Transom hung rudders

[sarabande]

I can't see a plain gudgeon and pintle working on that sloping transom. The rudder is going to have to be very deep to avoid being lifted out of the water in a chop.


Perhaps consider a steel framework bolted to the whole of the transom (spreads the load to the hull and deck) and extended out so that the g and p are vertical, with the lower fitting as close to the hull as you can get it.


In any case there are going to be some quite serious loads on whatever arrangement you install on the transom.


ANother option is to create a GRP / carbonfibre structure running from a couple of feet ahead of the broken skeg, along the residual keel, to bond in with the rudder supports. A kind of "shoe" onto the small bit of keel and around the skeg - on the outside of the hul - no internal work - properly done with decent material, would be very strong. That also keeps the rudder where it was designed to be, and doesn't play around with the CLR.

 

[Lakesailor]

Without some detail pics I can't see the problem. Like William H suggests the work could be done from the outside. Is there a reinforcing frame within the skeg or is it purely GRP?
An epoxy repair would surely give as much strength as the original. I'm not sure why the repair has to be taken back to inside the hull.

Still. If the OP has decided to install a transom hung rudder, that's what he will do.
Seems a shame as that design looks like it's "made to fit".

 

[skodster]

I can't see a plain gudgeon and pintle working on that sloping transom.

The intention would be for the blade to go vertically downwards after the transom. The very slight weather helm that you get would mean that as the boat heeled the blade of the rudder would become a little more perpendicular to the water than a normal rudder which could be a bonus?

Obviously the vertical blade would have to have a gap to accommodate fitting onto the pintles.

See here for an example but the blade on mine would be more vertical to accentuate the swung angle of the blade when under sail.

 

[skodster]

Without some detail pics I can't see the problem. Like William H suggests the work could be done from the outside. Is there a reinforcing frame within the skeg or is it purely GRP?
An epoxy repair would surely give as much strength as the original. I'm not sure why the repair has to be taken back to inside the hull.

My father has had the misfortune of having both(!!) keels (at different times!) come off his Colvic Atlanta and I have seen how the keels have been made and attached to the hull.

The keel is offered up to the hull and glassed in from the inside of the boat to the inside of the keel. This provides the same strength as when the hull was made as you have the glass strands over a large area to some thickness.

What is being suggested here is that the crack is basically glued albeit with strong epoxy. I have my doubts that the bond between the grp and the resin could ever be strong enough to be 'seaworthy'.

Have you any examples of this being done in a similar application?

 

[sarabande]

the more I look at your pic and that latest one, the more I think a transom hung rudder would be a lot of work, and pretty ineffective.

As LS and WH say, fix it from the outside; don't faff about with ideas of re-inforcing the interior - unless you have seen stress cracking / delamination as a result of the skeg impact.

 

[neilf39]

I have a transom hung rudder which pivots and is balanced when fully down. Came slightly up when rope holding it down slipped meaning it was set further aft and no longer balanced. Helmsman who had just taken over at the time was not aware and thought it was just bad weather helm so kept pulling. As a result the welds on the fitting just peeled and rudder became useless. I have now had extra stiffeners welded on. There are enormous sideways forces on the ruder you don't notice when it is balanced. If the rudder is hung at an angle then I would think the centre of balance shifts the further it turns making it harder. Other than making it strong enough then access, and maintenance are much easier. To get it repaired I just undid the nuts and took it all home.

 

[penfold]

The intention would be for the blade to go vertically downwards after the transom. The very slight weather helm that you get would mean that as the boat heeled the blade of the rudder would become a little more perpendicular to the water than a normal rudder which could be a bonus?

Obviously the vertical blade would have to have a gap to accommodate fitting onto the pintles.

See here for an example but the blade on mine would be more vertical to accentuate the swung angle of the blade when under sail.

I can't view your image, but from your description you propose having the pintles mounted onto your existing transom? If it's an overhanging transom, having that amount of rudder area aft of the pivot axis will give very high tiller loads. If it's a retrousse transom the opposite applies, the tiller loads will have a servo effect and it would be snatched out of your hand and probably break off the rudderblade.

