The Offshore Voyaging Reference Site

Outbound 46 Review—Part 2, Keel, Rudder, Bow Thruster, and Construction

In Part 1, we analyzed the Outbound 46 hull design, including comparisons to recent designs. She acquitted herself well.

And we who will never be able to afford a new Outbound 46 learned a lot from the boat that will help us choose a less expensive option.

Now let’s look at other hull-related stuff, including the keel, rudder, bow thruster or not, and some thoughts on construction, all relevant no matter what boat you are thinking of buying.

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More Articles From Outbound 46—A bench mark good offshore voyaging boat:

  1. Outbound 46 Review—Introduction
  2. Outbound 46 Review—Part 1, Hull Form
  3. Outbound 46 Review—Part 2, Keel, Rudder, Bow Thruster, and Construction
  4. Sailboat Deck Layouts
  5. Cockpits—Part 1, Safe and Seamanlike
  6. Cockpits—Part 2, Visibility and Ergonomics
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Ernest E Vogelsinger

Hi, John,
regarding Spade rudders – my reservations about this design are mainly that it is a system that is only suspended at a single point, together with a rather powerful lever arm. Not a good position if the tip of the blade comes in contact with the ground, or a rock, and not to mention the fact that in the event of a catastrophic issue the rudder can simply choose to leave you for good – although this in’t very likely it already has happened.
At least the single point suspension problem can effectively be countered with a skeg, and many skegged rudders are at least semi-balanced, as seen here:

Ernest E Vogelsinger

John, I’m not a skeg “hater”, just some reservations … anyway Matt shows below that it can be built right when engineered correctly. For my situation this gives me just another issue I have to deep-dive in when I’ll be actually starting to select the (used) boat for my retirement…

Alan Sexton

Hi John
Do we know for sure the if rudder stock is a solid shaft, or alternatively heavy wall pipe?
The Outbound site is not clear on this point. I know my own yacht’s “barn door” rudder, which the shallow draft Outbound’s closely resembles, functions very well with a shaft of what appears to be 100NB Sch 160/XXS SS pipe, and is very heavy! Solid shafting has a lot of extra weight for not much benefit

Eric Klem

Hi John,

The important thing here is that to carry a load, every material must deflect.  If you think about a cross section of a tube in bending, one side is in tension, one in compression and there is almost nothing going on in the center.  Therefore, the center contributes very little to strength and very little to stiffness.  This is the reason that I-beams exist, they concentrate the material in the areas of highest tensile and compressive stress and in the center of the connecting web, there is only a small amount of shear stress.  I-beams are great but they are directional, they must be loaded in bending in a specified directly, if you try to put one in torsion, you will find they are a very poor design, a cylinder or rod is the best in torsion.

You are correct that if you hold bending stiffness constant (sometimes this is called section modulus), the hollow shaft will need to be larger in diameter.  However, the difference is smaller than many think.  For a rod, stress is proportional to the cube of the radius as the moment of inertia is proportional to the fourth power and when you make it a hollow cylinder, the section modulus is proportional to (R^4-r^4)/R.  This means that a 4″ diameter hollow shaft with 3″ ID has equivalent stiffness to a 3.52″ solid shaft and if you compare the weights, the hollow shaft is only 56% of the solid one.  It is possible to push this too far and go to too large a diameter and too thin a wall which is hard to manufacturer, hard to connect to, etc but it is surprising how far you can push it (masts being a good example).  In the case of rudders, you need to watch your foil shape too.

Going back to a pure strength standpoint, the fact that maximum stress is at the surface of the part is really important to understand.  In a fatigue application, this means that any small blemish in the surface is also a blemish in the highest stress area so it presents an area for a crack to propagate from.  For this reason, in highly stressed fatigue applications, the surface is carefully spec’ed and then it needs to be maintained that way.  In some applications, it is necessary to go even further with processes like shot peening and even laster peening, if you want to go down a rabbit hole, these are really cool and really do work.  Of course, on a rudder shaft this doesn’t really apply as it is impractical to keep the surface that pristine and the shaft should be sized so that you are nowhere near the fatigue limit as the grounding load is so much higher.


Steven Schapera

The wheel on a truck is a “single point suspension” and we don’t often hear of the axle snapping. It’s all about the design – ensuring it’s up to the task of carrying the loads – not how many suspension points.

