someone tell me about sterntubes...

[aztec]

and shafts? i want to fit one to my launch.

how do i sellect size, length, type (what are the usual choices?)

i'm looking at a "glass in" type as i have a bare hull to play with. are there any benefits to a specific type?

your experience and knowlege are called for once again...

cheers, steve.

<hr width=100% size=1>

 

[gtmoore]

I've been having some problems with a setup that for one reason or another is not suitable. My boat has a 1" shaft running in a tube that is less than a quarter of an inch larger. Having an engine on soft mounts and a volvo low maintenance seal providing little shaft support is giving me problems with the shaft whipping round in the tube and knocking. Seems the only way to get rid of this is to use a fixed stuffing box (ie one that screws into the end of the tube) with a flexible coupling to the engine and maybe harder engine mounts.

Doesn't really answer your question but might give you something to bear in mind.

<hr width=100% size=1>Gavin

 

[pvb]

Catalogues...

Good place to start is by looking at some catalogues. Suggest you get hold of Vetus, ASAP and Volvo Penta Accessories catalogues - there's lots of info in them about sterntubes and pics of the various types.

<hr width=100% size=1>

 

[tillergirl]

Shaft size and therefore tube size will depend on engine hp. I have a 1 and a quarter inch shaft for a 30hp engine but when I re-engined I kept the old tube from the previous 38hp engine so that might be a little overlarge.

Length will depend on your installation - where you put the engine etc.

Type - well the advice for catalogues is very sound. You will need some sort of bearing at either end. Outboard is usually a cutlass or plain bearing. A plain bearing is just that - a hole in the bronze end fitting that screws onto the tube and then fixed to the boat either by screws or I guess by glassing. Lubrication is generally by water, the end fitting may have a water scoop so that forward motion of the boat drives water through it. Mine has water pumped through the tube and out through the plain bearing (taken off the water cooling circuit at the engine and delivered to the stuffing box) but this is probably a bit old fashioned. A cutlass bearing is used where you have a much larger hole in the end fitting which has the bearing pressed (pushed) into it. the bearing consists of a tube of external diameter equal to the internal diameter of the hole in the end fitting. the internal part of the tube is lined with fluted bearing material eg rubber. The gaps in the rubber allow water in to lubricate. Cutlass bearings can be replaced when worn, plain bearings need to be bushed or replaced when worn. Not sure I can advise you on which lasts longer. Mine plain bearing seems to be standing up well.

On the internal end you need at least a seal and there are a number of modern 'low maintenance' seals available such as 'Deep Sea Seals' I have no experience of them so I can advise. The old fashioned seal which I have is a stuffing box - a fitting that screws on the inboard end of the tube (so getting the length of the tube in which the shaft sits is critical) and is screwed or glassed to the boat. The stuffing box acts as both a seal and a inner bearing. The bearing and seal is provided by 'packing' = graphite packed square material (I can't think of the right word) which is cut to the circumference of the shaft and several of which are pushed in turn into the housing built into the stuffing box. This is then compressed by bronze ring which sits on studs from the stuffing box. A water tight seal is provided by tightening the ring on the studs. Not too tight to bind the shaft and overheat it, not too loose to allow excess water in. A drip or so a minute is conventional wisdom.

Choice - well the modern seals don't drip until they fail when I understand some then leak quite profusely. Stuffing boxes are simple technology that don't fail suddenly but need to be adjusted from time to time, can be messy to replace the packing and do allow a bead of moisture into a boat. Some people don't like the rigidity of a stuffing box with a flexibily mounted engine - on the other hand some think it keeps the shaft nice and true which otherwise might place undue stress on the external bearing.

Don't know where you are (this has taken so long to write, the link has dropped out and I can't look at your profile) but I suggest you also try T Norris of Isleworth. they cast props and things and sell tubes and shafts and end fittings. They do a catalogue. 0208-560-3453. I am sure they would advise you over the phone as to shaft diameter for the power of engine.

Good luck. It's worse reading about it than doing it!

<hr width=100% size=1>

 

[aztec]

a genuine thanks. that's given me the info i wanted. also cleared up some misunderstandings about bearings and seals. there is a firm just down the road from me. i'll go talk to them, but wouldn't have before (a little information etc)

thanks again, regards, steve.

<hr width=100% size=1>

 

[Robin2]

I strongly echo the point about the problems when the tube is not much bigger than the shaft. I have that problem - twice over - and I think the only way to solve it is to fit "aquadrive" couplings. In my case the problem is exacerbated by single cylinder engines. They always jump about more than multi-cylinder engines. I suggest you get a tube that gives you plenty of clearance.

I have used the American PSS seals which are very easy to fit and don't leak at all.

<hr width=100% size=1>

 

[Robin2]

One further point - Vetus have a booklet about engine installation stuff as well as their catalogue. One or other of them has info about the maximum lengths of shafts between bearings. If the unsupported shaft is too long nasty things will happen.

<hr width=100% size=1>

 

[colvic]

One of the best firms for getting advice is in Islesworth, T. Norris Ltd. Tel No: 020 8560 3453. You can ask a few "daft" questions and won't get laughed at. Not always the cheapest but were almost £20 cheaper than ASAP for a 16 x 12 prop the other week.

ASAP supply you with what you need, where as Norris will work out what you need.


Phil

<hr width=100% size=1>

 

[aztec]

cheers phil, a bit far away from me but it won't hurt to give them a ring. i'm still waiting for "a load of stuff" from lancing.

cheers, steve.

<hr width=100% size=1>

 

[aztec]

ok robbin, i'll bear that in mind. the engine i'm considering is a twin, the only thing that bothers me is that it may be too powerful... may need regulating down a bit, but untill i know the engine code i won't know the poke.

cheers, steve.

<hr width=100% size=1>

 

[Aeolus_IV]

Ahh - was going to suggest Lancing Marine - Mark there is very helpful, happy to talk with you about your problem. They seem reliable and are percieved to be competatively priced around here.

Regards, Jeff.

<hr width=100% size=1>