Bavaria 47 4-cabin converting to 3-cabin?

nigelmercier

nigelmercier

RIP
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www.bavariayacht.info
A year ago I asked this:

nigelmercier said:
I have a Bavaria 47 4-cabin built in 2000. According to [an] advert on YBW, it may be possible to convert to 3-cabins: "converting also to 3 cabins with easy removal of bulkhead separating the forward cabins "
Click to expand...

Since then I have investigated the top of the dividing bulkhead, and it appears to be bedded in silicone into grooves in the underside of the deck, so the bulkhead is almost certainly not structural.

However, this is the problem, the bracket that holds the baby stay (inner forestay):

97dd35dadbd69c5f9252c6f9c8856ccd_zps6f7d0e11.jpg


Thoughts?
 
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Do you want to convert it to 3 cabins? Won't this necessitate a lot of re-modelling of the forward area, even if the babystay isn't a problem? Is the flooring continuous under the bulkhead?
 
Hi Nigel,

My Dufour 40 had Bulkhead bedded into grooves in the hull with elastomer, it looked very similar to your photo. You could change the shape of the deck of the Dufour, by playing around with rig tension and the length of the tie bolts under the side decks. The decks just move and the elastomer stretched!

They are almost certainly non structural, but you will have to transfer the loads from the baby stay termination to the keel and ensure that the loads are transferred to the main load bearing structure, which take the keels loads, the compression load from the mast and the bending loads from the rest of the rigging. If it's anything like my Dufour, the deck won't take the loads from the baby stay without distorting.

This will most likely mean some form of internal structure connecting the deck under the baby stay attachment point to the keel. This will be in tension and should probably follow the line of the baby stay projected down to the keel. This could be a wire or a rod, but you most likely want to make it look nice, since it will be in the middle of your new master cabin.

I'd try and find a naval architect with experience of modern production boats to give you some advice.
 
My bet is on a translation error in the advert, and a touch of the Chinese Whispers, maybe it should read:

"It is a simple matter to supply the 47 as a 3, or 4 cabin, layout. An additional forward bulkhead is all that is really required"

Because I think there is a lot of work to do with that set up and then, when you come to sell, the next bloke will say: "I wish it was the four cabin" or "It's non standard, I think your are asking a bit much" etc.
 
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Was the baby stay an aftermarket fitment? I think that your choice may come down to which you want more, a baby stay or a three cabin layout. My Jeanneau 45.2 was built as a four cabin boat, convertible to three. The only one I have seen that has been fitted with a baby stay has the fitting bolted to the strong transverse bulkhead at the forward end to the cabins. Might it be possible to move the baby stay on the Bavaria forward so that it fixes to the transverse bulkhead rather than the divider? The existing hole in the deck can easily be glassed over.
 
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Don't think that is a babystay, but an inner forestay that has been added afterwards to take a storm jib. Therefore not essential for the rig. As Norman_E says it is normally fitted to the deck just aft of the most forward bulkhead with a similar internal bracing and made removable so it is stored at the mast or to the shrouds when not in use. On the deck of my 37 there is a reinforced pad where it would be fitted.
 
Just bare in mind that if the baby stay goes further forward on the deck it can provide more pull forward for the middle of the mast with less tension (that is good) but being further forward will foul the jib more when tacking. So there is a compromise. We assume the baby stay is necessary for mast integrity.
In which case as said the deck will need to be strenthened to take the loads. This could be done by a transverse beam either fore and aft or athwartships. This beam will however have to have some significant dimension in depth to give stiffness in itself so is going to mare the single cabin look. The better aleernative as said is a wire or rod with tensioner bottle screw going from the under deck at the baby stay attach down to the keel floor or bow. It could be somewhat off direct line of load but being of line will weaken the effect.
(I mean ideally the wire should be a continuation of the baby stay under the deck. But it could angle forward or aft by say 30 degrees without too much problem)
good luck olewill
 
nigelmercier said:
So it appears that the bottom-line is that I can't replace this bracket with a plate glassed under the deck? If this is the case, then it's a no-go.
Click to expand...

Hi Nigel the plate bonded under the deck may or may not be adequate. The stiffness if the plate will depend on the material and the size of the plate.If we assume a large square stainless steel plate that extends to near the gunwhale then it is the thickness of the plate that provides the stiffness. Obviously thin will bend easily. Hence the idea of a beam might be better than a thin plate. However the size of the plate ie how close to the edge of the deck it goes will determine how the load is transfered to the deck. The larger the plate the greater amount of deck transfering the load to the hull, assuming the deck can take the load. (better is to transfer load directly to the hull or keel)
So keeping these things in mind you need to decide just what is adequate.ie if you do fit a plate under the fitting bonded under the deck how big and how thick should it be. A design engineer might do calculations. If it were me I would just go on gut feeling . However this has been wrong in the past.
My point is it might be Ok to fit a plate say 30 cms square 6mm thick. Drill hole in the plate to aid bonding through the holes. Then when all assembled crank on the baby forestay tension and see what happens. Particularly measure if the deck bends up wards or the plate bends. My gut feeling again is that loads should not increase much when hard pressed in a gale compared to excessive static load you can apply to test.
Another option might be to make a carbon fibre plate. This could be tapered at the edges and thicker towards the middle. Leave cloth resin free when laying up so that it can be easily bonded to the GRP under deck. However again thickness is the key dimension and I reckon 10cms thick would be good. Use penny washers under the bolts to spread load.
Of course it is up to you as to what will satisfy your mind (imagination) when you are in that gale. good luck olewill
 
Hm, maybe time to insert some engineering arts? Starting with strength of materials.

A plate is by nature not stiff. Increasing thickness will increase stiffness, but also weight.
A beam is usually having one of the standard cross sections, I, U, L ... all where material is used where it contributes best to strenght and stiffness. Steiner's theorem gives an immediate understanding of this (stiffnes ~ r**2 (at least), where r is the distance from the centre line).
A plate is unlikely to take up the loads from a stay, if the stay is used as a stay.
A beam from one side to the other, designed to handle all loads would probably be best, in particular is the existing bulkhead most likely contributes to the strength of the deck also for compression loads.

The alternative with extending the stay in one way of the other to the hull should solve the issue of the loads on the stay, but not the loads on the deck.

Modern foredeck are usually not sufficient supported, resulting in some flex when walked upon, with time causing de-lamination. The probably large foredeck of the Bav 47 is likely to be supported by the existing dividing bulkhead.

Re-building boats always results in much more work than anticipated.

/J
 
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