murray (blush blush)
Sorry Dude... I was talking to Nomadís Willy
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