The ex-Doxy, now Zealous project

Jim in Halifax

Super Anarchist
1,675
751
Nova Scotia
My last boat had a replacement rudder built by Foss Foam of Florida. SS shaft with SS web welded to it, foam body over this (cast in a mould) and glass skins. This is pretty conventional production stuff. And it can be owner repaired on a beach in a pinch, assuming no damage to the SS bits. Why not follow the same build technique, substituting appropriately sized aluminum for SS?

 

floater

Super Duper Anarchist
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Aluminum rudder and post is the obvious, straightforward answer, only reason to do something else is that I can fix a FRP/composite rudder on the beach in the middle of nowhere back to good as new.  Aluminum is a lot more a pain to repair if it gets smashed up and would have to be bodged until getting to a major port.
if it ain't broke, don't fix it.

because its metal, you've already got a tough-as-shit boat. why worry about breaking it? 

minimizing maintenance seems like a smart move. To add dissimilar materials to your alu boat idk.

 

floater

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Skeg rudders are very powerful at speed. Slow speed maneuverability is not so hot, but no bending loads on the shaft.
can you attach a tiller to one though? I've always (been blessed) with a balanced rudder. I don't understand how you can get a balanced rudder behind a skeg.

or perhaps with a full skeg - you also need a wheel to muscle that thing around.

 

Jim in Halifax

Super Anarchist
1,675
751
Nova Scotia
can you attach a tiller to one though? I've always (been blessed) with a balanced rudder. I don't understand how you can get a balanced rudder behind a skeg.

or perhaps with a full skeg - you also need a wheel to muscle that thing around.
Lots and lots of tiller-steered boats that don't have balanced rudders - all those classic designs with keel-hung or stern-hung rudders for example.

 

accnick

Super Anarchist
3,240
2,261
can you attach a tiller to one though? I've always (been blessed) with a balanced rudder. I don't understand how you can get a balanced rudder behind a skeg.

or perhaps with a full skeg - you also need a wheel to muscle that thing around.
I've had a series of tiller-steered boats of various sizes with either keel-hung inboard rudders or a rudder hanging off the stern. It's how the boat balances under sail that determines rudder loads, as much as anything.

My last sailboat was a 40' heavy double-ender with outboard rudder, which I re-designed to a slightly more efficient Constellation-style rudder. The rudder loads were quite high in heavy air reaching, in part because there is so much immersed area in an outboard rudder as the boat heels and the stern wave gets higher. My very small wife had trouble steering that boat in those conditions, so I converted it to wheel steering after the initial 2,500 mile shakedown.

The biggest of these boats, a 48' on-deck yawl that was converted from a 1923 Class Q sloop, was the most radical under the water, with the rudder well forward and attached to the trailing edge of a very small, deep keel. It was also the easiest to steer and balance. The fact that it was yawl-rigged helped that balance a lot, but even sailing without the mizzen, it easily steered with one hand on the tiller.

Here's that boat is rounding Fort Adams into Newport Harbor in about 1976 in a pretty good sou'westerly seabreeze. We've just gone from almost dead downwind to beam reaching into the harbor, so my wife is trimming the headsail while I trim the main and steer. I am standing up to steer with one hand and trimming the main with the other, as we are overtaking a lot of smaller boats here and I needed to maneuver quickly.

We were moving along pretty briskly here, as you can see from the height of the quarter wave at the stern.

The boat is perfectly balanced at this point, despite the sub-optimal sail trim.

By the way, the boat had no engine at that time, so easy steering and maneuvering under sail was critical. A tiller is ideal for this, as the response is so direct.

Hobnob 1976.jpg

 
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bpw

Member
455
20
Check my assumptions please….

if the rig gets taller and bigger roach on the main it will likely increase weather helm a touch, but is extremely unlikely to increase Lee helm. 
 

Currently planning chainplate location, and going to allow space for the mast to move forward, but not back and want to make sure that’s not dumb.  I can’t think of any reason I would want to shift the mast back while going to a taller rig. 

 

estarzinger

Super Anarchist
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Aluminum rudder and post is the obvious, straightforward answer, only reason to do something else is that I can fix a FRP/composite rudder on the beach in the middle of nowhere back to good as new.  Aluminum is a lot more a pain to repair if it gets smashed up and would have to be bodged until getting to a major port.
I'd support the all aluminum approach from my experiences:

(1) we found aluminum working/fab capability to exist in some of the most remote little towns.  Essentially wherever there is fishing there will be aluminum working capability.  When there is dairy there is often mad metal working skills. Etc.  We had a new rudder made in Chile (better shape than the original one) and it was first class work - it was made 'one town up' from where we were docked, but they just threw it in the back of a pickup truck and delivered it to us and I installed it with the boat in the water.

