Screwing, not bolting, a small deck hatch an option?

demonboy

demonboy

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I was wanting to bolt down my small (0.5m x 0.3m) deck hatches using butyl tape. Unfortunately it is not possible to attach a nut underneath. I think they were bolted down through a threaded hole into the fibreglass without the nut on the end. Because of the design the bolts come through the deck close to the edge of the lip, so there's only so much fibreglass around the bolt. That is, to chisel away in order to make room for a nut means losing the thickness of the lip, making it very thin.

lip.gif


How sensible or stupid would it be to screw them down into a pre-drilled hole using 5mm screws (50mm in length) and Sika 291 instead? Because they are small I figured with 12 screws around each frame it should be enough to keep it in place with the Sika providing some strength that the butyl tape doesn't offer, but I'm worried about movement over time and forces on the screws in the fibreglass. Additionally, one of the problems is the lid, which is separate and has a 'tab' of aluminium which attaches to two of the bolt holes. Opening and closing exerts more force to those two holes than the others, especially if the lid is tight (I can loosen this off of course).

That said, my water and fuel caps are also screwed down with 291 and they also get a lot of force on them when unscrewing and screwing up the cap, so I'm wondering if the combination of strong, long screws and the Sika is fine.

My carpenter came up with an alternative: epoxy a nut into the top of the countersunk hole. This sounds good in theory but it means making sure every one of those 12 nuts are epoxied flat. If they're at an angle, the bolt won't go all the way through. Sounds a bit too fiddly.

Appreciate any thoughts/experience on this.

Thanks,

Jamie
 
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I can only say that the top of my fresh water tank about 1.5 by 0.5 metres has been held down with self tappers and sealant for the past 30 years. I have often wondered just how much force is applied to this lid in a seaway as it is possible to hear the water sloshing about from some distance away. Seems like a more demanding application than your small hatches and Sika 291 is pretty powerful stuff. Although there has been a post in the past few days suggesting that one of the 3M equivalents is even stronger.
 
I used screws on my small hatch with no problems. With mine i couldn't use nuts due to the timber ceiling lining in the saloon. No problems so far.I dipped each screw in sealant and used a neoprene type seal.
 
I think you need to find a way to bolt, or screw, the hatch down,

They need to be secure in case a larger than anticipated waves hits them, or it. I would not want to rely on Sika for a deck hatch.

That does not solve your problem.

I'm not entirely clear of the design as the way you have drawn it the bolt appears to come through internally on a curved surface - and I would think to tighten anything up you need to have an internal flat - but that you can make from a variety of materials. One option, depending on how much room there is might be to chop the edge of the relevant, internal, nuts so that they meet the bolts.

I might look at barrel bolts, also called Chicago bolts and much more imaginatively sex bolts - they have come up in the last month or so on a couple of threads. They are effectively an internally threaded cylinder with a variety of heads. They are often used in knockdown furniture. They come in standard metric sizes in a variety of materials, but including 316 stainless. Gebo use them in their hatches. Make a search here on YBW as there were a couple of UK suppliers mentioned.

I'm a bit far away to suggest from whom to buy but there are number of UK stockists and they come in a huge variety of designs to meet all sorts of applications.

I'd still use Sika, or something similar as a seal. But I do recommend you bolt them down onto wet Sika. And then when the Sika has set give each bolt an extra half turn.

Good luck

Jonathan
 
J Neeves said:
I think you need to find a way to bolt, or screw, the hatch down... I'd still use Sika, or something similar as a seal. But I do recommend you bolt them down onto wet Sika. And then when the Sika has set give each bolt an extra half turn.

Good luck

Jonathan
Click to expand...

Hi Jonathan. Perhaps I wasn't clear in my original post. I am looking to screw them down instead of bolting. I am not looking to use Sika only, it is used in addition to.

And... NEVER give Sika an extra half turn after it has set. This is a common misconception in using adhesive sealants and a mistake I used to make when I first purchased the boat, which resulted in various deck fittings forever leaking. Basically, by allowing the Sika to set and then giving it an extra turn, you break the seal. Sika and other adhesive sealants should be applied, screwed into place tightly, and that's it, job done. The only thing you should do after it has set is trim away any excess.
 
demonboy said:
Hi Jonathan. Perhaps I wasn't clear in my original post. I am looking to screw them down instead of bolting. I am not looking to use Sika only, it is used in addition to.

And... NEVER give Sika an extra half turn after it has set. This is a common misconception in using adhesive sealants and a mistake I used to make when I first purchased the boat, which resulted in various deck fittings forever leaking. Basically, by allowing the Sika to set and then giving it an extra turn, you break the seal. Sika and other adhesive sealants should be applied, screwed into place tightly, and that's it, job done. The only thing you should do after it has set is trim away any excess.
Click to expand...

We learn something every day!

