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PostPosted: Wed Nov 20, 2013 9:59 am 
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Joined: Tue Nov 19, 2013 11:48 pm
Posts: 53
Location: Missoula, Montana
I have mounted a modified Scotty Depthmaster downrigger on my 13” Hobie Revolution next to my right thigh, using the kayak’s water bottle holder to stabilize the mount. Here’s how it looks:

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It’s difficult to mount a downrigger on a 13’ Revolution, because there isn’t a big flat spot on the gunwales in a location where it is easy to mount and operate a downrigger. I stabilized my downrigger mount against twisting forces by bolting it down to two waterproofed nuts mounted inside the rather narrow right gunwale.

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Another option for attaching a downrigger mount to the gunwale is by attaching a section of track to the gunwale next to the water bottle holder, and by bolting the mount to the track. I explain that option at the end of this posting.

I prevented the mount from teetering left and right (inboard and outboard) on the gunwale by making a plug which fits snugly inside the water bottle holder. The plug isn’t bolted into the water bottle holder, but in combination with the two nuts inside the gunwale, it holds the downrigger mount solidly, with almost no play.

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I can install the downrigger mount on my kayak in a few seconds by screwing two hand bolts into the nuts inside the gunwale. When I am not using the downrigger, the only portions of the downrigger setup which remain on my kayak are the two nuts which are permanently mounted inside the right gunwale.

I shortened the boom of my downrigger from 23 inches to 8 inches in order to locate the cable as close as possible to the side of my kayak, and in order to reduce the stress which the downrigger places on my kayak. You can think of the boom of a downrigger as a crowbar which is trying to tear the base of the downrigger out of the kayak. Shortening the boom reduces the stress created by the boom. However, if you just shorten the boom, the pulley would end up well below the height of the cable drum, and the cable would be bent at a sharp angle over the edge of the cable drum. As a result, in order to shorten the boom, you need to create a new mount for the original pulley which raises the pulley so it feeds the cable into the center of the cable drum, as shown below, or you need to replace the original pulley with a new one in the correct location.

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Even with a shortened boom, a downrigger needs a strong and stable base, because you put a lot of twisting and rocking force on the downrigger’s base when you turn the crank, and because the weight and drag of the ball on the boom also put a lot of stress on the base of the downrigger.

The overall configuration of the downrigger and the rod holders on my Revolution is pretty much the same as the way I set up my 13’ Trident, but with a Scotty Depthmaster downrigger next to my right thigh rather than a Scotty Laketroller downrigger. I explained how and why I mounted the Laketroller and my rod holders on my Trident in a posting at http://www.northwestkayakanglers.com/in ... ic=11486.0 . The general suggestions that I made in that posting also apply to mounting a downrigger on any kayak, whether it is a Mirage Drive kayak or a paddle kayak. For example, I like to mount my rod holder in front of me with the rod pointing towards the side on which the downrigger is mounted, and I like to mount my fish finder on the same side as my downrigger, so I can easily watch the fish finder and the tip of my rod at the same time while trolling. However, being able to paddle with the downrigger installed is a huge issue with a paddle kayak, but much less of an issue with a Mirage Drive kayak. The Depthmaster interferes with paddling my Revolution, but I only use a paddle to get to shore after the water becomes too shallow for the fins of the Mirage Drive. If I wanted to use my paddle to get out through surf (not an issue where I live in Montana), or to paddle a section of shallow river, I could take the downrigger out of its base and put it in my front hatch while paddling.

When mounted in the area of the water bottle holder, the Depthmaster downrigger is easy to operate with one hand. To lower the ball, I move the brake lever clockwise (towards the center of the kayak) about 40 degrees, and control the descent of the ball with my thumb on the inside of the cable drum. To raise the ball, I just start turning the crank clockwise, which requires little effort due to the size of the crank handle, and which automatically releases the brake. I can lean forward and crank up my fishing line at the same time as I crank up the downrigger ball. When the ball has reached the level I want, I stop the crank handle above the brake arm and turn the handle back a quarter turn, while hooking the brake handle with one of my fingers to lock the cable drum. This stops the crank handle away from the center of the kayak, where it’s out of the way. The handle on the right side of the kayak makes a convenient holder for my downrigger ball when I’m not trolling. I find the cable counter to be useful, and it agrees with my fish finder within a foot or so.

