Fit Railblaza to binnacle

[SimonNZ]

Hi all

I'm removing cheap old cupholders and automotive phone mounts from the back of the instrument cluster at the helm of our Beneteau Oceanis 400, and replacing with Railblaza Starports.

I can't reuse the screw holes.

The cluster is fibreglass. I went to start, then realised I haven't drilled any holes on this boat yet! I want to get this as right as I can. I'm happy to screw the self-tappers through, that's what's been used before, though I guess a nut & bolt with washer and locking washer would be more proper. What's the best approach? Is it true that it's best to use a countersink little first to prevent cracking around the drill hole, and if I use self-tappers what's the hole-to-screw size recommendation?

cheers!

 

[RunAgroundHard]

You will find drill bit sizes for self tappers easily in google, but here you go What Drill Size Should I Use For Self Tappers | Drill Sizes I have measured the diameter of the shaft (not the threads) with a vernier and used that to drill a pilot hole with, as the OD of the thread cuts into the material.

For something light weight, self tappers may be useful but the GRP has to be thick enough to engage sufficient length. How thick is the GRP you want to screw into? If the GRP is thin, or if there is a chance the Railblaza Starports will be used to secure a more heavy item, then nut and bolts with appropriately sized backing pad may be a better option, especially if they could be grabbed accidentally to stop a fall or regularly bumped into.

 

[RJJ]

Countersinking the hole before screwing in helps protect the brittle gelcoat from cracking under movement/vibration etc. Also provides for a bit more volume of whatever flexible sealant you use.

To me the theory suggests you want to cut away sufficient gelcoat so that the screw is never in actual contact with it.

 

[SimonNZ]

Thanks very much! I know these seem obvious questions but there's nothing better than guidance from people who've done it before.

The GRP is 3mm thick. There's a lot of instrumentation wiring floating around in there, bare screw points are less than ideal - nut and bolt with a 3mm ply pad might be better.

Any recommendation on a good type of sealant for this scenario, Sikaflex or similar?

 

[thinwater]

... Any recommendation on a good type of sealant for this scenario, Sikaflex or similar?

Sika is a manufacturer, and they make LOT of products. Sika 291 is the one you want.

 

[SimonNZ]

Perfect, I was hoping to discover the product. Thank you!