Engine Bearers

[boatmad2]

Hi everybody, I need some help with my project boat.
In the course of replacing a Ford petrol engine with a Ford diesel I found the wooden engine bearers to be in poor condition so I removed them.
Now then since I have good access to metal working and materials I was thinking of making a box section sub frame and getting it hot dip gavanised and then bonding this into the hull. Question is does the resin for grp react with the zinc gavanising or are there any other reasons why the bearers should be made of wood. The boat by the way is a Teal22 and the engine is the 1600 xld.

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[craigbalsillie]

Sorry I can't answer you question and
I hope you don't mind me answering your question with a question...

Is there a reason why you can't take the engine mounts that would be used to mount the engine in it's natural environment, a Dagenham Dustbin, and make a
block to mount them on the hull..?

Is it to do with the amount these mounting blocks would allow the engine to move/vibrate thereby causing problems with the propshaft/gearbox..?

just a silly newbie type question..



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[boatmad2]

No its not the rubber mountings that are the problem Iv'e got new ones of them its what I bolt them to in the hull the original wooden bearers are us and for various reasons I was thinking of replacing them with a steel framebut before I do I wondered what everybody thought of the idea.

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[stamfordian]

hi ,
Metal vs wood when bonded to hull????...would have thought that wood would have the advantage of much more "give" over steel hyperlogical(speling!!)ly if you have grp hull that flexed when you hit a wave or a log/dead seal or whatever and your steel sub frame didn,t flex to the same degree...result a hard spot in the hull causing localised fracture of grp.
Purly a amature stab but hope it gives food for thought???

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[vyv_cox]

Metal engine beds are perfectly OK, the flexibility is provided by the rubber mountings, not the beds. Bonding of metal to GRP is always improved by providing something for the resin to adhere to, such as holes or a specially roughened surface. Hot-dip galvanised steel is no different. Drill some holes in the box section before galvanising, which will protect the inner and outer surfaces.

My engine beds are solid steel, 1 x 3 inch section. They are bolted to the GRP beneath.

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[Forbsie]

I too am installing an XLD416 and am currently pondering this very question. My previous engine was mounted on a frame hanging off the transom. This fact never occurred to me when I started un-bolting the frame to replace the transom. /forums/images/icons/crazy.gif

I am trying to decide whether to hang new engine off the transom or bed it onto the hull. I am concerned that the hull will not take the extra stress of the engine as the boat, a Buckingham 25, probably had an outboard initially.

With Den, h00, me and yourself all working with or considering the XLD, maybe we should start up a club. /forums/images/icons/wink.gif

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[Plum]

I agree with Vyv that this is a very sensible idea, but two items of caution:
1) The hot dip steel parts will eventually corrode, particularly where any seawater creeps between the GRP and the steel (You will never get a truly perfect bond) and then they will expand and break down the bond and will eventually need to be replaced. It would be better to make up GRP webs/beams (maybe with a durable wood core for added stiffness) to which you can bolt your steel subframe. (This sounds more like what Vyv has)
2) Particularly if you are going to bond the steel subframe to the hull, do ensure that the steel frame does not create any "hard spots" or stress raisers due to its possibly higher stiffness than the GRP hull. This could result in crazing or cracking of the hull.

Hope this helps

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[oldsaltoz]

G'day Peter,

Steel and GRP expand at different rates under normal conditions, this situation is made worse in a hot now cold later engine compartment, under these conditions the bond between metal and GPR will fail to some degree, the expansion and contraction will expose bare metal and rust is mist likely to form at the joints.

Two blocks of suitable timber glassed in and covered with GRP will outlast most engines if not boats; a steel frame can be bolted to them, just make sure you cut access holes for the nuts about 75 mm from the top and cover the whole thing in fibreglass, the bolt holes should be pre drilled 10 mm oversize and filled with epoxy filler, re drill to actual bolt size and set your bolts.

If you do decide to glass the frame to the hull, make sure you lay up a good size pad at least 150 mm (at least 4 layers) each layer to be 30 mm smaller than the layer it covers. The extra glass used to fix the frame to the now strengthened hull needs to be about 5 layers, each smaller as before; if the frame is square, run a fillet of epoxy and fibre filler to reduce the bend in the fibreglass lay-up.

Tip: You can reduce water entry at the interface, by fitting a couple of '0' rings about 3 mm apart and only 5 mm from the joint. I do this on rudder stocks when building rudders, seems to work very well in that none have had a problem in 15 years, make sure they are the high pressure type and a very tight fit, just glass over them.

I hope this helps...........

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[Bejasus]

When the toys come out the pram and the dummy disappears over the horizon, can I have first dibs on yer engine........./forums/images/icons/laugh.gif

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[Avocet]

GRP doesn't "stick" to steel (galvanised or otherwise). That said, lots of boats have steel reinforcements matted in to their hulls. It's OK as long as the steel is mechanically restrained from coming out i.e. glassed in completely and not relying on the adhesion between itself and the GRP. That said, I agree with other posts. A good piece of wood will be a better bet. My bearers are about 6" deep and 2" wide. They each have a huge piece of angle iron bolted to them which the rubber mounts sit on. They've been fine for the last 30 years!

Modern yachts seem to have GRP engine bearers. GRP is pretty strong if it's thick enough. You might be able to get away with small reinforcements (maybe in stainless) right under each of the rubber mounts. If you do decide to go for steel, bed the main members down on a good squashy layer of wet matting to make sure the loads are fed into a big area of hull. The steel will otherwise only rest on the hull "wher it touches".

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