PedalTheOcean.com



THIS BLOG HAS MOVED
adventuresofgreg.com





Your stability ideas

In my post after the capsize test:
http://www.adventuresofgreg.com/HPB/2007/10/capsize-test.html

I asked for your suggestions as to how I could gain some extra temporary stability in WiTHiN for standing up through the hatch, entry, exit and just general moving about the hull.

For this prototype version of WiTHiN, I'll be hauling it in and out of water often so I do need to consider the complications inherent in transport, but it is my goal to try as hard as I can to make the prototype version of WiTHiN as much like the actual ocean boat as possible.

Thanks for your replies - I received some really great suggestions. Here are some of them:

-----------------------------------------
Daniel Grow suggests a deployable dagger board. A thin, lead filled flat fin would slide down a narrow well similar to the drive leg well situated in about the middle of the boat - probably just behind my seat. When in place, it acts like a keel with ballast and can be removed for transport. Australian ocean expedition kayak Lot 41 uses something similar:

Lot41 dagger board inserts through outside top of the kayak deck

view of the dagger board from below

A problem with the removable dagger board is the amount of room the well would take up inside WiTHiN.
-----------------------------------------

-----------------------------------------
A suggestion from Jim Barrett is outriggers that slide out from under the seat. Something like this could work, as there may be room behind the seat back for two slots to hold the outrigger arms. I modelled up an idea that could work for the slide-riggers. I could glass two stainless steel tubes into the inside cockpit directly behind the seat (right around where the rear bulkhead is). These tubes could hold the outrigger arms as they slide out into extended position, and slide back into retracted position. I could hold the arms in place with pins inserted from the inside, but I'm not sure how I could move the outriggers out and back from inside the boat.


slide-riggers retracted

slide-riggers extended



When retracted, the floats would be up above the water level, and when extended, then would be right at the water level.

I did some calculations and found that with a moment arm of 36" to the float, the float would need to support about 36% of my weight as I stand up and climb in through the top hatch - or about 57 pounds. At a buoyancy of 60 lbs per cubic foot of foam, I would need about 1900 cubic inches. A bulb-type shape of around 8" diameter x 36" long would be close.

The danger in this approach is if I ever had the outrigger extended, and WiTHiN were to capsize, it could be fairly difficult to retract the arms from within an upside down WiTHiN. Also, even with the floats retracted, I am not sure that WiTHiN will still be capsize proof with these buoyant floats hanging off her sides - that is a major concern.
-----------------------------------------

-----------------------------------------
Warren Beauchamp had this great suggestion of making some flip-down water wings. I'm not sure how I could hold them down in place - possibly with some struts kept inside the boat. In the "up" position they should be fairly bullet proof. If they were in the down position, I'm not sure how well WiTHiN would right after a capsize. I'm not sure if these fairly small wings would be buoyant enough to support my weight climbing in through the top hatch


-----------------------------------------

-----------------------------------------
Alex came up with this novel idea for an articulating keel. The keel in the "up" position would allow for easy transport on the trailer and moving into and out of the water. It would also retract for normal 'cruising' operation when I don't require the full weight of the ballast for moving around. It is a bit complicated and could be prone to break. Click here to see the animation of Alex's articulating keel
-----------------------------------------

-----------------------------------------
Here is my idea called "Swing-rigger" a single (or double) outrigger that swings into position. Controls to activate the swing arm could be from inside the cockpit. I'm not crazy about all the moving parts.


-----------------------------------------

-----------------------------------------
Here is a new idea I had about using my spare paddles. It may have some merit. Since i must carry paddles with me, I could insert these paddles into stainless steel receptacles glassed into the roof of WiTHiN. The receptacles shown in the illustration below is shown on TOP of the roof, but they could easily be glassed in right below the roof. Paddle floats could be placed over the paddles. The paddles could be held in place with a lock pin from the inside. I think that there would not be enough floatation with standard paddle floats, as i would need about 1900 cubic inches. I also don't like the idea of having to stand up through the top hatch to assemble them and risk tipping over.



