Old boat new life

We finnaly got my dads 75 18ft Mark Twain on the lake yesterday affter a procrastinated summer project that took too many summers. We removed all the interor and had it re done and rebuilt the carb. It runs a 188hp merc 888 (ford 302). yesterday was a test and tune day that turned in to a pleasure cruse, The boat run great not a hicup, but seemed slugish on accelleration. top end we were running 3500rpm at 38mph (according to dash gauges) it ran too smooth to blame the engine, and we remember talking about changing the prop,(current prop is a 21 pitch we are thinking 19) we only had the boat a shord time before the teardown , but we ran it several years ago beside a friends allmost identical 76 and in seemed to be setup for more botom end. The boat is primaraly used for skiing and tubing so top end is not a issue.

Re: Old boat new life

You should be seeing 3800 to 4200 rpm with that engine. A change to a 17" pitch would get you maybe to 3900, and for skiing and tubing, you need to be up around 4200 rpm for best results which you may get with a 15" prop. Were you using the trim properly?

Moving to prop forum.

Re: Old boat new life

I think 188hp on in a 18ft should be twisting the tail off a 21"pitch.
There are lots of 130 hp I/Os running 19 and 21 with 18 footers.
running around 40 at max rpm.Little or no hole shot.
Generally they run 15 or 17 for sking and the like.Usually having to watch for over reving.You may want to do a compression check and check that all cylinders are firing.It easy for an 8 cylinder to be missing a cylinder an not be noticed except for performance.Also check that the throttle is opening all the way.