Production Boats Fit For Blue Water

[Cap Erict3]

Fastnet 79 investigation results.

Good read on which pleasure boats did what and why.

http://www.blur.se/images/fastnet-race-inquiry.pdf



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Looking for another pretty place to work on the boat.

[Island Time O25]

Originally Posted by El Pinguino

39 foot Westerly Sealord

Are the bolts 3/4" or larger? I can't figure it out just from the foto.

[Garrettw]

Originally Posted by minaret

Compare the laminate quality. This is a fairly new boat.

What would be your strategy to reinforce this, if asked?


Sent from my iPad using Cruisers Sailing Forum

[Polux]

Originally Posted by Dockhead

If you need shoal draft, and you intend to sail, you need a movable keel.

Rudder same depth as the keel is a recipe for trouble.

There's an Ovni getting a bottom job near me in the boatyard -- I was admiring the elaborate protection of the rudder today. Really beautifully engineered to prevent damage to the rudder. That's a hot tip for people who need shoal draft and like to take risks in shallow estuaries, etc.

Bilge-keelers with sturdy skegs made for drying out are also good for that.

Compromises are what they are: A centerboarder will not have the same performance upwind as a shallow deep keeler version (not mean too shallow but what is practice on the mass production boats).

Modern twin keels, if well designed, like the ones of the RM, offer a better compromise regarding performance then the swallow version of deep keelers but the only way not to lose almost no performance and have really swallow water capability is with modern swing keels (with all the ballast on the keel) or with lifting keel boats with a torpedo setup for ballast.

The last ones are only suited for boats of 50ft or bigger (due to the intrusion of the keel box on the interior) and they are by design a more expensive system and that's why swing keels have been used extensively on smallerperformance cruising boats that want not to lose performance but want swallow waters capability.

Some fast bluewater/ exploration boats like this one are adopting the system too:
Comet Explorer 46 EX - Comar Yachts

Anyway on all these cases (really swallow capacity boats) twin keels are required to have a good control with less deep rudders. Yes a system like the one used on OVNI with an articulated rudder can work too but they are complicated and less efficient then a "clean" rudder. They were used on OVNI before the development of the two rudder set up. Today OVNI new models have a two rudder setup.

[El Pinguino]

Originally Posted by Island Time O25

Are the bolts 3/4" or larger? I can't figure it out just from the foto.

About an inch and a quarter....

[El Pinguino]

or maybe just an inch
away from the boat just now... gorn bush

[Polux]

Originally Posted by minaret

Composite spade rudder post from a Sabre.

That looks massive but not too massive? It will not be so strong that will break the hull if the rudder hits a submerged massive object at speed?

Not easy to design a rudder regarding that kind of compromises and to know what is the right dimension for bending or broke clean before breaking the hull but having it strong enough for resisting tough conditions and even not break with shocks that would not compromise hull integrity. Lots of calculations needed and even experiences. Not enough just to do it as strong as one can.

The rudder of the Oceanis seems better designed with variable thickness conforming to the loads required. It is certainly not as resistant but then the one from the Sabre can be too strong for maintain hull integrity in case of shock. The quality of manufacture seems clearly superior on the Sabre one.

[Dockhead]

Originally Posted by Polux

That looks massive but not too massive? It will not be so strong that will break the hull if the rudder hits a submerged massive object at speed?

Not easy to design a rudder regarding that kind of compromises and to know what is the right dimension for bending or broke clean before breaking the hull but having it strong enough for resisting tough conditions and even not break with shocks that would not compromise hull integrity. Lots of calculations needed and even experiences. Not enough just to do it as strong as one can.

The rudder of the Oceanis seems better designed with variable thickness conforming to the loads required. It is certainly not as resistant but then the one from the Sabre can be too strong for maintain hull integrity in case of shock. The quality of manufacture seems clearly superior on the Sabre one.

A spade rudder should have a well designed weak point in it which will allow half of the rudder to break off before the shaft is bent to the point that the boat cannot be steered. But not so weak that it breaks when it is not supposed to. And the rudder post should be in a caisson so that the rudder's falling out won't sink the boat.

The intentional weak point is apparently hard to design well. A notable failure in this design feature was the rudder of the German Frers Hylas 54, where the weak point was so weak that many rudders broke without warning.

