How much weight can fibreglass take

[Jay Bee]

Hi all, I need to fit my new self steering vane to my transom with bolts/washers/nuts and wonder how much weight the fibreglass at the transom can take. Clearly it depends on the thickness of the GRP. I would guess that mine is 5mm thick. The self steering gear weighs approximately 20kg.
Do I run the risk of tearing the fibreglass with the weight and what work around solutions are there? Many thanks

 

[fredrussell]

What sort of windvane? It’s not so much the weight of the unit you need to worry about, it’s the force applied to mounting area by wind vane doing its business. Hydrovane will put a lot more pressure on transom than servo pendulum types. Either way I’d be putting a nice thick piece of ply in there as a backing plate between transom inner and washers & nuts.

 

[MontyMariner]

Horizontal bolts through vertical 5MM GRP.
Glassing in a ~15mm marine ply backing plate should do a job.

 

[PCUK]

A steel bracket bolted through the transom and deck will carry any load put on it.

 

[salar]

The larger the backing plate, the more you will spread the load so I would glass in a ply backing plate a good bit larger than the fixings for the vane. If you have difficulty accessing behind, a stainless plate glued to the inside of the hull will do a very good job, but probably more difficult to source.

 

[oldharry]

Yes definitely need backing plate such as those described to spread the load. Its not just taking the weight of the steerer, but just consider the loads if a line catches it, or it gets up against a neighbouring boat! Without any backing, it could just rip it off. As suggested a 15mm ply pad glassed in twice the size of the steerer mount would do it.

 

[Supertramp]

The larger the backing plate, the more you will spread the load so I would glass in a ply backing plate a good bit larger than the fixings for the vane. If you have difficulty accessing behind, a stainless plate glued to the inside of the hull will do a very good job, but probably more difficult to source.

Look on ebay. Hit and miss but there are often offcuts of stainless steel of various thicknesses and sizes. I used a 30cm x 15 cm piece of 5mm as a backing for a new mooring cleat. The deck will come off before that gives!

 

[William_H]

As said you need to move the loads out to the edge of the transom. No I think 5mm transom with 22 kg would fail (or be unsafe) with 4 bolts and just large penny washers. The backing board /plate needs to be at least as thick as transom and large enough to move loads outwards. Ideally use GRP that is tapered in thikckness at the edges to avert a sharp edge to the transition of loads form backing plate to transom. Yes any support down to the keel or up to the deck will also help a lot. ol'will

 

[Neeves]

We are all guessing as we no idea, at all, of the transom of your yacht. You have not even told us which yacht.

So get your phone out and take some pictures (that's why you have a camera in your phone) of where you intend to locate the self steering vane, tell us who makes the vane and maybe offer a link to the specific one you will attach....

Then you will receive educated answers to your question.

Jonathan

 

[rogerthebodger]

We are all guessing as we no idea, at all, of the transom of your yacht. You have not even told us which yacht.

So get your phone out and take some pictures (that's why you have a camera in your phone) of where you intend to locate the self steering vane, tell us who makes the vane and maybe offer a link to the specific one you will attach....

Then you will receive educated answers to your question.

Jonathan

I agree Jon I like how long is a piece of string type of question

 

[Geoff A]

I forget where I heard / read this, as It would have been sometime in the 1970s. It was something like, GRP provided the laminating is done correctly as in no air trapped between layers GRP weight for weight by aera is as strong as steel.

 

[PCUK]

I'm not guessing, a 6mm steel bracket with a knee, coated with epoxy will do the job regardless of the boat type.

 

[Jay Bee]

Many thanks for the your replies. The self steering gear is a servo-pendulum type so not Hydrovane. The yacht is a Sadler 290.

 

[Marco64]

This may be too late but I find this thread interesting as I will eventually fit a Hydrovane to my HR36 transom. Their manual suggests that if you fit a flat plate as reinforcement to a curved transom, you could sandwich between them a bag full of epoxy not yet hardened to take up the gap.

 

[LittleSister]

. . . Their manual suggests that if you fit a flat plate as reinforcement to a curved transom, you could sandwich between them a bag full of epoxy not yet hardened to take up the gap.

Alternatively, perhaps -

a) Assuming transom exterior is convex, then laminate it - use thinner ply, say 5mm (depending on how sharply curved the transom) for initial backing plate and bolt to transom until adhesive cured. Then repeat procedure twice (or whatever, depending on total thickness required). Don't forget to grease or whatever the bolts so they don't get permanently epoxied in place at any stage!

b) Build up the required thickness using glass fibre cloth and resin.

 

[Marco64]

Yes that would probably be the pros way of doing it. But my backing plate will be out of sight behind furniture so I’m opting for speed

 

[bob the ancient mariner]

Hi all, I need to fit my new self steering vane to my transom with bolts/washers/nuts and wonder how much weight the fibreglass at the transom can take. Clearly it depends on the thickness of the GRP. I would guess that mine is 5mm thick. The self steering gear weighs approximately 20kg.
Do I run the risk of tearing the fibreglass with the weight and what work around solutions are there? Many thanks

a good solid 10-15mm marine ply backing piece and then use freefix[ east coast fibreglass supplies for example] used as a bonding agent bteween hull and the backing piece. This stuff will bond both. and also take up any shape of the transom.Just ensure the transom is clean and free of wax, and abrade as necessary.. I had a problem with my fore and aft lower shrouds lifting the deck areas. I did use s/steel packing plates and the freefix as a filler/bonder. On tightening the shroud brackets the free fix squeezed out ,then you know the space is full. It is set when it changes colour. That was 5 years ago, and the decks have not lifted since

Yes that would probably be the pros way of doing it. But my backing plate will be out of sight behind furniture so I’m opting for speed

 

[Wansworth]

I some way what you can do will be dictated by access so to doaproperjob you may have to make a deck hatch to gain elbowroom