Model hydroplane plan enlarged

[TED W. LEE1]

I have plans for a 48" inboard hydro. If these plans were enlarged x3 would the 12' boat be safe to drive at flyby speed.Thanks, Ted.

[hoytedow]

Length would be 3x and beam would be 3x but the horsepower would have to go up exponentially. Stress would go up exponentially. Displacement would go up exponentially. You would have to re-engineer everything but the shape.

For example, a 1' by 1' cube would displace about 62.5 lbs. of water, whereas a 3' by 3' cube would displace about 562.5 lbs. of water, or 9 times the volume rather than 3. Do you see?

[TED W. LEE1]

Thanks for your reply Hoyt. The enlarged plan would be a APBA Y class Henry Lauterbach 12'x5' hydroplane powered by a 850 cc Sunbeam auto engine. Thanks, Ted.

[hoytedow]

I imagine the 48" model ran on about a 90cc engine?

[hoytedow]

26cc was the common size engine for 48" model. 850cc seems like a lot. What are others using to power 12' boats?

[hoytedow]

I would think between 500 and 600cc would be a better match for that size hull. You need to look at other builds in that size category to determine hull thickness/methods.

[TED W. LEE1]

Your correct on the 25cc for the models Hoyt. I checked on several Y class hydros on the vintage hydro web site, and the original Crosley was 44ci and later engines used were larger, in the 850 to 900 cc size. One boat had a 1993 Geo Sprint 3cyl?. engine. I suppose the larger engines are used for this size boat (12') because they are race boats? Thanks, Ted.

[hoytedow]

Always, safety first.

[hoytedow]

I believe the Sprint had a 1 to 1.3 liter engine according to Wikipedia.