Kickup rudder critique

[Scuff]

Since the board tapers is there a minimum the board can be retracted so that it doesn't cock in the sleeve. Looks good!

 

[freddyj]

The lower pin will be a wood rod, so it breaks if grounded. The board is not tapered so it van be used in different positions.

 

[tropostudio]

Kick-up transom taken even further: https: //pjkubis-designs.com/design-concept-and-naval. Takes care of a sugar scoop and swim steps if you need those, too.

 

[wet feet]

That's one way to do the job,but I don't see any advantage beyond reducing the draught of the boat.Having a hull section between the major part of the boat and the rudder won't make it easy to access the notch where rope or seaweed will be lodged.I believe a better solution is that which is commonly used in the IMOCA class.The diamond shaped frame is pivoted and very well located and there is good access to the underwater section.

 

[SolGato]

That's one way to do the job,but I don't see any advantage beyond reducing the draught of the boat.Having a hull section between the major part of the boat and the rudder won't make it easy to access the notch where rope or seaweed will be lodged.I believe a better solution is that which is commonly used in the IMOCA class.The diamond shaped frame is pivoted and very well located and there is good access to the underwater section.View attachment 195349

I think Tropostudio was pretty clear about what the advantages/benefits are over other designs -you can have a functional sugar scoop and even swim steps incorporated into the hinged section.

For those of us who like to get easily in and out of the water, or just closer to water level it makes a lot of sense.

It’s also a very clean design that doesn’t break up the traditional lines of a boat.

I’m sure the racing design does a fantastic job, but it’s pretty fugly if you ask me.

Interestingly the hinged false transom/stern section doesn't seem to be shown in the drawings.

 

[tropostudio]

I'm not so sure the 'kick-up transom' section on the trimaran would be any more prone to fouling or a hassle to clear than any other rudder, kick-up or not. The IMOCA rudder design actually looks very stout and functional. I bet there is more materials, time, and engineering (=$$) than most any other option discussed in this thread. What appeals to me from an engineering standpoint is any solution that gives decent lateral support to the rudder blade as it pivots back and up. Wide bearing support and triangles make sense.

 

[SolGato]

I see I posted about my Tri’s system earlier in the thread but didn’t post photos.

Just ran a new downhaul/kick up control line yesterday as the previous owner had too large a diameter line for the size blocks that are housed inside a vertical tube glassed to the inside of the transom.

I’m pretty sure at one point it had a trip cleat of some sort, but that went missing some time ago. I heard it liked to let go at high speeds so it was replaced with a standard cam cleat. I’m working on designing a new trip cleat snd have moved the line so that it remains in the trunk under the hatch rather than coming through and into the cockpit.

I also plan to install either a split mid step in the scoop or a drop in step. And I have added a removable support that holds the rudder assembly kicked slightly back and up at a shallow draft angle for launching and beaching that still provides some steerage.

With this design, the rudder system is a complete assembly that fits into a slot in the transom. It can easily be removed for servicing, trailering, painting, etc..

Once installed, it gets cross pinned at the top allowing it to swing up and back on impact.

There are as well two addition pinning points for a mid and full vertical lift out of the assembly.

When deployed, you have a functional sugar scoop that provides clutter free access onto and off of the boat.

 

[tropostudio]

That is pretty slick! I see where another step would be helpful. Would it land about where the current handholds are located? Split steps glassed in with slots to grab onto would look great, while blending in with the rest of the work.

 

[rob denney]

I'm not so sure the 'kick-up transom' section on the trimaran would be any more prone to fouling or a hassle to clear than any other rudder, kick-up or not. The IMOCA rudder design actually looks very stout and functional. I bet there is more materials, time, and engineering (=$$) than most any other option discussed in this thread. What appeals to me from an engineering standpoint is any solution that gives decent lateral support to the rudder blade as it pivots back and up. Wide bearing support and triangles make sense.

Me too. The rudder must be supported all the way to fully kicked up, otherwise the side loads will damage the hinges. The lifting stern and to a lesser extent Sol's will need very strong hinges if, eg a breaking wave hits them when they are kicked up and floating

 

[wet feet]

I quite like the rudder setup in post #37 and when down it shares with the IMOCA the use of a notched hull for lateral bracing.What might not be particularly clear is that the IMOCA also has about 350mm of hull beyond the actual transom to provide a step in the style of a sugar scoop.What I'm not so thrilled to see on the trimaran setup is the central moulding mounted a bit too high to provide a seating for the pivot,while leaving a lateral step in the immersed portion and a gap for water to move through.I'm guessing that somebody didn't loft the arrangement and include enough length for the rudder stock,otherwise the rudder could have been made to more closely conform to the keel line of the hull,for greater efficiency.I hope nobody thinks I'm being too harsh,but the thread title includes the word critique and I hope we will all gain knowledge from absorbing the various contributions.I would speculate that a tubular stainless fabrication that approximates the IMOCA principles,and has a hull shaped section located in a matching cutout might not be a huge amount more expensive than the enclosed moulding on the trimaran.I also hope that anybody interested in rudder design who lives within travelling distance of New York made the trip to ponder the solutions the IMOCAs use for all sorts of systems over the last couple of weeks.

