If you were fitting a teak rubbing strake to a steel boat......

tugboat

tugboat

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.........what sealant would you put between them? A bog standard sealant like Sikaflex, or something that doesn't set hard? Given the different coefficients of expansion of the steel and wood, I would have thought the latter. If that is correct, can anyone suggest a suitable product?
 
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Given the different coefficients of expansion of the steel and wood.....

[/ QUOTE ]What on earth does that have to do with it? If the rubbing strake is properly fixed to the hull, there won't be any differential movement.
 
[ QUOTE ]
[ QUOTE ]
Given the different coefficients of expansion of the steel and wood.....

[/ QUOTE ]What on earth does that have to do with it? If the rubbing strake is properly fixed to the hull, there won't be any differential movement.

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What it has to do with is........... a couple of years ago I paid someone a lot of dosh to do this job on my boat. Since then the boat has sat in the 'yard out of service. During that time the sealant has become detached from teak and/or steel (paintwork) in various places and water had got behind. What I'm trying to determine is whether incorrect/inappropriate materials have been used, or just crap workmanship with the correct materials!
 
Don,t put any wood on a steel boat Tug if you can avoid it, you are building in a rust trap. I built a 44ftr and have seen a lot with wood trim/decks etc that are nightmares after very few years, look very pretty when new but a hugemaintenance problem there after. I would not touch a steel boat, secondhand with laid decks or wood trimfor example.
 
Tugboat,
You should try posting your question on the Classic Boat forum - we're a much friendlier bunch over there.

For your application I'd be inclined towards a polysuphide sealant such as Arbokol. This will skin over for painting, but remain relatively soft to accomodate the inevitable movement.

A key element in designing the sealing detail is the need to get a suitably meaty bead of sealant in the joint. If it all gets squeezed out when you nip up the fastenings then there will only be a thin layer which won't cope with any movement. I'd think about routing channels on the back of the rubbing strake, say 6mm deep, 8mm wide and 5mm in from the edges. A round nose router bit would be ideal (aka core-box cutter) Fill the channels with the sealant. The extra volume of sealant contained in the channels will be more able to accomodate the relative movements of strake and hull.
 
No sealant, just a few raised "nailheads" to drop the teak profile ovr and push. Minimise rust trappig by minimising contact of teak-hull using lots of routed cutouts across the inside face. Elminate the rust traps by...not having a teak rubbing strake
 
Think I would go with the 'dont use teak' idea, rubber strip such as from Vetur will be a lot more durable and move with the steel. The traditional way of preventing problems between teak decks and steel when the navy used to use teak decking was not to bond at all but to bolt the deck down then inject a mix of linseed and white lead through the decking which allowed movement but prevented water ingress.
 
As ALL materials Move joiting them is a challenge, having been employed in the construction business for 47 years I've come across all sorts of differing expansion rate materials. Steel and wood being some of the worst.
With any jointing material it can only take up expansion in one plane without pulling away from the surface. As in the case of caulking a teak deck, each board is grooved along all sides, two boards are laid alongside each other. Now what you have is a vertical face followed be a horizontal face, then another vertical face. The sealant will only work properly applied to the top two vertical faces of the pair of boards, so the lower horizontal and lwer still vertical face have to be isolated, this is done using a lightly tacky tape. When movement occures both side of the joint can move away from the other and the sealant will stretch as the tape will allow the hozontal face to move and not drag the sealant wat from the above vertical face.
In all the leaking decks I've repaired I've yet to see Sika tape used along with the rest of the Sika system.

Now if your rubbing strake has been fitted as a butt joint, IE; two flat surfaces tape is not required.
If the rubbing strake has been rebated as with decking boards, then tape would be required in the bottom of the rebate.

The SikaFlex instruction manual will show this, I'm sure it will be available on line.

I hope this is off some help to you.
 
But their different coefficients of expansion have nothing to do with it. GRP has a different coefficient of expansion from wood, yet nobody even dreams of asking this question. Any sealant which will stick both to paint and to wood will do the job.
 
I quite agree, but as the boat already had the teak rubber, I'm pretty much stuck with it. If I were building a steel boat from scratch I would have a steel rubber welded on. I can't do this as a retro-fit as the hull is foam lined and the whole shooting match would go up in flames. I'm trying to find a way of using the correct materials and good practice to attain a durable result. Yonks ago I sailed on ships that had steel/teak interfaces all over the place and we didn't have nightmares about it. Sheesh, this is the 21st century, there must be some product that is suitable.
 
bodfish and LazyDayADLS........thanks for the constructive comments. I've read the articles about decking and understand the principles there. My rubbers are just flat face onto flat face, so hopefully no complicated conflicting forces.
 
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But their different coefficients of expansion have nothing to do with it. GRP has a different coefficient of expansion from wood, yet nobody even dreams of asking this question. Any sealant which will stick both to paint and to wood will do the job.

[/ QUOTE ]

As I said in my original post, the boat has been sat in the boatyard 'out of service' since the work was done 2 years ago, i.e has not been banged about alongside quays or other boats. Seasonal/ diurnal changes of temperature seem to me the most likely cause of the problem, possibly combined with incorrect materials and/or poor workmanship. I'm just trying to get to the bottom of the problem so that the job can be re-done properly and last a reasonable length of time. I can't be doing this job every couple of years.
Incidentally, the job was entrusted to a professional boatbuilder/shipwright or whatever they call themselves so I had expectations of a decent result.
 
DONT DO IT!!! On my previous boat I spent more time looking after the rubbing strake than the rest of the boat. It looked great but wood and steel dont mix.
 
I had this problem for years with our rubbing strakes. The wood went all manky and rust steaks developed from behind the rubbing strake.

After many years experimenting with different sealants the best result I achieved was with no sealant at all. I simply varnished the back of the rubbing strake and bolted it on.

Any sealant seems to have the opposite to the desired effect and detaches itself from the steel/wood and then forms a very effective moisture trap.

About 5 years ago I gave in to the inevitable and removed them permanently.
 
Further to previous post.if you are going to fit teak to steel the best result I had was sandwiching Denso tape behind the wood,On a real hot day I had to run a rag soaked in white spirit to remove the Denso liquid that ran down.Got better as time went by.Best to leave as painted steel.
 
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