SJ23 Tech Tip C14, (Updated 2021-08-30) Paul, Bob, Jimmy, Ron, David, Dennis.

Index

Companionway Boom Tent and Bimini.
INDEX - Ribbed Tent, Nylon Fly, Bimini, 2 Tier Bimini, Two Tier Bimini, Liberty Bell
A good awning or bimini is essential if you are going to survive a cockpit party in the hot sun or in liquid sunshine!  Whatever your situation, the cover should be convenient to put up, especially if a storm approaches, and slick to fold for storage.  If you seal the sides of an awning tight to the deck, it can add living space during inclement weather.  This is great in northern climates in which case I would use light coloured fabric to also let light in.  If the cover goes to the aft end of the cockpit a zipper door for stepping off the boat would be nice.

GENERAL DESIGN CONSIDERATIONS - First you have to decide if your awning or bimini is to keep the sun off your head or to keep the rain out.  It all depends on your local climate.  Of course you can always make it dual purpose, which is my preference. 

  1. A light coloured fabric reflects the heat and makes life more bearable under the awning.  Especially desirable in the hot southern US climate.
  2. A porous fabric, similar to the black "bug screen" used to shade a green house, will pass hot air up so it is cooler underneath and offers less resistance to the wind.  On the other hand it also passes rain, converting it to a fine mist as it passes through. 
  3. While nylon is extremely light and packs well when dry, it stretches when wet.  Fortunately it dries very quickly when the sun comes peaking out from behind the clouds.  Therefore the frame should be designed to maintain fabric tension. 
  4. Vinyl fabric does not stretch but it is bulky to fold, heavy and takes a long time to dry in the sun.
  5. Sunbrella does not stretch, dries fairly quick but is bulkier than nylon.
  6. Use stretchy bungee cords as tie down lines so the whole awning gives with the wind.  The stretch also permits you to nudge the awning aside to walk forward on the side deck.
  7. A PVC frame is light, strong, smooth and doesn't rust.  While it may be up to the job in light wind, aluminum or stainless steel is stronger.  Interlocking flexible fiberglass poles are every strong and pack very compact.
  8. If you want the whole cockpit covered, front to back, then use a (10x12)' tarp, with the 12' dimension along the boom.  This leaves it a bit open along the toe rail.
  9. If you want complete weather protection to the cabin then make the tarp 11' wide so there is enough fabric to pull down to the toe rail, closing off the sides.  You could also close off the forward end of the tent.
  10. If you want to cover more of the cockpit, either make a small hole 18" from the aft end of the tarp for the boom topping lift or install an 18" long zipper with a flap over it (closed with Velcro).  The 18" of fabric aft of the boom covers a surprisingly large area of cockpit, adding a lot of shaded or dry space.
  11. To leave the companionway unobstructed, position the main sheet block to one side and another line to the opposite side.  This will keep the boom centered over the cockpit.
  12. You could sew 3 hems across the tent to slip fibreglass poles through as shown below.  Remember to include a pocket for the end of the rib, otherwise it can pop out of the tarp slip into the drink!  The whole works can be rolled up as a long "stick" for storage or disassembled for more compact storage. 
     

RIBBED BOOM TENT for Mellow Yellow - Mellow Yellow's cockpit boom tent frame is made of (8 x 10)' vinyl stretched between 3 white PVC ribs.  The material is laid across the boom on the 8' width.

Construction - Each 8' rib consists of three interlocking sections joined together by two couplings.  The middle 3' long section is made from 3/4" PVC tube (1/2" ID).  The two 3.5' end sections are made of 1/2" PVC tube.  The coupling is created by gluing a mating fitting and then a 6" length of tube to the inboard end of the 1/2" tube.  The outer end of each 1/2" section has a T fitting to keep the bungee hook from slipping off. 