-----------------------------------------

-----------------------------------------
Rick Willoughby suggests that a keel with ballast is the only way to go for the ocean boat, and since I want this boat to be as much like the ocean boat as possible, I should probably heed his advice and pursue a keel-based solution. Rick says that ballast suspended 3 feet below the hull in a keel would be about 1/4 of the weight of ballast on the floor of WiTHiN. Since reduced weight would reduce the draft, weight carried in a keel below the floor would be more efficient in this case. But, the amount of weight in a keel required to balance the boat while standing or climbing in from water height would be quite a bit more.

Outriggers on an ocean boat have to be retractable for safety reasons (A capsized multi-hull is usually not correctable). Anything that big that is made to move would be complex and could (would) eventually break and I just don't think it is worth the risk. I am really tempted to take a short cut and add some removable outriggers (like the paddle-rigger concept or the slide-riggers) for this prototype boat, but that kind of defeats the whole purpose of the boat. I am trying to gain confidence that the final design we come up with will take me safely across an ocean. Experience in a boat that is as close to the final ocean crossing boat as possible will give me that confidence.

All that said, I think the best option is to build a permanent keel as illustrated below onto the bottom of WiTHiN. One departure from the final ocean boat that I would allow, is some kind of hinge to allow us to off-load WiTHiN from the trailer to the water without having to bolt-on this heavy keel (under water) every time. For transport and loading, the keel could be held up with a line and a winch or something and a lock-pin to secure it vertical once in deep water. Reaching down to insert a pin from a dock would be fairly easy to do.




According to my calculations, lead shot weighs 470 lbs / cubic foot, or .271 lbs / cubic inch. A cylindrically shaped ballast bulb measuring 24" long x 4" diameter would equate to a total area of 302 cubic inches and if filled with lead shot would weigh about 81 lbs. If ballast positioned 3 feet below the boat is 4 times as effective than ballast on the boat floor (due to the moment arm), then to convert my 80 lbs of floor ballast to keel ballast, I would require only 20 lbs in the bulb. To stand and climb in, I will require much more. During our capsize test at the lake last weekend, I tested a temporary keel with 50 lbs on it, and it was probably sufficient for standing and some simple maneuvering. Therefore, I think that a total of 80 lbs, 3.5' below the hull should work.

The keel could be bolted onto my seat rails, then glassed into the hull bottom, so I think it would be pretty strong. A hinge would be placed at about the same depth as the rudder and drive leg. This is easily reachable by a stretched out arm while lying down on a dock, so the insertion of a lock pin wouldn't be that difficult.

Another retraction option for this keel is to allow it to slide up or down a tube that is glassed into the boat. This would allow me to raise or lower as required. I am not sure that there would be any advantage to having the keel up against the hull bottom while under-way, as the weight would be the same and the drag would be very close to the same as if it were fully extended 3.5 feet down into the water. The only benefit being able to lift the keel up would have is for loading the boat onto and off the trailer. I think a side hinge is easier to make and avoids putting any holes through the boat.

Labels:

9 Responses to “Your stability ideas”

  1. # Anonymous Alex

    Greg, if you opt for a simple keel for Within why not make the spa section long and thin like an aerofoil? I'm not hydrodynamcs engineer but I would have thought that a long keel would be harder to tip than a thin weighted keel (if that makes sense?)

    If you had a keel shaped like a quarter circle, you could have it rotate rearwards into a slot along Within's centre line, you could either pull it up with a cord or just let it bump up if it hit anything.  

  2. # Anonymous alex

    Still like my parallelogram idea though *wink*  

  3. # Anonymous Anonymous

    How difficult would it be to merge drive leg and keel? I think having the axis of the propeler in the axis of the keel balast would simplify the submerged shapes a lot and therefore reduce the drag.
    Regards
    Jirka  

  4. # Blogger Adventures of Greg

    Merging the keel and the drive leg is a good idea, but I need to be able to remove the drive leg for servicing. If it were 3.5 feet deep and 80 to 100 lbs, that would be very difficult

    gk  

  5. # Blogger Michael Lampi

    How about placing lead-acid or NiCad batteries in the keel? The weight would then be additionally useful as a power storage device.

