Rudder Questions - 35 RP

[El Mar]

A friend of mine just got a 35 RP that is going through a make over as we speak.

Topic of the rudder came up and we're looking for a way to possible increase speed, maybe improve handling both in forward and reverse.

Basically have 10" before the post, and the rudder is 26" rectangle +/- and inch or so. Change shape?

Power is a 430 Cummins, Prop - 26 x 26 #3 cup with Hydro Slave steering.

Here are a few pics of what is currently in there, any comments or pointers would be greatly appreciate.

 

[F/V First Team]

Cut the lead down 4-5 inches, get rid of those ribs and angle the back.

Does the boat have power steering? If so you don't need that much rudder.

 

[Raider Ronnie]

Is it me or does the back edge of that rudder come pretty far back , almost to the transom ?
I'm sure that could be made into a whole different discussion of how a boat reacts different as far as placement of rudder forward or back.
I know my BHM the back edge of the rudder is about 4-5 ft before the transom.
I take notice all the time when in boat yards a see different boats and their rudder placement.

 

[El Mar]

Power is a 430 Cummins, Prop - 26 x 26 #3 cu.


Yes, Hydro slave steering.

 

[F/V First Team]

RP 35 rudder

I didn't do the painting, so don't say anything about the missed spot or the runs...

 

[El Mar]

Something like this? And mill the ribs down or off and mill the post down?

 

[Cfood]

Also might want to remove some of the bottom paint build up. Shed a few pounds and smooth out the surface. How much prop clearance do you have from the tip to the hull?

 

[captainlarry84]

In the photo it appears that you have a lot of unsupported shafting. I would want that shaft about 1.5" shorter or get a stern box 1.5" longer. Both will do nothing for speed, but it could prevent the snapping of a shaft.
I agree the rudder could be trimmed some, but it will do little for speed.

 

[traditions]

My son replaced his original fiberglass rudder with a new all stainless rudder with a full length shaft,1 3/4,with a small fin top and bottom.He lost 1 1/2 knots with the new rudder.Hauled out and put the glass one back in and gained back the lost speed.I would have never thought that glass rudder would go thru the water better,but swapping back proved me wrong.He's got a nice spare rudder now.I think we may foil it and try that later.How fast does that 35 go with the 430?It seems like getting one much over 20 is almost out of question.

 

[El Mar]

Basically a 16 knot boat.

Any other suggestions appreciated.

How do the cut lines look?

 

[F/V First Team]

Better, but maybe a bit long on the trailing edge. What is that made out of, steel? Why is it coated? And what's with all the extra stuff welded onto it all over the place?

 

[backman]

goo to know on the glass -> steel slow down. I got a glass one and cruise at 21 knots. I *was* going to replace it but...

 

[tunafishhkg]

Cape Island told me on the Duffy's at least, that the design like the pic by F/V First team, was the fastest FWIW

 

[El Mar]

Better, but maybe a bit long on the trailing edge. What is that made out of, steel? Why is it coated? And what's with all the extra stuff welded onto it all over the place?

Stainless, and don't know that is what came on the boat.

New owner painted it before the reinstall with epoxy paint.

 

[Brooksie]

My son replaced his original fiberglass rudder with a new all stainless rudder with a full length shaft,1 3/4,with a small fin top and bottom.He lost 1 1/2 knots with the new rudder.Hauled out and put the glass one back in and gained back the lost speed.I would have never thought that glass rudder would go thru the water better,but swapping back proved me wrong.He's got a nice spare rudder now.I think we may foil it and try that later.How fast does that 35 go with the 430?It seems like getting one much over 20 is almost out of question.

I know that is not the general opinion here, but of course an airfoil shape has less resistance than a flat plate, better lift too so can be smaller. What they are usually saying here is that frontal area is all important but that's not the whole story.

 

[hntrss]

Tell your friend good luck with the boat! That baby and I have a lot of history together! That was Huntress number 2. Currently getting ready to ramp up work on Huntess#4.

 

[eztbone]

soda blast

I had my bottom soda blasted last fall and Sean from East Coast Soda Blasting said they used 600# of soda and figures he was removing 1200-1500 #'s of waste (including the used soda). I used sea hawk tuff stuff epoxy 3 coats and 3 coats of their ablative paint. I haven't launched yet but I expect some improvement on my 15kts cruise if not at least a year or two off from painting the bottom. Good luck. BTW I have a fiberglass rudder and considered changing to stainless down the road...was surprised by hearing of loss of speed. Theres my 2 cents

 

[Blitzen]

I know that is not the general opinion here, but of course an airfoil shape has less resistance than a flat plate, better lift too so can be smaller. What they are usually saying here is that frontal area is all important but that's not the whole story.

Traditions,
The disturbed water flow over the stainless rudder from the full length shaft caused a lot of drag, resulting in lost speed. With the foil shaped fiberglass rudder, the water was efficiently flowing past the rudder causing minimal drag. If you had a stainless rudder like Travis posted I think your speed would have been the same if not better.

 

[Brooksie]

Traditions,
The disturbed water flow over the stainless rudder from the full length shaft caused a lot of drag, resulting in lost speed. With the foil shaped fiberglass rudder, the water was efficiently flowing past the rudder causing minimal drag. If you had a stainless rudder like Travis posted I think your speed would have been the same if not better.

I made a split rudder for a boat one time. Two airfoils really, split along the shaft centerline with each aligned with prop wash top & bottom respectively. Worked fine & I thought I noticed a speed increase but it could have been other things I did that winter layup.

 

[captainblast]

here is the rudder design we went with. cardboard version worked well. by removing 4" from the leading edge boat will track much better at cruise.