Keel hung rudders?

[Pylasteki]

Very interesting stuff.

Do I have it correct that the root gap, is the upper end closest to the hull/rudder shaft exit? I've only heard of root gaps in regard to spade hung rudders and welds...

I'm going to use a straight rudder shaft (may require relocating the rudder tube) and glassing a semi-circular groove in the hull, I assume that the more it overlaps the shaft, and the closer it is to the shaft the less the drag. Any ballparks distances where the gap for practical purposes disappears to the water flow?

Any thoughts on restraining the rudder? At this point it is able to move close to 90 degrees either way. If it were transom hung there would be limiting chains to keep a following sea from snapping it off if it ever goes sideways. (Say the tiller breaks its lashings.) Do you just place your bets and take your chances on that issue?

[MikeJohns]

Originally Posted by Pylasteki

Very interesting stuff.

Do I have it correct that the root gap, is the upper end closest to the hull/rudder shaft exit? I've only heard of root gaps in regard to spade hung rudders and welds...

Yes

Originally Posted by Pylasteki

I'm going to use a straight rudder shaft (may require relocating the rudder tube) and glassing a semi-circular groove in the hull, I assume that the more it overlaps the shaft, and the closer it is to the shaft the less the drag. Any ballparks distances where the gap for practical purposes disappears to the water flow?

By the time you get back to the rudder on a long keel the attached flow has long departed and things are pretty turbulent, the maximum pressure is well fwd and the rudder works by shifting the COP on the long keel, providing you cannot see through the gap looking beam on then a gap of 20mm will allow anti-fouling and cleaning without adding significant drag or rudder angle.

Originally Posted by Pylasteki

Any thoughts on restraining the rudder? At this point it is able to move close to 90 degrees either way. If it were transom hung there would be limiting chains to keep a following sea from snapping it off if it ever goes sideways. (Say the tiller breaks its lashings.) Do you just place your bets and take your chances on that issue?

Ideally there should be rudder stops on the shaft. If the rudder is free to turn to 90 deg then there's more probability of damage from motoring astern with the helm free and also grounding from dragging anchor.

[Pylasteki]

Thanks Mike.

I haven't found anything about shaft stops for a tiller steered boat. Looks like most everybody with chain and cable have a stop on each side of the quadrant. What do they look like?

This is what I'm thinking for the back half of the keel, complete with the flat directly above the rudder to serve as an end plate.

[MikeJohns]

Shaft stops are commonly on any rudder shaft that enters through a rudder tube into the hull. But yes; stops on the tiller will do fine.

Thats the sort of thing (photo) .

cheers

[Brent Swain]

A friend with an Alberg 37 put a daggerboard trunk and daggerboard behind the rudder and said it drastically improved downwind control , and self steering upwind. He wished he had done that before his circumnavigation. He said he wished he had simply put a rudder there, and got rid of the keel hung one.
You could put a balanced rudder on a shaft at the aft end of the waterline and hook it up to a horizontal vane ,like a hydrovane , only larger.
Monitors have a high structural failure rate. Carry the spare tubing for repairs.
Brent

[entropic]

Pylesteki,
Feel free to email me. I've made rudders for my Triton and my Alberg 35. I used to have Triton 628 and filled in the prop aperature and built a new rudder for it after ditching the Atomic 4. I now have an Alberg 35 and am keeping the Atomic 4 this time!

I never raced my Triton, but filling in the prop aperature did improve the sailing ability of the boat. I had a 3.5hp on the transom that pushed the boat in calms or in and out of harbor, but it was perilous at times because it would stall when the boat starts pitching. Perhaps the higher hp engines won't stall, like a 9.9.

I sandwiched two pieces of marine ply together, then glassed it, on a new rudder stock that had welded straps holding the rudder instead of lag bolts through the stock. This worked fine and was plenty strong. However- that rudder is bouyant and so the tiller would always want to turn into my cockpit lockers if I let it go. I coped by tucking it in the mainsheet lines. It will cause some damage if you are reversing and you let go the tiller, but it would most likely be cosmetic. I find the top edge of the rudder near the stock would contact the hull. You can see this when you haul out.

Try to add lead weight in between the plys as far from the stock as possible to avoid this problem.

Both my boats have had this issue, and I've just been careful with it. I've sailed the Alberg to BVI and back in some serious weather and the rudder has been fine. If the boat is moving forward at all, the water pressure will keep it centered. Made its rudder 5 years ago and all is well.

PS-you bought that boat in Annapolis, didn't you?

[Pylasteki]

Entropic,

Thanks for the reply!

Yes, I bought Pylasteki in Annapolis.

What thickness plywood did you use?

Do you have any pictures of the process? I'm thinking to replace the rudder shaft, and use one solid length, instead of the two part stock type.

Did you use one length or two? It seems like the blade would have to be bolted on for removal... or a really deep hole dug under it.

Thanks!
Zach

[entropic]

Hi Pylasteki,

I had a new, one-piece, straight shaft rudder post made for me and instead of using lagbolts going through the shaft, I had them weld some straps to the shaft. I don't have a picture of it, but the straps were about 3/16" thick stainless (on a stainless shaft) and they wrapped halfway around the stock. The straps extended about 8 inches or so. I think I had four straps along the length of the shaft. Each strap had three holes in it that I used to through-bolt the rudder.

If you had the straight shaft made in two parts, that would greatly simplify installation. You could attach the rudder to the lower stock, slide in the upper stock and then bolt it together.

The plywood equaled the rudder stock diameter. I think it was one inch, so a sheet of 1/2" ply should work. I used a belt sander to taper the aft edge. I've got a photo of my A35 rudder which does have an aperature, but the construction is the same. I sheathed it in glass cloth and that was the end of it.

This year I think I'm going to fair over the straps to give it something more resembling an airfoil shape, but I'm not gonna template it or anything scientific. I kept the original rudder shape instead of doing a straight edge for one reason on my aperature rudder. The shaft imparts the turning force on the wood on only the upper part of the rudder and going with a straigh aft edge would have reduced my material in the area around my aperature.

A one piece shaft without the aperature would distribute the load much more evenly and give you more options on rudder shape.