I constructed my mount out of ultra-high-molecular-weight polyethylene (UHMW), with stainless steel hardware available from my local hardware store. A friend helped me construct the plug, and silver soldered the nut assemblies which I mounted inside the gunwales. I constructed the rest of the mount and the nut assemblies using hand tools. For example, I sawed the plastic with a hand saw, and dressed the cuts with a wood plane. If you have welding, machining, and/or woodworking equipment, you should be able to improve on the design and construction of my mount.

The details of how I constructed and installed my mount, and ways to improve on my mount, are discussed below.

Choosing a downrigger. Before I bought my Depthmaster downrigger, in order to see how much room it occupies, and in order to determine whether I would be able to operate it conveniently if it was located next to my right thigh, I went to a local sporting goods store and sat down on a bench with the downrigger next to me. I realized that if the downrigger was mounted with the boom sticking straight out from the side of the kayak, the brake handle would be pointed straight back, and in order to release the brake, I would need to swing the brake handle into the side of my thigh. Consequently, I realized that in order to be able to operate the brake, I would need to mount the downrigger with the boom pointed forward about 30 degrees. This would have the added advantage of locating the pulley closer to the side of the kayak.

The Depthmaster has proved to be a good choice, but a number of models of downrigger can probably be installed next to your right thigh, in the area of the water bottle holder in a 13’ Revolution.

Shortening the boom and raising the pulley. I recommend that you shorten the boom of your downrigger before you start designing the top plate of the downrigger mount, because until you know where the pulley and cable will be located, you can’t make a good decision about how much to rotate the boom forward.

As I explained earlier, if you just shorten the boom, the pulley would end up well below the height of the cable drum, and the cable would be bent at a sharp angle over the edge of the cable drum. That won’t work. As a result, in order to shorten the boom, you need to create a new mount for the original pulley which feeds the cable into the center of the cable drum. My solution, which is shown in pictures earlier in this posting, was to construct a “U” shaped bracket out of UHMD. The base of the “U” slides over the stub of the boom and is held in place with two bolts, and the end of the boom with its pulley holder is mounted in the open end of the “U.” This works well. The bracket needs to tilt towards the stern of the kayak so the pulley can hang straight down when you’re pulling up the ball.

Because the original pulley is fairly bulky, another option is to replace the original pulley with a more compact pulley, perhaps using a compact block purchased from a sailboat equipment manufacturer. If you have welding equipment and you replace the original pulley with a more compact pulley, you could devise a considerably less bulky shortened boom system.

Making the plug which fits inside the water bottle holder. In an effort to help the downrigger mount absorb pressure from any direction, I decided to make a tapered cylindrical plug out of UHMD which fits inside the water bottle holder. I determined the dimensions of the inside of the water bottle holder by making a template out of the upper portions of two “Big Gulp” plastic drink cups obtained from Burger King or Taco Bell.

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The plug is six inches high, its bottom is 3 5/16” in diameter, and its top is 4” in diameter. It was the hardest part of the downrigger mount to construct. A friend fabricated it out of two layers of 3” thick UHMW by cutting the two layers separately on tapers with a bandsaw, and then bolting the pieces together and finishing them by putting them in a jig and turning them against a sander. In order to provide more room for my leg, I cut a slab off the inner side of the plug.

However, there is a much easier way to create a plug which should work just as well. All you need in order to keep the top plate of the mount from rocking left and right on the gunwale like a teeter-totter is a tapered block about an inch thick which sits in the water bottle holder at right angles to the gunwale, and is bolted to the bottom of the top plate of the mount. That block would be easier to make and lighter than the tapered cylinder on my mount. You can determine the dimensions of the plug by making a template out of two pieces of cardboard.