 

[lw395]

This is the project

Personally, I don't like the look of that and can well understand the urge to chop it off!
That skeg looks ugly, weak and pointless to my critical eyes.

The problem is the slope of the transom.
If the rudder pivots on an axis parallel to that, it will stick out behind the boat and be prone to being backed into things.
The blade must be 80% behind the axis or it will be unstable.
Also the tiller will move down as you pull it across the cockpit.

You could get around this to some extent by moving the upper pintle out from the transom, so that the rudder axis was more vertical.
Like the rudder gantry on a performance dinghy but not so extreme.
It would need to be pretty strong, but it's the lower pintle that takes the bigger loads.

A third alternative would be to get rid of the skeg and have a spade rudder.
Again that would probably mean reinforcing the hull from inside, but might be the best in the long run? It depends whether the top of the rudder tube is in a strong part of the deck or what?

I would consult some books regarding how big and strong it all needs to be.

 

[Lakesailor]

Have you any examples of this being done in a similar application?

I have done a skeg repair myself at the skeg root/hull joint.
It was surprising how flimsy the original moulding was.

Try a PM to Oldsaltoz who does a lot of grp and boat work

 

[Lakesailor]

Personally, I don't like the look of that and can well understand the urge to chop it off!
That skeg looks ugly, weak and pointless to my critical eyes.

I can't help but think that there is a frame within the skeg along the keel and turning down to the bottom rudder pivot. If not I would cut a side out of the skeg and install one, glassing the side back in afterwards. The strength would be in the frame, not the skin.

 

[lw395]

I can't help but think that their is a frame within the skeg along the keel and turning down to the bottom rudder pivot. If not I would cut a side out of the skeg and install one, glassing the side back in afterwards. The strength would be in the frame, not the skin.

Maybe.
I step back from guessing what was going through the designer's mind.

How do you make a frame strong in a skinny appendage like that?
Isn't it easier just to put the strength in the rudder?

 

[skodster]

unless you have seen stress cracking / delamination as a result of the skeg impact.

If I push on the skeg, the crack opens up which would suggest that the skeg isn't actually attached at that point. This worries me because of the structural issues.

Don't get me wrong, I would love to avaoid a major reconstruction if possible!!

 

[Tranona]

Don't think that skeg does much structurally - it is there more to fair the waterflow past the rudder. Very common in that era. The stock itself will provide good support for the rudder inside the tube, and as you can see from the small size of the lower bearing it is not expected to take high rudder loads..

Grind back on the outside to sound glass and build up with glass cloth and epoxy - will be stronger than the original. Doubt you will find any advantage of doing the repair from the inside.

As others have said the transom shape does not lend itself to a transom mounted rudder - which would interfere with the outboard as well. The only advantage is that you could build in some balance, but you may end up getting it wrong and having to do more work than a simple GRP repair.

 

[oldsaltoz]

G'day to one and all,

Thanks for PM Lakey,

One thing no one has mentioned is what a skeg is designed to do and why are they on some boats and not on others.

Just the fact that boats with skegs tend to broach much less should give you clue and the fact that even fewer broach to windward is another clue.

Putting a spade on a removing a skeg is a very brave move, not to mention a lot of time and money for a project that can end in total disaster, financially and from a performance point of view.

Most skegs are part of the hull mould, not a stick on after she is pulled from the mould, and most of newer boats have only a closed cell foam insert inside to reduce the amount of glass required and at the same time provide bouncy at the stern.

I have never seen any part of a skeg that extended up inside the hull either.

Repairing a skeg that has taken a hard grounding or strike is always done from the outside only, primarily because the hull is not damaged, and even if it was, the repairs can still be done from outside rather than dismantle fuel tanks quarter berths and the like.

My advice would be to repair the skeg, it will be cheaper, faster and more importantly not effect the performance or handling.

You only need to grind about a foot or 300mm above and below the crack, in your case with the crack being at the top of the skeg this means grinding an area 300mm each side of the skeg to hull joit and down the skeg on all sides for 300mm.

Start at the crack on one side only and grind till you have no crack, washing with Acetone will show if the crack is still there, it dry rapidly and even or dry and show a damp line if the crack is deeper.