That was not even a spade rudder, but a semi-balanced rudder like mine, and like on the Discoverys and many HRs. It was a fantastic idea, even if it was poorly executed. It should not have been nearly so hard to design as a spade with a built-in weak point, since you have the lower rudder bearing as a fulcrum to make the break. After which, you are left with a short skeg rudder

In my opinion, not nearly enough engineering work has been done, collectively throughout the industry, on rudders. Steve Dashew solved the spade rudder strength problem on the Sundeers just by massively overbuilding it with cost no object -- which is actually the right way to do it, if you're not building enough boats to justify a big engineering effort. This is not the place to save money or build to a price if you can't invest into the design work.


I love Beneteaus from the '90s and '00's -- I used to charter them and spent many happy weeks on them. I think they are in many ways superbly designed boats for their intended purpose and outstanding value for the money. But some of the rudder designs on Benes make you shake your head with wonder and horror. I have not seen how the rudders are built in the latest generation, but I bet they are much better.

[neilpride]

The diference is in the quality of the lay up on both composite stocks , to me the bene looks like resin rich uneven glassed and with voids ,and the sabre looks like CF with a even lay up and a quality finish,..

About the weak point in the rudder, most rudders this days are foam filled and glassed with a webing frame inside , so the weak point is the lower portion of the rudder but some collisions happen in the midle or top portion, then a rudder stock able to bend and not to break is in my opinión desirable, the rudder is going to hit the hull and get stuck, and a rudder stock designed to break is in my opinión a insane way to justify a weak poor construction, i will say strenght start from the inside of the hull, rudder post framing construction and from there going down to rudder stock , rudder blade in this order, be the lower portion of the blade the weak link.

[Polux]

Originally Posted by neilpride

T..

... a rudder stock designed to break is in my opinión a insane way to justify a weak poor construction, i will say strenght start from the inside of the hull, rudder post framing construction and from there going down to rudder stock , rudder blade in this order, be the lower portion of the blade the weak link.

So Don Casey is insane?

"However, a rudder stock should not be so strong that it pries open the bottom of a boat rather than bending in a collision or grounding. This makes spade rudders on lightly built boats unavoidably more vulnerable to a bent stock—the rudder is sacrificed to save the hull."
Know Your Rudder | Sail Magazine

[minaret]

Originally Posted by Polux

So Don Casey is insane?

"However, a rudder stock should not be so strong that it pries open the bottom of a boat rather than bending in a collision or grounding. This makes spade rudders on lightly built boats unavoidably more vulnerable to a bent stock—the rudder is sacrificed to save the hull."
Know Your Rudder | Sail Magazine

Mr Casey there is clearly in full agreement with Neil, not so sure about your English comprehension. Only solid stocks can bend, hollow tube will buckle and a composite stock will fracture. Casey is saying the stock should not be built stronger than the hull, for obvious reasons. Therefore lightly built boats with their accompanying weak hull strength must have very lightly built rudder stocks, which are prone to failure. Heavily built boats can have a very strong solid stock without worrying about opening up the hull-the stock will bend and jam long before causing hull failure. Another pro who shares the opinion of every other pro who has posted to this thread.

[Dockhead]

I'm struggling to see how you guys are disagreeing.

Everyone agrees that the rudder stock should not be so strong that it will break the hull.

Everyone agrees that the hull should be as strong as possible, and that the rudder tube should be strongly mounted in the hull. Not like we often see.

Everyone agrees that the rudder stock should be sacrificial. How it can be sacrificial, and not be designed to break, I don't quite understand. Obviously if it breaks off cleanly, ideally leaving some part of the rudder capable of steering, that would be ideal, although I guess it must be hard to design.

Among great designers who design rudders to break off, rather than bend and jam, are German Frers (Hylas 54 and others), and Steve Dashew. Here's what Dashew has to say about it:

"As you will see below, our rudder shafts are very conservatively engineered for the seagoing loads, and have huge factors of safety. What we are more concerned with is engineering for mistakes in navigation, i.e. hitting the bricks. The key here is trying to engineer the bottom portion of the rudder so that it is weaker than the shaft, and bends or breaks off
before the rudder shaft reaches its elastic limit (deforms). "

. . .

At a later date we will discuss making the tip of the rudder blades frangible, so they fail before the ruder stock permanently deflects.


SetSail » Blog Archive » FPB 78: Rudder Shaft Engineering – Steering The Right Course

[Polux]

Originally Posted by Dockhead

.....

