carsonaviation

sorry not trying to ruffle any feathers but i am an airplane guy
who used to help a friend work on his 36 foot skater cat that he raced offshore

i have lots of composite experience and know a good deal about converting gas motors to air use
and would like to glass up a big cat hull for twin engine use

but in airplanes i wouldnt even waste my time with the small gassers but power to weight is a bigger factor there i imagine but here is my main question

i have the ability to get motors for next to nothing so why are guys using stuff in the 25 cc range
does it have something to do with rpm ? prop availability ? the clutches ?

i would like to use a pair of 3.2 in stihl chain saw engines what problems or limitations would these have
they weigh about a pound more than a homelight and a lil more than that than a zenoa
but the power would be at least close to double

could i get props and drive stearing gear that will be compatable ?

OLD_SLOW and in the WAY

Rpm equals speed ....
i have also converted many chainsaw engines for rc plane use up to a 100cc husky and the rpm just aint there (we exploded a prop at 13,000 rpm) in a dive . a 3.2 is a great engine. and can be used with uor 1/4" drive components. now to start with the starter is on the opposite side which makes it seem that the rotation is wrong so first off this will have to be changed ...like a belt pully starter. very large props are out there (3"dia) with up to 5 blades.
our sanctioning bodies NAMBA and IMPBA have a set limit on displacement 35cc's and a 60" hull. but the AMA dont care and actually has better coverage for boats than the aforementioned ORG's

BajaBob-delete

NAMBA Gas class break point for classes is:
G1 : 15 to 25.99 cc
G2 : 26 tp 35.99 cc

There are weight and size restrictions also.
For play you can run larger engines/boats but aren't covered by insurance.

RPM = speed ,Marine Specialties determined the largest practical engine to use in a direct drive application is 42cc,after that over drive is recommended.

bkf

My Feedback: (5)

Nothing wrong with them chainsaw engines at all. Some have RPM limiting electronics but as long as it starts, idles, and runs well go for it.

Ron Olson

My Feedback: (1)

The IMPBA has a size limit of 1.8 cu. in. so that is why these motors are used. The Zenoahs have been tuned to get out 6+HP and 18,000+RPM and a current speed record of just over 100 MPH.