Hard Bimini Material & Layup Input

[panema]

Hello helpful friends of fixit anarchy... 

Planning to do a hard bimini for my Tayana 37 this spring for cockpit protection, prep for some new canvas, and to create some space for solar on top. I think I have a  plan for the support structure, but hoping to get some input on what materials, layup, and process I should use for the actual composite work of the bimini itself. I'm pretty novice when it comes to fiberglass and composite work but was thinking this will likely be done in fiberglass with a foam core and looking forward to building some skills in this area along the way.

The front of the bimini will mount or thru bolt to bottom of the boom crutch and will match the profile of the boom crutch. I will put in 2 support stands near the aft end of the cockpit to hold the aft end up. Since the bimini will have a camber that matches the profile of the bottom of the boom crutch I will add some small pads to the bottom of the bimini perpendicular to the deck for the rear stands to interface or connect to it. Canvas will attach via bolt rope channel all along the edge and allowing for a simplified dodger set up and canvas and a nice set up for closing in the entire cockpit with new canvas work for protection from the elements when needed. 

I was thinking I should use the shape of the bottom of the boom crutch to create a mold and start by laying up the bottom skin of the bimini first since that will be a more finished surface and can acheive a smoother finish on the side of the mold. Then core. Finally top skin. The top will likely just get non skid and can tolerate some more imperfections than the bottom. Solar will live on top and cover as much of it as feasible. 

Am thinking will make the mold and then make the entire bimini larger than it needs to be. Cut the final shape after all the layup work is done. Rabbet the edges and fill with thickened epoxy to create a sealed edge once the final shape is achieved. Sand, fair, paint. 

Please see attached for a rough sketch of what I have in mind. Hopefully my chicken scratching is helpful, haha. 

Would love input on: 

• Material selection: Laminate, epoxy, mold material, mold release, etc.
  
• Mold building and prep for finish surface
  
• Layup
  
• Any other process or material considerations I might miss being a novice
  

Thanks in advance for any input or links / tutorials that could be helpful for this project. 

Cheers, 

// Phil

 

[Zonker]

Going to stand on it (non skid)? That's a BIG span if a guy stands in the middle of it.

Picture if it was made of 3/4" plywood of the same dimensions with no support under it.... just to give you an idea of what might be the issue.

 

[slug zitski]

Hello helpful friends of fixit anarchy... 

Planning to do a hard bimini for my Tayana 37 this spring for cockpit protection, prep for some new canvas, and to create some space for solar on top. I think I have a  plan for the support structure, but hoping to get some input on what materials, layup, and process I should use for the actual composite work of the bimini itself. I'm pretty novice when it comes to fiberglass and composite work but was thinking this will likely be done in fiberglass with a foam core and looking forward to building some skills in this area along the way.

The front of the bimini will mount or thru bolt to bottom of the boom crutch and will match the profile of the boom crutch. I will put in 2 support stands near the aft end of the cockpit to hold the aft end up. Since the bimini will have a camber that matches the profile of the bottom of the boom crutch I will add some small pads to the bottom of the bimini perpendicular to the deck for the rear stands to interface or connect to it. Canvas will attach via bolt rope channel all along the edge and allowing for a simplified dodger set up and canvas and a nice set up for closing in the entire cockpit with new canvas work for protection from the elements when needed. 

I was thinking I should use the shape of the bottom of the boom crutch to create a mold and start by laying up the bottom skin of the bimini first since that will be a more finished surface and can acheive a smoother finish on the side of the mold. Then core. Finally top skin. The top will likely just get non skid and can tolerate some more imperfections than the bottom. Solar will live on top and cover as much of it as feasible. 

Am thinking will make the mold and then make the entire bimini larger than it needs to be. Cut the final shape after all the layup work is done. Rabbet the edges and fill with thickened epoxy to create a sealed edge once the final shape is achieved. Sand, fair, paint. 

Please see attached for a rough sketch of what I have in mind. Hopefully my chicken scratching is helpful, haha. 

Would love input on: 

• Material selection: Laminate, epoxy, mold material, mold release, etc.
  