Everyone agrees that the rudder stock should be sacrificial. How it can be sacrificial, and not be designed to break, I don't quite understand. Obviously if it breaks off cleanly, ideally leaving some part of the rudder capable of steering, that would be ideal, although I guess it must be hard to design.
. . .

I agree.

The important is the rudder being well designed and that means what you have said above; Partial sacrificial blade and on bigger forces bent or controlled broken shaft in a clean way. Obviously well designed steel shafts are designed to bend before breaking the hull, composite shafts are designed to break cleanly without damaging the hull.

The concept that a rudder should be as strong as possible, not taking into account what is said above, is a wrong one.

[Polux]

Originally Posted by neilpride

The diference is in the quality of the lay up on both composite stocks , to me the bene looks like resin rich uneven glassed and with voids ,and the sabre looks like CF with a even lay up and a quality finish,..

About the weak point in the rudder, most rudders this days are foam filled and glassed with a webing frame inside , so the weak point is the lower portion of the rudder but some collisions happen in the midle or top portion, then a rudder stock able to bend and not to break is in my opinión desirable, the rudder is going to hit the hull and get stuck, and a rudder stock designed to break is in my opinión a insane way to justify a weak poor construction, i will say strenght start from the inside of the hull, rudder post framing construction and from there going down to rudder stock , rudder blade in this order, be the lower portion of the blade the weak link.

Neil, sorry about the Don Casey reference. I missed that you agree that a steel shaft has to be a compromise between strength and the need to bend before breaking the hull and that the "insane" regarded only composite shafts.

I don't think that stainless steel shafts are better because they bend while composite shafts (that don't bend) are worse because they have to break before breaking the hull in case of a collision.

It has all to to with good design and regarding composite shafts, the place they are designed to break, that has to assure a clean break without destruction of the waterproof casing.

It has all to do with good design and engineering and both materials have advantages and disadvantages. The Composite ones after breaking cleaning just fall down while a steel one when bent, in case of repeated shocks (on the ground for instance), even if bent continue to make pressure on the hull and smashing the ruder against it increasing the risks of casing failure or hull compromise. Eventually regarding the composite ones it will be more difficult to create a clean breaking on the right place at the right force.

Many top cruiser boats, like the Oysters, use composite shafts (carbon) that will break, not bend.

Top yacht designers (that design most production boats) use FEA (Finite Element Analyses) and Computer Aided Yacht Engineering to predict loads and be able to dimension pieces namely rudders for having the right compromise of features.

Nobody is perfect neither engineering has reached absolute certitude but certainly today boast are much better designed and with much more information then 30 years ago an even Beneteau that does not represent a Benchmark in what is concerned top yacht building quality has not a rudder problem on their yachts.

Given the probably more then 30 000 Benes around, many of them without appropriated maintenance, it is surprising how few cases we have knowledge off. Certainly not a problem as it could be considered on some Hunters that are much less and much more problems are known, even if I think that they get it right by now.

[neilpride]

Top yacht designers (that design most production boats) use FEA (Finite Element Analyses) and Computer Aided Yacht Engineering to predict loads and be able to dimension pieces namely rudders for having the right compromise of features.

Nobody is perfect neither engineering has reached absolute certitude but certainly today boast are much better designed and with much more information then 30 years ago an even Beneteau that does not represent a Benchmark in what is concerned top yacht building quality has not a rudder problem on their yachts.

Given the probably more then 30 000 Benes around, many of them without appropriated maintenance, it is surprising how few cases we have knowledge off. Certainly not a problem as it could be considered on some Hunters that are much less and much more problems are known, even if I think that they get it right by now.




Well, glad you get it finally,, but you wreck your post in that final statment,, FEA, my arse Pol, regarding the low spectrum in production boats, you get what you pay for, some get better rudders some get junk , and Beneteau is not precisely the example, you cant settle the number of beneteaus with rudder problems looking at the net, not even in the beneteau fórums,,,, is in the boatyards where the pot is stirred.... just for example we split open 2 dufours rudders last month , one swollen and full of wáter , with a huge crack at the top edge, and the other with similar problems,,, both boats with just few years under their keels....

The picture at the top showing a bene 38 rudder stock framing show clear to me that bene start to rectify some bad practiques , definitely better than those horror old Oceanis series.....