Titanium bolts in marine environment?

contessaman

contessaman

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Hi folks.

I'm fitting a hydrovane self steering. Trying to make the best job of it that I can naturally.

The manual calls for the top H bracket to be secured by 2 x M10 stainless bolts which by the time they've gone through the bracket, backing pad, thickness of my transom and aluminium backing plate are 100mm long.

Having dry assembled it I was struck by just how much the whole contraption weighs just being held there let alone the rudder forces induced by slaloming down the face of heavy seas during an ocean crossing, suddenly those two M10 bolts that look chunky in my hand look very weedy considering the loads on them.

I notice that thanks to the internet I can quite easily order titanium nuts and bolts of the required size. I know this material is a lot stronger than stainless and is used a lot in aviation but can anyone give me some solid advice as to whether I should use them here? How does it fair corrosion wise? Especially when in contact with the alloy bracket of the hydrovane? What about fatigue?

Since its only two bolts, the extra cost is immaterial so just want to know what will be best to use. Thanks
 
I Know of one round the world racing yacht about 20 years ago had all fittings & bolts made of titanium & I never noticed any corrosion,wicked stuff to work.
 
I know very little about its properties but this alloy seems to offer just what you are looking for http://asm.matweb.com/search/SpecificMaterial.asp?bassnum=mtp641. The yield strength of 880 MPa is equivalent to heat-treated alloy steel and considerably more than you could achieve from duplex stainless steel, max about 550 MPa. Your 316 bolts will have a YS of little more than 200 MPa, although top quality ones made by cold forging could be higher. High mechanical strength usually gives high fatigue resistance, so this is unlikely to be a problem.

Corrosion resistance is excellent and its position in the galvanic series in seawater is very similar to that of 316, so galvanic corrosion should be insignificant.
 
bristoljim said:
wicked stuff to work.
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...and very prone to galling. (Installing irreplaceable titanium con-rods with titanium bolts and nuts in a factory engine was a bit nervy...)
Otherwise it's highly resistant to corrosion, even in dilute acids. Like aluminium and stainless steel it forms a passivated oxide layer, but a very robust one.

Many different grades are available with varying tensile strengths. For all the hype about the stuff, many have nothing like the tensile strength of the best steels, but substantially more than stainless. Perhaps Vyv will be along to take you through the options.
 
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You're looking for stronger bolts, but if the worst happens and the bolts don't fail something else will. This could be something that can't be replaced or bodged.
 
rotrax said:
If you read the OP he states he is worried about weight.

Titanium should address this percieved shortcoming.
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My reading is that he was concerned about the weight of the Hydrovane as a whole, which is considerable. (At a rough guess, 40kg or so: can't be bothered to look it up.) The weight saving on a fasteners is negligible. The main benefit provided by titanium would be in strength.

Given that reports of Hydrovanes falling off are far from commonplace, I'd err to the caution expressed by Penbarth: put the weak spot where it can do least damage. (Although if actually compelled to mount a Hydrovane, I'd use chewing gum.)
 
macd said:
My reading is that he was concerned about the weight of the Hydrovane as a whole, which is considerable. (At a rough guess, 40kg or so: can't be bothered to look it up.) The weight saving on a fasteners is negligible. The main benefit provided by titanium would be in strength.

Given that reports of Hydrovanes falling off are far from commonplace, I'd err to the caution expressed by Penbarth: put the weak spot where it can do least damage. (Although if actually compelled to mount a Hydrovane, I'd use chewing gum.)
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Yep you are correct the weight of the bolts themselves are the least of my worries! I was referring to the bulk of the hydrovane itself already putting a fairly high load on those bolts and that's before sailing forces are added to this.

Its an interesting point about having the bolts as a breakable link in the system. Certainly they would be a heck of a lot cheaper than the alloy castings to replace. Although I'd rather neither failed mid ocean thanks!

Which chewing gum would you recommend peppermint or spearmint? Wrigley's naturally.
 
