Rudder thickness and design

[Lee Y]

What is the maximum thickness of the Idasailer HDPE rudder below the water line? Also, what if you have a one inch thick HDPE rudder. Do you need do anything more than round the edges? I'm thinking of building a rudder but am trying to figure out how thick to make it below the water line and also, how will the boat handle as the rudder gets flatter. I know that HDPE is somewhat hard to shape so I want to avoid doing much shaping other than to round the edges with a router. I love to build and want to avoid the cost of a replacement. I appreciate the previous input. This website has been extremely helpful over the years.

Thanks for your input again

 

[C Jones]

I have the Ida Sailer Rudder/ Tiller on my h23. I have pictures of it posted on my Public profile. I can measure the thickness and length below water line for you today and post that info tomorrow. I was going to have a sunbrella cover made for it and if memory serves me right it is 1-7/8" thick from top to bottom on the leading edge. If you can duplicate the performance of the original Ida Sailer, you will not believe the performance. Its like going from an old pickup with no power steering that road walks all over the highway to a brand new Sports car. You won't believe your in the same boat. I love mine and hope you can duplicate the rudder for yours. I,ll post specs tonight or tomorrow. Charles

 

[C Jones]

Here it is
Length below water line 48"
Leading edge to back edge 12"
Maximum thickness 1-3/8"
Rounded leading edge to full thickness is done in 2"
Full thickness is 4"
Taper from full thickness to back edge is done in 6"
Back edge is 1/4" thick
Leading bottom edge is rounded at about a 3" diameter
2" + 4" + 6" = 12"
Take these measurments and look at the pics of it. Let me know if you need more info. Goodluck, Charles

 

[Alan]

Foil shape is a science with lots of technical info needed. All fixed shape foils are compromises. Short fat foil shapes generally have lower stall speeds and higher drag ratios. Long fine entry foils are more efficient for speed but have a narrow range of lift.

Of course, a piece of plywood can steer the boat but the shape is critical for good control and efficiency. Ida Sailer makes a good quality high efficiency foil. If you know someone with an Ida Sailer you could take the templates and make a duplicate but just guessing at a shape is like shooting craps.

 

[hagarone]

No need to guess at the shape of the Ida Sailor foil shape. It is purported to be a NACA (National Advisory Committee for Aeronautics) 0012 which is a standard calculation based on a standard formula. There are foil calculators available that easily calculate the points needed to determine the foil shape. One could use that to make a template of the surface curvature and get very close to perfect by shaping and checking the surface with the template. Another way may be to cut some "steps" in the form at various on the surface profile and fill the voids with fairing compound and while wet, use the template as a form, dragging it along the surface and leaving the wet compound in the shape of the foil. I doubt that a flat piece of material merely rounded on the leading and trailing edges would be very dynamic. Of course, maybe it would work great, just an opinion.

Here is a link to a foil generator, just get the thicknes and length (fore to aft) of the Ida Sailor and plug it into the 0012 profile. It will generate the points.

http://www.ppart.de/aerodynamics/profiles/NACA4.html

Hagar

 

[VT Fitz]

I would love a new Ida rudder. It's on the list. Unfortunately, there are several items ahead of it, such as stern rail with seats. A new 9.9 4-stroke was this season's big-ticket, hugely positive addition. The coffer is only so deep! So many choices, so little time...