Setup & Assembly - Assemble the ribs by inserting the 1/2" coupling into the 3/4" tube.  This combination maintains good flexibility to the rib.  Secure the tarp to the frame with short lengths of line looped through the grommets of the tent and the PVC frame work.  You could also sew a wide hem in the tarp for each rib and slip the tube inside.  Fasten the middle of the aft rib to the boom topping lift.  Then pull the middle of the forward rib to the mast with a long cord to stretch the tent forward.  Use a bungee cord at each T-fitting to pull the frame down to the toe rail.  It takes about 10 minutes to set it up.  The whole thing cost only $25 US and has served me well for several summers.  Paul Bailey  TOP 
 
A NYLON BOOM TENT for Panache (2021) - With the really hot weather here it reminded me of an old project I've wanted to do.  I have long needed a boom tent for shade or rain while at anchor so I blew the dust off a bag of double rip stop nylon that was in storage in the basement for many years.  This was an old tent fly that was perfect for Panache's new boom tent.  It started life about 30 years ago as a tent fly for the Scout troop I was a leader of.  I spent many nights under it, thankfully dry ones, so I knew the fabric was still good.  Thankfully cool dark storage protected the nylon during all those years. 

The dimensions are (10x8)' where the 10' dimension across the deck is perfect to just slide over each lifeline to be tied to the toe rail.  This should ensure that rain drips are kept out of the cockpit and it stays in place during a blow.  The boom tent has 3 guy lines per side plus a line around the mast and another to the end of the boom to keep the ridge tensioned.  A such it is the simplest version boom tent that can be tucked in a small bag. 

There is a fair amount of room under the tent and it creates nice weather protected standing head room in the companionway, always appreciated for activities on board.  While it is surprisingly easy to "walk" under the tent to go to the bow, my back does rub against the nylon which might be an issue if the nylon is wet.  In Panache's case I can drop a lifeline gate without disturbing the boom tent.  This will make boarding convenient.  Another surprise is that it felt slightly cooler under the tent despite the brown colour.  The breeze through it was pleasant. 

  

  
I haven't used the tent on a float yet to realize the pros and cons so for now I will keep it like this.  In the future I may slide it further aft in which case I'll need to add an 18" long zipper or a slot in the aft end to pass the boom topping lift through.  Sliding it aft covers more of the cockpit for shade or rain.  Although, moving it more than 18" could expose the forward end of the companionway to liquid sunshine.  The sides of the slot would have to be reinforced and the outbound corners would each have an eye to tie the line to.  A flap secured with Velcro over the slot will ensure it stays dry below.  On the other hand I could just zip an extension to the aft end.  Either of these is a lot easier than unclipping the topping lift. 

The only down side of this tent is that it blocks the sun to my solar panels!  But then there's no sun when it rains!  Oh well. 

I will store this tent in this nylon bag after it dries.  The advantage of nylon is that it dries in a matter of minutes when the sun comes out.  Nylon is easy to roll up and stuff in a wide open bag, the fabric breathes, and has a draw cord to hang it from.  It's small size lends to easy storage in a small place.  There is no point in reinventing the wheel.   Bob Schimmel   TOP 
 
BIMINI - While a cockpit awning is great at anchor, it doesn't work while sailing.  For this you need a bimini.  Shown at right is a terrific bimini that Jimmy Harrell made for his SJ23.
"I threw the first version together last year, a few days before a planned weekend trip to Lake Martin in Alabama.  I used what material I had, including a PVC framed Bimini from another boat.  The top is about (5 x 4)' and I thought at first that it would be too narrow (port/starboard) and not long enough (fore/aft) to be of much use.  I was also worried about not being able to see around the bimini to trim the sails or that the boom could not clear it.  After using it for the weekend, I now think that this size is a good compromise.  There is sufficient shade for the two of us, provided we move occasionally, and it is small enough that I can see around it to trim the sails.  The low height doesn't seem to be a problem since I can stand up in the cockpit behind the Bimini. 
  • The PVC frame has a slip joint in the middle of the crossovers that makes it storable in the cockpit locker.  I plan to make a frame from aluminum and maybe add a third crossover in the middle. 
  • The clamp on the pulpit can be tightened to position the height of the frame thereby avoiding the boom or your head. 
  • The parachute cords can be adjusted to control the angle of the frame.  A very nice feature to create head room while at anchor. 
  • The fabric is cotton with sleeves for the frame sewn along the front and back and a hem along the sides to keep the leech intact.  The finished size is (60x44)" but you should adjust the size to fit your own frame which must fit your pushpit. 
  • There is a loop of webbing sewn at each corner of the top for stretching the fabric slightly along the frame.  Through the center of the top are two web loops, one top and one bottom, that are used to tie the top to the boom while at anchor and to hang a light or whatever underneath.  Raising the center helps to shed rain while at anchor.  The lamp should be battery powered to prevent burning the cloth."  Jimmy Harrell  TOP 

