Mono hull rudder and turn fin questions
 

Hello all,

I am just curious to see the replies and any ongoing discussion these questions raise:

Do you modify your rudders at all? IE sharpened leading edges, rounded bottoms etc?

When mounting turn fins, do you mount them both sides (port and starboard)?

Also, do you sharpen them at all on the leading edges?

When mounting them, do you prefer to angle them to make them perpendicular to the bottom of the hull or do you mount them "straight up and down", ie parallel with rudder?

Look forward to any answers and discussions.

Thanks,

Glenn

RE: Mono hull rudder and turn fin questions
 

as for sharpening rudder or turn fin they should have a nice slim front edge
to knife blade them it will make the boat very twitchy to steer most guys round the bottom front of rudder like a 5 mm radius makes for better entry an reduces drag
as for turn fins position them at a roughly 90 degrees to bottom of boat is a good starting point even around 110-120 works good depends on boats corner speed an type of hull
some boats do not even need turn fins

RE: Mono hull rudder and turn fin questions
 

my rudder and turn fins are sharp and rudder is rounded on the bottom edge.turn fins are 90% to the bottom of the hull on my woody.on the stepped vee i dont have fins but the rudder is very sharp and thinned also rounded bottom edge i got the rudder from Ian Webster ;).my rudder is like the one in the drawing.

RE: Mono hull rudder and turn fin questions
 

I never sharped the rudder and turn fin but after looking at mart's third photo, I should do that because it might increase a little MPH I think.

RE: Mono hull rudder and turn fin questions
 

I would not get too carried away making razor sharp edges on the rudder or turnfins. Unless your after that 1/10 of a second increase per lap racing it is not going to do any more than spill blood (literally).

A sharp prop makes a lot more sense than a sharp rudder - how fast is the leading edge of a prop travelling through the water Vs a rudder blade?

RE: Mono hull rudder and turn fin questions
 

i use to round the bottom of my rudders, and play with all kinds of little tricks... basically, it was a waste of sanding, and i never saw any differences. now i run them the way they come.. with just a slight sharpen job on the leading edge.

RE: Mono hull rudder and turn fin questions
 

I agree with that a sharped prop can more speed, it could turn over 20000 RPM in the water vs a rudder blade hitting the water in 60-70 MPH, I can't figure out the sharped blade's adventage of speed increase.

RE: Mono hull rudder and turn fin questions
 

in real race i have worked on never sharpend leading edges of rudders foung that the small radused egde worked better as it causes a small vortice down sides of blade acting as a buffer reducing drag
plus if you hit something more likely to bend leading edge easier causing more drama than its worth

RE: Mono hull rudder and turn fin questions
 

plus if you hit something more likely to bend leading edge easier causing more drama than its worth

That's why I didn't use a brass sheer screw to the rudder for in case if the rudder hit something, the rudder blade might be saved.

RE: Mono hull rudder and turn fin questions
 

i dont use sheer screws either but the rudder still take a good hit to fling it up especially at 50 plus mph an when you thin it by sharpening it it is more likely to damage blade
but everyone has a preferance each to their own thats the fun of this sport so many variables in it ;)

RE: Mono hull rudder and turn fin questions
 

All i can say is my friend did some tests with diff rudder and strut setups in a water tes tank at uni and all the evidence he and his tutor who races full size offshore boats all showed a good % of increased performance.It might be hard to see but it is there,they also turn the struts round so the prop is further back from the strut blade which creates less drag.When water hits the strut blade it takes about 1" past the strut for it to join back together so if the prop is tight to the strut its in disturbed water whereas been 1" or so back its in clean undisturbed water again.It stands to reason if any blade is flat or blunt it will cause drag,the sharper or thinner it is the less drag.Also a flat rudder at the base is classed as a planing surface thus making your deep vee mono hull now a hydroplane ;).Matt my rudder blade is like a knife,(sharp) its also rounded on the bottom edge and at the leading bottom corner (curved)this was done by my friend Ian Webster who i bought it off its also thinned considerably compaired to a stock rudder,i can only asume he did this for a good reason as he spends a lot of time arround guys who race competativeley.

RE: Mono hull rudder and turn fin questions
 

Thanks for the replies gents, some interesting reading there.

Glenn

RE: Mono hull rudder and turn fin questions
 

the rudder i run on my new boat has only one bolt so if it hits anything it will kick back.on my woody i used a nylon sheer bolt.