Matt Marsh

I’ve never seen, or heard of, a spade rudder that’s supported at a single point. The rudder stock is usually supported by two bearings – upper & lower – spaced as far apart as possible inside the hull. The blade is then attached to the part of the stock that’s cantilevered below the lower bearing.

This is an inherently very strong approach that has the added benefit of being quite simple to analyze for structural design.

Back-of-the-envelope example. 4″ (101 mm) grade 316 solid stainless steel shaft, rudder bearings 60 cm apart, rudder blade 170 cm deep. I_z = 5.1E6 mm^4. Young’s modulus = 193 GPa, yield strength = 290 MPa.

That rudder would require hydrodynamic force of 34 kN (about three and a half tons) or a tip point load of 18 kN (about two tons) to bend the shaft, and about double that to break it. You’d select the bearings, and design their mounting structures, to withstand 102 kN at the upper and 168 kN at the lower, thus ensuring that the shaft will fail completely before the bearings or the tube will let go under any conceivable overload scenario.

Put another way, you could prop the boat up on shore at 90° of heel, hook a chainfall hoist to the tip of the rudder, and pick up an entire Ford F-150 with it….. and the rudder would only bend about 4 cm.

Ernest E Vogelsinger

Hi Matt,
thank you for the engineers inside view on that topic, makes me a bit more unstressed 😉
And I didn’t actually mean “single point” but “single side” with an open lever arm – but your calculations show that this can be perfectly valid if engineered correctly.
When looking for a used boat this needs to be counterchecked double or triple, of course.

Stephen Kaut

Thanks John, I have been looking forward to this instalment since I read the first. You’ve also go me reading and watching everything Outbound since then!? stay safe. ( now for part 3 ?)
SK in the UK.

James Kevern

As owner of#58 I have to disagree. The 4 inch diameter rudder post is mounted through two sleeve bearings about 2 1/2 ft apart mounted in substantial structure inside. Though I hate to admit it, due to distracted driving I clipped the bottom of the rudder on a rock doing 6 kts or more. Took a chunk out of the rudder, but that’s all. A long skeg would extend the support with a longer lever arm, but the longer the skeg the less stiff unless it’s the back end of the keel.

James Kevern

Should the rudder “choose to leave” (nicely put), the lower bearing mount extends above the water line so you still have a fighting chance.

Philip Wilkie

I have a question the very experienced people here might care to answer. It’s my impression that most cruisers plan for downwind passages, broad reaches at worst. How does this work out in reality? What fraction of time do people sail upwind?

If the answer is anything < 20% then how much value should be placed on a deep keel that optimises hard on the wind performance? Especially if it comes at the cost of not being able to anchor in shallower, more sheltered spots.

I've no doubt that there are times when being able to point close to the wind is a real safety advantage, clawing off a lee shore, or giving a headland more room all feel like important reasons. But to be honest, if I was caught in a situation where moving closer upwind was a vital concern, I'd be starting the engine.

Racing is of course a different paradigm, but for cruisers, just how important is upwind pointing performance really? (I'm entirely open to being educated on this.)

P D Squire

Any thoughts on how much the designers preferred 8′ draft would reduce the trip to Bermuda often used by AAC to compare boat types?

William Balme

Toodle-oo! is an Outbound 44 – hull #27: 2007 vintage – we are the second owners.
I agree fully John that a bow thruster is not necessary – it’s very easy to spin the boat on her axis (provided you turn to starboard!) – and only rarely do I feel one would be a benefit.
As to the rudder, initially I felt that the lack of a skeg might be a problem, but have learned to really like the spade – even though… in 2014 we were cruising up in Scotland and I very stupidly selected a small harbor with visitor’s mooring and a distillery but without optimal pilot instructions. The inevitable hard landing occurred and we got ourselves stuck on a rock on a falling tide. Having failed to kedge off once already, I accepted assistance from a friendly rib that came to investigate. He pulled us off but in the process the rudder took a serious hit and bent the shaft, jamming the rudder hard against the hull. The good part of this story is that once we were laid up at Ardfern a few days later, Phil was able to send me pictures of hull #27 during it’s build to show some critical elements. He also arranged a new rudder to be manufactured and shipped to us in Scotland and we were back cruising just 5 weeks later! That’s customer support – even though we didn’t actually purchase the boat from him!
One downside to the spade is that when motoring you can’t take your hands off the wheel – or you’ll be doing doughnuts in no time flat!
I’m glad that Toodle-oo! is a deep draft – she certainly does exceptionally well to weather and so far, we’ve not had to compromise our cruising grounds due to draft – including motoring through Holland’s ‘Standing Mast Route’.