• Mold building and prep for finish surface
  
• Layup
  
• Any other process or material considerations I might miss being a novice
  

Thanks in advance for any input or links / tutorials that could be helpful for this project. 

Cheers, 

// Phil

View attachment 497665

Find an old VW camper van, use its roof as a mold , trim to fit , 

 

[bgytr]

Make sure you account for the backstay, it's not shown in your sketches.

Also, your vertical post arrangement... not good.  You need triangle/truss type arrangement of the supporting structure to keep it stable both fore/aft and athwartships.

 

[Mark Morwood]

I built a 10' x 12' hard bimini for my Catana 48 without really knowing what I was doing in terms of layup, but got a result that worked.  I did build some test panels first. There are people on here who actually know what they are doing who could give you real advice on layup.

The layup that worked for me was one layer of DBM1708 biaxial with mat, a 1" balsa core, and another layer of DBM1708 biaxial with mat. I used epoxy resin. I included some carbon fiber reinforcing strips thinking they might stiffen it up, but knowing a little bit more about it now, I suspect they didn't do much, or if they did it would have been better to just double up the layup with glass in places of concern. It was plenty stiff enough to walk on anywhere. I had quite a few supports to make sure it was stiff enough. I had a flatish curve across the whole thing, but a tighter curve on the edges which I'm sure stiffened it up fore and aft. I made the single use curved mold for it out of drywall/plaster with a coat of epoxy to seal it. I laid it up and vacuum bagged it one long morning with a bunch of helpers.

 

[Zonker]

Mark,

Nice job. In your case, the big edge curvature and the post supports all around the perimeter help, but the really thick core is what made it stiff enough.

Totally agree with triangulating the support posts. Could be laminate foam sandwich or just s.s. tube fittings



For mold surfaces: 

- flat surfaces. Melamine coated MDF

- curved surfaces: 1/4" or thinner plywood on plywood curved formers (like Mark's picture). Then 1 or 2 sheets of kitchen laminate. Tape the seam with mylar packing tape to make sure it's vacuum tight.

Both surfaces will give you a glossy enough finish after paint. Wax well, 6 coats of mold release or hard paste car wax, applied and buffed well between each coat.

 

[panema]

God I love the input on this forum, that includes the requisite sarcastic input from slug, thanks everyone.  Mark for 'not really knowing' what you were doing your results look pretty damn good! 

- I will account for the backstay for sure.

- Will not stand on the structure, it is only needed for protection and to hold the solar panels up. Sorry if that was confusing I had not planned on vacuum bagging and figured my non mold skin (top skin in this case) would be hand laid and have quite a few imperfections and after painting... figured non skid would help hide some of those imperfections. I think I will shift gears and try to vacuum bag, it will be a great learning experience and result in a much better finish. My whole surface will have some curvature so I think the 1/4" plywood and kitchen counter material make a ton of sense. 

- I agree that the vertical only posts need some additional support. This was a shortcoming or an omission in my really robust schematic drawing... ; ) I've been noodling on this a bit. The boom crutch is fairly robust and is u-bolted into the side of the boat and is probably stronger both fore / aft and athwartship than my drawing would have communicated. I think for the rear posts I will have trusses fabricated into the top of them and account for how they will interface into the bottom of the bimini in my design to provide that additional strength. I will think about angling them into the cockpit as well and might be able to get both fore / aft and athwartship stiffening so long as it doesn't become something I'll easily bang my head on in the cockpit. Will continue to think on this and take some measurements at the boat. 

I'm leaning toward the following setup top to bottom: 

• Vacuum Bag w/ Mylar packing tape
  
• Kitchen counter material w/ mold release
  
• Top skin biaxial cloth with mat
  
• 3/4" foam core
  
• Bottom skin biaxial cloth with mat
  
• Kitchen counter material w/ mold release
  
• 1/4" plywood
  
• Mold supports
  

The DBM1708 biaxial with mat material looks pretty great. Not sure if I should be considering other laminant materials but will probably steer this direction for now. 

Would love to continue to take input if others have it. 

Thanks! 

