Skeg or Spade?

[poiu]

My lazarette is a watertight bulkhead with the whole rudder structure in it. A good safety feature.

I think it would be a simple and worthwhile mod to seal up that gap in most lazarettes, so long as the rudder is wholly in that area. Fit a pipe with a valve on it so you can drain it down now and then. A number of boats have sunk because of a lack of attention to this risk.

I have picked up a lot of fishing pots lately, but never on my skeg. Only on the prop and keel. A useful advantage of the skeg. It is a tough structure too. Not saying it is the best solution, but it isn't too bad.

[Juho]

Originally Posted by Dockhead

Many rudders are designed with sacrificial lower parts of the rudder, including German Frers' Hylas 54, all of Dashew's boats, and probably many others.


I agree strongly with you about the watertight compartment or at least cofferdam for the rudder post. One thing I hate about my boat is that the lazarette, where the rudder post is, has a strong bulkhead in it, and would have been simple to make a separate watertight compartment, but it was left open at the bottom to the main hull volume . In order to save a bilge and another pump, I guess, and to make it easier to run cables and pipes, but at the expense of a lost opportunity to make the boat much safer.

I have a cofferdam aka a bulkhead with a non-watertight door (could be better). And a breaking (semi balanced, skegged) rudder.

[Dockhead]

Originally Posted by poiu

My lazarette is a watertight bulkhead with the whole rudder structure in it. A good safety feature.

I think it would be a simple and worthwhile mod to seal up that gap in most lazarettes, so long as the rudder is wholly in that area. Fit a pipe with a valve on it so you can drain it down now and then. A number of boats have sunk because of a lack of attention to this risk.

I have picked up a lot of fishing pots lately, but never on my skeg. Only on the prop and keel. A useful advantage of the skeg. It is a tough structure too. Not saying it is the best solution, but it isn't too bad.

A full skeg should not pick up pot lines if it is shaped correctly. It's a partial skeg, like mine, which causes this problem.

Watertight compartment aft is just good sense, but a watertight lazarette is really not enough in my opinion. I like the Sundeer solution of separating the engine room and rest of the aft hull volume completely from the rest of the hull.

Sealing up my laz on my present boat would not be simple because of the multitude of wires and pipes and cables running from there to the main hull volume. So this safety feature will have to wait to my next boat.

[Dockhead]

Originally Posted by Juho

I have a cofferdam aka a bulkhead with a non-watertight door (could be better). And a breaking (semi balanced, skegged) rudder.

Cofferdam is already very good. Fulfills 90% of the purpose. The cofferdam will prevent flooding the boat if the rudder falls out or the seals blow out. My boat also has a very shallow cofferdam just barely extending above the waterline; helpful but not high enough to give real security.

A "semi balanced, skegged" rudder I presume means a partial skeg?

[Juho]

Originally Posted by Dockhead

A "semi balanced, skegged" rudder I presume means a partial skeg?

Yes.

And also my cofferdam is quite low.

[Greatketch33]

I have owned boats with each type of rudder: spade and skeg hung.

My observations are that the spade rudder made turns easier because it made the boat very responsive. The skeg hung rudder made turns less responsive and so I had to mentally prepare maneuvers well in advance; however, when unde sail the skeg rudder made that boat hold the line as if it was guided by laser.

Ah... How I enjoyed solo sailing the line while sitting at the bow taking in the sun and wind.

GreatKetch33

[noelex 77]

I recently went through this debate myself when deciding the specifications for our new yacht.

I look at most rudders and shudder in fright. Particularly how the upper and lower rudder bearings of most spade rudders are supported.

The problem is most rudder designs are engineered to cope with the hydrodynamic load, but are not designed to to survive hitting rocks, logs, whales etc.

No rudder can survive pounding on rocks for a prolonged period, but it is possible to engineer a rudder that gives you a fighting chance especially when hitting debris. It is also possible to design the rudder/hull so that if there is serious damage the boat is very unlikely to sink. Given that the rudder exit is usually quite close to waterline the latter is easy to do at the design stage, but surprisingly it is very rarely incorporated. My current boat has a large watertight cofferdam made of 6mm aluminium that is a few feet wider than the rudder base and extends several feet above the waterline. Even if the rudder was ripped out of the boat, the watertight integrity would likely stay intact. The new boat has the rudder in a sealed watertight compartment (in fact there are 5 watertight compartments).

