I can read Sketch up, would like to see your models.  You are definitely getting better at it.  Time to use curved lines instead of straight for the bent panels.

rob

 

I assume you are referring to the cabin top. Those are drawn with flat pieces because I wanted to make the build easier and faster (i.e. cheaper). I just don't know how hard it is to curve the foam, especially since the cabin top has to be pretty thick to allow me to walk on it and adding backing strips would add labor. It would also let me use cheaper material, like the honeycomb stuff, although I would prefer not to. I would like it all curved and pretty, but I don't have a feel for what is involved in doing that. Your thoughts?

- Gardner

On Tue, Feb 22, 2011 at 9:40 PM, Rob Denney <harryproa@gmail.com> wrote:

 

Variable depth is nice, but not essential, if the rudders will kick up.  Drawings of one possibility posted under  "lifting rudders"  in the files.  Wheel steering adds another dimension or two to the equation.  Tillers are much cheaper, much less complex and take up less space.

If you do use a wheel, an oval quadrant solves the variable speed of turn problem and having the steering lines run to the windward hull should give enough play to allow the rudder to kick up without needing any fuses in the steering lines. 

The rudders getting crosswise is not a problem if the kick up fuse is working.  Not sure this is a big advantage when you are surfing down a monster wave, but it is better than breaking them.  It is pretty easy to make indestructable rudders (lots of carbon in the shaft), less so to make the supporting structure strong enough and light.

The bury can be as little as 7.5%, but the hull and mast get heavy.  You can share the sideways load using the beam to support the mast, but not the nosedive loads.  How little you can get away with vs the weight added  is an engineering problem.  I would stick with what you have and make a note that you are aware of the problem and it needs to be engineered.

Get "The Gougeon's on Boat Building"  from your local library.  An excellent book which describes all the lines and drawings required, as well as a huge amount of info on wooden boats and epoxy. 

rob

On Tue, Feb 22, 2011 at 11:24 PM, Gardner Pomper <gardner@networknow.org> wrote:

 

On Tue, Feb 22, 2011 at 7:43 AM, Rob Denney <harryproa@gmail.com> wrote:

 

The rudders have to rotate to steer 60 degrees or 360 makes very little difference.  Why add complexity getting them to cant as well?  25% is near enough for the masts.  There are arguments for more and for less, but 25% is what I use.

My main reason for the canting asymmetrical rudders is that I can't (no pun intended) figure out how to make the regular rudders work for variable depth, kickup and not damage the steering when they do kick up. If you could post a diagram or photo showing how you do that, it would be great!

There are a few other factors, like I am concerned about the rudders getting crosswise and snapping off coming down a big wave, and I am not sure about the steering sensitivity when you have to rotate the rudders 180 degrees to shunt; will a small wheel change oversteer when you are just on a straight course, or will you have to turn the wheel a dozen times when shunting to get the rudders around 180 degrees. But, mostly, is I just can't figure out how to kick up regular rudders and not mess with the steering cables and such.

Work on 10% for the bury.  Can get away with less, but the weight and complexity go up.  Would not go less fore and aft, as it has to be strong enough to capsize it stern over bow.

So, you mean that I need to increase the height of the hull to at least 4' high for proper bury? And 4' in the beam too? I don't like that much, but I also don't like weight and complexity. Or are you saying that I can split that 10% bur between the hull and beam, the way I have my plans drawn?

Re help, ask away.  I would rather explain than do, but if you can't I will. 

I am fine with doing the work. Answering questions is great. It might help to get an example, but you could probably point me to one.

rob

On Tue, Feb 22, 2011 at 9:06 PM, Gardner Pomper <gardner@networknow.org> wrote:

 

On Mon, Feb 21, 2011 at 10:22 PM, Rob Denney <harryproa@gmail.com> wrote:

 

Looks good. 

The secondary beam is clever, but what happens to the rudders when it folds?

The rudders do limit how much the boat can reduce the beam. I haven't figured out exactly what the limit is, but I think it is between 10 and 11 feet, until you take masts out and can disassemble it. But, since it looks like I have other rudder issues, I will rework that part. 

My understanding of canting the rudders is that the centre of pressure has to end up behind the centre of rotation.  Canting the shaft and the blade may not do the trick.  Might also look at spreading the beams a little further to move the rudders more outboard.  

I have another rudder design that does not rotate the shaft along with the blade, but it is a little more complicated to place on the beam, instead of on the hull. I have some ideas on that, so I will rework it. That will also fix a number of other issues, by allowing the rudders to be outside the beams, instead of inside, and they also won't get in the way of the folding mechanism. I will draw it up and post.

