Brian,

It seems a shame that your post should go unanswered so I'll kick things off. I'm not sure how far you have got with Gwen M, but I find it easier to make provision for the shaft and tube whilst building the keel -ie cut a slot for the tube to fit in rather than trying to drill a hole after the boat is built. This may entail leaving a small tab at each end of the slot to keep the keel together whilst building is in progress- these are removed when everything is supported. Hope this is clear!

With regard to fixing the tube in the slot, people generally use car filler paste (Isopon) or thickened epoxy- I prefer the latter for some reason. I use Zpoxy with some colloidal silica or low density filler. The Isopon is probably easier to source.

There are a plethora of tubes and shafts on the market. For something like this you may just need a stern tube of the right length with bronze bushes and a steel shaft- probably threaded M4 each end and a suitable coupling for your motor and shaft.

With regard to the inboard end of the shaft being below the water line, it might help to fill the tube with grease – vaseline or grease sold for the purpose. I generally find it doesn't, and some ingress may be inevitable. It is possible to make a gland which will keep water out, but it may be more complicated than you want at this stage. Our own Mr Abell had a drawing for such a thing, if you look in his album.

Suppliers you might find useful are Model Boat Bits and Cornwall Model Boats. These are two I have found very helpful but, of course, there are many others.

As with all of these things, there is more than one way to skin a cat, but I hope this points you in the right direction. I'm sure others will chip in (shoot me down in flames) in the fullness of time.

Good luck….Ian

If its this one – **LINK**

then its about 30" long. To provide realistic auxiliary power for this type of boat a 385 motor (15 volt type run on much less, say a 7.2 volt pack) would be appropriate. It isn't a racer. A low drain motor generally means that it doesnt pull much current. Usually it also means that it doesn't rev at a high rate, but does produce good torque, ideal for a prop that is going to move a hefty boat (like this) at a modest speed, rather that a light boat at great speed. A 540/545/550/600 type would probably be overkill, and in a displacement hull, probably not do that much extra good. The 35 and 54 refer to the motor can length. See the thread about motor sizes for deeper confusion.

A larger battery pack will generally heavier. Archimedes principle applies – you can't put a big battery in a small boat. For any given voltage of battery, a wide range of capacity is available. More capacity, longer run time, Sadly, also heavier, so there are limits. Not all batteries can deliver the current required by any motor, so this is another area where size does matter.

Coupling. There are some rather nice ones on SHG's site, about page 21 on their catalogue.

The prop is threaded, but is is sensible to use a locknut. You want to keep the prop after reversing. One of Newtons laws applies here – the prop will try to unscrew itself when you chuck it in reverse.

Another approach to the inevitable water weep via the shaft is to arrange a sump to catch the drips. It does make it easier to catch the water for syringing out once it has found a way in. Probably why so many stands have a selection of syringes at shows.

In old time converted sailing boats, it was not uncommon to use a very hard wood such as lignum vitae as the bearings and to stuff the space between (hence the term "stuffing box" with a lead based grease to lubricate and help keep the water out. Fortunately, we can get prop shafts and tubes ready fitted with bearings from a shop.