M-382 Rudder Modifications

[barefoot]

If you have an M-382, check out Jim McEntyre's modification to
his rudder--a new item on the M-38 Home Page.

 

[dick]

<div>After reading Jim McEntyre's modification description, I decided to perform the mod on my 382 ("Calypso", #161). I followed the design idea of adding structural foam to the top and aft edge, tapering to 0 at the bottom. Fortunately, there was a 383 ("Puff", Cape Canaveral) in the yard next to me (how convenient!) for taking measurements. Lenny is correct in stating that the 383 rudder is indeed extended aft at the top, not just up.My layup was different from Jim's, however. I sanded the rudder way beyond the gel coat and carried the new laminate far forward. I also used carbon fiber tape (available from West System) wrapped from the aft edge, completely around the forward edge of the rudder, and carried back to the aft edge on the other side. I also laid a few tapes vertically to support the new top plate. Since the aft edge of the rudder was extended about 10", I felt the laminate needed to be strong to support the additional torque without the benefit of the steel reinforcement available to the original rudder.I am still in the yard and performing the final fairing, so I have no pictures, but it looks identical to Jim's. Jim's comments about performance improvement have me very anxious to try it out!A separate but interesting note: Lenny pointed out the significant difference in the location of the waterline at the stern between Jim's 382 and his 383. I also noticed that difference when studying the 383 (Puff) in the yard. Why is that? Mine is about where Jim has his line, and Puff's is about the same as Lenny's. In fact, I extended my rudder a bit farther aft and up at the top corner since I could "afford" to without poking excessively out of the water. Is the 383 really that much lighter?
</div>

 

[aistqm]

Take a close look at the relation to the top of the ruddershaft and the cockpit drains. Its hard to tell because the pictures are'nt real clear but, it looks to me like the cockpit drains are located higher up on the hull.

 

[budfet]

<div>If you are interested in a copy of a 383-4 rudder, you might
try Foss Foam @ 813-577-0478 for a complete rudder for around $1300. I had priced one a couple of years ago. I believe this company made the originals. You must remember
that adding area near the turbulence formed by the prop wash, even when not motoring, and the surface wake renders the upper portion of the rudder ineffectual. To gain effectiveness the rudder should be increased in area below the prop, especially if you have a 3 bladed prop. I have
pictures of one I designed on a 382 with a 6 ft. draught and
it performs much better than the original. I will send pics
to those that are interested.</div>

 

[bschnur]

To clear up the waterline question, my boat is full of cruising gear, and the original waterline disappeared, so the waterline was moved up about 4". After haulout last year, the travellift operator told me my boat weighed in at 24,000 pounds, so it's no surprise that the waterline had to be moved up to compensate. Because my boat is significantly lower in the water than a stock boat, I would guess that my rudder modifications have produced a rudder that is somewhat larger than the 383/384 rudder in the top end. I'm still lookng for the piece of paper that has all the new dimesions on it.
I don't know if carbon fiber tape is required or not, but it sure couldn't hurt. Maybe there's an engineer out there who can comment.