Forum Home
IntroductionBrowse
Our MacGregorExploringArticlesAbout this Website
ManualsDealer InfoSailing LinksTell a FriendSupport this Website
Forum Home

Modifying rudder, now I'm concerned about weight

A forum for discussing topics relating to older MacGregor/Venture sailboats.

Moderators: tangentair, beene, Heath_Mod, Hamin' X, kmclemore, Catigale

Re: Modifying rudder, now I'm concerned about weight

Postby Sumner » Mon Nov 13, 2017 7:48 pm

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


Image

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.

Image

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.

Image

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
User avatar
Sumner
Admiral
 
Posts: 2254
Joined: Sun Jan 04, 2009 6:20 pm
Location: SE Utah
Sailboat: MacGregor 26S

Re: Modifying rudder, now I'm concerned about weight

Postby sailboatmike » Tue Nov 14, 2017 1:39 am

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.
sailboatmike
Admiral
 
Posts: 1332
Joined: Fri Mar 13, 2015 12:17 am
Location: Australia
Sailboat: MacGregor 26X

Re: Modifying rudder, now I'm concerned about weight

Postby Ixneigh » Tue Nov 14, 2017 8:12 am

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
User avatar
Ixneigh
Admiral
 
Posts: 1741
Joined: Thu Sep 09, 2010 1:00 pm
Location: Key largo Florida
Sailboat: MacGregor 26M

Re: Modifying rudder, now I'm concerned about weight

Postby svscott » Tue Nov 14, 2017 8:37 am

sailboatmike wrote: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
svscott
Just Enlisted
 
Posts: 17
Joined: Fri Aug 12, 2016 10:35 pm
Sailboat: MacGregor 26D

Re: Modifying rudder, now I'm concerned about weight

Postby sailboatmike » Tue Nov 14, 2017 4:30 pm

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
sailboatmike
Admiral
 
Posts: 1332
Joined: Fri Mar 13, 2015 12:17 am
Location: Australia
Sailboat: MacGregor 26X

Re: Modifying rudder, now I'm concerned about weight

Postby svscott » Wed Nov 15, 2017 7:53 am

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!
svscott
Just Enlisted
 
Posts: 17
Joined: Fri Aug 12, 2016 10:35 pm
Sailboat: MacGregor 26D

Re: Modifying rudder, now I'm concerned about weight

Postby Sumner » Wed Nov 15, 2017 10:15 am

svscott wrote: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.....

Image

I made one for the Tohatsu.....

http://purplesagetradingpost.com/sumner/macgregor2/outside-28.html

and ...

Image

For the Honda before it....

http://purplesagetradingpost.com/sumner/macgregor/outside-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.

svscott wrote: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
User avatar
Sumner
Admiral
 
Posts: 2254
Joined: Sun Jan 04, 2009 6:20 pm
Location: SE Utah
Sailboat: MacGregor 26S

Previous

Return to MacGregor/Venture Discussion

Who is online

Users browsing this forum: No registered users and 2 guests

Copyright 2004 - 2018 © HK Innovations