Good evening everyone , I have a 72 commander 31 sedan with twin 350q engines , along with the original kohler Gen set that sits between them . The boat is rear heavy . I recently put the original size props on it , which per build sheet are 15”x17 pitch 3 blade bronze . When I hit half throttle it just goes nose up and chugs . On these old heavy gals , in order to get on plane do you have to go full throttle ? Or at least 3/4 throttle ? I’m used to smaller outboard powered boats , and lord knows I don’t want to hurt my baby, but man this thing is slow at a whopping 9 knots at what tachs say is 2100 rpm . The engines are both running well with no issues . It has a dual needle single face electric tach that’s probably 90s vintage so the old cable driven tachs are long gone . At a little over half throttle the tach is reading 4K rpm . That can’t be correct. The engines aren’t screaming . Any ideas ?
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Scot can you tell us what RPM / speed you pop up on a plane? 900lbs of fuel? What size tanks do you have and where are they located? My 31 has 2 original round steel tanks 50 gallons each aft. My 31 also sat stern down. I replaced the old scaled up cast iron mufflers and exhaust pipes with custom fiberglass which helped. No genset… my boat is a Sedan with no flybridge. 25 gallon steel water tank under the v berth. Just getting the newly rebuilt engines broken in and tuned, but have not run up beyond 2200 rpm yet.