Modifying rudder, now I'm concerned about weight

[Sumner]

.... So if I'm reading correctly, the bracket that actually holds the rudder broke, not the stern mounted brackets? ....

The cheek plates that are at the base of the post and on the sides of the rudder cracked and broke. There is a difference in the way the rudder mounts on my S vs. your D.



On the S, shown above, there is a rudder post that goes up inside the lazarette with bushings. The only thing out of the boat is the lower part of the post with the cheek plates and the tiller on the top of the post. The post is inside the boat.



On a D, shown above, all the hardware is off the back of the transom,

Sumner

============================
1300 miles to the Bahamas and back -- 2015

The MacGregor 26-S

The Endeavour 37

Trips to Utah, Wyoming, Idaho, Canada, Florida

Mac-Venture Links

[sailboatmike]

Just for reference I looked at the rudder setup of 3 or 4, 25 foot plus trailer sailors of different designs that are in the hard next to mine.

On average the length of the rudder is about 1.5 meters or around 4 foot 10 inches long.

Of that length they all have around 1.2 meters or 4 feet in the water

The average width of the rudder is around 600mm or 2 feet

The thickness if the rudder is governed by the NACA profile you decide to use, most use NACA 12 is best for these boats at around 6knts maximum, but at 2 feet wide the thickness would be around 2 and 7/8 inches (72mm). I have built a NACA 12 calculator for anyone interested, its just a simple google docs spreadsheet that gives the thickness of the rudder at 20 points of the width at 5% intervals

Now the million dollar question is how much rudder should I have in front of the pivot point, too little and the boat will be slow to respond, too much and the helm will become very tender and it will be hard to hold the boat of a nice even course.

Well of all the boats I looked at none had any blade forward of the pivot point, all the blade was behind the pivot point, of course this is in relation to the hull shape, I must say none of the ones I looked at had planing or even semi planing hulls (very flat bottom toward the rear of the boat), they were all full displacement hulls.

[Ixneigh]

You know creative application of duct tape and foam might allow experimentation in an easy and cheap manner...these rudders are not actually under much stress on a nice mild sailing day.
Ix

[svscott]

Just for reference I looked at the rudder setup of 3 or 4, 25 foot plus trailer sailors of different designs that are in the hard next to mine.

On average the length of the rudder is about 1.5 meters or around 4 foot 10 inches long.

Of that length they all have around 1.2 meters or 4 feet in the water

The average width of the rudder is around 600mm or 2 feet

The thickness if the rudder is governed by the NACA profile you decide to use, most use NACA 12 is best for these boats at around 6knts maximum, but at 2 feet wide the thickness would be around 2 and 7/8 inches (72mm). I have built a NACA 12 calculator for anyone interested, its just a simple google docs spreadsheet that gives the thickness of the rudder at 20 points of the width at 5% intervals

Now the million dollar question is how much rudder should I have in front of the pivot point, too little and the boat will be slow to respond, too much and the helm will become very tender and it will be hard to hold the boat of a nice even course.

Well of all the boats I looked at none had any blade forward of the pivot point, all the blade was behind the pivot point, of course this is in relation to the hull shape, I must say none of the ones I looked at had planing or even semi planing hulls (very flat bottom toward the rear of the boat), they were all full displacement hulls.

Mike, that's all great, very useful information, thank you for checking that out. There's not a single civilian boat last in my marina to look at anymore this season.
I decided on my 13" blade width based on the overall thickness to be about 2-1/8" thick at 30% back from the leading edge. There was a very well written article I came across about designing and building high performance rudders. It's been a little while since I read the article, but from what I recall, the author suggested about 25% of the blade width to be in front of the pivot point to help reduce weather helm and to ease the effort applied at the tiller. With a 10" stock rudder width, I added 3" for a 30% overall increase. I added 6" in length so the total rudder height is 54" with about 42" below water line.
Here's the article on rudder design: http://www.paceship.org/how_to/rudder.asp#theory

[sailboatmike]

Yes i have read that blog, its a great resource, the boat they are talking about there though has a full keel unlike our trailer sailors, I think this may make a difference in the amount of rudder forward of the pivot point.