    Of course, it would need to be accessible before and after the voyage for servicing and installation, but if done properly you should be able to have it completely sealed for the voyage.

    Optionally, your swing rigger has merit, especially if all you could do from the inside was to move it into position. To lock it into position you would have to use a strut and push buttons or pins from a standing position before the outrigger swung forward or backward.

    By the way, have you tried a capsize test with the hatch open? Does the boat right itself or fill with water?

    You might want to take this into consideration in your design decision, as well as determine under what situations you will want to be able to stand and exit or enter WiTHiN while on the open ocean.

    I've heard that after a number of days "out there" it feels very good to be able to take a bath, even in salt water.  

  6. # Anonymous Anonymous

    Have you considered outriggers that pivot in the middle of the boat? In the retracted position, they would be in line with the hull and fit into recessed compartments. Rotated 90 degrees, they would function as outriggers on both sides. You could deploy them with a crank on the inside of the hull...

    Buzz  

  7. # Anonymous Vic Garza

    Some consideration for the permanent keel idea: How many watts will the extra weight and water resistance cost compared to a cat design? If weeds or debis get lodged on the downward leg above the bulb vastly increasing water resistance, how can you clear them from inside? Can the keel joint be made strong enough to take severe impact blows and not cause even small leaks or more drastic fractures? If your main concern with outriggers is about capsize, maybe that could be solved with a one way (spring tensioned?) hinge about (midway?) down the strut that breaks TOWARD the hull upon capsize?

    What kind of bilge arrangement do you have, as marinating in salt water over long periods would appear to causes health complications? Even small blisters, scratches, etc. can become painful and infected as the nutrient rich saltwater vaporizes into the tiniest of wounds and orfices.... Where's the privy, inside or out?

    Hope this helps.

    Vic  

  8. # Blogger biff

    Perhaps the best answer is the simpelest. Don't do anything to make it more stable.

    Your boat needs to be able to handle water entering the cabin without sinking or damaging anything, otherwise when water comes in in when you are in the middle of the ocean you are dead. So why not just let water enter the cabin when doing deep water entery or exit. have your little rope lader attached to the hatch, start climbing, when the boat tips over, slide in. then use your bilge pump to remove the unwanted water.

    I can see that may be difficult to enter the boat when it is trying to roll back upright, but it might be worth trying because it actually requires no extra complications.  

  9. # Blogger Adventures of Greg

    Biff: I really like the way you think. In essence, that is what the chief engineer Rick Willoughby has in mind for WiTHiN.

    However, I see the need to gain some temporary stability when not underway to deal with a whole whack of jobs - like:

    1. going to the bathroom
    2. deploying a sea anchor
    3. pulling in, de-tangling repairing the sea anchor
    4. cleaning the hull
    5. sitting on the bow and paddling if I needed to
    6. standing up to stretch or lookout for traffic
    7. repair or maintenance of the rudder and/or lines
    8. repair or maintenance of the drive leg (not sure I will be able to access the drive leg from INSIDE. Space is VERY tight in there)
    9. Access to the bow storage compartment (again, space is so tight that I may only gain access to stores from a hatch in the bow compartment from outside).

    I believe that this journey is probably going to be as much about being within WiTHiN as outside WiTHiN.  

Post a Comment


Subscribe to email updates:

Name:
Email :


About Greg video:



    follow me on Twitter





      Adventures of Greg Home
      PedalTheOcean.com
      Motivational Speaker





      featured slide show:



      Archives (newest first)





        Web This Blog



    © 2006 PedalTheOcean.com | PedalTheOcean BLOG by Greg Kolodziejzyk.
    motivational speaker
    No part of the content or the blog may be reproduced without prior written permission.