Steel deck: tap or rivnut?

[apw3]

Fitting a Scott Boombrake. The idea is to attach the restraining line to folding pad eyes on the flush steel deck. The boat is a 36' Van de Stadt Migrant.
The question for you engineers out there is: should I fix the pad eye to the deck by tapping and bolting on a 4mm deck (I cannot get underneath the deck) or should I use stainless rivnuts set with a rivnut tool (not the pliers type).
The loads are potentially high and the angle of loading on the pad eye would be around 45 degrees.
The pad eye would have 3 fixing points , either 6mm or 8mm.
What do you recommend? Is there anything else I should consider.
Many thanks all.

 

[Wansworth]

Ask Brent!

 

[penberth3]

Consider the pitch of the bolt thread i.e. how many threads will be in the deck.

Is welding an option?

 

[GHA]

Is welding an option?

Best option otherwise just a matter of time before water will get into the holes & rust.

Can be a nightmare inside though to first get at the underside of the deck then take a little foam out and replace after welding.

 

[lw395]

I'd consider not fitting a boom brake, AKA boom breaker.

 

[stephen_h]

M6 nut is 5mm thick and an M8 is 6mm thick so 4mm
plate is not thick enough.

 

[john_morris_uk]

I'd consider not fitting a boom brake, AKA boom breaker.

Indeed. Gybe preventer from the end of the boom to forward and then back to the cockpit (so that you can release it and sail upwind without going forward if necessary.)

You only need to rig the preventer if there's a risk of a gybe.

(However one sailing school I taught at had a standing order that if the wind was abaft the beam, the instructor was NEVER to leave the helm area as the novice crew WOULD gybe you all standing at some point if you weren't there to stop them steering off on some crazy course.)

 

[rogerthebodger]

Fitting a Scott Boombrake. The idea is to attach the restraining line to folding pad eyes on the flush steel deck. The boat is a 36' Van de Stadt Migrant.
The question for you engineers out there is: should I fix the pad eye to the deck by tapping and bolting on a 4mm deck (I cannot get underneath the deck) or should I use stainless rivnuts set with a rivnut tool (not the pliers type).
The loads are potentially high and the angle of loading on the pad eye would be around 45 degrees.
The pad eye would have 3 fixing points , either 6mm or 8mm.
What do you recommend? Is there anything else I should consider.
Many thanks all.

Make up 2 pads of stainless steel at least 6 mm thick and tap the fixing holes for the pad eye in the pads.

Then weld the pads to the deck all round. Screw the pad eyes to the welded pads.

If the pad eyes break they can be replaced and no holes through the deck to leak.

 

[Spirit (of Glenans)]

Indeed. Gybe preventer from the end of the boom to forward and then back to the cockpit (so that you can release it and sail upwind without going forward if necessary.)

You only need to rig the preventer if there's a risk of a gybe.

(However one sailing school I taught at had a standing order that if the wind was abaft the beam, the instructor was NEVER to leave the helm area as the novice crew WOULD gybe you all standing at some point if you weren't there to stop them steering off on some crazy course.)

+1 for each paragraph, particularly the last!

 

[winsbury]

What about friction drilling to increase the thread available in thin metal: https://www.youtube.com/watch?v=FIgg6sey0C8

 

[William_H]

I also am not in favour of gybe preventer. However if OP wants to attach his pad eye. One option might be to attach the pad eye to a larger area plate on top of the deck which can then be riveted or screwed with tapped threads to the deck. The larger area giving option for more screws rivets etc. ol'will

 

[Ladybirdgaffcutter]

Make up 2 pads of stainless steel at least 6 mm thick and tap the fixing holes for the pad eye in the pads.

Then weld the pads to the deck all round. Screw the pad eyes to the welded pads.

If the pad eyes break they can be replaced and no holes through the deck to leak.

This^^ I've seen it done on a steel pilot cutter (Annabel J :encouragement: ) and it was a great solution to the problem.

I also think boom brakes are the work of the devil; not to blow my own trumpet but I routinely gybe a heavy gaffer singlehanded, if I can do it, anyone can!

 

[apw3]

Thanks for all the replies.
Couple of things. The majority of you are not in favour of the boombrake concept. Is that on the basis of first hand experience? Anecdotal evidence? Theoretical knowledge? It is difficult to evaluate the validity of the posts in this respect, particularly when the issue concerns the safety of the ship. On the other hand to balance things up, no one has posted in favour of boombrakes either although the subject has probably been aired in full elsewhere.

I have not considered welding the deck as I am thinking that the heat involved may pose a fire risk to the insulation underneath the deck and damage to the newly repainted deck. Similarly I have not considered friction drilling. Happy to be advised otherwise though. Thanks all, much appreciated.

Any further thoughts would be welcome

 

[Ladybirdgaffcutter]

1st hand experience of boom brake, professionally installed on a biggish, upmarket yacht; it was absolute dangerous liability. It also did not allow us to gybe in the correct, time-honoured (and definitely safe) manner. Total PITA.

But if you do go for it, I don't think your deck is thick enough to just screw bolts into, bearing in mind the loads. You have to bite the bullet, get the lining and insulation off the inside, whatever you do, in my opinion.

Sorry to sound so negative

 

[apw3]

That's helpful. Coming to same conclusion too.
Cheers.

 

[apw3]

Thank you all for the replies.
To conclude, I will remove the deck head lining, scrape away a patch of insulation, pop in a 10mm mild steel backing plate and through bolt the pad eye, then replace the insulation. Risk of a leak but minimal using proper sealant/adhesive.
Once again, thanks.