Anyway Im looking forward to a review of your new design and what difference it makes, beats me that such great boats all suffer from the same problem of poor rudder design, surely after making the 10's of thousands of boats that Macgregor did you would of thought they would of got a basic thing like the rudder design better.

While its not rocket science, NASA did the NACA calculations for everyone to use and share, and while I love my boat dearly when I get into open waters, i get more than a bit tense when I get into a crowded area at slow speeds, in some ways us power sailor owners are lucky as we can grab a big handful of throttle to get us out of situations and the big prop will do its magic, not so sure how I would go with a small motor on the back that wont give that instant response to a handful of throttle

[svscott]

I only have a little 5hp Nissan hanging off the transom and I have to turn around and reach way back to switch gears, which just adds to the difficulty and excitement of slow speed maneuvering in tight places. Aside from the rudder mod, I'm planning on buying and installing a Tohatsu 6hp carburetor for my outboard - $120 and 30 minutes for a bolt on 20% power increase sounds good to me!

[Sumner]

I only have a little 5hp Nissan hanging off the transom and I have to turn around and reach way back to switch gears, which just adds to the difficulty and excitement of slow speed maneuvering in tight places.

Consider an extension for the shifter.....



I made one for the Tohatsu.....

http://purplesagetradingpost.com/sumner ... de-28.html

and ...



For the Honda before it....

http://purplesagetradingpost.com/sumner ... de-18.html

Ruth and now Dottie are usually at the helm when docking and anchoring and they like the extensions on the shifter, throttle and the connector that is used at those times between the outboard tiller and rudder tiller. Also the outboard has a tiller extension as shown above.

I'm planning on buying and installing a Tohatsu 6hp carburetor for my outboard - $120 and 30 minutes for a bolt on 20% power increase sounds good to me!

We had (still have it) a Nissan 5 HP and liked it but then got the Honda and then the Tohatsu for the safety of the electric start for the Mac. The 5 HP moved the Mac fine but we wanted to use it on the inflatable. I had also considered the carb change but instead did a prop change. The one HP difference is probably only when the outboard is running between 5000-6000 rpm. Over the rest of the range the HP difference is less and probably far less at the low rpm limit used while docking and anchoring. Going to a higher thrust prop can offer a lot more in the way of returns in those situations. If you have a stock prop designed for say, a light jon boat, then think about making that change. Here is a link to a prop chart where they have recommendations for boats in the 1500-3000+ lbs......

http://www.tohatsu.com/accessories/prop.asp

It is on a Tohatsu page but the outboards are the same as the Nissan,

Sumner

============================
1300 miles to the Bahamas and back -- 2015

The MacGregor 26-S

The Endeavour 37

Trips to Utah, Wyoming, Idaho, Canada, Florida

Mac-Venture Links

[svscott]

I only have a little 5hp Nissan hanging off the transom and I have to turn around and reach way back to switch gears, which just adds to the difficulty and excitement of slow speed maneuvering in tight places.

Consider an extension for the shifter.....



I made one for the Tohatsu.....

http://purplesagetradingpost.com/sumner ... de-28.html

and ...



For the Honda before it....

http://purplesagetradingpost.com/sumner ... de-18.html

Ruth and now Dottie are usually at the helm when docking and anchoring and they like the extensions on the shifter, throttle and the connector that is used at those times between the outboard tiller and rudder tiller. Also the outboard has a tiller extension as shown above.

I'm planning on buying and installing a Tohatsu 6hp carburetor for my outboard - $120 and 30 minutes for a bolt on 20% power increase sounds good to me!

We had (still have it) a Nissan 5 HP and liked it but then got the Honda and then the Tohatsu for the safety of the electric start for the Mac. The 5 HP moved the Mac fine but we wanted to use it on the inflatable. I had also considered the carb change but instead did a prop change. The one HP difference is probably only when the outboard is running between 5000-6000 rpm. Over the rest of the range the HP difference is less and probably far less at the low rpm limit used while docking and anchoring. Going to a higher thrust prop can offer a lot more in the way of returns in those situations. If you have a stock prop designed for say, a light jon boat, then think about making that change. Here is a link to a prop chart where they have recommendations for boats in the 1500-3000+ lbs......