Jonathan
 
J Neeves said:
I might look at barrel bolts, also called Chicago bolts and much more imaginatively sex bolts - they have come up in the last month or so on a couple of threads. They are effectively an internally threaded cylinder with a variety of heads. They are often used in knockdown furniture. They come in standard metric sizes in a variety of materials, but including 316 stainless. Gebo use them in their hatches. Make a search here on YBW as there were a couple of UK suppliers mentioned.


Jonathan
Click to expand...

Thanks for that - I have now looked these up - I have used them in flat pack furniture but never knew what they were called.

Learn something every day
 
demonboy said:
With me, it's normally five new things a day, gleaned mainly from making stupid mistakes ;)
Click to expand...

I confess not to have used Sika for some time now. There are other 'similar' adhesives.

Most of these adhesives have incredible elastic, or compression, specifications. If you cannot compress them, with half a turn, and the seal is broken then the surfaces were incorrectly prepared.

Cleaning is critical, prior to application.

Speak to anyone who is required to remove Sika and they will advise, if correctly applied, it is a major issue to to remove

Jonathan
 
pvb said:
I think the most common name for them is "interscrews".
Click to expand...

When I was carrying out my first destructive tests on swivels I was not sure what to call them, other than interscrews. I phoned an expert whose name I found on the internet and he told me they were 'sex nuts'. When I remonstrated that this research was for a serious magazine article he got quite shirty, insisting that this was the correct description.
 
vyv_cox said:
When I was carrying out my first destructive tests on swivels I was not sure what to call them, other than interscrews. I phoned an expert whose name I found on the internet and he told me they were 'sex nuts'. When I remonstrated that this research was for a serious magazine article he got quite shirty, insisting that this was the correct description.
Click to expand...

;)
 
They were used for book binding, or files, and I think they were called Chicago Bolts.

The Chinese call them, in English, Sex Bolts. I've just bought some from an Oz supplier - they were called Barrel Bolts.

Most manufacturers will recognise exactly what you are talking about if you use any of these names - and there are a few more.

Jonathan
 
30boat said:
A friend's Jeanneau had it's hatches screwed down and at 23 years old hadn't had a leak.
Click to expand...

Maybe Jeanneau know something about applying sealants correctly:)

Many high rise buildings have their exterior glass panels simply attached with sealant - depends on using the right sealant for the job and the correct application ( edit the best example I know are the Petronas Towers in KL). For many of these adhesives if you use any solvents and do not remove the solvent completely (usually with water) the window (or in this case - hatch) will leak. Attaching with screws will be perfectly successful if the body to which the screws are attache is sound (and with enough depth, and is not mostly foam and filler). In the absence of this information, knowing hatch flanges (overlap) can be minimalist, I would prefer nuts and bolts with a decent area, backing plates (which in this case could be long and narrow) holding the whole thing together.

I'm guessing that Jeanneau, knowing they were to use screws, beefed up the area (lots of glass) to take the loads.

Jonathan

edit Most port lights (and hatches) have a backing plate matching the exterior frame and the whole thing is bolted together - hopefully they are not over engineering simply to charge us more money:( close edit
 
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Just a thought - could you not bond the hatch directly to the deck using epoxy fillets inside and out, reinforced with f/g tape?
Would make it an integral part of the deck, no worries about coming loose or leaking.

J.
 
J Neeves said:
Most port lights (and hatches) have a backing plate matching the exterior frame and the whole thing is bolted together - hopefully they are not over engineering simply to charge us more money:( close edit
Click to expand...

My side portlights are like this but the deck ones are all mounted to the deck with through-bolts only. No backing plate, unfortunately. I doubt getting hold of s/s sex-nuts would be easy here in south Thailand and time's running out for overseas delivery so I'll try the screwing route and see how I get on. I've filled in the holes with epoxy and tomorrow I'll attempt to screw them down, providing the screws are delivered.

Thanks for the replies.
 
I missed out on the Thailand location, sorry.

Equally sorry - I'm commenting - on the run.

You can get sex nuts out of Oz, Sentinel do a range. Sex nuts or a variation of them are used in the stainless wire used in balconies, the sort that are like stainless lifeline on a yacht. They use a sex nut at the end of the run, to tighten the wire (as we might use a bottle screw). The common sizes are 5mm and 6mm - but they do make 8mm and 10mm. Bridco in Oz supply them and someone told me they were made in Thailand (but Thailand is a big place so that's not much use). Sentinels are true sex nuts but they call them barrel nuts, the ones from Bridco are not quite so good (or not for what you want) - Sentinel's come in a variety of metals including 304, no 316 or not that I recall. stainless and are M4, M5, M6, M8, M10 and M12. Sentinel do some Imperial sizes as well.

Try this website:

www.sentinelgrp.com.au

prolock resytork

But I fear I might be a bit late:(

I've just bought from both companies, both were very helpful.

You only need buy the female part as you can get matching male parts in any stainless supplier.

Jonathan
 
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