Model Boat Mayhem
Mess Deck: General Section => Beginners start here...! => Topic started by: mal73 on November 18, 2007, 04:40:46 pm
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HI again
Just wondering if anyone had any tips on making the hole for a propshaft through a styrene hull. I have been told that the angle on the propshaft should be no more than 12.5 degrees. How do I ensure this before I actually drill the hole.
Cheers
Malcolm O0
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Malcolm,
What type of model is it and is it single prop or twin?
Bob
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I have a similar problem with a wooden hull but have started another thread.
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Hi Bob
It is a single prop, through a styrene hull.
Hope this helps.
Malcolm
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OK, so is it the type of hull with a flat underside, or one with a shaped support, like the back end of a trawler?
If its a flattie, cut a slot and set the tube in place with filler and any other support you deem necessary. If its a trawler type stern, you will need to drill out using a long bit of the appropriate diameter using plenty of support, a steady aim, and if you do it lik me, a bit of tongue sticking out the corner of the mouth.
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Its a model ASR launch that I got from Astec models, with a v shaped styrene hull. I had intended on doing as you suggest, tongue included :P, but was just checking before I made a >>:-( of it
Cheers
Malcolm
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Is this any help?
(http://i63.photobucket.com/albums/h136/IainM_2006/proptubekeel.gif)
With a styrene hull that doesn't have a full keel. you can cut a keel section fitted only at the stern and use the above method for prop tube location. This will give a much more rigid and longer lasting 'join' between hull and prop tube.
If you 'dummy fit' the tube to the keel section before gluing it into place (i.e. getting the angles right) you can then drill through from the inside of the hull to make the hole and, because the drill is guided you get a neater hole in the sytrene.
Of course if you are really keen, you could glue in an outer sheath (thin wall brass tube) and pass the prop tube through this, sealing it with silicon. This way it is easy to change the tube or the bearings at a later date.
Food for thought perhaps?
Good luck with the build
Iain
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Sorry to go on about this, but I forgot your question about shaft angles.
Ideally the shaft should be as close to horizontal as possible but its actual angle will depend on many things, not least of which is the diameter of the prop. You should leave around 5mm minimum clearance between the top blade and the hull underside.
Any angle of the shaft downwards will have an effect on the amount of thrust your prop delivers to the boat. Have a look at this link for a simple explanation. http://www.sfmbc.net/propshaft_angles.pdf I put it together as part of a Club tutorial so I hope it'll help.
Since both ends of the tube will be under water and since hopefully the water will be on the outside only ( :)), water will always tend to leak through the tube regardless of its actual angle.
If you look at the trouble the fast electric and IC guys go to to get their props normal to the water surface you get an idea of how big the effect can be.
Iain
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Top man Iain, thanks for all your help.
Cheers
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mal73
In a styrene hull support the propshaft as close to the INNER end as you can.
The whole styrene hull will flex which will give you vibration through misalignment.
If however you support the propshaft well, it becomes quite rigid and removes this problem.
Bob