Engine Chart

[A340 Pilot]

Can somebody make a engine chart that I could use to know what length hull and engine size I should use?

[patmat2350]

It would be a multi-level table- a 4 foot PT boat will take different power than a 4 foot freighter, different than a 4 foot tug.

Prop size also, which dictates motor speed... and number of props.

PM

[CG Bob]

If you're making a model of a known ship or class of ships, you can figure out some of that information based on the full size length, hp, displacement, etc.; and then convert to your scale size.

1 HP = 746 Watts
If the full size ship has two 2500 hp Diesels, that totals 3,730,000 Watts (1,865,00 Watts per engine). If I'm building a model of that ship in 1:48th scale (1/4" = 1'), I need to divide the hp-watt conversion by the cube of the scale: 3,730,000/110,592= 33.7 scale Watts (roughly 17 Watts per motor).

Since I can't scale down the water, maybe I add 10-15% to the scale Watts to compensate; so I need two motors rated for 19.5 Watts. Since you're looking for a hp figure, I need two engines rated between 0.022 and 0.26 hp. Now you got to figure out what size nitro engine will provide that hp - time to check the engine makers data sheets.

The full size ship in this example is 210' long; in 1:48th scale that's a hull 52" long.

Using Pat's 4' PT boat as an example. 3 Packard engines rated at 1500 HP gives a total of 4500 hp. Scaled down to our 1:20 scale model, we need between .56 and .65 hp to make the model run. The O.S. 21VZ-M (http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXKKP0&P=0) engine is rated at 2.5 hp, 5 times more than we need; but it might be an appropriate nitro engine for a 4' PT boat.

[patmat2350]

Or just ask around about what worked for someone else...

[A340 Pilot]

I am making a 1/13 scale model that in real life has 600hp. I has 2 engines.

[CG Bob]

It would help to know what kind of boat you're planning to build. We could give a better recommendation on the proposed power plant.

Given the original 600 hp of the full size boat, you need somewhere between 0.27 and 0.31 hp (or 204-234 Watts) in the model. Again, you're going to have to check the different engine makers claims for hp before deciding which one to use.

The size of the hull is partly decided by the size of the power plant and its fittings.

Maybe you should check the IMPBA (http://www.impba.net/) or NAMBA (http://www.namba.com/content/default.asp) rule books for engine and hull size requirements.

IMPA list the following classes of nitro engines:
Class Cubic Inch Displacement Metric Class
A = 0.000 thru 0.129 = 2.1 CC
B = 0.130 thru 0.219 = 3.5 CC
C = 0.220 thru 0.300 = 4.9 CC
D = 0.301 thru 0.458 = 7.5 CC
E = 0.459 thru 0.670 = 11.0 CC
F = 0.671 thru 1.830 = 30.0 CC

[A340 Pilot]

New York Water taxi Ferry Catamaran.

[A340 Pilot]

Will the O.S 21VZM Turbo engine work for a 5 foot model?