On a related topic, how do you determine how far apart to space your masts in a schooner rig. I wanted to keep the end of the boom within the length of the boat, so it seemed that the masts should be at least 25% of the lw hull length away from the ends. Do you have a better rule of thumb?

 

Upstairs galley is neat.  Is there enough room above it for cooker and kettle? 

I am not sure what you are asking. The galley floor is level with the cockpit floor, 2' above the waterline. Then there are standard size cabinets (3' high, 2' deep). The stove (cooker?) is mounted in one of those cabinets. The only thing above it is the hardtop, which would be 3.5' higher, to give a 6.5' headroom clearance.

If this is for the Wooden Boat competition, let me know if you want any help getting the drawings into the design format.

Yes, this is for that competition. I wasn't naming it that way, because they say it has to be a previously unpublished design, but I don't consider posting it in this forum as "publishing" it. I would be thrilled if you were willing to help out with the lines. I expect I will also be asking for help with some other dimensions, like mast diameter and the bury and overhang for the beams.

Speaking of bury, I was curious if you think that splitting the bury between the lee hull (2') and the beam (3') was reasonable. Most all the heeling force will be on the beam, so I wasn't sure if 3' was enough, but the forward force will all go to the hull, so is 2' enough for that? Having to have 4' of bury in each would be disadvantageous.

- Gardner 

rob

On Tue, Feb 22, 2011 at 9:52 AM, Gardner Pomper <gardner@networknow.org> wrote:

 

Hi all,

I haven't posted a design in a while. I have been working on one that is more involved than the others, I have done; particularly when it comes to drawing them. Anyway, there is a new directory, Raider, under "Gardner's layouts" in the file section.

To get through the basics, this is a design for the "raids" that are becoming popular here in the states. This will sleep 3, for short periods of time, and is designed to be easy to transport and launch. It can be shipped in a container, folded while on the water and trailered. Bare weight should run about 1000 lbs, but I have not calculated it out exactly yet.

Now to get on with the odder things about the design. I don't know how well I can explain these with just words, so you will probably have to refer to the drawings to make sense of them.

It has a new folding system, where he beams pivot around the masts (it is a 2 mast schooner rig). By having the masts support the beams, the lw hull can be truly minimal. As drawn, it can be made from a single 8' wide panel, 38' feet long. The beams come up the mast and there is a bearing so that they can pivot around the mast to let the boat stay upright while folding. The beams are each a single piece from the mast to under the bridgedeck area, so they should be easy to make strong. There is a second, half-length, lightweight beam with a pivot pin under the bridgedeck and another at the midpoint of the real crossbeam. This secondary beam only has to be strong enough to support the boat in calm water while folding.

The rudders are beam mounted. The are also asymmetrical, so they don't need to flip 180 degrees when shunting. Instead, the beam bearing is free to rotate +/- 20 degrees or so to let the rudders cant to bring the center of pressure "aft". I know this was tried before and found that the rudders will not cant on their own, due to the water pressure. So, I have added a mechanism that will pull the rudder into the correct position automatically.

The direction the rudder should cant is the same as the direction of movement of the boat. The wingmast and boom will always be trailing aft of the direction of boat movement, so I have added a bulge on each side of the mast, to act like a cam when the mast rotates. When the boom is brought around to the opposite direction during a shunt, the cam will move a lever, which is attached to a bungee, that will pull on the rudder assembly to make it rotate to the new position. As the boat stops at the midpoint of the shunt, there will be no water pressure on the rudder and the bungee with rotate the rudder assembly to the correct canted position.

The rudder assembly is constructed around a beam mounted drum, to allow the canting back and forth, and also has a breakaway "fuse" that allows full rotating in case of the rudder striking something in the water. There is an arm coming out from the bearing, which has a vertical pin, allowing the port/starboard rotation of the rudder for steering. The arm is positioned to act as a stop to prevent the rudder from oversteering to the point where there would be excessive stress. It is anticipated that a steering range of +/- 30 degrees should be adequate. The steering pin is attached to a daggerboard case, which secures the rudder blade, but also allows it to be raised and lowered. When fully raised, it can be above the level of the boom, because in the event that the boat is backwinded, the boom hitting the rudder blade will act like a grounding and break the fuse, allowing the rudder to rotate out of the way.

The rudders are mounted inside the beams, because the canting mechanism means that the rudder is lower in the water when the boat is travelling in one direction vs the other. With this rudder placement, the stern rudder will be deeper in the water that the forward rudder, moving the boat's center of lateral resistance aft.

I have put quite a number of ideas into this design that I have not seen drawn up this way before, so i am particulary interested in how it looks to the rest of the group. Please give me feedback.

- Gardner Pomper

Pasadena, MD