Schmango,
Love the picture's of your Sea Rover up on the plane. She looks wicked. Shame about she leaks a bit though.
I have just been and mixed up some good old Cascamite and dribbled
that along the keel of the boat I am building.
But there are plenty of other epoxy resins out her that you can run down the keel to stop the leaks. But she sure looks great oup on the plane.

After all the calculations are done, nothing beats put the boat in the water and see how she goes. Then perform temperature evaluation by putting hand on motor.

Looking great to meeting

Update - the 550 drill motor worked a treat on the 16.4v . I didn’t push it too hard and it still got pretty hot. I think 8.4v will be sufficient so that’s my next test.
Turns out these old boats aren’t made from the best materials….. the skin is leaking around the keel ☹️ which means the old circ 1960 ply is now wet inside my new paint. I should have epoxied it .

Exactly Chris, very good.

Thanks ChrisF. Too many variables, besides the motor and prop dimensions (diameter, pitch, lead, etc.). Got to consider the hull size, shape, weight, even the wind resistance when you talk about speed. Always nice to hear the actual results (run in the water) given the equipment and boat used. Good luck.

Lew
Florida 💤, USA

Hi Lew

Unloaded refers to the rpm of the motor that it is designed to achieve when it is running in fresh air. The manufacturer for instance may state 10k. rpm on 12 volts.

Loaded refers to when the motor is actually being used in a boat etc. The resistance of the water and to a lesser extent losses due to the coupling and bearings mean that less than 10k. rpm will be achieved. 80% is usually used, so that may drop to 8k. rpm.

Obviously using a too big a diameter prop, or one that is very coarse will reduce this further. Hence why I'm thinking that a 40mm prop should be Ok. Better to have a motor spinning freely near its max. design speed than one labouring at a lower rpm and producing heat.

As Boatshed says, trying different props is the way to choose the best one for this boat, but unlike for a race boat, a number of sizes, within reason should work.

I still want to be convinced by the battery being used and until sufficient rpm is achieved you are never going to get decent performance. The basics of the battery and particularly the motor have got to be sorted.

Chris

Surely you could get it up on the plane by swapping and playing with different propellors.
Try using S type props as well they work well, and compared to the same size as a standard size they give a fair bit more speed.

ChrisF...

I noticed in your posting: "To plane you want around 9000 - 10000rpm loaded, so around 12000rpm unloaded."

Why would you need more RPM to make a lighter boat achieve the same speed as a loaded boat? Are the numbers reversed? Just curious.

Lew
Florida, USA

Boatshed... good observation. I pulled the prop (still in the original packet) out of my "drives box" and you are correct. In fact I have two of these "Graupner 2308.40" and they both state "CW". Over on this side of the ocean that would be "CCW". This is an older prop from Graupner, perhaps before 2010. Some of the pictures of props in the closed bags show right of left hand rotation instead of CW and CCW.

(The intent of this posting was to help solve a lack of speed for the "Sea Rover", and was supposed to suggest the size, type, and pitch of the propeller as inadequate. I'm glad you pointed this out though.)

Thanks',

Lew
Florida ☀️😎, USA

I see what you mean. I seem to remember reading somewhere that confusion arises because some prop manufacturers describe props using one convention but others state the opposite!

From the Prop Shop web-site: "Please note that propeller rotation is based on the British and American standard (viewing the boat from the stern) which is the opposite to that in Germany."

As Graupner are German then that probably explains it?

Chris