You might think given my concerns I would opt for a skeg hung rudder for the new boat, but instead I specified an overbuilt (actually way overbuilt) spade rudder and associated hull attachment. There is no reason why a spade rudder cannot be made strong. Even increasing the shaft thickness slightly produces an enormous increase in strength. The better hydrodynamic performance of the spade rudder has been mentioned. This is especially helpful easing the burden on the autopilot, but for me the major advantages of a spade rudder is the ease of repair and the simplicity. It can even be dropped while the boat is in the water. This can be especially important when cruising in out of the way places or if the rudder is jammed out of centre after a collision at sea. I am specifying an emergency rudder for my boat, but this has little hope of overcoming the power of the existing rudder if it is damaged in such a way to turn the boat in one direction. With a spade rudder you stand some chance of being able to force the damaged rudder to a position where it can be centred or even completely dropped out of the boat.

I did consider sacrificial parts to the rudder. Most rudders, especially metal versions, naturally have a less strong tip. Once the shaft, which acts as the main spar, finishes about 3/4 down the rudder, the tip has a natural break/bend point. This effect can be exaggerated. The tip can be deliberately made of much thinner aluminium or even fibreglass. Interesting the Garcia Exploration has a sacrificial TOP (not bottom) to the rudder. If the rudder is bent backwards the sacrificial, fibreglass top breaks preventing damage to the hull. This also allows the rudder to be turned or at least centred. Both a sacrificial tip and top to the rudder are fundamentally good ideas and worth considering, but in the end I decided against the complication and elected to design a rudder as strong as possible.

Anyway, my solution to best rudder in a long distance cruising boat is a very over engineered spade rudder with a correspondingly heavily reinforced hull and bearing support. This is all mounted in a waterproof compartment and there is an emergency rudder.

This is rudder tube for the new boat. The shaft will be 130mm:

[Van Der Beek]

Originally Posted by Greatketch33

However, when unde sail the skeg rudder made that boat hold the line as if it was guided by laser.

A skeg rudder gives you better stability and better comfort and wont tire you as fast to the point of you feeling you need an autopilot to take over. Just as you said, you can walk away from a skeg rudder for minutes and the boat will hold the line just fine. Try that with a "nervous" spade rudder.

For me cruising is more about comfort and safety than it is about speed, speed can be a nice bonus sure, however, in rough seas speed and lightness usually means loss of comfort.

Ninja edit.
I often see people use the argument "In harbour spade is easier to steer" and "it is more responsive and quicker to change course" All of which is true, my response would be A: you're not sailing in a harbour B: You're not sailing akin to how a slalom skiier moves between poles when at sea"

[malbert73]

Originally Posted by Van Der Beek

A skeg rudder gives you better stability and better comfort and wont tire you as fast to the point of you feeling you need an autopilot to take over. Just as you said, you can walk away from a skeg rudder for minutes and the boat will hold the line just fine. Try that with a "nervous" spade rudder.

For me cruising is more about comfort and safety than it is about speed, speed can be a nice bonus sure, however, in rough seas speed and lightness usually means loss of comfort.

Ninja edit.
I often see people use the argument "In harbour spade is easier to steer" and "it is more responsive and quicker to change course" All of which is true, my response would be A: you're not sailing in a harbour B: You're not sailing akin to how a slalom skiier moves between poles when at sea"

I agree that extreme high aspect spade rudders like found on raceboats can be very twitchy. But a skeg isn't really what changes this behavior, it's a lower aspect rudder profile blade, or blade +skeg. So many cruising boats with lower aspect spade ruddersare not at all twitchy and track wonderfully. And best of all, they don't load up as much due to being balanced, which reduces load on autopilot, etc, and makes steering in heavy stuff require much less effort.



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[Dockhead]

Originally Posted by Van Der Beek

A skeg rudder gives you better stability and better comfort and wont tire you as fast to the point of you feeling you need an autopilot to take over. Just as you said, you can walk away from a skeg rudder for minutes and the boat will hold the line just fine. Try that with a "nervous" spade rudder.

For me cruising is more about comfort and safety than it is about speed, speed can be a nice bonus sure, however, in rough seas speed and lightness usually means loss of comfort.

Ninja edit.
I often see people use the argument "In harbour spade is easier to steer" and "it is more responsive and quicker to change course" All of which is true, my response would be A: you're not sailing in a harbour B: You're not sailing akin to how a slalom skiier moves between poles when at sea"

An unbalanced skeg hung rudder on the contrary requires far greater steering force when sailing upwind, greatly increasing stress on helmsman or autopilot.

