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Old 15-10-2019, 13:19   #1
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Making hard Coach Roof/ Bimini - questions

Greetings from Miami

I have and EDELCAT33 that has served me well but the Admiral does not like the center pod, too hot and claustrophobic for her.

For those not familiar with EDELCAT33, is 3 separate structures and is demountable
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So I am thinking of getting rid of it and make a hard coach roof like a Mainecat 38 or 41. My thought is to have Aluminum posts and build the hard to out of either foam Divinycell or Nida-Core Honeycomb. The latter has the option of having pre-laminated with 1 layer of 18oz woven roving in either side with polyester.

The coach roof or hard top would be roughly 8 ft long by 16 wide.
My question is which thickness to get so if I have to walk on top, it would hold. They offer 1/2, 3/4, 1 inch.

Looking at the new Maincat38, I see they use hard sides instead of the zip up vinyl they normally do

Any thoughts?
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Old 15-10-2019, 13:37   #2
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Re: Making hard Coach Roof/ Bimini - questions

I am in the process of having a 8'W x 11'L hard top professionally constructed for my boat (displacement trawler) with dual-posts at the corners without additional exoskeleton - spec is to be able to walk on it and a place to mount solar panels. No engineering involved, just years of experience from a yard that has done them for years. They recommended 1-inch Divinylcell and five layers of glass on top and four on bottom. Design has 6-inch camber side-to-side, and a 2-1/2" 'rim' around the edge, both of which add structural strength.

Also, if you plan to run any hidden electrical wires, you may need to route-out a channel, which slightly weakens the foam core (though most of the strength comes not from the foam, but the space it creates)

Sounds like you do not plan a frame either, just post(s) at the corners. My opinion only, 1-inch foam core to span 16-feet may not be adequate unless it has a a great deal of camber. If it was 8-foot wide and 16-feet long, maybe. But hey, maybe there are some engineers out there who can say for certain...
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Old 15-10-2019, 18:00   #3
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Re: Making hard Coach Roof/ Bimini - questions

If you worry about strength over the span why not use fiberglass stringers just like single skin hulls have. I'll lay up my glass over a ply male mold using CSM/WR.CSM/Divynicell/CSM/WR/CSM. Of course there will be cut-outs for opening hatches (front/top) and windows
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Old 15-10-2019, 20:14   #4
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Re: Making hard Coach Roof/ Bimini - questions

I agree, thinking on using schedule40 pipe cut lengthwise in half as stringers and to run any wire needed on top.
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Old 15-10-2019, 23:46   #5
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Re: Making hard Coach Roof/ Bimini - questions

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Originally Posted by carlosproa View Post
I agree, thinking on using schedule40 pipe cut lengthwise in half as stringers and to run any wire needed on top.
Or use strips of foam or as the pic above timber profile forms. Its the verticle surfaces (perpendicular to the surface) that really adds the strength. With a cut pipe you have semi circular profile so your vertical surface is only on the cut edge the diminishes.

Of course pipe is still a big improvement on nothing. And often its about what is easy and convenient.

Just saying.
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Old 16-10-2019, 00:12   #6
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Re: Making hard Coach Roof/ Bimini - questions

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Old 16-10-2019, 00:29   #7
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Re: Making hard Coach Roof/ Bimini - questions

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Originally Posted by Q Xopa View Post
Or use strips of foam or as the pic above timber profile forms. Its the verticle surfaces (perpendicular to the surface) that really adds the strength.

Just saying.

I'll be using Divynicell as it is light weight but it is the fiberglass that gives it strength and stiffens it up

The other consideration is whether you want it to be "sacrificial" or fixed. If a large sold wave swept over the hull do you want the dodger to be swept away without damage to the hull or do you want to build it so it can take any condition? I suppose that is one thing going for a " soft" dodger.
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Old 16-10-2019, 04:17   #8
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Re: Making hard Coach Roof/ Bimini - questions

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Originally Posted by Q Xopa View Post
Or use strips of foam or as the pic above timber profile forms. Its the verticle surfaces (perpendicular to the surface) that really adds the strength. With a cut pipe you have semi circular profile so your vertical surface is only on the cut edge the diminishes.

Of course pipe is still a big improvement on nothing. And often its about what is easy and convenient.

Just saying.
Actually, it's not that they are vertical, it's the distance from the center of bending.

Assuming a 3" half pipe (6" total diameter pipe) vs a 3"x1" rectangular wood stringer and both covered with equivalent fiberglass (which provides the bulk of the strength, I would have to run the numbers but the pipe is likely stronger design because the cross sectional area of fiberglass 3" away is larger with the pipe.

With a little pre-planning to run wires, it does double duty.
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Old 16-10-2019, 04:48   #9
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Re: Making hard Coach Roof/ Bimini - questions

Builder of my hard top (trawler 11' L x 8'W) is using 1/2" cpvc pipe as electrical conduit to lights.