James Peto

We were considering the purchase of a New Outbound 46 last year and contacted Steve D’Antonio who confirmed that I should be allowing some $50,000 plus all of his expenses for a full “Holding of Hands and Advice” Service for the specification preparation, contract writing, construction and commissioning overseeing of a New Sail Yacht.
I too like the idea of a Carbon Fibre Rudder Shaft, though perhaps one should also apply the idea of being able to “lower the rudder” as applied in the Nordkyn design in the event of it being hit and jamming on the hull.

Lee Corwin

I own hull #50. She’s my 8th boat so have cruised and raced all sorts of appendages. The advantage of this design is she tracks well so can sail under the hydrovane without constantly trimming to maintain perfect balance but equally if not more important backs up under power predictably and with a responsive helm. We live on the hook but occasionally forced to take a slip. I sleep well the night before docking now. With prior boats (full keel or skeg hung) I dreaded backing up in tight quarters. Phil’s support is amazing. The top bearing was a fraction off at time of her initial delivery from China. She would spit a minute amount of water on passage. A satphone call and a new one was there shortly after arriving. The set up is such that the support structure ends above the waterline and is massive unlike lesser boats where troubles would mean a very quick swim.

Michel Richard

May not be exactly on topic, but close. And I could not find a comment in the “rudder” article above.
In any event, what do you think of bronze for rudder shafts? I’m looking at a couple older yachts (eighties vintage) that apparently have those. Are they more durable than stainless steel?

Matt Marsh

Bronze can be an excellent choice for this, if properly engineered, but it’s very difficult to generalize. “Bronze” describes a huge range of alloys, spanning an order of magnitude in mechanical properties. The best of them are stronger and much more corrosion resistant than stainless steel; some others aren’t much better than pot metal.

Michel Richard

Matt, fair enough.
Other than finding actual builder data, is there a way to figure the class of alloy used? Builder is out of business (Bristol), but there may still be ways to find info.
Only comment I could find online is that “the bronze used was pretty tough”

Michel Richard

Two good points, many thanks

Scott Halpern

I sail Océane (2016 hull #61) and as an ME agree with Matt’s back of the envelope math. The two well designed bearings and thick-walled 4.0” diameter stock are robust. Still I worried about the scenario Bill on Toodle-oo described and choose to score a sharp 0.020” stress-riser line 12” above the tip using a router to create a “break away” section to reduce the likelihood of bending the stock and jamming the rudder. It’s filled with epoxy only, barrier coated and I left the trailing edge in tact in hopes of recovering the tip if this event should ever happen.

Steven Schapera

The “tube” vs “solid” shaft debate is not a simple one. It’s about managing load: a thick-walled tube of diameter X is almost as capable as a solid shaft of (nearly) the same diameter. None of us want a solid mast, for obvious reasons, and we understand the benefit of it being hollow.
The operating load on a rudder is not that significant; it’s the impact load that needs consideration!
My issue with a solid rudder shaft, very heavily engineered to handle a shock load (impact loading) is that whilst the shaft will not bend or break when stressed we should NOT assume that means we save the rudder and are safe.
If the consequences of impact is that the HULL then fractures (because the shaft didn’t)….well I’d rather be in a floating hull with no rudder than a sinking hull with a rudder!
It’s all about design balance and the idea I like best is the one cited earlier where a fracture point is designed into the shaft. If the rudder is hit at the lower end, it breaks away leaving a stub that is better than nothing. This same tech is often used with roadside signs – they deliberately don’t build them strong enough to handle the impact of a car, with a fracture point designed and inch or two above the ground.

Matt Marsh

It’s important that the rudder itself be weaker than the hull & structure above it. I’d hope that, at the design stage, someone did the following:
Calculate the load that causes the rudder shaft to totally fail (trivially easy, for a spade rudder with a metal shaft; see above).
Then calculate the radial loads on the upper & lower bearings when the rudder shaft fails in bending (also trivially easy).
Then calculate the maximum axial load on the bearings. (This is probably the hardest part, because it requires you to either make assumptions about how hard the boat will pound on a rock when grounded rudder-first, or assume that the boat won’t run aground.)
Then use those loads as the basis for designing the support structure, applying an appropriate safety factor / factor of ignorance. (Not trivial, but not terribly difficult.)

