Newport 27 Rudder??

Hi, a couple of questions hoping for some guidance.

I recently acquired a Newport 27. After doing some research a universal complaint seems to be severe weather helm especially while under power. The consensus seems to be a problem with the rudder design. The rudder is angled backward a fair amount with the thickest section located approximately 1/5 of the distance behind the leading edge. The widest part of the section also seems fairly thick, over 3" since the rudder stock is 3" pipe. Also the rudder is quite wide(leading edge to trailing edge) in relation to its length(top to bottom) it's amost square in dimension(roughly 20"wide by 27" long). It is ingenious in a way since the rudder can be dropped while the boat is on jack stands. But I think that convenience is outweighed by the performance of the rudder. My goal is to try to replace the rudder but I'm not quite sure if I'm going about it properly. After doing a bit of research I've decided on a NACA0012 section with a high aspect ratio rudder, my draft is a little over 4' so I'm thinking roughly 38" or more of length and possibly 18" of width, mostly rectangular in shape, also moving the rudder slightly to the rear of the current rudder and making it vertical rather than angled. I have a fair amount of experience with epoxy and fiberglass but no experience with replacing a rudder. So bearing that in mind here are a few questions.

1) Can you have too much rudder? (I've read as long as you have around 10% surface area in front of the stock you'll get fair balance but still enough feel so that you get adequate feedback).
2) How do I determine the rudder stock size that I need, the current 3" rudderstock seems excessive? I'd like to go down to 1.5" or 1.75"(I've found industrial supply houses that have schedule 40 stainless pipe, is that what most people use?)
3) Do I need some sort of skeleton welded to the rudder post or will epoxy bonds around the sides of the pipe be sufficient?
3) I've looked at rudder bearings from tides marine and from edson. Is there anything I should keep in mind?
4) Will moving the rudder to the rear cause any problems?

Thanks.

 

I wouldn't be looking at the rudder so much, unless I'd determined the rig wasn't in need of attention first. Though I'm not familiar with the Newport 27, weather helm isn't that uncommon a problem and rig tuning can fix this in most cases without having to make major design changes to the underwater profile.

The first thing I'd look at is mast rake. Rake it forward a couple of degrees and see how much this helps. Try larger head sails, maybe even on a sprit. The helm heavy situation you describe under power isn't rig related, but I'm not sure what you mean either. Auxiliaries don't power all that well, but that barn door of a rudder you described, may be trying to operate in disturbed water from the prop.

If you are bound and determined to change out the rudder, don't change it's position as the rudder tube will need moving and this is a substantial structure that if not done correctly can cause steering failure or sinking. Leave it inclined as well or you'll snag everything out there to catch (lobster pot warps, weeds, etc.) Go look at a J 27 for an idea of a well shaped rudder profile. You'll note the slight fore and aft sweep and the high aspect ratio you're after. DO NOT balance the rudder, with even the 10% you've thought would be safe, as designing a balanced rudder isn't an easy thing to do well and one that isn't is a *****.

I don't think the average person at the helm would notice the difference between NACA 0012 or other shapes from a plate steel rudder. Racers and the experienced helm person would notice changes to the helm feel if a rudder was changed, but the average guy . . .

The higher aspect ratio rudder will steer better then that barn door, but keep the draft 10% below the full craft draft. (4' draft would mean a 3' 7" deep rudder) This keeps it from banging into whatever you just ran aground on.

You're correct in that the thickness seems overly so, but this may a result of using pipe for the rudder shaft rather than solid stock (which would be my recommendation) Be very careful in redesigning this. It needs to surprisingly strong and is a common weak spot on production boats. Pipe may have saved the builder some construction costs, but it may also required compromising the design in this area as well. 3" pipe should give you an idea of the loads the designer expected the thing to have to eat (get the picture?)

Yes the rudder stock will need a skeleton welded to the stock and bonded to the material you use to fair the shape with (cloth & mat in epoxy) I'd recommend a mold to help make the shape as close to the one you want.

