Upscaling models and electric engines?

[twiglet]

Hello all
Right I'm fairly new to all of this so please be gentle.
I'm interested in creating my own boat and I wondered whether it is a sensible idea to upscale a model boat to get a good shape for a hull.
I was thinking something along the lines of the following link as an example to what I had in mind, http://www.toughracing.com/zc126d/index.php?main_page=product_info&products_id=264
I am not sure how the hydrodynamics etc would differ from the small and the full size but I'm sure there will be something I don't know about.

My other question is to what extent have electric motors been used in powerboats and how effective have they been, I would imagine they could certainly help from the point of having the boat totaly sealed stopping engine's from being flooded in heavy seas etc.
They are also apparently a lot easier to maintain and at least in cars can chuck out some down right scary acceleration at times.
Any light anyone can shed on the subject would be much appreciated.

Regards Twiglet

[Guest625101138]

The physics of planing does not change a lot with scale. If the boat performs when in scale form then you could expect similar performance in a larger scale.

The things to know is that weight to drag ratio for the two cases will be similar if weight distribution is similar. Also required power is speed times drag.

There are also Savitsky calculators that will give you a good indication of the required power for checking the scale values.

From the above you can guage that planing boats are sensitive to weight. The batteries are the biggest factor. To get the sort of performance a boat like this suggests you will only get short running time with a set of batteries. Maybe 15 minutes at full throttle - similar to the scale model. You would do better with lithium-ion batteries but these are expensive. Most of the electric cars and bikes you see drag racing are using lithium-ion.

There are a few examples of fast electric boats. Here is some background:
http://www.electricrecordteam.com/history.htm
Rick W

[twiglet]

Thanks thats a big help.
I'm told lithium polymer are the current high end batteries but they are supposed to be really expensive.

[Guest625101138]

Thanks thats a big help.
I'm told lithium polymer are the current high end batteries but they are supposed to be really expensive.

Not quite correct - not SUPPOSED to be they ARE really expensive compared with sealed VRLA you see used in the UK record breaker.

These are the lowest cost I have found:
http://www.batteryspace.com/index.asp?PageAction=VIEWPROD&ProdID=4403
you would need maybe three of these to get reasonable run time in a small boat. You need to be careful that they do not get wet as they might explode.


Rick W.

[twiglet]

You need to be careful that they do not get wet as they might explode. ........Well at least I won't be bored!

Thanks for the link, I didn't realise they went for such high prices, Perhaps I will have to somehow convince universities and colleges to donate them to me.

[Guest625101138]

........Well at least I won't be bored!

Thanks for the link, I didn't realise they went for such high prices, Perhaps I will have to somehow convince universities and colleges to donate them to me.

The above link shown has the cheapest I have found. The ones used by the top dragsters are being manufactured by A123. These are reportedly not prone to explosion in water. Here is an example of application on land:
http://www.killacycle.com/
http://www.youtube.com/watch?v=fHtAkM3CYLA

You will need to be a smooth talker to get funding from a university. There is another fellow on this board seeking a battery sponsor.

Rick W.