Frangible rudder tips may have value in some situations. They’re pretty easy to design.

Dick Stevenson

Hi Matt,
Does this get more complicated if you figure that for most spade rudders I am aware of: the trailing end of the rudder will dig right into the hull with just a little deflection of the shaft? This “pinned” rudder may be more of a problem than a completely lost rudder. I would be curious how much of a blow on the lower end of a spade rudder say on the Outbound 46, would cause the rudder’s trailing edge of ~~1/2 inch or so to dig into the hull. Breakaway figures seem to become less important looked at this way, I would think.
My best, Dick Stevenson, s/v Alchemy

Dick Stevenson

Hi John,
I was not intending my comment to enter the realm of skegs vs spade: I was only responding to Matt’s saying that it was not hard to figure the breaking strength of shafts and suggesting that the breaking strength (and strength in general) may be less important than the load that causes shaft deflection/bending enough to jam the trailing edge onto/into the hull. Spade or skeg hung, it seems that it would not take a great deal of shaft deflection to “pin” the trailing edge and that this shaft deflection may a be more important figure than overall breaking strength.
That said, it was interesting to hear that some boats have that trailing edge be “collapse-able”: what a smart design/engineering decision.
My best, Dick Stevenson, s/v Alchemy

Lee Corwin

Think missing from this conversation is the purpose of the rudder. That is to steer the boat. The end plate effect makes most spades more efficient. This above and beyond the easy ability to get a balanced spade pr partially balanced spade compared to other choices. Every time you steer you slow the boat. More you deflect from midline the more you slow. The more the rudder is balanced the less effort involved. All to often in an attempt to get rid of the stub between canoe body and skeg the rudder is holding up the skeg not the other way around. For a cruiser the less the rudder needs to deflect to steer, and the less steering slows the boat the less electricity used by the autopilot, easier to run under windvane and better the days work. Unfortunately saragasso has gotten out of hand. Seems the spade clears weed faster and better on passage across the edge of the saragasso or doldrums. Especially as many skegs have a aperture for the prop.
Outbound #50

Ray Marc-Aurele

Hi to the group,
Just a suggestion to Michel Richard, the alloy can be determined easily by contacting a testing company to come to the boat and use a X-Ray metallurgical machine to examine the shaft end. This will give you a very accurate analysis of the chemical makeup of the alloy. This service is relatively inexpensive . Results are immediately known. The machine is portable and can be carried by the technician in one hand. Welding inspectors and metallurgical testing companies would have this service. I have used this service many times to reverse engineer aircraft engine components.

Stay healthy and go sailing.

Michael Lambert

First, I cruise in Maine and had often caught pots, but I switched from a feathering prop to folding, and now it only happens if I’m motoring.

Second, I’m thinking about a Boréal, and wonder about what it might be like to maneuver with the board up in the back of a shallow marina, with a cross wind. You have prop wash, but maybe no good pivot point from a keel. Even if the board was partway down, the cor would be well aft so might act funny. Therefore I may opt for a thruster just in case, particularly since I believe it retracts.

Dick Stevenson

Hi Michael,
I suspect you are correct that board-up any boat like the Boreal could be skittish indeed maneuvering in a marina with cross-winds. I have a relatively challenging boat to maneuver in close quarters, not the worst, but far from the best, and I went in and out of European marinas for years, many times with trepidation, but always without incident. So, I suspect Boreals, and boats of like design, figure it out and may even benefit from an “adjustable” pivot point.
Now, I know you are referring to the retractable design of bow thruster (which may have its own issues, but does not put a drag on the boat), but I would be interested in real data documenting the “hit” that many of the bow thruster designs (through hull type) give to the sailing characteristics of sailboats. I suspect it is substantial for many of the designs, especially in light air. When in Europe, my sense is that many of the marinas were designing their layout with the expectation that the vessels had bow thrusters (in other words, jam packed). And many EU boats did have bow thrusters, especially more modern ones. When I asked about the speed hit they felt the thruster engendered, most had not considered this aspect. I, myself, after sailing in tandem with a few would not be surprised that the speed hit in light air approached 20% and was above 10% across boat speeds.
I remember a Dave Gerr article from decades ago where he discusses this issue, especially with regards to the fairing around the thru-hull that some designs use. But I have not been able to find the article.
My best, Dick Stevenson, s/v Alchemy

Michael Gillingham

Hi John,
I thought you might be interested to know that Island Packet is employing a water jet thruster system. I don’t own one, but am friends with the plant manager. He describes it as much more efficient in power usage and versatile in installation, as it uses a single pump that can service the bow, stern or both if desired. If you haven’t already, perhaps you could do some investigating and use the information for an article that includes it as one of the now three types of thrusters. This water jet system may be a good alternative as it likely reduces the drag created by the tunnel design while is less complex than a retractable.

