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Drilling holes through the rudder stock


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Any tips on how to drill 2 x 12mm holes squarely through a 35mm rudder stock?

 

My boat is coming out of the water and as part of the work I'm going to be taking the rudder off and epoxying the rudder stock tube.

 

I'm going to put this new rudder on because I've had it laying about for the past 15 years and I think I may as well use it. It might be interesting to see if the profile works any better than the flat plate rudder that's on there now. 

 

The two bolts in the picture are pinch bolts that don't go all the way through. The idea was that I drill two recesses into the rudder stock for the bolts to clamp into, but it doesn't seem very secure to me so I want to go all the way through with A4 stainless bolts and use the welded on nuts + A4 nyloc nuts on the other side.

 

That's all fine but I'm not sure how to drill the holes through the rudder stock squarely to make sure they meet the holes in the rudder on the other side. I could use one of the pinch bolts to hold it in place and drill through the rudder stock and the other side of the rudder together but that would risk stripping the threads in the welded on M12 nuts. I suppose I could go through carefully with a narrower drill bit but just wondered if there was a better way?

 

 

IMG_20220619_181915.jpg

IMG_20220619_181921.jpg

Edited by blackrose
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5 minutes ago, blackrose said:

Any tips on how to drill 2 x 12mm holes squarely through a 35mm rudder stock?

 

My boat is coming out of the water and as part of the work I'm going to be taking the rudder off and epoxying the rudder stock tube.

 

I'm going to put this new rudder on because I've had it laying about for the past 15 years and I think I may as well use it. It might be interesting to see if the profile works any better than the flat plate rudder that's on there now. 

 

The two bolts in the picture are pinch bolts that don't go all the way through. The idea was that I drill two recesses into the rudder stock for the bolts to clamp into, but it doesn't seem very secure to me so I want to go all the way through with A4 stainless bolts and use the welded on nuts + A4 nyloc nuts on the other side.

 

That's all fine but I'm not sure how to drill the holes through the rudder stock squarely to make sure they meet the holes in the rudder on the other side. I could use one of the pinch bolts to hold it in place and drill through the rudder stock and the other side of the rudder together but that would risk stripping the threads in the welded on M12 nuts. I suppose I could go through carefully with a narrower drill bit but just wondered if there was a better way?

 

 

IMG_20220619_181915.jpg

IMG_20220619_181921.jpg

I don't see how you can even guarantee the welded nuts are 100% square to the shaft.

Edited by ditchcrawler
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1 hour ago, ditchcrawler said:

I don't see how you can even guarantee the welded nuts are 100% square to the shaft.

 

This is also true...

 

So perhaps I should just put a M12 drill through those welded on nuts using them as guides and not worry about the threads, drill through the rudder stock and use M12 nyloc nuts on the other side?

Edited by blackrose
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I would go bigger, 14mm, and drill right through.  Liverpool Boats bolted rudders on like this and they used smaller bolts and they always come lose and eventually shear off'

Use bolts rather than machine screws, high tensile fitted shank cap heads would be best.

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I assume you are using a hand held pistol drill.   Start with a 6mm hole.  Enlarge it to 8 then 10 then 12 then to 13 then 14.  That way you have some chance of getting the hole close to size and for the bolts to tighten up straight. 

 

Then put  either A4 stainless or HT hex cap screw  bolts through the whole lot into stainless nyloc nuts.  Coat any stainless bolts in grease.  The bit through he rudder stock is an ideal site for crevice corrosion, and stainless is very susceptible.

 

If you can beg or borrow a  magnetic  base drill life will be a lot  easier.  That will enable you to whack a 14mm hole through stock and new blade in one go, knowing it is square  in both planes.

 

N

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49 minutes ago, Tracy D'arth said:

I would go bigger, 14mm, and drill right through.  Liverpool Boats bolted rudders on like this and they used smaller bolts and they always come lose and eventually shear off'

Use bolts rather than machine screws, high tensile fitted shank cap heads would be best.

 

I think Liverpool Boats used 8mm or 10mm. I'm still on the original bolts after 17 years. All I did was tighten them up once during blacking.

 

If I go too big doesn't it weaken the rudder stock itself? I was going to use A2 stainless hex bolts. Anything else will just corrode won't it? I read that A2 is stronger than A4 and there's no need for A4 anyway because it's not in saltwater. 

