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White smoke when starting; sterngland re-packing; blacking the hull using a roller; fitting a water pressure reducing valve; the right way to wire up a battery bank; raising up ballast for ventilation; and problems starting a Yanmar engine
QI have a 58 ft narrowboat and at the last docking in 2015 the marina pointed our that the propeller was rather too close to the end point of the swim.
Is there an optimum distance for the prop boss from the end point of the swim? I have an 18” x 13” Axiom propeller and at the last docking fitted a stainless weed cutter disc on the shaft for which there was just enough space.
We are having it blacked at the same marina next month April and I wanted to extend or fit new shaft to fix the problem. MICHAEL MARSH
ATONY REPLIES: You say you have a problem, yet do not tell me what it is and it seems the yard gave you no reason for their advice so I can only guess.
The problem with having the prop too close to the stern post is that the stern post masks the water flow into the prop but your boat appears to have an exceptionally fine stern swim and effectively no stern post at all. The aft shaft bearing is even in an extension to the stern tube that brings the prop even further back from the stern post. Be aware that moving the prop back might increase tiller vibration.
I do not think there is a problem on your particular boat and if there is one it is more likely to be prop-related.
For canal work I would want the minimum unsupported shaft overhang commensurate with ensuring easy water flow into the prop. Your engine will move forwards and backwards on its rubber mounts when you go into ahead and astern so unless you have thrust bearing fitted you need a minimum clearance/ shaft length between the prop boss or weed cutter and the end of your stern tube of 5 to 10mm with a maximum shaft overhang of about 1 shaft diameter.
See http://www.propprotector.co.uk/information. php? info_ id=2&o sC sid=5f62c 99 a8ce 700 de 444 cafd 34 ac 67 a 14
In your case because of that very fine swim end you will probably get away with the lower figure.
Before spending money on this, my advice is to get the yard to give you a written guarantee that the work they recommend will make a measurable and noticeable difference to the boat’s handling and performance.