Aquadrive fitting

john_morris_uk

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With the engine out, it seemed like a good idea (at the time) to fit an Aquadrive from Halyard Marine. This involves fitting a dwarf bulkhead for the thrust bearing at the inboard end of the prop shaft to be attached to. My problem is deciding what to make it out of and how thick it should be.

It will be between the engine bearers and will measure about 500 mm by 250 mm.

Clearly it needs to withstand the thrust of the prop pushing the boat along in all conditions and the instructions indicate that it should not flex in operation.

One idea is to make it out of marine ply (perhaps a couple of layers of 12mm epoxied together to make 24mm then glassed in place with epoxy and glass matt etc.

Another idea would be to have something cut/welded up in stainless that I can try to bolt in place between the engine bearers.

At the moment I am stuck in the stage of 'well that looks strong enough in my mind'.

Anyone got any experience/ideas?

Many thanks in advance.
 

Steve_N

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I'm in the middle of the same process at the moment, John. For what it's worth I've decided on mild steel plate, suitable coated, for the thrust bulkhead. I'm planning to use 10mm plate with strengthening ribs welded down both sides as in my installation the shaft is a good distance up from the bottom of the hull, so the bulkhead will be quite large. 65hp to accomodate BTW.

I decided against ply as there simply isn't enough meat around the Aquadrive mounting bolts, although this may be different on yours as this dimension varies with the shaft size. Mine is a Moduline 10.5 for a 1.5" shaft, and the new style shaft clamp on the inboard side of the unit is enormous, larger than the thrust bearing body itself - it barely clears the mounting bolts by 10mm. In this respect I think the older style 20xxx series with the traditional split shaft clamp were better..
Steve
 

Graham_Wright

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One thing you might consider, is whether it would be worth while changing the drive arrangement at the same time to allow removal of the stern tube and prop shaft (i.e. without having to remove the engine).
I did as your first suggestion and glassed in a new 25 thick floor (real term! (=bulkhead)). The stern tube is secured at the skeg by the stern bearing but the inboard end is clamped to a stainless steel hoop glassed to the hull. Unbolting the stern bearing and drive flange (needs puller) and removing this clamp allows the prop shaft and stern tube to be raised and the prop shaft can then be extracted through the skeg.
Your second idea would work as long as you can restrain the athwartships movement of the aquadrive assembly. Halyard told me not to over-estimate the thrust from a 17" prop.
 

colin_jones

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I did this about 5 years ago. The unit has been brilliant. For 2 years it ran at its maximum 'out of kilter' angles and showed no sign of wear.

I was advised against metal and over estimation, so ended up with a 2 - 2.5" thick wooden cross member glassed into the V-shaped bilge section well inboard of the stern gland tubing. It has worked very well.

The 'strength and thickness required' argument is; "Just think how little force you need to push your boat away from the quay by hand."

Why not contact Halyard for advice. They are very approachable. The head tech guy is Bob Dole.
 

john_morris_uk

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Apologies!! I should have indicated the engine and shaft size size etc as well!

The engine is a Volvo 2040 (40 hp) driving a 19 by 11 prop. The stern shaft 'floats' inside the stern tube - that is it hopefully doesn't touch the walls of the GRP tube, but is suspended between the cutlass bearing and the Aqadrive thrust bearing. (There is a PSS shaft seal at the inboard end to keep the oggin in its right place.)

The shaft is 30 mm and is not that long (meter and a half or so I guess) so it shouldn't 'whip' as it rotates.

The Aquadrive is a B10 and has the device that 'grips the shaft' not a flange that bolts onto the shaft and grips it, although I don't think that this makes any differenece to my problem.

As the shaft load is smaller than yours, I am tempted by the ply/laminate/glass approach, as this could be end up with an aesthetically pleasing job with no rust problems and easy to keep clean. However I have also noticed the lack of space relatively round the thrust bearing.
 

Steve_N

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Yes, I really wish I could use ply/glass too. It would make for an easier and neater job.
This pic illustrates my particular problem: see how the shaft clamp intrudes on where the bulkhead goes, effectively limiting the thickness of the bulkhead to about 12mm.

aq.jpg


I'm not sure I'm that impressed with this element of the design really..
 

john_morris_uk

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Ha! Yours looks just like mine - what a coincidence...?

I note on the instructions that the dimensions given for the dwarf bulkhead allow a clearance on the rotating part of the thrust bearing. Doesn't leave much meat for the fixings to go through. I might try and shape the ply and make it fit a little better. At least the fixings don't take the thrust load!
 
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