Alloy hull, which fixings??

[rusty McCaw]

Hi guys, currently arranging where things are going to live on my boat but can't figure what fixings will be best. Hull is alloy but I believe stainless bolts and rivets are stronger than alloy ones, but will having these stainless fittings promote electrolysis or other deterioration problems..

[Jon.esp]

Yes always best not to mix metals where ever possible with alloy hulls but the problem will not be that bad if using ss, the boat is not left afloat and rinsed off with fresh water after recovering. If it were me I would go and see your local yacht mast rigger, explain what you are doing and see if you could scrounge a handful of his rivets. With the bolts, if using ss, I would use nylon or similar washers / grommets and ensure there is no metal to metal contact. But I though you Kiwis had lots of experience with alloy boats so there must be an abundance of local advice and help. Oh….. and I assume it is a rib hull not sib with floor boards but you have posted in the sib section.

Jon

[captnjack]

316 stainless is standard. Then add zincs to address corrosion just as you would with any other boat. If in fresh/brackish water you might consider manganese anodes as zinc isn't sacrificial enough and different aluminum alloys might end up being preferentially corroded (e.g. in your engine or remote from the zinc).

Aluminum bolts are: 1) not really available 2) 1/3rd weaker and will need to be massive to compensate.

[rusty McCaw]

Ended up using alloy rivets at this stage, thanx for you advice

[jyasaki]

Keep an eye on those aluminum rivets. They tend to weaken with stress.

jky

[Jon.esp]

Agree with JKY. I think a rigger would have given you Monel ones and some Duralac or similar compound but perhaps that’s a bit OTT as we don’t know what you are attaching to what. Hope it works out fine.

Jon

[rusty McCaw]

Yea thanx guys, I used some high quality alloy rivets to fix a strap to support my fuel cell. Looking at shear strength I think I'm going to be fine

[jyasaki]

Pretty much what I did on my SIB (a few times.) Eventually the rivets break the heads off, presumably from repeated stress. Hopefully you have better luck.

jky

[rusty McCaw]

If I have any issues I will go straight to stainless, I don't see this strap moving anytime soon tho.