Deciding whether to use the quick release deck mounting bracket. The Depthmaster comes with a quick-release slide-in deck mounted bracket. You can either bolt this bracket on top of your mount, or you can bolt the downrigger permanently to the top of the mount. I decided to use the deck-mounted bracket. It doesn’t add much size or weight to the downrigger set-up, it was easier to use the deck mounted bracket than it was to figure out a way to bolt the downrigger directly to the mount, and there are times when it may be convenient to remove the downrigger from my mount without taking the mount off my kayak.

Buying the handbolts which will attach the mount to the gunwale of your kayak. Hardware stores sell bolts which have a plastic handle attached to them. Buy a pair of these handbolts of an appropriate size. You need to buy these bolts so you know what size of nuts to install inside the gunwale of your kayak, and so you know how large to make the top plate of your mount so there will be clearance between the handbolts and the base of the downrigger.

Determining where you can attach the nuts inside the gunwale. Before you construct the nuts which will be installed inside the gunwale, you need to determine where there is space for those nuts. Reach inside the kayak and feel around. In a Revolution, cables running to the rudder run under the gunwale in the area of the water bottle holder. These cables shouldn’t interfere with mounting the downrigger, but you need to know where they are located. In the area behind the water bottle holder, there is a fairly large flat area inside the gunwale, but there is a bulge which contains the cast-in base for the padeye to which the right seat strap attaches. You will need to locate the rear nut in the flat area in front of this bulge. In the area in front of the water bottle holder, one of the screws which holds down the right netting pocket protrudes into the area inside the gunwale, and the inside of the gunwale is narrow and somewhat arched. You will need to locate the front nut in front of this screw, and you will need to line up the bracket to which the nut is attached carefully with the top of the arched underside of the gunwale. I marked the location of these restrictions on masking tape stuck on the gunwale.

You need to find a place for the nuts where the axis of the hole through the nut will be at right angles to the top plate of the mount. If you install the nuts in an area under the gunwale which isn't parallel to the top plate of the mount, the bolts which attach the mount to the gunwale won’t run through the top plate at a right angle, so they won’t work well.

Making the nuts which will be mounted inside the gunwale. A friend made me the nuts which are mounted inside the gunwale by silver soldering a stainless steel nut to a narrow strip of stainless steel. The strip needs to be narrow to fit in the narrow arched area under the gunwale in front of the water bottle holder. To permit the nuts to be waterproofed after they are installed, I bolted a block of UHMD on top of each nut unit. A better way to construct the nut system would be to machine it out of a single block of stainless steel. You can probably devise other ways of waterproofing the nuts which can be constructed with whatever equipment is available to you.

Deciding where to locate the downrigger with respect to the water bottle holder and the gunwale. Once you have shortened the downrigger’s boom and raised the pulley, constructed the plug for the water bottle holder, bought the handbolts, and determined what restrictions there are on the location of nuts under the gunwale, you can decide how to locate the downrigger with respect to the plug and the right gunwale, and you can design the shape of the top plate of the mount. I attached a piece of cardboard to the top of the plug, set the downrigger on the piece of cardboard, and decided where I wanted to locate and orient the base of the downrigger with respect to the plug and the gunwale. If I had mounted the downrigger directly on top of the plug, it would get in the way of my leg when I was pedaling. To avoid that problem, I mounted the downrigger pretty much centered on the gunwale. If I had mounted the downrigger with the boom sticking out at right angles to the side of the kayak, my leg would get in the way of the brake handle. To avoid that problem, I mounted the downrigger with the boom pointing forward about 30 degrees. Once I decided how I wanted to locate and orient the base of the downrigger, I marked that location on the cardboard.