(2) If you make the rudder 'quite strong' even the worst case ruder strikes will only result in small bent metal on the narrow edges - I can say this from personal experience.  We hit a rock ledge in maine with the rudder at speed, thought we were in serious trouble, found no leaking, got to a near by fishing port, dropped the rudder (while in the water) and it just had a little bend on the bottom edge when we pressed out in a big metal press they had.  We also pounded up and down on rocks on the rudder in Iceland for about an hour, got ourselves unstuck, sail 180 miles around to the next fishing port, hired a diver to go look at things, and he came up and said 'well, you may have broken some rocks but the rudder looks fine' (he had underwater video to show to us).  And this rudder floated (positive buoyancy) - so while it was brick shithouse strong, it was not all so heavy (yes it was way heavier than an all carbon one). One of the good properties of aluminum vs carbon is that it will (often) deform/bend rather than crack.

(3) I never needed to on the rudder, but it is quite possible to make decent epoxy glass fixed on aluminum.  We had a weld crack on a tank at sea (with a long way still to go), and I sanded it, and glassed/epoxied it, and it held for 3 years until I got around to getting it rewelded.  I was surprised it held that well, this on a boat that was subject to temp extremes and the tank was in the bilge (so it did sweat/get wet).

oth - carbon can work well also - use e-glass surface layers to insulate the carbon.  It can also be made brick shithouse strong and will still be lighter, but it will likely be rather more expensive.  I would want a composite shaft on a composite blade - not a fan of metal shafts on composite blades.

 
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bpw

Member
455
20
Chainplates almost ready to get welded in, once they are in place the decks can start going on.  Still need final shaping and to build some gussets.  These will allow a spreader sweep angle from 15-30 degrees depending on final rig design or allow the mast to move forward about a foot if needed for helm balance.  Its a lot easier to design for adjustment now than change things later.  These are optimized to take lashings, but could take turnbuckles if needed.

Thats 1/4" 5083 plate and a 1.5" solid rod for size reference.  Pretty sure it will be strong enough.

2022-03-31 13.57.40.jpg

 
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Panoramix

Super Anarchist
can you attach a tiller to one though? I've always (been blessed) with a balanced rudder. I don't understand how you can get a balanced rudder behind a skeg.

or perhaps with a full skeg - you also need a wheel to muscle that thing around.
Not quite a balanced rudder but the solution to this is a fletner.

Late 70s, there was a very interesting Franco American design called the Trismus 37.

Long keel with a wide base to allow drying without legs, rudder aft of the keel with a fletner to let you steer with a finger and twin boards to keep the boat perfectly balanced. Not a racing boat but perfect for a couple who want to keep churning 150Nm days without drama.

 

Israel Hands

Super Anarchist
2,914
1,664
coastal NC
instead of a shaft - you've got a structural beam welded to the hull - which is dragging in the water. from this pov - the skeg-less rudder really seems a technological innovation.
Enough of your anti-skeg bias! 

But seriously...the fact that the skeg is fixed in place does not, in and of itself, mean that the skeg/rudder assembly creates more drag. If a skeg/rudder assembly is designed to be hydrodynamically efficient and similar in wetted area to a spade rudder, then who is to say which outperforms the other.

And... when those Orcas off Portugal take out your spade rudder, you'll be thankful for the guy with the skeg-mounted rudder who comes to your aid.  :p

 

floater

Super Duper Anarchist
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quivira regnum
Not quite a balanced rudder but the solution to this is a fletner.

Late 70s, there was a very interesting Franco American design called the Trismus 37.

Long keel with a wide base to allow drying without legs, rudder aft of the keel with a fletner to let you steer with a finger and twin boards to keep the boat perfectly balanced. Not a racing boat but perfect for a couple who want to keep churning 150Nm days without drama.
very cool. http://les.trismus.free.fr/barbaou.html

don't quite understand the fletner though.

attachment.php


 

Steve

Anarchist
563
77
duluth, mn
Balance on a skeg rudder was not uncommon, the rudder was typically deeper than the skeg and extended forward at the bottom. Not saying it was a good idea as it would be easy for a stray line or debris to get caught in the gap between the bottom of the skeg and rudder. 

 




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