Comparison testing of an Atkin tunnel-stern v-bottom Seabright skiff and another boat

[masalai]

Redu, what cad do you use?

[FAST FRED]

the bigger and the more like, (sort of) an aircraft propeller, the more potentially efficient (lots of caveats, but you get the drift?)

On old aircraft where they had tiny power a single blade prop (with counterbalance) was used. Very low induced drag , but a large diameterabsorbed the tiny power.

On most boats the power is too high to even contemplate a 2 blade prop , as cavitation rears its inefficient head.

FF

[kengrome]

After seeing that boat from Sweden and a couple of the recent posts it occured to me that I had posted a similar concept design for a new type of local banca boat in this or another forum a while back. I could not find the same image so I generated the new ones from the same design.

If you can get over the awful colors you can probably see my concept here -- basically a simple inverted vee aft bottom that creates a substantial 'tunnel' over the prop, with more propeller shrouding from the planing shoe below.

The idea here was to use the Atkin concept not only for prop and rudder protection, but also to create even more of a tunnel or 'channeling' effect, hopefully for higher fuel efficiency. The inverted vee could be made even deeper if it proved worthwhile.

[redu]

Played www.DelftShip.net
Lenght(wl) = 7.7m, beam(wl) = 0.9m, weight = 940kg (batteries 400kg)
Instead of that swedish trimaran, this is a mono with same sort of a propeller channel. Prop water channel is longer and less curved in forward direction. Still shaft to motor is short due to a motor "bulb" in the middle.

Supposed to be an effective hull form up to 15 knots. Should build a 0.77m model and a 7.7m ref. model too?

redu

[FAST FRED]

A std tunnel will probably help make sure as much thrust as possible is directed aft.

The Atkin BKRD used the thrust to keep the stern from going down , as it directs the thrust aft.

So the Atkin should be more efficient boat over displacement speed , but before full plaining is achieved.

This I guess is why the Atkin selected engines were modest in size , and the speeds in the 12 -16 mph range .

Also what portion of the total displacement should the box keel float , is still an open question.

The Austrians went for 75% of the boat weight , Atkin was less, although his wooden boats were heavier too..

Any way to ask Delft Ship a question like that?

FF