Assimetric Spinnakers

Hi all,
just wondering if any of you have made a rc boat with a fixed bowsprit assimetric spinnaker on a monohull?
if so can you please give me details on how to make it work?

I see said the blind man to the crippled nudist who put his hands in his pockets & promptly walked away.

Hey Yachtie2k4,

I started such a project on and old Fairwind Hull. I got the bowsprit installed (deploys about 9") and built a sail “template” out of garbage bag plastic (I had no idea what the sail shape was going to look like, so I decided to make it out of “trow away material” first and then when I got the sail shape right, I would use that as the pattern for the real sail).

I started working on the internal workings of the sheeting and halyard system but never finished.

The key to the whole thing is that you have a LOT of sheet length that you need to be able to gybe from side to side. I built a closed loop drum winch system for the sheets. The drum winch pulls a double pulley from the bow of the boat to the stern of the boat. The starboard sheet is connected to the stern of the boat, then runs through the shuttle and then back to the stern of the boat (through another pulley) before passing through the fairlead in the deck. That way when the shuttle is moved by the winch from the stern of the boat to the bow (35 inches total travel) the sheet is trimmed in DOUBLE that length (70 inches). In a similar way, the port sheet is attached to the bow, then runs through the shuttle and then back to a pulley in the bow before passing through the fairlead in the deck. So when the starboard sheet is trimmed in, the port sheet is eased by the same amount (a total of 70 inches of travel available).

A second drum winch is rigged with a similar shuttle system from bow to stern. This system has the halyard and “belly button” retrieval line running on it. Again, each of these has a total of 70 inches of travel avaailable. But this system does not require the full 70 inches. The mast is 48" tall and I am using a masthead hoist. I figure I need about 60 inches of total travel to get the head of the sail down to the bow (where the opening of the sail tube is located - more on this in a minute) and to give me a little slack. The belly button line is attached to the middle of the sail and runs through the tube. The same 60 inches allows the sail to be fully sucked in to the tube and allows for enough slack when deployed so that the sail can fill and gybe without the belly botton line getting in the way. The deployment line for the bowsprit is attached to the shuttle (not with a 1:2 system, but just straight to the shuttle). There is initially slack in this line, but as the shuttle moves aft, the line pulls tight and pulls the bowsprit out over the last 9 inches of the shuttle travel. Retrieval of the bowsprit is with an elastic shock cord.

The sail is stowed in a sail tube that runs from near the bow (about 4" back from the bow) to the transom below deck. It is a simple tapered sock. It is held fairly tight and the aft end of the tube contains a drain hole out the transom as well as a hole for the retrieval line to pass into the sock.

Now there are a few tricks to the system. Remeber up above where I said that the bitter end of the sheets were attached to the boat (at the bow and stern)? That was a simplification to help explain the basic working of the system. In reality, the bitter ends of the two sheets are attached to the halyard retrieval shuttle such that when the sail goes up, the system eases 25" into the sheets and when the sail is stowed, it pulls in 25" of sheet. This helps to prevent the sheet from having so much slack that it drags in the water or gets tangled.

Lessons learned so far:

1: There are a LOT of lines that can get tangled down below. The biggest problem I have had to date are figureing out ways to keep all these lines straight and to keep them from getting sucked into places they don’t belong. It is fairly common for the sheets to get wrapped around the drum winches for example. My solution to this is to build a shroud (thin plastic “roof” over the drums to prevent the sheets from getting sucked into the shuttle lines.

2: Keep the closed loop systems well tensioned with some sort of spring or shock cord. I have had a devil lof a time keeping the main closed loop system running clean without skipping off the drum. A good fairlead leading onto each side of the drum seems to help and a good spring loaded tensioner also helps.

3: Color code your lines! I can’t tell you how many times I have gotten frustrated when trying to untagle something and I had no idea which line had gotten tangled and where it should go.

4: Prototype your system on a 2x4 before you try to build it into your boat. After several attempts to fix things that were installed in the boat and not being able to reach the bits I needed to reach because they were stuffed way up in the bow, I decided to pull the whole system out and build it on a 2x4. I taped down my servo tray onto the 2x4 and carefully measured where the bow and stern locations were in relation to tray. Then I positioned the end blocks on the 2x4 at the right positions and started tweaking the tensioners and fairleads and so on. I attached all those bits to the servo tray so that once the system was working right, I could simply transplant the whole thing into the boat.

Whew! that was a lot to digest.

By the way, here is a fairly good schematic that I used as my starting point. You will see many of the features I described above on that sketch:

In retrospect, it has been a lot of work and rather frustrating. and it is not class legal, so it is really just for fun. Given that level of frustration, I’m not sure I would do it again unless there were a class where it was legal to use. I still have not finished my system and gotten it to work on the water. But it is working failry well on the 2x4 and is ready for me to transplant into the hull…

I’ll try to get some pitcures this weekend of the system on the “build rack” (the fancy name I have given to the 2x4) so that you can get an idea of the inner workings…

  • Will

Will Gorgen

Ah spinnakers
I agree will Will you need to knock up a mockup model to sort out the lenghts of sheets halyards etc.

I went thru the process earlier this year in sorting out the setup for the F100.

The first rig was a standard rig design with an extending prod for the gennaker, this setup was had problems when retrieving the gennaker after a gybe, as the retrieval cord can be setup for a starboard or port hoist/retrieval. The second trial rig I based on the swing rig, after a bit of time I came up with the idea of making the retrieval tube been part of the rig ie the rotates around, The gennaker tack is attached to the front end of the tube and the sheets to the aft end, in the retrieval cords runs thru the tube which pulls the gennaker down to the tube. The forces of the gennaker tack and clew are approximately equalized out, but could rotate the rig if the standard swing rig sheeting system was used… More grey matter, I settled on a belt drive to turn the base of the mast to give positive location. Windward work the mast will be centred on the centreline of the boat with the jib and main booms setups adjusted with minimum sheet moment. For off wind sail the mast will be rotated to suit the wind angle, and the gennaker can be hoisted. The shape of the tube has changed as development progressed; it started as a round tube, then a rectangular and final design the tube starts at the bow with a triangular opening fitted with little rollers to guide the gennaker in and out. At the mast it is of elliptical shape with the long axis vertical as the mast is mould around the outside of the tube, at the stern the tube will be circular. The tube will be moulded over a male mould out of carbon fibre with uni direction fibre for strength.
The mast section begins as a standard Marblehead B rig to which a slotted smaller carbon tube with be glued to the aft side, this will allow for quicker mainsail changes, as the #1 main will be a square top.

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Bowsprit model

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Swing rig left bowsprit right

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Swing rig

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Spinnakers Down (of course)
Swing rig left Bowsprit right

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Swing rig left Bowsprit right

I will do another posting descriding the sheeting setup

mm, do you have any better drawings of the systems that both of you have used?

I see said the blind man to the crippled nudist who put his hands in his pockets & promptly walked away.

You sure don’t have much freeboard on your boats [:D][:D]



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