Here's what it looked like:
Tom Lack had received complaints about windward performance of the lifting steel rudders and in 1980 he redesigned the rudders and gave the Catalac 8M and 9M new underwater profiles. This was a newly designed skeg hung rudder system. I heard this modification was a success and greatly improved the windward performance of the boats. Since this upgrade was on all Lack family designs going forward, I figure this will improve my 8M's handling and tracking. Here's an example of the redesigned skeg hung rudders:
After some inquiring on various forums and this web site, I found out (obvious?) pros and cons of both Catalac setups
|Original Lifting steel blade Rudders|
|Pro||keep rudders out of water when not sailing|
|no rudder fouling|
|no rudder constraints when 'beaching' common in some UK areas|
|Directional stability provides for snake tracks (more work on helmsman / autopilot)|
|Tendency to stall ie create turbulence when turned quickly|
|Heavier - a single rudder with its wood support block weighs about 20 kg|
|Poor windward ability|
|New Style Skeg Hung Rudders|
|Pro||better tracking stability|
|improved windward sailing (no figures provided)|
|lighter - rudders and skegs I built weighted 20 kg for both port and stbd|
|Con:||not always clear of grounding when 'beaching'|
I'm sorry to say that I'm unable to provide improvement figures on this redesign, as I never sailed the boat with the original rudder configuration. It may be a bit late in the game, but if anyone has done this conversion and can provide data on the Catalac before and after conversion, I would be more than happy to incorporate his findings/data into this article!
Phase One: decide on rudder/skeg dimensions... Initially I was thinking of building big skegs. After all, the whole purpose of adding skegs is to improve boat handling...
However, a second thought slowed me down. Skegs are a good thing, but keep them a reasonable size. I didn't want to end up with a boat which wouldn't tack anymore due to too much stability! Over sizing the skegs might mean backing the headsail to tack, maybe even having several attempts before a successful tack or even worse, I'd have to start the engine just to tack...
As I had no intention of going through trial and error sessions I decided to stay close to the original dimensions.
No one seems to have any dimensions or data readily available but the webmaster of this site (Rick) provided me pictures of his boat on the hard. From the pictures it wasn't difficult to determine the dimensions of his rudders and skegs...
The total rudder/skeg surface being a bit smaller than the surface of the original steel blades, I made my rudders just a bit larger than Rick's rudders, not exaggerating as I did not feel I needed to match up the surface area with the surface of the steel blades. (so maybe even bigger rudders would be OK)
The drawing below this sentence shows the dimensions I used, and could be used as a template or draft for others...
I then purchased a few marine grade plywood panels: 18mm plywood for skeg & rudder main part and
10mm plywood for rudder top. I then cut out all required parts, 4 of each :
Skegs : 4 sets
Rudders : 4 sets
Rudder top : 4 sets
The panels were then glued together with epoxy glue. I used woodscrews to hold the panels together... Screws were countersunk and covered with epoxy, then sanded smooth:
The rudder trailing edge, no router, no saw, we have abused our planing tool to do this one...
Next step was to attach the skegs to the hulls. I saw two options... Bolt the skegs through or glass them on. The Catalac skegs were glassed to the hulls, they were not part of the original hull mold.
My initial idea was to bolt the skegs through the hull into the rear wet locker.
In investigating this option I discovered the wet lockers had a double bottom. If I persisted in bolting the skegs onto the boat, this would actually mean removing the bottom of the wet locker just to be able to access the bolts and then creating and re-installing a new locker bottom or at a minimum install a big inspection hatch.
In considering both options again, I reasoned that if the boat stuck an underwater object, resulting in ripping the skeg off and causing a gap in the hull, that the damage would obviously be under that locker behind the main rear bulkhead. I could see no large difference between having the bolts ripped out with the reinforcement or a glassed skeg ripping out a hole when hitting something at speed. The result would be the same, and the boat would be in no danger of sinking.
This pretty much dissuaded me from going through the difficulties of bolting and remanufacturing the locker bottom. I glassed the skegs to the hulls under the rear lockers. I made sure to have a very strong hull attachment expecting the skeg to break before anything being ripped off the boat structure...
So to glue/glass the skegs to the hulls, the procedure I used was the following :
- Installed the rudders
- Put a thick cloth around the rudders to provide for space as both rudders and skegs will need some spacing and they both will still receive an epoxy underwater coating.
- Aligned the rudders straight, presented the skegs to the hulls and, taking into account the skegs are a few cm longer than the rudders. I then corrected the top of the skeg to the hull curvature (I had to check this on the boat as both hulls did not seem equal so I could not easily have measured this). Then we glued the skegs to the boat with epoxy glue, using the portable workmate bench in the photo.
After this all that was left was the underwater epoxy coating....
Here is a photo of the nearly completed skeg/rudder installation. (in this picture the stainless steel skeg shoe is not installed yet, there is a plug in the bushing in order to keep it clean from excessive epoxy. The shoe has been bolted to the skeg through this bushing)