Rudder placement

[sean-nós]

Hi guy's this is the crackerbox I am building and I would like to get some advice on the rudder, it has a plate on it to stop air been sucked in and I'm not sure weather the plate should be recessed into the hull to leave it flush or will it be ok left a few mm off the hull like this.
Any advice would be great thanks.

[daiquiri]

My two cents worth... It will make a little bit more drag this way but nothing to excessively worry about. It will work inside the boundary layer of the hull, where the water velocity is much lower than the free-stream velocity. On the other hand, the prop shaft and strut will be exposed to the free-stream water flow, and will hence produce much more drag. If you still want to minimize the profile drag of the anti-aeration plate, you can round or bevel it's forward and lateral edges.
Cheers

[philSweet]

I think the simplest might be to boss the hull so that the plate lands on a flat. The gap looks like it is purpose made to conduct air to the front of the rudder. Not really my thing, though. Hopefully one of the go fast guys will chime in.

[johneck]

I think that the gap may help keep water flowing between the plate and hull and avoid air being sucked in from the transom. If you fair the plate to the hull it may no longer work properly. However, it would be an interesting experiment.
I also agree that the drag associated with this gap/bump is probably quite small compared to the shaft/strut and the rudder itself. The drag of an angled cylinder (shaft) is over 20X the drag of a flat plate on edge.

[johneck]

I also forgot to add that a fairing at the fwd end of the bearing barrel would probably help greatly as well.

[sean-nós]

Thanks for the replies guy's. interesting point johneck the gap could help the flow of water over the top of the plate and stop water been sucked in Hmmmm
I am not too worried about a bit of drag but I like the idea of maybe fitting a cone on the shaft infront of the strut, can you buy such a thing ? I'm sure the lads that race hydros and the like don't have a blunt bearing face like mine.

[johneck]

I am not sure where, but I have seen the fairing added onto the shaft in two halves, bolted together, just forward of the barrel.

[sean-nós]

How about one of these cut in half kill two birds with the one stone


Or this one.

[johneck]

Yes, that seems like a good way to go, until the anode is excessively corroded.

[mr hot rod]

Hi Fergal !

The Glenwood Marine Equipment Catalog lists a stainless steel strut collar which is set-screwed to the propeller shaft just ahead of the strut.
It prevents the shaft from backing out of the shaft coupler when in reverse. Always a good idea to run one !!

See page 42, Item # 4001 for a 1" shaft and Item # 4002 for a 1-1/8" shaft :

http://www.glenwoodmarine.net/Catalog/STRUTS.pdf

You won't find this part in Glen-L's Inboard Hardware Catalog, but if you give them the Glenwood part number they will ship it to you.

________________
Paul Kane
Kane Custom Boats
Chelsea, Quebec

Building the Glen-L Hot Rod : http://www.kanecustomboats.com

[sean-nós]

Thats great Mr hot rod cheers Makes sense to put one on and yet I have never seen one in place.

P.S. What do you think of my setup will it work, I could only get the strut down to 14 degrees so I'm a bit worried about stern lift if so could I fit a rocker plate under the engine to lift the bow a bit.

[mr hot rod]

No doubt that a two or three blade propeller and a wedge rudder would be better suited to that style of boat, but sometimes you just have to run the parts that you've got. Once you've got a few hours on it, you can always upgrade parts as your budget allows.

You can see the strut collar in this photo :

________________
Paul Kane
Kane Custom Boats
Chelsea, Quebec

Building the Glen-L Hot Rod : http://www.kanecustomboats.com