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Old 16 October 2009, 12:15   #1
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Country: UK - England
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Make: Avon 5.4 Searider
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MCA Coding transom freeboard

I have an Avon 5.4 Searider with a Mariner 60hp which is required to be coded as Class 4 workboat.The engine size and weight is within Avon's recommendation.

One of the requirements is that it has to have a minimum of 250mm freeboard on its transom when fully laden with gear and personnel.With the cutaway in the centre where the engine sits it is currently only 180mm.

A false hyperlon bulkhead is permissible attached to the tubes and the top of the transom and it is permissible to have cables,tubes,leads etc passing through the false bulkhead in grommets.

Allowing for the engine to be tilted up means that the material must either be loose for when the enigne is up or it must be able to stretch if it is tight when the engine is down.
Has anyone ever made one of these or know how to overcome the problem ?

thanks
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Old 16 October 2009, 15:00   #2
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This is how I achieved it.....

Hi GG,

My Ocean currently runs a 20 inch L shaft with a stepped down transom. When afloat with say 4 people it achieves the 250mm freeboard (the sponsons do not sit in the water at rest /in this state). However, when we did the stability test with 8 persons - for the coding - it dropped below the 250mm (sponsons now touching the water).....

I found several ways to achieve the build up /250mm freeboard.....The best remedial solution I came across was to build a seperate inner well (welded stainless or GRP) which would need to be large enough to allow the engine to trim up....However, I had intended (and still do) to change my OB and when I do I'm going to plate /build up my Transom to accept an XL shaft which will then well exceed the 250mm requirement (it will be flush /straight across).

As such, the Hypalon skirt solution was the best quick /short term (in my case) fix.

Because i didn't want to glue to the sponsons etc, I came up with the below solution. It is a SS bracket made up to the shape of the step in the transom. THere is then a thick rubber strip which seals against the transom (cut from commercial generator mounting rubber) and a doubled over Hypalon skirt (whioch as you say flexes when you trim up the engine). THe whol lot is then fixed tight with large SS self tappers with silicon in pilot holes for good measure. It's proven water tight and simple (and ticked the box for the assesor.....)

Having said all that i can't wait to get rid of it as I think it looks a bit of a 'lash up'....but was a relatively simple and quick fix.....might be worth considering.
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Old 17 October 2009, 05:19   #3
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i've got a grp mould of a transom shield that bolts on much like the pics, made it years ago when i worked at ribtec, works well, you can borrow it if you like
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Old 19 October 2009, 18:11   #4
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Quote:
Originally Posted by Dan Worth View Post
Hi GG,

My Ocean currently runs a 20 inch L shaft with a stepped down transom. When afloat with say 4 people it achieves the 250mm freeboard (the sponsons do not sit in the water at rest /in this state). However, when we did the stability test with 8 persons - for the coding - it dropped below the 250mm (sponsons now touching the water).....

I found several ways to achieve the build up /250mm freeboard.....The best remedial solution I came across was to build a seperate inner well (welded stainless or GRP) which would need to be large enough to allow the engine to trim up....However, I had intended (and still do) to change my OB and when I do I'm going to plate /build up my Transom to accept an XL shaft which will then well exceed the 250mm requirement (it will be flush /straight across).

As such, the Hypalon skirt solution was the best quick /short term (in my case) fix.

Because i didn't want to glue to the sponsons etc, I came up with the below solution. It is a SS bracket made up to the shape of the step in the transom. THere is then a thick rubber strip which seals against the transom (cut from commercial generator mounting rubber) and a doubled over Hypalon skirt (whioch as you say flexes when you trim up the engine). THe whol lot is then fixed tight with large SS self tappers with silicon in pilot holes for good measure. It's proven water tight and simple (and ticked the box for the assesor.....)

Having said all that i can't wait to get rid of it as I think it looks a bit of a 'lash up'....but was a relatively simple and quick fix.....might be worth considering.

Thanks Dan , That is exactly what I thought I would have to do. Thanks for the pic
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Old 19 October 2009, 18:12   #5
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Originally Posted by biffer View Post
i've got a grp mould of a transom shield that bolts on much like the pics, made it years ago when i worked at ribtec, works well, you can borrow it if you like

Anything is worth a look, where are you and how can I contact you?
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Old 20 October 2009, 03:41   #6
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i'm in swanwick so not too far away, call me 07946 330001
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Old 20 October 2009, 19:09   #7
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How about a large tractor type inner tube under the stern???
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