 

28 minutes ago, BEngo said:

I assume you are using a hand held pistol drill.   Start with a 6mm hole.  Enlarge it to 8 then 10 then 12 then to 13 then 14.  That way you have some chance of getting the hole close to size and for the bolts to tighten up straight. 

 

Then put  either A4 stainless or HT hex cap screw  bolts through the whole lot into stainless nyloc nuts.  Coat any stainless bolts in grease.  The bit through he rudder stock is an ideal site for crevice corrosion, and stainless is very susceptible.

 

If you can beg or borrow a  magnetic  base drill life will be a lot  easier.  That will enable you to whack a 14mm hole through stock and new blade in one go, knowing it is square  in both planes.

 

N

 

Yes, hand held drill. My idea was to start by using a 12mm drill using the welded on nuts as a guide. That way I can mark a point in the centre of the nut hole. Then I'll use the 6mm drill, and gradually go bigger. If I try starting off with a 6mm drill I'll never get the centre of the nut hole and the whole thing will go askew. 

 

I was going to put PU sealant on the bolts when pushing them through. 

Edited by blackrose
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As has been said, stainless will suffer crevice corrosion, the rest of your steel boat is subject to the same rusting as the bolts will be. Mixing metals in water needs to be considered.

 

How thick is the rudder shaft?  Most are at least 30mm or bigger,

 

Its your boat, do what you want, I was only advising what I would do, but then I have been known to be sometimes wrong, but usually my experience proves me to be  correct.

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17 minutes ago, blackrose said:

 

Yes, hand held drill. My idea was to start by using a 12mm drill using the welded on nuts as a guide. That way I can mark a point in the centre of the nut hole. Then I'll use the 6mm drill, and gradually go bigger. If I try starting off with a 6mm drill I'll never get the centre of the nut hole and the whole thing will go askew. 

 

Marking the centre of the 12mm hole then working up is a good start. 

 

The aim is to get a hole through stock and rudder which is a close fit on the bolts all along and around the bolts. That way the steering  loads are spread across the biggest possible areas. The angle of the bolts does not really matter much.  It will be easy to get a tight fit on the edges of the holes in the new rudder blade and at either side  of the rudder stock, but with regular use, and plenty of normal vibration in the prop wake there will be fretting, wear and looseness.

 

N

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44 minutes ago, Tracy D'arth said:

As has been said, stainless will suffer crevice corrosion, the rest of your steel boat is subject to the same rusting as the bolts will be. Mixing metals in water needs to be considered.

 

How thick is the rudder shaft?  Most are at least 30mm or bigger,

 

Its your boat, do what you want, I was only advising what I would do, but then I have been known to be sometimes wrong, but usually my experience proves me to be  correct.

 

Rudder stock is 35mm. The original stainless bolts were still fine last time I checked. No crevice corrosion. 

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11 minutes ago, PD1964 said:

It looks like it will be susceptible to corrosion from the inside, it not completely welded top and bottom and made watertight? Has the internal surfaces been blacked/treated?

 

I'll epoxy the inside of the tube that goes through the rudder. It's no different to the rudder that's been on the boat for the past 17 years in that respect. There's been no fretting, wear or looseness. It's not welded or watertight. If if was fully welded the rudder couldn't be removed. 

Edited by blackrose
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10 minutes ago, blackrose said:

 

I'll epoxy the inside of the tube that goes through the rudder. It's no different to the rudder that's been on the boat for the past 17 years in that respect. There's been no fretting, wear or looseness. It's not welded or watertight. If if was fully welded the rudder couldn't be removed. 

Yes I was just editing, to ask if it was one through run of tube 

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The new rudder doesn't have any protrusion on the top edge to stop it going under the counter. The current one stops when it hits the uxter plate on each side. So I've measured it as best I can with it in the water and made a sketch. The current rudder is about 12mm thick and the rudder stop on the top is about an inch thick for some reason! 

 

I spoke to a steel fabricator this morning and he offered to make one from 12mm steel. It occurred to me that I might be replacing a perfectly good rudder with something weaker? Is a 12mm plate welded onto the top of the rudder going to be ok? My stern button fender protects the rudder and I suppose anything hitting the back of the boat that hard is going to damage the rudder whatever is there?