I've touched on a number of things here, I hope you don't try them all. Talk with the other owners. Find out who designed it and see if they are available for comment. He/she may have addressed this years ago. Most every designer wants their stuff to do well and please the owners, but most owners don't bother with contacting them. I don't know why this is, maybe they read too many magazines and figure they can do it themselves. I hope this trend continues as I fix a lot of owner screw ups.

Let us know how it works out for you . . .

 

PAR says that you shouldn't try all his suggestions. That's right - you should never, ever try to do an unbalanced spade rudder!!!
The 10% surface area in front of the rudder stock is a little on the low side. I would go for something between 12 and 14%. Looking at the numbers, the difference may not be that big, but - believe me - you will be able to feel it!
But the amount of surface area in front of the stock is really not the important thing. What is important is the distance between the center of pressure and the centerline of the stock, measured at right angles to the stock. If it is about 40 to 50 mm, you'll be OK. Maybe a little closer to the 40 than to the 50.
And how do you find the center of pressure? It's not that difficult if you stick to a rectangular shaped rudder. Find the geometric center and draw a horizontal line through it. The center of pressure will lie on this line at a distance of 25% of the line's lenght measured from the leading edge.
Another bad suggestion is to use a plate rudder, especially so on a sailboat or on a motorsailer. Your idea about using a NACA 0012 is good - this foilsection is probably the most used for rudders.
I'm sorry PAR - I didn't mean to put you in a bad light, but I honestly think that you are dead wrong here! The rest of your advice is very wise, though!

Kind regards,
Søren Flening

 

Thanks for the reply's.

Interesting, I think that the weather helm under power is indicative of a rudder problem not a rig tuning problem. Under sail the problem goes away but probably because of the compensation by the rig.

I'm not sure if I was clear in the original post but the angle is in the rudder stock not the shape of the rudder. So the stock slides out at an angle sloped to the rear. This makes for a complex shape to maintain close contact with the hull. Also looking at the majority of the rudders out there almost all have vertical or close to vertical stocks so I don't think the rake is really necessary to avoid lobster pots. Isn't that what the keel is for?

Yes, I agree the J27 is quite nice and relatively simple but the transom mount isn't what I would be aiming for. That's the overall shape I'm aiming for.

The question about the rudder stock diameter is troubling, but a owner of a Newport 31 claimed that his rudder stock was 1.5" schedule 40 stainless pipe? If that's the case I would doubt my 27 would need a rudder stock of twice the diameter? Do most manufacturers of sailboats use solid rudder stocks or hollow stocks? Aren't hollow stocks much stiffer for the weight?

Soren, Yes I would still go for a balanced rudder, I really don't believe an unbalanced one would work very well. I've sailed a bit, I'm pretty sure I can tell between squirrelly rudders/heavy helm rudders/ and rudders with good feel.

Again, thanks for the reply's.

 

What is "weather helm under power"? This makes no sense because there's no wind orientation when the boat's under power. Do you mean it pulls in one direction? You say the problem goes away when under sail, so it sounds like the boat is basically well balanced and the rudder is doing its job.

I think you might look for other causes of the boat turning under power. It could be the propwash impinging on the rudder, but it could also be a misaligned prop shaft. If the thrust line were directed to the side, that would account for what you describe. A thrust problem will still be there after you go to the trouble of replacing your rudder.

 

The tiller must be pulled hard(with a lot of force, not distance) to starboard to maintain course.

If it's prop wash wouldn't a more balanced rudder solve the problem? Likewise wouldn't a thrust problem would be alleviated with a more balanced rudder?

Thanks.

 

Yes, that does sound like it could benefit from better balance, and I suspect a narrower chord rudder would be less affected as well.

There may be other ways than building a new rudder to get the balance. For example, a trim tab could be cut into or mounted behind the trailing edge. When powering deflect the tab to trim out the prop-induced moment. The tab could be linked to the boat to reduce the loads proportional to rudder deflection - this would do the same thing as balancing the rudder, but it would affect the feel of the helm when sailing, too.

But it still seems to me there's something awry with the propulsion installation.

 

lots of great advice has been given!!! But, check to make sure the rudder is plumb athwartships. I just fixed a Bravaria that needed the top rudder bearing moved 1.25" to align the rudder vertically. The boat had exibited similar behavior to yours.