 

[slug zitski]

God I love the input on this forum, that includes the requisite sarcastic input from slug, thanks everyone.  Mark for 'not really knowing' what you were doing your results look pretty damn good! 

- I will account for the backstay for sure.

- Will not stand on the structure, it is only needed for protection and to hold the solar panels up. Sorry if that was confusing I had not planned on vacuum bagging and figured my non mold skin (top skin in this case) would be hand laid and have quite a few imperfections and after painting... figured non skid would help hide some of those imperfections. I think I will shift gears and try to vacuum bag, it will be a great learning experience and result in a much better finish. My whole surface will have some curvature so I think the 1/4" plywood and kitchen counter material make a ton of sense. 

- I agree that the vertical only posts need some additional support. This was a shortcoming or an omission in my really robust schematic drawing... ; ) I've been noodling on this a bit. The boom crutch is fairly robust and is u-bolted into the side of the boat and is probably stronger both fore / aft and athwartship than my drawing would have communicated. I think for the rear posts I will have trusses fabricated into the top of them and account for how they will interface into the bottom of the bimini in my design to provide that additional strength. I will think about angling them into the cockpit as well and might be able to get both fore / aft and athwartship stiffening so long as it doesn't become something I'll easily bang my head on in the cockpit. Will continue to think on this and take some measurements at the boat. 

I'm leaning toward the following setup top to bottom: 

• Vacuum Bag w/ Mylar packing tape
  
• Kitchen counter material w/ mold release
  
• Top skin biaxial cloth with mat
  
• 3/4" foam core
  
• Bottom skin biaxial cloth with mat
  
• Kitchen counter material w/ mold release
  
• 1/4" plywood
  
• Mold supports
  

The DBM1708 biaxial with mat material looks pretty great. Not sure if I should be considering other laminant materials but will probably steer this direction for now. 

Would love to continue to take input if others have it. 

Thanks! 

Make the core thick or you will not be able to bury electric cable conduits, backing plates , structure and will have difficulty radius profiling the perimeter  

the inside surface is the most difficult the finish… make this the mold side

a sail trim window or opening hatch is needed

 

[jsaronson]

I've done 2 hard biminis using 4x8 FRP wall panels from Home Depot for the skins with Divinycell, 6 ounce glass and epoxy.  I made forms using 2x6s that followed the curve of the stainless frame held together with 2x3s.Smotth side out, sand off some of the bumps before you lay it up.  Great for solar panels.

Don't worry about a 'window' for sail trim if you are adding solar.

 

[NZK]

You could always try and get hold of an old IACC foredeck complete with bow hatch to create a decent sized 'trimming window'....

 

[slug zitski]

You could always try and get hold of an old IACC foredeck complete with bow hatch to create a decent sized 'trimming window'.... View attachment 498046

Nice hatch 

expensive 

many has a gas bottle and inflatable seals 

the vent hatch is important in the tropics .. underneath that hard top gets mighty hot 

if possible build a curtain assembly to turn off sun penetration 

 

[basketcase]

Every time someone says, 'im a novice who wants to build a Bimini for my boat' i hear, 'i really want to spend way too much time sticky and dusty and devalue my boat by 20k'.

 

[SloopJonB]

Every time someone says, 'im a novice who wants to build a Bimini for my boat' i hear, 'i really want to spend way too much time sticky and dusty and devalue my boat by 20k'.

Yeah - they should be directed to the Ugly Dodger thread and told to study it at length.

 

[Kenny Dumas]

Hey Sluggo, your politics are laughable but I appreciate your sailing input. Any pics or more info on pressurized inflatable seals?

 

[Autonomous]

Why the heck do you drag politics into this??? In case you missed it this is a sailing forum-thread.

FWIW, I've learned a lot from slug z, not so much from you.

 

[Gissie]

Maybe something like this. 

 

[panema]

@slug zitski

// Make the core thick or you will not be able to bury electric cable conduits, backing plates , structure and will have difficulty radius profiling the perimeter the inside surface is the most difficult the finish… make this the mold side. 