http://www.tohatsu.com/accessories/prop.asp

It is on a Tohatsu page but the outboards are the same as the Nissan,

Sumner

============================
1300 miles to the Bahamas and back -- 2015

The MacGregor 26-S

The Endeavour 37

Trips to Utah, Wyoming, Idaho, Canada, Florida

Mac-Venture Links

I haven't been on the forum in a long time and missed this post... I like the idea of adding extensions to the outboard controls and we'll consider this for next year. I just swapped out the carb and picked up about 1/2 knot at full throttle and now I have a spare carburetor on board. I'll be buying a high thrust prop for next season - boost funds went to other areas this year - new carb, LED lighting, new standard horizon gx1700 vhf, new stereo, all new standing rigging and some new Dyneema endura braid halyards.
I still haven't finished glassing the new rudder - for this year, I got some great advice and drilled new pivot / lock holes on the stock rudder to angle the bottom leading edge forward a bit. The tiller is now super light and I'm not fighting the weather helm that I used to. I suspect my new rudder will be better yet, once completed

[svscott]

I'm finally resurrecting this thread with some major updates and progress! My rudder post has finally been reinforced and the oversize rudder is finally glassed, faired, barrier coated, and ready to test.

The past couple years, this rudder project got tabled while I worked on a myriad of other projects and otherwise just enjoyed the boat. I don't remember who it was but during a conversation about what I was doing, someone at BWY recommended redrilling and angling my rudder blade forward, so I took his advice and it made a HUGE difference for no cost and minimal effort but I've had this big rudder sitting in the garage 75% finished and I believe the improvement of the big rudder over the angled rudder will be even better so I took the time to better my fiberglass skills and finish this beast.

Pic of new vs old rudders. The stock rudder shows the 2nd set of holes I drilled to angle the bottom forward. I'll stash this rudder under the aft berth just in case.



My rudder post pivot brackets (the 3/8" thick welded tabs with holes to slide onto the pintles) were terribly worn out and I was afraid to add any extra load without replacing the post or reinforcing it. I cut and fit a couple reinforcement brackets from 1/4" aluminum plate and had a local shop weld them to the existing tabs and post. Now there is no more repetitive clunk when turning and I'm not afraid of losing my entire rudder when bashing through waves!





This shows the worn out pivot bracket... notice how out of alignment the tab is and the hole is 11/16" diameter instead of 1/2".



We sandwiched the new and old aluminum tabs together and fully welded and filled the old pivot holes then I redrilled. The original tabs were very far off from being centered on the spine of the rudder post. I used a laser line and framing square to lay out the new hole locations.





With the reinforced rudder post finally completed, I dug out the project rudder and finished laying several layers of fiberglass cloth then faired with west system 407 and barrier coated with 6 coats of west system 422. It could use a final sanding and top coat of epoxy to smooth everything out but it's good enough and further work on it will have to wait until more pressing projects on the other boat are checked off the list.








I learned a lot more about composites work through this project and have gotten better because of it. I'm not thrilled with the weight of this rudder (about 40 lbs!) but it's below the waterline so it should be ok. I'll use the back stay to haul the rudder up out of the water at the ramp. I'm really looking forward to sailing soon and trying this new modified rudder and post!

[svscott]

I got to take Three Hour Tour out for a few hours this evening and the new rudder and reinforced rudder post behaved brilliantly. The rudder is decently balanced and it literally only takes a finger to control the tiller and the boat responds almost immediately. There is a bit of weather helm that I may try to tune out by adjusting the rig at a later time.
The weather today was 78 degrees and sunny with 5-8 mph East wind. We sailed a couple miles across the bay then dropped sails and tied up to the courtesy dock at Rum Runners, a local bar and grill and had dinner and a beer on their outdoor patio. Docking in front of a handful of onlookers was perfectly executed and without drama. After dinner was finished, my buddy untied the lines and we shoved off and motored about 25' and quickly raised the 150 genoa, filling it out at a broad reach. We then shut off and raised the Tohatsu Sailpro outboard and glided silently away. If the wind was from the opposite direction, I would have certainly sailed of the dock. I've never sailed on or off a dock but am looking forward to trying!
The conditions were ideal for an easy sea trial but now I'm looking forward to a 15 plus mph wind to see how the boat behaves when leaned hard over and bashing through 3' chop on Lake Erie.