Doug

 

Apologies for the spellin in this message, my competer does not work well with these forums.

I have a 1968 28 footer on which I replaced a similar low-aspect rudder. In my case, the rudder was skeg hung.

The new rudder is only 4" shallower than the keel and is a balanced elliptical spade.

The upwind perfoprmance has been dramatically improved;. The weak point of my boats and its sisters, it was partly caused by poor foils. We now seem to go upwind "on the rudder" and instead of playing with good 25' mid '70s IOR boats, we now play with good 30' mid '70s IOR boats.

It is a problem when running aground and the rudder has a tendency to go hard over under power at medium to high speeds. But the overall sailing performance has improved dramatically; faster and more manouvrable and much, much nicer ton the helm.

The rudder, by the way, is a second-hand unit from a 31' racer, with a 2" solid SS shaft.

 

By the way, if (like me) you are on a budget - my rudder bearings are the end caps from PVC pipes. Sprayed with WD 40, they feel as good as the more expensive units (as an America's Cup designer I know says, a "decent" set of rudder bearings would cost more than my entire boat).

Secondly, re "too much rudder". One of the biggest trends in yacht design has been towards ever bigger rudders (when comparing them to the size of the keel and other contributors to lateral resistance ie the hull form). The old idea that rudders do not contribute to lateral resistance has been junked AFAIK. The ultimate example is in really fast small boats, like the 11' Moth which goes upwind faster than the 20' long Flying Dutchman, with about 1' of centreboard and 2' of rudder showing. Or the Formula Windsurdfing boards, which go upwind almost as fast as a Tornado cat yet have no centreboard at all. Even in older boats, like the 20' long International Flying 15 keelboat, there's been a trend to using the rudder, not the keel, to generate much of the sideforce

 

Thanks for all the advice. I'll check and see if the alignment and position might be affecting the rudder. But I think I would still like to replace the rudder. Chris, you've got some great ideas, I'm definitely on a budget and if I can pick up a used rudder on the cheap, it'll definitely be easier than making one. I've been pricing rudder bearings and a rudder seal as well, your friends right. Thanks again.

 

Rudder construction

Par,
I like your no bull answeres to technical questions, so I'm looking for a little guidance. I have just spent 2 years restoring a 1979 Chrisler 26. The last thing I have to do before I drop it in the water for the first time is build a new rudder. The origonal was a kick-up that was stolen before I bought the boat ($800.00). I have done all the research. Viewed all the software and now I am completly confused. Can all that tecnical air foil shape line generators make that much differance on a tub that might go 6 knots in a hurricane going north in the gulf stream? I am planning a spade rudder a few inches shorter than the hard keel. (It's a swing keel boat) I can get stainless shafts from the local boat salvage yard and I was going to weld 3 or 4 "fingers" to that, bond a foam core, shape by eye then cover with 'glass. I still don't know the width, or if I should try to square the bottom or try for a elliptical shape?
Will I be making a big mistake if I don't try to use the xfoil or other design generators?
Also I have no hardware at all. Is there a place that sells self centering bushings and the other parts I will need to secure the posts?

Thanks,
Jerry

 

I know this question was for PAR, but still...

You don't need Xfoil (or any other software) - you can find the coordinates of relevant foil sections in Abbott & van Doenhoff: "Theory of Wing Sections" or here: http://www.nasg.com/afdb/index-e.phtml.

There are a lot of sections to choose from, but you will never go wrong with a NACA 0012 section.

Good luck!

 

Can't you get a rudder there from some other boat of about the same displacement?

On the original question, I presume the Newport 27 is the flush-deck, C&C design. (Newport 27S) If so, they have been raced PHRF a lot, and I would be surprised to find any gross flaw in the design, though there are always compromises in construction. They did design some rudders that look strange by today's standards.

 

Listen Guys,
I'm an Architect, I use Auto Cad all day. I lofted lines from Herrishof's notebook for a previous boat I built, but I have no idea how to transulate the numbers I downloaded (NACA0012) into a plottable (is that a word?) set of coordinates. If someone can direct me to a help section I can get the curve into my cad program and plot out a full size template.