If you get half way and still have a crack, lay up a section with epoxy resin and bidirectional cloth (crows foot) 200 to 300 gram, fill the ground area and chock the skeg then let it cure for 24 hrs.

Next day, grind and check the other side of the skeg again crack testing as you go.

When you are happy you gave ground out any remaining crack/s, continue grinding the 300mm above and below the damaged area, feathering out to nothing at the extremities.

Again using an epoxy resin and bidirectional cloth glass it all up and add a layer or two of rovings as the get toward the end, this will even the work out
and reduce sanding.

Important: You can put 3 or layers of mat onto a plastic sheet and wet them out then lift and stick them to the hull when working overhead; Just be sure to roll out as much resin as you can, less resin means a stronger repair.

Good luck and fair winds.

 

[William_H]

The intention would be for the blade to go vertically downwards after the transom. The very slight weather helm that you get would mean that as the boat heeled the blade of the rudder would become a little more perpendicular to the water than a normal rudder which could be a bonus?

Obviously the vertical blade would have to have a gap to accommodate fitting onto the pintles.

See here for an example but the blade on mine would be more vertical to accentuate the swung angle of the blade when under sail.

That rudder arrangement must be truly horrible. Done more for style than function. Perhaps in the same way the OPs rudder is designed. Consider that a rudder is intended to give lift in a sideways direction when a turn is commanded. A rudder angled at 45 degrees to water flow will give as much lift upwards as in the desired direction. Lift that creates drag with no purpose. Or the rudder will have huge loads on the tip which have a large turning moment (leverage).
I have a swing rudder on my little boat and as with another poster after beaching the rudder was not fully down. So swung aft somewhat. With an unfamiliar person on the helm he didn't complain about the high tiller loads until the tiller snapped. Anyone with a swing rudder will know how badly the boat sails with rudder not fully down.
IMHO a rudder axis should be vertical. One popular design of 22ft boat around here was originally put out with a rudder something like that in the picture. You never see one now that has not been modified with a ss outrigger for the top pintle to give a vertical axis and far better performance. olewill

 

[LittleSister]

A rudder angled at 45 degrees to water flow will give as much lift upwards as in the desired direction. Lift that creates drag with no purpose.

Why would it do that? Popular myth, surely? The water flowing over the rudder is horizontal (give or take) and will not 'see' the 45 degree angle.

An aircraft's swept-back wings do not waste half their power trying to tear the plane apart! A yacht's foresail on a sloping forestay doesn't waste much of it's power trying to lift the bow out of the water (because the wind is (largely) parallel to the sea surface, not perpendicular to the forestay). My rudder slopes steeply the other way (long-keeler) but I've never noticed any tendency for the stern to sink when the ruddeer is applied.

 

[DownWest]

Why would it do that? Popular myth, surely? The water flowing over the rudder is horizontal (give or take) and will not 'see' the 45 degree angle.

An aircraft's swept-back wings do not waste half their power trying to tear the plane apart! A yacht's foresail on a sloping forestay doesn't waste much of it's power trying to lift the bow out of the water (because the wind is (largely) parallel to the sea surface, not perpendicular to the forestay). My rudder slopes steeply the other way (long-keeler) but I've never noticed any tendency for the stern to sink when the ruddeer is applied.

Only true if your boat is vertical, as soon as it heels, there is a pitching force from the rudder, if it not dead ahead.
The most efficient wings are not swept (think gliders)
Not sure how you can get a vertical forestay, so no choice there;-)
DW

 

[LittleSister]

Only true if your boat is vertical, as soon as it heels, there is a pitching force from the rudder, if it not dead ahead.

True, but applies equally to a forward swept, aft swept or vertical rudder, does it not?.

The most efficient wings are not swept (think gliders)

Not sure this is true, but in any case irrelevant to the point I was making about the direction of the force generated by swept back wings (as featured on most airliners, for instance).

Not sure how you can get a vertical forestay, so no choice there;-)

If the verticality of the leading edge of a sail was that important we (or at least racers) wouldn't be hanging our sails on sloping wires at all - we'd be using cat rigged boats, or have T shaped masts, etc., etc.