Rudder Post

[SailorHarry]

Hello all,

The boat I'm building is 22.5' long with around 5' beam. It's a Selway-Fisher double chine design in aluminum. I have made slight modification to move the rudder into the transom. This won't leave much room for balancing but I'm using a wheel so I think it'll be liveable.

The rudder will be welded aluminum on a stainless rod supported by three nylon bushings, two at the transom and one at the skeg. What size should the rod be? I'm thinking 3/4" or perhaps 1". Or is that overkill?

Thanks,
Harry

[fredrosse]

The rudder post will at times be subjected to potential stress from groundings, floating debris, etc. In terms of strength required, 3/4 inch diameter would be more than adequate, but how big a log might come down the river?

I would recommend an aluminum post, 1 inch diameter, made of 6061T alloy. This aluminum alloy has a yield strength similar to steel, and would avoid the "dissimilar metals" corrosion issues entirely. With nylon bushings the potential problems with galling (aluminum on aluminum) will not be a problem.

I think this is a first for this forum, a true "post reply".

[DetroiTug]

I wouldn't go any less than 1" as Fred wrote. I'm using a 1" diameter 1018 cold drawn steel post and welded rudder, with the weight on the boat, I think that is bare minimum. Haven't had any issues with corrosion as the stuffing box for it is above the idle water line - and it's painted.

To determine the strength, calculate/estimate it as if it were mounted on the bow stem, that is what it needs to be on the stern. The stern can see the same impacts and side-loads as the bow.

-Ron

[SailorHarry]

"I think this is a first for this forum, a true "post reply"."

Hah, good one.

Very good suggestions. For some reason I had not considered aluminum for the post, but make it thicker and of a good alloy...it makes sense. I was picturing the post being a separate piece, fitting into a sleeve in the rudder itself such that for repair the post could be removed from the top via a plug in the deck. The deck plug would also be removed to fit a tiller handle to the top of the rudder post in case of a steering failure. I found a hefty galvanized cast iron steering quadrant and will be using cables to the wheel.

Aluminum might be better just to reduce weight. It's no big deal on a tug but a thick, three foot steel rod is anything but light.

Thanks,
Harry

[farmerden]

Good idea Harry on the spare tiller handle.I known people to come home steering with a pair of vice grips under the deck and the wife yelling "turn left" It's fun to learn at other people's mistakes!! Den