Michael Gillingham

Well, as stated the efficiency discussion was from an electrical perspective as tunnel type propeller thrusters use a butt ton of current and can only be used in short bursts. The reduced drag would likely be a result of a small through hull rather than a large tunnel causing disturbance in laminar flow. I am sure that there are debates that could be had on the subject and had imagined that some of your readers might have enjoyed the comparison. At any rate, if you should decide to investigate it, I can arrange an introduction if needed. Thanks for the reply.

Lisa Rowell

If there are any areas that you would like extra photographs of, I’ll have an older, non-bow thruster, one out of the water on Friday and could take some. I’m not the owner, but hopefully will be soon, if all goes well.

Lisa Rowell

Thanks. There were a few things that came up in the surveys, but she’s got a lot of miles on her so that’s not surprising. She’s a sweet boat and I’m a very excited sailor.

John Maturo

A long preface follows to help bootstrap my opinion. Also, I am life long sailor and racer and club level instructor.

I sail a 1978 Baltic 39 that I refit myself: new teak decks from rough lumber, electronics, cutter stay with runners, retracting sprit for asymmetric sails, sail drive hull seals and oil seals, auto pilot below deck linear drive (no pilot before so the 3” post was a bear to drill for the through bolt for the tiller arm ) engine components, cooling, Balmar alternator, solar panels on Bimini, refrigeration, electronics and new wiring, and cosmetic items below and above. I hired 3 items, new rod, new Alwgrip topsides and new North sails.

I heartily concur about a spade rudder. I have a 7 foot draft with bolted lead keel and huge balanced rudder on a 3” stainless post and a 2 blade folding racing prop on a sail drive. At 42 years old no sign of any stress at the rudder post structure and the boat was raced for its first 30 seasons in Maine. Rudder is in excellent structural condition. In 15 knots close hauled she will track for 20 minutes at a time without touching the wheel given the characteristic light chop in Southern New England.

Because of the spade and sail drive tight maneuvering, forward and reverse is easy. The draft has been no issue in New England. Neither has snagging pots while cruising Maine.

The boat is heavy though fully cored with 1” balsa, deck and hull, at 18,000 with 7,800 in the keel. No hint of water infiltration or osmosis. The gel coat below the water is clear so when I had the bottom paint stripped the core could be visibly inspected to verify moisture meter readings.

I can take no credit for understanding what I bought 8 years ago. The observations of strength and build quality were discovered through the refit and by working with Baltic to obtain the build plans and through the generous time allotted to me by the designer Robby Ball.

This boat has traditional teak joinery in 2 cabins plus saloon, but it is dark due to a nearly flush deck. It has a bridge deck with 6 steep steps at the companionway. It is not my wife’s cup of tea until the wind pipes up off shore.

I would prefer a larger more commodious boat but it is stable, fast, goes to weather extremely well in any wind and sea state, and it is rock solid in a blow. The other advantage is it requires no electric winches even at my age, 66 and it is easy to manage single handed.

We are cruising to Maine, PEI, and Madeline I. this summer, if things open.

Thank you for this site and sharing your thoughts and advice.

James Kevern

re: thruster
I chose to have one installed when I ordered our Outbound – figuring it’s cheap insurance. A couple of times on our Sabre 38 I found having enough way on for steerage was a bit fast for comfort. This was especially problematic for Ann getting the outer dock line over a very tall piling on a transient slip too big for the boat. With the thruster we can always get back upwind to it. And you have steerage with no way on.
The other time I was glad we had it was exiting a fuel dock into strong current. (I know, should have anticipated and given the corner more room). The thruster kept the bow up while the rudder kept the stern off. In fact it’s nice to sort of be able to move sideways that way.
Did I give up some performance? Certainly, but I’m happy with that trade off for us.