 

If I got the fabricator to double up the plate thickness, any impact on the rudder while it's hard over will just bend the rudder rather than the 24mm thick plate wouldn't it? 

 

IMG_20220620_094033.jpg

Edited by blackrose
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4 minutes ago, blackrose said:

This is what I have at the moment. The underwater part of the rudder is about half that thickness. 

 

IMG_20220620_145615.jpg

But how do your old rudder and the new one compare. Are the trailng part and balance part of similar sizes dimentions.

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Incidentally. If your worried about the rudder stock tube you could also while the rudder and stock are out poke another length of tube up inside as far as it will go up the existing one and weld around it's bottom, of course the top of it can't be welded but it's good insurance all the same, and providing of course that there will be enough room, clearance  for the stock to pass through it.

Edited by bizzard
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15 minutes ago, bizzard said:

Incidentally. If your worried about the rudder stock tube you could also while the rudder and stock are out poke another length of tube up inside as far as it will go up the existing one and weld around it's bottom, of course the top of it can't be welded but it's good insurance all the same, and providing of course that there will be enough room, clearance  for the stock to pass through it.

 

Ok but as well as clearance inside the new tube for the rudder stock wouldn't I need a tube of exactly the right OD to fit inside the current tube to enable it to be welded? Also if it can't be welded at the top what's the point as water will just get between the two tubes and could cause all sorts of corrosion problems? I think it might be better just to blast & epoxy the existing tube.

Edited by blackrose
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3 minutes ago, blackrose said:

You can see how agricultural the current rudder is in comparison to the new one.

 

DSC00340.jpg

Common on Liverpool boata and others. If drilling right through rudder and stock, the bolt needs to have a long unthreaded shank and fit with precision. Drill the hole slightly undersize and then use a reamer to size it accurately for the bolt, Any slop and if the other pinch bolts let go then the bolt and hole will wear quickly.

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4 minutes ago, blackrose said:

 

Ok but as well as clearance inside the new tube for the rudder stock wouldn't I need a tube of exactly the right OD to fit inside the current tube to enable it to be welded? Also if it can't be welded at the top what's the point as water will just get between the two tubes and could cause all sorts of corrosion problems? I think it might be better just to blast & epoxy the existing tube.

Inspect the inside of the existing tube first and if it looks badly deeply pitted might be worth doing. It might or will get between but believe me the double thickness will outlast the rest of the boat and probably a life time. A circular rubber or silicone disc slipped down the stock will help to stop water spilling over.

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4 minutes ago, bizzard said:

Common on Liverpool boata and others. If drilling right through rudder and stock, the bolt needs to have a long unthreaded shank and fit with precision. Drill the hole slightly undersize and then use a reamer to size it accurately for the bolt, Any slop and if the other pinch bolts let go then the bolt and hole will wear quickly.

 

Yes, the new rudder won't use pinch bolts, just two 12mm through bolts. I don't have a reamer so it will just be done with a drill. I'll do it as accurately as I can. I could always get the rudder spot welded on the top and bottom of the tube, but then that sort of defeats the object of the bolts and makes the rudder impossible to remove in the water.

Just now, bizzard said:

Inspect the inside of the existing tube first and if it looks badly deeply pitted might be worth doing. It might or will get between but believe me the double thickness will outlast the rest of the boat and probably a life time. A circular rubber or silicone disc slipped down the stock will help to stop water spilling over.

 

But water comes up the tube from underneath. On another thread someone else suggested using a car CV boot over the bearing to keep water out, apparently not realising that water comes up the tube from below.

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3 minutes ago, blackrose said:

 

Yes, the new rudder won't use pinch bolts, just two 12mm through bolts. I don't have a reamer so it will just be done with a drill. I'll do it as accurately as I can. I could always get the rudder spot welded on the top and bottom of the tube, but then that sort of defeats the object of the bolts and makes the rudder impossible to remove in the water.

Reamers arn't expensive. Just drilling and bolting through. there will be a slackish fit which will wear and cause on going slop. reaming accurately for an interferance fit this cannot happen. If you don't ream them retain the pinch bolts as well.

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