Transom flexing with new outboard- strengthening advice ?

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markpageant

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Ive fitted nearly 40kg outboard to my wetserly pageant transon. Ther is a lot of flex which I want to minimise. Convention suggests a large backing plate either side of the transom. As the transom is slightly convex I need to fill the concave interior of the transom to give a flat surface to which the ply backing pate can then attach. Can I do this with an epoxy filler or should I use glass mat and epoxy ? Anty adviec very welcome
 
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fibre-glass a foam or rope frame into the transom...

That is what I would do.

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Effective and a pretty easy to do, but make sure you distress the surface of the GRP where you are going to glass in the frame, to provide a decent key.
 
I'd tend to go a bit further than a rope or foam,which might be a bit shallow to give you much strength, I'd suggest a deep stringer or stringers of ply, glassed in, edge-on to the transom. Or even better, a backing glassed to the transom to spread the load with a stringer glassed on top of that for stiffness.
HOWEVER, you have to be careful that whole lot is properly fitted and bedded onto the hull or else there's a good chance of point-loading your hull to the point of serious damage.

(Having said that, unless you do something, there's a good chance of the outboard coming through your hull anyway!)
Edit -
What's meant by rope or foam form is simply a light, bulky object over which the glas is laid to form a 'U' beam stuck to the hull. You could use twisted paper too but probably wouldn't look so good.
 
Given (slight) curve of transom would it be sensible to flatten the (inside of the boat) curve with expoxy, adhere to this a sheet of 18mm wbp ply ? If so with what would i fill the curve ? And to what extent is a backing pad on the outside of the transom important ?
 
I guess it couldn't hurt, and might be quicker / easier than my solution, but would possibly be heavier / more expensive and not as stiff as a stringer.
I hadn't suggested a pad on the outside - I had meant both pad and stringer to be inside - but the advantage of a pad outside is that it would sacrificially protect your hull when mounting/demounting the o/b'd.
 
All of the above assumes easy access to the inside of the transom. I had a similar problem with rudder pintles but in my case the inside of thee the transom was not accessable enough for anything more than fitting nuts to through bolts.
I removed the pintle and epoxied on a square piece of heavy carbon fibre mat that was about 30cms square and then another over that. It would have looked better on the inside but I did it on the outside. Faired it off with filler and painted the transom. The raised area looks business like and OK and not so noticeable under the fittings and rudder.
Use the largest washers you can get in stainless steel. My troubles started becuase aluminium was used as a big washer with SS bolts and it disappeared in dust after 20 years. good luck olewill
 
If your transom is flexing it is not stiff enough so flushing with filler and overlaying with plywood will spread the load across the transom to the sides more where it is closer to the quarters/bilge. Having said that, the principle is to take the imposed load of the engine and distribute it over as much of your boat's structure as you can. I would suggest looking at fitting gussets or brackets to take some of that load down/up/sideways and into the hull via the stringers/frames and also upwards into your stern deck/counter rather than risk tearing off the entire transom through eventual stress fatigue.
 
With no pictures or information to indicate the actual construction of the existing set up any solution offered would have to amount to some sort of overkill, better to strong than not strong enough.

With this in mind, you could cut a suitable section of marine ply that covers the inside of the transom from top to bottom and side to side.

This would have to be treated with an epoxy to prevent any water getting in and rotting it. Any treatment of this ply would have to be done only after all cuts and holes had been cut.

The void between ply and transom can be filled by mixing some micro fibres with the resin, this cures to a very hard finish and is an very glue.

By drilling 6 mm holes on a 30 mm grid pattern all over the ply, any trapped air or excess glue will escape through the holes when the ply is pushed into position.

Use the excess material to form a gusset right around the edge of the ply and apply epoxy cloth strips between the ply and hull, make sure each strip is at least 40 mm wider than the one it covers and apply at least 4 layers on 300 gram cloth.

I hope this helps.

Avagoodweekend......
 
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Given (slight) curve of transom would it be sensible to flatten the (inside of the boat) curve with expoxy, adhere to this a sheet of 18mm wbp ply ? If so with what would i fill the curve ? And to what extent is a backing pad on the outside of the transom important ?

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Plane the ply down to fit the curve before bedding it to the transom. Ply is *much* cheaper than epoxy.

0.02p

Andy
 
I would use three layers of 6 mm ply inside and out glued and screwed in place. the 6mm will follow the curve easilly then give a strong and rigid reinforcement once its all glued together.

To cut the cost glue the first layer to the transom with epoxy then use cheaper waterproof glue such as cascamite to glue the next two layers on.
 
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