i am currently redesigning my gasser airboat and would like to take my homemade prop adaptor away. my motor is a homie 25cc with a pullstart and casing up front.
now my question is what is the effect of having the prop mounted with less than half an inch between the prop and the motor casing? will this create anything bad for the motor or the prop or to how the motor will run? or its perfectly alright?
ernest

puller or pusher?

if it is a pusher it SHOULD be ok but i don't have any expirience.
i tryes having a long straight exhaust on my 25cc boat once and that was about 1" away from the prop.
it affected the steering BADLY!

shaun

You will loose a LOT from the prop being that close ...
A prop ( to put it in simple terms ) , sucks in the air closer to the center of the prop , and basically , swirls it around to the outer most edges of the prop before "releasing" it . ( like I said ... this is described , as simple as it gets ... LOL )

its puller setup. i was thinking that its not a very good idea, but i might try test it

Ok ... let us know , but for a prop to be the most efficient , it need to be a bit away from anything - front or rear .
Do a simple test ...
Take ANY prop , on ANY boat, plane . ( use a piece of wood here folks , don;t get stupid and try your hand )
Place the wood in FRONT of the prop near the center ( hub ) . Now , increase the size of the wood . And increase again ... notice any difference ? ( you bet you do )
Now , do the same with it in BACK of the engine ... seems like you LOST a lot , huh ?
see the pic below .
In the circled area , this is MOST vital area for air to get to for the props efficiency . The less area that is covered/blocked , the better the prop does its thing .

thanks terbo, i will try to test it first and post feedback here.[8D]