Until your solution this http://www.boatdesign.net/forums/hybrid/greencat-605-retractable-electric-propulsion-44542.html seemed to be the best solution yet. It is not the best price. It would be interesting to hear your take on this as your reasonings are at least as interesting as the results you show.

As the arm is locked anyway when the prop is in operation I suppose there would not be an adverse effect pivoting the arm sideways at a forward angle making sure the prop would end up in front of the beam instead of remaining under the deck when pivoting straight sideways.

Are you concerned at all about overheating the engine as it is not submerged or do you count on the heat conduction of the aluminum housing extending in the submerged shaft covering foil?

The difference in the props pulling vs pushing the boat would be interesting.

What is the clearance between tip of the props and the hulls when in operation?

Would it be worth it to design the draft of the hulls to surpass the draft of the props to protect them from floor strikes or would you rather extend the shaft cover downward below the prop diam?

--- In harryproa@yahoogroups.com.au, Rick Willoughby <rickwill@...> wrote:
>
> Luc
> The prop torque can get to 190Nm so will easily overcome the weight
> of the thruster meaning it needs to be locked both ways. There is a
> line from an eye off the side of the hull to one of the pivot arms
> that can be tensioned from the deck and secured. It preloads the
> lifting line and needs to be released to enable the unit to be raised.
>
> The prop has a maximum rotational speed of 700rpm. Gearbox has a
> reduction ratio of 1/3.3. We considered a planetary gearbox with an
> inline motor for submersible mounting of motor but the lowest price
> we found was over AUD500 and that is without any stainless shaft
> extension for the prop and shaft sealing system. The right angle
> gearboxes we are using started out at AUD110 each but we added a pair
> of angular contact bearings for the thrust and a stainless shaft that
> brings total cost to AUD190 each.
>
> There were other factors for the choice of gearbox. We have already
> tested the gearbox we are using on the trial unit and four of the
> same boxes are used for the steering. They are simple, robust boxes;
> literally agricultural by design and intended use.
>
> We didd not get far enough into design of a submersible pod to
> consider the lifting load but it needs consideration. As it is we
> can lift by hand (about 20kgf dead lift) but have also used the sheet
> winch to make it easy. Pods off the side of the hull that can be
> raised and lowered would be nice if you can find suitable planetary
> boxes.
>
> Rick
> On 22/12/2012, at 4:09 AM, LucD wrote:
>
> > Rick, this is a very good price (OK that is without the high
> > modulus rope ;-) Does the arm lock in vertical position? Apparently
> > you do not advocate an engine pod behind the propeller. Is that
> > because of the increased drag or a heavier moment with the engine
> > weight at the very end of the arm?
> > Thank you.
> > Luc
> >