Titanium is lighter ,used inside engines there's less inertia it can rev more .
It's not just a straight swap the whole internals are Ti. Usually bigger ( still lighter) like for like the the " cooking " bog std engine .

Down side it's brittle ,less elastic . Compared with the same size Dia of SS
So a shock load = more likely to snap , which kinda defeats the reason the op is thinking using .
Why not just if poss drill bigger holes and fit bigger 316 stainless .
 
I have a Hydrovane and I think you are worrying about nothing.

Unlike the servo-pendulum's (Aries, Monitor), which work directly on the rudder and the loads can be considerable, with the Hydrovane the boat is balanced using the rudder which is then clamped in place, and all the Hydrovane does is use a trim tab which involves only light forces - nothing like the loads of a servo-pendulum (which was fitted to my previous boat).

My Hydrovane has been around the world once, then Australia and back, and the mountings are rock solid.
 
Minchsailor said:
Unlike the servo-pendulum's (Aries, Monitor), which work directly on the rudder and the loads can be considerable, with the Hydrovane the boat is balanced using the rudder which is then clamped in place, and all the Hydrovane does is use a trim tab which involves only light forces - nothing like the loads of a servo-pendulum (which was fitted to my previous boat).
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You have that exactly the wrong way round. The loads on a servo-pendulum system are relatively slight - just those generated by the 'oar', which is small. Steering rudders, whether the ship's own or part of a wind-vane system, must sustain much greater loads.
 
macd said:
You have that exactly the wrong way round. The loads on a servo-pendulum system are relatively slight - just those generated by the 'oar', which is small. Steering rudders, whether the ship's own or part of a wind-vane system, must sustain much greater loads.
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I was going to say the same. The rudder on my hydrovane is as big as the main rudder on my dads little 27 footer. Whilst not astronomical, the loads must be significant. The hydrovane installation manual uses the phrase 'loads will be enormous at times' and the installation needs to be 'rock solid' and 'over engineered'.

That said, it sounds like everyone else has used M10 316 stainless bolts without trouble so I should probably do the same.
 
The first thing that will go is the shear pin well before the loads that will shear either the mounting bolts or the transom to which the Hydrovane is mounted on. You are worrying too much.
 
Daverw said:
Just wondered how titanium gets on with dissimilar metals etc re corrosion
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Don't know about electrolytic corrosion, but like aluminium, it develops a strong oxide coating on the surface so it resists corrosion well. Looking at the electrochemical series, it lookslike Aluminium will corrode preferentially to titanium, which will corrode preferentially over iron. It's about half-way between the two.
 
vyv_cox said:
I know very little about its properties but this alloy seems to offer just what you are looking for ASM Material Data Sheet. The yield strength of 880 MPa is equivalent to heat-treated alloy steel and considerably more than you could achieve from duplex stainless steel, max about 550 MPa. Your 316 bolts will have a YS of little more than 200 MPa, although top quality ones made by cold forging could be higher. High mechanical strength usually gives high fatigue resistance, so this is unlikely to be a problem.

Corrosion resistance is excellent and its position in the galvanic series in seawater is very similar to that of 316, so galvanic corrosion should be insignificant.
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The A brackets that support my propshafts are bolted to the hull with stainless bolts. The brackets themselves are fabricated in stainless.

I've no idea of the history of the bolts or how well they have been protected with anodes, so I plan to replace them.

I see titanium as a suitable material. Anyone disagree?
 
Why not use 316? No problem with compatibility with the brackets and provided you seal well where the bolts go through the hull, should be no issue with crevice corrosion. Wise to use new bolts though.
 
I had crevice corrosion in ss (don't know what though) bolts going through the ply hull securing the rudder stocks on mine. Replaced them with ss, should check again, but I'd probably try bronze next time...
titanium is impressive, but also as someone mentioned v.brittle and doesn't take bending (iirc)
 
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