I have to say, I'm surprised there have been scant comments on (1) structural strength of spanning a 16-foot width; and (2) single layer of glass OP proposes over/under the foam. If this were a floor in a house, would see something like 2x10s on 16" centers.
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Old 16-10-2019, 04:53   #10
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Re: Making hard Coach Roof/ Bimini - questions

"Half-round and foam cores

Half-round or foam reinforcements with a fiberglass skin are a simple way of strengthening panels. With this method, the core material primarily serves as a form and the laminated fiberglass fabric provides the stiffening strength.For light-duty applications, an economical core material for this method of reinforcement is a cardboard or paper tube cut in half lengthwise. Pieces can be placed end to end to reinforce larger areas. The tube should be heavy enough to hold its shape during the lay-up and cure of the fabric laminate. Low-density foam also makes an economical core material. Cut the foam on a table or band saw to a trapezoid shaped cross section. The trapezoidal cross section is more effective than the half-round cross section because it places more reinforcing fibers on the top of the stringer, away from the stringerís neutral axis"


There's a lot more you can read here.
https://www.westsystem.com/wp-conten...anual-2015.pdf
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Old 16-10-2019, 04:59   #11
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Re: Making hard Coach Roof/ Bimini - questions

Quote:
Originally Posted by mvweebles View Post
Builder of my hard top (trawler 11' L x 8'W) is using 1/2" cpvc pipe as electrical conduit to lights.

I have to say, I'm surprised there have been scant comments on (1) structural strength of spanning a 16-foot width; and (2) single layer of glass OP proposes over/under the foam. If this were a floor in a house, would see something like 2x10s on 16" centers.

I must be going blind!!

What OP has suggested only one layer of glass under and over the foam?

Please elucidate.
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Old 16-10-2019, 05:19   #12
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Re: Making hard Coach Roof/ Bimini - questions

I may have misread slightly. Below is quote from original post (for some reason, I can't use the "quote" feature on my online, thus cut paste)


"My thought is to have Aluminum posts and build the hard to out of either foam Divinycell or Nida-Core Honeycomb. The latter has the option of having pre-laminated with 1 layer of 18oz woven roving in either side with polyester."
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Old 16-10-2019, 05:46   #13
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Re: Making hard Coach Roof/ Bimini - questions

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Originally Posted by coopec43 View Post
"Half-round and foam cores

Half-round or foam reinforcements with a fiberglass skin are a simple way of strengthening panels. With this method, the core material primarily serves as a form and the laminated fiberglass fabric provides the stiffening strength.For light-duty applications, an economical core material for this method of reinforcement is a cardboard or paper tube cut in half lengthwise. Pieces can be placed end to end to reinforce larger areas. The tube should be heavy enough to hold its shape during the lay-up and cure of the fabric laminate. Low-density foam also makes an economical core material. Cut the foam on a table or band saw to a trapezoid shaped cross section. The trapezoidal cross section is more effective than the half-round cross section because it places more reinforcing fibers on the top of the stringer, away from the stringerís neutral axis"


There's a lot more you can read here.
https://www.westsystem.com/wp-conten...anual-2015.pdf
This paragraph is wrong unless you define the sizes of both shapes.

Assuming a similar overall depth (say 3" tall half round vs a high aspect 3" tall by 1" wide trapezoidal shape), this paragraph is incorrect assuming a similar fiberglass layup for both.

If you make the trapezoid 3" tall by 6" wide, the trapezoid will be stronger.
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Old 16-10-2019, 05:47   #14
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Re: Making hard Coach Roof/ Bimini - questions

Quote:
Originally Posted by mvweebles View Post
I may have misread slightly. Below is quote from original post (for some reason, I can't use the "quote" feature on my online, thus cut paste)


"My thought is to have Aluminum posts and build the hard to out of either foam Divinycell or Nida-Core Honeycomb. The latter has the option of having pre-laminated with 1 layer of 18oz woven roving in either side with polyester."

I have never used "Nida-Core Honeycomb" but I assume you buy it with the WR on either side and go from there. It looks as though that is right.


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Old 16-10-2019, 07:18   #15
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Re: Making hard Coach Roof/ Bimini - questions

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Originally Posted by valhalla360 View Post
This paragraph is wrong unless you define the sizes of both shapes.



Assuming a similar overall depth (say 3" tall half round vs a high aspect 3" tall by 1" wide trapezoidal shape), this paragraph is incorrect assuming a similar fiberglass layup for both.



If you make the trapezoid 3" tall by 6" wide, the trapezoid will be stronger.


My bad on explaining. I am not saying that I will use a layer of FG, I am saying there is a choice of prepegged FB material sold. From there, I can always add layers.
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