Bimini Hardtop considerations

[Cpt Mark]

Hi all,

I'm about to start building my hardtop bimini for my IPY Packet cat 35.

Besides sun/rain protection solar is going up there the other big reason is to move the mainsheet up there as well. Where it sits now is right behind the helms persons head. Not comfortable. Having tried to hire naval architects without success the current plan is to use 2.5" SS going about 7' up, 10 feet over and then back down again. The SS will be attached on the horizontal bottom with bolts and the vertical edge will have 6 bolts in reinforced wider area with G10 backing plates epoxied to the hull.

I contacted a person with a Lagoon 44 who just has 2 poles going up. The poles are 3" (80mm) and probably connected with a crossbeam which may be connected to the bimini structure. The mainsail on the Lagoon is around 750 sq feet. which is greater than my total sail area. My Main is 229 sq feet.

I'm fairly confident that 2.5" SS would be more than strong enough to handle the loads. 2.5" aluminum would be better from a weigh perspective as would 2" SS but now I'm not so confident.

If you have 35-40 footish cat with the traveller mounted above please let me know what size/material tubes you have and any other structure support facts you know. I spoke with a couple who have a Mahe 38? Hurricane damages. Bimini missing. Looks like it was held on by 1.5" SS poles. Some of the poles were still attached.

Another question for those that have a hardtop bimini is solar panels. When reefing do you ever have issues with the sail getting caught up in the solar panels?

Last question. What mods do you have on your hardtop that like, dislike, wish you had?

Long post, thank you for reading and any input you may have.

[Sailorman Ed]

Mark, I have made 2 hard biminis, one for my 34 ft Prout and a much larger one for my 12m cat. Both had an edge hand hold/rain gutter which also stiffens the bimini, I also arched the back but used a straight board so that in the middle, the board was below the bimini but above at the ends. I have 2 large solar panels on the 12m cat, never had a problem with the lines getting tangled but I have the panels flush to the bimini. I did put in pivot points to orient the panels but never had to do so.
I used aluminum support poles but the next one will be a aluminum structure so I can make the bimini lighter. The Prout used a polypropylen panel, the bigger one used 1" balsa. Divynicell foam is much lighter and will used that for the next one.
Focus on making the underside smooth, the top side you want a little rough to keep your footing. We keep all kinds of stuff up there ( water jugs getting warm for showers, boat hooks, cockpit clutter while at anchor).
Consider putting in some wires for speakers and lights.

[Alistair242]

Theses guys built a pretty decent hard top from scratch. Worth a watch.
This is part 1.

https://youtu.be/-RPaxTwvCXg

[Cpt Mark]

Originally Posted by Alistair242

Theses guys built a pretty decent hard top from scratch. Worth a watch.
This is part 1.

https://youtu.be/-RPaxTwvCXg

Yes they did. t
hanks

[Cpt Mark]

Originally Posted by Sailorman Ed

Mark, I have made 2 hard biminis, one for my 34 ft Prout and a much larger one for my 12m cat. Both had an edge hand hold/rain gutter which also stiffens the bimini, I also arched the back but used a straight board so that in the middle, the board was below the bimini but above at the ends. I have 2 large solar panels on the 12m cat, never had a problem with the lines getting tangled but I have the panels flush to the bimini. I did put in pivot points to orient the panels but never had to do so.
I used aluminum support poles but the next one will be a aluminum structure so I can make the bimini lighter. The Prout used a polypropylen panel, the bigger one used 1" balsa. Divynicell foam is much lighter and will used that for the next one.
Focus on making the underside smooth, the top side you want a little rough to keep your footing. We keep all kinds of stuff up there ( water jugs getting warm for showers, boat hooks, cockpit clutter while at anchor).
Consider putting in some wires for speakers and lights.

Thanks for your info. I'm thinking Nida Core as it's even lighter. How thick of glass did you put on yours? My measurements are roughly 10'x13'.

[UYA]

Cpt Mark,
recently we built a hard top bimini for our monohull. Here is the list of what we deemed important. Maybe it gives you some food for thought...

solar panels in bimini (not on top)

• flat surface, no snagging of lines
• slimmer build
• cooler panels due to wind exposure on back - better performance

rim around top

• as rain catcher, backup to water maker
• gives extra rigidity
• protects solar panels if mizzen boom falls down

rim around bottom

• water doesn't come inside
• holes in rim allow for hanging up canvas for extra sun protection
• more rigidity

We used Nidacore with Epoxy.

[Cpt Mark]

Originally Posted by UYA

Cpt Mark,
recently we built a hard top bimini for our monohull. Here is the list of what we deemed important. Maybe it gives you some food for thought...

solar panels in bimini (not on top)

• flat surface, no snagging of lines
• slimmer build
• cooler panels due to wind exposure on back - better performance

rim around top

• as rain catcher, backup to water maker
• gives extra rigidity
• protects solar panels if mizzen boom falls down

rim around bottom

• water doesn't come inside
• holes in rim allow for hanging up canvas for extra sun protection
• more rigidity

We used Nidacore with Epoxy.

Questions. How thick of Nidacore, how thick/many layers of epoxy? Can you stand easily on it? Your
solar panels, are those flexible or hard panels?

Mark

[Cpt Mark]

Hi all, thank you for the suggestions etc. I appreciate it.

Mark

[Tupaia]

Originally Posted by Cpt Mark

Thanks for your info. I'm thinking Nida Core as it's even lighter. How thick of glass did you put on yours? My measurements are roughly 10'x13'.

I built a bimini that is 17' x 7'6" from 16mm Polycore there is about 1mm epoxy skin with woven rovings top and bottom. The panel weighs 19kgs and is supported on an aluminium frame. The Polycore is just able to support walking on but the 1m frame spacing does not allow walking on without additional support.


If you use nidacore or polycore then the edge treatment needs to be carefully considered otherwise any weight advantage can be easily lost.


I fitted a plastic bolt rope channel top and bottom that allows for screens and shade cloths as required, protects the edges and also provides a hand grip.

[UYA]

Originally Posted by Cpt Mark

Questions. How thick of Nidacore, how thick/many layers of epoxy? Can you stand easily on it? Your
solar panels, are those flexible or hard panels?

Mark

• Our Bimini is not designed to stand on (it's on a monohull). I just used 2 layers of fiberglass
• I believe the Nidacore is about 10mm thick. I added additionally support beams on the underside (see pictures)
• The panels are hard panels. They are embedded into the structure so that they are flush on the top

[Cpt Mark]

Originally Posted by UYA

• Our Bimini is not designed to stand on (it's on a monohull). I just used 2 layers of fiberglass
• I believe the Nidacore is about 10mm thick. I added additionally support beams on the underside (see pictures)
• The panels are hard panels. They are embedded into the structure so that they are flush on the top

Thanks. And thanks for the photos