CONTINUOUSWAVE

[I am] working with a 1971 13-footer with a 1987 Evinrude E30 tiller outboard engine, and currently running the OMC four-blade 14-pitch by 10-inch diameter wheel. With three adults and one child this propeller still blows out in a straight line on the third-to-last trim hole. Speed is 27-nautical-miles-per-hour; engine speed 5700-RPM. Trimming down provides less speed but [the propeller] still blows out.

Local prop guy says go to 16" 4 blade aluminum

Power tech tells me that it's impossible for 13-foot Boston Whaler boat to turn a 14" four-blade with three adults or get on a plane.

Read this thread:

http://continuouswave.com/ubb/Forum4/HTML/006637.html

Bucketmouth wrote:...propeller still blows out ...on the third-to-last trim hole...

Are you trying to say the engine mounting has been raised from the lowest position?

How many increments of 0.75-inch--the hole spacing--is the engine mounted above the lowest position?

Or are you describing the fixed position of the engine trim on an engine without power trim?

Generally if a propeller is ventilating, the remedy is to lower the engine mounting height. If a propeller ventilates if trimmed out too high, the remedy is to reduce the amount of trim out. Changing the propeller pitch would not tend to affect any change in the propeller ventilating.

Bucketmouth wrote:...Speed is 27-nautical-miles-per-hour...

Most discussions about small boats and their speed uses MPH (statute miles per hour). The cited 27-nautical-miles-per-hour would be 31-MPH.

How many increments of 0.75-inch--the hole spacing--is the engine mounted above the lowest position?

Most small tiller steer OBs have clamp on brackets and basically only have one mounting height. They do not use the typical four hole mounting that allows for easy adjustment.

It does sound like the engine is likely mounted too high or shaft too short if prop is blowing out. Cavitation plate distance from bottom of hull should measured and reported back to give more information.
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