Next I marked the edges of the top plate on the cardboard. The top plate needs to cover the top of the plug so you can attach it securely to the plug. The top plate also needs to include wings which extend far enough in front of and in back of the base of the downrigger so you can drill holes for the handbolts which attach the top plate to the gunwale. Be sure to make the top plate large enough to accommodate the handbolts in a location where nuts can be installed inside the gunwale, and in a location where the base of the downrigger won’t interfere with turning the handbolts.

Constructing and attaching the top plate of the mount. Once you have completed the cardboard template for the top plate, you can cut out the top plate, finish it, attach it to the top of the plug, and attach the quick-release slide-in base to the top of the top plate.

Drilling the bolt holes and installing the nuts under the gunwale. One way to drill holes in the top plate and the gunwale of your kayak is by starting from the top. To do this, set the plug in the water bottle holder, and orient the top plate accurately with the gunwale. Then mark and drill holes in the top plate for the handbolts. Continue those holes through the gunwale of the kayak. Then drill holes for the screws which attach the nut units inside the gunwale, and bolt the nut units inside the gunwale.

However, because the location of the nut units inside the gunwales is critical, a better way is to start by determining exactly where you want to locate the nut units inside the gunwales. Drill small guide holes through the nut unit from inside the kayak, enlarge the holes to full size from outside the kayak, and bolt the nut units in place. Then take a bolt of the same size as the hand bolts which go in the nut units, cut off a short piece of the end of the bolt and sharpen it to a point, screw the section of bolt into the nut unit, and use the sharpened tip to mark the underside of the top plate. Then you can drill the hand bolt holes through the top plate.

Waterproofing the nut units. In order to waterproof the nut units, I turned the kayak upside down, and then used Marine Goop to seal the area where the inside of the gunwale, the stainless steel strip, and the block of plastic meet. In addition, because I'm a belt-and-suspenders kind of guy, when I'm not using the downrigger, I seal the holes with a pair of nylon bolts and rubber washers, as shown below:

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Keeping the handbolts attached to the mount. When you remove the downrigger mount from your kayak, it would be easy to misplace the hand bolts. To avoid this, I clip the handbolts to the mount, as shown below.

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How a downrigger mount could be attached to a track. Instead of mounting waterproof nuts inside the gunwale of your kayak, you could mount a section of track on the gunwale in the area next to the water bottle holder, and you could bolt the downrigger mount to the track. If I wanted to do this, I would make the following changes to the design of the mount: (a) Instead of drilling holes in the mount for handbolts, I would cut slots in the front and the back of the mount, so you can slide the bolts along the track and into the slots before tightening the bolts. (b) Instead of using handbolts (bolts with a plastic knob attached to their heads) to clamp down the mount, I would take a stainless steel carriage bolt about two inches long and cut and/or grind its head down into a rectangle which fits inside the track. Then I would buy a hand nut (a plastic knob with a nut attached inside it) which screws onto the bolt. (c) I would use a router to make a groove on the bottom of the mount for the track. This would reduce the height of the mount slightly, and would help the mount resist the twisting forces placed on the mount when you turn the handle of the downrigger.

To attach the mount to the track, I would drop the plug into the water bottle holder and settle the groove on the bottom of the mount over the track. Then I would slide the modified carriage bolts into the ends of the track and along the track into the slots in the front and back of the mount, and then tighten the bolts with the hand nuts. I think this design should work fine, and would be easier to construct than mounting waterproof nuts inside the gunwale of your kayak.

The bottom line. Making the downrigger base took a lot of time, and a lot of trips to the hardware store for stainless steel hardware. But the mount is very solid, and the Depthmaster downrigger is very easy to use when mounted by the water bottle holder. I’m real happy with the downrigger setup. However, the next time I install a downrigger on a kayak, I'm going to try attaching the mount to a track mounted on the gunwale, as that is easier for several reasons than installing waterproof nuts inside the gunwale. And if I make another mount for a Revolution, I'd stabilize it with a 1" thick block in the water bottle holder at right angles to the gunwale, rather than a round plug, because a 1" thick block is lighter and a lot easier to make than a round plug.

(I originally posted this description on the Northwest Kayak Angler forum).


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