Beginner question on FRP parts on Deck

[AdvCom]

I have been asked to make some benches in FRP for a deck on a existing FRP boat. Im a furniture builder with plenty experience Wood , Metal Casting etc but only a few years with resins in my designs.

Could anyone offer some typical lamination schedules for a pretty basic bench 8ft long with a back height of 30" and a seat depth of 22". Its all enclosed and pretty basic.. the outside appearance is a white gel coat matching the boat.

thoughts ? Thanks

 

[bajansailor]

Welcome to the Forum AC.

Re how it is 'all enclosed', does this mean that there are lockers under the bench?
If so, are they accessed from the top or the side?
Do you have any rough sketches that you can post showing what you have in mind?

 

[fallguy]

Cannot be done without more details.

structure? Bulkhead or stringers?

Core , no core?

solid frp requires a mould

to build no mould requires a core

..etc

 

[rwatson]

Yeah, what the others said AND how many bodies, scuba tanks, big bodies stepping of the deck onto them, gear stowage sizes needed, strength of fastening locations would also be handy.

 

[KD8NPB]

I have been asked to make some benches in FRP for a deck on a existing FRP boat. Im a furniture builder with plenty experience Wood , Metal Casting etc but only a few years with resins in my designs.

Could anyone offer some typical lamination schedules for a pretty basic bench 8ft long with a back height of 30" and a seat depth of 22". Its all enclosed and pretty basic.. the outside appearance is a white gel coat matching the boat.

thoughts ? Thanks

Bench bottom;
Gelcoat
450g CSM
450g CSM
12mm core
450g CSM
450g CSM

Bench back;
same, no core.

You could possibly eliminate the core in the bench bottom, but it will make the panel flexible which will probably cause cracks if people stand on it.

 

[wet feet]

I find it a bit curious that nobody has raised the point that it will need to be attached to the deck and it is something that needs to be factored in.There is also the convention that boat decks are normally cambered and the bottom face of the part needs to match the surface.If you have no prior experience of working with FRP it may be a good idea to make a small piece to gain some familiarity.The geometry of the part must be of a nature that will allow it to be removed from the mould and an understanding of draft is important.A complex shape may require the use of a multi piece mould to allow the part to be extracted and I really wouldn't recommend contemplating a male former and the need to achieve a good finish on the outside of the seat.It is less work to build a good plug and make a mould that is just good enough to produce the required number of parts.It also uses skills that a woodworker will already have.

 

[rwatson]

I find it a bit curious that nobody has raised the point that it will need to be attached to the deck .

Yeah, my contribution gets ignored "strength of fastening locations would also be handy."

 

[philSweet]

You need to post a detailed sketch with dimensions. Show the area on deck that it gets attached to, and the attachment method. You need to specify the manufacturing process - female mold, plug, assembled flat panels, etc. You need to specify the resin system, and whether it is chopper gunned, open hand layup, or vacuum bag infusion, and the types of glass you have available. Please post a photo of the vessel.

(your profile location is "phil" ??)

 

[wet feet]

I agree that a location of Phil isn't really helpful,could be the Philippines or Philadelphia or some other place.Now would we really expect a woodworker with no prior experience of laminating to go to the expense and trouble of equipping himself with a chopper gun?More likely to send the job to somebody equipped for the job,I would have thought.I have built a mould for a one off seat box from sheets of melamine faced board and accepted the need for an amount of detail finishing when the component was released.It could be an option,but we would need a sketch of the cross section to make constructive suggestions.

 

[AdvCom]

Wow you guys are fantastic! thanks for all the sound advice . Im going to study this a bit and add in your suggestions . Experiment and make a few mock ups . Ill keep you all posted as i progress. Thanks to all for the great advise and thought proving suggestions questions etc.

 

[AdvCom]

Welcome to the Forum AC.

Re how it is 'all enclosed', does this mean that there are lockers under the bench?
If so, are they accessed from the top or the side?
Do you have any rough sketches that you can post showing what you have in mind?

thanks BanjanSailor

Two benches opposite each other have storage area but not enclosed , open so they can slide their gear crates out and accessed from front of bench
I will post CAD or PDF

Thanks

 

[AdvCom]

Cannot be done without more details.

structure? Bulkhead or stringers?

Core , no core?

solid frp requires a mould

to build no mould requires a core

..etc

Thanks FALL GUY

I was thinking versus total core type lamination using my armacel 25mm in 50mm strips like making a stick built house on 40cm centers everywhere and cross trussing too strategically

I will make simple panel molds as the design is very linear and straight.

thanks

 

[AdvCom]

Yeah, what the others said AND how many bodies, scuba tanks, big bodies stepping of the deck onto them, gear stowage sizes needed, strength of fastening locations would also be handy.

Thanks R Watson,

Two benches are 21 people long, 2 more are 10 people long , 3 are 5 people long
the two long benches are over the crates that hold the Gear. Tentative plan is supports to seat height on 40cm centers outta laminated Armacel cores
Fastening was spec'd as 7.7 Cm angle tabbing at 8mm laminated over all thickness on all sections that touch the deck
Deck is a textured Core 40mm Armacel or a 48mm over all laminated thickness
thanks

 

[AdvCom]

Bench bottom;
Gelcoat
450g CSM
450g CSM
12mm core
450g CSM
450g CSM

Bench back;
same, no core.

You could possibly eliminate the core in the bench bottom, but it will make the panel flexible which will probably cause cracks if people stand on it.

Thanks KD8NPB,

Great advice .. so no WR sheet? on this schedule need if all cored armacel at 12mm for seats ?

thanks

 

[AdvCom]

I find it a bit curious that nobody has raised the point that it will need to be attached to the deck and it is something that needs to be factored in.There is also the convention that boat decks are normally cambered and the bottom face of the part needs to match the surface.If you have no prior experience of working with FRP it may be a good idea to make a small piece to gain some familiarity.The geometry of the part must be of a nature that will allow it to be removed from the mould and an understanding of draft is important.A complex shape may require the use of a multi piece mould to allow the part to be extracted and I really wouldn't recommend contemplating a male former and the need to achieve a good finish on the outside of the seat.It is less work to build a good plug and make a mould that is just good enough to produce the required number of parts.It also uses skills that a woodworker will already have.

Thanks Wet feet ,

the deck a has a mild texture and a center rise of 2 degrees to shed sea spray to the rebrand sides. The naval engineers said they will attach with something they call tabbing but to my eye its like angle iron but in a lamination form. Its pretty big i thought as about 7.5 cm and like 6mm thick if memory serves me.
The designs are linear and basic.. i was going to make hinged molds and lay up the actual parts and roll and demold polish up a bit and spray in all grip to make it spank.
thanks