 
2 TIER BIMINI - The frame work consists of four ribs, two high & two low with a zip out window joining the two.  The difficult part is to make the top section.  I designed the top so that it will be fully functional while under full sail.  This means you can stand up under it.  As you know an SJ23 boom is pretty low, the cockpit is small and a regular top won't work well.  In this design the top section extends over the stern about 18" and is high enough to stand under. This provides shade in the back of the boat. The front section fits under the boom and extends forward to the cockpit mounted traveller. The drop in the middle (about 12") is where I installed the window (similar to a dodger). 

This bimini design is a blessing when you are out in the middle of nowhere and looking for a little shade to keep from poaching your brain.  I can fabricate the metal bows and my guy can make the cloth cover for you using mine as a model.  (the first one was the hard one). Ron Katz.  TOP 
 
TWO TIER BIMINI - Continuing with the two tier concept  is this excellent design made by David Langton in Kelowna.  This dodger has a really robust frame that can stand up independent of the fabric.  The outside grab handles are functional and the visibility through the vinyl is excellent.  The hatch can slide under the fabric to stay sealed to the weather.  Notice the storage area on top; provided you don't push the hatch in all the way so everything falls on the cabin floor!  The mainsail track has been moved to the coach roof, ahead of the dodger.  This clears the cockpit and allows the dodger to be carried further aft, proving more protection.

While I dislike the restricted access to the winches and line lockers, I can sure get used to a dodger when the sun is beating down on you or the clouds dump rain on you.  In cold wind it gives great protection.  One time I sat in my shorts under the dodger while the crew wore a ski jacket at the helm.  Despite all this protection I would still like the option of rolling the vinyl window down for reduced windage and extra ventilation when needed.  I consider myself an occasional round the buoys racer but prefer long distance racing which is closer to fast cruising. 
 

The bimini is also built with a free standing frame and a large "window" in the top to see the mainsail trim.

I like the BBQ support bar and remote control lines to the outboard. 

 

 

 

 

 

 

 

 

 

 

 

 

 

Frames only. 

 

 

 

 

 

 

 

 

 

 

All the blue fabric in this photo makes it difficult to pick out David's bimini but take a close look at the zipper across the middle.  This would allow you to change the size of the bimini to adjust the amount of shade.  My guess is that with the fabric removed, it might clear the cockpit for some "active" sailing.  And yet I can't help but feel that David has a section of fabric to close the top completely, just like his neighbour.  It would be very comfortable at anchor in a drizzle.  I wonder who copied who? 

Also take note of the solar panel and the roll up panel to reveal a window on top of the bimini.  This is well thought out.  David Langton

 

 

 

 

 

 

 

 

 

 

 

 

 


 

2019 - This bimini for Liberty Bell was ordered online from a chandler.  It fits under the boom and has plenty of headroom when sitting or crouching in the cockpit.  All the chandler needs are boat dimensions.  The cover has been renewed once and the spare cloth was used to make the boot for storage.  The only change I would make is to sew a window over the tiller so I can check sail trim while sitting.  Currently I have to hang my head over the side, which is an awkward position to say the least!  Maybe next season.  Dennis Wolfe.


 

Return to Tech Tip Index. . . . . . . . . . . . . . . Have a Question?