Endplates on some fast boat rudders is common - seen this in many multihulls. Same idea as on wing keeled boats such as the ever popular Catalina 22. I believe the Jerry built M23s had.the same rudder setup as Idescribed for the M17. :: Dave Scobie :: M17 #375 SWEET PEA - m17-375.com On Tue, Jun 12, 2018, 9:23 AM Gerald Wolczanski <jerrywlinux@comcast.net> wrote:
The rudder on my M-23, "Robin's Nest" was considerably deeper than the keel with the CB up. Mercifully, the Chesapeake has a sandy bottom, and my few groundings resulted in no damage. The Mahogany rudder could not be raised because of the protruding stainless steel boomkin.
So I made a constant chord NACA0012 foil just a few inches shorter than the keel. I also put a Phil Bolger "end-plate" on the new rudder. The new rudder is 720 square inches (underwater) and the old rudder was 540 square inches (underwater).
The performance difference was dramatic. That old Mahogany high-aspect rudder looked cool, but performance-wise, it was no match for the new rudder. Before, when pressed, the boat would want to naturally round-up. This is a rare occurrence now....I guess the new rudder (and the end-plate) may provide more lateral resistance than the high-aspect rudder.
The new rudder really shines in slow speed maneuvering (docking). The high-aspect rudder was ineffectual.
I made a template, as suggested by Scobie. The rudder center was 1/2" ply and I just epoxied wood strips vertical and shaped it with a planer. I coated the rudder with epoxy, paint, and then ablative paint.
Judging by comments on other forums, the idea of an end-plate is controversial, but I think for shallow rudders (and airplane wings!), it works fine. YMMV
Jerry Wolczanski "Robin's Nest" Flag Harbor Marina St. Leonard, MD
On Tue, 2018-06-12 at 07:57 -0700, Bill Dixon wrote:
What is the best way to place and hold the mahogany rudder in its UP position?
Bill M-17 Robbin Windsor, CA
-----Original Message----- From: montgomery_boats [mailto: montgomery_boats-bounces@mailman.xmission.com] On Behalf Of Dave Scobie Sent: Tuesday, June 12, 2018 7:20 AM To: For and about Montgomery Sailboats Subject: Re: M_Boats: Rudder Craft Kick Up Rudder
The solid mahogany one piece rudders that Jerry made are very good and not at all prone to failure. In the 'up' position they are higher than the keel (centerboard up).
If you believe the rudder shape isn't right look online for a NACA12 foil and make a template to confirm the shape of your boat's. Very easy to refine the shape on a nice piece of wood.
:: Dave Scobie :: M17 #375 SWEET PEA - m17-375.com
On Tue, Jun 12, 2018, 7:14 AM Kevin Sandwick <ksandwick@hotmail.com> wrote:
Just curious, Is anybody using the Rudder Craft High Performance Kick Up Rudder on an M-17 ?
Not an inexpensive modification. Any thoughts?
Thanks
Kevin