Roger that. Will definitely think through cable runs before production. 

I need to take some final measurements at the boat but am leaning toward 3/4" core. Total final unit would probably end up in the ball park of 1". Thing I'm fighting against here is I'm 6' 1" and want to make sure I can stand up at the helm. Want to go as thick as possible but also run out of room pretty quickly with total height. Going to get to the boat soon on a quiet day and run up the main and see how much total room I'm working with for the entire thing and go with the thickest possible material that won't look too chunky when complete. 

// Sail trim window or opening hatch is needed

Great consideration. I will have permanent hard panel solar on top but will continue to think this through. I will play around with panel arrangement to see if I can accommodate something here. Another option - again need to confirm a few things at the boat - is I might be able to build this in a way where I can easily poke my head out the back of it to evaluate trim. Will continue to noodle plan on this. 

@jsaronson

// I've done 2 hard biminis using 4x8 FRP wall panels from Home Depot for the skins with Divinycell, 6 ounce glass and epoxy.  I made forms using 2x6s that followed the curve of the stainless frame held together with 2x3s.Smotth side out, sand off some of the bumps before you lay it up.  Great for solar panels.

Thanks - took a look at the FRP board and looks like another great option for the form material. Your description of how you built the mold is exactly what I had in mind as well at this point so thats encouraging. 

After getting out to the boat once or twice more I think I'll have a pretty solid plan for shape and direction. If there is any additional input on: 

• Types of suitable foam core material
  
• Type and weight of cloth material
  
• Any input on finishing process and prep for painting
  

I'd love to keep taking input. Thanks everyone! 

// Phil

 

[slug zitski]

@slug zitski

// Make the core thick or you will not be able to bury electric cable conduits, backing plates , structure and will have difficulty radius profiling the perimeter the inside surface is the most difficult the finish… make this the mold side. 

Roger that. Will definitely think through cable runs before production. 

I need to take some final measurements at the boat but am leaning toward 3/4" core. Total final unit would probably end up in the ball park of 1". Thing I'm fighting against here is I'm 6' 1" and want to make sure I can stand up at the helm. Want to go as thick as possible but also run out of room pretty quickly with total height. Going to get to the boat soon on a quiet day and run up the main and see how much total room I'm working with for the entire thing and go with the thickest possible material that won't look too chunky when complete. 

// Sail trim window or opening hatch is needed

Great consideration. I will have permanent hard panel solar on top but will continue to think this through. I will play around with panel arrangement to see if I can accommodate something here. Another option - again need to confirm a few things at the boat - is I might be able to build this in a way where I can easily poke my head out the back of it to evaluate trim. Will continue to noodle plan on this. 

@jsaronson

// I've done 2 hard biminis using 4x8 FRP wall panels from Home Depot for the skins with Divinycell, 6 ounce glass and epoxy.  I made forms using 2x6s that followed the curve of the stainless frame held together with 2x3s.Smotth side out, sand off some of the bumps before you lay it up.  Great for solar panels.

Thanks - took a look at the FRP board and looks like another great option for the form material. Your description of how you built the mold is exactly what I had in mind as well at this point so thats encouraging. 

After getting out to the boat once or twice more I think I'll have a pretty solid plan for shape and direction. If there is any additional input on: 

• Types of suitable foam core material
  
• Type and weight of cloth material
  
• Any input on finishing process and prep for painting
  

I'd love to keep taking input. Thanks everyone! 

// Phil

Heat rises

your head is in the hot zone 

think of this when building the top

typically. The inside structural perimeter frame is set back from the roof edge and designed to accept enclosure curtains 

you could probably avoid stainless supports and go composite 

g10, Fiberglas , carbon tubes are readily available and much easier to work with 

 

[2airishuman]

• Types of suitable foam core material
  
• Type and weight of cloth material
  
• Any input on finishing process and prep for painting
  

Core material - let price and availability be your guide.  Balsa, divinycell, corecell.

Insulation foam from the lumberyard is cheap but even the heavier of the two widely available grades isn't nearly as dense the foam sold as core material.  So, not as strong, and you would need thicker.