A skeg might add some stability when off the wind, but not more than a simply larger rudder would. And the skeg can't be steered, so upwind, the skeg is steering against you. The hydrodynamic disadvantages of skeg rudders are not such a big deal off the wind. But upwind, where keel and rudder are wings, no less important than your sails, skeg hung rudders really hurt you.

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[Stumble]

Originally Posted by Van Der Beek

A skeg rudder gives you better stability and better comfort and wont tire you as fast to the point of you feeling you need an autopilot to take over. Just as you said, you can walk away from a skeg rudder for minutes and the boat will hold the line just fine. Try that with a "nervous" spade rudder.

For me cruising is more about comfort and safety than it is about speed, speed can be a nice bonus sure, however, in rough seas speed and lightness usually means loss of comfort.

Ninja edit.
I often see people use the argument "In harbour spade is easier to steer" and "it is more responsive and quicker to change course" All of which is true, my response would be A: you're not sailing in a harbour B: You're not sailing akin to how a slalom skiier moves between poles when at sea"

Well sure, if you try and use a rudder with a very narrow chord like a race boat it will be prone to stalling and be nervous. Heck the rudders on my cat at max thickness are only 8mm. But there is no need to design a spade like this. You just go with a thicker easier to drive spade and call it a day.

I am just having a hard time even understanding what the argument is...

There is absolutely nothing about spades or skeg rudders that inherently make one or the other stronger. Just like there is nothing inherent to the design that makes a double spreader rig stronger than a tripple spreader rig. You can build a good one out of either, you can build a bad one of either. But at the end of the day it's the quality of the engineering and build that determines the strength of the end result.

On the other hand skegs are inherently worse at actually driving the boat because they have a fixed leading edge that interrupts the flow of water, and the attachment restricts the shape of the fin. You can have better and worse ones, but even the best skeg is going to interfere with water flow and reduce steering ability.

As for actual design... Beyond my pay grade. But my preference would be for a monolithic structure. So there is no seam to leak and no way for water to intrude. Of course this increases the cost of construction since you can't marry the two halfs later, but in terms of lifespan I am pretty convinced it's the best option.

I would like a sacrificial tip section however. The Dashew's do this very well, and accomplishing it with daggerboards is very commonly done. It just takes a little more work with carbon and foam at the yard.

[Spindrift NH]

Of course everything is a compromise, I'd take my skeg rudder for safety and tracking under sail but I sure liked the spade on my Catalina for tight places.
I feel as though I've got a reasonably well attached skeg that should be able to handle a few bumps.
About 6 months ago I saw a Tartan with a partial skeg hung rudder, the skeg broke off after hitting an object. There really wasn't much holding it on the hull, I believe 4 bolts, and the skeg was thin walled and hollow. I believe that even though the skeg broke off, the rudder was still attached. The owner was able to get hauled out and had a replacement skeg shipped and was able to make the repair.

[Charlie]

What I have gained from this discussion is that a spade rudder is a better foil and that a skeg is not necessarily stronger depending on attachment. So if I could have the boat designed to my standard I would go for an over engineered spade rudder. I would guess that on most production boats the spade is not over engineered. For that reason I like the skeg.

[Stumble]

Originally Posted by Spindrift NH

Of course everything is a compromise, I'd take my skeg rudder for safety and tracking under sail but I sure liked the spade on my Catalina for tight places.
I feel as though I've got a reasonably well attached skeg that should be able to handle a few bumps.
About 6 months ago I saw a Tartan with a partial skeg hung rudder, the skeg broke off after hitting an object. There really wasn't much holding it on the hull, I believe 4 bolts, and the skeg was thin walled and hollow. I believe that even though the skeg broke off, the rudder was still attached. The owner was able to get hauled out and had a replacement skeg shipped and was able to make the repair.

The same thing happened to one of Bob Perry's boats, Nightrunner it think... The decision was to just leave the skeg off. It wasn't actually required, it was just there as a styling cue, the real strength was in the rudder stock.

[TeddyDiver]

Originally Posted by Spindrift NH

About 6 months ago I saw a Tartan with a partial skeg hung rudder, the skeg broke off after hitting an object. There really wasn't much holding it on the hull, I believe 4 bolts, and the skeg was thin walled and hollow. I believe that even though the skeg broke off, the rudder was still attached. The owner was able to get hauled out and had a replacement skeg shipped and was able to make the repair.

So it wasn't skeg hung after all, instead a spade with a bottom hung foil infront of it..