 

[SolGato]

Ya, out of all the setups I’ve seen I think I like the cassette/hinged hybrid design best.

The cassette for its optimum steer ability/vertically trimming of the board, and the hinge with a fuse to allow it to kick back on impact.

But it would be hard to give up the scoop. It just makes life on mooring so much easier. Small boats, especially multihulls can be awkward to board unless you’re steeping onto one from off a dock.

My setup is good for the occasional coconut or sandbar strike, but not the kind of stuff one might see crossing oceans or sailing around the PNW!

Agree that a wide pivot/hinge supporting full kick up is best. I know some people slot the cassette housings at the rear and install fuses so the blade can bust out.

I like what the poster did - the hinged false transom/cassette combo. It sort of a a modern take on the Seaclipper design.

tropostudio - Yes, mid step at the handle level. The handles were primarily installed to support the mast cradle for trailering. It has legs that drop in the open slots.

Before I go hog wild, I’ll probably make a split drop in version that uses the handles in the same way as the mast cradle since they are already well anchored.

My thought was a mid step would also double as a secondary fence for the rudder assembly when it kicks back so as to alleviate some side loading from the upper pivot point,

I’ve even considered adding a Linear actuator for electric trim. It would be hidden inside the stern. Why? I launch and retrieve my boats from a small narrow shallow river sometimes with rolling swell pushing from behind. A trim switch on the tiller would be pretty handy.

 

[wet feet]

I would like the hinged false transom a bit more if there were some kind of positive lateral location near the keel line and it was less reliant on the rigidity of the hinge pivots.I found a better view of an IMOCA that clearly shows the scoop and you can see that it is large enough for a liferaft to sit on.

 

[SolGato]

I quite like the rudder setup in post #37 and when down it shares with the IMOCA the use of a notched hull for lateral bracing.What might not be particularly clear is that the IMOCA also has about 350mm of hull beyond the actual transom to provide a step in the style of a sugar scoop.What I'm not so thrilled to see on the trimaran setup is the central moulding mounted a bit too high to provide a seating for the pivot,while leaving a lateral step in the immersed portion and a gap for water to move through.I'm guessing that somebody didn't loft the arrangement and include enough length for the rudder stock,otherwise the rudder could have been made to more closely conform to the keel line of the hull,for greater efficiency.I hope nobody thinks I'm being too harsh,but the thread title includes the word critique and I hope we will all gain knowledge from absorbing the various contributions.I would speculate that a tubular stainless fabrication that approximates the IMOCA principles,and has a hull shaped section located in a matching cutout might not be a huge amount more expensive than the enclosed moulding on the trimaran.I also hope that anybody interested in rudder design who lives within travelling distance of New York made the trip to ponder the solutions the IMOCAs use for all sorts of systems over the last couple of weeks.

Not sure what you are describing, but in the last photo the assembly is not home in the slot. I have to leave it popped out slightly so I can step aboard without the rudder hitting the ground while keeping a good water drainage angle. Perhaps it not being home is creating the lateral step you are describing?

When the rudder assembly is fully home in its pocket, it completes the shape of the hull perfectly like a puzzle piece.

I like the IOMCA design. As a fabricator it makes total sense.

Here’s my take on a kick up motor mount design I made for my solar electric cat. No direct relation to rudders since I use differential thrust to steer, but the kick up feature is applicable.

The design parameters were that the system needed to mount in place of the stock rudders using factory threaded inserts, that the system have adjustable trim, and anti cavitation plates built in.

I had always planned to add linear actuators for electric trim, but started out with collars that could be slid and locked in place along the deploying arms for preset trim settings -trailering, shallow trim, full depth. The collars were caught against the slot in the transom boards and the weight of the motors and thrust kept the motors submerged. When something is hit, they can kick.

Years later I finally added actuators which required a bit more complexity by adding some roller bearings, a fence, and a double jointed arm to allow kick up.

I just discovered you can trim YouTube video clips and send links that start at a specific start point.

Let’s see if this works:

https://youtube.com/clip/UgkxeikiXdbiiRlKOHDqGbmsYy1na-yKs0a4?si=c44pcqw0sS8ghiw5

https://youtube.com/clip/UgkxR-ryupkH3QbqP-IE9-94cXtRKXimmGP6?si=c2Ch3vKfOYawv4F5

 

[peterbike]

Solgato, the last one is brilliant.
I think you have just started a new trend !

 

[C. Dog]

@SolGato I've been checking out AliExpress a bit lately as they have reasonable gear cheap if you can eliminate the dud stuff. They do wireless relays for your linear actuators with a small remote transmitter like a garage door one. I've bought one for a portable bilge pump system I'm assembling with an 18V drill battery. They also have lots of actuators.